Android中的Touch事件
16lz
2022-05-23
Android中的Touch事件处理
主要内容
Activity或View类的onTouchEvent()回调函数会接收到touch事件。
一个完整的手势是从ACTION_DOWN开始，到ACTION_UP结束。
简单的情况下，我们只需要在onTouchEvent()中写个switch case语句，处理各种事件（Touch Down、 Touch Move、 Touch Up等），但是比较复杂的动作就需要更多的处理了。
ViewGroup作为一个parent是可以截获传向它的child的touch事件的。
如果一个ViewGroup的onInterceptTouchEvent()方法返回true，说明Touch事件被截获，子View不再接收到Touch事件，而是转向本ViewGroup的 onTouchEvent()方法处理。从Down开始，之后的Move，Up都会直接在onTouchEvent()方法中处理。
先前还在处理touch event的child view将会接收到一个 ACTION_CANCEL。
如果onInterceptTouchEvent()返回false，则事件会交给child view处理。
Android中提供了ViewGroup、View、Activity三个层次的Touch事件处理。
处理过程是按照Touch事件从上到下传递，再按照是否消费的返回值，从下到上返回，即如果View的onTouchEvent返回false，将会向上传给它的parent的ViewGroup，如果ViewGroup不处理，将会一直向上返回到Activity。
即隧道式向下分发，然后冒泡式向上处理。
Activity的Touch事件分发
Activity的dispatchTouchEvent (MotionEvent ev)：
/** * Called to process touch screen events. You can override this to * intercept all touch screen events before they are dispatched to the * window. Be sure to call this implementation for touch screen events * that should be handled normally. * * @param ev The touch screen event. * * @return boolean Return true if this event was consumed. */ public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { return true; } return onTouchEvent(ev); }
处理屏幕触摸事件，你可以覆写这个方法来截获所有的触摸屏幕事件，是在它们分发到窗口之前截获。
对于要正常处理的触摸屏幕事件，要确认调用这个实现。
返回值为true的时候，表明这个事件被消费。
Activity的onTouchEvent (MotionEvent event)：
/** * Called when a touch screen event was not handled by any of the views * under it. This is most useful to process touch events that happen * outside of your window bounds, where there is no view to receive it. * * @param event The touch screen event being processed. * * @return Return true if you have consumed the event, false if you haven't. * The default implementation always returns false. */ public boolean onTouchEvent(MotionEvent event) { if (mWindow.shouldCloseOnTouch(this, event)) { finish(); return true; } return false; }
如果一个屏幕触摸事件没有被这个Activity下的任何View所处理，Activity的onTouchEvent将会调用。
这对于处理window边界之外的Touch事件非常有用，因为通常是没有View会接收到它们的。
返回值为true表明你已经消费了这个事件，false则表示没有消费，默认实现中返回false。
View的Touch事件
View的dispatchTouchEvent (MotionEvent event)：
/** * Pass the touch screen motion event down to the target view, or this * view if it is the target. * * @param event The motion event to be dispatched. * @return True if the event was handled by the view, false otherwise. */ public boolean dispatchTouchEvent(MotionEvent event) { if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onTouchEvent(event, 0); } if (onFilterTouchEventForSecurity(event)) { //noinspection SimplifiableIfStatement ListenerInfo li = mListenerInfo; if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) { return true; } if (onTouchEvent(event)) { return true; } } if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(event, 0); } return false; }View --> dispatchTouchEvent
将touch屏幕的事件向下传递到目标View，或者传递到本View，如果它就是目标View。
如果事件被这个View处理，则返回true，否则返回false。
onTouchEvent (MotionEvent event)：
/** * Implement this method to handle touch screen motion events. * * @param event The motion event. * @return True if the event was handled, false otherwise. */ public boolean onTouchEvent(MotionEvent event) { final int viewFlags = mViewFlags; if ((viewFlags & ENABLED_MASK) == DISABLED) { if (event.getAction() == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) { setPressed(false); } // A disabled view that is clickable still consumes the touch // events, it just doesn't respond to them. return (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)); } if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } } if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) { switch (event.getAction()) { case MotionEvent.ACTION_UP: boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0; if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) { // take focus if we don't have it already and we should in // touch mode. 