上一篇我們介紹了View的事件分發(fā)機(jī)制，不熟悉的可以先了解一下
上一篇：Android事件分發(fā)機(jī)制（View篇）
引言
本篇我們接著上一篇，來(lái)繼續(xù)學(xué)習(xí)一下Android ViewGroup的事件分發(fā)機(jī)制
本來(lái)View的事件分發(fā)機(jī)制和ViewGroup的事件分發(fā)機(jī)制是緊密聯(lián)系在一起的，但是因?yàn)槠渲械脑聿皇侨齼删淠軌蛘f(shuō)清楚的，也為了方便理解，就先拆開(kāi)來(lái)講，然后融合起來(lái)統(tǒng)一歸納總結(jié)，這樣結(jié)構(gòu)更清晰，好了，廢話不多，我們進(jìn)入正文。
正文
本篇ViewGroup的事件分發(fā)機(jī)制的場(chǎng)景和上一篇Android事件分發(fā)機(jī)制（View篇）開(kāi)始的場(chǎng)景是一樣的，這里不再重復(fù)。
上篇也提到過(guò)對(duì)于ViewGroup我們關(guān)注三個(gè)方法：
ViewGroup 三個(gè)方法:
-
dispatchTouchEvent (
MotionEvent event)//負(fù)責(zé)事件分發(fā) -
onInterCeptTouchEvent(
MotionEvent event)//處理是否攔截當(dāng)前事件 -
onTouchEvent(
MotionEvent event)//當(dāng)前View自己處理當(dāng)前事件
我們先新建一個(gè)project: ViewGroupDemo
- 新建一個(gè)MyLinearLayout繼承LinearLayout
重寫(xiě)dispatchTouchEvent、onInterceptTouchEvent、onTouchEvent三個(gè)方法并打印log
/**
* @author Charay
* @data 2017/10/31
*/
public class MyLinearLayout extends LinearLayout {
private static final String TAG = MyLinearLayout.class.getSimpleName();
public MyLinearLayout(Context context) {
super(context);
}
public MyLinearLayout(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
switch (ev.getAction()){
case MotionEvent.ACTION_DOWN:
Log.e(TAG,"--MyLinearLayout--dispatchTouchEvent---ACTION_DOWN---");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG,"--MyLinearLayout--dispatchTouchEvent---ACTION_MOVE---");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG,"--MyLinearLayout--dispatchTouchEvent---ACTION_UP---");
break;
}
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
switch (ev.getAction()){
case MotionEvent.ACTION_DOWN:
Log.e(TAG,"--MyLinearLayout--onInterceptTouchEvent---ACTION_DOWN---");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG,"--MyLinearLayout--onInterceptTouchEvent---ACTION_MOVE---");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG,"--MyLinearLayout--onInterceptTouchEvent---ACTION_UP---");
break;
}
return super.onInterceptTouchEvent(ev);
// return true;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
Log.e(TAG,"--MyLinearLayout--onTouchEvent---ACTION_DOWN---");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG,"--MyLinearLayout--onTouchEvent---ACTION_MOVE---");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG,"--MyLinearLayout--onTouchEvent---ACTION_UP---");
break;
}
return super.onTouchEvent(event);
}
}
- 新建一個(gè)MyButton繼承Button
重寫(xiě)dispatchTouchEvent、onTouchEvent兩個(gè)方法并打印log
/**
* @author Charay
* @data 2017/10/31
*/
public class MyButton extends Button {
private static final String TAG = MyButton.class.getSimpleName();
public MyButton(Context context) {
super(context);
}
public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
switch (ev.getAction()){
case MotionEvent.ACTION_DOWN:
Log.e(TAG,"--MyButton--dispatchTouchEvent---ACTION_DOWN---");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG,"--MyButton--dispatchTouchEvent---ACTION_MOVE---");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG,"--MyButton--dispatchTouchEvent---ACTION_UP---");
break;
}
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
