How to use BottomSheetDialog?

Question

I want to try BottomSheetDialog introduced in Android Support Library 23.2 but it doesn\'t seem to work correctly. Here is what the doc says:

Answer 1

This is the layout file of BottomSheetDialog.

Your content view is inside the view design_bottom_sheet, it will be positioned center vertically by CoordinatorLayout, and BottomSheetBehavior will offset it.

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);
}

It intented to positon design_bottom_sheet at mMaxOffset, but actually the initial getTop of the child view is not 0, but (mParentHeight - childHeight) / 2, so you view if offset more than the desired offset.

Find the view design_bottom_sheet and set its gravity to Gravity.TOP | Gravity.CENTER_HORIZONTAL will fix it. But, if the childHeight is less than mPeekHeight, there will be blank area below you content view.

However, if peekHeight > childHeight, the mMaxOffset will less than mMinOffset, which will cause weird behavior.

Maybe the code should be changed to

mMaxOffset = Math.max((mParentHeight - mPeekHeight), mMinOffset);

insted of

mMaxOffset = mParentHeight - child.getHeight();