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); } if (!mHasPerformedLongPress) { // This is a tap, so remove the longpress check removeLongPressCallback(); // Only perform take click actions if we were in the pressed state 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) { postDelayed(mUnsetPressedState, ViewConfiguration.getPressedStateDuration()); } else if (!post(mUnsetPressedState)) { // If the post failed, unpress right now mUnsetPressedState.run(); } removeTapCallback(); } break; case MotionEvent.ACTION_DOWN: mHasPerformedLongPress = false; if (performButtonActionOnTouchDown(event)) { break; } // Walk up the hierarchy to determine if we're inside a scrolling container. boolean isInScrollingContainer = isInScrollingContainer(); // For views inside a scrolling container, delay the pressed feedback for // a short period in case this is a scroll. if (isInScrollingContainer) { mPrivateFlags |= PFLAG_PREPRESSED; if (mPendingCheckForTap == null) { mPendingCheckForTap = new CheckForTap(); } postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout()); } else { // Not inside a scrolling container, so show the feedback right away setPressed(true); checkForLongClick(0); } break; case MotionEvent.ACTION_CANCEL: setPressed(false); removeTapCallback(); removeLongPressCallback(); break; case MotionEvent.ACTION_MOVE: final int x = (int) event.getX(); final int y = (int) event.getY(); // Be lenient about moving outside of buttons if (!pointInView(x, y, mTouchSlop)) { // Outside button removeTapCallback(); if ((mPrivateFlags & PFLAG_PRESSED) != 0) { // Remove any future long press/tap checks removeLongPressCallback(); setPressed(false); } } break; } return true; } return false; }View --> onTouchEvent
实现这个方法来处理touch屏幕的事件。
返回true如果这个事件被处理了。
ViewGroup的Touch事件
因为ViewGroup是View的子类，所以它覆写方法时会加上Override注解，如果没有覆写，则沿用父类实现，如onTouchEvent()。
dispatchTouchEvent (MotionEvent ev)：
/** * {@inheritDoc} */ @Override public boolean dispatchTouchEvent(MotionEvent ev) { if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onTouchEvent(ev, 1); } boolean handled = false; if (onFilterTouchEventForSecurity(ev)) { final int action = ev.getAction(); final int actionMasked = action & MotionEvent.ACTION_MASK; // Handle an initial down. if (actionMasked == MotionEvent.ACTION_DOWN) { // Throw away all previous state when starting a new touch gesture. // The framework may have dropped the up or cancel event for the previous gesture // due to an app switch, ANR, or some other state change. cancelAndClearTouchTargets(ev); resetTouchState(); } // Check for interception. final boolean intercepted; if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { intercepted = onInterceptTouchEvent(ev); ev.setAction(action); // restore action in case it was changed } else { intercepted = false; } } else { // There are no touch targets and this action is not an initial down // so this view group continues to intercept touches. intercepted = true; } // Check for cancelation. final boolean canceled = resetCancelNextUpFlag(this) || actionMasked == MotionEvent.ACTION_CANCEL; // Update list of touch targets for pointer down, if needed. final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0; TouchTarget newTouchTarget = null; boolean alreadyDispatchedToNewTouchTarget = false; if (!canceled && !intercepted) { if (actionMasked == MotionEvent.ACTION_DOWN || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { final int actionIndex = ev.getActionIndex(); // always 0 for down final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex) : TouchTarget.ALL_POINTER_IDS; // Clean up earlier touch targets for this pointer id in case they // have become out of sync. removePointersFromTouchTargets(idBitsToAssign); final int childrenCount = mChildrenCount; if (newTouchTarget == null && childrenCount != 0) { final float x = ev.getX(actionIndex); final float y = ev.getY(actionIndex); // Find a child that can receive the event. // Scan children from front to back. final View[] children = mChildren; final boolean customOrder = isChildrenDrawingOrderEnabled(); for (int i = childrenCount - 1; i >= 0; i--) { final int childIndex = customOrder ? getChildDrawingOrder(childrenCount, i) : i; final View child = children[childIndex]; if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { continue; } newTouchTarget = getTouchTarget(child); if (newTouchTarget != null) { // Child is already receiving touch within its bounds. // Give it the new pointer in addition to the ones it is handling. newTouchTarget.pointerIdBits |= idBitsToAssign; break; } resetCancelNextUpFlag(child); if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) { // Child wants to receive touch within its bounds. mLastTouchDownTime = ev.getDownTime(); mLastTouchDownIndex = childIndex; mLastTouchDownX = ev.getX(); mLastTouchDownY = ev.getY(); newTouchTarget = addTouchTarget(child, idBitsToAssign); alreadyDispatchedToNewTouchTarget = true; break; } } } if (newTouchTarget == null && mFirstTouchTarget != null) { // Did not find a child to receive the event. // Assign the pointer to the least recently added target. newTouchTarget = mFirstTouchTarget; while (newTouchTarget.next != null) { newTouchTarget = newTouchTarget.next; } newTouchTarget.pointerIdBits |= idBitsToAssign; } } } // Dispatch to touch targets. if (mFirstTouchTarget == null) { // No touch targets so treat this as an ordinary view. handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS); } else { // Dispatch to touch targets, excluding the new touch target if we already // dispatched to it. Cancel touch targets if necessary. TouchTarget predecessor = null; TouchTarget target = mFirstTouchTarget; while (target != null) { final TouchTarget next = target.next; if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) { handled = true; } else { final boolean cancelChild = resetCancelNextUpFlag(target.child) || intercepted; if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) { handled = true; } if (cancelChild) { if (predecessor == null) { mFirstTouchTarget = next; } else { predecessor.next = next; } target.recycle(); target = next; continue; } } predecessor = target; target = next; } } // Update list of touch targets for pointer up or cancel, if needed. if (canceled || actionMasked == MotionEvent.ACTION_UP || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { resetTouchState(); } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) { final int actionIndex = ev.getActionIndex(); final int idBitsToRemove = 1 << ev.getPointerId(actionIndex); removePointersFromTouchTargets(idBitsToRemove); } } if (!handled && mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1); } return handled; }ViewGroup --> dispatchTouchEvent
将Touch事件向下传递到目标View，因为自身也是View，所以目标View如果是自己，则传递给自己。
返回true，如果这个事件是被本View所处理。
onInterceptTouchEvent (MotionEvent ev)
ViewGroup中比较特殊的一个方法。默认实现如下：
public boolean onInterceptTouchEvent(MotionEvent ev) { return false; }
这个方法注释很长：
/** * Implement this method to intercept all touch screen motion events. This * allows you to watch events as they are dispatched to your children, and * take ownership of the current gesture at any point. * * <p>Using this function takes some care, as it has a fairly complicated * interaction with {@link View#onTouchEvent(MotionEvent) * View.onTouchEvent(MotionEvent)}, and using it requires implementing * that method as well as this one in the correct way. Events will be * received in the following order: * * <ol> * <li> You will receive the down event here. * <li> The down event will be handled either by a child of this view * group, or given to your own onTouchEvent() method to handle; this means * you should implement onTouchEvent() to return true, so you will * continue to see the rest of the gesture (instead of looking for * a parent view to handle it). Also, by returning true from * onTouchEvent(), you will not receive any following * events in onInterceptTouchEvent() and all touch processing must * happen in onTouchEvent() like normal. * <li> For as long as you return false from this function, each following * event (up to and including the final up) will be delivered first here * and then to the target's onTouchEvent(). * <li> If