数据库实现增删改查

布局
<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="${relativePackage}.${activityClass}" >

    <Button 
        android:id="@+id/btn1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="添加"
        android:onClick="add"
        />
    
    <Button 
        android:id="@+id/btn2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="查询"
        android:onClick="select"
        />
    
    
    <Button 
        android:id="@+id/btn3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="删除"
        android:onClick="delete"
        />
    
    
    <Button 
        android:id="@+id/btn4"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="修改"
        android:onClick="update"
        />

</LinearLayout>

package com.example.nshujuk3;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends Activity {

UerDao uerdao;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    
    uerdao = new UerDao(this);
}

public void add(View v){
	uerdao.add("张","20");
}
public void delete(View v){
	uerdao.delete("张");
}
public void update(View v){
	uerdao.update("霍","20","张");
}
public void select(View v){
	String name = uerdao.select();
	Toast.makeText(MainActivity.this,name,Toast.LENGTH_SHORT).show();
}

}

package com.example.nshujuk3;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class Sql extends SQLiteOpenHelper{

public Sql(Context context) {
	super(context,"User-db",null,1);
	// TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db) {
	// TODO Auto-generated method stub
	db.execSQL("create table user(id integer primary key autoincrement,"+"name text,"+"age text)");
	 
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
	// TODO Auto-generated method stub
	
}

}

package com.example.nshujuk3;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.view.View;

public class UerDao {

Sql sql;
SQLiteDatabase database;
public UerDao(Context context){
	sql = new Sql(context);
	
	database = sql.getReadableDatabase();
}
public void add(String string, String string2) {
	// TODO Auto-generated method stub
	database.execSQL("insert into user (name,age) values(?,?)",
			new Object[]{string,string2}
			);
}
public void delete(String string) {
	// TODO Auto-generated method stub
	database.execSQL("delete from user where name = ?",
			new Object[]{string}
			);
}
public void update(String string, String string2, String string3) {
	// TODO Auto-generated method stub
	database.execSQL("update user  set name=?,age=? where name=?",
			new Object[]{string,string2,string3}
			);
	
	
	 
}
public String select() {
	// TODO Auto-generated method stub
	Cursor cursor = database.rawQuery("select * from user",null);
	StringBuffer buffer = new StringBuffer();
	while(cursor.moveToNext()){
		String name = cursor.getString(cursor.getColumnIndex("name"));
		String age = cursor.getString(cursor.getColumnIndex("age"));
		buffer.append(name+age);
	}
	return buffer.toString();
}

}