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简介
Android自带了一种轻量级数据库SQLite，而且它支持SQL语句。
SQLiteOpenHelper
是SQLiteDatabase一个辅助类，主要生成一个数据库，并对数据库进行管理。SQLiteOpenHelper 是一个抽象类，我们通常需要继承它，并且实现里面的3个函数：
onCreate（SQLiteDatabase db）
在数据库第一次生成的时候会调用这个方法，也就是说，只有在创建数据库的时候才会调用，当然也有一些其它的情况，一般我们在这个方法里边生成数据库表。onUpgrade（SQLiteDatabase db, int oldVersion, int newVersion）
当数据库需要升级的时候，Android系统会主动的调用这个方法。一般我们在这个方法里边删除数据表，并建立新的数据表。insert(String table, String nullColumnHack, ContentValues values)
api里面是这样描述的，插入一行数据到数据库里面。
/**
* Convenience method for inserting a row into the database.
*
* @param table the table to insert the row into
* @param nullColumnHack optional; may be <code>null</code>.
* SQL doesn't allow inserting a completely empty row without
* naming at least one column name. If your provided <code>values</code> is
* empty, no column names are known and an empty row can't be inserted.
* If not set to null, the <code>nullColumnHack</code> parameter
* provides the name of nullable column name to explicitly insert a NULL into
* in the case where your <code>values</code> is empty.
* @param values this map contains the initial column values for the
* row. The keys should be the column names and the values the
* column values
* @return the row ID of the newly inserted row, or -1 if an error occurred
*/
public long insert(String table, String nullColumnHack, ContentValues values) {
try {
return insertWithOnConflict(table, nullColumnHack, values, CONFLICT_NONE);
} catch (SQLException e) {
Log.e(TAG, "Error inserting " + values, e);
return -1;
}
}- delete(String table, String whereClause, String[] whereArgs)
api里面的描述，参数（表名，删除条件，删除条件值数组）
/**
* Convenience method for deleting rows in the database.
*
* @param table the table to delete from
* @param whereClause the optional WHERE clause to apply when deleting.
* Passing null will delete all rows.
* @param whereArgs You may include ?s in the where clause, which
* will be replaced by the values from whereArgs. The values
* will be bound as Strings.
* @return the number of rows affected if a whereClause is passed in, 0
* otherwise. To remove all rows and get a count pass "1" as the
* whereClause.
*/
public int delete(String table, String whereClause, String[] whereArgs) {
acquireReference();
try {
SQLiteStatement statement = new SQLiteStatement(this, "DELETE FROM " + table +
(!TextUtils.isEmpty(whereClause) ? " WHERE " + whereClause : ""), whereArgs);
try {
return statement.executeUpdateDelete();
} finally {
statement.close();
}
} finally {
releaseReference();
}
}- update(String table, ContentValues values, String whereClause, String[] whereArgs)
api里面描述，参数（表名，更新值，更新条件，更新条件值数组）
/**
* Convenience method for updating rows in the database.
*
* @param table the table to update in
* @param values a map from column names to new column values. null is a
* valid value that will be translated to NULL.
* @param whereClause the optional WHERE clause to apply when updating.
* Passing null will update all rows.
* @param whereArgs You may include ?s in the where clause, which
* will be replaced by the values from whereArgs. The values
* will be bound as Strings.
* @return the number of rows affected
*/
public int update(String table, ContentValues values, String whereClause, String[] whereArgs) {
return updateWithOnConflict(table, values, whereClause, whereArgs, CONFLICT_NONE);
}- query(String table, String[] columns, String selection,
String[] selectionArgs, String groupBy, String having,
String orderBy)
查询返回的是一个Cursor，参数（表名称，列名数组，查询条件，查询条件值数组，分组列，分组条件，排序，分页查询限制）
/**
* Query the given table, returning a {@link Cursor} over the result set.
*
* @param table The table name to compile the query against.
* @param columns A list of which columns to return. Passing null will
* return all columns, which is discouraged to prevent reading
* data from storage that isn't going to be used.
* @param selection A filter declaring which rows to return, formatted as an
* SQL WHERE clause (excluding the WHERE itself). Passing null
* will return all rows for the given table.
* @param selectionArgs You may include ?s in selection, which will be
* replaced by the values from selectionArgs, in order that they
* appear in the selection. The values will be bound as Strings.
* @param groupBy A filter declaring how to group rows, formatted as an SQL
* GROUP BY clause (excluding the GROUP BY itself). Passing null
* will cause the rows to not be grouped.
* @param having A filter declare which row groups to include in the cursor,
* if row grouping is being used, formatted as an SQL HAVING
* clause (excluding the HAVING itself). Passing null will cause
* all row groups to be included, and is required when row
* grouping is not being used.
* @param orderBy How to order the rows, formatted as an SQL ORDER BY clause
* (excluding the ORDER BY itself). Passing null will use the
* default sort order, which may be unordered.
* @return A {@link Cursor} object, which is positioned before the first entry. Note that
* {@link Cursor}s are not synchronized, see the documentation for more details.
