高级UI-事件传递

事件传递在Android中有着举足轻重的作用，那么事件的传递在Android中又是怎么样实现的呢，在这里我们将进一步探讨Android的事件传递机制

从一个例子入手

首先是一个简单的onTouch和onClick事件的例子

public class TouchAndClickActivity extends AppCompatActivity implements View.OnTouchListener, View.OnClickListener {    private static final String TAG = "TouchAndClickActivity";    private LinearLayout linearLayout;    private Button button;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_touch_and_click);        linearLayout = findViewById(R.id.linear_layout);        button = findViewById(R.id.button);        linearLayout.setOnTouchListener(this);        button.setOnTouchListener(this);        linearLayout.setOnClickListener(this);        button.setOnClickListener(this);    }    @Override    public boolean onTouch(View v, MotionEvent event) {        Log.d(TAG, "onTouch: view -> " + v.getClass().getSimpleName());        return false;    }    @Override    public void onClick(View v) {        Log.d(TAG, "onClick: view -> " + v.getClass().getSimpleName());    }}

此时观察打印日志

D/TouchAndClickActivity: onTouch: view -> AppCompatButtonD/TouchAndClickActivity: onTouch: view -> AppCompatButtonD/TouchAndClickActivity: onClick: view -> AppCompatButtonD/TouchAndClickActivity: onTouch: view -> LinearLayoutD/TouchAndClickActivity: onTouch: view -> LinearLayoutD/TouchAndClickActivity: onClick: view -> LinearLayout

经过观察发现，控件的事件触发顺序是先onTouch再onClick，并且onTouch会在触摸和松开时各执行一次，并且onClick是在抬起时候执行的，相当于keyUp
然后我们修改onTouch的返回值为true，再次实验，观察输出日志

D/TouchAndClickActivity: onTouch: view -> AppCompatButtonD/TouchAndClickActivity: onTouch: view -> AppCompatButtonD/TouchAndClickActivity: onTouch: view -> LinearLayoutD/TouchAndClickActivity: onTouch: view -> LinearLayout

通过修改onTouch的返回值，我们得到这样的结论：当onTouch返回true时，代表事件被消费了，不会再向下传递，即onClick事件不会得到执行
那么为何会产生上面的现象呢，这其实是由于View的事件分发机制造成的，接下来就来看一看View的事件分发机制具体是怎么做的

View的事件分发

要知道View的事件分发机制是如何运行的，我们就需要到源码中去一探究竟，由于View的代码比较庞大，这里只需要重点关注的有如下四个点(这里以SDK25的源代码为例)

dispatchTouchEvent()onTouchListener.onTouch()onTouchEvent()onClickListener.onClick()

首先到dispatchTouchEvent()，这里是处理事件的地方

/** * Pass the touch screen motion event down to the target view, or this * view if it is the target. * * @param event The motion event to be dispatched. * @return True if the event was handled by the view, false otherwise. */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;}

这其中需要重点关注的代码如下

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;    }}

这里面的ListenerInfo是一个内部类，保存了View的所有监听
再看这个判断条件

if (li != null && li.mOnTouchListener != null        && (mViewFlags & ENABLED_MASK) == ENABLED        && li.mOnTouchListener.onTouch(this, event)) {    result = true;}

里面涉及到了onTouch方法，正是因为这样，当onTouch返回true的时候，result = true得以执行，并且这里一旦赋值，后面的判断条件就为false，即不会再执行onTouchEvent(event)，并且最终返回的result就是true了，如果onTouch返回的是false，那么就会执行onTouchEvent(event)，在onTouchEvent(event)里面主要涉及到以下四种状态

MotionEvent.ACTION_UPMotionEvent.ACTION_DOWNMotionEvent.ACTION_CANCELMotionEvent.ACTION_MOVE

而在UP中，我们找到了点击事件

mPerformClick -> new PerformClick() -> performClickInternal() -> performClick()

