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本文來自http://blog.csdn.net/hellogv/ ，引用必須註明出處！

         上次介紹MediaPlayer

        先來看看程式執行的截圖：

截圖1主要演示了直接把正弦波繪畫在SurfaceView上

對比上面的左右兩圖，右圖用.lockCanvas(null)，而左圖用.lockCanvas(new Rect(oldX, 0, oldX + length,
    getWindowManager().getDefaultDisplay().getHeight()))，對比一下兩個效果，由於左圖是按指定Rect繪畫，所以效率會比右圖的全控制元件繪畫高些，並且在清屏之後(canvas.drawColor(Color.BLACK))不會留有上次繪畫的殘留。

接下來貼出main.xml的原始碼:

<?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="簡單繪畫"></Button>  <Button android:id="@+id/Button02" android:layout_width="wrap_content"   android:layout_height="wrap_content" android:text="定時器繪畫"></Button> </LinearLayout> <SurfaceView android:id="@+id/SurfaceView01"  android:layout_width="fill_parent" android:layout_height="fill_parent"></SurfaceView></LinearLayout>

接下來貼出程式原始碼：

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[],//儲存正弦波的Y軸上的點 centerY,//中心線 oldX,oldY,//上一個XY點  currentX;//當前繪製到的X軸上的點 @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();  //動態繪製正弦波的定時器  mTimer = new Timer();  mTimerTask = new MyTimerTask();  // 初始化y軸資料  centerY = (getWindowManager().getDefaultDisplay().getHeight() - sfv    .getTop()) / 2;  Y_axis = new int[getWindowManager().getDefaultDisplay().getWidth()];  for (int i = 1; i < Y_axis.length; i++) {// 計算正弦波   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);//直接繪製正弦波      } else if (v == btnTimerDraw) {    oldY = centerY;    mTimer.schedule(mTimerTask, 0, 5);//動態繪製正弦波   }  } } class MyTimerTask extends TimerTask {  @Override  public void run() {   SimpleDraw(currentX);   currentX++;//往前進   if (currentX == Y_axis.length - 1) {//如果到了終點，則清屏重來    ClearDraw();    currentX = 0;    oldY = centerY;   }  } }  /*  * 繪製指定區域  */ void SimpleDraw(int length) {  if (length == 0)   oldX = 0;  Canvas canvas = sfh.lockCanvas(new Rect(oldX, 0, oldX + length,    getWindowManager().getDefaultDisplay().getHeight()));// 關鍵:獲取畫布  Log.i("Canvas:",    String.valueOf(oldX) + "," + String.valueOf(oldX + length));  Paint mPaint = new Paint();  mPaint.setColor(Color.GREEN);// 畫筆為綠色  mPaint.setStrokeWidth(2);// 設定畫筆粗細  int y;  for (int i = oldX + 1; i < length; i++) {// 繪畫正弦波   y = Y_axis[i - 1];   canvas.drawLine(oldX, oldY, i, y, mPaint);   oldX = i;   oldY = y;  }  sfh.unlockCanvasAndPost(canvas);// 解鎖畫布，提交畫好的影象 } void ClearDraw() {  Canvas canvas = sfh.lockCanvas(null);  canvas.drawColor(Color.BLACK);// 清除畫布  sfh.unlockCanvasAndPost(canvas); }}

注意一下 for (int i = oldX + 1; i < length; i++) {// 繪畫正弦波 這句，在.lockCanvas()指定Rect內減少迴圈畫線的次數，可以提高繪圖效率。

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