Android下Touch事件的分发机制
pgl198
7年前
<p>我们通过一个示例来分析Touch事件的分发过程。</p> <p><strong>示例：</strong></p> <p>布局文件：</p> <pre> <code class="language-java"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/rootview" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context="com.example.maimingliang.test.view.TestTouchActivity"> <TextView android:id="@+id/txt" android:layout_width="match_parent" android:gravity="center" android:layout_height="55dp" android:text="textView"/> <ImageView android:id="@+id/img" android:layout_marginTop="20dp" android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@mipmap/ic_launcher"/> </LinearLayout></code></pre> <p>Activity：</p> <pre> <code class="language-java">public class TestTouchActivity extends AppCompatActivity { private static final String TAG = "TestTouchActivity"; @Bind(R.id.txt) TextView tv; @Bind(R.id.img) ImageView img; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_test_touch); ButterKnife.bind(this); initView(); } private void initView() { tv.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Log.d(TAG,"-------> tv Onclick"); } }); tv.setOnTouchListener(new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { Log.d(TAG, "-------> tv onTouch"); return false; } }); img.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Log.d(TAG, "--------> img onClick"); } }); img.setOnTouchListener(new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { Log.d(TAG, "--------> img onTouch"); return true; } }); }</code></pre> <p>点击图片，现象</p> <p><img src="https://simg.open-open.com/show/3c94c7a6ba88fb07c2da73d51122858f.png"></p> <p style="text-align:center">这里写图片描述</p> <p>可以看到onTouch事件比onClick事件优先级高。</p> <p>再看看把setOnTouchListener事件的返回值改为true：</p> <p><img src="https://simg.open-open.com/show/51afbad157f963283b7b5bfd144ffab0.png"></p> <p style="text-align:center">这里写图片描述</p> <p>可以看到onClick事件没有了。这是为什么？我们透过源码来看看这个现象。</p> <h3><strong>事件分发机制源码分析</strong></h3> <p>当我们触摸屏幕上的某个控件时，底层的设备硬件传递给InputManager经过一 定的处理后，传递给AmS，再经过AmS的处理后就传递到我们的Activity，接着传递Window，最后传递到顶级View。</p> <p>触摸事件的分发过程有三个重要的方法：</p> <p>public boolean dispatchTouchEvent(MotionEvent ev)</p> <p>用来分发事件的，如果当前事件能传递到该View，该 方法一定调用，View的onTouchEvent方法会调用，而该方法的返回值所onTouchEvent影响。</p> <p>public boolean onInterceptHoverEvent(MotionEvent event)</p> <p>用来拦截事件的，如果返回值为true，表示拦截。否则不拦截。</p> <p>public boolean onTouchEvent(MotionEvent event)</p> <p>处理当前事件的。如果返回值为true表示消耗该事件。否则无法再接收同一个序列的事件。</p> <p>同一个序列的事件是；DOWN事件－－》多个MOVE事件－－》UP事件。</p> <p>Activity触摸事件分发过程</p> <p>当触摸事件传递到Activity，Activity的dispatchTouchEvent（）方法就会调用，我们去看看：</p> <pre> <code class="language-java">public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { return true; } return onTouchEvent(ev); }</code></pre> <p>如果当前事件是DOWN事件，调用了onUserInteraction方法，该方法是一个空方法，我们可以重载该方法，在DOWN事件做一些处理。接着就把事件传递给Window来处理该事件。如果返回true，表示有View处理该事件，onTouch Event（）方法返回了true，整个事件处理完成。否则Activity的onTouchEvent方法就会被调用。</p> <p>Window触摸事件的分发过程</p> <p>Window类是abstract的，唯一的具体实现类是PhoneWindow类，我们去看看PhoneWindow的superDispatchTouchEvent（）方法：</p> <pre> <code class="language-java">@Override public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event); } private DecorView mDecor;</code></pre> <p>DecorView类继承于FrameLayout：</p> <pre> <code class="language-java">private final class DecorView extends FrameLayout implements RootViewSurfaceTaker ｛....｝</code></pre> <p>因此就是调用了DecorView的superDispatchTouchEvent方法：</p> <pre> <code class="language-java">public boolean superDispatchTouchEvent(MotionEvent event) { return super.dispatchTouchEvent(event); }</code></pre> <p>可以看到，其实就是调用了父类的dispatchTouchEvent（）方法。DecorView继承于FrameLayout，FrameLayout继承于ViewGroup。因此就是调用了ViewGroup的dispatchTouchEvent（）方法。</p> <p>DecorView就是我们的顶层View，当我们通过setContentView（）方法设置的是顶层View的一个子View。DecorView组成为：</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/fb49138b1cfac2c43315d0c3b9610e57.png"></p> <p style="text-align:center">这里写图片描述</p> <p>可以看出，事件传递的大概过程：</p> <p>Activity－－》Window－－》View。