NonLockingScrollView.java revision bc47398187c6ffd132435e51d8d61e6ec79a79db 
1/*
2 * Copyright (C) 2011 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
18package com.android.email.view;
19
20import android.content.Context;
21import android.graphics.Rect;
22import android.util.AttributeSet;
23import android.view.MotionEvent;
24import android.view.View;
25import android.view.ViewGroup;
26import android.webkit.WebView;
27import android.widget.ScrollView;
28
29import java.util.ArrayList;
30
31/**
32 * A {@link ScrollView} that will never lock scrolling in a particular direction.
33 *
34 * Usually ScrollView will capture all touch events once a drag has begun. In some cases,
35 * we want to delegate those touches to children as normal, even in the middle of a drag. This is
36 * useful when there are childviews like a WebView tha handles scrolling in the horizontal direction
37 * even while the ScrollView drags vertically.
38 *
39 * This is only tested to work for ScrollViews where the content scrolls in one direction.
40 */
41public class NonLockingScrollView extends ScrollView {
42    public NonLockingScrollView(Context context) {
43        super(context);
44    }
45    public NonLockingScrollView(Context context, AttributeSet attrs) {
46        super(context, attrs);
47    }
48    public NonLockingScrollView(Context context, AttributeSet attrs, int defStyle) {
49        super(context, attrs, defStyle);
50    }
51
52    /**
53     * Whether or not the contents of this view is being dragged by one of the children in
54     * {@link #mChildrenNeedingAllTouches}.
55     */
56    private boolean mInCustomDrag = false;
57
58    /**
59     * The list of children who should always receive touch events, and not have them intercepted.
60     */
61    private final ArrayList<View> mChildrenNeedingAllTouches = new ArrayList<View>();
62
63    @Override
64    public boolean onInterceptTouchEvent(MotionEvent ev) {
65        final int action = ev.getActionMasked();
66        final boolean isUp = action == MotionEvent.ACTION_UP;
67
68        if (isUp && mInCustomDrag) {
69            // An up event after a drag should be intercepted so that child views don't handle
70            // click events falsely after a drag.
71            mInCustomDrag = false;
72            onTouchEvent(ev);
73            return true;
74        }
75
76        if (!mInCustomDrag && !isEventOverChild(ev, mChildrenNeedingAllTouches)) {
77            return super.onInterceptTouchEvent(ev);
78        }
79
80        // Note the normal scrollview implementation is to intercept all touch events after it has
81        // detected a drag starting. We will handle this ourselves.
82        mInCustomDrag = super.onInterceptTouchEvent(ev);
83        if (mInCustomDrag) {
84            onTouchEvent(ev);
85        }
86
87        // Don't intercept events - pass them on to children as normal.
88        return false;
89    }
90
91    @Override
92    protected void onFinishInflate() {
93        super.onFinishInflate();
94        excludeChildrenFromInterceptions(this);
95    }
96
97    /**
98     * Traverses the view tree for {@link WebView}s so they can be excluded from touch
99     * interceptions and receive all events.
100     */
101    private void excludeChildrenFromInterceptions(View node) {
102        // If additional types of children should be excluded (e.g. horizontal scrolling banners),
103        // this needs to be modified accordingly.
104        if (node instanceof WebView) {
105            mChildrenNeedingAllTouches.add(node);
106        } else if (node instanceof ViewGroup) {
107            ViewGroup viewGroup = (ViewGroup) node;
108            final int childCount = viewGroup.getChildCount();
109            for (int i = 0; i < childCount; i++) {
110                final View child = viewGroup.getChildAt(i);
111                excludeChildrenFromInterceptions(child);
112            }
113        }
114    }
115
116    private static final Rect sHitFrame = new Rect();
117    private static boolean isEventOverChild(MotionEvent ev, ArrayList<View> children) {
118        final int actionIndex = ev.getActionIndex();
119        final float x = ev.getX(actionIndex);
120        final float y = ev.getY(actionIndex);
121
122        for (View child : children) {
123            if (!canViewReceivePointerEvents(child)) {
124                continue;
125            }
126            child.getHitRect(sHitFrame);
127
128            // child can receive the motion event.
129            if (sHitFrame.contains((int) x, (int) y)) {
130                return true;
131            }
132        }
133        return false;
134    }
135
136    private static boolean canViewReceivePointerEvents(View child) {
137        return child.getVisibility() == VISIBLE || (child.getAnimation() != null);
138    }
139}
140