android事件分发源码解析(下)
2016-12-04 00:53
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一 前言
上一篇我们介绍了android事件分发的view相关的事件分发源码,我们接着这篇分析一下ViewGroup的相关源码,把事件分发这个机制梳理一次,只有自己认真的分析一次才有收获。二 例子现象
我们简单写一个例子测试一下:自定义一个简单的LinearLayout,代码如下:
public class MyLayout extends LinearLayout{ public MyLayout(Context context) { super(context); } public MyLayout(Context context, AttributeSet attrs) { super(context, attrs); } @Override public boolean dispatchTouchEvent(MotionEvent ev) { Log.d("TAG", "mylayout dispatchTouchEvent" + ev.getAction()); return super.dispatchTouchEvent(ev); } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { Log.d("TAG", "mylayout onInterceptTouchEvent" + ev.getAction()); return super.onInterceptTouchEvent(ev); } @Override public boolean onTouchEvent(MotionEvent event) { Log.d("TAG", "mylayout onTouchEvent" + event.getAction()); return super.onTouchEvent(event); }
布局界面如下:
<?xml version="1.0" encoding="utf-8"?> <com.ww.viewgroupevent.MyLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/layout" android:layout_width="match_parent" android:layout_height="match_parent" > <Button android:id="@+id/btn" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="button" android:textSize="16sp"/> </com.ww.viewgroupevent.MyLayout>
public class MainActivity extends AppCompatActivity { private Button btn; private MyLayout layout; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); btn = (Button) findViewById(R.id.btn); layout = (MyLayout) findViewById(R.id.layout); btn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Log.d("TAG", "button click"); } }); layout.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Log.d("TAG", "layout click"); } }); } }
上面布局都很简单,运行界面如下所示:
我们点击button,log日志如下所示:
我们可以看到点击button先执行的是ViewGroup的dispatchTouchEvent,即LinearLayout的dispatchTouchEvent,而且比view多了一个方法,onInterceptTouchEvent,最后执行的是Button的点击事件,那么我们可以看到执行的一个顺序是父布局开始,dispatchTouchEvent->onInterceptTouchEvent->向子view传递。
当我们点击空白区域的时候,log日志如下所示:
这里跟上面有点不一样的地方,就是在action0,即按下的时候,执行的是dispatchTouchEvent->onInterceptTouchEvent->onTouchEvent,而action1的时候就没有执行onInterceptTouchEvent,这里是一个疑问,先记住,源码里面找到答案。可以发现,其实跟view的分发还是有很多不一样的。
三 ViewGroup的事件分发
ViewGroup的事件分发过程android执行点击事件,一般是从
dispatchTouchEvent开始的,我们也从这里开始大致的分析一次源码吧,下面是源码:
public boolean dispatchTouchEvent(MotionEvent ev) { if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onTouchEvent(ev, 1); } // If the event targets the accessibility focused view and this is it, start // normal event dispatch. Maybe a descendant is what will handle the click. if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) { ev.setTargetAccessibilityFocus(false); } 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; } // If intercepted, start normal event dispatch. Also if there is already // a view that is handling the gesture, do normal event dispatch. if (intercepted || mFirstTouchTarget != null) { ev.setTargetAccessibilityFocus(false); } // 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 the event is targeting accessiiblity focus we give it to the // view that has accessibility focus and if it does not handle it // we clear the flag and dispatch the event to all children as usual. // We are looking up the accessibility focused host to avoid keeping // state since these events are very rare. View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus() ? findChildWithAccessibilityFocus() : null; 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 ArrayList<View> preorderedList = buildOrderedChildList(); final boolean customOrder = preorderedList == null && isChildrenDrawingOrderEnabled(); 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 there is a view that has accessibility focus we want it // to get the event first and if not handled we will perform a // normal