Android view触摸反馈原理和源码分析

爱被打了一巴掌 2023-06-11 07:27 7阅读 0赞

*  重写onTouchEvent(),在方法内部定制触摸反馈算法
    
     *  是否消费事件取决于ACTION\_DOWN事件或POINTER\_DOWN事件是否返回true
     *  MotionEvent
        
         *  getActionMasked()和getAction()有什么区别
         *  POINTER\_DOWN/POINTER\_UP和getActionIndex()的联系

首先了解下getAction(),getActionMasked()和getActionIndex()区别

> getAction() 返回的是响应的事件，考虑使用getActionMasked或者getActionIndex来得到分隔开的动作和手指的下标。返回的一般是ACTION\_DOWN，合并起来的已经转移的手指下标的ACTION\_POINTER\_DOWN。

> getActionMasked()返回的是具体的响应事件，没有手指下标的信息。可以使用getActionIndex来返回和手指动作相关的下标，返回的值：比如：ACTION\_DOWN，ACTION\_POINTER\_DOWN。

> getActionIndex()返回的是如果调用getActionMasked返回ACTION\_POINTER\_DOWN或者ACTION\_POINTER\_UP,这个方法返回的是ACTION\_POINTER\_DOWN，ACTION\_POINTER\_UP相关的下标，这个下标可能会在getPointerId，getX,getY,getPressed,getSize中用到来获取手指的关于按下或者抬起的信息。

event.getAction()是早期代码中使用的，在多点触控时期才有的event.getActionMasked()方法，由于需要区分是第一个手指按下或者非第一个手指按下，最后一个手指抬起还是非最后一个手指抬起，所以有了ACTION\_DOWN和ACTION\_POINTER\_DOWN,ACTIN\_UP和ACTION\_POINTER\_UP，如果是普通的DOEN,MOVE,UP,CANCLE事件这两个方法都可以用，如果支持多点触控，那就只能用getActionMasked()，所以直接用getActionMasked()即可

## 源码分析 ##

查看view的的源码onTouchEvent方法

public boolean onTouchEvent(MotionEvent event) {
            //获取基本信息
            final float x = event.getX();
            final float y = event.getY();
            final int viewFlags = mViewFlags;
            final int action = event.getAction();
            //判断是否是可点击，CONTEXT_CLICKABLE上下文菜单类似于右键
            final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
                    || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
                    || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
            // 如果是不可用状态，返回clickable，问题来了，问什么不可用状态还要返回clickable呢，打个比方，
            个人中页面上面的头像区域和头像背景区域都能点击，当头像的imageview设置了DISABLED，只是头像不能点击了，
            但是头像的背景区域仍能点击，相当于头像只把事件吃掉，但不处理事件。
            if ((viewFlags & ENABLED_MASK) == DISABLED) {
                if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
                    setPressed(false);
                }
                mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                // 可单击的禁用视图仍然消耗触摸事件，只是不响应它们
                return clickable;
            }
            //增大点击范围，一般不需要考虑
            if (mTouchDelegate != null) {
                if (mTouchDelegate.onTouchEvent(event)) {
                    return true;
                }
            }
            //关键代码
            if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
               ...
               ...
               ...
            }

在看onTouchEvent()关键代码 之前，什么叫TOOLTIP  
Android API 28的时候加入的属性，看个例子  
![format_png][]  
在view任意位置长按，显示文本  
![format_png 1][]  
它的作用是解释这个view是什么，干什么用等，进入上述话题，关键代码：

if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
                switch (action) {
                    case MotionEvent.ACTION_UP:
                        ...
                    case MotionEvent.ACTION_DOWN:
                        ...
                    case MotionEvent.ACTION_CANCEL:
                        ...
                    case MotionEvent.ACTION_MOVE:
                        ...
                }
                return true;
            }

### MotionEvent.ACTION\_DOWN ###

case MotionEvent.ACTION_DOWN:
                        //是否触摸到屏幕
                        if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
                            mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
                        }
                        mHasPerformedLongPress = false;
                        
                        if (!clickable) {
                            //1.如果不可点击，设置长按等待器，
                            //checkForLongClick的源码见 1.
                            checkForLongClick(0, x, y);
                            break;
                        }
                        //2.检测鼠标和右键点击
                        //performButtonActionOnTouchDown源码见 2.
                        if (performButtonActionOnTouchDown(event)) {
                            break;
                        }
    
                        // 是否在滑动控件内.
                        boolean isInScrollingContainer = isInScrollingContainer();
    
                        //在滑动控件内
                        if (isInScrollingContainer) {
                            //状态置为预按下
                            mPrivateFlags |= PFLAG_PREPRESSED;
                            if (mPendingCheckForTap == null) {
                            //点击等待期，是一个runnable
                            //CheckForTap 源码见 3.
                                mPendingCheckForTap = new CheckForTap();
                            }
                            mPendingCheckForTap.x = event.getX();
                            mPendingCheckForTap.y = event.getY();
                            postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                        } else {   
                        //如果不在滑动控件内，设置为按下状态和长按等待器(设置长按事件但不触发)
                            setPressed(true, x, y);
                            checkForLongClick(0, x, y);
                        }
                        break;

#### 1.checkForLongClick（delayOffset，x, y） ####

private void checkForLongClick(int delayOffset, float x, float y) {
    //在滑动控件内，预按下等待时间减去100等待期
            if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE || (mViewFlags & TOOLTIP) == TOOLTIP) {
                mHasPerformedLongPress = false;
    
                if (mPendingCheckForLongPress == null) {
                    mPendingCheckForLongPress = new CheckForLongPress();
                }
                mPendingCheckForLongPress.setAnchor(x, y);
                mPendingCheckForLongPress.rememberWindowAttachCount();
                mPendingCheckForLongPress.rememberPressedState();
                postDelayed(mPendingCheckForLongPress,
                        ViewConfiguration.getLongPressTimeout() - delayOffset);
            }
        }