在performClick()里面，就看到了click方法

public boolean performClick() {    // We still need to call this method to handle the cases where performClick() was called    // externally, instead of through performClickInternal()    notifyAutofillManagerOnClick();    final boolean result;    final ListenerInfo li = mListenerInfo;    if (li != null && li.mOnClickListener != null) {        playSoundEffect(SoundEffectConstants.CLICK);        li.mOnClickListener.onClick(this);        result = true;    } else {        result = false;    }    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);    notifyEnterOrExitForAutoFillIfNeeded(true);    return result;}

之所以绕这么大个弯，是要保证安全
通过以上的源代码分析，我们可以得出以下结论

当onTouchListener的onTouch方法返回了true，那么view里面的onTouchEvent就不会被调用了，返回false时候才会调用onTouchEvent
如果view为disenable，则onTouchListener里面不会执行，但是会执行onTouchEvent(event)方法
onTouchEvent方法中的ACTION_UP分支中触发onclick事件监听
其顺序为dispatchTouchEvent() -> onTouchListener.onTouch()[return false] -> onTouchEvent() -> onClickListener.onClick()

到这里就解释了为何onTouch的返回值会控制到onClick的执行了
那么来验证下我们的猜想，自定义一个Button，主要打印dispatchTouchEvent()和onTouchEvent()的执行时机

public class MyButton extends AppCompatButton {    private static final String TAG = "cj5785";    public MyButton(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    public boolean dispatchTouchEvent(MotionEvent event) {        Log.d(TAG, "dispatchTouchEvent : action -> " + event.getAction());        return super.dispatchTouchEvent(event);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        Log.d(TAG, "onTouchEvent : action -> " + event.getAction());        return super.onTouchEvent(event);    }}

在log中看到以下信息，完成了两次dispatchTouchEvent，一次按下，一次抬起（试验时，onTouch返回false）

D/cj5785: dispatchTouchEvent : action -> 0D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent : action -> 0D/cj5785: dispatchTouchEvent : action -> 1D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent : action -> 1D/TouchAndClickActivity: onClick: view -> MyButton

此时再来看看onTouchEvent()，如果该写为以下代码

@Overridepublic boolean onTouchEvent(MotionEvent event) {    Log.d(TAG, "onTouchEvent : action -> " + event.getAction());    super.onTouchEvent(event);    return true;}

打印日志如下

D/cj5785: dispatchTouchEvent : action -> 0D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent : action -> 0D/cj5785: dispatchTouchEvent : action -> 1D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent : action -> 1D/TouchAndClickActivity: onClick: view -> MyButton

返回false时，打印如下

D/cj5785: dispatchTouchEvent : action -> 0D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent : action -> 0D/TouchAndClickActivity: onTouch: view -> LinearLayoutD/TouchAndClickActivity: onTouch: view -> LinearLayoutD/TouchAndClickActivity: onClick: view -> LinearLayout

直接使用true，不使用super

@Overridepublic boolean onTouchEvent(MotionEvent event) {    Log.d(TAG, "onTouchEvent : action -> " + event.getAction());    return true;}

打印日志如下

D/cj5785: dispatchTouchEvent : action -> 0D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent : action -> 0D/cj5785: dispatchTouchEvent : action -> 1D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent : action -> 1

如果直接返回false，打印如下

D/cj5785: dispatchTouchEvent : action -> 0D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent : action -> 0D/TouchAndClickActivity: onTouch: view -> LinearLayoutD/TouchAndClickActivity: onTouch: view -> LinearLayoutD/TouchAndClickActivity: onClick: view -> LinearLayout

通过以上实验发现，onTouchEvent的返回值决定是否继续传递事件，第一个super+true，代表调用父类方法，然后返回true，也就是说在调完父类方法以后，消费此次事件，不再传递。第二个super+false，表示不消费此次事件，继续传递，此时传递给父布局，所以打印出LinearLayout，同时事件在后面被处理了，第三个true，表示消费此次事件，不再传递，由于没有super，自然也就没有click方法调用，第四个，表示不消费此次事件，继续传递，父布局继续处理

