Touch.java revision d24b8183b93e781080b2c16c487e60d51c12da31 
1/*
2 * Copyright (C) 2008 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 android.text.method;
18
19import android.text.Layout;
20import android.text.NoCopySpan;
21import android.text.Layout.Alignment;
22import android.text.Spannable;
23import android.view.MotionEvent;
24import android.view.View;
25import android.view.ViewConfiguration;
26import android.widget.TextView;
27
28public class Touch {
29    private Touch() { }
30
31    /**
32     * Scrolls the specified widget to the specified coordinates, except
33     * constrains the X scrolling position to the horizontal regions of
34     * the text that will be visible after scrolling to the specified
35     * Y position.
36     */
37    public static void scrollTo(TextView widget, Layout layout, int x, int y) {
38        int padding = widget.getTotalPaddingTop() +
39                      widget.getTotalPaddingBottom();
40        int top = layout.getLineForVertical(y);
41        int bottom = layout.getLineForVertical(y + widget.getHeight() -
42                                               padding);
43
44        int left = Integer.MAX_VALUE;
45        int right = 0;
46        Alignment a = null;
47
48        for (int i = top; i <= bottom; i++) {
49            left = (int) Math.min(left, layout.getLineLeft(i));
50            right = (int) Math.max(right, layout.getLineRight(i));
51
52            if (a == null) {
53                a = layout.getParagraphAlignment(i);
54            }
55        }
56
57        padding = widget.getTotalPaddingLeft() + widget.getTotalPaddingRight();
58        int width = widget.getWidth();
59        int diff = 0;
60
61        if (right - left < width - padding) {
62            if (a == Alignment.ALIGN_CENTER) {
63                diff = (width - padding - (right - left)) / 2;
64            } else if (a == Alignment.ALIGN_OPPOSITE) {
65                diff = width - padding - (right - left);
66            }
67        }
68
69        x = Math.min(x, right - (width - padding) - diff);
70        x = Math.max(x, left - diff);
71
72        widget.scrollTo(x, y);
73    }
74
75    /**
76     * Handles touch events for dragging.  You may want to do other actions
77     * like moving the cursor on touch as well.
78     */
79    public static boolean onTouchEvent(TextView widget, Spannable buffer,
80                                       MotionEvent event) {
81        DragState[] ds;
82
83        switch (event.getAction()) {
84        case MotionEvent.ACTION_DOWN:
85            buffer.setSpan(new DragState(event.getX(), event.getY()),
86                           0, 0, Spannable.SPAN_MARK_MARK);
87            return true;
88
89        case MotionEvent.ACTION_UP:
90            ds = buffer.getSpans(0, buffer.length(), DragState.class);
91
92            for (int i = 0; i < ds.length; i++) {
93                buffer.removeSpan(ds[i]);
94            }
95
96            if (ds.length > 0 && ds[0].mUsed) {
97                return true;
98            } else {
99                return false;
100            }
101
102        case MotionEvent.ACTION_MOVE:
103            ds = buffer.getSpans(0, buffer.length(), DragState.class);
104
105            if (ds.length > 0) {
106                if (ds[0].mFarEnough == false) {
107                    int slop = ViewConfiguration.get(widget.getContext()).getScaledTouchSlop();
108
109                    if (Math.abs(event.getX() - ds[0].mX) >= slop ||
110                        Math.abs(event.getY() - ds[0].mY) >= slop) {
111                        ds[0].mFarEnough = true;
112                    }
113                }
114
115                if (ds[0].mFarEnough) {
116                    ds[0].mUsed = true;
117
118                    float dx = ds[0].mX - event.getX();
119                    float dy = ds[0].mY - event.getY();
120
121                    ds[0].mX = event.getX();
122                    ds[0].mY = event.getY();
123
124                    int nx = widget.getScrollX() + (int) dx;
125                    int ny = widget.getScrollY() + (int) dy;
126
127                    int padding = widget.getTotalPaddingTop() +
128                                  widget.getTotalPaddingBottom();
129                    Layout layout = widget.getLayout();
130
131                    ny = Math.min(ny, layout.getHeight() - (widget.getHeight() -
132                                                            padding));
133                    ny = Math.max(ny, 0);
134
135                    scrollTo(widget, layout, nx, ny);
136                    widget.cancelLongPress();
137                    return true;
138                }
139            }
140        }
141
142        return false;
143    }
144
145    private static class DragState implements NoCopySpan {
146        public float mX;
147        public float mY;
148        public boolean mFarEnough;
149        public boolean mUsed;
150
151        public DragState(float x, float y) {
152            mX = x;
153            mY = y;
154        }
155    }
156}
157