* @see Cursor
*/
public Cursor query(String table, String[] columns, String selection,
String[] selectionArgs, String groupBy, String having,
String orderBy) {
return query(false, table, columns, selection, selectionArgs, groupBy,
having, orderBy, null /* limit */);
}demo继承SQLiteOpenHelper代码
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DemoHelper extends SQLiteOpenHelper {
public static final int VERSION = 1;
public static final String DB_TABLE = "demo_table";
public DemoHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version){
super(context,name,factory,version);
}
@Override
public void onCreate(SQLiteDatabase db) {
String sql = "create table "+DB_TABLE+"(id int,tellname varchar(20),tell varchar(20))";
Log.d("song--->","create table demo_table");
db.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.d("song--->","update table demo_table");
}
}使用DemoHelper代码
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
public class MainActivity extends AppCompatActivity {
DemoHelper mDemoHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
private void createDabase(){
//mDemoHelper = new DemoHelper(this, "demo_db", null, DemoHelper.VERSION);
Log.d("song--->","create db");
mDemoHelper = new DemoHelper(this, "demo_db", null, DemoHelper.VERSION);
}
public void clickCreate(View v){
createDabase();
}
public void clickInsert(View v){
//id int,name varchar(20),tell varchar(20)
if(null == mDemoHelper) createDabase();
SQLiteDatabase db = mDemoHelper.getWritableDatabase();
//方法一
// ContentValues values = new ContentValues();
// values.put("id","1");
// values.put("tellname","song");
// values.put("tell","110");
// db.insert(DemoHelper.DB_TABLE,null,values);
// Log.d("song--->","insert values id = 1,tellname = song,tell = 110");
//方法二：
String sqlInsert = "insert into "+DemoHelper.DB_TABLE+"(id,tellname,tell) values('3','InsertSong','111')";
db.execSQL(sqlInsert);
Log.d("song--->","insert values id = 3,song = InsertSong,tell = 111");
db.close();
}
public void clickDelete(View v){
if(null == mDemoHelper) createDabase();
SQLiteDatabase db = mDemoHelper.getWritableDatabase();
//方法一：
// db.delete(DemoHelper.DB_TABLE,"id=?",new String[]{"1"});
// Log.d("song--->","delete values id = 1");
//方法二：
String sqlDelete = "delete from "+DemoHelper.DB_TABLE+" where id = 3";
db.execSQL(sqlDelete);
Log.d("song--->","delete values id = 3");
db.close();
}
public void clickquery(View v){
if(null == mDemoHelper) createDabase();
SQLiteDatabase db = mDemoHelper.getReadableDatabase();
Cursor cursor = db.query(DemoHelper.DB_TABLE, /*new String[]{"id","tellname","tell"}*/null, /*"id=?"*/null, /*new String[]{"1"}*/null, null, null, null);
//Cursor cursor = db.query(DemoHelper.DB_TABLE, new String[]{"id","tellname","tell"}, "id=?", new String[]{"1"}, null, null, null);
while (cursor.moveToNext()){
int id = cursor.getInt(cursor.getColumnIndex("id"));
String tellname = cursor.getString(cursor.getColumnIndex("tellname"));
String tell = cursor.getString(cursor.getColumnIndex("tell"));
Log.d("song--->","query message id = "+id+",tellname = "+tellname+",tell = "+tell);
}
cursor.close();
db.close();
}
public void clickUpdate(View v){
if(null == mDemoHelper) createDabase();
SQLiteDatabase db = mDemoHelper.getWritableDatabase();
//方法一：
// ContentValues contentValues = new ContentValues();
// contentValues.put("tellname","song111");
// db.update(DemoHelper.DB_TABLE, contentValues, "id=?", new String[]{"1"});
//方法二：
String sqlUpdate = "update "+DemoHelper.DB_TABLE+" set tellname = 'songUpdate' where id = 3";
db.execSQL(sqlUpdate);
Log.d("song--->","update...");
clickquery(v);
db.close();
}
}布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
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="60dp"
android:layout_marginTop="4dp"
android:background="@color/colorGreay"
android:gravity="center"
android:onClick="clickCreate"
android:text="onClickCreate" />
<TextView
android:layout_width="match_parent"
android:layout_height="60dp"
android:layout_marginTop="4dp"
android:background="@color/colorGreay"
android:gravity="center"
android:onClick="clickInsert"
android:text="onClickInsert" />
<TextView
android:layout_width="match_parent"
android:layout_height="60dp"
android:layout_marginTop="4dp"
android:background="@color/colorGreay"
android:gravity="center"
android:onClick="clickDelete"
android:text="onClickDelete" />
<TextView
android:layout_width="match_parent"
android:layout_height="60dp"
android:layout_marginTop="4dp"
android:background="@color/colorGreay"
android:gravity="center"
android:onClick="clickquery"
android:text="onClickQuery" />
<TextView
android:layout_width="match_parent"
android:layout_height="60dp"
android:layout_marginTop="4dp"
android:background="@color/colorGreay"
android:gravity="center"
android:onClick="clickUpdate"
android:text="onClickUpdate" />
</LinearLayout>demo地址
最后附上demo的地址，感兴趣的同学可以去下载玩玩，点击传送