O uso de banco de dados Android

Others 2021-03-28 03:53:05 views: null

 

Prefácio

Para o desenvolvimento do Android, o banco de dados deve ser familiar, mas de uma perspectiva prática, pode não ser capaz de ser usado com proficiência. Claro, nem todos os aplicativos precisam usar um banco de dados, porque essa coisa é muito pesada. Mas se você encontrar alguns projetos particularmente grandes, especialmente incluindo mensagens instantâneas, mensagens e armazenamento e operações frequentes de big data, você basicamente usará bancos de dados, como aplicativos bancários, aplicativos de bate-papo e grandes aplicativos de sites oficiais. Nesse tipo de projeto, o banco de dados precisa ser empacotado de maneira unificada: criação de banco de dados, criação de tabela, adição de banco de dados, exclusão, modificação, consulta e operações de atualização de banco de dados. Não há muito a dizer, basta começar do ponto de vista do código!

 

Um, a criação do banco de dados:

1. Crie um banco de dados com a ajuda de SQLiteOpenHelper, o código é o seguinte:

 

public class MySqliteOpenHelper extends SQLiteOpenHelper {
    private String mName="";//数据库名字

创建数据库表的语句，一般写在会放在对应的数据库中(StudentDao)
public static final String TBL_FRIEND_CREATE_SQL =
        "CREATE TABLE IF NOT EXISTS " + STUDENT_TABLE + " (" +
                STUDENT_ID + " INT64 PRIMARY KEY," +
                STUDENT_NAME + " TEXT," +
                STUDENT_CHINESE + " TEXT," +
                STUDENT_MATH + " TEXT," +
                STUDENT_ENGLISH + " TEXT," +
                STUDENT_AGE + " TEXT" + ");";
    public static final String[] INIT_ALL_TABLE={
            UserDao.TBL_USERDAO_CREATE_SQL,
            FriendDao.TBL_FRIEND_CREATE_SQL,
            StudentDao.TBL_FRIEND_CREATE_SQL
    };


    public MySqliteOpenHelper(@Nullable Context context, @Nullable String name, int version) {
        super(context, name, null, version);
        mName=name;
    }


/**
  *在当第一次执行数据库操作的时候会通过SqliteOpenHelper去创建数据库，对应的走onCreate方法。
  *如果需要新增一个表格，需要将创建表格的语句在onCreate方法里面去执行，如下所示。这个for循环会将需要的表一次性全部创建完毕
/
    @Override
    public void onCreate(SQLiteDatabase db) {
        if (INIT_ALL_TABLE!=null&&INIT_ALL_TABLE.length>0)
        for (int i = 0; i <INIT_ALL_TABLE.length ; i++) {
            db.execSQL(INIT_ALL_TABLE[i]);
        }
    }

/*
*这个方法是当数据库中的某个表格需要升级的时候（比如，新增一些字段）
*此时需要将数据库的版本号增加一个，通过获取本地数据库的oldVersion和APP中的数据库版本号进行比较
*如果小于当前的版本号，则会走对应的方法，对应的去执行一些语句，插入一些新的字段。如下：
*/
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        if (oldVersion==newVersion){
            return;
        }

        if (oldVersion<4){
            //数据库升级版本为4，此时有表格结构变动，需要更新对应的表格
            updateDbVersion4(db);
        }
        if (oldVersion<5){
            //数据库升级版本为5，此时有表格结构变动，需要更新对应的表格
            updateDbVersion5(db);
        }


private void updateDbVersion4(SQLiteDatabase db) {
    ArrayList<String> list = updateDbVersionSqlArray4(db);
    db.beginTransaction();
    if (list!=null&&list.size()>0){
        for (int i = 0; i < list.size(); i++) {
            String sql = list.get(i);
            db.execSQL(sql);
        }
    }
    db.setTransactionSuccessful();
    db.endTransaction();
}


/**
 * 数据库版本4.0，user_info_table  表格新增字段 student_chinese 和  student_math
 */
private ArrayList<String> updateDbVersionSqlArray4(SQLiteDatabase db) {
    ArrayList<String> sqlList = new ArrayList<>();
    try {
        Cursor cursor = db.query(String.valueOf("sqlite_master"), null, null, null, null, null, null);
        try {
            while (cursor.moveToNext()) {
                if ("table".equals(cursor.getString(cursor.getColumnIndex("type")))) {
                    String tableName = cursor.getString(cursor.getColumnIndex(String.valueOf("name")));
                    if (tableName.equals(StudentDao.STUDENT_TABLE)) {
                        if (!checkColumnExists(db,StudentDao.STUDENT_TABLE,StudentDao.STUDENT_CHINESE)) {
                            String str1 = "ALTER TABLE " + tableName + " ADD COLUMN " + "student_chinese" + " TEXT;";
                            sqlList.add(str1);
                        }
                        if (!checkColumnExists(db,StudentDao.STUDENT_TABLE,StudentDao.STUDENT_MATH)) {
                            String str2 = "ALTER TABLE " + tableName + " ADD COLUMN " + "student_math" + " TEXT;";
                            sqlList.add(str2);
                        }

                    }
                }
            }
        } finally {
            cursor.close();
        }

    } catch (Exception e) {
        return new ArrayList<String>();
    }
    return sqlList;
}
    }

2. Depois que a classe auxiliar SqliteOpenHelper for gravada, você precisará usar o ContentProvider para criar o banco de dados.

