Android 进阶学习(五) Android 事件传递View
2020-11-11 本文已影响0人
Tsm_2020
上一篇文章我们总结了事件在Activity 和View之间的传递,我们知道还有一种特殊的情况那就是需要加上ViewGroup, 这样才是一个完整的事件传递过程,因为View 就是绘制过程中最小的粒子,不能包含其他view ,而ViewGroup 是可以包含其他View 的,
我们将上一篇的例子在加上一个RelativeLayout ,我们贴一下代码
public class TsmRelativeLayout extends RelativeLayout {
public TsmRelativeLayout(Context context) {
super(context);
}
public TsmRelativeLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public TsmRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
log ("TsmRelativeLayout dispatchTouchEvent"+" " + "action"+event.getAction());
// if(event.getAction()==MotionEvent.ACTION_DOWN){
// return true;
// }
return super.dispatchTouchEvent(event);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
log ("TsmRelativeLayout onInterceptTouchEvent"+" " + "action"+event.getAction());
return false;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
log ("TsmRelativeLayout onTouchEvent"+" " + "action"+event.getAction());
return super.onTouchEvent(event);
}
public void log(String tag){
LogUtils.i(tag);
}
}
public class TsmTextView extends androidx.appcompat.widget.AppCompatTextView {
public TsmTextView(Context context) {
super(context);
}
public TsmTextView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
public TsmTextView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
log ("TsmTextView dispatchTouchEvent"+" " + "action"+event.getAction());
return super.dispatchTouchEvent(event);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
log ("TsmTextView onTouchEvent"+" " + "action"+event.getAction());
return super.onTouchEvent(event);
}
public void log(String tag){
LogUtils.i(tag);
}
}
public class MainActivity extends AppCompatActivity implements View.OnClickListener, View.OnTouchListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TsmTextView tv_view= findViewById(R.id.tv_view);
tv_view.setOnClickListener(this);
// tv_view.setOnTouchListener(this);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
LogUtils.i("MainActivity dispatchTouchEvent action:"+ev.getAction());
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
LogUtils.i("MainActivity onTouchEvent action:"+event.getAction());
return super.onTouchEvent(event);
}
@Override
public void onClick(View v) {
LogUtils.i("onClick");
}
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (v.getId()){
case R.id.tv_view:
LogUtils.i("MainActivity onTouch"+" action:"+ event.getAction());
}
return false;
}
}
打印结果
msg:==>MainActivity dispatchTouchEvent action:0
msg:==>TsmRelativeLayout dispatchTouchEvent action0
msg:==>TsmRelativeLayout onInterceptTouchEvent action0
msg:==>TsmTextView dispatchTouchEvent action0
msg:==>MainActivity onTouch action:0
msg:==>TsmTextView onTouchEvent action0
msg:==>MainActivity dispatchTouchEvent action:2
msg:==>TsmRelativeLayout dispatchTouchEvent action2
msg:==>TsmRelativeLayout onInterceptTouchEvent action2
msg:==>TsmTextView dispatchTouchEvent action2
msg:==>MainActivity onTouch action:2
msg:==>TsmTextView onTouchEvent action2
msg:==>MainActivity dispatchTouchEvent action:2
msg:==>TsmRelativeLayout dispatchTouchEvent action2
msg:==>TsmRelativeLayout onInterceptTouchEvent action2
msg:==>TsmTextView dispatchTouchEvent action2
msg:==>MainActivity onTouch action:2
msg:==>TsmTextView onTouchEvent action2
msg:==>MainActivity dispatchTouchEvent action:1
msg:==>TsmRelativeLayout dispatchTouchEvent action1
msg:==>TsmRelativeLayout onInterceptTouchEvent action1
msg:==>TsmTextView dispatchTouchEvent action1
msg:==>MainActivity onTouch action:1
msg:==>TsmTextView onTouchEvent action1
msg:==>onClick
我们发现增加了RelativeLayout后 多了一个方法,那就是onInterceptTouchEvent ,而整个过程就是Activity.dispatchTouchEvent --> RelativeLayout.dispatchTouchEvent -->RelativeLayout.onInterceptTouchEvent -->View.dispatchTouchEvent -->View.onTouch -->View.onTouchEvent 处理完按下事件后又循环处理其他事件,最后执行了onClick方法,消费完事件
增加了RelativeLayout后和View 事件的派发有相似的地方也有不同的地方,到底有什么不同我们就从ViewGroup 的dispatchTouchEvent 源码来看
@Override
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 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<View> 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 (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;
}
这一段代码相对于View 的dispatchTouchEvent还要复杂,我们就将它拆分一下,慢慢来分析
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();
}
这段代码从字面上的意思就是在按下状态时清除原有的flag,并重置state,
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);
}
这段代码主要是为了判断是否打断这个事件,继续分发,判断如果打断 intercepted 或者 目标View mFirstTouchTarget 已经找到,那么就执行event.setTargetAccessibilityFocus(false);字面意思就是设置后续event的访问权限,但是具体怎么执行的是native 方法,看不到了,但是从修改onInterceptTouchEvent的返回值我发现如果设置打断后,那么Viewgroup会立即执行自身的onTouchEvent,并且不会执行与该事件相关的后续事件,肯定还有一些别的操作我们就无法猜测了
这里面还有一个关于disallowIntercept 的判断, ViewGroup 里面包含了一个设置disallowIntercept 的方法,
@Override
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);
}
}
在child里面可以设置是否让ViewGroup 拦截该事件,看到过很多下拉刷新View中都包含了该方法,非常实用的一个方法
接下来又判断 cancel的状态,
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
判断完cancel状态就进入了 根据不同的action 来执行不同的动作,
接下来判断是否是ACTION_DOWN ,在按下的状态必须要找到和这个按下相关的child 也就是 newTouchTarget ,
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 = 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 (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;
}
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
发现在寻找newTouchTarget会调用方法dispatchTransformedTouchEvent()将Touch事件传递给特定的子View。该方法十分重要，在该方法中为一个递归调用，会递归调用dispatchTouchEvent()方法。在dispatchTouchEvent()中如果子View为ViewGroup并且Touch没有被拦截那么递归调用dispatchTouchEvent()，如果子View为View那么就会调用其onTouchEvent()。dispatchTransformedTouchEvent方法如果返回true则表示子View消费掉该事件，同时进入该if判断。
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;
}
还发现如果在发现在寻找newTouchTarget的View 过程中如果dispatchTransformedTouchEvent 循环调用的过程中如果发现有子View消费了事件,那么就要给mFirstTouchTarget 赋值
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
在按下状态时,如果找到不到 newTouchTarget 并且有mFirstTouchTarget , 会通过mFirstTouchTarget 找到newTouchTarget
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;
}
在执行完ACTION_DOWN的判断,后就是又执行了dispatchTransformedTouchEvent 分发事件,如果找到不到子View 消费事件则执行
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
注意上面第三个参数为null,
如果找到了消费事件的子View 则 执行
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;
}
就是说找到了可以消费Touch事件的子View且后续Touch事件可以传递到该子View。可以看见在源码的else中对于非ACTION_DOWN事件继续传递给目标子组件进行处理，依然是递归调用dispatchTransformedTouchEvent()方法来实现的处理。
总结
ViewGroup 事件的派发是由顶层VeiwGroup 递归调用分发给View的,我们可以使用onInterceptTouchEvent 打断这个分发的过程,onInterceptTouchEvent返回true则表示需要拦截当前这个事件,切该事件的后续事件也不会派发给当前的ViewGroup
