android TextureView 浅析

最近，在修改Android4.4的原生相机Camera2，很习惯的去寻找SurfaceView，结果任凭我使用grep还是ack，都无法搜索到SurfaceView，最后还是通过代码CameraActivity-->CameraModule-->PhotoUI-->R.layout.photo_module找到，原来是使用了TextureView。不是很了解此控件，百度之，在官方API文档中找到此控件：

 

官方文档大概的意思是：

TextureView可以用来显示内容流。这样一个内容流例如可以视频或者OpenGL的场景。内容流可以来自本应用程序以及其他进程。

Textureview必须在硬件加速开启的窗口中。

与SurfaceView相比，TextureView不会创建一个单独的窗口，这使得它可以像一般的View一样执行一些变换操作，比如移动、动画等等，例如,你可以通过调用myView.setAlpha(0.5f)将TextureView设置成半透明。

使用TextureView很简单：你需要使用的就是SurfaceTexture，SurfaceTexture可以用于呈现内容。

 

下面是我写一个小例子来演示如何渲染相机预览到TextureView，在官方文档例子的基础上稍微改动了一下：

main.xml:

 

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<!--?xml version= 1.0 encoding=utf- 8 ?--> <linearlayout android:layout_height= "fill_parent" android:layout_width= "fill_parent" android:orientation= "horizontal" xmlns:android= "http://schemas.android.com/apk/res/android" >        <framelayout android:id= "@+id/camera_preview" android:layout_height= "fill_parent" android:layout_weight= "1" android:layout_width= "fill_parent" ><button android:id= "@+id/button_capture" android:layout_gravity= "center" android:layout_height= "wrap_content" android:layout_width= "wrap_content" android:text= "Capture" ></button></framelayout></linearlayout>

 

CameraPreview.java:

 

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import java.io.IOException;   import android.annotation.SuppressLint; import android.content.Context; import android.graphics.SurfaceTexture; import android.hardware.Camera; import android.view.TextureView;   @SuppressLint (NewApi) public class CameraPreview extends TextureView implements          TextureView.SurfaceTextureListener {      private Camera mCamera;      private TextureView mTextureView;      public CameraPreview(Context context , Camera camera) {          super (context);          mCamera = camera;          // TODO Auto-generated constructor stub      }          public void onSurfaceTextureAvailable(SurfaceTexture surface, int width,              int height) { //        mCamera = Camera.open();          try {              mCamera.setPreviewTexture(surface);              mCamera.startPreview();          } catch (IOException ioe) {              // Something bad happened          }      }        public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width,              int height) {          // Ignored, Camera does all the work for us      }        public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {          mCamera.stopPreview();          mCamera.release();          return true ;      }        public void onSurfaceTextureUpdated(SurfaceTexture surface) {          // Invoked every time there's a new Camera preview frame      }   }

CameraTest.java:

 

 

