扩大View的点击区域
TouchDelegate
可以通过设置TouchDelegate 给View的父类来实现点击事件的区域扩充（拦截父View的Touch事件）
View child;
ViewGroup parent;
// 上下左右各扩充10px的点击范围
int sizeDifference = 10;
Rect delegateArea = new Rect();
delegateArea.right += sizeDifference;
delegateArea.bottom += sizeDifference;
delegateArea.left -= sizeDifference;
delegateArea.top -= sizeDifference;
TouchDelegate delegate = new TouchDelegate(bounds, child);
parent.setTouchDelegate(delegate);
系统提供的默认TouchDelegate有一定的局限性:
- 一个ViewGroup下只能添加一个View的点击区域扩充
- 点击区域扩充, 不能超出父View的显示区间
查看TouchDelegate的实现, 可以看到TouchDelegate的处理方式就是拦截Touch事件，然后判断事件范围是否是在扩充区域内，然后根据是否是点击，来决定事件坐标系是否转换成View内部的 并直接通过dispatchTouchEvent方法来触发delegateView的Click事件，来看下onTouchEvent中的实现：
public boolean onTouchEvent(@NonNull MotionEvent event) {
int x = (int)event.getX();
int y = (int)event.getY();
boolean sendToDelegate = false;
boolean hit = true;
boolean handled = false;
switch (event.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
// 判断当前是否命中范围
mDelegateTargeted = mBounds.contains(x, y);
sendToDelegate = mDelegateTargeted;
break;
case MotionEvent.ACTION_POINTER_DOWN:
case MotionEvent.ACTION_POINTER_UP:
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_MOVE:
sendToDelegate = mDelegateTargeted;
if (sendToDelegate) {
Rect slopBounds = mSlopBounds;
// 判断是否是hit
if (!slopBounds.contains(x, y)) {
hit = false;
}
}
break;
case MotionEvent.ACTION_CANCEL:
sendToDelegate = mDelegateTargeted;
mDelegateTargeted = false;
break;
}
if (sendToDelegate) {
if (hit) {
// 将Event坐标转换为View的中心位置并
// Offset event coordinates to be inside the target view
event.setLocation(mDelegateView.getWidth() / 2, mDelegateView.getHeight() / 2);
} else {
// 将Event坐标转换到View的触控范围以外, 避免触发按下态
// Offset event coordinates to be outside the target view (in case it does
// something like tracking pressed state)
int slop = mSlop;
event.setLocation(-(slop * 2), -(slop * 2));
}
// 分发事件
handled = mDelegateView.dispatchTouchEvent(event);
}
return handled;
}
为了解决多个View的问题我们可以将传入的bounds 和 delegateView 换成一个列表, 为了解决点击范围限制的问题, 我们可以将TouchDelegate 设置到RootView上，然后命中区间转换都转换成相对于RootView的相对坐标，而不是使用相对于父View的相对坐标。
首先我们先定义一个类用来存储delegateView 和 bounds信息:
class TouchDelegateItem {
// 扩展点击范围
Rect appendRect;
// 扩展后的点击范围，相对于root
Rect clickBounds = new Rect();
// 扩展后的点击溢出范围, 相对于root
Rect slopBounds = new Rect();
// delegateView的弱引用
WeakReference<View> viewRef;
// 相对于Window的location 用于计算和root的相对坐标
int[] location = new int[2];
}
然后我们给TouchDelegateItem补充更新这些数据对应的方法：
void updateClickBoundsAndSlop(int[] rootLocation, int slop) {
if (viewRef == null || viewRef.get() == null) {
return;
}
View view = viewRef.get();
view.getLocationInWindow(location);
clickBounds.set(view.getLeft(), view.getTop(), view.getRight(), view.getBottom());
// 坐标转换 计算相对位置
clickBounds.offsetTo(location[0] - rootLocation[0], location[1] - rootLocation[1]);
// 追加扩展区域
clickBounds.left -= appendRect.left;
clickBounds.right += appendRect.right;
clickBounds.top -= appendRect.top;
clickBounds.bottom += appendRect.bottom;
// 设置溢出区域
slopBounds.set(clickBounds);
slopBounds.inset(-slop, -slop);
}
boolean contains(int x, int y) {
return viewRef != null && viewRef.get() != null && clickBounds.contains(x, y);
}
boolean slopContains(int x, int y) {
