常見的滑動(dòng)沖突場(chǎng)景可以簡(jiǎn)單分為以下三種：
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場(chǎng)景1：外部滑動(dòng)方向和內(nèi)部滑動(dòng)方向不一致
場(chǎng)景2：外部滑動(dòng)方向和內(nèi)部滑動(dòng)方向一致
場(chǎng)景3：上面兩種情況的嵌套
如圖：
場(chǎng)景1，主要是將ViewPager和Fragment配合使用所組成的頁(yè)面滑動(dòng)效果，主流應(yīng)用幾乎都會(huì)使用這個(gè)效果。在這個(gè)效果中可以通過左右滑動(dòng)來切換頁(yè)面，而每個(gè)頁(yè)面內(nèi)部往往又是一個(gè)ListView，所以就造成了滑動(dòng)沖突，但是在ViewPager內(nèi)部處理了這種滑動(dòng)沖突，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，那就必須自己手動(dòng)處理，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(chǎng)景2，就復(fù)雜一點(diǎn)，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。因?yàn)楫?dāng)手指開始滑動(dòng)的時(shí)候，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(huì)出現(xiàn)問題，要么只有一層滑動(dòng)，要么就是內(nèi)外兩層都滑動(dòng)但很卡頓。
場(chǎng)景3，是場(chǎng)景1和場(chǎng)景2兩種情況的嵌套，顯得更復(fù)雜了。比如外部有一個(gè)SlideMenu效果，內(nèi)部有一個(gè)ViewPager，ViewPager的每一個(gè)頁(yè)面中又是一個(gè)ListView。雖然場(chǎng)景3滑動(dòng)沖突看起來很復(fù)雜，但都是幾個(gè)單一的滑動(dòng)沖突的疊加，因此需要一一拆解開來即可。
一般來說，不管滑動(dòng)沖突有多么復(fù)雜，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。
對(duì)于場(chǎng)景1，它的處理規(guī)則就是：當(dāng)用戶左右滑動(dòng)時(shí)，需要讓外部的View攔截點(diǎn)擊事件，當(dāng)用戶上下滑動(dòng)，需要讓內(nèi)部View攔截點(diǎn)擊事件。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(shuí)來攔截事件。
如圖：
簡(jiǎn)單來說，就是根據(jù)水平方向和豎直方向的距離差來判斷，如果是Dx>Dy，那么則是水平滑動(dòng)，如果是Dy>Dx，那么則是豎直滑動(dòng)。
場(chǎng)景2，則是比較特殊，它無法根據(jù)滑動(dòng)的角度，距離差以及速度差來做判斷。這個(gè)時(shí)候就需要從業(yè)務(wù)上找到突破點(diǎn)，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)，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(duì)于場(chǎng)景3的話，它的滑動(dòng)規(guī)則也更復(fù)雜，和場(chǎng)景2一樣，同樣是從業(yè)務(wù)上找到突破點(diǎn)。
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，如果不需要此事件，就不攔截了，這樣就可以解決滑動(dòng)沖突的問題，外部攔截法需要重寫父容器的onInterceptTouchEvent方法，在內(nèi)部做相應(yīng)的攔截即可，偽代碼如下：
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@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，父容器必須返回false，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，如果父容器攔截就返回true，否則返回false。
實(shí)現(xiàn)一個(gè)自定義類似ViewPager的控件，嵌套ListView的效果，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(duì)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，否則就不攔截，繼續(xù)傳遞事件。
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，如果子元素需要此事件就直接消耗掉，否則就交給父容器進(jìn)行處理，這種方法和Android中的事件分發(fā)機(jī)制不一致，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。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)，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，現(xiàn)在重寫一個(gè)ListView，我們可以自定義一個(gè)ListView，叫做ListViewEx，然后對(duì)內(nèi)部攔截法的模板代碼進(jìn)行修改即可。
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(duì)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。
