Google自Android4.0出了TextureView，为什么推出呢？就是为了弥补Surfaceview的不足，另外一方面也是为了平衡GlSurfaceView，当然这是本人揣度的。关于TextureView、Surfaceview、SurfaceTexture、GLSurfaceView的关系，待咱家推出GLSurfaceview预览Camera后再专门分析。本文主要介绍使用TextureView预览Camera。
其实关于如何用TextureView预览Camera，官网已经给出了demo，参见这里。另外，链接1链接2也给出了完整的预览Camera的demo，但都是一堆东西染在一块。本文就利用前文搭建的一个轻量级的Camera框架来快速替换掉Surfaceview。因为用Surfaceview预览的话传一个SurfaceHolder进去，用Textureview预览的话需要传进去一个SurfaceTexture。其他的Camera流程不变。
一、新建CameraTextureView类继承TextureView，并实现TextureView.SurfaceTextureListener接口。实现这个接口就像实现SurfaceHolder.Callback，最主要的目的是在SurfaceTexture准备好后能够知道，也即onSurfaceTextureAvailable这个函数。
CameraTextureView.java
1 <span style="font-family:Comic Sans MS;font-size:18px;">packageorg.yanzi.camera.preview; 2 3 importorg.yanzi.camera.CameraInterface; 4 5 importandroid.content.Context; 6 importandroid.graphics.PixelFormat; 7 importandroid.graphics.SurfaceTexture; 8 importandroid.util.AttributeSet; 9 importandroid.util.Log; 10 importandroid.view.SurfaceHolder; 11 importandroid.view.SurfaceView; 12 importandroid.view.TextureView; 13 14 public class CameraTextureView extends TextureView implementsTextureView.SurfaceTextureListener { 15 private static final String TAG = "yanzi"; 16 Context mContext; 17 SurfaceTexture mSurface; 18 publicCameraTextureView(Context context, AttributeSet attrs) { 19 super(context, attrs); 20 //TODO Auto-generated constructor stub 21 mContext =context; 22 this.setSurfaceTextureListener(this); 23 } 24 @Override 25 public void onSurfaceTextureAvailable(SurfaceTexture surface, intwidth, 26 intheight) { 27 //TODO Auto-generated method stub 28 Log.i(TAG, "onSurfaceTextureAvailable..."); 29 mSurface =surface; 30 //CameraInterface.getInstance().doStartPreview(surface, 1.33f); 31 } 32 @Override 33 public booleanonSurfaceTextureDestroyed(SurfaceTexture surface) { 34 //TODO Auto-generated method stub 35 Log.i(TAG, "onSurfaceTextureDestroyed..."); 36 CameraInterface.getInstance().doStopCamera(); 37 return true; 38 } 39 @Override 40 public void onSurfaceTextureSizeChanged(SurfaceTexture surface, intwidth, 41 intheight) { 42 //TODO Auto-generated method stub 43 Log.i(TAG, "onSurfaceTextureSizeChanged..."); 44 } 45 @Override 46 public voidonSurfaceTextureUpdated(SurfaceTexture surface) { 47 //TODO Auto-generated method stub 48 Log.i(TAG, "onSurfaceTextureUpdated..."); 49 50 } 51 52 /*让Activity能得到TextureView的SurfaceTexture 53 * @see android.view.TextureView#getSurfaceTexture() 54 */ 55 publicSurfaceTexture _getSurfaceTexture(){ 56 returnmSurface; 57 } 58 } 59 </span>
二、在布局文件里把它加上就行了，因为他的父类就是View，当成一般的View就行
1 <span style="font-family:Comic Sans MS;font-size:18px;"><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 2 xmlns:tools="http://schemas.android.com/tools" 3 android:layout_width="match_parent" 4 android:layout_height="match_parent" 5 tools:context=".CameraActivity" > 6 <FrameLayout 7 android:layout_width="wrap_content" 8 android:layout_height="wrap_content" > 9 <org.yanzi.camera.preview.CameraTextureView 10 android: 11 android:layout_width="0dip" 12 android:layout_height="0dip" /> 13 </FrameLayout> 14 <ImageButton 15 android: 16 android:layout_width="wrap_content" 17 android:layout_height="wrap_content" 18 android:background="@drawable/btn_shutter_background" 19 android:layout_alignParentBottom="true" 20 android:layout_centerHorizontal="true" 21 android:layout_marginBottom="10dip"/> 22 </RelativeLayout> 23 </span>
