Android多点触控MultiTouch浅析

申明：

参考：http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2013/0226/914.html

下面实现如何通过应用层支持多点触控操作，对于常规的控件触控操实现onTouchEvent()方法来处理。同时对onTouchEvent方法的参数MotionEvent进行一些了解。

正文：

下面会用两个应用示例来初步学习一下Android中的多点触控。

示例一（DemoMultiTouch-Canvas）：
核心技术介绍

本示例是在SurfaceView中利用Canvas来展示用户的多点触控，不过核心技术还是一个常见的方法：onTouchEvent(MotionEvent event)

MotionEvent有以下几个方法需要大家注意一下，不过了是一些常见的方法，如果你onTouchEvent使用得多的话。

event.getAction() // 获取触控动作比如ACTION_DOWN
event.getPointerCount(); // 获取触控点的数量，比如2则可能是两个手指同时按压屏幕
event.getPointerId(nID); // 对于每个触控的点的细节，我们可以通过一个循环执行getPointerId方法获取索引
event.getX(nID); // 获取第nID个触控点的x位置
event.getY(nID); // 获取第nID个点触控的y位置
event.getPressure(nID); // LCD可以感应出用户的手指压力，当然具体的级别由驱动和物理硬件决定的
event.getDownTime() // 按下开始时间
event.getEventTime() // 事件结束时间
event.getEventTime()-event.getDownTime()); // 总共按下时花费时间

代码展示：

public class MTView extends SurfaceView implements SurfaceHolder.Callback {

    private static final int MAX_TOUCHPOINTS = 10;
    private static final String START_TEXT = "请随便触摸屏幕进行测试";
    private Paint textPaint = new Paint();
    private Paint touchPaints[] = new Paint[MAX_TOUCHPOINTS];
    private int colors[] = new int[MAX_TOUCHPOINTS];

    private int width, height;
    private float scale = 1.0f;

    public MTView(Context context) {
        super(context);
        SurfaceHolder holder = getHolder();
        holder.addCallback(this);
        setFocusable(true); // 确保我们的View能获得输入焦点
        setFocusableInTouchMode(true); // 确保能接收到触屏事件
        init();
    }

    private void init() {
        // 初始化10个不同颜色的画笔
        textPaint.setColor(Color.WHITE);
        colors[0] = Color.BLUE;
        colors[1] = Color.RED;
        colors[2] = Color.GREEN;
        colors[3] = Color.YELLOW;
        colors[4] = Color.CYAN;
        colors[5] = Color.MAGENTA;
        colors[6] = Color.DKGRAY;
        colors[7] = Color.WHITE;
        colors[8] = Color.LTGRAY;
        colors[9] = Color.GRAY;
        for (int i = 0; i < MAX_TOUCHPOINTS; i++) {
            touchPaints[i] = new Paint();
            touchPaints[i].setColor(colors[i]);
        }
    }

    /**
     * 处理触屏事件
     */
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // 获得屏幕触点数量
        int pointerCount = event.getPointerCount();
        if (pointerCount > MAX_TOUCHPOINTS) {
            pointerCount = MAX_TOUCHPOINTS;
        }

        // 锁定Canvas,开始进行相应的界面处理
        Canvas c = getHolder().lockCanvas();
        if (c != null) {
            c.drawColor(Color.BLACK);
            if (event.getAction() == MotionEvent.ACTION_UP) {
                // 当手离开屏幕时，清屏
            } else {
                // 在每一个触点上绘制一个十字和坐标信息
                for (int i = 0; i < pointerCount; i++) {
                    int id = event.getPointerId(i);
                    int x = (int) event.getX(i);
                    int y = (int) event.getY(i);
                    drawCrosshairsAndText(x, y, touchPaints[id], i, id, c);
                }

                // 在每一个触点上绘制一个圆
                for (int i = 0; i < pointerCount; i++) {
                    int id = event.getPointerId(i);
                    int x = (int) event.getX(i);
                    int y = (int) event.getY(i);
                    drawCircle(x, y, touchPaints[id], c);
                }
            }

            // 画完后，unlock
            getHolder().unlockCanvasAndPost(c);
        }
        return true;
    }