dispatch. We may do a double iteration but this is // safer given the timeframe. if (childWithAccessibilityFocus != null) { if (childWithAccessibilityFocus != child) { continue; } childWithAccessibilityFocus = null; i = childrenCount - 1; } if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { ev.setTargetAccessibilityFocus(false); 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(); 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; } // The accessibility focus didn't handle the event, so clear // the flag and do a normal dispatch to all children. ev.setTargetAccessibilityFocus(false); } if (preorderedList != null) preorderedList.clear(); } 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; }
我们看到这里源码很长,我们只分析主要的:
8-10行:这里主要判断是否是针对可访问视图焦点,这个东西呢主要是帮助残障人士的,一般我们手机的设置里面就有一个无障碍功能,就是跟这个有关系,主要是通过AccessibilityService服务运行在后台的,感兴趣的可以查看这篇文章看看:
Android进阶——学习AccessibilityService实现微信抢红包插件
18-24行:我们执行按下操作的时候,首先执行了
ACTION_DOWN,一般来说执行第一步的都是初始化各种值,我们可以看到17-24行首先清除以前Touch的状态,开始一个新的手势,然后在
cancelAndClearTouchTargets(ev)这个方法里面对
mFirstTouchTarget设置为null了,这个是一个很关键的一个地方,对分析后面的事件分发比较重要,接着在
resetTouchState()里面清楚Touch的状态。
27-41行:VIewGroup会在两种情况下判断是否要拦截当前事件,通过事件类型
ACTION_DOWN和
mFirstTouchTarget != null,其实前面按下事件很好理解,主要是后面这个
TouchTarget的对象
mFirstTouchTarget != null这个是关键,当找到目标view接收Touch事件的时候,那么这个对象就会被赋值并指向子元素,进入里面接着判断
disallowIntercept,这个也在ViewGroup也提供了相应的设置方法:
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) { if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) { // We're already in this state, assume our ancestors are too return; } if (disallowIntercept) { mGroupFlags |= FLAG_DISALLOW_INTERCEPT; } else { mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT; } // Pass it up to our parent if (mParent != null) { mParent.requestDisallowInterceptTouchEvent(disallowIntercept); } }
这里就是通过改变mGroupFlags的值来确定是否拦截,当你调用这个方法的时候,disallowIntercept为true的时候,将这个
FLAG_DISALLOW_INTERCEPT标记位添加到mGroupFlags里面,当设置为false的时候,就清除mGroupFlags中的
FLAG_DISALLOW_INTERCEPT。所以在disallowIntercept为true的时候前面判断了mGroupFlags是否包含了这个标记位,如果包含了,说明这个状态已经存在,就不必在添加了。当设置后,那么
disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;这条语句就为true,那么
intercepted = false;就默认不拦截事件,交由子元素处理;如果没设置这个拦截标志呢,按照正常的分发,首先调用
onInterceptTouchEvent(ev);将它赋值给intercepted,我们看看这个方法:
public boolean onInterceptTouchEvent(MotionEvent ev) { return false; }
没错,默认返回为false,我们如果不重写这个方法的话,不会拦截事件分发的。
如果没找到目标view接收Touch事件或者找到了接收的目标view但是没有处理,上述28-29行的if语句不成立,直接将
intercepted = true,并且
onInterceptTouchEvent(ev)事件将不会调用,那么后续到来的事件都会交给它来处理。 上面那个疑问也就解释了,自己处理就不会调用拦截事件了。
总结一下:
事件传递总是先传递给父View的,然后才有父元素分发给子View,可以通过
requestDisallowInterceptTouchEvent方法在子元素中干预父元素的事件分发,但是ACTION_DOWN除外,因为每一次都要通过
resetTouchState();这个方法里面的
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;清除这个标记位。
50-51行检查事件是否被取消。
54行还是通过标记位检查事件是否支持分发多个view,默认是true,也提供了设置方法,跟上面设置拦截标记的类似,一个套路。
57行
if (!canceled && !intercepted)判断了是否取消和拦截。 如果没有取消和拦截,则进入if里面。
67-69行是一大串if语句,里面判断了是不是按下,第二个条件则是一个点被按下,此时在按下其它点触发,第三个条件就是鼠标在view上面。下面开始处理ACTION_DOWN事件。
79行判断childrenCount是否为0,首先获取触摸位置。84行拿到了子view的集合preorderedList,然后通过倒序遍历所有子View,一般布局或者addview的话,后添加的肯定在上面,这也比较符合思维方式,如果点击的地方有两个view的话,如果两个view都可以点击,那么肯定是最上层的先响应。
判断子元素是否能够接收到点击事件,主要由两点来判断,子元素是否在播放动画和点击事件是否落在子元素的区域内。
98-104:还是判断视图是否是一个可访问性焦点,我们首先让它获取事件,不处理就正常分发,虽然会分发两次,但是可以保证在给定的时间内更安全的执行。还是一开始提到的方便使用有关系,其它地方也有这个判断。
106-110行:检查view是否允许接收事件,是否处于visible状态或者正在播放动画和点击事件的坐标是否落在子元素的范围内。
112-118行:getTouchTarget这个判断了当前子view是否包含在了mFirstTouchTarget.next这个链表的某一个 target中,找到了就返回这个target,没找到就返回null。接着if判断找到了这个target就进入内部,childView已经准备接收在其区域内的点击事件,并且执行break跳出for循环。
如果没有跳出的话就执行121-140行,这里首先通过
dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)将touch事件传递给子view,这个方法内部会递归调用
dispatchTouchEvent(event)方法,这个方法后面讲解,需要明白的一点是,这个方法返回true,那么就表示消费了这个事件,就进入这个if内部。
123-136行,从这几个变量的注释看,仅供debug调式用。
