Android中Sqlite使用初步
1、使用Sqlite的关键是创建一类，这个类继承SQLiteOpenHelper，继承的类必须重写三个方法：构造方法，onCreate方法，onUpgrate方法
2、SQLiteDatabase是直接操作数据库的对象，可以使用SQLiteOpenHelper的getReadableDatabase或getWritableDatabase方法得到SQLiteDatabase对象。具体使用这两个方法得到的SQLiteDatabase对象的不用点，根据方法名就可以看出。一个是得到可读的，一个是得到可写的。
实例代码：
1、布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<Button android:id="@+id/createDatabase" android:layout_width="fill_parent"
android:layout_height="wrap_content" android:text="Create Database"></Button>
<Button android:id="@+id/upgrateDatabase" android:layout_width="fill_parent"
android:layout_height="wrap_content" android:text="Upgrate Database"></Button>
<Button android:id="@+id/insert" android:layout_width="fill_parent"
android:layout_height="wrap_content" android:text="Insert"></Button>
<Button android:id="@+id/update" android:layout_width="fill_parent"
android:layout_height="wrap_content" android:text="Update"></Button>
<Button android:id="@+id/query" android:layout_width="fill_parent"
android:layout_height="wrap_content" android:text="Query"></Button>
<Button android:id="@+id/delete" android:layout_width="fill_parent"
android:layout_height="wrap_content" android:text="Delete"></Button>
</LinearLayout>
2、自定义继承SQLiteOpenHelper的类，重写三个方法
package yyl.db;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper {
//构造函数
public DatabaseHelper(Context context,String name,CursorFactory factory, int version)
{
super(context,name,factory,version);
}
//该函数在第一次创建数据库的时候执行
@Override
public void onCreate(SQLiteDatabase db) {
System.out.println("Creaet a database test_user and table user");
db.execSQL("create table user (id int,name varchar(20))");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
System.out.println("upgrate a database");
}
}
3、数据库操作代码
package yyl.sqlite;
import yyl.db.DatabaseHelper;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class SqliteActivity extends Activity {
// 定义变量
private Button createDatabase = null;
private Button upgrateDatabase = null;
private Button insert = null;
private Button update = null;
private Button query = null;
private Button delete = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// 根据ID得到控件对象
createDatabase = (Button) findViewById(R.id.createDatabase);
upgrateDatabase = (Button) findViewById(R.id.upgrateDatabase);
insert = (Button) findViewById(R.id.insert);
update = (Button) findViewById(R.id.update);
query = (Button) findViewById(R.id.query);
delete = (Button) findViewById(R.id.delete);
// 给按钮绑定单击事件监听器
createDatabase.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//生成DatabaseHelper对象
DatabaseHelper databaseHelper = new DatabaseHelper(SqliteActivity.this,"sqlite_user",null,1);
//只有调用了getReadableDatabase方法，或者getWritableDatabase方法，才会创建数据库
databaseHelper.getReadableDatabase();
}
});
upgrateDatabase.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//生成DatabaseHelper对象
DatabaseHelper databaseHelper = new DatabaseHelper(SqliteActivity.this,"sqlite_user",null,2);
//只有调用了getReadableDatabase方法，或者getWritableDatabase方法，才会更新数据库
databaseHelper.getReadableDatabase();
}
});
insert.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//创建ContentValue对象
ContentValues values = new ContentValues();
//插入键值对，注意值的类型必须和数据库表中字段的类型一致
values.put("id", 1);
values.put("name", "yangyulin");
//生成SQLiteDatabase对象
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this,"test_user",null,1);
SQLiteDatabase db = dbHelper.getWritableDatabase();
//执行插入
db.insert("user", null, values);
}
});
update.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//生成DatabaseHelper对象
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this,"test_user",null,1);
//调用DatabaseHelper的getWritableDatabase方法，生成SQLiteDatabase对象
SQLiteDatabase db = dbHelper.getWritableDatabase();
//生成ContentValues对象，并设定键值对
ContentValues values = new ContentValues();
values.put("name", "newSky");
//更新表信息:update user set name = 'newSky' where id =1;
db.update("user", values, " id=?", new String[]{"1"});
}
});
query.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//生成DatabaseHelper对象
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this,"test_user",null,1);
//调用DatabaseHelper的getReadableDatabase方法，生成SQLiteDatabase对象
SQLiteDatabase db = dbHelper.getReadableDatabase();
//执行查询，将查询结果放入到Cursor中
Cursor cursor = db.query("user", new String[]{"id","name"}, " id =?", new String[]{"1"}, null, null, null);
//打印查询结果
while(cursor.moveToNext())
{
String name = cursor.getString(cursor.getColumnIndex("name"));
System.out.println("name --> " + name);
}
}
});
delete.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//生成DatabaseHelper对象
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this,"test_user",null,1);
//调用DatabaseHelper的getReadableDatabase方法，生成SQLiteDatabase对象
SQLiteDatabase db = dbHelper.getWritableDatabase();
db.delete("user", "id =?", new String[]{"1"});
}
});
}
}
查看数据库：
1、在CMD命令行下输入以下命令
>adb shelll
#>cd data/data/yyl.sqlite
#>cd databases
#>sqlite3 test_user
#>.schema
#>select * from user;