三、在CameraInterface里，我封装了两个函数:
1 <span style="font-family:Comic Sans MS;font-size:18px;">/**使用Surfaceview开启预览 2 * @paramholder 3 * @parampreviewRate 4 */ 5 public void doStartPreview(SurfaceHolder holder, floatpreviewRate){ 6 Log.i(TAG, "doStartPreview..."); 7 if(isPreviewing){ 8 mCamera.stopPreview(); 9 return; 10 } 11 if(mCamera != null){ 12 try{ 13 mCamera.setPreviewDisplay(holder); 14 } catch(IOException e) { 15 //TODO Auto-generated catch block 16 e.printStackTrace(); 17 } 18 initCamera(previewRate); 19 } 20 21 22 } 23 /**使用TextureView预览Camera 24 * @paramsurface 25 * @parampreviewRate 26 */ 27 public void doStartPreview(SurfaceTexture surface, floatpreviewRate){ 28 Log.i(TAG, "doStartPreview..."); 29 if(isPreviewing){ 30 mCamera.stopPreview(); 31 return; 32 } 33 if(mCamera != null){ 34 try{ 35 mCamera.setPreviewTexture(surface); 36 } catch(IOException e) { 37 //TODO Auto-generated catch block 38 e.printStackTrace(); 39 } 40 initCamera(previewRate); 41 } 42 43 }</span>
分别对应Surfaceview和TextureView预览。可以看到就是传进来的参数不一样，initCamera()的东西都一样。
1 <span style="font-family:Comic Sans MS;font-size:18px;"> private void initCamera(floatpreviewRate){ 2 if(mCamera != null){ 3 4 mParams =mCamera.getParameters(); 5 mParams.setPictureFormat(PixelFormat.JPEG);//设置拍照后存储的图片格式 6 //CamParaUtil.getInstance().printSupportPictureSize(mParams); 7 //CamParaUtil.getInstance().printSupportPreviewSize(mParams); 8 //设置PreviewSize和PictureSize 9 Size pictureSize =CamParaUtil.getInstance().getPropPictureSize( 10 mParams.getSupportedPictureSizes(),previewRate, 800); 11 mParams.setPictureSize(pictureSize.width, pictureSize.height); 12 Size previewSize =CamParaUtil.getInstance().getPropPreviewSize( 13 mParams.getSupportedPreviewSizes(), previewRate, 800); 14 mParams.setPreviewSize(previewSize.width, previewSize.height); 15 16 mCamera.setDisplayOrientation(90); 17 18 //CamParaUtil.getInstance().printSupportFocusMode(mParams); 19 List<String> focusModes =mParams.getSupportedFocusModes(); 20 if(focusModes.contains("continuous-video")){ 21 mParams.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO); 22 } 23 mCamera.setParameters(mParams); 24 mCamera.startPreview();//开启预览 25 26 27 28 isPreviewing = true; 29 mPreviwRate =previewRate; 30 31 mParams = mCamera.getParameters(); //重新get一次 32 Log.i(TAG, "最终设置:PreviewSize--With = " +mParams.getPreviewSize().width 33 + "Height = " +mParams.getPreviewSize().height); 34 Log.i(TAG, "最终设置:PictureSize--With = " +mParams.getPictureSize().width 35 + "Height = " +mParams.getPictureSize().height); 36 } 37 }</span>
四、在Activity里，依旧开一个线程去open Camera:
1 <span style="font-family:Comic Sans MS;font-size:18px;"> Thread openThread = newThread(){ 2 @Override 3 public voidrun() { 4 //TODO Auto-generated method stub 5 CameraInterface.getInstance().doOpenCamera(CameraActivity.this); 6 } 7 }; 8 openThread.start();</span>
在Camera Open完的回调里开预览:
1 <span style="font-family:Comic Sans MS;font-size:18px;">@Override 2 public voidcameraHasOpened() { 3 //TODO Auto-generated method stub 4 SurfaceTexture surface =textureView._getSurfaceTexture(); 5 CameraInterface.getInstance().doStartPreview(surface, previewRate); 6 }</span>
之后就能正常运行了，可以看到与前文Surfaceview预览Camera改动非常之小。
几个注意事项:
1、TextureView是Android 4.0之后加入的，低版本么这个类。TextureView必须工作在开启硬件加速的环境中，也即配置文件里Activity的设置项里：android:hardwareAccelerated="true" 默认的这个属性就是true，因此不用再写了。但如果写成false，可以看到onSurfaceTextureAvailable()这个回调就进不来了，TextureView没有了SurfaceTexture还玩个屁啊。