137-139行,给newTouchTarget赋值,设置
alreadyDispatchedToNewTouchTarget为true,然后执行break跳出for循环,因为已经找到了View接收Touch事件。其实mFirstTouchTarget的赋值过程 是在
addTouchTarget内部完成的,代码如下:
private TouchTarget addTouchTarget(View child, int pointerIdBits) { TouchTarget target = TouchTarget.obtain(child, pointerIdBits); target.next = mFirstTouchTarget; mFirstTouchTarget = target; return target; }
mFirstTouchTarget 是一种单链表的结构,是否赋值将直接影响到ViewGroup对事件的拦截,如果为null的话,默认拦截接下来的同一序列中所有的点击事件,比如ACTION_MOVE,ACTION_UP。
149-157行:
if (newTouchTarget == null && mFirstTouchTarget != null)这个if语句就是没有找到子View接收Touch事件,并且之前的
mFirstTouchTarget不为null,那么将newTouchTarget指向了最初的TouchTarget。
162-196行:这里经过上面的分析,主要就是两种情况,第一种情况就是
mFirstTouchTarget==null,没有找到能消费Touch事件的view或者被View拦截了。那么在ViewGroup的
dispatchTransformedTouchEvent方法里面处理Touch事件和普通的View一样,自己无法消费,传递给上一层进行处理。这里调用
dispatchTransformedTouchEvent方法时第三个参数为null,下面会讲解这个方法,先记住就行。
第二种情况就是找到了能消费Touch事件的view,那么后续的同一序列事件,都应该交由它处理。
173-175行:前面利用ACTION_DOWN事件找到了符合接收touch事件的子view同时消费掉了ACTION_DOWN事件,这里直接返回true。
176-192行:对于非ACTION_DOWN事件,继续传递给目标view进行处理,依然是递归调用
dispatchTransformedTouchEvent方法处理。如果ACTION_DOWN 没有被拦截,但是同一序列的其它事件被拦截,则需要发送ACTION_CANCLE给目标view。
199行-203行:如果是ACTION_UP或者ACTION_HOVER_MOVE,那么将重置Touch状态标识,mFirstTouchTarget = null。
ViewGroup的dispatchTouchEvent事件分析完了,我们看到在上述分析的时候
dispatchTransformedTouchEvent这个方法执行了多次,我们接下来看看这个方法,源码如下:
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; } // Calculate the number of pointers to deliver. final int oldPointerIdBits = event.getPointerIdBits(); final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits; // If for some reason we ended up in an inconsistent state where it looks like we // might produce a motion event with no pointers in it, then drop the event. if (newPointerIdBits == 0) { return false; } // If the number of pointers is the same and we don't need to perform any fancy // irreversible transformations, then we can reuse the motion event for this // dispatch as long as we are careful to revert any changes we make. // Otherwise we need to make a copy. final MotionEvent transformedEvent; if (newPointerIdBits == oldPointerIdBits) { if (child == null || child.hasIdentityMatrix()) { if (child == null) { handled = super.dispatchTouchEvent(event); } else { final float offsetX = mScrollX - child.mLeft; final float offsetY = mScrollY - child.mTop; event.offsetLocation(offsetX, offsetY); handled = child.dispatchTouchEvent(event); event.offsetLocation(-offsetX, -offsetY); } return handled; } transformedEvent = MotionEvent.obtain(event); } else { transformedEvent = event.split(newPointerIdBits); } // Perform any necessary transformations and dispatch. if (child == null) { handled = super.dispatchTouchEvent(transformedEvent); } else { final float offsetX = mScrollX - child.mLeft; final float offsetY = mScrollY - child.mTop; transformedEvent.offsetLocation(offsetX, offsetY); if (! child.hasIdentityMatrix()) { transformedEvent.transform(child.getInverseMatrix()); } handled = child.dispatchTouchEvent(transformedEvent); } // Done. transformedEvent.recycle(); return handled; }
这里我们可以看到对事件具体的处理,代码比较多,我们分析关键点。
我们应当重点关注第三个参数,因为上面再调用的时候,一会儿为null,一会儿不为null,这里就给出了解释,重点是这段代码:
if (child == null) { handled = super.dispatchTouchEvent(event); } else { handled = child.dispatchTouchEvent(event); }
我们可以看到,在child为null的时候,Touch事件会传递给viewGroup自身的dispatchTouchEvent处理,即父类view的方法,在里面处理ontouch,上一篇已经分析过了,就不在多讲。当child不为null的时候,那么会调用childview的
dispatchTouchEvent处理,childView可能是一个view也可能是一个viewGroup。
这个方法里面后面讲的就是一些多点触控的相关处理,就不在赘述。
四 总结
Android事件分发是先传递到ViewGroup,再由ViewGroup传递到View的,一层一层向下传递。在ViewGroup中可以通过onInterceptTouchEvent方法对事件传递进行拦截,onInterceptTouchEvent方法返回true代表不允许事件继续向子View传递,返回false代表不对事件进行拦截,默认返回false。
子View中如果将传递的事件消费掉,ViewGroup中将无法接收到任何事件。
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