两次返回退出应用

public class MainActivity extends Activity{

//定义一个变量，来标识是否退出

private static boolean isExit=false;


Handler handler=new Handler(){

@Override

public void handleMessage(Message msg){

super.handleMessage(msg);

isExit=false;

}

};


@Override

public boolean onKeyDown(int keyCode,KeyEvent event){

if(keyCode==KeyEvent.KEYCODE_BACK){

exit();

return false;

}

return super.onKeyDown(keyCode,event);

}


private void exit(){

if(!isExit){

isExit=true;

Toast.makeText(getApplicationContext(),"再按一

退出程序",Toast.LENGTH_SHORT).show();

//利用handler延迟发送更改状态信息

handler.sendEmptyMessageDelayed(0,2000);

}

else{

finish();

System.exit(0);

}

}