return viewRef != null && viewRef.get() != null && slopBounds.contains(x, y);
}
然后回头来看TouchDelegate的构造方法，我们改造一下, 只接受一个ViewGroup用作root 然后通过方法可以追加代理的View：
public IVOSTouchDelegate(ViewGroup viewGroup) {
super(new Rect(), viewGroup);
mSlop = ViewConfiguration.get(viewGroup.getContext()).getScaledTouchSlop();
mRootView = viewGroup;
viewGroup.setTouchDelegate(this);
}
然后我们添加对TouchDelegateItem的增,删，查方法，因为涉及到View 所以我们要尽可能避免内存泄漏使用弱引用，并检查无效的数据及时清除:
public void addDelegateItem(@NonNull View view, int left, int top, int right, int bottom) {
if (mDelegateItems == null) {
mDelegateItems = new ArrayList<>();
}
// 避免重复添加
TouchDelegateItem item = removeDelegateItem(view);
if (item != null) {
item.appendRect.set(left, top, right, bottom);
} else {
item = new TouchDelegateItem(view, new Rect(left, top, right, bottom));
}
mDelegateItems.add(item);
}
public @Nullable
TouchDelegateItem removeDelegateItem(View view) {
if (mDelegateItems == null || mDelegateItems.isEmpty()) {
return null;
}
for (int i = 0, n = mDelegateItems.size(); i < n; ) {
TouchDelegateItem item = mDelegateItems.get(i);
if (item.viewRef.get() == null) {
// 清除无效数据
mDelegateItems.remove(i);
} else if (item.viewRef.get() == view) {
return mDelegateItems.remove(i);
} else {
i++;
}
}
return null;
}
private TouchDelegateItem getDelegateTarget(int x, int y, boolean needUpdate) {
if (mCurTouchDelegateItem != null && mCurTouchDelegateItem.contains(x, y)) {
return mCurTouchDelegateItem;
}
if (mDelegateItems == null || mDelegateItems.isEmpty()) {
return null;
}
mRootView.getLocationInWindow(mRootLocation);
for (int i = 0, n = mDelegateItems.size(); i < n; i++) {
TouchDelegateItem item = mDelegateItems.get(i);
if (needUpdate) {
item.updateClickBoundsAndSlop(mRootLocation, mSlop);
}
if (item.slopContains(x, y)) {
return item;
}
}
return null;
}
然后我们再添加一个总的开关:
public void doDelegate(boolean doDelegate) {
this.mDoDelegate = doDelegate;
}
然后我们复写onTouchEvent方法，将父类中的事件处理copy出来进行改造，将坐标范围判断，改为从添加的TouchDelegateItem的列表中查找：
@Override
public boolean onTouchEvent(MotionEvent event) {
if (!mDoDelegate) {
return false;
}
int x = (int) event.getX();
int y = (int) event.getY();
boolean hit = true;
boolean handled = false;
TouchDelegateItem cur = null;
switch (event.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
mCurTouchDelegateItem = getDelegateTarget(x, y, true);
cur = mCurTouchDelegateItem;
break;
case MotionEvent.ACTION_POINTER_DOWN:
case MotionEvent.ACTION_POINTER_UP:
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_MOVE:
cur = mCurTouchDelegateItem;
if (cur != null && cur.contains(x, y)) {
if (!cur.slopContains(x, y)) {
hit = false;
}
}
break;
case MotionEvent.ACTION_CANCEL:
cur = mCurTouchDelegateItem;
mCurTouchDelegateItem = null;
break;
default:
break;
}
if (cur != null) {
final View delegateView = cur.viewRef.get();
if (hit) {
// Offset event coordinates to be inside the target view
event.setLocation(delegateView.getWidth() / 2, delegateView.getHeight() / 2);
} else {
// Offset event coordinates to be outside the target view (in case it does
// something like tracking pressed state)
int slop = mSlop;
event.setLocation(-(slop * 2), -(slop * 2));
}
handled = delegateView.dispatchTouchEvent(event);
}
return handled;
}