再来，如果dispatchTouchEvent()的返回值直接返回true，而不使用super，那么将会什么都执行不到，这也从另一侧说明了dispatchTouchEvent()是事件分发的入口
其实dispatchTouchEvent()的返回值的作用可以从调用处看出

public final boolean dispatchPointerEvent(MotionEvent event) {    if (event.isTouchEvent()) {        return dispatchTouchEvent(event);    } else {        return dispatchGenericMotionEvent(event);    }}

ViewGroup和View的事件分发

这里我们关注的三个方法为

dispatchTouchEvent()onTouchEvent()onInterceptTouchEvent()

自定义一个LinearLayout，然后包裹自定义的Button，自定义Button中返回的是super

public class MyLinearLayout extends LinearLayout {    private static final String TAG = "cj5785";    public MyLinearLayout(Context context, @Nullable AttributeSet attrs) {        super(context, attrs);    }    @Override    public boolean dispatchTouchEvent(MotionEvent ev) {        Log.d(TAG, "dispatchTouchEvent: view->" + getClass().getSimpleName() + ",action->" + ev.getAction());        return super.dispatchTouchEvent(ev);    }    @Override    public boolean onInterceptTouchEvent(MotionEvent ev) {        Log.d(TAG, "onInterceptTouchEvent: view->" + getClass().getSimpleName() + ",action->" + ev.getAction());        return super.onInterceptTouchEvent(ev);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        Log.d(TAG, "onTouchEvent: view->" + getClass().getSimpleName() + ",action->" + event.getAction());        return super.onTouchEvent(event);    }}

得到的打印日志

D/cj5785: dispatchTouchEvent: view->MyLinearLayout,action->0D/cj5785: onInterceptTouchEvent: view->MyLinearLayout,action->0D/cj5785: dispatchTouchEvent: view->MyButton,action->0D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent: view->MyButton,action->0D/cj5785: dispatchTouchEvent: view->MyLinearLayout,action->1D/cj5785: onInterceptTouchEvent: view->MyLinearLayout,action->1D/cj5785: dispatchTouchEvent: view->MyButton,action->1D/TouchAndClickActivity: onTouch: view -> MyButtonD/cj5785: onTouchEvent: view->MyButton,action->1D/TouchAndClickActivity: onClick: view -> MyButton

由打印信息得知，先得到事件的是MyLinearLayout，然后再传递给MyButton
先执行dispatchTouchEvent，再执行onInterceptTouchEvent()，由于MyButton消费了事件，所以MyLinearLayout没有执行到onTouchEvent()
此时如果点击的是MyLinearLayout，那么onTouchEvent()就会得到执行

D/cj5785: dispatchTouchEvent: view->MyLinearLayout,action->0D/cj5785: onInterceptTouchEvent: view->MyLinearLayout,action->0D/TouchAndClickActivity: onTouch: view -> MyLinearLayoutD/cj5785: onTouchEvent: view->MyLinearLayout,action->0D/cj5785: dispatchTouchEvent: view->MyLinearLayout,action->1D/TouchAndClickActivity: onTouch: view -> MyLinearLayoutD/cj5785: onTouchEvent: view->MyLinearLayout,action->1D/TouchAndClickActivity: onClick: view -> MyLinearLayout

接下来去看看源代码，由于源代码较多，这里就只贴出关键代码
在方法里面，有这样一段代码

// 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;}

也就是说，onInterceptTouchEvent()是在这里调用的，查看代码，也只有这一处调用，而在这段代码后面，有很多需要使用intercepted去做判断的地方，onInterceptTouchEvent()源代码如下，其作用就是拦截触摸事件，返回false表示不拦截

public boolean onInterceptTouchEvent(MotionEvent ev) {    if (ev.isFromSource(InputDevice.SOURCE_MOUSE)            && ev.getAction() == MotionEvent.ACTION_DOWN            && ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)            && isOnScrollbarThumb(ev.getX(), ev.getY())) {        return true;    }    return false;}