此类是用来存储数据库信息配置的类:

public class DBConstants {
 /**
 * 数据库的名字，LK+“用户的账号”+DB 拼接成的，如果切换账号则会生成新的数据库。不同的账号之间的数据绝对隔离，故称之为私库。
 */
    public static final String DB_NAME = "LK%sDB.db";
    /**
     * 数据库升级为版本4  StudentDao新增语文Chinese 数学Math字段
     */
    public static final int DB_VERSION=4;


}
/**
 * 1.核心：此类继承ContentProvider，在此类中进行数据库的创建，以及实现数据库的  增，删，改，查，替换，批量操作。
 * 2.此处实现的数据库表格的 增，删，改，查，批量操作等方法并非直接使用。而是通过contentRelsover去操作，
 *   内部会进一步的调用此类中对应的方法。
 * 3."com.example.mydbproject.liukang"是MyContentProvider唯一标识（这个类对应的唯一数据库），不允许重复，并且需要注册才能使用。
 * <provider
 *             android:authorities="com.example.mydbproject.liukang"
 *             android:name=".help.MyContentProvider"
 *             android:enabled="true"
 *             android:exported="false"/>
 *
 */
public class MyContentProvider extends ContentProvider {

    public static final String AUTHORITY = "content://com.example.mydbproject.liukang/";
    public static final String AUTHORITY_APPLY = "com.example.mydbproject.liukang";//这个是唯一标识，注册的时候需要使用
    public static final String URI_RAWQUERY = "content://com.example.mydbproject.liukang/defined/action/rawQuery";
    public static final String URI_EXECSQL = "content://com.example.mydbproject.liukang/defined/action/execSql";

    Object mLock = new Object();
    MySqliteOpenHelper mySqliteOpenHelper;
    String mUserId = "";

    @Override
    public boolean onCreate() {
        return initHelper();
    }

    private boolean initHelper() {
        synchronized (mLock) {
            if (mySqliteOpenHelper != null) {
                mySqliteOpenHelper.close();
            }
            mUserId = getUserId();
            String name = String.format(DBConstants.DB_NAME, mUserId);
            mySqliteOpenHelper = new MySqliteOpenHelper(getContext(),
                    name,
                    DBConstants.DB_VERSION);
            return true;
        }

    }

    public SQLiteDatabase getWritableDatabase() {
        if (mySqliteOpenHelper != null) {
            if (!mUserId.equals(getUserId())) {
                initHelper();
            }
            SQLiteDatabase writableDatabase = mySqliteOpenHelper.getWritableDatabase();
            return writableDatabase;
        }
        return null;
    }

    /**
     * 查询操作
     * @param uri  1：URI_RAWQUERY则直接用db执行查询的sql语句 （sql语句已经包含了条件）
     *             2：AUTHORITY+“table_name”此时直接根据条件查询
     * @param projection
     * @param selection
     * @param selectionArgs
     * @param sortOrder
     * @return
     */
    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        String tableName = getTableName(uri);
        SQLiteDatabase db = getWritableDatabase();
        if (db == null) {
            return null;
        }
        if (uri.equals(Uri.parse(URI_RAWQUERY))) {
            //URI_RAWQUERY则直接用db执行查询的sql语句
            Cursor cursor = db.rawQuery(selection, selectionArgs);
            return cursor;
        }
        if (TextUtils.isEmpty(tableName)) {
            return null;
        }
        //直接根据条件查询
        Cursor cursor = db.query(tableName, projection, selection, selectionArgs, null, null, sortOrder, null);
        return cursor;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        return null;
    }

    /**
     * 插入新数据操作
     * @param uri
     * @param values
     * @return
     */
    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        String tableName = getTableName(uri);
        SQLiteDatabase db = getWritableDatabase();
        if (db == null || TextUtils.isEmpty(tableName)) {
            return null;
        }
        long insertId = db.insert(tableName, null, values);
        if (insertId == -1) {
            //失败
            Log.e("TAGS", tableName + ":" + "insert:" + insertId);
            return null;
        }
        //成功是一个大于0的数===size    失败是-1
        Log.e("TAGS", tableName + ":" + "insert:" + insertId);
        return ContentUris.withAppendedId(uri, insertId);
    }

    /**
     * 删除一条新数据     1：如果uri为  MyContentProvider.URI_EXECSQL则执行sql语句即可（可以是增，删，改）
     *                   2：如果不是则根据表格以及条件进行某条数据的删除
     * @param uri
     * @param selection
     * @param selectionArgs
     * @return
     */
    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        SQLiteDatabase db = getWritableDatabase();
        if (db == null) {
            return 0;
        }
        if (uri.equals(Uri.parse(MyContentProvider.URI_EXECSQL))) {
            db.execSQL(selection);
            return 1;
        } else {
            String tableName = getTableName(uri);
            if (TextUtils.isEmpty(tableName)) {
                return 0;
            }
            int delete = db.delete(tableName, selection, selectionArgs);
            //失败是0    成功是1
            Log.e("TAGS", tableName + ":" + "delete:" + delete);
            return delete;
        }
    }

