一、View的基础知识
1、View是界面层的控件的一种抽象,包括ViewGroup
2、View的位置参数
VIew的位置主要由四个顶点来决定,对应View的四个属性:top,left,right,bottom
VIew的坐标系:X轴和Y轴正方向分别为下和右;
注意:以下参数都是相对于View的父布局坐标
Left = getLeft() 获取左上角横坐标
Top = getTop() 获取左上角纵坐标
Right = getRight() 获取右下角横坐标
Bottom = getBottom() 获取右下角纵坐标
x = getX() 获取左上角x坐标
y= getY() 获取左上角y坐标
translationX = getTranslationX() 获取左上角相对于父容器偏移量
translationY = getTranslationY() 获取左上角相对于父容器偏移量
注意:这两个参数是相对于手机屏幕左上角的坐标
rawX = getRawX() 获取左上角x坐标
rawY = getRawY() 获取左上角y坐标
View事件相关对象
1、MotionEvent:
触摸事件对象,包括坐标
2、TouchSlop:
系统所能识别的被认为是滑动的最小距离
获取方式:ViewConfiguration.get(Context).getScaledTouchSlop();
3、VelocityTracker:
速度追踪,用于追踪手指在滑动过程中的速度,包括水平和垂直方向速度,由上往下为正值;
速度 =(终点位置- 起点位置)/时间
4、GestureDetoctor:
手势检测,用于辅助检测用户的单击、滑动、长按、双击等行为;一般使用检测双击;
5、Scroller:
弹性滑动对象,用于实现View的弹性滑动.
二、View的滑动
View滑动方式三种:
1、使用scrollTo/scrollBy,滑动的是内容
scroolTo:绝对滑动
mScrollX = view的边缘- view中内容边缘
所以从左往右滑动,mScrollX为负值,反之为正值;
从上往下滑动,mScroolY为负值,反之为正值;
scroolBy:相对滑动,其内部调用的scrollTo方法
2、平移动画
translationX,translationY
3、改变布局参数MarginLayoutParams
三、View的弹性滑动
即滑动渐进式滑动,三种方式
1、使用Scroller
2、使用动画
3、使用延时策略
四、View的事件分发机制
事件分发机制包括三部分：
- 从屏幕到App；
- 从App到对应页面；
- 页面内具体分发。
1、事件分发从屏幕到App
- 硬件与内核部分
Linux内核会将硬件产生的触摸事件包装为Event存到/dev/input/event[x]目录下； - SystemServer部分
在SystemServer进程中管理事件输入的InputManagerService，会启动一个读线程，也就是InputReader，它会从系统也就是/dev/input/目录拿到任务，并且分发给InputDispatcher线程，然后进行统一的事件分发调度。 - 跨进程通信传递给App
我们的App中的Window与InputManagerService之间的通信实际上使用的InputChannel(在ViewRootImpl.setView()过程中，也会同时注册InputChannel)；InputChannel是一个pipe，底层实际是通过socket进行通信。最终会走到InputEventReceiver.dispachInputEvent方法。
2、事件分发从App到对应页面
1. 事件回传到ViewRootImpl
InputEventReceiver.dispachInputEvent方法即ViewRootImpl中WindowInputEventReceiver实现了InputEventReceiver接口，最终调用
ViewRootImpl.enqueueInputEvent方法
//InputEventReceiver.java
private void dispatchInputEvent(int seq, InputEvent event) {
mSeqMap.put(event.getSequenceNumber(), seq);
onInputEvent(event);
}
//ViewRootImpl.java ::WindowInputEventReceiver
final class WindowInputEventReceiver extends InputEventReceiver {
public void onInputEvent(InputEvent event) {
enqueueInputEvent(event, this, 0, true);
}
}
//ViewRootImpl.java
void enqueueInputEvent(InputEvent event,
InputEventReceiver receiver, int flags, boolean processImmediately) {
adjustInputEventForCompatibility(event);
QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
QueuedInputEvent last = mPendingInputEventTail;
if (last == null) {
mPendingInputEventHead = q;
mPendingInputEventTail = q;
} else {
last.mNext = q;
mPendingInputEventTail = q;
}
mPendingInputEventCount += 1;
if (processImmediately) {
//责任链分发
doProcessInputEvents();
} else {
scheduleProcessInputEvents();
}
}
2. 第一次责任链分发
调用doProcessInputEvents()方法，涉及到事件分发中的第一次责任链分发(InputStage的责任链ViewRootImpl.setView方法中就已经组装好了)
不同责任链作用：
SyntheticInputStage。综合处理事件阶段，比如处理导航面板、操作杆等事件。
ViewPostImeInputStage。视图输入处理阶段，比如按键、手指触摸等运动事件，我们熟知的view事件分发就发生在这个阶段。
NativePostImeInputStage。本地方法处理阶段，主要构建了可延迟的队列。
EarlyPostImeInputStage。输入法早期处理阶段。
ImeInputStage。输入法事件处理阶段，处理输入法字符。
ViewPreImeInputStage。视图预处理输入法事件阶段，调用视图view的dispatchKeyEventPreIme方法。
NativePreImeInputStage。本地方法预处理输入法事件阶段。
3. View触摸事件分发给ViewPostImeInputStage
最终ViewPostImeInputStage中会调用mView.dispatchPointerEvent方法；(ViewRootImpl中的mView就是DecorView)
//View.java
public final boolean dispatchPointerEvent(MotionEvent event) {
if (event.isTouchEvent()) {
return dispatchTouchEvent(event);
} else {
return dispatchGenericMotionEvent(event);
}
}
4. 事件在Activity,Window,DecorView中的传递
最终调用DecorView的dispatchTouchEvent
//DecorView.java
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//cb其实就是对应的Activity/Dialog
final Window.Callback cb = mWindow.getCallback();
return cb != null && !mWindow.isDestroyed() && mFeatureId < 0
? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);
}
//Activity.java
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
//PhoneWindow.java
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
//DecorView.java
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
