Android提高之SurfaceView的基本用法實例分析

前文介紹了Android中MediaPlayer用法的時候稍微介紹了SurfaceView，SurfaceView由於可以直接從內存或者DMA等硬件接口取得圖像數據，因此是個非常重要的繪圖容器，這次我就來較為詳細的介紹SurfaceView的用法。網上介紹SurfaceView的用法有很多，寫法也層出不同，例如繼承SurfaceView類，或者繼承SurfaceHolder.Callback類等，這個可以根據功能實際需要自己選擇，本文所述方法就直接在普通的用戶界面調用SurfaceHolder的lockCanvas和unlockCanvasAndPost。

先來看看程序運行效果的截圖如下：

截圖1主要演示了直接把正弦波繪畫在SurfaceView上。

再來看看下面兩幅截圖：

對比上面的上下兩圖，下圖用.lockCanvas(null)，而上圖用.lockCanvas(new Rect(oldX, 0, oldX + length,
getWindowManager().getDefaultDisplay().getHeight()))，對比一下兩個效果，由於上圖是按指定Rect繪畫，所以效率會比下圖的全控件繪畫高些，並且在清屏之後(canvas.drawColor(Color.BLACK))不會留有上次繪畫的殘留。

main.xml的源碼如下:

<?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="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Java程序源碼如下：

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軸上的點
 centerY,//中心線
 oldX,oldY,//上一個XY點 
 currentX;//當前繪制到的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();

 //動態繪制正弦波的定時器
 mTimer = new Timer();
 mTimerTask = new MyTimerTask();

 // 初始化y軸數據
 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);//直接繪制正弦波
 } else if (v == btnTimerDraw) {
 oldY = centerY;
 mTimer.schedule(mTimerTask, 0, 5);//動態繪制正弦波
 }
 }
 }
 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;
 }
 }
 }
 /*
 * 繪制指定區域
 */
 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);// 設置畫筆粗細
 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，提交畫好的圖像
 }
 void ClearDraw() {
 Canvas canvas = sfh.lockCanvas(null);
 canvas.drawColor(Color.BLACK);// 清除畫布
 sfh.unlockCanvasAndPost(canvas);
 }
}

這裡還需要注意一下： for (int i = oldX + 1; i < length; i++) {// 繪畫正弦波 這句，在.lockCanvas()指定Rect內減少循環畫線的次數，可以提高繪圖效率。