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 -> AppCompatButton
D/TouchAndClickActivity: onTouch: view -> AppCompatButton
D/TouchAndClickActivity: onClick: view -> AppCompatButton
D/TouchAndClickActivity: onTouch: view -> LinearLayout
D/TouchAndClickActivity: onTouch: view -> LinearLayout
D/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 -> AppCompatButton
D/TouchAndClickActivity: onTouch: view -> AppCompatButton
D/TouchAndClickActivity: onTouch: view -> LinearLayout
D/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_UP
MotionEvent.ACTION_DOWN
MotionEvent.ACTION_CANCEL
MotionEvent.ACTION_MOVE

而在UP中，我们找到了点击事件

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

此时再来看看onTouchEvent()，如果该写为以下代码

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

返回false时，打印如下

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

直接使用true，不使用super

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

打印日志如下

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

如果直接返回false，打印如下

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

@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);
    }
}

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
事件传递-事件分发流程图
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…
事件传递-滑动冲突
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
事件传递-滑动冲突解决
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
事件传递-展开ListView

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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