Android BottomSheetBehavior, how to disable snap?

问题:

Standard android BottomSheetBehavior has tree state: hidden, collapsed and expanded.

I want to allow user to "leave" bottom sheet between collapsed and expanded. Now, with the default behavior, it will snap to collapsed or expanded based which is closest. How should I disable this snap functionality?

回答1:

I will present a way to achievie such functionality for a View extending BottomSheetDialogFragment.

Expanding:

First of all overrive onResume:

@Override
public void onResume() {
    super.onResume();
    addGlobaLayoutListener(getView());
}

private void addGlobaLayoutListener(final View view) {
    view.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
        @Override
        public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
            setPeekHeight(v.getMeasuredHeight());
            v.removeOnLayoutChangeListener(this);
        }
    });
}

public void setPeekHeight(int peekHeight) {
    BottomSheetBehavior behavior = getBottomSheetBehaviour();
    if (behavior == null) {
        return;
    }
    behavior.setPeekHeight(peekHeight);
}

What the code above is supposed to do is just setting the BottomSheet peekHeight to the heigth of the view. The key here is the function getBottomSheetBehaviour(). The implementation is below:

private BottomSheetBehavior getBottomSheetBehaviour() {
    CoordinatorLayout.LayoutParams layoutParams = (CoordinatorLayout.LayoutParams) ((View) getView().getParent()).getLayoutParams();
    CoordinatorLayout.Behavior behavior = layoutParams.getBehavior();
    if (behavior != null && behavior instanceof BottomSheetBehavior) {
        ((BottomSheetBehavior) behavior).setBottomSheetCallback(mBottomSheetBehaviorCallback);
        return (BottomSheetBehavior) behavior;
    }
    return null;
}

This just check if the parent of View has 'CoordinatorLayout.LayoutParams' set. If yes, sets appropriate BottomSheetBehavior.BottomSheetCallback (which is needed in the next part), and more importantly returns the CoordinatorLayout.Behavior, which is supposed to be BottomSheetBehavior.

Collapsing:

Here a [`BottomSheetBehavior.BottomSheetCallback.onSlide (View bottomSheet, float slideOffset)``](https://developer.android.com/reference/android/support/design/widget/BottomSheetBehavior.BottomSheetCallback.html#onSlide(android.view.View, float)) is just exactly what is needed. From the [documentation](https://developer.android.com/reference/android/support/design/widget/BottomSheetBehavior.BottomSheetCallback.html#onSlide(android.view.View, float)):

Offset increases as this bottom sheet is moving upward. From 0 to 1 the sheet is between collapsed and expanded states and from -1 to 0 it is between hidden and collapsed states.

This means, that just checking the second parameter is needed for collapse detection:

define BottomSheetBehavior.BottomSheetCallback in the same class:

private BottomSheetBehavior.BottomSheetCallback mBottomSheetBehaviorCallback = new BottomSheetBehavior.BottomSheetCallback() {

    @Override
    public void onStateChanged(@NonNull View bottomSheet, int newState) {
        if (newState == BottomSheetBehavior.STATE_HIDDEN) {
            dismiss();
        }
    }

    @Override
    public void onSlide(@NonNull View bottomSheet, float slideOffset) {
        if (slideOffset < 0) {
            dismiss();
        }
    }
};