    /**
     * 更新操作：   1.如果uri是包含replace，对应的操作是  存在则更新，不存在则新增
     *             2.如果不包含replace,则执行更新操作
     * @param uri
     * @param values
     * @param selection
     * @param selectionArgs
     * @return
     */
    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        String tableName = getTableName(uri);
        SQLiteDatabase db = getWritableDatabase();
        if (db == null || TextUtils.isEmpty(tableName)) {
            return 0;
        }
        //成功是1  失败是0
        int update = db.update(tableName, values, selection, selectionArgs);
        if (update == 0) {
            if (getReplace(uri)) {
                long insertId = db.insert(tableName, null, values);
                Log.e("TAGS", tableName + ":" + "update:__insert:" + insertId);
                return 1;
            } else {
                return 0;
            }
        }
        Log.e("TAGS", tableName + ":" + "update:" + update);
        return update;
    }

    /**
     * 获取当前账号的唯一标识，userId。
     * @return
     */
    public String getUserId() {
        String user_id = AccountManager.getAccountId(getContext());
        return user_id;
    }

    /**
     * 根据uri操作表示来获取表格名称
     *MyContentProvider.AUTHORITY+ “student_table”
     * MyContentProvider.AUTHORITY+  “place/student_table”  替换操作
     * @param uri
     * @return
     */
    public String getTableName(Uri uri) {
        List<String> pathSegments = uri.getPathSegments();
        if (pathSegments != null && pathSegments.size() == 1) {
            return pathSegments.get(0);
        } else if (pathSegments != null && pathSegments.size() == 2) {
            return pathSegments.get(1);
        } else {
            return "";
        }
    }

    /**
     * 判断是不是替换的操作
     * @param uri
     * @return
     */
    public boolean getReplace(Uri uri) {
        List<String> pathSegments = uri.getPathSegments();
        if (pathSegments != null && pathSegments.size() == 2) {
            String placeStr = pathSegments.get(0);
            if (!TextUtils.isEmpty(placeStr) && placeStr.equals("place")) {
                return true;
            }
            return false;
        } else {
            return false;
        }
    }

    /**
     * 批量操作
     * 如果一次性插入或者查询多条数据可以使用此方法，性能好
     * @param operations
     * @return
     * @throws OperationApplicationException
     */
    @NonNull
    @Override
    public ContentProviderResult[] applyBatch(ArrayList<ContentProviderOperation> operations)
            throws OperationApplicationException {
        SQLiteDatabase db = getWritableDatabase();
        if (db == null) {
            return null;
        }
        ContentProviderResult[] results = new ContentProviderResult[operations.size()];
        db.beginTransaction();
        try {
            results = super.applyBatch(operations);
            db.setTransactionSuccessful();
        } catch (Exception e) {
            e.printStackTrace(); //NOSONAR
            results = null;
        } finally {
            db.endTransaction();
        }
        return results;
    }
}

2. Crie uma tabela de dados:

1. O método de operação da classe base

/**
 * 所有数据库表格的基类，
 * 1：通过ContentValues，进行增，删，改，查
 * 2：通过sql语句进行增，删，改，查
 * 3.当新增某个数据库操作可以继承该类。如果需要执行某个操作，只需要对应的调用对应方法并传入相关参数即可。
 * （可参考StudentDao）
 */
public abstract class BaseDao {


    /**
     * 单个插入一条数据
     * @param tableName  表名称
     * @param contentValues 将插入的数据封装为ContentValues进行插入（key,value）
     */
    public void insertValue(String tableName, ContentValues contentValues) {
        MyApplication.getContext().getContentResolver().insert(getUri(tableName), contentValues);
    }



    /**
     * 删除单个数据
     * @param tableName  表名称
     * @param selection  查找的条件字段
     * @param selectionArgs  字段条件字段对应的值
     */
    public void deleteValue(String tableName, String selection, String[] selectionArgs) {
        MyApplication.getContext().getContentResolver().delete(getUri(tableName), selection, selectionArgs);
    }

    /**
     * 更新一条数据
     * @param tableName   表名称
     * @param values  插入的ContentValues
     * @param selection  查找的条件字段
     *  @param selectionArgs  字段条件字段对应的值
     */
    public void updateValue(String tableName, ContentValues values, String selection, String[] selectionArgs) {
        MyApplication.getContext().getContentResolver().update(getUri(tableName), values, selection, selectionArgs);
    }

    /**
     * 查询数据
     * @param tableName  表名称
     * @param cloum  想要查询的哪个字段    null则是所有
     * @param selection  查找的条件字段
     *  @param selectionArgs  字段条件字段对应的值
     * @param sortOrder   排序
     */
    public Cursor queryValue(String tableName, String[] cloum, String selection, String[] selectionArgs, String sortOrder) {
        return MyApplication.getContext().getContentResolver().query(getUri(tableName), cloum,selection,selectionArgs,sortOrder);
    }

