Android -FAB Behaviour with half list

问题

I have the FAB working when recyclerview has enough items to scroll, but i need to handle the case when recyclerview does not scroll (the total of items do not cover the screen).

At the moment this is how I handle the scroll:

public class FABBehavior extends FloatingActionButton.Behavior {

public FABBehavior() {
    super();
}

public FABBehavior(final Context context, final AttributeSet attrs) {
    super(context, attrs);
}

@Override
public void onNestedScroll(final CoordinatorLayout coordinatorLayout, final FloatingActionButton child, final View target, final int dxConsumed, final int dyConsumed, final int dxUnconsumed, final int dyUnconsumed) {
    super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);

    if (dyConsumed > 0) {
        CoordinatorLayout.LayoutParams layoutParams = (CoordinatorLayout.LayoutParams) child.getLayoutParams();
        int fab_bottomMargin = layoutParams.bottomMargin;
        child.animate().translationY(child.getHeight() + fab_bottomMargin).setInterpolator(new LinearInterpolator()).start();
    } else if (dyConsumed < 0) {
        child.animate().translationY(0).setInterpolator(new LinearInterpolator()).start();
    }
}

@Override
public boolean onStartNestedScroll(final CoordinatorLayout coordinatorLayout, final FloatingActionButton child, final View directTargetChild, final View target, final int nestedScrollAxes) {
    return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL;
}
}

How to handle when recyclerview has few items?

回答1:

You have to handle another case independently from CoordinatorLayout.

override a function layoutDependsOn:

@Override
public boolean layoutDependsOn(CoordinatorLayout parent, FloatingActionButton child, View dependency) {
    return super.layoutDependsOn(parent, child, dependency) || dependency instanceof RecyclerView;
}

onNestedScroll should also handle another case:

if (target instanceof RecyclerView) {
    handleRecyclerViewScrolling(target, child);
    return;
}

handleRecyclerViewScrolling should look like:

private void handleRecyclerViewScrolling(View target, FloatingActionButton child) {
    if (scrollListener != null) {
        return;
    }
    RecyclerView recyclerView = (RecyclerView) target;
    scrollListener = new RecyclerViewScrollListener(child);
    recyclerView.addOnScrollListener(scrollListener);
}

scrollListener should be a field in your FABBehavior class. Also declare inner class inside FABBehavior:

private class RecyclerViewScrollListener extends RecyclerView.OnScrollListener {
    FloatingActionButton mChild;

    public RecyclerViewScrollListener(FloatingActionButton child) {
        this.mChild = child;
    }

    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        super.onScrollStateChanged(recyclerView, newState);
        if (newState == RecyclerView.SCROLL_STATE_IDLE) {
            mChild.show();
        } else {
            mChild.hide();
        }
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        if (!recyclerView.canScrollVertically(Integer.MAX_VALUE)) {
            mChild.show();
        }
    }
}

RecyclerViewScrollListener hides FAB, when it is scrolling and shows it when it is in idle state.

来源：https://stackoverflow.com/questions/40215211/android-fab-behaviour-with-half-list