<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:orientation="vertical">

 <TextureView
  android:id="@+id/camera_texture_view"
  android:layout_width="match_parent"
  android:layout_height="match_parent" />

 <ImageButton
  android:id="@+id/capture_ib"
  android:layout_width="60dp"
  android:layout_height="60dp"
  android:layout_marginBottom="10dp"
  android:layout_gravity="bottom|center"
  android:background="@drawable/send_pres"/>
</LinearLayout>

mTextureView.setSurfaceTextureListener(new TextureView.SurfaceTextureListener() {
  @Override
  public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int width, int height) {
  mWidth = width;
  mHeight = height;
  getCameraId();
  openCamera();
  }

  @Override
  public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int i, int i1) {

  }

  @Override
  public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
  return false;
  }

  @Override
  public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {
  }
 });

private CameraDevice.StateCallback mCameraDeviceStateCallback = new CameraDevice.StateCallback() {
 @Override
 public void onOpened(CameraDevice cameraDevice) {
  mCameraDevice = cameraDevice;
  createCameraPreview();
 }

 @Override
 public void onDisconnected(CameraDevice cameraDevice) {
  mCameraDevice.close();
  mCameraDevice = null;
 }

 @Override
 public void onError(CameraDevice cameraDevice, int i) {
  mCameraDevice.close();
  mCameraDevice = null;
 }
 };

private void createCameraPreview() {
 try {
  SurfaceTexture texture = mTextureView.getSurfaceTexture();
  assert texture != null;
  CameraCharacteristics characteristics = mCameraManager.getCameraCharacteristics(mCameraId);
  StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
  int deviceOrientation = getWindowManager().getDefaultDisplay().getOrientation();
  int totalRotation = sensorToDeviceRotation(characteristics, deviceOrientation);
  boolean swapRotation = totalRotation == 90 || totalRotation == 270;
  int rotatedWidth = mWidth;
  int rotatedHeight = mHeight;
  if (swapRotation) {
  rotatedWidth = mHeight;
  rotatedHeight = mWidth;
  }
  mPreviewSize = getPreferredPreviewSize(map.getOutputSizes(SurfaceTexture.class), rotatedWidth, rotatedHeight);
  texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
  Log.e("CameraActivity", "OptimalSize width: " + mPreviewSize.getWidth() + " height: " + mPreviewSize.getHeight());
  ...

private Size getPreferredPreviewSize(Size[] sizes, int width, int height) {
 List<Size> collectorSizes = new ArrayList<>();
 for (Size option : sizes) {
  if (width > height) {
  if (option.getWidth() > width && option.getHeight() > height) {
   collectorSizes.add(option);
  }
  } else {
  if (option.getHeight() > width && option.getWidth() > height) {
   collectorSizes.add(option);
  }
  }
 }
 if (collectorSizes.size() > 0) {
  return Collections.min(collectorSizes, new Comparator<Size>() {
  @Override
  public int compare(Size s1, Size s2) {
   return Long.signum(s1.getWidth() * s1.getHeight() - s2.getWidth() * s2.getHeight());
  }
  });
 }
 return sizes[0];
 }

这里 Sizes 是相机返回的支持的分辨率，从我们传递的参数找找到一个最接近的分辨率。

接下来就要通过 CaptureRequest.Builder以及 CameraCaptureSession.StateCallback 来创建及更新预览界面：

...
Surface surface = new Surface(texture);
  mBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
  // 设置预览对象
  mBuilder.addTarget(surface);
  mCameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
  @Override
  public void onConfigured(CameraCaptureSession cameraCaptureSession) {
   if (null == mCameraDevice) {
   return;
   }
   mSession = cameraCaptureSession;
   mBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
   try {
   // 不停地将捕捉的画面更新到 TextureView
   mSession.setRepeatingRequest(mBuilder.build(), mSessionCaptureCallback, mBackgroundHandler);
   } catch (CameraAccessException e) {
   e.printStackTrace();
   }
  }
  @Override
  public void onConfigureFailed(CameraCaptureSession cameraCaptureSession) {
   Toast.makeText(CameraActivity.this, "Camera configuration change", Toast.LENGTH_SHORT).show();
  }
  }, null);
 } catch (CameraAccessException e) {
  e.printStackTrace();
 }