Android提高21篇之二：SurfaceView的基本使用方法

     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/HTML代码

<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 android:id="@+id/Button02" android:layout_width="wrap_content"
                        android:layout_height="wrap_content" android:text="定时器绘画">

        <surfaceview android:id="@+id/SurfaceView01"
                android:layout_width="fill_parent" android:layout_height="fill_parent">

接下来贴出程序源码：

Java代码

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。