core/java/android/text/method/LinkMovementMethod.java

/*
 * 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.method;

import android.text.Layout;
import android.text.NoCopySpan;
import android.text.Selection;
import android.text.Spannable;
import android.text.style.ClickableSpan;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.widget.TextView;

/**
 * A movement method that traverses links in the text buffer and scrolls if necessary.
 * Supports clicking on links with DPad Center or Enter.
 */
public class LinkMovementMethod extends ScrollingMovementMethod {
    private static final int CLICK = 1;
    private static final int UP = 2;
    private static final int DOWN = 3;

    @Override
    protected boolean handleMovementKey(TextView widget, Spannable buffer, int keyCode,
            int movementMetaState, KeyEvent event) {
        switch (keyCode) {
            case KeyEvent.KEYCODE_DPAD_CENTER:
            case KeyEvent.KEYCODE_ENTER:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    if (event.getAction() == KeyEvent.ACTION_DOWN &&
                            event.getRepeatCount() == 0 && action(CLICK, widget, buffer)) {
                        return true;
                    }
                }
                break;
        }
        return super.handleMovementKey(widget, buffer, keyCode, movementMetaState, event);
    }

    @Override
    protected boolean up(TextView widget, Spannable buffer) {
        if (action(UP, widget, buffer)) {
            return true;
        }

        return super.up(widget, buffer);
    }
        
    @Override
    protected boolean down(TextView widget, Spannable buffer) {
        if (action(DOWN, widget, buffer)) {
            return true;
        }

        return super.down(widget, buffer);
    }

    @Override
    protected boolean left(TextView widget, Spannable buffer) {
        if (action(UP, widget, buffer)) {
            return true;
        }

        return super.left(widget, buffer);
    }

    @Override
    protected boolean right(TextView widget, Spannable buffer) {
        if (action(DOWN, widget, buffer)) {
            return true;
        }

        return super.right(widget, buffer);
    }

    private boolean action(int what, TextView widget, Spannable buffer) {
        Layout layout = widget.getLayout();

        int padding = widget.getTotalPaddingTop() +
                      widget.getTotalPaddingBottom();
        int areatop = widget.getScrollY();
        int areabot = areatop + widget.getHeight() - padding;

        int linetop = layout.getLineForVertical(areatop);
        int linebot = layout.getLineForVertical(areabot);

        int first = layout.getLineStart(linetop);
        int last = layout.getLineEnd(linebot);

        ClickableSpan[] candidates = buffer.getSpans(first, last, ClickableSpan.class);

        int a = Selection.getSelectionStart(buffer);
        int b = Selection.getSelectionEnd(buffer);

        int selStart = Math.min(a, b);
        int selEnd = Math.max(a, b);

        if (selStart < 0) {
            if (buffer.getSpanStart(FROM_BELOW) >= 0) {
                selStart = selEnd = buffer.length();
            }
        }

        if (selStart > last)
            selStart = selEnd = Integer.MAX_VALUE;
        if (selEnd < first)
            selStart = selEnd = -1;

        switch (what) {
        case CLICK:
            if (selStart == selEnd) {
                return false;
            }

            ClickableSpan[] link = buffer.getSpans(selStart, selEnd, ClickableSpan.class);

            if (link.length != 1)
                return false;

            link[0].onClick(widget);
            break;

        case UP:
            int beststart, bestend;

            beststart = -1;
            bestend = -1;

            for (int i = 0; i < candidates.length; i++) {
                int end = buffer.getSpanEnd(candidates[i]);

                if (end < selEnd || selStart == selEnd) {
                    if (end > bestend) {
                        beststart = buffer.getSpanStart(candidates[i]);
                        bestend = end;
                    }
                }
            }

            if (beststart >= 0) {
                Selection.setSelection(buffer, bestend, beststart);
                return true;
            }

            break;

        case DOWN:
            beststart = Integer.MAX_VALUE;
            bestend = Integer.MAX_VALUE;

            for (int i = 0; i < candidates.length; i++) {
                int start = buffer.getSpanStart(candidates[i]);

                if (start > selStart || selStart == selEnd) {
                    if (start < beststart) {
                        beststart = start;
                        bestend = buffer.getSpanEnd(candidates[i]);
                    }
                }
            }

            if (bestend < Integer.MAX_VALUE) {
                Selection.setSelection(buffer, beststart, bestend);
                return true;
            }

            break;
        }

        return false;
    }

    @Override
    public boolean onTouchEvent(TextView widget, Spannable buffer,
                                MotionEvent event) {
        int action = event.getAction();

        if (action == MotionEvent.ACTION_UP ||
            action == MotionEvent.ACTION_DOWN) {
            int x = (int) event.getX();
            int y = (int) event.getY();

            x -= widget.getTotalPaddingLeft();
            y -= widget.getTotalPaddingTop();

            x += widget.getScrollX();
            y += widget.getScrollY();

            Layout layout = widget.getLayout();
            int line = layout.getLineForVertical(y);
            int off = layout.getOffsetForHorizontal(line, x);

            ClickableSpan[] link = buffer.getSpans(off, off, ClickableSpan.class);

            if (link.length != 0) {
                if (action == MotionEvent.ACTION_UP) {
                    link[0].onClick(widget);
                } else if (action == MotionEvent.ACTION_DOWN) {
                    Selection.setSelection(buffer,
                                           buffer.getSpanStart(link[0]),
                                           buffer.getSpanEnd(link[0]));
                }

                return true;
            } else {
                Selection.removeSelection(buffer);
            }
        }

        return super.onTouchEvent(widget, buffer, event);
    }

    @Override
    public void initialize(TextView widget, Spannable text) {
        Selection.removeSelection(text);
        text.removeSpan(FROM_BELOW);
    }

    @Override
    public void onTakeFocus(TextView view, Spannable text, int dir) {
        Selection.removeSelection(text);

        if ((dir & View.FOCUS_BACKWARD) != 0) {
            text.setSpan(FROM_BELOW, 0, 0, Spannable.SPAN_POINT_POINT);
        } else {
            text.removeSpan(FROM_BELOW);
        }
    }

    public static MovementMethod getInstance() {
        if (sInstance == null)
            sInstance = new LinkMovementMethod();

        return sInstance;
    }

    private static LinkMovementMethod sInstance;
    private static Object FROM_BELOW = new NoCopySpan.Concrete();
}