1 /*
2  * Copyright (C) 2013 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package androidx.core.widget;
18 
19 import android.view.View;
20 import android.widget.ListView;
21 
22 import org.jspecify.annotations.NonNull;
23 
24 /**
25  * An implementation of {@link AutoScrollHelper} that knows how to scroll
26  * through a {@link ListView}.
27  */
28 public class ListViewAutoScrollHelper extends AutoScrollHelper {
29     @SuppressWarnings("HidingField")
30     private final ListView mTarget;
31 
ListViewAutoScrollHelper(@onNull ListView target)32     public ListViewAutoScrollHelper(@NonNull ListView target) {
33         super(target);
34 
35         mTarget = target;
36     }
37 
38     @Override
scrollTargetBy(int deltaX, int deltaY)39     public void scrollTargetBy(int deltaX, int deltaY) {
40         mTarget.scrollListBy(deltaY);
41     }
42 
43     @Override
canTargetScrollHorizontally(int direction)44     public boolean canTargetScrollHorizontally(int direction) {
45         // List do not scroll horizontally.
46         return false;
47     }
48 
49     @Override
canTargetScrollVertically(int direction)50     public boolean canTargetScrollVertically(int direction) {
51         final ListView target = mTarget;
52         final int itemCount = target.getCount();
53         if (itemCount == 0) {
54             return false;
55         }
56 
57         final int childCount = target.getChildCount();
58         final int firstPosition = target.getFirstVisiblePosition();
59         final int lastPosition = firstPosition + childCount;
60 
61         if (direction > 0) {
62             // Are we already showing the entire last item?
63             if (lastPosition >= itemCount) {
64                 final View lastView = target.getChildAt(childCount - 1);
65                 if (lastView.getBottom() <= target.getHeight()) {
66                     return false;
67                 }
68             }
69         } else if (direction < 0) {
70             // Are we already showing the entire first item?
71             if (firstPosition <= 0) {
72                 final View firstView = target.getChildAt(0);
73                 if (firstView.getTop() >= 0) {
74                     return false;
75                 }
76             }
77         } else {
78             // The behavior for direction 0 is undefined and we can return
79             // whatever we want.
80             return false;
81         }
82 
83         return true;
84     }
85 }
86