    /**
     * 替换一条数据（有则更新，无则插入）使用的是这个Uri：getReplaceUri(tableName)
     * getContentResolver().update() ==> MyContentProvider.update() 根据Uri区分：update or replace
     * @param tableName
     * @param values
     * @param selection
     * @param selectionArgs
     */
    public void replaceValue(String tableName, ContentValues values, String selection, String[] selectionArgs) {
        MyApplication.getContext().getContentResolver().update(getReplaceUri(tableName), values, selection, selectionArgs);
    }


    /**
     * 批量操作数据（增，删，改）
     * @param authority
     * @param operations:此集合中包含ContentProviderOperation类
     *         ContentProviderOperation可以理解为封装的sql语句
     *         一个集合里面可以是（增 删 改）共同组成的集合
     * @return
     */
    public ContentProviderResult[] applyBatch(String authority, ArrayList<ContentProviderOperation> operations) {
        try {
            return  MyApplication.getContext().getContentResolver().applyBatch(authority, operations);
        } catch (Exception e) {
            e.printStackTrace(); //NOSONAR
        }
        return null;
    }


    /**
     * 直接sql语句执行查询  注意Uri是这个哦：getRawQueryUri()
     * getContentResolver().query()===>对应的MyContentProvider.query()
     * ==>对应的MyContentProvider会根据Uri区分是直接执行sql语句，还是使用传过来的条件
     * @param sql
     * @param selectionArgs
     * @return
     */
    public Cursor querySql(String sql,String[] selectionArgs){
        return MyApplication.getContext().getContentResolver().query(getRawQueryUri(),null,sql,selectionArgs,null);
    }

    /**
     * 直接执行sql语句进行 增 删 改操作 （ 注意使用的是uri:getExecSqlUri()）
     * getContentResolver().delete()===>对应的MyContentProvider.delete()
     *      * ==>对应的MyContentProvider会根据Uri区分是直接执行sql语句（增 删 改）
     *      ，还是使用传过来的条件进行删除操作
     * @param sql
     */
    public void execSql(String sql){
        MyApplication.getContext().getContentResolver().delete(getExecSqlUri(),sql,null);
    }


    /**
     * AUTHORITY+表名称，MyContentProvider会使用传过来的条件进行 增 删 改 查 操作
     * @param tableName
     * @return
     */
    public Uri getUri(String tableName) {
        return Uri.parse(MyContentProvider.AUTHORITY + tableName);
    }

    /**
     *含有replace: MyContentProvider会使用传过来的条件进行替换操作（无则插入，有则替换）
     * @param tableName
     * @return
     */
    public Uri getReplaceUri(String tableName) {
        return Uri.parse(MyContentProvider.AUTHORITY +"replace/"+ tableName);
    }

    /**
     * 获取getRawQueryUri()：直接执行sql查询的Uri表示
     * @return
     */
    public Uri getRawQueryUri(){
        return Uri.parse(MyContentProvider.URI_RAWQUERY);
    }

    /**
     * getExecSqlUri()：直接执行sql语句的表示：增 删 改
     * @return
     */
    public Uri getExecSqlUri(){
        return Uri.parse(MyContentProvider.URI_EXECSQL);
    }

}

2. Por exemplo: tabela de aluno: chave primária StudentDao: student_id (único)

/**
 * 增删改查替换，只要对应的调用方法即可
 * sql:如果是直接执行相关的sql语句则需要对一些表达式有所了解才行
 * newInsertMessageOperation：批量插入，删除，替换返回的ContentProviderOperation，实际上就
 * 是对增 删 改 替的语句的封装，然后组成集合，调用applyBatch（）方法开启数据库事务进行遍历操作
 * 进一步的实际上还是调用 增 删 改
 */
public class StudentDao extends BaseDao {

    StudentBean studentBean = null;
    private static StudentDao mInstance;
    public static String STUDENT_TABLE = "student_table";
    public static String STUDENT_ID = "student_id";
    public static String STUDENT_NAME = "student_name";
    public static String STUDENT_AGE = "student_age";
    public static String STUDENT_CHINESE = "student_chinese";
    public static String STUDENT_MATH = "student_math";
    public static String STUDENT_ENGLISH = "student_english";
    public static final String TBL_FRIEND_CREATE_SQL =
            "CREATE TABLE IF NOT EXISTS " + STUDENT_TABLE + " (" +
                    STUDENT_ID + " INT64 PRIMARY KEY," +
                    STUDENT_NAME + " TEXT," +
                    STUDENT_CHINESE + " TEXT," +
                    STUDENT_MATH + " TEXT," +
                    STUDENT_ENGLISH + " TEXT," +
                    STUDENT_AGE + " TEXT" + ");";


    public static StudentDao getInstance() {
        if (mInstance == null) {
            mInstance = new StudentDao();
        }
        return mInstance;
    }

    /**
     * 插入一条数据
     */
    public void insert(StudentBean student) {
        ContentValues contentValues = getContentValues(student);
        super.insertValue(STUDENT_TABLE, contentValues);
    }

