BottomScrollView.java revision 8c10c403c063aff3f17c4949b0fe9a88536ae580 
1/*
2 * Copyright (C) 2015 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
17package com.android.setupwizardlib.view;
18
19import android.content.Context;
20import android.util.AttributeSet;
21import android.view.View;
22import android.widget.ScrollView;
23
24import com.android.setupwizardlib.annotations.VisibleForTesting;
25
26/**
27 * An extension of ScrollView that will invoke a listener callback when the ScrollView needs
28 * scrolling, and when the ScrollView is being scrolled to the bottom. This is often used in Setup
29 * Wizard as a way to ensure that users see all the content before proceeding.
30 */
31public class BottomScrollView extends ScrollView {
32
33    public interface BottomScrollListener {
34        void onScrolledToBottom();
35        void onRequiresScroll();
36    }
37
38    private BottomScrollListener mListener;
39    private int mScrollThreshold;
40    private boolean mRequiringScroll = false;
41
42    private final Runnable mCheckScrollRunnable = new Runnable() {
43        @Override
44        public void run() {
45            checkScroll();
46        }
47    };
48
49    public BottomScrollView(Context context) {
50        super(context);
51    }
52
53    public BottomScrollView(Context context, AttributeSet attrs) {
54        super(context, attrs);
55    }
56
57    public BottomScrollView(Context context, AttributeSet attrs, int defStyle) {
58        super(context, attrs, defStyle);
59    }
60
61    public void setBottomScrollListener(BottomScrollListener l) {
62        mListener = l;
63    }
64
65    @VisibleForTesting
66    public int getScrollThreshold() {
67        return mScrollThreshold;
68    }
69
70    @Override
71    protected void onLayout(boolean changed, int l, int t, int r, int b) {
72        super.onLayout(changed, l, t, r, b);
73        final View child = getChildAt(0);
74        if (child != null) {
75            mScrollThreshold = Math.max(0, child.getMeasuredHeight() - b + t - getPaddingBottom());
76        }
77        if (b - t > 0) {
78            // Post check scroll in the next run loop, so that the callback methods will be invoked
79            // after the layout pass. This way a new layout pass will be scheduled if view
80            // properties are changed in the callbacks.
81            post(mCheckScrollRunnable);
82        }
83    }
84
85    @Override
86    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
87        super.onScrollChanged(l, t, oldl, oldt);
88        if (oldt != t) {
89            checkScroll();
90        }
91    }
92
93    private void checkScroll() {
94        if (mListener != null) {
95            if (getScrollY() >= mScrollThreshold) {
96                mListener.onScrolledToBottom();
97            } else if (!mRequiringScroll) {
98                mRequiringScroll = true;
99                mListener.onRequiresScroll();
100            }
101        }
102    }
103
104}
105