BottomScrollView.java revision 2646e1d82ec6d133b35b775f044e156fca6d9d75 
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
24/**
25 * An extension of ScrollView that will invoke a listener callback when the ScrollView needs
26 * scrolling, and when the ScrollView is being scrolled to the bottom. This is often used in Setup
27 * Wizard as a way to ensure that users see all the content before proceeding.
28 */
29public class BottomScrollView extends ScrollView {
30
31    public interface BottomScrollListener {
32        void onScrolledToBottom();
33        void onRequiresScroll();
34    }
35
36    private BottomScrollListener mListener;
37    private int mScrollThreshold;
38    private boolean mRequiringScroll = false;
39
40    private final Runnable mCheckScrollRunnable = new Runnable() {
41        @Override
42        public void run() {
43            checkScroll();
44        }
45    };
46
47    public BottomScrollView(Context context) {
48        super(context);
49    }
50
51    public BottomScrollView(Context context, AttributeSet attrs) {
52        super(context, attrs);
53    }
54
55    public BottomScrollView(Context context, AttributeSet attrs, int defStyle) {
56        super(context, attrs, defStyle);
57    }
58
59    public void setBottomScrollListener(BottomScrollListener l) {
60        mListener = l;
61    }
62
63    @Override
64    protected void onLayout(boolean changed, int l, int t, int r, int b) {
65        super.onLayout(changed, l, t, r, b);
66        View child = getChildAt(0);
67        if (child != null) {
68            mScrollThreshold = Math.max(0, getChildAt(0).getHeight() - b + t
69                    - getPaddingBottom());
70        }
71        if (b - t > 0) {
72            // Post check scroll in the next run loop, so that the callback methods will be invoked
73            // after the layout pass. This way a new layout pass will be scheduled if view
74            // properties are changed in the callbacks.
75            post(mCheckScrollRunnable);
76        }
77    }
78
79    @Override
80    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
81        super.onScrollChanged(l, t, oldl, oldt);
82        if (oldt != t) {
83            checkScroll();
84        }
85    }
86
87    private void checkScroll() {
88        if (mListener != null) {
89            if (getScrollY() >= mScrollThreshold) {
90                mListener.onScrolledToBottom();
91            } else if (!mRequiringScroll) {
92                mRequiringScroll = true;
93                mListener.onRequiresScroll();
94            }
95        }
96    }
97
98}
99