事件分发经过了: ViewRootImpl -> DecorView -> Activity -> PhoneWindow -> DecorView
3、事件分发页面内部
1. ViewGroup分发事件
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
// If the event targets the accessibility focused view and this is it, start
// normal event dispatch. Maybe a descendant is what will handle the click.
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// 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();
}
//检查是否拦截：只有ActionDown或者mFirstTouchTarget为空时才会判断是否拦截
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;
}
// If intercepted, start normal event dispatch. Also if there is already
// a view that is handling the gesture, do normal event dispatch.
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
final boolean isMouseEvent = ev.getSource() == InputDevice.SOURCE_MOUSE;
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0
&& !isMouseEvent;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
//事件传递给子view
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;
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) {
final float x =
isMouseEvent ? ev.getXCursorPosition() : ev.getX(actionIndex);
final float y =
isMouseEvent ? ev.getYCursorPosition() : ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
final ArrayList preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
//遍历子View
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
//2.判断事件坐标
if (!child.canReceivePointerEvents()
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
//3.传递事件
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();
//如果子View消耗了则给mFirstTouchTarget赋值
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
//mFirstTouchTarget不为空时会调用dispatchTransformendTouchEvent
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;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
private boolean dispatchTransformedTouchEvent(View child) {
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
}
- 只有当Action_Down或者mFirstTouchTarget不为空时才判断是否拦截；
- mFirstTouchTarget是个链表结构，代表某个子View消费了事件，为null则表示没有子View消费事件
- disallowIntercept字段是用来是否不拦截；由子View调用方法控制；
getParent().requestDisallowInterceptTouchEvent(true);
- mFirstTouchTarget==null有两种情况，一是ViewGroup拦截，二是子View没有处理事件,两种情况最后都回调到ViewGroup.onTouchEvent；
- dispatchTransformedTouchEvent做的主要就是两个事，如果child不为null，则事件分发到child,否则调用super.dispatchTouchEvent,并最终返回结果
- 利用dispatchTransformedTouchEvent,如果返回true,则通过addTouchTarget对mFirstTouchTarget赋值。
2. 子View分发事件
public boolean dispatchTouchEvent(MotionEvent event) {
//如果事件应该首先由可访问性焦点处理。
if (event.isTargetAccessibilityFocus()) {
// 我们没有焦点或没有虚拟后代有它，不要处理事件。
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
// 我们有焦点并得到了事件，然后使用正常的事件调度。
event.setTargetAccessibilityFocus(false);
}
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// 新手势的防御性清理
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
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);
}
// 如果这是手势的结束，则在嵌套滚动后清理；如果我们尝试了 ACTION_DOWN 但我们不想要其余的手势，也可以取消它。
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
子View的onTouchEvent方法
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
if ((viewFlags & ENABLED_MASK) == DISABLED
&& (mPrivateFlags4 & PFLAG4_ALLOW_CLICK_WHEN_DISABLED) == 0) {
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
return clickable;
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
if ((viewFlags & TOOLTIP) == TOOLTIP) {
handleTooltipUp();
}
if (!clickable) {
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
}
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
// take focus if we don't have it already and we should in
// touch mode.
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
if (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
}
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// Only perform take click actions if we were in the pressed state
if (!focusTaken) {
// Use a Runnable and post this rather than calling
// performClick directly. This lets other visual state
// of the view update before click actions start.