2、本文demo打开camera并预览的正常log是:
1 <span style="font-family:Comic Sans MS;font-size:18px;"> Line 417: 06-22 12:37:43.682 I/yanzi ( 4917): Camera open.... 2 Line 489: 06-22 12:37:43.758 I/yanzi ( 4917): onSurfaceTextureAvailable... 3 Line 533: 06-22 12:37:43.819 I/yanzi ( 4917): Camera open over.... 4 Line 535: 06-22 12:37:43.819 I/yanzi ( 4917): doStartPreview... 5 Line 537: 06-22 12:37:43.825 I/yanzi ( 4917): PictureSize : w = 1280h = 720 6 Line 539: 06-22 12:37:43.825 I/yanzi ( 4917): PreviewSize:w = 800h = 448 7 Line 555: 06-22 12:37:43.874 I/yanzi ( 4917): 最终设置:PreviewSize--With = 800Height = 448 8 Line 557: 06-22 12:37:43.874 I/yanzi ( 4917): 最终设置:PictureSize--With = 1280Height = 720 9 Line 577: 06-22 12:37:44.106 I/yanzi ( 4917): onSurfaceTextureUpdated... 10 Line 579: 06-22 12:37:44.138 I/yanzi ( 4917): onSurfaceTextureUpdated... 11 Line 583: 06-22 12:37:44.169 I/yanzi ( 4917): onSurfaceTextureUpdated... 12 Line 585: 06-22 12:37:44.220 I/yanzi ( 4917): onSurfaceTextureUpdated... 13 Line 587: 06-22 12:37:44.253 I/yanzi ( 4917): onSurfaceTextureUpdated...</span>
测试手机为中兴Geek，这个手机Camera还是很牛逼的，比手里的华为G700强，就是偶尔会连不上Camera Service，汗。从log可以看到，onSurfaceTextureAvailable这个回调需要一定时间。Camera.open()这句话用了130多ms。但有两点跟Surfaceview不同。第一，TextureView创建过程中没有进到onSurfaceTextureSizeChanged()这个函数里。而SurfaceView在创建过程中，从无到有的时候会进到大小发生变化回调里。第二，onSurfaceTextureUpdated()这个函数每上来一帧数据，这块就进来一次。这是跟Surfaceview相比，最伟大的一个地方。通过这个接口，可以将上来的SurfaceTexture送给OpenGL再去处理。这个回调是实时的，而非用Camera的PreviewCallback这种2次回调的方式。从时间看，基本上每32ms左右上来一帧数据，即每秒30帧，跟本手机的Camera的性能吻合。
3、Camera再执行startPreview时必须保证TextureView的SurfaceTexture上来了，如果因为一些性能原因onSurfaceTextureAvailable()这个回调上不来就开预览，就开不了的。如果发生这种情况，就在onSurfaceTextureAvailable()回调里执行open和startPreview操作，保证万无一失。
4、TextureView本身就有getSurfaceTexture()这个函数，我又封装了个:
1 <span style="font-family:Comic Sans MS;font-size:18px;"> /*让Activity能得到TextureView的SurfaceTexture 2 * @see android.view.TextureView#getSurfaceTexture() 3 */ 4 publicSurfaceTexture _getSurfaceTexture(){ 5 returnmSurface; 6 }</span>
这里的mSurface就是onSurfaceTextureAvailable()回调里传上来的SurfaceTexture。测试证明，开预览时直接调
textureView.getSurfaceTexture(),把它传给Camera：mCamera.setPreviewTexture(surface);也是能正常预览的。但是推荐使用前者，原因见官方上的这段话:
A TextureView's SurfaceTexture can be obtained either by invokinggetSurfaceTexture()or by using aTextureView.SurfaceTextureListener. It is important to know that a SurfaceTexture is available only after the TextureView is attached to a window (andonAttachedToWindow()has been invoked.) It is therefore highly recommended you use a listener to be notified when the SurfaceTexture becomes available.
两种方式获得SurfaceTexture，推荐使用监听。因为只有在TextureView执行完onAttachedToWindow时，它的tSurfaceTexture才上来。
5、SurfaceTexture和TextureView的关系:
Using a TextureView is simple: all you need to do is get itsSurfaceTexture. TheSurfaceTexturecan then be used to render content
如果说TextureView是一幅画的话，那SurfaceTexture就是画布，真正渲染的载体是SurfaceTexture。
6、TextureView可以像一般View执行各种变化，其中有个textureView.setAlpha(1.0f);默认不写这句话，它的alpha也是1.0f,即不透明。如果设成透明0.0f，可以看到啥都看不到了，这一点跟Surfaceview刚好相反。Surfaceview的SurfaceHolder一般要设一下Transparent即透明。但TextureView因为是个view，任何一个png的照片透明度设成0肯定啥都看不到。
7、如果认为预览个Camera这就是TextureView和SurfaceTexture的使命的话，就大错特错了，真正用意是和OpenGL无缝连接。
--------------------本文系原创，转载请注明作者yanzi1225627
版本号:PlayCamera_V2.0.0[2014-6-22].zip
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