#### 2.performButtonActionOnTouchDown（event） ####

protected boolean performButtonActionOnTouchDown(MotionEvent event) {
            //如果是鼠标右键
            if (event.isFromSource(InputDevice.SOURCE_MOUSE) &&
                (event.getButtonState() & MotionEvent.BUTTON_SECONDARY) != 0) {
                //显示上下文菜单
                showContextMenu(event.getX(), event.getY());
                mPrivateFlags |= PFLAG_CANCEL_NEXT_UP_EVENT;
                return true;
            }
            return false;
        }

#### 3.CheckForTap ####

private final class CheckForTap implements Runnable {
            public float x;
            public float y;
    
            @Override
            public void run() {
                //把预按下状态置空
                mPrivateFlags &= ~PFLAG_PREPRESSED;
                setPressed(true, x, y);//设置按下状态
                // 设置长按的等待期
                //checkForLongClick源码见 4.
                checkForLongClick(ViewConfiguration.getTapTimeout(), x, y);
            }
        }

#### 4.checkForLongClick(delayOffset, x, y) ####

//delayOffset 预按下的延时时间，最终会被减掉，比如上面的3.CheckForTap,在滑动控件中的延时时间是ViewConfiguration.getTapTimeout(),非滑动控件内的延时就是0
    private void checkForLongClick(int delayOffset, float x, float y) {
            if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE || (mViewFlags & TOOLTIP) == TOOLTIP) {
                mHasPerformedLongPress = false;
    
                if (mPendingCheckForLongPress == null) {
                    mPendingCheckForLongPress = new CheckForLongPress();
                }
                mPendingCheckForLongPress.setAnchor(x, y);
                mPendingCheckForLongPress.rememberWindowAttachCount();
                mPendingCheckForLongPress.rememberPressedState();
                //减掉预按下状态的延时时间
                postDelayed(mPendingCheckForLongPress,
                        ViewConfiguration.getLongPressTimeout() - delayOffset);
            }
        }

### MotionEvent.ACTION\_MOVE ###

case MotionEvent.ACTION_MOVE:
                        if (clickable) {
                            //改变水波纹中心位置
                            drawableHotspotChanged(x, y);
                        }
    
                        // 如果没有在view范围，移出状态
                        if (!pointInView(x, y, mTouchSlop)) {
                            // mTouchSlop：溢出距离，默认为8dp
                            // 删除后续所有的长按/点击检查
                            removeTapCallback();//从预按下到按下
                           removeLongPressCallback();//长按Callback
                            if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
                                setPressed(false);
                            }
                            mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                        }
                        break;

### MotionEvent.ACTION\_UP ###

case MotionEvent.ACTION_UP:
                        //TOOLTIP是否额外移动给置空
                        mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                        //松手之后TOOLTIP消失
                        if ((viewFlags & TOOLTIP) == TOOLTIP) {
                            handleTooltipUp();
                        }
                        //如果不可点击，初始化状态
                        if (!clickable) {
                            removeTapCallback();
                            removeLongPressCallback();
                            mInContextButtonPress = false;
                            mHasPerformedLongPress = false;
                            mIgnoreNextUpEvent = false;
                            break;
                        }
                        
                        boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
                        //按下或预按下
                        if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                            //isFocusableInTouchMode实体按键，比如电视
                            boolean focusTaken = false;
                            if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
                                focusTaken = requestFocus();
                            }
    
                            if (prepressed) {
                                // The button is being released before we actually
                                // showed it as pressed.  Make it show the pressed
                                // state now (before scheduling the click) to ensure
                                // the user sees it.
                                setPressed(true, x, y);
                            }
                            //处理点击事件
                            if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                                // This is a tap, so remove the longpress check
                                removeLongPressCallback();
    
                                //仅在我们处于按下状态时才执行点击操作
                                if (!focusTaken) {
                                    // Use a Runnable and post this rather than calling
                                    // performClick directly. This lets other visual state
                                    // of the view update before click actions start.
                                    if (mPerformClick == null) {
                                        mPerformClick = new PerformClick();
                                    }
                                    if (!post(mPerformClick)) {
                                        performClick();
                                    }
                                }
                            }
    
                            if (mUnsetPressedState == null) {
                                mUnsetPressedState = new UnsetPressedState();
                            }
    
                            if (prepressed) {
                                //预按下状态，手动加4帧延迟，稍后触发UP事件点击事件
                                postDelayed(mUnsetPressedState,
                                        ViewConfiguration.getPressedStateDuration());
                            } else if (!post(mUnsetPressedState)) {
                                // If the post failed, unpress right now
                                mUnsetPressedState.run();
                            }
    
                            removeTapCallback();
                        }
                        mIgnoreNextUpEvent = false;
                        break;

### MotionEvent.ACTION\_CANCEL ###

case MotionEvent.ACTION_CANCEL:
                        //恢复状态
                        if (clickable) {
                            setPressed(false);
                        }
                        removeTapCallback();
                        removeLongPressCallback();
                        mInContextButtonPress = false;
                        mHasPerformedLongPress = false;
                        mIgnoreNextUpEvent = false;
                        mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                        break;

[format_png]: /images/20230531/038de6f49a5945a9b5a8dfac3149b6c8.png
[format_png 1]: /images/20230531/dc86b206a04c4dc986e25e0c94b32fde.png