專案中有個需求：當用戶長按某個鍵，當有5秒的時候，提示使用者鬆手。需求非常簡單，如何用簡單高效的方法來實現呢？

剛開始是打算用個計時器，如果計時達到了5s，就提示使用者鬆手，後面回想android button的長按點選事件，它又是如何實現的呢？

view 的長按點選事件部分原始碼：

//這是一個runnable
private CheckForLongPress mPendingCheckForLongPress;


private final class CheckForLongPress implements Runnable {
        private int mOriginalWindowAttachCount;
        private
 
 float mX;
        private float mY;

        @Override
        public void run() {
            if (isPressed() && (mParent != null)
                    && mOriginalWindowAttachCount == mWindowAttachCount) {
                if (performLongClick(mX, mY)) {
                    mHasPerformedLongPress = true
 
;
                }
            }
        }

        public void setAnchor(float x, float y) {
            mX = x;
            mY = y;
        }

        public void rememberWindowAttachCount() {
            mOriginalWindowAttachCount = mWindowAttachCount;
        }
    }


//初始化的地方：
private void checkForLongClick
 
(int delayOffset, float x, float y) {
        if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
            mHasPerformedLongPress = false;

            if (mPendingCheckForLongPress == null) {
                mPendingCheckForLongPress = new CheckForLongPress();
            }
            mPendingCheckForLongPress.setAnchor(x, y);
            mPendingCheckForLongPress.rememberWindowAttachCount();
            //關鍵是這個postDelay：500ms之後，執行runnable
            postDelayed(mPendingCheckForLongPress,
                    ViewConfiguration.getLongPressTimeout() - delayOffset);
        }
    }

從上面原始碼中推斷出：當用戶按下的時候，過500ms post 一個runnable, 如果在500ms的時候，使用者一直都是沒有鬆手的狀態，那麼就設定longclicklistener，否則就不是長按事件。當然原始碼比這個複雜，但是大致思路是這樣的，同理，我們也仿照這個流程來做：

public class LongPressActivity extends Activity implements View.OnTouchListener{

    private Button mButton;
    private CheckForLongPress1 mCheckForLongPress1;
    private volatile boolean  isLongPressed = false;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_long_press);
        mButton = (Button) findViewById(R.id.btn_long);
        mCheckForLongPress1 = new CheckForLongPress1();
        mButton.setOnTouchListener(this);

    }


    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()){
            case MotionEvent.ACTION_DOWN:
                Log.d("hxy","action down");
                isLongPressed = true;
                mButton.postDelayed(mCheckForLongPress1,5000);
                break;
            case MotionEvent.ACTION_MOVE:
                isLongPressed = true;
                break;
            case MotionEvent.ACTION_UP:
                isLongPressed = false;
                Log.d("hxy","action up");
                break;

        }

        return super.onTouchEvent(event);
    }

    private class CheckForLongPress1 implements Runnable{

        @Override
        public void run() {
            //5s之後，檢視isLongPressed的變數值：
            if(isLongPressed){//沒有做up事件
                Log.d("hxy","5s的事件觸發");
            }else{
                mButton.removeCallbacks(mCheckForLongPress1);
            }
        }
    }

}