Android事件分发机制源码解析

更简单的学习Android事件分发中,使用日志、比喻、流程图相结合的方式,以更简单的方法去分析了Android的事件分发机制。本篇文章将采用分析源码的方式,更深入的解析Android的事件分发机制。

自定义View系列目录

一、从Activity开始

Android的触摸事件,是由windowManagerService进行采集,之后传递到Activiy进行处理。我们这里从Activity#dispatchTouchEvent方法开始解析

1
2
3
4
5
6
7
8
9
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}

上述代码中,onUserInteraction()是一个空的实现,我们直接来看下
getWindow().superDispatchTouchEvent(ev)方法。window是一个抽象的方法,不过系统给它提供了一个实现类PhoneWindow,我们这里看下它的superDispatchTouchEvent(ev)方法。

1
2
3
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}

上述代码调用了DecorView类的superDispatchTouchEvent方法,继续跟进

1
2
3
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}

上述代码调用了父类的dispatchTouchEvent方法,DecorView的父类为FrameLayout,其直接继承了ViewGroup#dispatchTouchEvent方法。

二、ViewGroup中的事件分发

ViewGroup#dispatchTouchEvent方法比较长,这里只截取部分进行分析

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
public boolean dispatchTouchEvent(MotionEvent ev) {
...
// 在ACTION_DOWN事件时,初始化Touch标记
// 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) {
// 是否拦截的标志位,假如设置requestDisallowInterceptTouchEvent(true),
// 则为true,不拦截事件
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
// 默认返回false
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;
// 不是ACTION_CANCEL事件,并且不拦截事件
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) {
// 获取触摸坐标
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;
// 遍历所有子View
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);
...
resetCancelNextUpFlag(child);
// 把事件(ACTION_DOWN、ACTION_POINTER_DOWN、ACTION_HOVER_MOVE)传递给子View处理
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;
}
...
}
...
}
...
}
}
}
// 分发事件到目标View
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// 没有找到事件分发目标的情况,将会调用自己的onTouchEvent方法
// 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;
// 这里找到了事件分发的目标
while (target != null) {
final TouchTarget next = target.next;
// ACTION_DOWN已经完成事件分发,并消费了事件,直接返回true
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
// 其余事件则需要传递给目标View进行处理
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;
}
}
// 对ACTION_CANCEL事件进行处理
// Update list of touch targets for pointer up or cancel, if needed.
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
// 重置Touch状态
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
...
return handled;
}
// 默认返回false
public boolean onInterceptTouchEvent(MotionEvent ev) {
return false;
}

我们现在来看看传递事件的dispatchTransformedTouchEvent方法,同样我也只是截取了其中比较关键的部分

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
...
final MotionEvent transformedEvent;
// 对transformedEvent的一系列计算
...
if (child == null) {
// 如果没有子View,则执行super.dispatchTouchEvent方法,
// 调用自己的onTouchEvent方法
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());
}
// 如果有子View,则调用子View#dispatchTouchEvent方法
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}

三、View中的事件处理

ViewGroup中不拦截事件,调用子View#dispatchTouchEvent方法进行处理

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
public boolean dispatchTouchEvent(MotionEvent event) {
...
if (onFilterTouchEventForSecurity(event)) {
// 如果设置了OnTouchListener,使用onTouch对事件进行处理,
// 并返回true,则不需要再执行onTouchEvent方法
//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;
}

这里继续看看View#onTouchEvent方法

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
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 & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
...
// 移除长按
removeLongPressCallback();
...
// 检查单击
performClick();
...
break;
case MotionEvent.ACTION_DOWN:
...
// 检测是否为长按
checkForLongClick(0);
...
break;
....
}
return true;
}
return false;
}

上述代码,主要是检查View是否可以点击,如果可点击,则会返回true,同时也会执行可点击的事件。

四、小结

通过本文的源码解析,我们可以更深入的理解Android的事件分发。可以简单的推出一个流程 : Activity→PhoneWindow→DecorView→ViewGroup→View。如果在阅读过程中,有任何疑问与问题,欢迎与我联系。

博客:www.idtkm.com

GitHub:https://github.com/Idtk

微博:http://weibo.com/Idtk

邮箱:IdtkMa@gmail.com


文章作者:Idtk

本文标题:Android事件分发机制源码解析

原始链接:http://www.idtkm.com/2016/08/21/12、TouchEventSource/

许可协议: 署名-非商业性使用-禁止演绎 4.0 国际 转载请保留原文链接及作者。