you return true from here, you will not receive any * following events: the target view will receive the same event but * with the action {@link MotionEvent#ACTION_CANCEL}, and all further * events will be delivered to your onTouchEvent() method and no longer * appear here. * </ol> * * @param ev The motion event being dispatched down the hierarchy. * @return Return true to steal motion events from the children and have * them dispatched to this ViewGroup through onTouchEvent(). * The current target will receive an ACTION_CANCEL event, and no further * messages will be delivered here. */ViewGroup onInterceptTouchEvent
实现这个方法可以截获所有的Touch事件。这样你就可以控制向child分发的Touch事件。
一般实现这个方法，需要同时实现View.onTouchEvent(MotionEvent)方法。
事件是按照如下的顺序被接收的：
1.首先在onInterceptTouchEvent()中接收到Down事件。
2.Down事件将会：要么给这个ViewGroup的一个child view处理，要么是这个ViewGroup自己的onTouchEvent()处理。
处理意味着你应该在onTouchEvent()的实现中返回true，这样你就可以继续看到这个gesture的其他部分，如果返回false，将会返回寻找一个parent view去处理它。
如果在onTouchEvent()中返回true，你将不会再在onInterceptTouchEvent()再收到接下来的事件，所有的Touch处理必须放在onTouchEvent()中正常处理。
3.如果你在onInterceptTouchEvent()中返回false，接下来的每一个事件都会先传到onInterceptTouchEvent()，之后传递到目标view的onTouchEvent()中。
4.如果你在onInterceptTouchEvent()中返回true，将不会再接收到手势中的其他事件，当前的目标view将会接收到同一个事件，但是动作是ACTION_CANCEL。其他所有的事件将会被直接传递到onTouchEvent()中，并且不再在onInterceptTouchEvent()中出现。
onInterceptTouchEvent()的返回值：true将会从子view中偷取运动事件，把它们分配到这个ViewGroup的onTouchEvent()中，当前目标view将会接收到取消动作，并且接下来的动作都不会再经过onInterceptTouchEvent()。
ViewGroup的onTouchEvent()是采用父类View的默认实现，有需要的话可以覆写。
代码示例
写了一个Demo观察输出和调用关系，代码如下：
package com.mengdd.hellotouch;import android.util.Log;import android.view.MotionEvent;public class Utils { public static void showMotionEventType(MotionEvent event, String logTag, String methodName) { final int action = event.getActionMasked(); switch (action) { case MotionEvent.ACTION_DOWN: Log.i(logTag, methodName + ": " + action + ": ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.i(logTag, methodName + ": " + action + ": ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.i(logTag, methodName + ": " + action + ": ACTION_UP"); break; case MotionEvent.ACTION_CANCEL: Log.i(logTag, methodName + ": " + action + ": ACTION_CANCEL"); break; default: break; } } public static void showReturnValue(boolean returnValue, String logTag, String methodName) { Log.w(logTag, methodName + " return: " + returnValue); } public static void showInfo(String info, String logTag, String methodName) { Log.e(logTag, methodName + " info: " + info); }}Utils
package com.mengdd.hellotouch;import com.example.helloscroller.R;import android.app.Activity;import android.os.Bundle;import android.view.MotionEvent;public class HelloTouchActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_hello_scroller); } @Override public boolean dispatchTouchEvent(MotionEvent ev) { Utils.showMotionEventType(ev, "Activity", "dispatchTouchEvent"); boolean result = super.dispatchTouchEvent(ev); Utils.showReturnValue(result, "Activity", "dispatchTouchEvent"); return result; } @Override public boolean onTouchEvent(MotionEvent event) { Utils.showMotionEventType(event, "Activity", "onTouchEvent"); boolean result = super.onTouchEvent(event); Utils.showReturnValue(result, "Activity", "onTouchEvent"); return result; }}Activity
package com.mengdd.hellotouch;import android.content.Context;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;import android.widget.LinearLayout;public class MyViewGroup extends LinearLayout { public MyViewGroup(Context context, AttributeSet attrs) { super(context, attrs); init(); } public MyViewGroup(Context context) { super(context); init(); } private void init() { setOnClickListener(mOnClickListener); setOnLongClickListener(mOnLongClickListener); } @Override public boolean onInterceptTouchEvent(MotionEvent event) { Utils.showMotionEventType(event, "ViewGroup", "onInterceptTouchEvent"); boolean returnValue = super.onInterceptTouchEvent(event); // This method JUST determines whether we want to intercept the motion. // If we return true, onTouchEvent will be called