一、什么是事件分发
所谓事件分发,就是将一次完整的点击所包含的点击事件传递到某个具体的View或ViewGroup,让该View或该ViewGroup处理它(消费它)。分发是从上往下(父到子)依次传递的,其中可能经过的对象有最上层Activity,中间层ViewGroup,最下层View。
二、Activity的层次结构
源码查找:
1.自己的Activity的setContentView()方法
@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_event_distribution); } |
2.跳转到Activity.java的setContentView()方法,可以看到,调用了getWindow()的方法
public void setContentView(@LayoutRes int layoutResID) { getWindow().setContentView(layoutResID); initWindowDecorActionBar(); } |
3.Activity.java的mWindow来自PhoneWindow
mWindow = new PhoneWindow(this, window, activityConfigCallback); |
4.PhoneWindow.java-->setContentView()--> installDecor(),在PhoneWindow中调用了installDecor()方法
@Override public void setContentView(int layoutResID) { // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window // decor, when theme attributes and the like are crystalized. Do not check the feature // before this happens. if (mContentParent == null) { installDecor(); //继续执行 } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) { mContentParent.removeAllViews(); } .................. |
5.PhoneWindow.java-->setContentView()--> installDecor()--> generateLayout(mDecor),在 installDecor()中又继续执行了generateLayout(mDecor)方法。
mContentParent = generateLayout(mDecor); |
6.PhoneWindow.java-->generateLayout()
ViewGroup generateLayout(DecorView decor) |
7.PhoneWindow.java-->generateLayout()--> int layoutResource,layoutResource根据不同情况,返回不同的资源文件,也就是布局文件。
int layoutResource; |
8.PhoneWindow.java-->generateLayout()-->R.layout.screen_title; 拿出一个常用的布局文件,screen_title.xml
layoutResource = R.layout.screen_title; |
9.screen_title.xml的代码, ViewStub是用来显示ActionBar的,另外两个FrameLayout,一个显示TitleView,一个显示ContentView,平时写的内容,正是ContentView。
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:fitsSystemWindows="true"> <!-- Popout bar for action modes --> <ViewStub android:id="@+id/action_mode_bar_stub" android:inflatedId="@+id/action_mode_bar" android:layout="@layout/action_mode_bar" android:layout_width="match_parent" android:layout_height="wrap_content" android:theme="?attr/actionBarTheme" /> <FrameLayout android:layout_width="match_parent" android:layout_height="?android:attr/windowTitleSize" style="?android:attr/windowTitleBackgroundStyle"> <TextView android:id="@android:id/title" style="?android:attr/windowTitleStyle" android:background="@null" android:fadingEdge="horizontal" android:gravity="center_vertical" android:layout_width="match_parent" android:layout_height="match_parent" /> </FrameLayout> <FrameLayout android:id="@android:id/content" android:layout_width="match_parent" android:layout_height="0dip" android:layout_weight="1" android:foregroundGravity="fill_horizontal|top" android:foreground="?android:attr/windowContentOverlay" /> </LinearLayout> |
如以下结构图:
三、事件分发涉及到的主要方法
涉及到的方法
@Override public boolean dispatchTouchEvent(MotionEvent ev) { //分发事件 return super.dispatchTouchEvent(ev); } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { //拦截事件 return super.onInterceptTouchEvent(ev); } @Override public boolean onTouchEvent(MotionEvent event) { //消费事件 return super.onTouchEvent(event); } |
Activity涉及到的方法:dispatchTouchEvent()、onTouchEvent()
ViewGroup涉及到的方法:dispatchTouchEvent()、onInterceptTouchEvent()
View涉及到的方法:dispatchTouchEvent()、onTouchEvent()
四、事件分发流程
1.Activity把事件分发到ViewGroup
(1)事件传递
每一次事件分发,都是从dispatchTouchEvent()开始的。
1)查看Activity的源码,调用了getWindow().superDispatchTouchEvent(ev)
public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { return true; } return onTouchEvent(ev); } |
2)在Activity.java中可以看到,所以getWindow().superDispatchTouchEvent(ev)实际上是调用了PhoneWindow.java中的superDispatchTouchEvent(ev)方法。