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClickInternal();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_DOWN:
if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
}
mHasPerformedLongPress = false;
if (!clickable) {
checkForLongClick(
ViewConfiguration.getLongPressTimeout(),
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
break;
}
if (performButtonActionOnTouchDown(event)) {
break;
}
// Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer();
// For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(
ViewConfiguration.getLongPressTimeout(),
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
}
break;
case MotionEvent.ACTION_CANCEL:
if (clickable) {
setPressed(false);
}
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
break;
case MotionEvent.ACTION_MOVE:
if (clickable) {
drawableHotspotChanged(x, y);
}
final int motionClassification = event.getClassification();
final boolean ambiguousGesture =
motionClassification == MotionEvent.CLASSIFICATION_AMBIGUOUS_GESTURE;
int touchSlop = mTouchSlop;
if (ambiguousGesture && hasPendingLongPressCallback()) {
if (!pointInView(x, y, touchSlop)) {
// The default action here is to cancel long press. But instead, we
// just extend the timeout here, in case the classification
// stays ambiguous.
removeLongPressCallback();
long delay = (long) (ViewConfiguration.getLongPressTimeout()
* mAmbiguousGestureMultiplier);
// Subtract the time already spent
delay -= event.getEventTime() - event.getDownTime();
checkForLongClick(
delay,
x,
y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
}
touchSlop *= mAmbiguousGestureMultiplier;
}
// Be lenient about moving outside of buttons
if (!pointInView(x, y, touchSlop)) {
// Outside button
// Remove any future long press/tap checks
removeTapCallback();
removeLongPressCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
}
final boolean deepPress =
motionClassification == MotionEvent.CLASSIFICATION_DEEP_PRESS;
if (deepPress && hasPendingLongPressCallback()) {
// process the long click action immediately
removeLongPressCallback();
checkForLongClick(0 ,x,y,
TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DEEP_PRESS);
}
break;
}
return true;
}
return false;
}
- 如果设置了setOnTouchListener并且返回为true，那么onTouchEvent就不再执行
- 否则执行onTouchEvent，我们常用的OnClickListenr就是在onTouchEvent里的Up事件中触发的。
总结：
1、事件分发的本质就是一个递归方法，通过往下传递，调用dispatchTouchEvent方法，找到事件的处理者，这也就是项目中常见的责任链模式。
2、在分发过程中，ViewGroup通过onInterceptTouchEvent判断是否拦截事件
3、在分发过程中，View的默认通过onTouchEvent处理事件
4、如果底层View不消费，则默认一步步往上执行父元素onTouchEvent方法。
5、如果所有View的onTouchEvent方法都返回false，则最后会执行到Activity的onTouchEvent方法，事件分发也就结束了。
参考：
Android事件分发8连问
Android事件分发
五、View的滑动冲突
解决方法:
1、外部拦截法
核心思想:父容器需要的事件拦截,不需要的不拦截;
重写父容器的onInterceptTouchEvent方法,在内部MotionEvent.ACTION_MOVE事件中做相应拦截;
/**
* 拦截事件
* @param ev
* @return
*/
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
boolean intercepted = false;
int x = (int) ev.getX();
int y = (int) ev.getY();
switch (ev.getAction()) {
/*如果拦截了Down事件,则子类不会拿到这个事件序列*/
case MotionEvent.ACTION_DOWN:
lastXIntercept = x;
lastYIntercept = y;
intercepted = false;
break;
case MotionEvent.ACTION_MOVE:
final int deltaX = x - lastXIntercept;
final int deltaY = y - lastYIntercept;
/*根据条件判断是否拦截该事件*/
if (Math.abs(deltaX) > Math.abs(deltaY)) {
intercepted = true;
} else {
intercepted = false;
}
break;
case MotionEvent.ACTION_UP:
intercepted = false;
break;
}
lastXIntercept = x;
lastYIntercept = y;
return intercepted;
}
2、内部拦截法
核心思想:父容器不拦截所有事件,子元素需要此事件就消耗掉,否则交给父容器处理;
重写子View的dispatchTouchEvent方法,在内部MotionEvent.ACTION_DOWN事件中做相应拦截;
MotionEvent.ACTION_MOVE事件中根据条件取消拦截;
ViewGroup中onInterceptTouchEvent方法处理
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
//内部拦截法
int action = ev.getAction();
if (action==MotionEvent.ACTION_DOWN)//down事件不进行拦截
{
return false;
}else {
return true;
}
}
子View中dispatchTouchEvent方法处理
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
parent= getParent();
switch (ev.getAction()){
case MotionEvent.ACTION_DOWN:
parent.requestDisallowInterceptTouchEvent(true);
break;
case MotionEvent.ACTION_MOVE:
if (viewgroup需要此事件) //根据实际情况换成你自己的判定条件
{
parent.requestDisallowInterceptTouchEvent(false);
}
break;
case MotionEvent.ACTION_UP:
break;
}
return super.dispatchTouchEvent(ev);
}