    /**
     * 删除一条数据
     */
    public void delete(String studentId) {
        if (TextUtils.isEmpty(studentId)) {
            return;
        }
        String selection = STUDENT_ID + " = ?";
        super.deleteValue(STUDENT_TABLE, selection, new String[]{studentId});
    }

    /**
     * 删除一条数据
     */
    public void deleteAll() {
        super.deleteValue(STUDENT_TABLE, null, null);
    }


    /**
     * 更新一条数据
     */
    public void update(StudentBean studentBean) {
        ContentValues contentValues = getContentValues(studentBean);
        String selection = STUDENT_ID + " = ?";
        super.updateValue(STUDENT_TABLE, contentValues, selection, new String[]{String.valueOf(studentBean.getStudentId())});
    }


    /**
     * 根据studentId查询单条数据
     *
     * @param studentId
     * @return
     */
    public StudentBean queryItem(String studentId) {
        String selection = STUDENT_ID + " = ?";
        Cursor cursor = super.queryValue(STUDENT_TABLE, null, selection, new String[]{studentId}, null);
        try {
            while (cursor != null && cursor.moveToNext()) {
                StudentBean studentBean = initStudentBean(cursor);
                return studentBean;
            }
            return null;
        } catch (Exception e) {
            return null;
        } finally {
            cursor.close();
        }
    }

    /**
     * 更新一条数据
     */
    public void replace(StudentBean studentBean) {
        ContentValues contentValues = getContentValues(studentBean);
        String selection = STUDENT_ID + " = ?";
        super.replaceValue(STUDENT_TABLE, contentValues, selection, new String[]{String.valueOf(studentBean.getStudentId())});
    }


    /**
     * 根据表中所有的学生信息
     *
     * @param
     * @return
     */
    public List<StudentBean> queryAll() {
        List<StudentBean> list = new ArrayList<>();
        Cursor cursor = super.queryValue(STUDENT_TABLE, null, null, null, null);
        try {
            while (cursor != null && cursor.moveToNext()) {
                StudentBean studentBean = initStudentBean(cursor);
                list.add(studentBean);
            }
            return list;
        } catch (Exception e) {
            return null;
        } finally {
            cursor.close();
        }
    }

    /**
     * 统一修改，对于英语成绩超过95分的学生，语文成绩和数学分别扣除1分
     */
    public void updateStudentChinese() {
        String sql = " update " + STUDENT_TABLE + " set student_chinese = student_chinese -1 , student_math = student_math -1 where " + STUDENT_ENGLISH + " >=95";
        super.execSql(sql);
    }


    /**
     * 查询
     * 英语成绩由高到低，查询所有的数据
     * limit 3:查询前三条数据
     * limit 2,10   查询从index=2（第三条数据开始的算起，共10条数据：【3，12】）
     */
    public List<StudentBean> querySql1() {
        String querySql = "select * from " + STUDENT_TABLE + "  order by student_english desc limit 3";
        Cursor cursor = super.querySql(querySql, null);
        List<StudentBean> list = new ArrayList<>();
        try {
            while (cursor != null && cursor.moveToNext()) {
                StudentBean studentBean = initStudentBean(cursor);
                list.add(studentBean);
            }
            return list;
        } catch (Exception e) {
            return null;
        } finally {
            cursor.close();
        }
    }


    /**
     * 插入语句
     * 创建ContentProviderOperation对象
     */
    public ContentProviderOperation newInsertMessageOperation(StudentBean studentBean) {
        ContentValues contentValues = getContentValues(studentBean);
        ContentProviderOperation operation = ContentProviderOperation.newInsert(getUri(STUDENT_TABLE))
                .withValues(contentValues)
                .build();
        return operation;
    }

    /**
     * 删除语句
     * 创建ContentProviderOperation对象
     */
    public ContentProviderOperation newDeleteMessageOperation(String studentId) {
        String selection = STUDENT_ID + " = ?";
        String[] selectionValue = new String[]{studentId};
        ContentProviderOperation operation = ContentProviderOperation.newDelete(getUri(STUDENT_TABLE))
                .withSelection(selection, selectionValue)
                .build();
        return operation;
    }

    /**
     * 更新语句
     * 创建ContentProviderOperation对象
     */
    public ContentProviderOperation newUpdateMessageOperation(String studentId, StudentBean studentBean) {
        String selection = STUDENT_ID + " = ?";
        String[] selectionValue = new String[]{studentId};
        ContentValues contentValues = getContentValues(studentBean);
        ContentProviderOperation operation = ContentProviderOperation.newUpdate(getUri(STUDENT_TABLE))
                .withSelection(selection, selectionValue)
                .withValues(contentValues)
                .build();
        return operation;
    }

