前言
上一篇講了Android觸摸事件的傳遞機(jī)制敷燎，具體可以看這里 初識Android觸摸事件傳遞機(jī)制暂筝。既然知道Android中觸摸事件的傳遞分發(fā)响鹃，那么它能解決什么樣的問題，在我們實(shí)際開發(fā)中如何應(yīng)用淑仆，這點(diǎn)很重要荸百，知道原理是為了解決問題而準(zhǔn)備的。這篇文章的核心講的如何解決View的滑動(dòng)沖突党觅，這個(gè)問題在日常開發(fā)中很常見肌厨，比如內(nèi)部嵌套Fragment視圖是左右滑動(dòng)滚婉，外部用一個(gè)ScrollView來包含墨状，可以上下滑動(dòng)卫漫，如果不進(jìn)行滑動(dòng)沖突處理的話，就會造成外部滑動(dòng)方向和內(nèi)部滑動(dòng)方向不一致肾砂。
目錄
- 常見的滑動(dòng)沖突場景
- 滑動(dòng)沖突的處理規(guī)則
- 外部攔截法
- 內(nèi)部攔截法
- 小結(jié)
常見的滑動(dòng)沖突場景
常見的滑動(dòng)沖突場景可以簡單分為以下三種：
- 場景1：外部滑動(dòng)方向和內(nèi)部滑動(dòng)方向不一致
- 場景2：外部滑動(dòng)方向和內(nèi)部滑動(dòng)方向一致
- 場景3：上面兩種情況的嵌套
如圖：
場景1列赎，主要是將ViewPager和Fragment配合使用所組成的頁面滑動(dòng)效果，主流應(yīng)用幾乎都會使用這個(gè)效果镐确。在這個(gè)效果中可以通過左右滑動(dòng)來切換頁面包吝，而每個(gè)頁面內(nèi)部往往又是一個(gè)ListView，所以就造成了滑動(dòng)沖突源葫，但是在ViewPager內(nèi)部處理了這種滑動(dòng)沖突诗越，因此在采用ViewPager時(shí)我們就無須關(guān)注這個(gè)問題，而如果把ViewPager換成ScrollView息堂，那就必須自己手動(dòng)處理嚷狞，不然造成的結(jié)果就是內(nèi)外兩層只能一層能夠滑動(dòng)。
場景2荣堰，就復(fù)雜一點(diǎn)床未，當(dāng)內(nèi)外兩層都在同一個(gè)方向可以滑動(dòng)的時(shí)候，顯然存在邏輯問題振坚。因?yàn)楫?dāng)手指開始滑動(dòng)的時(shí)候薇搁，系統(tǒng)無法知道用戶到底是想讓哪一層滑動(dòng)，所以當(dāng)手指滑動(dòng)的時(shí)候就會出現(xiàn)問題渡八，要么只有一層滑動(dòng)啃洋，要么就是內(nèi)外兩層都滑動(dòng)但很卡頓。
場景3呀狼，是場景1和場景2兩種情況的嵌套裂允，顯得更復(fù)雜了。比如外部有一個(gè)SlideMenu效果哥艇，內(nèi)部有一個(gè)ViewPager绝编，ViewPager的每一個(gè)頁面中又是一個(gè)ListView。雖然場景3滑動(dòng)沖突看起來很復(fù)雜貌踏，但都是幾個(gè)單一的滑動(dòng)沖突的疊加十饥，因此需要一一拆解開來即可。
滑動(dòng)沖突的處理規(guī)則
一般來說祖乳，不管滑動(dòng)沖突有多么復(fù)雜逗堵，它都有既定的規(guī)則，根據(jù)這些規(guī)則我們就可以選擇合適的方法去處理眷昆。
對于場景1蜒秤，它的處理規(guī)則就是：當(dāng)用戶左右滑動(dòng)時(shí)汁咏，需要讓外部的View攔截點(diǎn)擊事件，當(dāng)用戶上下滑動(dòng)作媚，需要讓內(nèi)部View攔截點(diǎn)擊事件攘滩。具體來說就是根據(jù)滑動(dòng)是水平滑動(dòng)還是豎直滑動(dòng)來判斷到底是由誰來攔截事件。
如圖：
簡單來說纸泡，就是根據(jù)水平方向和豎直方向的距離差來判斷漂问，如果是Dx>Dy，那么則是水平滑動(dòng)女揭，如果是Dy>Dx蚤假，那么則是豎直滑動(dòng)。
場景2吧兔，則是比較特殊磷仰，它無法根據(jù)滑動(dòng)的角度，距離差以及速度差來做判斷掩驱。這個(gè)時(shí)候就需要從業(yè)務(wù)上找到突破點(diǎn)芒划，比如，當(dāng)處于某種狀態(tài)時(shí)需要外部View響應(yīng)用戶的滑動(dòng)欧穴，而處于另外一種狀態(tài)時(shí)需要內(nèi)部View來響應(yīng)View的滑動(dòng)
對于場景3的話民逼，它的滑動(dòng)規(guī)則也更復(fù)雜，和場景2一樣涮帘，同樣是從業(yè)務(wù)上找到突破點(diǎn)拼苍。
外部攔截法
外部攔截法是指點(diǎn)擊事件都是先經(jīng)過父容器的攔截處理，如果父容器需要此事件就攔截调缨，如果不需要此事件疮鲫，就不攔截了，這樣就可以解決滑動(dòng)沖突的問題弦叶，外部攔截法需要重寫父容器的onInterceptTouchEvent方法俊犯，在內(nèi)部做相應(yīng)的攔截即可，偽代碼如下：
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
boolean intercepted = false;
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
intercepted = false;
break;
}
case MotionEvent.ACTION_MOVE: {
if (父容器需要點(diǎn)擊當(dāng)前事件) {
intercepted = true;
} else {
intercepted = false;
}
break;
}
case MotionEvent.ACTION_UP: {
intercepted = false;
break;
}
default:
break;
}
mLastXIntercept = x;
mLastYIntercept = y;
return intercepted;
}
首先ACTION_DOWN這個(gè)事件伤哺，父容器必須返回false燕侠，這樣保證后續(xù)move和up的事件可以傳遞給子View，根據(jù)move事件來決定是否攔截立莉，如果父容器攔截就返回true绢彤，否則返回false。
實(shí)現(xiàn)一個(gè)自定義類似ViewPager的控件蜓耻，嵌套ListView的效果茫舶，源代碼如下：
public class HorizontalScrollViewEx extends ViewGroup {
private static final String TAG = "HorizontalScrollViewEx";
private int mChildrenSize;
private int mChildWidth;
private int mChildIndex;
// 分別記錄上次滑動(dòng)的坐標(biāo)
private int mLastX = 0;
private int mLastY = 0;
// 分別記錄上次滑動(dòng)的坐標(biāo)(onInterceptTouchEvent)
private int mLastXIntercept = 0;
private int mLastYIntercept = 0;
private Scroller mScroller; //彈性滑動(dòng)對象
private VelocityTracker mVelocityTracker; //追蹤滑動(dòng)速度
public HorizontalScrollViewEx(Context context) {
