Android开发之多点触摸（Multitouch）

[转载请注明] 来源:www.ideasandroid.com 原文: http://www.ideasandroid.com/archives/422


   如果您对开发多点触摸程序感兴趣的话，那么本文将是一个很好的开始，android应用程序开发中，多点触摸不是那么遥不可及，实现起来也很简单，本例只需要两个类就能实现多点触摸。

首先来看看我们的视图类MTView.java:

package com.ideasandroid.demo;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

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 {
                // 先在屏幕上画一个十字，然后画一个圆
                for (int i = 0; i < pointerCount; i++) {
                    // 获取一个触点的坐标，然后开始绘制
                    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);
                }
                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) {
            // 背景黑色
            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) {
    }

}

代码中都做了相应的注释，这里就不多说。
        接下来看看我们的Activity，MultitouchVisible.java

package com.ideasandroid.demo;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;

public class MultitouchVisible extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //隐藏标题栏
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        //设置成全屏
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        //设置为上面的MTView
        setContentView(new MTView(this));
    }
}