目录
前言:
Android 提供了 SQLiteOpenHelper 接口用作使用SQLite 数据库，提供的方法已经可以非常方便且简洁的使用增删改查操作，但是在调用的时候需要设置很多变量。所以我写了一个更加简洁，可以直接将类传入的保存的工具类.
这个工具类使用起来非常简洁，我将int类与long 类识别出来存储，其他的类型全部都用字符串类型。如果不想还原为类对象，或许使用Json解析的工具包
FastJSON 或者Gson
效果会更好
创建数据库 这个推荐在onCreate方法内使用
这里需要使用存放数据的类。
DBItem.java
public class DBItem {
public int id = -1;
public String name;
public String drive;
@Override
public boolean equals(Object obj) {
return obj instanceof DBItem && ((DBItem) obj).id == id;
}
@Override
public String toString() {
return "{id: "+id+", name: "+name+", drive: "+drive+" }";
}
}
创建数据库
DBOpenHelper dbOpenHelper = DBOpenHelper.createDBHelper(
context,
"数据库名",
DBOpenHelper.DBTable.asDBTable(DBItem.class),
1);增加数据
dbOpenHelper.add(new DBItem());删除数据
// 根据对象删除
dbOpenHelper.remove(new DBItem());
//根据ID 删除
dbOpenHelper.remove(id);修改数据
// 直接修改内容 这个会识别内部的 id 根据ID更新
dbOpenHelper.set(new DBItem());
// 手动更新内容
dbOpenHelper.set(int id,ContentValues values);查询数据
// 获取全部的数据
List<DBItem> dbItems = dbOpenHelper.getAll(DBItem.class);
//根据ID查询到存入的类
DBItem dbItems = dbOpenHelper.get(id,DBItem.class);完整代码
DBOpenHelper.java
public class DBOpenHelper extends SQLiteOpenHelper {
private SQLiteDatabase database;
private static String NAME = "drive";
private static String TAG = NAME+"DB";
private static String TABLE = NAME;
private static String DB_FILE = NAME+".db";
private static DBTable tables;
private Context context;
private DBOpenHelper(Context context,
String name,
SQLiteDatabase.CursorFactory factory,
int version) {
super(context, name, factory, version);
database = getWritableDatabase();
this.context = context;
}
//id integer primary key autoincrement,step integer,time varchar(20)
@Override
public void onCreate(SQLiteDatabase db) {
String sql = "create table "+TABLE+"("+tables.asSql()+")";
db.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
/**
* 增加数据
* */
public <T> DBOpenHelper add(T values){
if(database != null){
ContentValues contentValues = new ContentValues();
Class c = values.getClass();
for(Field field: c.getFields()){
try {
if(field.getType() == int.class || field.getType() == long.class){
if(field.getName().equalsIgnoreCase("id")){
continue;
}
if(field.getType() == int.class ){
contentValues.put(field.getName(),field.getInt(values));
}else{
contentValues.put(field.getName(),field.getLong(values));
}
}else{
contentValues.put(field.getName(),field.get(values).toString());
}
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
database.insert(TABLE,null,contentValues);
}else{
Log.e(TAG,"数据库不存在");
}
return this;
}
/**
* 增加数据
* */
public DBOpenHelper add(ContentValues values){
if(database != null){
database.insert(TABLE,null,values);
}else{
Log.e(TAG,"数据库不存在");
}
return this;
}
/**
* 删除数据
* */
public DBOpenHelper remove(int id){
if(database != null) {
database.delete(TABLE, "id=?", new String[]{id + ""});
}else{
Log.e(TAG,"数据库不存在");
}
return this;
}
/**
* 删除数据
* */
public DBOpenHelper remove(Object id){
try{
if(id.getClass().getField("id") != null){
return remove(id.getClass().getField("id").getInt(id));
}
}catch (Exception e){
throw new NullPointerException("传入的类必须要有 id");
}
return this;
}
public <T> DBOpenHelper set(T values){
ContentValues contentValues = new ContentValues();
Class c = values.getClass();
int id = -1;
for(Field field: c.getFields()){
try {
if(field.getType() == int.class || field.getType() == long.class){
if(field.getName().equalsIgnoreCase("id")){
id = field.getInt(values);
continue;
}
if(field.getType() == int.class ){
contentValues.put(field.getName(),field.getInt(values));
}else{
contentValues.put(field.getName(),field.getLong(values));
}
}else{
contentValues.put(field.getName(),field.get(values).toString());
