Android提高第三篇之SurfaceView(下)

简 单介绍了SurfaceView的使用，这次就介绍SurfaceView的双缓冲使用。双缓冲是为了防止动画闪烁而实现的一种多线程应用，基于 SurfaceView的双缓冲实现很简单，开一条线程并在其中绘图即可。本文介绍基于SurfaceView的双缓冲实现，以及介绍类似的更高效的实现 方法。

        本文程序运行截图如下，左边是开单个线程读取并绘图，右边是开两个线程，一个专门读取图片，一个专门绘图：

对 比一下，右边动画的帧速明显比左边的快，左右两者都没使用Thread.sleep()。为什么要开两个线程一个读一个画，而不去开两个线程像左边那样都 “边读边画”呢？因为SurfaceView每次绘图都会锁定Canvas,也就是说同一片区域这次没画完下次就不能画，因此要提高双缓冲的效率，就得开一条线程专门画图，开另外一条线程做预处理的工作。

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
=
"单个独立线程"
>
</
Button
>
        <
Button
 
android:id
=
"@+id/Button02"
 
android:layout_width
=
"wrap_content"
            android:layout_height
=
"wrap_content"
 
android:text
=
"两个独立线程"
>
</
Button
>
    </
LinearLayout
>
    <
SurfaceView
 
android:id
=
"@+id/SurfaceView01"
        android:layout_width
=
"fill_parent"
 
android:layout_height
=
"fill_parent"
>
</
SurfaceView
>
</
LinearLayout
>

<?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="单个独立线程"></Button>
		<Button android:id="@+id/Button02" android:layout_width="wrap_content"
			android:layout_height="wrap_content" android:text="两个独立线程"></Button>
	</LinearLayout>
	<SurfaceView android:id="@+id/SurfaceView01"
		android:layout_width="fill_parent" android:layout_height="fill_parent"></SurfaceView>
</LinearLayout>

本文程序的源码：

 

package
 com.testSurfaceView;

import
 java.lang.reflect.Field;
import
 java.util.ArrayList;
import
 android.app.Activity;
import
 android.graphics.Bitmap;
import
 android.graphics.BitmapFactory;
import
 android.graphics.Canvas;
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 btnSingleThread, btnDoubleThread;
    SurfaceView sfv;
    SurfaceHolder sfh;
    ArrayList<Integer> imgList = new
 ArrayList<Integer>();
    int
 imgWidth, imgHeight;
    Bitmap bitmap;//独立线程读取，独立线程绘图

    @Override
    public
 
void
 onCreate(Bundle savedInstanceState) {
        super
.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        btnSingleThread = (Button) this
.findViewById(R.id.Button01);
        btnDoubleThread = (Button) this
.findViewById(R.id.Button02);
        btnSingleThread.setOnClickListener(new
 ClickEvent());
        btnDoubleThread.setOnClickListener(new
 ClickEvent());
        sfv = (SurfaceView) this
.findViewById(R.id.SurfaceView01);
        sfh = sfv.getHolder();
        sfh.addCallback(new
 MyCallBack());
// 自动运行surfaceCreated以及surfaceChanged
    }

    class
 ClickEvent 
implements
 View.OnClickListener {

        @Override
        public
 
void
 onClick(View v) {

            if
 (v == btnSingleThread) {
                new
 Load_DrawImage(
0
, 
0
).start();
//开一条线程读取并绘图
            } else
 
if
 (v == btnDoubleThread) {
                new
 LoadImage().start();
//开一条线程读取
                new
 DrawImage(imgWidth + 
10
, 
0
).start();
//开一条线程绘图
            }

        }

    }

    class
 MyCallBack 
implements
 SurfaceHolder.Callback {

        @Override
        public
 
void
 surfaceChanged(SurfaceHolder holder, 
int
 format, 
int
 width,
                int
 height) {
            Log.i("Surface:"
, 
"Change"
);

        }

        @Override
        public
 
void
 surfaceCreated(SurfaceHolder holder) {
            Log.i("Surface:"
, 
"Create"
);

            // 用反射机制来获取资源中的图片ID和尺寸
            Field[] fields = R.drawable.class
.getDeclaredFields();
            for
 (Field field : fields) {
                if
 (!
"icon"
.equals(field.getName()))
// 除了icon之外的图片
                {
                    int
 index = 
0
;
                    try
 {
                        index = field.getInt(R.drawable.class
);
                    } catch
 (IllegalArgumentException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } catch
 (IllegalAccessException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    // 保存图片ID
                    imgList.add(index);
                }
            }
            // 取得图像大小
            Bitmap bmImg = BitmapFactory.decodeResource(getResources(),
                    imgList.get(0
));
            imgWidth = bmImg.getWidth();
            imgHeight = bmImg.getHeight();
        }

        @Override
        public
 
void
 surfaceDestroyed(SurfaceHolder holder) {
            Log.i("Surface:"
, 
"Destroy"
);

        }

    }

    /*
     * 读取并显示图片的线程
     */
    class
 Load_DrawImage 
extends
 Thread {
        int
 x, y;
        int
 imgIndex = 
0
;

        public
 Load_DrawImage(
int
 x, 
int
 y) {
            this
.x = x;
            this
.y = y;
        }

        public
 
void
 run() {
            while
 (
true
) {
                Canvas c = sfh.lockCanvas(new
 Rect(
this
.x, 
this
.y, 
this
.x
                        + imgWidth, this
.y + imgHeight));
                Bitmap bmImg = BitmapFactory.decodeResource(getResources(),
                        imgList.get(imgIndex));
                c.drawBitmap(bmImg, this
.x, 
this
.y, 
new
 Paint());
                imgIndex++;
                if
 (imgIndex == imgList.size())
                    imgIndex = 0
;

                sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容
            }
        }
    };

    /*
     * 只负责绘图的线程
     */
    class
 DrawImage 
extends
 Thread {
        int
 x, y;

        public
 DrawImage(
int
 x, 
int
 y) {
            this
.x = x;
            this
.y = y;
        }

        public
 
void
 run() {
            while
 (
true
) {
                if
 (bitmap != 
null
) {
//如果图像有效
                    Canvas c = sfh.lockCanvas(new
 Rect(
this
.x, 
this
.y, 
this
.x
                            + imgWidth, this
.y + imgHeight));

                    c.drawBitmap(bitmap, this
.x, 
this
.y, 
new
 Paint());

                    sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容
                }
            }
        }
    };

    /*
     * 只负责读取图片的线程
     */
    class
 LoadImage 
extends
 Thread {
        int
 imgIndex = 
0
;

        public
 
void
 run() {
            while
 (
true
) {
                bitmap = BitmapFactory.decodeResource(getResources(),
                        imgList.get(imgIndex));
                imgIndex++;
                if
 (imgIndex == imgList.size())
//如果到尽头则重新读取
                    imgIndex = 0
;
            }
        }
    };
}