SurfaceView绘图机制_surfaceview ondraw绘制背景不消失

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虽然前面都使用的View来进行绘图，但View绘图机制存在两个缺陷：

1、缺乏双缓冲机制

2、更新图像时，必须更新View上的整张图片，效率低。

所以在游戏绘制中推荐使用SurfaceView。它可以只对指定区域进行更新，可以提高效率。下面用一个简单示例来演示SurfaceView的使用：

Activity：

package com.home.activity;
 
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;
import android.view.View;
import android.view.View.OnTouchListener;
 
import com.home.surfaceviewtest.R;
 
public class SurfaceViewActivity extends Activity {
	// SurfaceHolder负责维护SurfaceView上绘制的内容
	private SurfaceHolder holder;
	private Paint paint;
 
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		paint = new Paint();
		// 获取SurfaceView实例
		SurfaceView surface = (SurfaceView) findViewById(R.id.main_sv);
		// 初始化SurfaceHolder对象
		holder = surface.getHolder();
		holder.addCallback(new Callback() {
			//当surface将要被销毁时回调该方法
			@Override
			public void surfaceDestroyed(SurfaceHolder holder) {
 
			}
			//当surface被创建时回调该方法
			@Override
			public void surfaceCreated(SurfaceHolder holder) {
				// 锁定整个SurfaceView
				Canvas canvas = holder.lockCanvas();
				// 获取背景资源
				Bitmap bitmap = BitmapFactory.decodeResource(
						SurfaceViewActivity.this.getResources(),
						R.drawable.image2);
				// 绘制背景
				canvas.drawBitmap(bitmap, 0, 0, null);
				// 绘制完成，释放画布，提交修改
				holder.unlockCanvasAndPost(canvas);
				// 重新锁两次，避免下次lockCanvas遮挡
				holder.lockCanvas(new Rect(0, 0, 0, 0));
				holder.unlockCanvasAndPost(canvas);
				holder.lockCanvas(new Rect(0, 0, 0, 0));
				holder.unlockCanvasAndPost(canvas);
			}
			//当一个surface的格式或大小发生改变时回调该方法
			@Override
			public void surfaceChanged(SurfaceHolder holder, int format,
					int width, int height) {
 
			}
		});
		surface.setOnTouchListener(new OnTouchListener() {
 
			@Override
			public boolean onTouch(View v, MotionEvent event) {
				// 只处理按下事件
				if (event.getAction() == MotionEvent.ACTION_DOWN) {
					int cx = (int) event.getX();
					int cy = (int) event.getY();
					// 锁定SurfaceView的局部区域，只更新局部内容
					Canvas canvas = holder.lockCanvas(new Rect(cx - 60,
							cy - 60, cx + 60, cy + 60));
					// 保存canvas的当前状态
					canvas.save();
					// 旋转画布
					canvas.rotate(30, cx, cy);
					paint.setColor(Color.RED);
					// 绘制红色方块
					canvas.drawRect(cx - 40, cy - 40, cx, cy, paint);
					// 恢复canvas之前的保存状态
					canvas.restore();
					paint.setColor(Color.GREEN);
					// 绘制绿色方块
					canvas.drawRect(cx, cy, cx + 40, cy + 40, paint);
					// 绘制完成，释放画布，提交修改
					holder.unlockCanvasAndPost(canvas);
				}
				return false;
			}
		});
	}
 
}

布局XML：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
 
    <SurfaceView
        android:id="@+id/main_sv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
 
</LinearLayout>