28.android简单的双击退出

//1.---------------------------使用onKeyUp()----------------------------------------------------

//记录用户首次点击返回键的时间
private long firstTime=0;

@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
    switch (keyCode){
        case KeyEvent.KEYCODE_BACK:
            long secondTime=System.currentTimeMillis();
            if(secondTime-firstTime>2000){
                Toast.makeText(MainActivity.this,"再按一次退出程序",Toast.LENGTH_SHORT).show();
                firstTime=secondTime;
                return true;
            }else{
                System.exit(0);
            }
            break;
    }
    return super.onKeyUp(keyCode, event);
}


//2.----------------------------------------使用onKeyDown()---------------------------------------------

//记录用户首次点击返回键的时间
private long firstTime=0;

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(keyCode==KeyEvent.KEYCODE_BACK && event.getAction()==KeyEvent.ACTION_DOWN){
        if (System.currentTimeMillis()-firstTime>2000){
            Toast.makeText(MainActivity.this,"再按一次退出程序",Toast.LENGTH_SHORT).show();
            firstTime=System.currentTimeMillis();
        }else{
            finish();
            System.exit(0);
        }
        return true;
    }
    return super.onKeyDown(keyCode, event);
}

//3.--------------------------------------------------------------onKeyDown()--------------------------------------------------------------------

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    // TODO Auto-generated method stub
    if(keyCode == KeyEvent.KEYCODE_BACK)
    {
        exitBy2Click(); //调用双击退出函数
    }
    return false;
}


//默认为false
private static Boolean isExit = false;

private void exitBy2Click() {
    Timer tExit = null;
    if (isExit == false) {
        isExit = true; // 准备退出
        Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
        tExit = new Timer();
        tExit.schedule(new TimerTask() {
            @Override
            public void run() {
                isExit = false; // 取消退出
            }
        }, 2000); // 如果2秒钟内没有按下返回键，则启动定时器取消掉刚才执行的任务

    } else {
        finish();
        System.exit(0);
    }
}