Utils.showReturnValue(returnValue, "ViewGroup", "onInterceptTouchEvent"); return returnValue; } @Override public boolean dispatchTouchEvent(MotionEvent event) { Utils.showMotionEventType(event, "ViewGroup", "dispatchTouchEvent"); boolean returnValue = super.dispatchTouchEvent(event); Utils.showReturnValue(returnValue, "ViewGroup", "dispatchTouchEvent"); return returnValue; } // ViewGroup自己的Touch事件处理，如果在onInterceptTouchEvent返回true，则会到这里处理，不传入child @Override public boolean onTouchEvent(MotionEvent event) { Utils.showMotionEventType(event, "ViewGroup", "onTouchEvent"); boolean returnValue = super.onTouchEvent(event); Utils.showReturnValue(returnValue, "ViewGroup", "onTouchEvent"); return returnValue; } private OnClickListener mOnClickListener = new OnClickListener() { @Override public void onClick(View v) { Utils.showInfo("onClick", "ViewGroup", "mOnClickListener"); // onClick是ACTION_UP后调用的 } }; private OnLongClickListener mOnLongClickListener = new OnLongClickListener() { @Override public boolean onLongClick(View v) { // onLongClick按下到一定的时间就调用了 Utils.showInfo("onLongClick", "ViewGroup", "mOnLongClickListener"); // 如果返回false，则长按结束的ACTION_UP调用onClick // 如果返回true，onLongClick后不再调用onClick return true; } };}ViewGroup
package com.mengdd.hellotouch;import android.content.Context;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;import android.widget.TextView;public class MyView extends TextView { public MyView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(); } public MyView(Context context, AttributeSet attrs) { super(context, attrs); init(); } public MyView(Context context) { super(context); } private void init() { setOnClickListener(mOnClickListener); setOnLongClickListener(mOnLongClickListener); } @Override public boolean dispatchTouchEvent(MotionEvent event) { Utils.showMotionEventType(event, "View", "dispatchTouchEvent"); boolean returnValue = super.dispatchTouchEvent(event); Utils.showReturnValue(returnValue, "View", "dispatchTouchEvent"); return returnValue; } @Override public boolean onTouchEvent(MotionEvent event) { Utils.showMotionEventType(event, "View", "onTouchEvent"); boolean returnValue = super.onTouchEvent(event); Utils.showReturnValue(returnValue, "View", "onTouchEvent"); return returnValue; } private OnClickListener mOnClickListener = new OnClickListener() { @Override public void onClick(View v) { Utils.showInfo("onClick", "View", "mOnClickListener"); } }; private OnLongClickListener mOnLongClickListener = new OnLongClickListener() { @Override public boolean onLongClick(View v) { Utils.showInfo("onLongClick", "View", "mOnLongClickListener"); // 如果返回false，则长按结束的ACTION_UP调用onClick return false; } };}View
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context=".HelloTouchActivity" > <com.mengdd.hellotouch.MyViewGroup android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <com.mengdd.hellotouch.MyView android:layout_width="100dp" android:layout_height="100dp" android:layout_gravity="center" android:text="Hello" android:background="#FFBBFFBB" /> </com.mengdd.hellotouch.MyViewGroup></RelativeLayout>layout
Click事件处理
Click事件：View的短按和长按都是注册监听器的（setListener）：
onClick是在ACTION_UP之后执行的。
onLongClick则是按下到一定时间之后执行的，这个时间是ViewConfiguration中的：
private static final int TAP_TIMEOUT = 180; //180毫秒
这里需要注意onLongClick的返回值，如果是false，则onLongClick之后，手指抬起，ACTION_UP之后还是回执行到onClick；但是如果onLongClick返回true，则不会再调用onClick。
参考资料
本博客中：
Android 触摸手势基础 官方文档概览
http://www.cnblogs.com/mengdd/p/3335508.html
Android的Touch事件处理机制
http://www.cnblogs.com/frydsh/archive/2012/11/08/2760408.html
Android FrameWork——Touch事件派发过程详解
http://blog.csdn.net/stonecao/article/details/6759189
Android事件传递机制【Touch事件】
http://orgcent.com/android-touch-event-mechanism/
Android 编程下 Touch 事件的分发和消费机制
http://www.cnblogs.com/sunzn/archive/2013/05/10/3064129.html
更多相关文章
- Android热插拔事件处理流程--Vold
- android包Android(安卓)"java.lang.NoClassDefFoundError:*"报错
- android UI事件
- Android的用户界面
- Android(安卓)TextUtils类介绍
- ListView.setOnItemClickListener、setOnCreateContextMenuListe
- Android判断是否有网络连接
- android里面的点击事件总结
- Android判断是否有网络连接