Touch.java revision 58b971d733a2c700cabd3db02b6ea4d5faca6939 
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.ViewConfiguration;
25import android.widget.TextView;
26
27public class Touch {
28    private Touch() { }
29
30    /**
31     * Scrolls the specified widget to the specified coordinates, except
32     * constrains the X scrolling position to the horizontal regions of
33     * the text that will be visible after scrolling to the specified
34     * Y position.
35     */
36    public static void scrollTo(TextView widget, Layout layout, int x, int y) {
37        int padding = widget.getTotalPaddingTop() +
38                      widget.getTotalPaddingBottom();
39        int top = layout.getLineForVertical(y);
40        int bottom = layout.getLineForVertical(y + widget.getHeight() -
41                                               padding);
42
43        int left = Integer.MAX_VALUE;
44        int right = 0;
45        Alignment a = null;
46
47        for (int i = top; i <= bottom; i++) {
48            left = (int) Math.min(left, layout.getLineLeft(i));
49            right = (int) Math.max(right, layout.getLineRight(i));
50
51            if (a == null) {
52                a = layout.getParagraphAlignment(i);
53            }
54        }
55
56        padding = widget.getTotalPaddingLeft() + widget.getTotalPaddingRight();
57        int width = widget.getWidth();
58        int diff = 0;
59
60        if (right - left < width - padding) {
61            if (a == Alignment.ALIGN_CENTER) {
62                diff = (width - padding - (right - left)) / 2;
63            } else if (a == Alignment.ALIGN_OPPOSITE) {
64                diff = width - padding - (right - left);
65            }
66        }
67
68        x = Math.min(x, right - (width - padding) - diff);
69        x = Math.max(x, left - diff);
70
71        widget.scrollTo(x, y);
72    }
73
74    /**
75     * Handles touch events for dragging.  You may want to do other actions
76     * like moving the cursor on touch as well.
77     */
78    public static boolean onTouchEvent(TextView widget, Spannable buffer,
79                                       MotionEvent event) {
80        DragState[] ds;
81
82        switch (event.getAction()) {
83        case MotionEvent.ACTION_DOWN:
84            ds = buffer.getSpans(0, buffer.length(), DragState.class);
85
86            for (int i = 0; i < ds.length; i++) {
87                buffer.removeSpan(ds[i]);
88            }
89
90            buffer.setSpan(new DragState(event.getX(), event.getY(),
91                            widget.getScrollX(), widget.getScrollY()),
92                    0, 0, Spannable.SPAN_MARK_MARK);
93            return true;
94
95        case MotionEvent.ACTION_UP:
96            ds = buffer.getSpans(0, buffer.length(), DragState.class);
97
98            for (int i = 0; i < ds.length; i++) {
99                buffer.removeSpan(ds[i]);
100            }
101
102            if (ds.length > 0 && ds[0].mUsed) {
103                return true;
104            } else {
105                return false;
106            }
107
108        case MotionEvent.ACTION_MOVE:
109            ds = buffer.getSpans(0, buffer.length(), DragState.class);
110
111            if (ds.length > 0) {
112                if (ds[0].mFarEnough == false) {
113                    int slop = ViewConfiguration.get(widget.getContext()).getScaledTouchSlop();
114
115                    if (Math.abs(event.getX() - ds[0].mX) >= slop ||
116                        Math.abs(event.getY() - ds[0].mY) >= slop) {
117                        ds[0].mFarEnough = true;
118                    }
119                }
120
121                if (ds[0].mFarEnough) {
122                    ds[0].mUsed = true;
123
124                    float dx = ds[0].mX - event.getX();
125                    float dy = ds[0].mY - event.getY();
126
127                    ds[0].mX = event.getX();
128                    ds[0].mY = event.getY();
129
130                    int nx = widget.getScrollX() + (int) dx;
131                    int ny = widget.getScrollY() + (int) dy;
132
133                    int padding = widget.getTotalPaddingTop() +
134                                  widget.getTotalPaddingBottom();
135                    Layout layout = widget.getLayout();
136
137                    ny = Math.min(ny, layout.getHeight() - (widget.getHeight() -
138                                                            padding));
139                    ny = Math.max(ny, 0);
140
141                    scrollTo(widget, layout, nx, ny);
142                    widget.cancelLongPress();
143                    return true;
144                }
145            }
146        }
147
148        return false;
149    }
150
151    public static int getInitialScrollX(TextView widget, Spannable buffer) {
152        DragState[] ds = buffer.getSpans(0, buffer.length(), DragState.class);
153        return ds.length > 0 ? ds[0].mScrollX : -1;
154    }
155
156    public static int getInitialScrollY(TextView widget, Spannable buffer) {
157        DragState[] ds = buffer.getSpans(0, buffer.length(), DragState.class);
158        return ds.length > 0 ? ds[0].mScrollY : -1;
159    }
160
161    private static class DragState implements NoCopySpan {
162        public float mX;
163        public float mY;
164        public int mScrollX;
165        public int mScrollY;
166        public boolean mFarEnough;
167        public boolean mUsed;
168
169        public DragState(float x, float y, int scrollX, int scrollY) {
170            mX = x;
171            mY = y;
172            mScrollX = scrollX;
173            mScrollY = scrollY;
174        }
175    }
176}
177