super(context);
init();
}
public HorizontalScrollViewEx(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public HorizontalScrollViewEx(Context context, AttributeSet attrs,
int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
mScroller = new Scroller(getContext());
mVelocityTracker = VelocityTracker.obtain();
}
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
boolean intercepted = false;
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
intercepted = false;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
intercepted = true;
}
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastXIntercept;
int deltaY = y - mLastYIntercept;
if (Math.abs(deltaX) > Math.abs(deltaY)) {
intercepted = true;
} else {
intercepted = false;
}
break;
}
case MotionEvent.ACTION_UP: {
intercepted = false;
break;
}
default:
break;
}
Log.d(TAG, "intercepted=" + intercepted);
mLastX = x;
mLastY = y;
mLastXIntercept = x;
mLastYIntercept = y;
return intercepted;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
mVelocityTracker.addMovement(event);
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastX;
scrollBy(-deltaX, 0);
break;
}
case MotionEvent.ACTION_UP: {
int scrollX = getScrollX();
mVelocityTracker.computeCurrentVelocity(1000);
float xVelocity = mVelocityTracker.getXVelocity();
if (Math.abs(xVelocity) >= 50) {
mChildIndex = xVelocity > 0 ? mChildIndex - 1 : mChildIndex + 1;
} else {
mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;
}
mChildIndex = Math.max(0, Math.min(mChildIndex, mChildrenSize - 1));
int dx = mChildIndex * mChildWidth - scrollX;
smoothScrollBy(dx, 0);
mVelocityTracker.clear();
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return true;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int measuredWidth = 0;
int measuredHeight = 0;
final int childCount = getChildCount();
measureChildren(widthMeasureSpec, heightMeasureSpec);
int widthSpaceSize = MeasureSpec.getSize(widthMeasureSpec);
int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
int heightSpaceSize = MeasureSpec.getSize(heightMeasureSpec);
int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
if (childCount == 0) {
setMeasuredDimension(0, 0);
} else if (heightSpecMode == MeasureSpec.AT_MOST) {
final View childView = getChildAt(0);
measuredHeight = childView.getMeasuredHeight();
setMeasuredDimension(widthSpaceSize, childView.getMeasuredHeight());
} else if (widthSpecMode == MeasureSpec.AT_MOST) {
final View childView = getChildAt(0);
measuredWidth = childView.getMeasuredWidth() * childCount;
setMeasuredDimension(measuredWidth, heightSpaceSize);
} else {
final View childView = getChildAt(0);
measuredWidth = childView.getMeasuredWidth() * childCount;
measuredHeight = childView.getMeasuredHeight();
setMeasuredDimension(measuredWidth, measuredHeight);
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childLeft = 0;
final int childCount = getChildCount();
mChildrenSize = childCount;
for (int i = 0; i < childCount; i++) {
final View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE) {
final int childWidth = childView.getMeasuredWidth();
mChildWidth = childWidth;
childView.layout(childLeft, 0, childLeft + childWidth,
childView.getMeasuredHeight());
childLeft += childWidth;
}
}
}
private void smoothScrollBy(int dx, int dy) {
mScroller.startScroll(getScrollX(), 0, dx, 0, 500);