    /**
     * 替换语句
     * 创建ContentProviderOperation对象
     */
    public ContentProviderOperation newReplaceMessageOperation(String studentId, StudentBean studentBean) {
        String selection = STUDENT_ID + " = ?";
        String[] selectionValue = new String[]{studentId};
        ContentValues contentValues = getContentValues(studentBean);
        ContentProviderOperation operation = ContentProviderOperation.newUpdate(getReplaceUri(STUDENT_TABLE))
                .withSelection(selection, selectionValue)
                .withValues(contentValues)
                .build();
        return operation;
    }


    private StudentBean initStudentBean(Cursor cursor) {
        studentBean = new StudentBean();
        studentBean.setStudentId(cursor.getInt(cursor.getColumnIndex(STUDENT_ID)));
        studentBean.setName(cursor.getString(cursor.getColumnIndex(STUDENT_NAME)));
        studentBean.setAge(cursor.getString(cursor.getColumnIndex(STUDENT_AGE)));
        studentBean.setChinese(cursor.getString(cursor.getColumnIndex(STUDENT_CHINESE)));
        studentBean.setMath(cursor.getString(cursor.getColumnIndex(STUDENT_MATH)));
        studentBean.setEnglish(cursor.getString(cursor.getColumnIndex(STUDENT_ENGLISH)));
        return studentBean;
    }


    public ContentValues getContentValues(StudentBean student) {
        if (student == null) {
            return null;
        }
        ContentValues contentValues = new ContentValues();
        contentValues.put(STUDENT_ID, student.getStudentId());
        contentValues.put(STUDENT_NAME, student.getName());
        contentValues.put(STUDENT_AGE, student.getAge());
        contentValues.put(STUDENT_CHINESE, student.getChinese());
        contentValues.put(STUDENT_MATH, student.getMath());
        contentValues.put(STUDENT_ENGLISH, student.getEnglish());
        return contentValues;
    }


}

Três: Demo usa StudentDao

1. Simule a conta de login, principalmente use o userId para criar o banco de dados

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="20dp"
        android:text="登录,请输入账号密码"
        android:background="#E0EBF0"
        android:textSize="30sp"
        />
    <EditText
        android:id="@+id/user_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:background="#EBCCD6"
        android:layout_marginTop="100dp"
        android:layout_marginLeft="20dp"
        android:layout_marginRight="20dp"
        android:textSize="20sp"
        android:inputType="number"
        android:hint="请输入账号"
        />
    <EditText
        android:layout_marginTop="30dp"
        android:id="@+id/user_psw"
        android:layout_width="match_parent"
        android:layout_margin="20dp"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:textSize="20sp"
        android:background="#EBCCD6"
        android:hint="请输入密码"
        />
    <TextView
        android:id="@+id/bt_login"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:text="登录"
        android:background="#C2F8C4"
        android:gravity="center"
        android:layout_marginTop="20dp"
        android:textSize="22sp"
        />

</LinearLayout>

Java correspondente:

public class MainActivity extends AppCompatActivity {

    private EditText et_userName;
    private EditText et_userPsw;
    private TextView tv_login;
    Activity activity;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        activity = this;
        et_userName = findViewById(R.id.user_name);
        et_userPsw = findViewById(R.id.user_psw);
        tv_login = findViewById(R.id.bt_login);
        tv_login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String userName = et_userName.getText().toString().trim();
                String userPsw = et_userPsw.getText().toString().trim();
                if (TextUtils.isEmpty(userName) || userName.length() != 11) {
                    MyToast.showToast(activity, "请输入正确的账号");
                    return;
                }
                if (TextUtils.isEmpty(userPsw) || !userPsw.equals("1111")) {
                    MyToast.showToast(activity, "请输入正确的密码");
                    return;
                }
                AccountManager.setAccountId(activity, userName);
                activity.startActivity(new Intent(activity, StudentActivity.class));
            }
        });
    }


}

2. O funcionamento do formulário do aluno

layout xml:

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        >
<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="10dp"
    android:text="学生表数据库"
    android:textSize="22sp"
    android:textStyle="bold"
    android:gravity="center"
    />
    <EditText
        android:layout_marginTop="20dp"
        android:id="@+id/et_student_id"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:hint="请输入学生编号"
        android:textSize="20sp"
        android:background="#F5D1D1"
        />
    <EditText
        android:id="@+id/et_student_name"
        android:layout_marginTop="20dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:hint="请输入学生姓名"
        android:textSize="20sp"
        android:background="#E0ECF5"
        />
    <EditText
        android:id="@+id/et_student_age"
        android:layout_marginTop="20dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:hint="请输入学生年龄"
        android:textSize="20sp"
        android:background="#F0D6CD"
        />
    <EditText
        android:id="@+id/et_student_chinese"
        android:layout_marginTop="20dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:hint="请输入学生语文成绩"
        android:textSize="20sp"
        android:background="#D8ECEE"
        />
    <EditText
        android:id="@+id/et_student_math"
        android:layout_marginTop="20dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:hint="请输入数学成绩"
        android:textSize="20sp"
        android:background="#F5E4EA"
        />
        <EditText
            android:layout_marginTop="20dp"
            android:id="@+id/et_student_english"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:hint="请输入英语成绩"
            android:textSize="20sp"
            android:background="#F5D1D1"
            />
    <TextView
        android:id="@+id/insert"
        android:layout_marginTop="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:text="新增一条数据"
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="#4056D3"
        android:gravity="center"
        android:background="#BFD8DB"
        />
    <TextView
        android:id="@+id/delete"
        android:layout_marginTop="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:text="删除一条数据"
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="#4056D3"
        android:gravity="center"
        android:background="#BFD8DB"
        />
    <TextView
        android:id="@+id/update"
        android:layout_marginTop="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:text="更新一条数据"
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="#4056D3"
        android:gravity="center"
        android:background="#BFD8DB"
        />
    <TextView
        android:id="@+id/query"
        android:layout_marginTop="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:text="查询一条数据"
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="#4056D3"
        android:gravity="center"
        android:background="#BFD8DB"
        />
    <TextView
        android:id="@+id/query_all"
        android:layout_marginTop="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:text="查询所有数据"
        android:textSize="20sp"
        android:textStyle="bold"
        android:textColor="#4056D3"
        android:gravity="center"
        android:background="#F8D0DE"
        />
        <TextView
            android:id="@+id/replace"
            android:layout_marginTop="10dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:text="替换一条数据"
            android:textSize="20sp"
            android:textStyle="bold"
            android:textColor="#4056D3"
            android:gravity="center"
            android:background="#E7DECF"
            />
        <TextView
            android:id="@+id/apply_replace"
            android:layout_marginTop="10dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:text="批量替换"
            android:textSize="20sp"
            android:textStyle="bold"
            android:textColor="#4056D3"
            android:gravity="center"
            android:background="#E7DECF"
            />
        <TextView
            android:id="@+id/delete_all"
            android:layout_marginTop="10dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:text="批量删除"
            android:textSize="20sp"
            android:textStyle="bold"
            android:textColor="#4056D3"
            android:gravity="center"
            android:background="#E7DECF"
            />
        <TextView
            android:id="@+id/tv_update_sql"
            android:layout_marginTop="10dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:text="sql语句更新"
            android:textSize="20sp"
            android:textStyle="bold"
            android:textColor="#4056D3"
            android:gravity="center"
            android:background="#E7DECF"
            />
        <TextView
            android:id="@+id/tv_query_sql_1"
            android:layout_marginTop="10dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:text="sql语句查询"
            android:textSize="20sp"
            android:textStyle="bold"
            android:textColor="#4056D3"
            android:gravity="center"
            android:background="#E7DECF"
            />
    </LinearLayout>
</ScrollView>

Código Java:

public class StudentActivity extends Activity {
    EditText etStudentId;
    EditText etStudentName;
    EditText etStudentAge;
    EditText etStudentChinese;
    EditText etStudentMath;
    EditText etStudentEnglish;
    TextView tvInsert;
    TextView tvDelete;
    TextView tvUpdate;
    TextView tvQuery;
    TextView tvQueryAll;
    TextView tvPlace;
    TextView tvapplyReplace;
    TextView tvDeleteAll;
    TextView tvUpdateSql;
    TextView tvQuerySql1;


    String studentId;
    String studentName;
    String studentAge;
    String studentChinese;
    String studentMath;
    String studentEnglish;
    Activity activity;


    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        activity = this;
        setContentView(R.layout.activity_student);
        etStudentId = findViewById(R.id.et_student_id);
        etStudentName = findViewById(R.id.et_student_name);
        etStudentAge = findViewById(R.id.et_student_age);
        etStudentChinese = findViewById(R.id.et_student_chinese);
        etStudentMath = findViewById(R.id.et_student_math);
        etStudentEnglish = findViewById(R.id.et_student_english);
        tvInsert = findViewById(R.id.insert);
        tvDelete = findViewById(R.id.delete);
        tvUpdate = findViewById(R.id.update);
        tvQuery = findViewById(R.id.query);
        tvQueryAll = findViewById(R.id.query_all);
        tvPlace = findViewById(R.id.replace);
        tvapplyReplace = findViewById(R.id.apply_replace);
        tvDeleteAll = findViewById(R.id.delete_all);
        tvUpdateSql = findViewById(R.id.tv_update_sql);
        tvQuerySql1 = findViewById(R.id.tv_query_sql_1);
        /**
         * 插入一个学生信息
         */
        tvInsert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
                if (CheckId() && CheckStudentName() && CheckStudentAge()) {
                    StudentBean studentBean = new StudentBean();
                    studentBean.setStudentId(Integer.valueOf(studentId));
                    studentBean.setName(studentName);
                    studentBean.setAge(studentAge);
                    studentBean.setChinese(studentChinese);
                    studentBean.setMath(studentMath);
                    studentBean.setEnglish(studentEnglish);
                    StudentDao.getInstance().insert(studentBean);
                }

            }
        });

        /**
         * 根据UserId删除一个学生信息
         */
        tvDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
                StudentDao.getInstance().delete(studentId);
            }
        });

        /**
         * 根据UserId修改一条数据信息
         */
        tvUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
                StudentBean studentBean = new StudentBean();
                studentBean.setStudentId(Integer.valueOf(studentId));
                studentBean.setName(studentName);
                studentBean.setAge(studentAge);
                studentBean.setChinese(studentChinese);
                studentBean.setMath(studentMath);
                studentBean.setEnglish(studentEnglish);
                StudentDao.getInstance().update(studentBean);
            }
        });
        /**
         * 根据UserId查询一条数据信息
         */
        tvQuery.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
                if (CheckId()) {
                    StudentBean studentBean = StudentDao.getInstance().queryItem(studentId);
                    Log.e("TAGS", "query:" + studentId + ":：：" + getString(studentBean));
                } else {
                    MyToast.showToast(activity, "请输入学生证编号");
                }
            }
        });