public Window getWindow() { return mWindow; } mWindow = new PhoneWindow(this, window, activityConfigCallback); //mWindow的定义 |
3)然后再看PhoneWindow.java中的superDispatchTouchEvent(ev)方法,是调用DecorView.java的mDecor.superDispatchTouchEvent(event)
@Override public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event); } |
4)而DecorView是继承FrameLayout,再继承ViewGroup的
private DecorView mDecor; //实例对象 class DecorView extends FrameLayout; //继承FrameLayout FrameLayout extends ViewGroup; //继承ViewGroup |
5)从上面四步来分析,Avtivity的getWindow().superDispatchTouchEvent()方法最后调用的是ViewGroup的dispatchTouchEvent()方法,从而实现了事件从Activity的dispatchTouchEvent()向下传递到ViewGroup的dispatchTouchEvent()方法。
(2)总结
6)返回值分析。
如果Avtivity的getWindow().superDispatchTouchEvent()返回true,则Avtivity的dispatchTouchEvent(),也会返回true,表示点击事件顺利分发给ViewGroup,由ViewGroup继续进行下一层的分发,Avtivity的分发任务结束。
如果返回false,表示此次点击事件由Avtivity层消费,会执行Avtivity的onTouchEvent(),无论onTouchEvent()这个方法返回的是true或者false,本次的事件分发都结束了。
(3)流程图
2.ViewGroup把事件分发到ViewGroup或View
(1)事件拦截
ViewGroup.java中的部分代码
ViewGroup-->dispatchTouchEvent()
public boolean dispatchTouchEvent(MotionEvent ev) { if (!disallowIntercept) { intercepted = onInterceptTouchEvent(ev); ev.setAction(action); // restore action in case it was changed } else { intercepted = false; } } |
方法中使用了onInterceptTouchEvent(ev)方法
如果返回true,则表示ViewGroup拦截此次事件。
如果返回false,则表示ViewGroup不拦截,事件继续往下分发。
onInterceptTouchEvent(ev)默认返回不拦截,可以在ViewGroup中重写改方法来拦截事件。
不拦截事件,则会调用ViewGroup的onTouchEvent()来处理点击事件,把事件消费掉。
(2)分发
这个源码中,使用到了intercepted这个变量,主要作用是来遍历子ViewGroup和View,
当intercepted为false的时候,遍历子ViewGroup和子View,因为这个事件没有被消费掉,继续分发到子ViewGroup和子View。
当intercepted为true的时候,该事件已经被消费,不会继续往下分发,也不会遍历子ViewGroup和子View,也不会执行if语句里面的方法。
进入if语句中判断点击事件的触摸范围(焦点)是否属于某个子ViewGroup或者子View。
如果触摸范围属于子View,则调用子View的dispatchTouchEvent()方法。
如果触摸范围属于子ViewGroup,则继续遍历下一层的ViewGroup或者View。
遍历到最下层的View,还是找不到消费此处事件的View,则依次回调上一层的ViewGroup的onTouchEvent()方法,直到回调到Activity的onTouchEvent()方法。
// Check for interception. final boolean intercepted; 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; |
(3)流程图
3.View的事件分发
(1)分析
View的dispatchTouchEvent()的源码
public boolean dispatchTouchEvent(MotionEvent event) { // If the event should be handled by accessibility focus first. if (event.isTargetAccessibilityFocus()) { // We don't have focus or no virtual descendant has it, do not handle the event. if (!isAccessibilityFocusedViewOrHost()) { return false; } // We have focus and got the event, then use normal event dispatch. event.setTargetAccessibilityFocus(false); } boolean result = false; if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onTouchEvent(event, 0); } final int actionMasked = event.getActionMasked(); if (actionMasked == MotionEvent.ACTION_DOWN) { // Defensive cleanup for new gesture stopNestedScroll(); } if (onFilterTouchEventForSecurity(event)) { if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) { result = true; } //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; } } if (!result && mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(event, 0); } // Clean up after nested scrolls if this is the end of a gesture; // also cancel it if we tried an ACTION_DOWN but we didn't want the rest // of the gesture. if (actionMasked == MotionEvent.ACTION_UP || actionMasked == MotionEvent.ACTION_CANCEL || (actionMasked == MotionEvent.ACTION_DOWN && !result)) { stopNestedScroll(); } return result; } |
在View的dispatchTouchEvent()方法中首先会调用onTouch()方法,如果onTouch()方法能够消费该事件,就会直接返回True,从而直接结束View的dispatchTouchEvent()方法,不再执行onTouchEvent()方法;
如果onTouch()方法不能消费该事件,就会返回False,从而继续执行onTouchEvent`()`方法。
如果onTouchEvent()能够消费该事件,就会返回True从而直接结束dispatchTouchEvent()方法。
