1 /*
2  * Copyright (C) 2016 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.os.Build;
20 import android.view.View;
21 import android.widget.ListView;
22 
23 import androidx.annotation.NonNull;
24 
25 /**
26  * Helper for accessing features in {@link ListView}
27  */
28 public final class ListViewCompat {
29 
30     /**
31      * Scrolls the list items within the view by a specified number of pixels.
32      *
33      * @param listView the list to scroll
34      * @param y the amount of pixels to scroll by vertically
35      */
scrollListBy(@onNull ListView listView, int y)36     public static void scrollListBy(@NonNull ListView listView, int y) {
37         if (Build.VERSION.SDK_INT >= 19) {
38             // Call the framework version directly
39             listView.scrollListBy(y);
40         } else {
41             // provide backport on earlier versions
42             final int firstPosition = listView.getFirstVisiblePosition();
43             if (firstPosition == ListView.INVALID_POSITION) {
44                 return;
45             }
46 
47             final View firstView = listView.getChildAt(0);
48             if (firstView == null) {
49                 return;
50             }
51 
52             final int newTop = firstView.getTop() - y;
53             listView.setSelectionFromTop(firstPosition, newTop);
54         }
55     }
56 
57     /**
58      * Check if the items in the list can be scrolled in a certain direction.
59      *
60      * @param direction Negative to check scrolling up, positive to check
61      *            scrolling down.
62      * @return true if the list can be scrolled in the specified direction,
63      *         false otherwise.
64      * @see #scrollListBy(ListView, int)
65      */
canScrollList(@onNull ListView listView, int direction)66     public static boolean canScrollList(@NonNull ListView listView, int direction) {
67         if (Build.VERSION.SDK_INT >= 19) {
68             // Call the framework version directly
69             return listView.canScrollList(direction);
70         } else {
71             // provide backport on earlier versions
72             final int childCount = listView.getChildCount();
73             if (childCount == 0) {
74                 return false;
75             }
76 
77             final int firstPosition = listView.getFirstVisiblePosition();
78             if (direction > 0) {
79                 final int lastBottom = listView.getChildAt(childCount - 1).getBottom();
80                 final int lastPosition = firstPosition + childCount;
81                 return lastPosition < listView.getCount()
82                         || (lastBottom > listView.getHeight() - listView.getListPaddingBottom());
83             } else {
84                 final int firstTop = listView.getChildAt(0).getTop();
85                 return firstPosition > 0 || firstTop < listView.getListPaddingTop();
86             }
87         }
88     }
89 
ListViewCompat()90     private ListViewCompat() {}
91 }
92