    /**
     * 画十字及坐标信息
     * 
     * @param x
     * @param y
     * @param paint
     * @param ptr
     * @param id
     * @param c
     */
    private void drawCrosshairsAndText(int x, int y, Paint paint, int ptr,
            int id, Canvas c) {
        c.drawLine(0, y, width, y, paint);
        c.drawLine(x, 0, x, height, paint);
        int textY = (int) ((15 + 20 * ptr) * scale);
        c.drawText("x" + ptr + "=" + x, 10 * scale, textY, textPaint);
        c.drawText("y" + ptr + "=" + y, 70 * scale, textY, textPaint);
        c.drawText("id" + ptr + "=" + id, width - 55 * scale, textY, textPaint);
    }

    /**
     * 画圆
     * 
     * @param x
     * @param y
     * @param paint
     * @param c
     */
    private void drawCircle(int x, int y, Paint paint, Canvas c) {
        c.drawCircle(x, y, 40 * scale, paint);
    }

    /**
     * 进入程序时背景画成黑色，然后把START_TEXT写到屏幕
     */
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        this.width = width;
        this.height = height;
        if (width > height) {
            this.scale = width / 480f;
        } else {
            this.scale = height / 480f;
        }
        textPaint.setTextSize(14 * scale);
        Canvas c = getHolder().lockCanvas();
        if (c != null) {
            c.drawColor(Color.BLACK);
            float tWidth = textPaint.measureText(START_TEXT);
            c.drawText(START_TEXT, width / 2 - tWidth / 2, height / 2, textPaint);
            getHolder().unlockCanvasAndPost(c);
        }
    }

    public void surfaceCreated(SurfaceHolder holder) {
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
    }
}

使用上也是so easy：

setContentView(new MTView(this));

运行效果图：

示例二（DemoMultiTouch-ImageView）：

通过多点触屏放大或缩小图像 beforeLenght用来保存前一时间两点之间的距离 afterLenght用来保存当前时间两点之间的距离

public void scaleWithFinger(MotionEvent event) {
            float moveX = event.getX(1) - event.getX(0);
            float moveY = event.getY(1) - event.getY(0);

            switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                beforeLenght = (float) Math.sqrt((moveX * moveX)
                        + (moveY * moveY));
                break;
            case MotionEvent.ACTION_MOVE:
                // 得到两个点之间的长度
                afterLenght = (float) Math.sqrt((moveX * moveX)
                        + (moveY * moveY));

                float gapLenght = afterLenght - beforeLenght;

                if (gapLenght == 0) {
                    break;
                }

                // 如果当前时间两点距离大于前一时间两点距离，则传0，否则传1
                if (gapLenght > 0) {
                    this.setScale(scale, 0);
                } else {
                    this.setScale(scale, 1);
                }

                beforeLenght = afterLenght;
                break;
            }
        }
    }

让图片跟随手指触屏的位置移动 beforeX、Y是用来保存前一位置的坐标 afterX、Y是用来保存当前位置的坐标。它们的差值就是ImageView各坐标的增加或减少值。

public void moveWithFinger(MotionEvent event) {

            switch (event.getAction()) {

            case MotionEvent.ACTION_DOWN:
                beforeX = event.getX();
                beforeY = event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                afterX = event.getX();
                afterY = event.getY();

                this.setLocation((int) (afterX - beforeX),
                        (int) (afterY - beforeY));

                beforeX = afterX;
                beforeY = afterY;
                break;

            case MotionEvent.ACTION_UP:
                break;
            }
        }

用来放大缩小ImageView 因为图片是填充ImageView的，所以也就有放大缩小图片的效果 flag为0是放大图片，为1是缩小图片

private void setScale(float temp, int flag) {

            if (flag == 0) {
                this.setFrame(this.getLeft() - (int) (temp * this.getWidth()),
                        this.getTop() - (int) (temp * this.getHeight()),
                        this.getRight() + (int) (temp * this.getWidth()),
                        this.getBottom() + (int) (temp * this.getHeight()));
            } else {
                this.setFrame(this.getLeft() + (int) (temp * this.getWidth()),
                        this.getTop() + (int) (temp * this.getHeight()),
                        this.getRight() - (int) (temp * this.getWidth()),
                        this.getBottom() - (int) (temp * this.getHeight()));
            }
        }

onTouchEvent事件则如下：

public boolean onTouchEvent(MotionEvent event) {
        if (inView(imageView, event)) {
            if (event.getPointerCount() == 2) {
                imageView.scaleWithFinger(event);
            } else if (event.getPointerCount() == 1) {
                imageView.moveWithFinger(event);
            }
        }
        return true;
    }

http://download.csdn.net/detail/u013761665/8719349