如果onTouchEvent()方法也不能消费该事件,就会返回默认的False从而回调到上一层ViewGroup的onTouchEvent()方法,直到回调到Activity的onTouchEvent`()`方法。
(2)流程图
五、具体例子
(0)测试代码
共有三种类型和四个测试代码
Activity:EventDistributionActivity
ViewGroup:EventDistributionLinearLayout1、EventDistributionLinearLayout2
View:EventDistributionButton
分别代码:
EventDistributionActivity.java
public class EventDistributionActivity extends BaseActivity { Button mBtn; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_event_distribution); mBtn = findViewById(R.id.btn); OnClick(); } public void OnClick() { mBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Log.v("showLog", "按钮被点击!"); } }); mBtn.setOnTouchListener(new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { boolean dis = false; Log.v("showLog", "Button.Touch()=" + dis); return dis; } }); } @Override public boolean dispatchTouchEvent(MotionEvent ev) { //分发事件 boolean dis = super.dispatchTouchEvent(ev); Log.v("showLog", "Activity.dispatchTouchEvent()=" + dis); return dis; } @Override public boolean onTouchEvent(MotionEvent event) { //处理事件 boolean dis = super.onTouchEvent(event); Log.v("showLog", "Activity.onTouchEvent()=" + dis); return dis; } } |
EventDistributionLinearLayout1.java
public class EventDistributionLinearLayout1 extends LinearLayout { public EventDistributionLinearLayout1(Context context, AttributeSet attrs) { super(context, attrs); } @Override public boolean dispatchTouchEvent(MotionEvent ev) { //分发事件 boolean dis = super.dispatchTouchEvent(ev); Log.v("showLog", "LinearLayout1.dispatchTouchEvent()=" + dis); return dis; } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { //拦截事件 boolean dis = super.onInterceptTouchEvent(ev); Log.v("showLog", "LinearLayout1.onInterceptTouchEvent()=" + dis); return dis; } @Override public boolean onTouchEvent(MotionEvent event) { //消费事件 boolean dis = super.onTouchEvent(event); Log.v("showLog", "LinearLayout1.onTouchEvent()=" + dis); return dis; } } |
EventDistributionLinearLayout2.java
public class EventDistributionLinearLayout2 extends LinearLayout { public EventDistributionLinearLayout2(Context context, AttributeSet attrs) { super(context, attrs); } @Override public boolean dispatchTouchEvent(MotionEvent ev) { //分发事件 boolean dis = super.dispatchTouchEvent(ev); Log.v("showLog", "LinearLayout2.dispatchTouchEvent()=" + dis); return dis; } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { //拦截事件 boolean dis = super.onInterceptTouchEvent(ev); dis = true; Log.v("showLog", "LinearLayout2.onInterceptTouchEvent()=" + dis); return dis; } @Override public boolean onTouchEvent(MotionEvent event) { //消费事件 boolean dis = super.onTouchEvent(event); Log.v("showLog", "LinearLayout2.onTouchEvent()=" + dis); return dis; } } EventDistributionButton.java public class EventDistributionButton extends Button { public EventDistributionButton(Context context, AttributeSet attrs) { super(context, attrs); } @Override public boolean dispatchTouchEvent(MotionEvent event) { //分发事件 boolean dis = super.dispatchTouchEvent(event); Log.v("showLog", "Button.dispatchTouchEvent()=" + dis); return dis; } @Override public boolean onTouchEvent(MotionEvent event) { //消费事件 boolean dis = super.onTouchEvent(event); Log.v("showLog", "Button.onTouchEvent()=" + dis); return dis; } @Override public boolean performClick() { boolean dis = super.performClick(); Log.v("showLog", "Button.performClick()="+dis); return dis; } } |
activity_event_distribution.xml
