Android提高之SurfaceView的基本用法实例分析

前文介绍了Android中MediaPlayer用法的时候稍微介绍了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，这次我就来较为详细的介绍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，本文所述方法就直接在普通的用户界面调用SurfaceHolder的lockCanvas和unlockCanvasAndPost。

先来看看程序运行效果的截图如下：

截图1主要演示了直接把正弦波绘画在SurfaceView上。

再来看看下面两幅截图：

对比上面的上下两图，下图用.lockCanvas(null)，而上图用.lockCanvas(new Rect(oldX, 0, oldX + length,
getWindowManager().getDefaultDisplay().getHeight()))，对比一下两个效果，由于上图是按指定Rect绘画，所以效率会比下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。

main.xml的源码如下:

<?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Java程序源码如下：

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);
 }
}

这里还需要注意一下： 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。