Log.e(TAG,"--MyButton--onTouchEvent---ACTION_DOWN---");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG,"--MyButton--onTouchEvent---ACTION_MOVE---");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG,"--MyButton--onTouchEvent---ACTION_UP---");
break;
}
return super.onTouchEvent(event);
}
}
在布局文件中添加 MyLinearLayout 和 MyButton
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
>
<com.marco.viewgroupdemo.MyLinearLayout
android:id="@+id/my_linearlayout"
android:layout_width="300dp"
android:layout_height="368dp"
android:background="@color/colorPrimaryDark"
android:gravity="center">
<com.marco.viewgroupdemo.MyButton
android:id="@+id/my_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@color/colorAccent"
android:text="按鈕"
/>
</com.marco.viewgroupdemo.MyLinearLayout>
</LinearLayout>
在MainActivity中初始化 MyLinearLayout 和 MyButton并添加setOnTouchListener,然后打印log
public class MainActivity extends Activity {
private static final String TAG = MainActivity.class.getSimpleName();
private MyLinearLayout mMyLinearLayout;
private MyButton mMyButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mMyLinearLayout = (MyLinearLayout) findViewById(R.id.my_linearlayout);
mMyButton = (MyButton) findViewById(R.id.my_button);
mMyLinearLayout.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
switch (motionEvent.getAction()){
case MotionEvent.ACTION_DOWN:
Log.e(TAG,"--MyLinearLayout--onTouch---ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG,"--MyLinearLayout--onTouch---ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG,"--MyLinearLayout--onTouch---ACTION_UP");
break;
}
return false;
}
});
mMyButton.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
switch (motionEvent.getAction()){
case MotionEvent.ACTION_DOWN:
Log.e(TAG,"--mMyButton--onTouch---ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG,"--mMyButton--onTouch---ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG,"--mMyButton--onTouch---ACTION_UP");
break;
}
return false;
}
});
}
}
為了能完整看到事件分發(fā)攔截的整個(gè)流程，我們?cè)谏厦娲a中沒(méi)有更改任何一個(gè)方法的返回值，只是打印了log
現(xiàn)在我們運(yùn)行程序，點(diǎn)擊MyButton,打印日志log如下：
11-01 11:54:02.993 E/MyLinearLayout: --MyLinearLayout--dispatchTouchEvent---ACTION_DOWN---
11-01 11:54:02.993 E/MyLinearLayout: --MyLinearLayout--onInterceptTouchEvent---ACTION_DOWN---
11-01 11:54:02.993 E/MyButton: --MyButton--dispatchTouchEvent---ACTION_DOWN---
11-01 11:54:02.994 E/MainActivity: --mMyButton--onTouch---ACTION_DOWN
11-01 11:54:02.994 E/MyButton: --MyButton--onTouchEvent---ACTION_DOWN---
11-01 11:54:03.004 E/MyLinearLayout: --MyLinearLayout--dispatchTouchEvent---ACTION_MOVE---
11-01 11:54:03.004 E/MyLinearLayout: --MyLinearLayout--onInterceptTouchEvent---ACTION_MOVE---
11-01 11:54:03.004 E/MyButton: --MyButton--dispatchTouchEvent---ACTION_MOVE---
11-01 11:54:03.005 E/MainActivity: --mMyButton--onTouch---ACTION_MOVE
11-01 11:54:03.005 E/MyButton: --MyButton--onTouchEvent---ACTION_MOVE---
11-01 11:54:03.028 E/MyLinearLayout: --MyLinearLayout--dispatchTouchEvent---ACTION_UP---
11-01 11:54:03.028 E/MyLinearLayout: --MyLinearLayout--onInterceptTouchEvent---ACTION_UP---