        /**
         * 查询学生表的所有数据
         */
        tvQueryAll.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
                List<StudentBean> list = StudentDao.getInstance().queryAll();
                if (list != null && list.size() > 0) {
                    for (int i = 0; i < list.size(); i++) {
                        StudentBean studentBean = list.get(i);
                        Log.e("TAGS", "query_all:::" + getString(studentBean));
                    }
                }
            }
        });

        /**
         * 根据UserId去替换一条数据（如果不存在则直接插入）
         */
        tvPlace.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
                StudentBean studentBean = new StudentBean();
                studentBean.setStudentId(Integer.valueOf(studentId));
                studentBean.setName(studentName);
                studentBean.setAge(studentAge);
                studentBean.setChinese(studentChinese);
                studentBean.setMath(studentMath);
                studentBean.setEnglish(studentEnglish);
                StudentDao.getInstance().replace(studentBean);
            }
        });

        /**
         * 批量插入
         * 将newInsertMessageOperation换成newReplaceMessageOperation则是批量替换
         */
        tvapplyReplace.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Random random = new Random();
                ArrayList<ContentProviderOperation> operationList = new ArrayList<>();
                for (int i = 100; i < 110; i++) {
                    StudentBean studentBean = new StudentBean();
                    studentBean.setStudentId(i);
                    studentBean.setName("liukang" + i);
                    studentBean.setAge(random.nextInt(10) + 90 + "");
                    studentBean.setChinese(random.nextInt(10) + 90 + "");
                    studentBean.setMath(random.nextInt(10) + 90 + "");
                    studentBean.setEnglish(random.nextInt(10) + 90 + "");
                    operationList.add(StudentDao.getInstance().newInsertMessageOperation(studentBean));
                }
                StudentDao.getInstance().applyBatch(MyContentProvider.AUTHORITY_APPLY, operationList);
            }
        });

        /**
         * 删除表中所有的数据
         */
        tvDeleteAll.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                StudentDao.getInstance().deleteAll();
            }
        });

        /**
         * 编写sql语句进行更新操作
         */
        tvUpdateSql.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                StudentDao.getInstance().updateStudentChinese();
            }
        });

        /**
         *编写sql进行查询操作
         */
        tvQuerySql1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                StudentDao.getInstance().querySql1();
                List<StudentBean> list = StudentDao.getInstance().querySql1();
                if (list != null && list.size() > 0) {
                    for (int i = 0; i < list.size(); i++) {
                        StudentBean studentBean = list.get(i);
                        Log.e("TAGS", "query_all:::" + getString(studentBean));
                    }
                }
            }
        });

    }


    public void getData() {
        studentId = etStudentId.getText().toString().trim();
        studentName = etStudentName.getText().toString().trim();
        studentAge = etStudentAge.getText().toString().trim();
        studentChinese = etStudentChinese.getText().toString().trim();
        studentMath = etStudentMath.getText().toString().trim();
        studentEnglish = etStudentEnglish.getText().toString().trim();
    }

    public boolean CheckId() {
        if (!TextUtils.isEmpty(studentId)) {
            return true;
        }

        return false;
    }

    public boolean CheckStudentName() {
        if (!TextUtils.isEmpty(studentName)) {
            return true;
        }

        return false;
    }

    public boolean CheckStudentAge() {
        if (!TextUtils.isEmpty(studentAge)) {
            return true;
        }

        return false;
    }

    public String getString(StudentBean bean) {
        Gson gson = new Gson();
        String s = gson.toJson(bean);
        return s;
    }
}

public class StudentBean {
    private int studentId;
    private String name;
    private String age;
    private String Chinese;
    private String Math;
    private String English;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getStudentId() {
        return studentId;
    }

    public void setStudentId(int studentId) {
        this.studentId = studentId;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    public String getChinese() {
        return Chinese;
    }

    public void setChinese(String chinese) {
        Chinese = chinese;
    }

    public String getMath() {
        return Math;
    }

    public void setMath(String math) {
        Math = math;
    }

    public String getEnglish() {
        return English;
    }

    public void setEnglish(String english) {
        English = english;
    }
}

Resumindo:

1. Armazenamento comumente usado:

sharePrefrence: geralmente armazena dados simples, como interruptores e logotipos. Armazenado na forma de xml, quando o cache for limpo ou desinstalado, ele será limpo de acordo.

Banco de dados: geralmente armazenado no diretório data \ data \ package name \ db, limpar o cache ou desinstalar também será limpo

Armazenamento de arquivos: o mesmo que acima se for a memória do telefone, se estiver no cartão SD, não será apagado (Q envolve sandbox)

Cache de rede: upload, download.

2. Pontos de conhecimento do banco de dados: a criação do banco de dados, atualização     b pacote de classe base: adição, exclusão, modificação, substituição, operação em lote e instrução sql    

3. O conteúdo é muito longo. Copie-o e execute-o diretamente. Basicamente, não há problema em repetir essas operações.

 

 

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