dim.red
新出的design:23.2.0 引入了一个新的Behavior :BottomSheetBehavior
问题
设置 BottomSheetBehavior 没有设置 PeekHeight 或者 PeekHeight为0 的时候. 底部的BottomSheetBehavior 视图滑动不出来.
分析
根据进入源码,具体的问题是
@Override
public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
// First let the parent lay it out
if (mState != STATE_DRAGGING && mState != STATE_SETTLING) {
parent.onLayoutChild(child, layoutDirection);
}
// Offset the bottom sheet
mParentHeight = parent.getHeight();
mMinOffset = Math.max(0, mParentHeight - child.getHeight());
mMaxOffset = mParentHeight - mPeekHeight;
if (mState == STATE_EXPANDED) {
ViewCompat.offsetTopAndBottom(child, mMinOffset);
} else if (mHideable && mState == STATE_HIDDEN) {
ViewCompat.offsetTopAndBottom(child, mParentHeight);
} else if (mState == STATE_COLLAPSED) {
ViewCompat.offsetTopAndBottom(child, mMaxOffset);
}
if (mViewDragHelper == null) {
mViewDragHelper = ViewDragHelper.create(parent, mDragCallback);
}
mViewRef = new WeakReference<>(child);
mNestedScrollingChildRef = new WeakReference<>(findScrollingChild(child));
return true;
}
一开始view 的位置是屏幕中的.因为 mState 的初始状态为STATE_COLLAPSED,mPeekHeight 为0,
mMaxOffset 变成了 rv 的高度,所以view 马上就被移出了屏幕.
然后后面View就全程透明了.很奇葩.
解决方案
解决方案 1
主动发起requestLayout 强制重绘.
behavior.setBottomSheetCallback(new BottomSheet.BottomSheetCallback() {
public boolean hasRequest;
@Override
public void onStateChanged(@NonNull View bottomSheet, int newState) {
}
@Override
public void onSlide(@NonNull View bottomSheet, float slideOffset) {
if (!hasRequest && behavior.getPeekHeight() == 0 && slideOffset > 0) {
hasRequest = true;
bottomSheet.requestLayout();
}
}
});
缺点是使用了requestLayout 方法.
解决方案2
这是幸运Science提供的
bottomSheet.setTranslationY(statusbarheight);
behavior.setBottomSheetCallback(new BottomSheet.BottomSheetCallback() {
public boolean hasRequest;
@Override
public void onStateChanged(@NonNull View bottomSheet, int newState) {
}
@Override
public void onSlide(@NonNull View bottomSheet, float slideOffset) {
if (!hasRequest && behavior.getPeekHeight() == 0 && slideOffset > 0) {
hasRequest = true;
bottomSheet.setTranslationY(0);
}
}
});
通过设置TranslationY的差值.让他重绘出来.
恍惚间记得google Design 包下有类似的解决方案,同样使用的是TranslationY差值的方式.
类:android.support.design.widget.ViewOffsetHelper
方法:updateOffsets
private void updateOffsets() {
ViewCompat.offsetTopAndBottom(mView, mOffsetTop - (mView.getTop() - mLayoutTop));
ViewCompat.offsetLeftAndRight(mView, mOffsetLeft - (mView.getLeft() - mLayoutLeft));
// Manually invalidate the view and parent to make sure we get drawn pre-M
if (Build.VERSION.SDK_INT < 23) {
tickleInvalidationFlag(mView);
final ViewParent vp = mView.getParent();
if (vp instanceof View) {
tickleInvalidationFlag((View) vp);
}
}
}
private static void tickleInvalidationFlag(View view) {
final float y = ViewCompat.getTranslationY(view);
ViewCompat.setTranslationY(view, y + 1);
ViewCompat.setTranslationY(view, y);
}
可以看出这是一个23以下都有可能存在的bug.
同时需要注意的是ViewOffsetHelper是一个私有的类,updateOffsets是一个私有的方法.所以你只能copy,不能直接使用.
最终的方案
就是在方案2的基础上做一点小修改,改使用google的方案.
behavior.setBottomSheetCallback(new BottomSheet.BottomSheetCallback() {
public boolean hasRequest;
@Override
public void onStateChanged(@NonNull View bottomSheet, int newState) {
}
@Override
public void onSlide(@NonNull View bottomSheet, float slideOffset) {
if (!hasRequest && behavior.getPeekHeight() == 0 && slideOffset > 0) {
hasRequest = true;
updateOffsets(bottomSheet);
}
}
});
private void updateOffsets(View view) {
// Manually invalidate the view and parent to make sure we get drawn pre-M
if (Build.VERSION.SDK_INT < 23) {
tickleInvalidationFlag(view)
final ViewParent vp = view.getParent();
if (vp instanceof View) {
tickleInvalidationFlag((View) vp);
}
}
}
private static void tickleInvalidationFlag(View view) {
final float y = ViewCompat.getTranslationY(view);
ViewCompat.setTranslationY(view, y + 1);
ViewCompat.setTranslationY(view, y);
}
尾巴
google 在开发这个的时候应该并没有考虑这样的应用场景. 如果场景是这样的话可以是使用BottomSheetDialog 这个代替.