11-01 11:54:03.028 E/MyButton: --MyButton--dispatchTouchEvent---ACTION_UP---
11-01 11:54:03.028 E/MainActivity: --mMyButton--onTouch---ACTION_UP
11-01 11:54:03.029 E/MyButton: --MyButton--onTouchEvent---ACTION_UP---
雖然日志比較長(zhǎng)，但是不要怕，上面把ACTION_DOWN、ACTION_MOVE、ACTION_UP都打印了出來(lái)，
我們只需要看一組ACTION_DOWN即可，因?yàn)橐粋€(gè)View一旦消費(fèi)了ACTION_DOWN事件，那么其他兩個(gè)事件一定都是這個(gè)View消費(fèi)。
從log中我們發(fā)現(xiàn)ACTION_DOWN、ACTION_MOVE、ACTION_UP三個(gè)手勢(shì)動(dòng)作規(guī)律是一樣的，執(zhí)行順序都是從最外層ViewGroup向內(nèi)層View（或ViewGroup傳遞）：先是MyLinearLayout的dispatchTouchEvent在這個(gè)方法中先執(zhí)行onInterceptTouchEvent判斷事都攔截這個(gè)事件，如果不攔截（默認(rèn)不攔截）就傳遞給MyButton,然后事件分發(fā)給MyButton的dispatchTouchEvent，執(zhí)行MyButton的dispatchTouchEvent，由于MyButton及其父View沒(méi)有onInterceptTouchEvent方法，所以直接在dispatchTouchEvent中先判斷onTouch的返回值，默認(rèn)為false，再執(zhí)行MyButton的onTouchEvent
如果我們?cè)贛yLinearLayout中攔截了這個(gè)事件結(jié)果將是怎樣呢？
下面我們?cè)贛yLinearLayout中的重寫(xiě)的onInterceptTouchEvent中把返回值改為true
onInterceptTouchEvent
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
switch (ev.getAction()){
case MotionEvent.ACTION_DOWN:
Log.e(TAG,"--MyLinearLayout--onInterceptTouchEvent---ACTION_DOWN---");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG,"--MyLinearLayout--onInterceptTouchEvent---ACTION_MOVE---");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG,"--MyLinearLayout--onInterceptTouchEvent---ACTION_UP---");
break;
}
// return super.onInterceptTouchEvent(ev);
return true;
}
然后運(yùn)行程序分別點(diǎn)擊MyButton和MyLinearLayout,發(fā)現(xiàn)打印的log是一樣的：
//點(diǎn)擊MyButton
11-02 11:07:14.207 E/MyLinearLayout: --MyLinearLayout--dispatchTouchEvent---ACTION_DOWN---
11-02 11:07:14.207 E/MyLinearLayout: --MyLinearLayout--onInterceptTouchEvent---ACTION_DOWN---
11-02 11:07:14.207 E/MainActivity: --MyLinearLayout--onTouch---ACTION_DOWN
11-02 11:07:14.207 E/MyLinearLayout: --MyLinearLayout--onTouchEvent---ACTION_DOWN---
//點(diǎn)擊MyLinearLayout
11-02 11:07:21.667 E/MyLinearLayout: --MyLinearLayout--dispatchTouchEvent---ACTION_DOWN---
11-02 11:07:21.677 E/MyLinearLayout: --MyLinearLayout--onInterceptTouchEvent---ACTION_DOWN---
11-02 11:07:21.677 E/MainActivity: --MyLinearLayout--onTouch---ACTION_DOWN
11-02 11:07:21.677 E/MyLinearLayout: --MyLinearLayout--onTouchEvent---ACTION_DOWN---
一分鐘思考一下下面兩個(gè)問(wèn)題：
- 為什么
MyButton沒(méi)有任何有關(guān)log，而且這次還執(zhí)行了MyLinearLayout的onTouch和onTouchEvent方法？ - 為什么我們把返回值改為true之前，只執(zhí)行了
MyLinearLayout的dispatchTouchEvent和onInterceptTouchEvent，而沒(méi)有執(zhí)行onTouch和onTouchEvent方法？
下面我們來(lái)看一下 ViewGroup 中的源碼（android-10,即2.3.3的源碼）
dispatchTouchEvent
/**
* {@inheritDoc}
*/
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (!onFilterTouchEventForSecurity(ev)) {
return false;
}
final int action = ev.getAction();
final float xf = ev.getX();
final float yf = ev.getY();
final float scrolledXFloat = xf + mScrollX;
final float scrolledYFloat = yf + mScrollY;
final Rect frame = mTempRect;
boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (action == MotionEvent.ACTION_DOWN) {
if (mMotionTarget != null) {
// this is weird, we got a pen down, but we thought it was
// already down!
