| /* |
| * Copyright (C) 2013 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package androidx.core.widget; |
| |
| import android.view.View; |
| import android.widget.ListView; |
| |
| import androidx.annotation.NonNull; |
| |
| /** |
| * An implementation of {@link AutoScrollHelper} that knows how to scroll |
| * through a {@link ListView}. |
| */ |
| public class ListViewAutoScrollHelper extends AutoScrollHelper { |
| private final ListView mTarget; |
| |
| public ListViewAutoScrollHelper(@NonNull ListView target) { |
| super(target); |
| |
| mTarget = target; |
| } |
| |
| @Override |
| public void scrollTargetBy(int deltaX, int deltaY) { |
| ListViewCompat.scrollListBy(mTarget, deltaY); |
| } |
| |
| @Override |
| public boolean canTargetScrollHorizontally(int direction) { |
| // List do not scroll horizontally. |
| return false; |
| } |
| |
| @Override |
| public boolean canTargetScrollVertically(int direction) { |
| final ListView target = mTarget; |
| final int itemCount = target.getCount(); |
| if (itemCount == 0) { |
| return false; |
| } |
| |
| final int childCount = target.getChildCount(); |
| final int firstPosition = target.getFirstVisiblePosition(); |
| final int lastPosition = firstPosition + childCount; |
| |
| if (direction > 0) { |
| // Are we already showing the entire last item? |
| if (lastPosition >= itemCount) { |
| final View lastView = target.getChildAt(childCount - 1); |
| if (lastView.getBottom() <= target.getHeight()) { |
| return false; |
| } |
| } |
| } else if (direction < 0) { |
| // Are we already showing the entire first item? |
| if (firstPosition <= 0) { |
| final View firstView = target.getChildAt(0); |
| if (firstView.getTop() >= 0) { |
| return false; |
| } |
| } |
| } else { |
| // The behavior for direction 0 is undefined and we can return |
| // whatever we want. |
| return false; |
| } |
| |
| return true; |
| } |
| } |