Android example source code file (Touch.java)

This example Android source code file (Touch.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

alignment, android, dragstate, layout, motionevent, nocopyspan, spannable, text, touch, ui, util, utilities, view

The Touch.java Android example source code

/*
 * Copyright (C) 2008 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.Layout.Alignment;
import android.text.Spannable;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ViewConfiguration;
import android.widget.TextView;
import android.view.KeyEvent;

public class Touch {
    private Touch() { }

    /**
     * Scrolls the specified widget to the specified coordinates, except
     * constrains the X scrolling position to the horizontal regions of
     * the text that will be visible after scrolling to the specified
     * Y position.
     */
    public static void scrollTo(TextView widget, Layout layout, int x, int y) {
        int padding = widget.getTotalPaddingTop() +
                      widget.getTotalPaddingBottom();
        int top = layout.getLineForVertical(y);
        int bottom = layout.getLineForVertical(y + widget.getHeight() -
                                               padding);

        int left = Integer.MAX_VALUE;
        int right = 0;
        Alignment a = null;

        for (int i = top; i <= bottom; i++) {
            left = (int) Math.min(left, layout.getLineLeft(i));
            right = (int) Math.max(right, layout.getLineRight(i));

            if (a == null) {
                a = layout.getParagraphAlignment(i);
            }
        }

        padding = widget.getTotalPaddingLeft() + widget.getTotalPaddingRight();
        int width = widget.getWidth();
        int diff = 0;

        if (right - left < width - padding) {
            if (a == Alignment.ALIGN_CENTER) {
                diff = (width - padding - (right - left)) / 2;
            } else if (a == Alignment.ALIGN_OPPOSITE) {
                diff = width - padding - (right - left);
            }
        }

        x = Math.min(x, right - (width - padding) - diff);
        x = Math.max(x, left - diff);

        widget.scrollTo(x, y);
    }

    /**
     * @hide
     * Returns the maximum scroll value in x.
     */
    public static int getMaxScrollX(TextView widget, Layout layout, int y) {
        int top = layout.getLineForVertical(y);
        int bottom = layout.getLineForVertical(y + widget.getHeight()
                - widget.getTotalPaddingTop() -widget.getTotalPaddingBottom());
        int left = Integer.MAX_VALUE;
        int right = 0;
        for (int i = top; i <= bottom; i++) {
            left = (int) Math.min(left, layout.getLineLeft(i));
            right = (int) Math.max(right, layout.getLineRight(i));
        }
        return right - left - widget.getWidth() - widget.getTotalPaddingLeft()
                - widget.getTotalPaddingRight();
    }

    /**
     * Handles touch events for dragging.  You may want to do other actions
     * like moving the cursor on touch as well.
     */
    public static boolean onTouchEvent(TextView widget, Spannable buffer,
                                       MotionEvent event) {
        DragState[] ds;

        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            ds = buffer.getSpans(0, buffer.length(), DragState.class);

            for (int i = 0; i < ds.length; i++) {
                buffer.removeSpan(ds[i]);
            }

            buffer.setSpan(new DragState(event.getX(), event.getY(),
                            widget.getScrollX(), widget.getScrollY()),
                    0, 0, Spannable.SPAN_MARK_MARK);
            return true;

        case MotionEvent.ACTION_UP:
            ds = buffer.getSpans(0, buffer.length(), DragState.class);

            for (int i = 0; i < ds.length; i++) {
                buffer.removeSpan(ds[i]);
            }

            if (ds.length > 0 && ds[0].mUsed) {
                return true;
            } else {
                return false;
            }

        case MotionEvent.ACTION_MOVE:
            ds = buffer.getSpans(0, buffer.length(), DragState.class);

            if (ds.length > 0) {
                if (ds[0].mFarEnough == false) {
                    int slop = ViewConfiguration.get(widget.getContext()).getScaledTouchSlop();

                    if (Math.abs(event.getX() - ds[0].mX) >= slop ||
                        Math.abs(event.getY() - ds[0].mY) >= slop) {
                        ds[0].mFarEnough = true;
                    }
                }

                if (ds[0].mFarEnough) {
                    ds[0].mUsed = true;
                    boolean cap = (MetaKeyKeyListener.getMetaState(buffer,
                                   KeyEvent.META_SHIFT_ON) == 1) ||
                                   (MetaKeyKeyListener.getMetaState(buffer,
                                    MetaKeyKeyListener.META_SELECTING) != 0);
                    float dx;
                    float dy;
                    if (cap) {
                        // if we're selecting, we want the scroll to go in
                        // the direction of the drag
                        dx = event.getX() - ds[0].mX;
                        dy = event.getY() - ds[0].mY;
                    } else {
                        dx = ds[0].mX - event.getX();
                        dy = ds[0].mY - event.getY();
                    }
                    ds[0].mX = event.getX();
                    ds[0].mY = event.getY();

                    int nx = widget.getScrollX() + (int) dx;
                    int ny = widget.getScrollY() + (int) dy;

                    int padding = widget.getTotalPaddingTop() +
                                  widget.getTotalPaddingBottom();
                    Layout layout = widget.getLayout();

                    ny = Math.min(ny, layout.getHeight() - (widget.getHeight() -
                                                            padding));
                    ny = Math.max(ny, 0);
        
                    int oldX = widget.getScrollX();
                    int oldY = widget.getScrollY();

                    scrollTo(widget, layout, nx, ny);

                    // If we actually scrolled, then cancel the up action.
                    if (oldX != widget.getScrollX()
                            || oldY != widget.getScrollY()) {
                        widget.cancelLongPress();
                    }

                    return true;
                }
            }
        }

        return false;
    }

    public static int getInitialScrollX(TextView widget, Spannable buffer) {
        DragState[] ds = buffer.getSpans(0, buffer.length(), DragState.class);
        return ds.length > 0 ? ds[0].mScrollX : -1;
    }
    
    public static int getInitialScrollY(TextView widget, Spannable buffer) {
        DragState[] ds = buffer.getSpans(0, buffer.length(), DragState.class);
        return ds.length > 0 ? ds[0].mScrollY : -1;
    }
    
    private static class DragState implements NoCopySpan {
        public float mX;
        public float mY;
        public int mScrollX;
        public int mScrollY;
        public boolean mFarEnough;
        public boolean mUsed;

        public DragState(float x, float y, int scrollX, int scrollY) {
            mX = x;
            mY = y;
            mScrollX = scrollX;
            mScrollY = scrollY;
        }
    }
}