// XXX: We should probably send an ACTION_UP to the current
// target.
mMotionTarget = null;
}
// If we're disallowing intercept or if we're allowing and we didn't
// intercept
if (disallowIntercept || !onInterceptTouchEvent(ev)) {
// reset this event's action (just to protect ourselves)
ev.setAction(MotionEvent.ACTION_DOWN);
// We know we want to dispatch the event down, find a child
// who can handle it, start with the front-most child.
final int scrolledXInt = (int) scrolledXFloat;
final int scrolledYInt = (int) scrolledYFloat;
final View[] children = mChildren;
final int count = mChildrenCount;
for (int i = count - 1; i >= 0; i--) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null) {
child.getHitRect(frame);
if (frame.contains(scrolledXInt, scrolledYInt)) {
// offset the event to the view's coordinate system
final float xc = scrolledXFloat - child.mLeft;
final float yc = scrolledYFloat - child.mTop;
ev.setLocation(xc, yc);
child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
if (child.dispatchTouchEvent(ev)) {
// Event handled, we have a target now.
mMotionTarget = child;
return true;
}
// The event didn't get handled, try the next view.
// Don't reset the event's location, it's not
// necessary here.
}
}
}
}
}
boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) ||
(action == MotionEvent.ACTION_CANCEL);
if (isUpOrCancel) {
// Note, we've already copied the previous state to our local
// variable, so this takes effect on the next event
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
}
// The event wasn't an ACTION_DOWN, dispatch it to our target if
// we have one.
final View target = mMotionTarget;
if (target == null) {
// We don't have a target, this means we're handling the
// event as a regular view.
ev.setLocation(xf, yf);
if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
}
return super.dispatchTouchEvent(ev);
}
// if have a target, see if we're allowed to and want to intercept its
// events
if (!disallowIntercept && onInterceptTouchEvent(ev)) {
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
ev.setAction(MotionEvent.ACTION_CANCEL);
ev.setLocation(xc, yc);
if (!target.dispatchTouchEvent(ev)) {
// target didn't handle ACTION_CANCEL. not much we can do
// but they should have.
}
// clear the target
mMotionTarget = null;
// Don't dispatch this event to our own view, because we already
// saw it when intercepting; we just want to give the following
// event to the normal onTouchEvent().
return true;
}
if (isUpOrCancel) {
mMotionTarget = null;
}
// finally offset the event to the target's coordinate system and
// dispatch the event.
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
ev.setLocation(xc, yc);
if ((target.mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
target.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
mMotionTarget = null;
}
return target.dispatchTouchEvent(ev);
}
代碼比較多，我們拋開(kāi)干擾，只看對(duì)我們有用的
先看這行boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
disallowIntercept的含義是禁用攔截事件,下面看 if (disallowIntercept || !onInterceptTouchEvent(ev))判斷,
進(jìn)入判斷條件的情況有兩種：
-
disallowIntercept為true,即禁用攔截事件，這時(shí)候即使攔截事件onInterceptTouchEvent(ev)返回值為true，也不會(huì)攔截 -
disallowIntercept為false，即允許攔截，但是不攔截onInterceptTouchEvent(ev)返回值為false
默認(rèn)情況下是允許攔截的，即disallowIntercept為false，只有當(dāng)我們調(diào)用mMyLinearLayout.requestDisallowInterceptTouchEvent(true);的時(shí)候，即禁止攔截，disallowIntercept的值才為true.
