Android提高第二篇之SurfaceView(上)

本文来自http://blog.csdn.net/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。