某个View的onTouchEvent（）方法被调用。如果返回true，传递会Window，Window再传递会Activity，事件处理结束。否则返回false，再同样的传递会Activity。</p> <h3><strong>顶层View事件分发的过程</strong></h3> <p>DecorView继承与FrameLayout，是一个ViewGroup，ViewGroup继承于View，继承图：</p> <p><img src="https://simg.open-open.com/show/9ceb506c4b0db51dee91fc15ec429054.png"></p> <p style="text-align:center">这里写图片描述</p> <p>ViewGroup重载了dispatchTouchEvent（）方法。那我们去看看该方法：</p> <pre> <code class="language-java">@Override public boolean dispatchTouchEvent(MotionEvent ev) { .... boolean handled = false; if (onFilterTouchEventForSecurity(ev)) { final int action = ev.getAction(); final int actionMasked = action & MotionEvent.ACTION_MASK; 1. // 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(); } 2. // 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; } .... 3. if (!canceled && !intercepted) { .... final int childrenCount = mChildrenCount; if (newTouchTarget == null && childrenCount != 0) { final float x = ev.getX(actionIndex); final float y = ev.getY(actionIndex); .... final View[] children = mChildren; for (int i = childrenCount - 1; i >= 0; i--) { final int childIndex = customOrder ? getChildDrawingOrder(childrenCount, i) : i; final View child = (preorderedList == null) ? children[childIndex] : preorderedList.get(childIndex); .... if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { ev.setTargetAccessibilityFocus(false); continue; } .... if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) { // Child wants to receive touch within its bounds. mLastTouchDownTime = ev.getDownTime(); if (preorderedList != null) { // childIndex points into presorted list, find original index for (int j = 0; j < childrenCount; j++) { if (children[childIndex] == mChildren[j]) { mLastTouchDownIndex = j; break; } } } else { mLastTouchDownIndex = childIndex; } mLastTouchDownX = ev.getX(); mLastTouchDownY = ev.getY(); newTouchTarget = addTouchTarget(child, idBitsToAssign); alreadyDispatchedToNewTouchTarget = true; break; } .... } } .... } } .... return handled; }</code></pre> <p>这个方法很长我们分几部分来分析。代码中标有1.2.3.....。</p> <p>1.ViewGroup对DOWN事件重置状态的操作。</p> <pre> <code class="language-java">private void resetTouchState() { clearTouchTargets(); resetCancelNextUpFlag(this); mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT; mNestedScrollAxes = SCROLL_AXIS_NONE; }</code></pre> <p>标志FLAG_DISALLOW_INTERCEPT可以通过requestDisallowInterceptTouchEvent方法设置。因此在DOWN事件该方法不影响该标志，简单来说，就是不影响ViewGroup处理DOWN事件的操作。</p> <p>2.判断是否拦截事件。</p> <p>首先判断是否DOWN事件或者mFirstTouchTarget != null。</p> <p>mFirstTouchTarget的意思是，如果ViewGroup的有子元素成功处理，mFirstTouchTarget就会指向该元素。</p> <p>如果当前事件是DOWN：FLAG_DISALLOW_INTERCEPT不影响ViewGroup对DOWN事件的处理，因此调用了onInterceptTouchEvent（）方法。是否拦截取决于该方法的返回值。</p> <p>如果onInterceptTouchEvent（）返回true，说明ViewGroup拦截事件，mFirstTouchTarget为null，同一序列的事件都由它处理，onInterceptTouchEvent也不会再调用了，因为actionMasked == MotionEvent.ACTION_DOWN|| mFirstTouchTarget != null条件都不满足。如果子 View调用了requestDisallowInterceptTouchEvent（）方法后，ViewGroup将无法拦截除DOWN事件以外的其他事件。该方法不影响ViewGroup的DOWN事件。</p> <p>3.如果ViewGroup不拦截，ViewGroup遍历所有的子View，判断子View是否满足当前的事件。满足的条件有两个：子View是否播放动画和事件的坐标是否在子View的区域。</p> <p>如果满足条件，调用了dispatchTransformedTouchEvent（）方法。去看看：</p> <pre> <code class="language-java">private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel, View child, int desiredPointerIdBits) { final boolean handled; // Canceling motions is a special case. We don't need to perform any transformations // or filtering. The important part is the action, not the contents. final int oldAction = event.getAction(); if (cancel || oldAction == MotionEvent.ACTION_CANCEL) { event.setAction(MotionEvent.ACTION_CANCEL); if (child == null) { handled = super.dispatchTouchEvent(event); } else { handled = child.dispatchTouchEvent(event); } event.setAction(oldAction); return handled; } .... ｝</code></pre> <p>其实就是调用了子View的dispatchTouchEvent（）方法。