進(jìn)入到if判斷中后，我們看
for (int i = count - 1; i >= 0; i--) {
final View child = children[i];
......
if (child.dispatchTouchEvent(ev)) {
// Event handled, we have a target now.
mMotionTarget = child;
return true;
}
......
}
這時(shí)遍歷子View,把事件傳給子View的dispatchTouchEvent，如果子View是ViewGroup,那就繼續(xù)遍歷，直到遍歷到子View是View類(lèi)型的，然后調(diào)用調(diào)用這個(gè)子View的dispatchTouchEvent，之后的判斷就干我們上一篇的Android事件分發(fā)機(jī)制（View篇）原理一致了。
而我們剛才的代碼中把onInterceptTouchEvent(ev)返回值改為true，則不符合上面的兩種情況，因此進(jìn)入不到if判斷中，事件被攔截了，因此事件到不了MyButton的dispatchTouchEvent方法，也就不會(huì)有MyButton的任何有log。
下面我們看這幾行代碼：
// The event wasn't an ACTION_DOWN, dispatch it to our target if
// we have one.
final View target = mMotionTarget;
if (target == null) {
// We don't have a target, this means we're handling the
// event as a regular view.
ev.setLocation(xf, yf);
if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
}
return super.dispatchTouchEvent(ev);
}
雖然我們?cè)?code>onInterceptTouchEvent(ev)中返回true攔截了這個(gè)事件，但這并不代表我們當(dāng)前MyLinearLayout就是消費(fèi)當(dāng)前事件的消費(fèi)者，因?yàn)槲覀儧](méi)有target，所以進(jìn)入了上面代碼中，最后一行return super.dispatchTouchEvent(ev);即進(jìn)入了View的dispatchTouchEvent(ev)，同樣跟我們上一篇Android View的事件分發(fā)機(jī)制（上）原理一致，雖然和上面for循環(huán)中一樣也是在View中，但是是有區(qū)別的，這個(gè)是MyLinearLayout這個(gè)（ViewGroup）繼承的View,其操作是針對(duì)MyLinearLayout的，即之后所走的onTouch和onTouchEvent也都是針對(duì)MyLinearLayout的；而for循環(huán)中的是MyButton這個(gè)（View）繼承的View，其操作是針對(duì)MyMutton的，即之后所走的onTouch和onTouchEvent也都是針對(duì)MyBUtton的。
既然我們?cè)?code>onInterceptTouchEvent(ev)中返回true攔截了這個(gè)事件，攔截后，就走到了MyLinearLayout的onTouch方法，默認(rèn)返回false，然后執(zhí)行了MyLinearLayout的onTouchEvent方法，所以剛好符合我們上面的log。
總結(jié)
下面我們總結(jié)一下ViewGroup的事件分發(fā)機(jī)制的關(guān)鍵點(diǎn)，以及和View的事件分發(fā)機(jī)制的異同
ViewGroup比View多了一個(gè)攔截事件的方法onInterceptTouchEvent(ev)
ViewGroup比View中最先執(zhí)行的方法，都是dispatchTouchEvent方法，然后View執(zhí)行了onTouch方法
但是ViewGroup中在執(zhí)行onTouch方法之前多了一個(gè)onInterceptTouchEvent(ev)判斷，這個(gè)判斷決定了事件在本ViewGroup中消費(fèi)，還是將事件繼續(xù)分發(fā)給它的子View.
而View是沒(méi)有onInterceptTouchEvent(ev)的，所以沒(méi)有攔截，事件能不能在View中消費(fèi)掉，關(guān)鍵是看這個(gè)View中的onTouch方法或者onTouchEvent的返回值，如果返回值都是false，那就會(huì)將事件返回給其父View的onTouch和onTouchEvent方法，直到找到一個(gè)能消費(fèi)此次事件的ViewGroup。
好了關(guān)與Android中View和ViewGroup的事件分發(fā)機(jī)制兩篇都講完了，如果有不足或者不理解的地方可在評(píng)論中回復(fù)，我們共同進(jìn)步。
最后附上ViewGroupDemo源碼：github下載