invalidate();
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
@Override
protected void onDetachedFromWindow() {
mVelocityTracker.recycle();
super.onDetachedFromWindow();
}
}
這個(gè)情況的攔截條件就是父容器在滑動(dòng)過程中水平距離差比垂直距離差大，那么就進(jìn)行攔截刹淌，否則就不攔截饶氏，繼續(xù)傳遞事件讥耗。
內(nèi)部攔截法
內(nèi)部攔截法是指父容器不攔截任何事件，所有的事件都傳遞給子元素嚷往，如果子元素需要此事件就直接消耗掉葛账，否則就交給父容器進(jìn)行處理柠衅，這種方法和Android中的事件分發(fā)機(jī)制不一致皮仁，需要配合requestDisallowInterceptTouchEvent方法才能正常工作，使用起來較外部攔截法復(fù)雜菲宴。偽代碼如下：
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
mHorizontalScrollViewEx2.requestDisallowInterceptTouchEvent(true);
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastX;
int deltaY = y - mLastY;
if (父容器需要此類點(diǎn)擊事件) {
mHorizontalScrollViewEx2.requestDisallowInterceptTouchEvent(false);
}
break;
}
case MotionEvent.ACTION_UP: {
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return super.dispatchTouchEvent(event);
}
當(dāng)子元素調(diào)用requestDisallowInterceptTouchEvent(false)方法時(shí)贷祈，父元素才能繼續(xù)攔截所需的事件。
前面是用自定義類似的ViewPager喝峦，現(xiàn)在重寫一個(gè)ListView势誊，我們可以自定義一個(gè)ListView，叫做ListViewEx谣蠢，然后對內(nèi)部攔截法的模板代碼進(jìn)行修改即可粟耻。
public class ListViewEx extends ListView {
private static final String TAG = "ListViewEx";
private HorizontalScrollViewEx2 mHorizontalScrollViewEx2;
// 分別記錄上次滑動(dòng)的坐標(biāo)
private int mLastX = 0;
private int mLastY = 0;
public ListViewEx(Context context) {
super(context);
}
public ListViewEx(Context context, AttributeSet attrs) {
super(context, attrs);
}
public ListViewEx(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public void setHorizontalScrollViewEx2(
HorizontalScrollViewEx2 horizontalScrollViewEx2) {
mHorizontalScrollViewEx2 = horizontalScrollViewEx2;
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
mHorizontalScrollViewEx2.requestDisallowInterceptTouchEvent(true);
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastX;
int deltaY = y - mLastY;
Log.d(TAG, "dx:" + deltaX + " dy:" + deltaY);
if (Math.abs(deltaX) > Math.abs(deltaY)) {
mHorizontalScrollViewEx2.requestDisallowInterceptTouchEvent(false);
}
break;
}
case MotionEvent.ACTION_UP: {
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return super.dispatchTouchEvent(event);
}
}
同時(shí)對于包含ListViewEx外部布局進(jìn)行修改，在onInterceptTouchEvent事件上不進(jìn)行攔截
public class HorizontalScrollViewEx2 extends ViewGroup {
private static final String TAG = "HorizontalScrollViewEx2";
private int mChildrenSize;
private int mChildWidth;
private int mChildIndex;
// 分別記錄上次滑動(dòng)的坐標(biāo)
private int mLastX = 0;
private int mLastY = 0;
// 分別記錄上次滑動(dòng)的坐標(biāo)(onInterceptTouchEvent)
private int mLastXIntercept = 0;
private int mLastYIntercept = 0;
private Scroller mScroller;
private VelocityTracker mVelocityTracker;
public HorizontalScrollViewEx2(Context context) {
super(context);
init();
}
public HorizontalScrollViewEx2(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public HorizontalScrollViewEx2(Context context, AttributeSet attrs,
int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
mScroller = new Scroller(getContext());
mVelocityTracker = VelocityTracker.obtain();
}
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
int action = event.getAction();
if (action == MotionEvent.ACTION_DOWN) {
mLastX = x;
mLastY = y;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
return true;
}