当onInterceptTouchEvent()的返回值为false时候，表示不拦截，就会进入到以下判断，最终调用dispatchTransformedTouchEvent()

if (!canceled && !intercepted) {···    if (actionMasked == MotionEvent.ACTION_DOWN            || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)            || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {···        if (newTouchTarget == null && childrenCount != 0) {            ···            for (int i = childrenCount - 1; i >= 0; i--) {                ···                if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {                    ...                }            }        }    }}

而在dispatchTransformedTouchEvent()中，根据其是否有子控件，从而决定调用的dispatchTouchEvent()，到底是将事件交给子控件还是自己处理，其判断就是在这里做出的，事件分发的重难点也就在这，很绕，涉及到ViewGroup的递归和子控件的dispatchTouchEvent()返回值，简单来说就是这里会得到子空间时候会消费事件，如果要消费事件，那么就返回true

private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,            View child, int desiredPointerIdBits) {    final boolean handled;···    // 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;}

分析到这，我们也就知道了之前打印出的日志原因了，ViewGroup的事件分发流程也差不多就是这样

ViewGroup的一些细节

上面分析了ViewGroup的事件分发，那么在时间分发时候有哪些是值得注意的呢
第一个地方，在按下时候会清除之前的一些状态

// 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();}

在cancelAndClearTouchTargets()和resetTouchState()里面都调用了clearTouchTargets()，这个方法用来清除TouchTarget，防止触摸操作的干扰，这是调用dispatchTouchEvent()最开始就会执行的代码，保证了mFirstTouchTarget为空

private void clearTouchTargets() {    TouchTarget target = mFirstTouchTarget;    if (target != null) {        do {            TouchTarget next = target.next;            target.recycle();            target = next;        } while (target != null);        mFirstTouchTarget = null;    }}

第二个地方就是是否拦截，在按下，移动，抬起时候都会做判断，源代码中这样写到

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;}

而intercepted代表着是否拦截，而intercepted的赋值取决于disallowIntercept，那么在使用时候会发现有这么一个方法，可以指定是否拦截，而在这里设置的的mGroupFlags会决定disallowIntercept的真假，从而影响intercepted

@Overridepublic 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);    }}

第三个是重叠控件的执行问题，有这样一段代码

// Find a child that can receive the event.// Scan children from front to back.final ArrayList<View> preorderedList = buildTouchDispatchChildList();

这个方法最终会调用如下方法，也就是按照Z轴的大小从大到小排序，这也就是为何上面的空间会相应

ArrayList<View> buildOrderedChildList() {    final int childrenCount = mChildrenCount;    if (childrenCount <= 1 || !hasChildWithZ()) return null;    if (mPreSortedChildren == null) {        mPreSortedChildren = new ArrayList<>(childrenCount);    } else {        // callers should clear, so clear shouldn't be necessary, but for safety...        mPreSortedChildren.clear();        mPreSortedChildren.ensureCapacity(childrenCount);    }    final boolean customOrder = isChildrenDrawingOrderEnabled();    for (int i = 0; i < childrenCount; i++) {        // add next child (in child order) to end of list        final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);        final View nextChild = mChildren[childIndex];        final float currentZ = nextChild.getZ();        // insert ahead of any Views with greater Z        int insertIndex = i;        while (insertIndex > 0 && mPreSortedChildren.get(insertIndex - 1).getZ() > currentZ) {            insertIndex--;        }        mPreSortedChildren.add(insertIndex, nextChild);    }    return mPreSortedChildren;}

这段代码就是用来添加view，形成按Z轴大小排序的集合，那么就会先先执行到上面的控件，如果拦截了，下面的控件就得不到执行，不拦截则会执行下去
第四个就是ViewGroup的事件消费问题了
其主要处理逻辑在下列代码中

// 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;    }}

这里主要是判断，而判断条件在前面做了赋值

newTouchTarget = addTouchTarget(child, idBitsToAssign);

