Android提高第二篇之SurfaceView的基本使用

本文来自http://blog.youkuaiyun.com/hellogv/ ，引用必须注明出处！

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。