Java tutorial
/* * Copyright (C) 2006 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.text; import android.annotation.TestApi; import android.annotation.UnsupportedAppUsage; import java.text.BreakIterator; /** * Utility class for manipulating cursors and selections in CharSequences. * A cursor is a selection where the start and end are at the same offset. */ public class Selection { private Selection() { /* cannot be instantiated */ } /* * Retrieving the selection */ /** * Return the offset of the selection anchor or cursor, or -1 if * there is no selection or cursor. */ public static final int getSelectionStart(CharSequence text) { if (text instanceof Spanned) { return ((Spanned) text).getSpanStart(SELECTION_START); } return -1; } /** * Return the offset of the selection edge or cursor, or -1 if * there is no selection or cursor. */ public static final int getSelectionEnd(CharSequence text) { if (text instanceof Spanned) { return ((Spanned) text).getSpanStart(SELECTION_END); } return -1; } private static int getSelectionMemory(CharSequence text) { if (text instanceof Spanned) { return ((Spanned) text).getSpanStart(SELECTION_MEMORY); } return -1; } /* * Setting the selection */ // private static int pin(int value, int min, int max) { // return value < min ? 0 : (value > max ? max : value); // } /** * Set the selection anchor to <code>start</code> and the selection edge * to <code>stop</code>. */ public static void setSelection(Spannable text, int start, int stop) { setSelection(text, start, stop, -1); } /** * Set the selection anchor to <code>start</code>, the selection edge * to <code>stop</code> and the memory horizontal to <code>memory</code>. */ private static void setSelection(Spannable text, int start, int stop, int memory) { // int len = text.length(); // start = pin(start, 0, len); XXX remove unless we really need it // stop = pin(stop, 0, len); int ostart = getSelectionStart(text); int oend = getSelectionEnd(text); if (ostart != start || oend != stop) { text.setSpan(SELECTION_START, start, start, Spanned.SPAN_POINT_POINT | Spanned.SPAN_INTERMEDIATE); text.setSpan(SELECTION_END, stop, stop, Spanned.SPAN_POINT_POINT); updateMemory(text, memory); } } /** * Update the memory position for text. This is used to ensure vertical navigation of lines * with different lengths behaves as expected and remembers the longest horizontal position * seen during a vertical traversal. */ private static void updateMemory(Spannable text, int memory) { if (memory > -1) { int currentMemory = getSelectionMemory(text); if (memory != currentMemory) { text.setSpan(SELECTION_MEMORY, memory, memory, Spanned.SPAN_POINT_POINT); if (currentMemory == -1) { // This is the first value, create a watcher. final TextWatcher watcher = new MemoryTextWatcher(); text.setSpan(watcher, 0, text.length(), Spanned.SPAN_INCLUSIVE_INCLUSIVE); } } } else { removeMemory(text); } } private static void removeMemory(Spannable text) { text.removeSpan(SELECTION_MEMORY); MemoryTextWatcher[] watchers = text.getSpans(0, text.length(), MemoryTextWatcher.class); for (MemoryTextWatcher watcher : watchers) { text.removeSpan(watcher); } } /** * @hide */ @TestApi public static final class MemoryTextWatcher implements TextWatcher { @Override public void beforeTextChanged(CharSequence s, int start, int count, int after) { } @Override public void onTextChanged(CharSequence s, int start, int before, int count) { } @Override public void afterTextChanged(Editable s) { s.removeSpan(SELECTION_MEMORY); s.removeSpan(this); } } /** * Move the cursor to offset <code>index</code>. */ public static final void setSelection(Spannable text, int index) { setSelection(text, index, index); } /** * Select the entire text. */ public static final void selectAll(Spannable text) { setSelection(text, 0, text.length()); } /** * Move the selection edge to offset <code>index</code>. */ public static final void extendSelection(Spannable text, int index) { extendSelection(text, index, -1); } /** * Move the selection edge to offset <code>index</code> and update the memory horizontal. */ private static void extendSelection(Spannable text, int index, int memory) { if (text.getSpanStart(SELECTION_END) != index) { text.setSpan(SELECTION_END, index, index, Spanned.SPAN_POINT_POINT); } updateMemory(text, memory); } /** * Remove the