/** * Adds a touch target for specified child to the beginning of the list. * Assumes the target child is not already present. */private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {    final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);    target.next = mFirstTouchTarget;    mFirstTouchTarget = target;    return target;}

在这里就得到了target，如果说此时mFirstTouchTarget为空，那么就是一个普通控件，传递的子控件为nul，不包含touch事件，如果不为空，那么会将touch事件从mFirstTouchTarget链表中一个一个取出来，得到最后能相应事件的View
那么用一张图来说明这个过程
高级UI-事件传递_第1张图片
在这里面，省略了dispatchTouchEvent()的返回值，无论dispatchTouchEvent()返回真假，都会告诉调用者
细细品味，细思极恐，这段代码是真的经典！！！

事件分发冲突问题

在ScrollView嵌套ListView类似这种情况并且其总高度超过屏幕的时候，会产生冲突
下面来展示这种冲突
首先是一个布局，ScrollView里面嵌套了ListView

<?xml version="1.0" encoding="utf-8"?><ScrollView xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/scroll_view"    android:layout_width="match_parent"    android:layout_height="match_parent">    <LinearLayout        android:layout_width="match_parent"        android:layout_height="match_parent"        android:orientation="vertical">        <ListView            android:id="@+id/list_view"            android:layout_width="match_parent"            android:layout_height="500dp" />        <TextView            android:layout_width="match_parent"            android:layout_height="200dp"            android:background="@android:color/holo_orange_light"            android:text="@string/scroll_conflict" />        <TextView            android:layout_width="match_parent"            android:layout_height="200dp"            android:background="@android:color/darker_gray"            android:text="@string/scroll_conflict" />        <TextView            android:layout_width="match_parent"            android:layout_height="200dp"            android:background="@android:color/holo_green_light"            android:text="@string/scroll_conflict" />        <TextView            android:layout_width="match_parent"            android:layout_height="200dp"            android:background="@android:color/holo_blue_light"            android:text="@string/scroll_conflict" />    LinearLayout>ScrollView>

然后简单的准备ListView的数据

public class ScrollConflictActivity extends AppCompatActivity {    private ListView listView;    private List<String> list;    private ArrayAdapter<String> adapter;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_scroll_conflict);        listView = findViewById(R.id.list_view);        list = new ArrayList<>();        for (int i = 0; i < 30; i++) {            list.add("item " + i);        }        adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, list);        listView.setAdapter(adapter);    }}

然后…
高级UI-事件传递_第2张图片
这时候只能滑动整个布局，也就是ScrollView，里面的ListView无法滑动，通过上面源代码的分析，我们知道了造成这种现象的原因就是ScrollView拦截了ListView的滑动，造成ListView无法滑动
所以这时候我们就要让ScrollView不拦截ListView
那么根据对源代码的分析，这里就有很多种解决办法
最简单粗暴的方法就是自定义ScrollView，然后复写dispatchTouchEvent()，调用requestDisallowInterceptTouchEvent()，设置为true

public class MyScrollView extends ScrollView {    public MyScrollView(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    public boolean dispatchTouchEvent(MotionEvent ev) {        //不拦截        requestDisallowInterceptTouchEvent(true);        return super.dispatchTouchEvent(ev);    }}

这样便解决了这个滑动冲突问题
高级UI-事件传递_第3张图片
随之而来的又一个问题产生了，要如何展开ListView呢，在这里使用match_parent是没有效果的，那么此时就需要展开ListView了
其实这个的解决办法也是很多的，例如计算每一个条目的高度，相加得到总高度，还有重写onMearsure()方法都可以实现这个效果

public class MyListView extends ListView {    public MyListView(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        int expandHeight = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2, MeasureSpec.AT_MOST);        super.onMeasure(widthMeasureSpec, expandHeight);    }}

这里只使用自定义ListView，而不使用自定义ScrollView
高级UI-事件传递_第4张图片

从一个例子入手

View的事件分发

ViewGroup和View的事件分发

ViewGroup的一些细节

事件分发冲突问题

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