Android的简单应用（二）——使用dispatchKeyEvent双击退出程序

Android系统按键操作最先是在dispatchKeyEvent中进行处理的，然后才是onKeyDown(int keyCode, KeyEvent event)和onKeyUp(int keyCode, KeyEvent event)。

同理，触摸操作也是先在dispatchTouchEvent中进行处理，在分发给onTouchEvent进行处理。

代码很简单，只要掌握好事件的分发顺序就ok了。
Activity中的代码：

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // TODO Auto-generated method stub
        Log.d("CPACM","onKeyDown");
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        // TODO Auto-generated method stub
        Log.d("CPACM","onKeyUp");
        return super.onKeyUp(keyCode, event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        Log.d("CPACM","onTouchEvent");
        return super.onTouchEvent(event);
    }

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        Log.d("CPACM","dispatchKeyEvent");
        if(event.getKeyCode() == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN){
            if(System.currentTimeMillis() - preTime < 2000){//在两秒内，退出

                return super.dispatchKeyEvent(event);
            }            Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();             //System.exit(0);
            preTime = System.currentTimeMillis();
            return true;
        }
        // TODO Auto-generated method stub
        return super.dispatchKeyEvent(event);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        // TODO Auto-generated method stub
        Log.d("CPACM","dispatchTouchEvent");
        return super.dispatchTouchEvent(ev);
    }

顺便附一张截图~