Android提高第二篇之SurfaceView(上)

http://blog.csdn.net/hellogv/archive/2010/11/03/5985090.aspx
上次 介绍MediaPlayer的时候稍微介绍了SurfaceView，SurfaceView由于可以直接从内存或者DMA等硬件接口取得图像数据，因此是个非常重要的绘图容器，这次我就用两篇文章来介绍SurfaceView的用法。网上介绍SurfaceView的用法有很多，写法也层出不同，例如继承SurfaceView类，或者继承SurfaceHolder.Callback类等，这个可以根据功能实际需要自己选择，我这里就直接在普通的用户界面调用SurfaceHolder的lockCanvas和unlockCanvasAndPost。

        先来看看程序运行的截图：



截图1主要演示了直接把正弦波绘画在SurfaceView上




对比上面的左右两图，右图用.lockCanvas(null)，而左图用.lockCanvas(new Rect(oldX, 0, oldX + length,
    getWindowManager().getDefaultDisplay().getHeight()))，对比一下两个效果，由于左图是按指定Rect绘画，所以效率会比右图的全控件绘画高些，并且在清屏之后(canvas.drawColor(Color.BLACK))不会留有上次绘画的残留。

接下来贴出main.xml的源码:

<?xml version="1.0" encoding="utf-8"?>  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:layout_width="fill_parent" android:layout_height="fill_parent"  
    android:orientation="vertical">  
  
    <LinearLayout android:id="@+id/LinearLayout01"  
        android:layout_width="wrap_content" android:layout_height="wrap_content">  
        <Button android:id="@+id/Button01" android:layout_width="wrap_content"  
            android:layout_height="wrap_content" android:text="简单绘画"></Button>  
        <Button android:id="@+id/Button02" android:layout_width="wrap_content"  
            android:layout_height="wrap_content" android:text="定时器绘画"></Button>  
    </LinearLayout>  
    <SurfaceView android:id="@+id/SurfaceView01"  
        android:layout_width="fill_parent" android:layout_height="fill_parent"></SurfaceView>  
</LinearLayout>  

接下来贴出程序源码：

package com.testSurfaceView;  
  
import java.util.Timer;  
import java.util.TimerTask;  
  
import android.app.Activity;  
import android.graphics.Canvas;  
import android.graphics.Color;  
import android.graphics.Paint;  
import android.graphics.Rect;  
import android.os.Bundle;  
import android.util.Log;  
import android.view.SurfaceHolder;  
import android.view.SurfaceView;  
import android.view.View;  
import android.widget.Button;  
  
public class testSurfaceView extends Activity {  
    /** Called when the activity is first created. */  
    Button btnSimpleDraw, btnTimerDraw;  
    SurfaceView sfv;  
    SurfaceHolder sfh;  
  
    private Timer mTimer;  
    private MyTimerTask mTimerTask;  
    int Y_axis[],//保存正弦波的Y轴上的点  
    centerY,//中心线  
    oldX,oldY,//上一个XY点   
    currentX;//当前绘制到的X轴上的点  
  
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.main);  
  
        btnSimpleDraw = (Button) this.findViewById(R.id.Button01);  
        btnTimerDraw = (Button) this.findViewById(R.id.Button02);  
        btnSimpleDraw.setOnClickListener(new ClickEvent());  
        btnTimerDraw.setOnClickListener(new ClickEvent());  
        sfv = (SurfaceView) this.findViewById(R.id.SurfaceView01);  
        sfh = sfv.getHolder();  
  
        //动态绘制正弦波的定时器  
        mTimer = new Timer();  
        mTimerTask = new MyTimerTask();  
  
        // 初始化y轴数据  
        centerY = (getWindowManager().getDefaultDisplay().getHeight() - sfv  
                .getTop()) / 2;  
        Y_axis = new int[getWindowManager().getDefaultDisplay().getWidth()];  
        for (int i = 1; i < Y_axis.length; i++) {// 计算正弦波  
            Y_axis[i - 1] = centerY  
                    - (int) (100 * Math.sin(i * 2 * Math.PI / 180));  
        }  
    }  
  
    class ClickEvent implements View.OnClickListener {  
  
        @Override  
        public void onClick(View v) {  
  
            if (v == btnSimpleDraw) {  
                SimpleDraw(Y_axis.length-1);//直接绘制正弦波  
              
            } else if (v == btnTimerDraw) {  
                oldY = centerY;  
                mTimer.schedule(mTimerTask, 0, 5);//动态绘制正弦波  
            }  
  
        }  
  
    }  
  
    class MyTimerTask extends TimerTask {  
        @Override  
        public void run() {  
  
            SimpleDraw(currentX);  
            currentX++;//往前进  
            if (currentX == Y_axis.length - 1) {//如果到了终点，则清屏重来  
                ClearDraw();  
                currentX = 0;  
                oldY = centerY;  
            }  
        }  
  
    }  
      
    /* 
     * 绘制指定区域 
     */  
    void SimpleDraw(int length) {  
        if (length == 0)  
            oldX = 0;  
        Canvas canvas = sfh.lockCanvas(new Rect(oldX, 0, oldX + length,  
                getWindowManager().getDefaultDisplay().getHeight()));// 关键:获取画布  
        Log.i("Canvas:",  
                String.valueOf(oldX) + "," + String.valueOf(oldX + length));  
  
        Paint mPaint = new Paint();  
        mPaint.setColor(Color.GREEN);// 画笔为绿色  
        mPaint.setStrokeWidth(2);// 设置画笔粗细  
  
        int y;  
        for (int i = oldX + 1; i < length; i++) {// 绘画正弦波  
            y = Y_axis[i - 1];  
            canvas.drawLine(oldX, oldY, i, y, mPaint);  
            oldX = i;  
            oldY = y;  
        }  
        sfh.unlockCanvasAndPost(canvas);// 解锁画布，提交画好的图像  
    }  
  
    void ClearDraw() {  
        Canvas canvas = sfh.lockCanvas(null);  
        canvas.drawColor(Color.BLACK);// 清除画布  
        sfh.unlockCanvasAndPost(canvas);  
  
    }  
}  

注意一下 for (int i = oldX + 1; i < length; i++) {// 绘画正弦波 这句，在.lockCanvas()指定Rect内减少循环画线的次数，可以提高绘图效率。