View的弹性滑动
相信开发Android的人都会有这种体会：从网上下载的demo运行的好好的，但是只要出现了滑动冲突，Demo就无法正常工作了。但是不用担心，解决滑动冲突有固定的模式，常见的有内部拦截和外部拦截两种，只要按照这个模式来就可以顺利解决。
介绍
相信开发Android的人都会有这种体会：从网上下载的demo运行的好好的，但是只要出现了滑动冲突，Demo就无法正常工作了。但是不用担心，解决滑动冲突有固定的模式，常见的有内部拦截和外部拦截两种，只要按照这个模式来就可以顺利解决。本文会涉及到View事件分发的相关知识，关于事件分发请参考http://sparkyuan.me/2016/03/11/View%E4%BA%8B%E4%BB%B6%E5%88%86%E5%8F%91%E6%9C%BA%E5%88%B6/
常见的滑动冲突场景
示例
处理规则
对于场景1，处理规则为：当用户左右滑动时，让外部的View拦截点击事件，当用户上下滑动时，让内部的View拦截点击事件。当产生滑动时，根据滑动的起始点与终点坐标位置，如果垂直方向滑动距离大，就判断为垂直滑动，否则判断为水平滑动。其他两种情况处理方法相似，都是从业务需求上得出相应的规则。
解决方法
外部拦截发
所有的点击事件都先经过父容器拦截处理，如果父容器需要拦截就拦截，不需要就传给内部的View。伪代码如下
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public boolean onInterceptTouchEvent(MotionEvent event) {
boolean intercepted = false;
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
intercepted = false;
break;
}
case MotionEvent.ACTION_MOVE: {
if (满足父容器的拦截要求) {
intercepted = true;
} else {
intercepted = false;
}
break;
}
case MotionEvent.ACTION_UP: {
intercepted = false;
break;
}
default:
break;
}
mLastXIntercept = x;
mLastYIntercept = y;
return intercepted;
}
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注：
ACTION_DOWN这个事件是不能拦截的，因为一旦拦截后续的事件都会由父容器处理了。
内部拦截法
父容器不拦截任何事件，所有事件都传给子元素。如果子元素需要此事件就直接消耗，否则就交给父容器进行处理。完成这个功能需要配合requestDisallowInterceptTouchEvent()方法才可。这个方法表示是否让父容器拦截事件。伪代码如下：
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public boolean dispatchTouchEvent(MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
parent.requestDisallowInterceptTouchEvent(true);
break;
}
case MotionEvent.ACTION_MOVE: {
if (满足父容器的拦截要求) {
parent.requestDisallowInterceptTouchEvent(false);
}
break;
}
case MotionEvent.ACTION_UP: {
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return super.dispatchTouchEvent(event);
}
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注
父容器默认拦截除了ACTION_DOWN以外的其他事件，这样子当元素调用parent.requestDisallowInterceptTouchEvent(false)时，父元素才能拦截所需的事件。
总结
- 解决滑动冲突有两种方法，推荐外部拦截法，实现起来简单。
- 本文以场景1为例做了讲解，场景2,3的做法与1类似，都是根据业务需要制定处理规则。
示例效果的源码
Activity
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public class DemoActivity_1 extends Activity {
private static final String TAG = "DemoActivity_1";
private HorizontalScrollViewEx mListContainer;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.demo_1);
Log.d(TAG, "onCreate");
initView();
}
private void initView() {
LayoutInflater inflater = getLayoutInflater();
mListContainer = (HorizontalScrollViewEx) findViewById(R.id.container);
final int screenWidth = MyUtils.getScreenMetrics(this).widthPixels;
final int screenHeight = MyUtils.getScreenMetrics(this).heightPixels;
for (int i = 0; i < 3; i++) {
ViewGroup layout = (ViewGroup) inflater.inflate(
R.layout.content_layout, mListContainer, false);
layout.getLayoutParams().width = screenWidth;
TextView textView = (TextView) layout.findViewById(R.id.title);
textView.setText("page " + (i + 1));
layout.setBackgroundColor(Color.rgb(255 / (i + 1), 255 / (i + 1), 0));
createList(layout);
mListContainer.addView(layout);
}
}
private void createList(ViewGroup layout) {
ListView listView = (ListView) layout.findViewById(R.id.list);
ArrayList<String> datas = new ArrayList<String>();
for (int i = 0; i < 50; i++) {
datas.add("name " + i);
}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
R.layout.content_list_item, R.id.name, datas);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
Toast.makeText(DemoActivity_1.this, "click item",
Toast.LENGTH_SHORT).show();
}
});
}
}
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水平滑动的View
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public class HorizontalScrollViewEx extends ViewGroup {
private static final String TAG = "HorizontalScrollViewEx";
private int mChildrenSize;
private int mChildWidth;
private int mChildIndex;
// 分别记录上次滑动的坐标
private int mLastX = 0;
private int mLastY = 0;
// 分别记录上次滑动的坐标(onInterceptTouchEvent)
private int mLastXIntercept = 0;
private int mLastYIntercept = 0;
private Scroller mScroller;
private VelocityTracker mVelocityTracker;
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();
}
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: {
Log.d(TAG, "onInterceptTouchEvent: ACTION_DOWN");
intercepted = false;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
intercepted = true;
}
break;
}
case MotionEvent.ACTION_MOVE: {
Log.d(TAG, "onInterceptTouchEvent: 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;
}
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: {
Log.d(TAG, "onTouchEvent: ACTION_DOWN");
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
break;
}
case MotionEvent.ACTION_MOVE: {
Log.d(TAG, "onTouchEvent: ACTION_MOVE");
int deltaX = x - mLastX;
int deltaY = y - mLastY;
Log.d(TAG, "onTouchEvent: deltaX" + deltaX);
scrollBy(-deltaX, 0);
break;
}
case MotionEvent.ACTION_UP: {
int scrollX = getScrollX();
int scrollToChildIndex = scrollX / mChildWidth;
mVelocityTracker.computeCurrentVelocity(1000);
float xVelocity = mVelocityTracker.getXVelocity();
//滑的速度到达阈值就认为需要进入下一页
if (Math.abs(xVelocity) >= 100) {
mChildIndex = xVelocity > 0 ? mChildIndex - 1 : mChildIndex + 1;
} else {
//滑动的距离超过一半，就进入下一页
mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;
}
//保证在0页和最后一页滑动时不会越界
mChildIndex = Math.max(0, Math.min(mChildIndex, mChildrenSize - 1));
//没有达到进入下一页的要求，恢复原样
int dx = mChildIndex * mChildWidth - scrollX;
smoothScrollBy(dx, 0);
Log.d(TAG, "onTouchEvent: dx = " + dx);
mVelocityTracker.clear();
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return true;
}
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);
}
}
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();
}
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
protected void onDetachedFromWindow() {
mVelocityTracker.recycle();
super.onDetachedFromWindow();
}
}
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