return false;
} else {
return true;
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.d(TAG, "onTouchEvent action:" + event.getAction());
mVelocityTracker.addMovement(event);
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastX;
int deltaY = y - mLastY;
Log.d(TAG, "move, deltaX:" + deltaX + " deltaY:" + deltaY);
scrollBy(-deltaX, 0);
break;
}
case MotionEvent.ACTION_UP: {
int scrollX = getScrollX();
int scrollToChildIndex = scrollX / mChildWidth;
Log.d(TAG, "current index:" + scrollToChildIndex);
mVelocityTracker.computeCurrentVelocity(1000);
float xVelocity = mVelocityTracker.getXVelocity();
if (Math.abs(xVelocity) >= 50) {
mChildIndex = xVelocity > 0 ? mChildIndex - 1 : mChildIndex + 1;
} else {
mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;
}
mChildIndex = Math.max(0, Math.min(mChildIndex, mChildrenSize - 1));
int dx = mChildIndex * mChildWidth - scrollX;
smoothScrollBy(dx, 0);
mVelocityTracker.clear();
Log.d(TAG, "index:" + scrollToChildIndex + " dx:" + dx);
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return true;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int measuredWidth = 0;
int measuredHeight = 0;
final int childCount = getChildCount();
measureChildren(widthMeasureSpec, heightMeasureSpec);
int widthSpaceSize = MeasureSpec.getSize(widthMeasureSpec);
int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
int heightSpaceSize = MeasureSpec.getSize(heightMeasureSpec);
int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
if (childCount == 0) {
setMeasuredDimension(0, 0);
} else if (heightSpecMode == MeasureSpec.AT_MOST) {
final View childView = getChildAt(0);
measuredHeight = childView.getMeasuredHeight();
setMeasuredDimension(widthSpaceSize, childView.getMeasuredHeight());
} else if (widthSpecMode == MeasureSpec.AT_MOST) {
final View childView = getChildAt(0);
measuredWidth = childView.getMeasuredWidth() * childCount;
setMeasuredDimension(measuredWidth, heightSpaceSize);
} else {
final View childView = getChildAt(0);
measuredWidth = childView.getMeasuredWidth() * childCount;
measuredHeight = childView.getMeasuredHeight();
setMeasuredDimension(measuredWidth, measuredHeight);
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
Log.d(TAG, "width:" + getWidth());
int childLeft = 0;
final int childCount = getChildCount();
mChildrenSize = childCount;
for (int i = 0; i < childCount; i++) {
final View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE) {
final int childWidth = childView.getMeasuredWidth();
mChildWidth = childWidth;
childView.layout(childLeft, 0, childLeft + childWidth,
childView.getMeasuredHeight());
childLeft += childWidth;
}
}
}
private void smoothScrollBy(int dx, int dy) {
mScroller.startScroll(getScrollX(), 0, dx, 0, 500);
invalidate();
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
@Override
protected void onDetachedFromWindow() {
mVelocityTracker.recycle();
super.onDetachedFromWindow();
}
}
這個(gè)攔截規(guī)則也是父容器在滑動(dòng)過程中水平距離差與垂直距離差相比眉踱。
小結(jié)
總的來說挤忙，滑動(dòng)沖突的場景可以分為三種，內(nèi)外部方向不一致谈喳、內(nèi)外部方向一致册烈、嵌套前面兩種情況。如何解決婿禽，不管多么復(fù)雜的滑動(dòng)沖突赏僧，可以進(jìn)行拆分，根據(jù)的一定的規(guī)則扭倾，第一種情況可根據(jù)滑動(dòng)距離差淀零、速度差和角度差來解決，第二種和第三種情況膛壹，可根據(jù)業(yè)務(wù)上找到突破點(diǎn)驾中，業(yè)務(wù)上一種狀態(tài)需要響應(yīng)，切換到另外一種狀態(tài)時(shí)則不響應(yīng)恢筝，根據(jù)業(yè)務(wù)需求得出相應(yīng)的處理規(guī)則哀卫，有了處理規(guī)則可以進(jìn)行下一步處理。