selection or cursor, if any, from the text. */ public static final void removeSelection(Spannable text) { text.removeSpan(SELECTION_START, Spanned.SPAN_INTERMEDIATE); text.removeSpan(SELECTION_END); removeMemory(text); } /* * Moving the selection within the layout */ /** * Move the cursor to the buffer offset physically above the current * offset, to the beginning if it is on the top line but not at the * start, or return false if the cursor is already on the top line. */ public static boolean moveUp(Spannable text, Layout layout) { int start = getSelectionStart(text); int end = getSelectionEnd(text); if (start != end) { int min = Math.min(start, end); int max = Math.max(start, end); setSelection(text, min); if (min == 0 && max == text.length()) { return false; } return true; } else { int line = layout.getLineForOffset(end); if (line > 0) { setSelectionAndMemory(text, layout, line, end, -1 /* direction */, false /* extend */); return true; } else if (end != 0) { setSelection(text, 0); return true; } } return false; } /** * Calculate the movement and memory positions needed, and set or extend the selection. */ private static void setSelectionAndMemory(Spannable text, Layout layout, int line, int end, int direction, boolean extend) { int move; int newMemory; if (layout.getParagraphDirection(line) == layout.getParagraphDirection(line + direction)) { int memory = getSelectionMemory(text); if (memory > -1) { // We have a memory position float h = layout.getPrimaryHorizontal(memory); move = layout.getOffsetForHorizontal(line + direction, h); newMemory = memory; } else { // Create a new memory position float h = layout.getPrimaryHorizontal(end); move = layout.getOffsetForHorizontal(line + direction, h); newMemory = end; } } else { move = layout.getLineStart(line + direction); newMemory = -1; } if (extend) { extendSelection(text, move, newMemory); } else { setSelection(text, move, move, newMemory); } } /** * Move the cursor to the buffer offset physically below the current * offset, to the end of the buffer if it is on the bottom line but * not at the end, or return false if the cursor is already at the * end of the buffer. */ public static boolean moveDown(Spannable text, Layout layout) { int start = getSelectionStart(text); int end = getSelectionEnd(text); if (start != end) { int min = Math.min(start, end); int max = Math.max(start, end); setSelection(text, max); if (min == 0 && max == text.length()) { return false; } return true; } else { int line = layout.getLineForOffset(end); if (line < layout.getLineCount() - 1) { setSelectionAndMemory(text, layout, line, end, 1 /* direction */, false /* extend */); return true; } else if (end != text.length()) { setSelection(text, text.length()); return true; } } return false; } /** * Move the cursor to the buffer offset physically to the left of * the current offset, or return false if the cursor is already * at the left edge of the line and there is not another line to move it to. */ public static boolean moveLeft(Spannable text, Layout layout) { int start = getSelectionStart(text); int end = getSelectionEnd(text); if (start != end) { setSelection(text, chooseHorizontal(layout, -1, start, end)); return true; } else { int to = layout.getOffsetToLeftOf(end); if (to != end) { setSelection(text, to); return true; } } return false; } /** * Move the cursor to the buffer offset physically to the right of * the current offset, or return false if the cursor is already at * at the right edge of the line and there is not another line * to move it to. */ public static boolean moveRight(Spannable text, Layout layout) { int start = getSelectionStart(text); int end = getSelectionEnd(text); if (start != end) { setSelection(text, chooseHorizontal(layout, 1, start, end)); return true; } else { int to = layout.getOffsetToRightOf(end); if (to != end) { setSelection(text, to); return true; } } return false; } /** * Move the selection end to the buffer offset physically above * the current selection end. */ public static boolean extendUp(Spannable text, Layout layout) { int end = getSelectionEnd(text); int line = layout.getLineForOffset(end); if (line > 0) { setSelectionAndMemory(text, layout, line, end, -1 /* direction */, true /* extend */); return true; } else if (end != 0) { extendSelection(text, 0); return true; } return