<?xml version="1.0" encoding="utf-8"?> <com.lanjiabin.systemtest.event.EventDistributionLinearLayout1 xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".event.EventDistributionActivity"> <com.lanjiabin.systemtest.event.EventDistributionLinearLayout2 android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <com.lanjiabin.systemtest.event.EventDistributionButton android:background="@drawable/button_color_circle_shape1" android:id="@+id/btn" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center" android:layout_marginTop="300dp" android:text="点击" /> </com.lanjiabin.systemtest.event.EventDistributionLinearLayout2> </com.lanjiabin.systemtest.event.EventDistributionLinearLayout1> |
效果图:一个LinearLayout1包含LinearLayout2再包含一个Button
界面只有一个按钮
(1)测试1
测试用例:按钮消费事件,和空白处不消费事件
按住按钮不松开,事件被Button的onTouchEvent()消费
LinearLayout1.onInterceptTouchEvent()=false LinearLayout2.onInterceptTouchEvent()=false Button.Touch()=false Button.onTouchEvent()=true Button.dispatchTouchEvent()=true LinearLayout2.dispatchTouchEvent()=true LinearLayout1.dispatchTouchEvent()=true Activity.dispatchTouchEvent()=true |
按住空白处不松开,没有事件被消费
LinearLayout1.onInterceptTouchEvent()=false LinearLayout2.onInterceptTouchEvent()=false LinearLayout2.onTouchEvent()=false LinearLayout2.dispatchTouchEvent()=false LinearLayout1.onTouchEvent()=false LinearLayout1.dispatchTouchEvent()=false Activity.onTouchEvent()=false Activity.dispatchTouchEvent()=false |
(2)测试2
测试用例:在LinearLayout2处截断
修改代码:EventDistributionLinearLayout2.java
@Override public boolean onInterceptTouchEvent(MotionEvent ev) { //拦截事件 boolean dis = super.onInterceptTouchEvent(ev); dis = true; Log.v("showLog", "LinearLayout2.onInterceptTouchEvent()=" + dis); return dis; } |
按住按钮不松开:事件截断生效,将不会继续遍历下层的ViewGroup或者View,所以日志中看不到Button的日志打印。
LinearLayout1.onInterceptTouchEvent()=false LinearLayout2.onInterceptTouchEvent()=true //截断生效 LinearLayout2.onTouchEvent()=false LinearLayout2.dispatchTouchEvent()=false LinearLayout1.onTouchEvent()=false LinearLayout1.dispatchTouchEvent()=false Activity.onTouchEvent()=false Activity.dispatchTouchEvent()=false |
(3)测试3
测试用例:在View中onTouch()中返回true
也就是在Button中设置onTouch()返回true,则不会产生点击事件,完整的点击事件是被按下和松开的,所以上面没有点击按钮的监听事件的打印日志。
首先,看看完整的点击事件日志,去掉先前测试的改变的代码。
LinearLayout1.onInterceptTouchEvent()=false LinearLayout2.onInterceptTouchEvent()=false Button.Touch()=false Button.onTouchEvent()=true //触摸按下事件被消费 Button.dispatchTouchEvent()=true LinearLayout2.dispatchTouchEvent()=true LinearLayout1.dispatchTouchEvent()=true Activity.dispatchTouchEvent()=true //触摸按下的事件处理结束 LinearLayout1.onInterceptTouchEvent()=false //开始触摸i抬起的事件 LinearLayout2.onInterceptTouchEvent()=false Button.Touch()=false Button.onTouchEvent()=true //触摸抬起的事件被消费 Button.dispatchTouchEvent()=true LinearLayout2.dispatchTouchEvent()=true LinearLayout1.dispatchTouchEvent()=true Activity.dispatchTouchEvent()=true 按钮被点击! //onClick Button.performClick()=true |
开始测试用例:
修改代码:
EventDistributionActivity.java,将boolean dis = false;修改为boolean dis = true;
mBtn.setOnTouchListener(new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { boolean dis = true; Log.v("showLog", "Button.Touch()=" + dis); return dis; } }); |
按下和松开按钮:可以看到,事件被Button.Touch()消费了,因为在Touch()返回了true,事件没有继续传递下去,所以onClick事件没有被触发,没有生效。
LinearLayout1.onInterceptTouchEvent()=false LinearLayout2.onInterceptTouchEvent()=false Button.Touch()=true //触摸事件被消费 Button.dispatchTouchEvent()=true LinearLayout2.dispatchTouchEvent()=true LinearLayout1.dispatchTouchEvent()=true Activity.dispatchTouchEvent()=true //触摸按下事件处理完毕 LinearLayout1.onInterceptTouchEvent()=false LinearLayout2.onInterceptTouchEvent()=false Button.Touch()=true Button.dispatchTouchEvent()=true LinearLayout2.dispatchTouchEvent()=true LinearLayout1.dispatchTouchEvent()=true Activity.dispatchTouchEvent()=true |
编程中我们会遇到多少挫折?表放弃,沙漠尽头必是绿洲。
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