如果返回了true，就会通过addTouchTarget（）方法对mFirstTouchTarget赋值并停止遍历子View。</p> <pre> <code class="language-java">private TouchTarget addTouchTarget(View child, int pointerIdBits) { TouchTarget target = TouchTarget.obtain(child, pointerIdBits); target.next = mFirstTouchTarget; mFirstTouchTarget = target; return target; }</code></pre> <p>可以看到，mFirstTouchTarget是一个单链表的数据结构。</p> <p>如果遍历全部的子View都没有成功处理的，mFirstTouchTarget成员变量为null，当该成员变量为null，就会调用：</p> <pre> <code class="language-java">if (mFirstTouchTarget == null) { // No touch targets so treat this as an ordinary view. handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS); }</code></pre> <p>因为第三个参数为null，就会调用super.dispatchTouchEvent（）方法，调用到了View的dispatchTouchEvent（）方法。</p> <h3><strong>View的事件分发过程</strong></h3> <p>dispatchTouchEvent方法如下：</p> <pre> <code class="language-java">/** * 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 (onFilterTouchEventForSecurity(event)) { //noinspection SimplifiableIfStatement ListenerInfo li = mListenerInfo; if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) { result = true; } if (!result && onTouchEvent(event)) { result = true; } } .... return result; }</code></pre> <p>从上面的代码可以看出，判断了是否设置了setOnTouchListener，是否为ENABLED，onTouch是否返回了true。</p> <p>ENABLED对这个判断没有影响。</p> <p>但onTouch返回true，onTouchEvent方法就不会执行了。而onClick的方法是在onTouchEvent（）方法执行的。因此onTouch事件的优先级比onClick事件高，而且还当onTouch方法返回了true，onClick事件就不会调用了。说明了上面的示例的现象。</p> <p>我们去看看onClick事件是否在onTouch Event方法中执行的。</p> <pre> <code class="language-java">public boolean onTouchEvent(MotionEvent event) { final float x = event.getX(); final float y = event.getY(); final int viewFlags = mViewFlags; final int action = event.getAction(); if ((viewFlags & ENABLED_MASK) == DISABLED) { if (action == 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) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE); } if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } } if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) { switch (action) { 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, x, y); } if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) { // 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(); } mIgnoreNextUpEvent = false; break; ..... ..... } return true; } return false; }</code></pre> <p>从上述代码看到，判断了viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE判断是否可点击或者长点击。只要有一个为true，就会返回true，表示消耗此事件。</p> <p>CLICKABLE和LONG_CLICKABLE的值可以在清单文件中通过android:clickable和 android:longClickable属性设置，也可以通过setOnclickListener（）和setLongClickListener（）方法设置。</p> <p>当设置了点击事件调用了performClick（）方法：</p> <pre> <code class="language-java">public boolean performClick() { final boolean result; final ListenerInfo li = mListenerInfo; if (li != null && li.mOnClickListener != null) { playSoundEffect(SoundEffectConstants.CLICK); li.mOnClickListener.onClick(this); result = true; } else { result = false; } sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED); return result; }</code></pre> <p>可以看到回调了我们设置的onClick方法。由此看出onClick事件是在onTouch Event方法执行的。</p> <p>这就是事件分发的大概流程。</p> <p>我们根据上面的示例走一下整个触摸事件的分发流程。</p> <p>我们从顶View开始分析：</p> <p>整个View树的结构如下：</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/74695a014029be73a1d59d6e535245d6.png"></p> <p style="text-align:center">这里写图片描述</p> <p>上面的示例，我们点击的图片。</p> <p>首先由顶层View（FrameLayout）的dispatchTouch（）方法根据点击图片等坐标首先分发到第一个LinearLayout的，然后调用了ViewGroup的dispatchTouch（）方法，又根据点击图片等坐标:u6709:️分发到了第二个LinearLayout，接着有调用了ViewGroup的dispatchTouch（）方法，又根据点击图片的坐标分发到了ImageView，然后调用了View的dispatchTouch（）方法。ImageView设置setOnTouchListener方法和setOnclickListener方法，如果setOnTouchListener方法返回了false，接着调用了onTouchEvent（）方法，从而onClick方法调用，onTouchEvent返回true，消耗了此事件。否则dispatchTouch（）方法直接返回了true，消耗此事件。</p> <p>ViewGroup的onInterceptTouchEvent（）方法默认返回false，默认不拦截。</p> <p>END.</p> <p> </p> <p>来自：http://www.jianshu.com/p/1e2d439487f0</p> <p> </p>