How to make bottom sheet (BottomSheetBehavior) expandable to arbitrary position?

Question

I have bottom sheet, and I want to change its behavior so it would work like on the main screen of Google Maps application, where you can expand it to any position and leave it there and it won't automatically stick to the bottom or to the top. Here's my layout with bottom sheet:

<android.support.design.widget.CoordinatorLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.gms.maps.MapView
        android:id="@+id/map"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    <View
        android:id="@+id/shadow"
        android:layout_width="match_parent"
        android:layout_height="16dp"
        android:background="@drawable/shape_gradient_top_shadow"
        app:layout_anchor="@+id/map_bottom_sheet" />


    <LinearLayout
        android:id="@+id/map_bottom_sheet"
        android:layout_width="match_parent"
        android:layout_height="300dp"
        android:fillViewport="false"
        android:orientation="vertical"
        app:behavior_peekHeight="50dp"
        android:background="@color/lightGray"
        app:layout_behavior="android.support.design.widget.BottomSheetBehavior">

        <include layout="@layout/bottom_sheet_top_buttons"/>
        <android.support.v4.widget.NestedScrollView
            android:id="@+id/bottom_sheet_content_fragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="@color/lightGray"/>

    </LinearLayout>

</android.support.design.widget.CoordinatorLayout>

What I need in essence is eliminate forcing of STATE_EXPANDED and STATE_COLLAPSED states when dragging is ended.

Here's a visual explanation of what I try to achieve:


As you can see, bottom sheet doesn't automatically anchor to the top or the bottom but stays at whatever position it was left.

Answer 1

Copy the code from android.support.design.widget.BottomSheetBehavior to make your own custom behavior. Then modify the onViewReleased() method which is responsible for the movement of the sheet after the drag ends. You also have to introduce a new state besides the existing ones - the state is helpful to restore the position and let others know in which state your sheet is at the moment with getState().

@Override
public void onViewReleased(View releasedChild, float xVel, float yVel) {
    int top;
    @State int targetState;

    // Use the position where the drag ended as new top
    top = releasedChild.getTop();

    // You have to manage the states here, too (introduce a new one)
    targetState = STATE_ANCHORED;

    if (mViewDragHelper.settleCapturedViewAt(releasedChild.getLeft(), top)) {
        setStateInternal(STATE_SETTLING);
        ViewCompat.postOnAnimation(releasedChild, new SettleRunnable(releasedChild, targetState));

    } else {
        setStateInternal(targetState);
    }
}