Android应用开发基础篇(8)-----SurfaceView

一、概述

      SurfaceView也是一个用来画图的部件,不过由于它的效率比较高,因此一般多用在游戏编程中,在摄像头编程中也会用到,还有它和View比较大的不同是它可以在非UI线程里画图。下面的实现中会提到使用SurfaceView来画图需要注意的几个地方。


二、要求

     会使用SurfaceView来画图。


三、实现

     新建工程MySurface,修改/res/layout/main.xml文件,在里面添加一个Button和一个SurfaceView,完整的main.xml文件如下:

 1 <?xml version="1.0" encoding="utf-8"?>
2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
3 android:layout_width="fill_parent"
4 android:layout_height="fill_parent"
5 android:orientation="vertical" >
6
7
8 <Button
9 android:id="@+id/button"
10 android:layout_width="fill_parent"
11 android:layout_height="wrap_content"
12 android:text="画线"
13 />
14
15 <SurfaceView
16 android:id="@+id/surface"
17 android:layout_width="fill_parent"
18 android:layout_height="fill_parent"
19 />
20
21 </LinearLayout>

修改MySurfaceActivity.java文件,主要实现Button的监听和SurfaceHolder.Callback的接口,完整的内容如下:

 

 1 package com.nan.surface;
2
3
4 import android.app.Activity;
5 import android.graphics.Canvas;
6 import android.graphics.Color;
7 import android.graphics.Paint;
8 import android.graphics.Rect;
9 import android.os.Bundle;
10 import android.view.SurfaceHolder;
11 import android.view.SurfaceView;
12 import android.view.View;
13 import android.widget.Button;
14
15
16 public class MySurfaceActivity extends Activity
17 {
18 private int OldX = 0;
19 private int OldY = 0;
20 private Button mButton = null;
21 private SurfaceView mSurfaceView = null;
22 private SurfaceHolder mSurfaceHolder = null;
23 private Paint mPaint = null;
24
25 @Override
26 public void onCreate(Bundle savedInstanceState)
27 {
28 super.onCreate(savedInstanceState);
29 setContentView(R.layout.main);
30
31 mButton = (Button)findViewById(R.id.button);
32 mSurfaceView = (SurfaceView)findViewById(R.id.surface);
33 mSurfaceHolder = mSurfaceView.getHolder();
34 mSurfaceHolder.addCallback(new MyHolder());
35
36 mPaint = new Paint();
37 //画笔的颜色
38 mPaint.setColor(Color.RED);
39 //画笔的粗细
40 mPaint.setStrokeWidth(10.0f);
41 //按钮监听
42 mButton.setOnClickListener(new View.OnClickListener()
43 {
44
45 public void onClick(View v)
46 {
47 // TODO Auto-generated method stub
48 //锁定整个SurfaceView
49 Canvas mCanvas = mSurfaceHolder.lockCanvas();
50 mCanvas.drawLine(OldX, OldY, OldX+10, OldY+10, mPaint);
51 //横坐标增加
52 OldX = OldX + 10;
53 //纵坐标增加
54 OldY = OldY + 10;
55 // 绘制完成,释放画布,提交修改
56 mSurfaceHolder.unlockCanvasAndPost(mCanvas);
57 //重新锁一次
58 //mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));
59 //mSurfaceHolder.unlockCanvasAndPost(mCanvas);
60 }
61 });
62 }
63
64 //定义一个类,实现Callback接口
65 public class MyHolder implements SurfaceHolder.Callback
66 {
67
68 public void surfaceChanged(SurfaceHolder holder, int format, int width,
69 int height)
70 {
71 // TODO Auto-generated method stub
72 //add your code
73 }
74
75 public void surfaceCreated(SurfaceHolder holder)
76 {
77 // TODO Auto-generated method stub
78 //add your code
79 }
80
81 public void surfaceDestroyed(SurfaceHolder holder)
82 {
83 // TODO Auto-generated method stub
84 //add your code
85 }
86
87 }
88
89 }

此时运行该程序,并点击几下“画线”按钮,效果如下所示:

Android应用开发基础篇(8)-----SurfaceView

可以看到,画出来的线是断断续续的,把上面程序的第58,59行的注释去掉,再运行一次,效果如下:

 

Android应用开发基础篇(8)-----SurfaceView

可以看到,线已经没有断开的现象了。

还有一点需要注意的是,如果希望程序在后台运行时还能画图且不报程序出错的问题,就要修改成以下这样的形式:

 

 1                 //锁定整个SurfaceView
2 Canvas mCanvas = mSurfaceHolder.lockCanvas();
3 try
4 {
5 if(mCanvas!=null)
6 {
7 mCanvas.drawLine(OldX, OldY, OldX+10, OldY+10, mPaint);
8 //横坐标增加
9 OldX = OldX + 10;
10 //纵坐标增加
11 OldY = OldY + 10;
12 //绘制完成,释放画布,提交修改
13 mSurfaceHolder.unlockCanvasAndPost(mCanvas);
14 }
15 }
16 catch(Exception e)
17 {
18 e.printStackTrace();
19 }
20 finally
21 {
22 if(mCanvas!=null)
23 {
24 //重新锁一次
25 mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));
26 mSurfaceHolder.unlockCanvasAndPost(mCanvas);
27 }
28 }

再运行,效果同第2幅图的一样。



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