}
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
if(id == -1){
throw new NullPointerException("无 id 信息");
}
return set(id,contentValues);
}
/**
* 更新数据
* */
public DBOpenHelper set(int id,ContentValues values){
if(database != null) {
database.update(TABLE, values, "id=?", new String[]{id + ""});
}else {
Log.e(TAG,"数据库不存在");
}
return this;
}
public <T> T get(int id, Class<T> a){
T t = null;
try (Cursor cursor = database.query(TABLE, null, "id=?",
new String[]{id + ""}, null, null, null)) {
t = a.newInstance();
Class tc = t.getClass();
t = explainClass(cursor,tc,t);
} catch (IllegalAccessException | InstantiationException e) {
e.printStackTrace();
}
return t;
}
public <T> LinkedList<T> getAll(Class<T> a){
LinkedList<T> datas = new LinkedList<>();
Cursor cursor = database.query(TABLE, null, null,
null, null, null,null);
while (cursor.moveToNext()){
T t;
try {
t = a.newInstance();
Class tc = t.getClass();
t = explainClass(cursor,tc,t);
datas.add(t);
} catch (IllegalAccessException | InstantiationException e) {
e.printStackTrace();
}
}
cursor.close();
return datas;
}
public static class DBTable {
LinkedHashMap<String,String> tables = new LinkedHashMap<>();
public DBTable(String key,String value){
tables.put(key, value);
}
public DBTable(Map<String,String> m){
System.out.println(m);
tables.putAll(m);
}
public DBTable put(String key,String value){
tables.put(key, value);
return this;
}
public String asSql(){
StringBuilder s = new StringBuilder();
for (Map.Entry<String,String> e:tables.entrySet()) {
s.append(e.getKey()).append(" ").append(e.getValue()).append(",");
}
return s.toString().substring(0,s.length() - 1);
}
public static DBTable asDBTable(Class t){
Field[] fields = t.getFields();
LinkedHashMap<String,String> stringStringLinkedHashMap = new LinkedHashMap<>();
boolean isId = false;
// 先找自增id
for(Field field: fields){
if(field.getName().equalsIgnoreCase("id") && field.getType() == int.class){
//找到了
isId = true;
}
}
if(!isId){
throw new NullPointerException("数据库类需要一个id");
}
stringStringLinkedHashMap.put("id","integer primary key autoincrement");
for(Field field: fields){
if(field.getName().equalsIgnoreCase("id") && field.getType() == int.class){
//找到了
continue;
}
if(field.getType() == float.class || field.getType() == double.class){
stringStringLinkedHashMap.put(field.getName().toLowerCase(),field.getType().getName());
}else{
stringStringLinkedHashMap.put(field.getName().toLowerCase(),"varchar(20)");
}
}
return new DBTable(stringStringLinkedHashMap);
}
}
public static DBOpenHelper createDBHelper(Context context,String tableName,DBTable tables,int version){
DBOpenHelper.NAME = tableName;
DBOpenHelper.tables = tables;
return new DBOpenHelper(context,DBOpenHelper.DB_FILE,null,version);
}
private <T> T explainClass(Cursor cursor, Class tc, T t){
for (String name : cursor.getColumnNames()) {
try {
Field field = tc.getField(name);
if(field.getType() == int.class){
field.set(t, cursor.getInt(cursor.getColumnIndex(name)));
}else
if(field.getType() == float.class || field.getType() == double.class){
field.set(t, cursor.getFloat(cursor.getColumnIndex(name)));
}else
if(field.getType() == boolean.class){
field.set(t, Boolean.valueOf(cursor.getString(cursor.getColumnIndex(name))));
}else
if(field.getType() == long.class){
field.set(t, cursor.getLong(cursor.getColumnIndex(name)));
}else{
field.set(t, cursor.getString(cursor.getColumnIndex(name)));
}
} catch (IllegalAccessException | NoSuchFieldException e) {
e.printStackTrace();
}
}
return t;
}
public void clear(){
context.deleteDatabase(DB_FILE);
}
}
后话
当数据存储过多的时候使用 getAll 是很不理智的，最好改写一下，读取改为分页读取。