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import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date;   import android.annotation.SuppressLint; import android.app.Activity; import android.content.Intent; import android.hardware.Camera; import android.hardware.Camera.PictureCallback; import android.os.Bundle; import android.os.Environment; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.FrameLayout; import android.widget.Toast;   import com.example.mycamera.R.id;   @SuppressLint (NewApi) public class CameraTest extends Activity {      public static final int MEDIA_TYPE_IMAGE = 1 ;      public static final int MEDIA_TYPE_VIDEO = 2 ;      private static final int CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE = 100 ;      private static final int CAPTURE_VIDEO_ACTIVITY_REQUEST_CODE = 200 ;      private Camera mCamera;      private CameraPreview mPreview;      private static final String TAG = ERROR;      private PictureCallback mPicture = new PictureCallback() {          @Override          public void onPictureTaken( byte [] data, Camera camera) {              File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);              if (pictureFile == null ) {                  Log.d(TAG,                          Error creating media file, check storage permissions:                                  + e.getMessage());                  return ;              }              try {                  FileOutputStream fos = new FileOutputStream(pictureFile);                  fos.write(data);                  fos.close();              } catch (FileNotFoundException e) {                  Log.d(TAG, File not found:  + e.getMessage());              } catch (IOException e) {                  Log.d(TAG, Error accessing file:  + e.getMessage());              }          }      };        @Override      protected void onCreate(Bundle savedInstanceState) {          // TODO Auto-generated method stub          super .onCreate(savedInstanceState);          setContentView(R.layout.main);          // 创建Camera实例          mCamera = getCameraInstance();          // 创建Preview view并将其设为activity中的内容          mPreview = new CameraPreview( this , mCamera);          mPreview.setSurfaceTextureListener(mPreview);          //设置浑浊          mPreview.setAlpha( 0 .5f);          FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);          // preview.setAlpha(0.0f);          preview.addView(mPreview);          // 在Capture按钮中加入listener          Button captureButton = (Button) findViewById(id.button_capture);          captureButton.setOnClickListener( new View.OnClickListener() {              @Override              public void onClick(View v) {                  // 从摄像头获取图片                  mCamera.takePicture( null , null , mPicture);              }          });      }        /** 安全获取Camera对象实例的方法 */        public static Camera getCameraInstance() {          Camera c = null ;          try {              c = Camera.open(); // 试图获取Camera实例          }          catch (Exception e) {              // 摄像头不可用（正被占用或不存在）          }          return c; // 不可用则返回null      }              /** 为保存图片或视频创建File */      private static File getOutputMediaFile( int type) {          // 安全起见，在使用前应该          // 用Environment.getExternalStorageState()检查SD卡是否已装入          File mediaStorageDir = new File(                  Environment                          .getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),                  MyCameraApp);          // 如果期望图片在应用程序卸载后还存在、且能被其它应用程序共享，          // 则此保存位置最合适          // 如果不存在的话，则创建存储目录          if (!mediaStorageDir.exists()) {              if (!mediaStorageDir.mkdirs()) {                  Log.d(MyCameraApp, failed to create directory);                  return null ;              }              Log.d(MyCameraApp, failed to create directory);          }          // 创建媒体文件名          String timeStamp = new SimpleDateFormat(yyyyMMdd_HHmmss)                  .format( new Date());          File mediaFile;          if (type == MEDIA_TYPE_IMAGE) {              mediaFile = new File(mediaStorageDir.getPath() + File.separator                      + IMG_ + timeStamp + .jpg);          } else if (type == MEDIA_TYPE_VIDEO) {              mediaFile = new File(mediaStorageDir.getPath() + File.separator                      + VID_ + timeStamp + .mp4);          } else {              return null ;          }          return mediaFile;      }        @Override      protected void onActivityResult( int requestCode, int resultCode, Intent data) {          if (requestCode == CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE) {              if (resultCode == RESULT_OK) {                  // 捕获的图像保存到Intent指定的fileUri                  Toast.makeText( this , Image saved to:   + data.getData(),                          Toast.LENGTH_LONG).show();              } else if (resultCode == RESULT_CANCELED) {                  // 用户取消了图像捕获              } else {                  // 图像捕获失败，提示用户              }          }            if (requestCode == CAPTURE_VIDEO_ACTIVITY_REQUEST_CODE) {              if (resultCode == RESULT_OK) {                  // 捕获的视频保存到Intent指定的fileUri                  Toast.makeText( this , Video saved to:   + data.getData(),                          Toast.LENGTH_LONG).show();              } else if (resultCode == RESULT_CANCELED) {                  // 用户取消了视频捕获              } else {                  // 视频捕获失败，提示用户              }          }      }        @Override      protected void onPause() {          super .onPause();          releaseCamera(); // 在暂停事件中立即释放摄像头      }        private void releaseCamera() {          if (mCamera != null ) {              mCamera.release(); // 为其它应用释放摄像头              mCamera = null ;          }      }   }