true; } /** * Move the selection end to the buffer offset physically below * the current selection end. */ public static boolean extendDown(Spannable text, Layout layout) { int end = getSelectionEnd(text); int line = layout.getLineForOffset(end); if (line < layout.getLineCount() - 1) { setSelectionAndMemory(text, layout, line, end, 1 /* direction */, true /* extend */); return true; } else if (end != text.length()) { extendSelection(text, text.length(), -1); return true; } return true; } /** * Move the selection end to the buffer offset physically to the left of * the current selection end. */ public static boolean extendLeft(Spannable text, Layout layout) { int end = getSelectionEnd(text); int to = layout.getOffsetToLeftOf(end); if (to != end) { extendSelection(text, to); return true; } return true; } /** * Move the selection end to the buffer offset physically to the right of * the current selection end. */ public static boolean extendRight(Spannable text, Layout layout) { int end = getSelectionEnd(text); int to = layout.getOffsetToRightOf(end); if (to != end) { extendSelection(text, to); return true; } return true; } public static boolean extendToLeftEdge(Spannable text, Layout layout) { int where = findEdge(text, layout, -1); extendSelection(text, where); return true; } public static boolean extendToRightEdge(Spannable text, Layout layout) { int where = findEdge(text, layout, 1); extendSelection(text, where); return true; } public static boolean moveToLeftEdge(Spannable text, Layout layout) { int where = findEdge(text, layout, -1); setSelection(text, where); return true; } public static boolean moveToRightEdge(Spannable text, Layout layout) { int where = findEdge(text, layout, 1); setSelection(text, where); return true; } /** {@hide} */ public static interface PositionIterator { public static final int DONE = BreakIterator.DONE; public int preceding(int position); public int following(int position); } /** {@hide} */ @UnsupportedAppUsage public static boolean moveToPreceding(Spannable text, PositionIterator iter, boolean extendSelection) { final int offset = iter.preceding(getSelectionEnd(text)); if (offset != PositionIterator.DONE) { if (extendSelection) { extendSelection(text, offset); } else { setSelection(text, offset); } } return true; } /** {@hide} */ @UnsupportedAppUsage public static boolean moveToFollowing(Spannable text, PositionIterator iter, boolean extendSelection) { final int offset = iter.following(getSelectionEnd(text)); if (offset != PositionIterator.DONE) { if (extendSelection) { extendSelection(text, offset); } else { setSelection(text, offset); } } return true; } private static int findEdge(Spannable text, Layout layout, int dir) { int pt = getSelectionEnd(text); int line = layout.getLineForOffset(pt); int pdir = layout.getParagraphDirection(line); if (dir * pdir < 0) { return layout.getLineStart(line); } else { int end = layout.getLineEnd(line); if (line == layout.getLineCount() - 1) return end; else return end - 1; } } private static int chooseHorizontal(Layout layout, int direction, int off1, int off2) { int line1 = layout.getLineForOffset(off1); int line2 = layout.getLineForOffset(off2); if (line1 == line2) { // same line, so it goes by pure physical direction float h1 = layout.getPrimaryHorizontal(off1); float h2 = layout.getPrimaryHorizontal(off2); if (direction < 0) { // to left if (h1 < h2) return off1; else return off2; } else { // to right if (h1 > h2) return off1; else return off2; } } else { // different line, so which line is "left" and which is "right" // depends upon the directionality of the text // This only checks at one end, but it's not clear what the // right thing to do is if the ends don't agree. Even if it // is wrong it should still not be too bad. int line = layout.getLineForOffset(off1); int textdir = layout.getParagraphDirection(line); if (textdir == direction) return Math.max(off1, off2); else return Math.min(off1, off2); } } private static final class START implements NoCopySpan { } private static final class END implements NoCopySpan { } private static final class MEMORY implements NoCopySpan { } private static final Object SELECTION_MEMORY = new MEMORY(); /* * Public constants */ public static final Object SELECTION_START = new START(); public static final Object SELECTION_END = new END(); }