仿Android 源码处理长按事件

项目中有个需求：当用户长按某个键，当有5秒的时候，提示用户松手。需求非常简单，如何用简单高效的方法来实现呢？

刚开始是打算用个计时器，如果计时达到了5s，就提示用户松手，后面回想android button的长按点击事件，它又是如何实现的呢？

view 的长按点击事件部分源码：

//这是一个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();
            //关键是这个postDelay：500ms之后，执行runnable
            postDelayed(mPendingCheckForLongPress,
                    ViewConfiguration.getLongPressTimeout() - delayOffset);
        }
    }

从上面源码中推断出：当用户按下的时候，过500ms post 一个runnable, 如果在500ms的时候，用户一直都是没有松手的状态，那么就设置longclicklistener，否则就不是长按事件。当然源码比这个复杂，但是大致思路是这样的，同理，我们也仿照这个流程来做：

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之后，查看isLongPressed的变量值：
            if(isLongPressed){//没有做up事件
                Log.d("hxy","5s的事件触发");
            }else{
                mButton.removeCallbacks(mCheckForLongPress1);
            }
        }
    }

}