touch事件最开始从Activity 的 dispatchTouchEvent() 方法开始的
/frameworks/base/core/java/android/app/Activity.java
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
//这一段逻辑很重要，我们大部分界面的touch事件，都是从这里开始传的
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
//调用Activity自身的onTouchEvent()方法
return onTouchEvent(ev);
}
getWindow() 相信很多人都知道，我们在需要 Acitivity 全屏或者开发一些主题效果时经常用到，它是返回的 Window 对象。
/frameworks/base/core/java/android/app/Activity.java
public Window getWindow() {
return mWindow;
}在Android系统中，Window 类是一个抽象类，目前唯一的实现类是 PhoneWindow.java，我们从官方给 Window 类的注释中就可以看出来。
/framworks/base/core/java/android/view/Window.java
public abstract class Window {
...
}我们紧接着看 PhoneWindow 的 superDispatchTouchEvent 方法，逻辑也很简单。
/framworks/base/core/java/com/android/internal/policy/PhoneWindow.java
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
@Override
public final @NonNull View getDecorView() {//这个方法是不是感觉很熟悉
if (mDecor == null || mForceDecorInstall) {
installDecor();
}
return mDecor;
}mDecor是一个DecorView对象，他包含两部分：Title和Content，对应的id 是 android.id.title 和 android.id.content，我们经常用到的setContentView对应的就是这一部分。来看DecorView.java是如何定义的：
/framworks/base/core/java/com/android/internal/policy/DecorView.java
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
...
}可以看到，DecorView 是一个 FrameLayout ，而 FrameLayout 又是继承自 ViewGroup ，因此，我们可以继续看 ViewGroup 中touch事件是如何分发的。由于这部分代码比较多，为了能说明流程，我们只保留关键代码：
/framworks/core/java/android/view/ViewGroup.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;
// 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);//清除所有之前touch事件处理结果
resetTouchState();//重置touch状态
}
// Check for interception.查看是否需要拦截
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
/// M : add log to help debugging
if (intercepted == true && ViewDebugManager.DEBUG_TOUCH) {
Log.d(TAG, "Touch event was intercepted event = " + ev
+ ",this = " + this);
}
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 accessibility 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 preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, 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 (!child.canReceivePointerEvents()
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (ViewDebugManager.DEBUG_MOTION) {
Log.d(TAG, "(ViewGroup)dispatchTouchEvent to child 3: child = "
+ child + ",childrenCount = " + childrenCount + ",i = " + i
+ ",newTouchTarget = " + newTouchTarget
+ ",idBitsToAssign = " + idBitsToAssign);
}
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 (ViewDebugManager.DEBUG_MOTION) {
Log.d(TAG, "dispatchTouchEvent middle 5: cancelChild = " + cancelChild
+ ",mFirstTouchTarget = " + mFirstTouchTarget + ",target = "
+ target + ",predecessor = " + predecessor + ",next = " + next
+ ",this = " + this);
}
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;
}未完待续...
作者：冒泡彩虹
