<h2>前言</h2>    <p>笔者因为项目需要自定义相机，所以了解了一下 Android 关于 camera 这块的 API。Android SDK 21（LOLLIPOP） 开始已经弃用了之前的 Camera 类，提供了 camera2 相关 API，目前网上关于 camera2 API 介绍的资料比较少，笔者搜集网上资料，结合自己的实践，在这里做一个总结。</p>    <h2>流程</h2>    <p>因为 camera2 提供的接口比较多，虽然很灵活，但是也增加了使用的复杂度。首先来大致了解一下调用 camera2 的流程，方便我们理清思路。</p>    <p style="text-align:center"><img src="https://simg.open-open.com/show/8cf9cbe8916c9023a267906404127e11.png"></p>    <p>要显示相机捕捉的画面，只需要三步：初始化相机，预览，更新预览。也就是上图中左侧的部分。要实现这三步，需要用到的主要接口类和它们的作用步骤如上图右侧部分所示。下面就用代码来详解一下。</p>    <h2>案例</h2>    <p>首先创建一个相机界面：</p>    <p>activity_camera.xml</p>    <pre>  <code class="language-java"><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></code></pre>    <p>界面很简单，只有一个 TexureView 和一个按钮。</p>    <p>接下来在 Activity 中初始化并显示相机捕捉的画面。</p>    <p>首先要解决的一个问题就是画面拉伸的问题。</p>    <p>要解决这个问题，首先要从 TextureView 下手。</p>    <p>CameraActivity.java</p>    <pre>  <code class="language-java">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) {                }          });</code></pre>    <p>在 onSurfaceTextureAvailable 中初始化相机。通过 CameraManager 对象 openCamera，这正是流程图中 Init 步骤中的第一步。openCamera 有三个参数，第一个是 String 类型的 cameraId，第二个是 CameraDevice.StateCallback，第三个是 Handler。这里我们要声明一个 StateCallback：</p>    <pre>  <code class="language-java">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;          }      };</code></pre>    <p>可以看到，在 camera 准备完毕之后就可以创建预览界面了。解决画面拉伸的问题就是要为预览界面设置一个合适比例的 SurfaceTexture buffer size。</p>    <pre>  <code class="language-java">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());              ...</code></pre>    <p>这里根据当前设备及传感器的旋转角度来判断是否交换宽高值，然后通过 CameraCharacteristics 来得到最适合当前大小比例的宽高，然后把这个宽高设置给 SurfaceTexture 。</p>    <pre>  <code class="language-java">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];      }</code></pre>    <p>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。</p>    <p>接下来就要通过 CaptureRequest.Builder以及 CameraCaptureSession.StateCallback 来创建及更新预览界面：</p>    <pre>  <code class="language-java">...  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();          }</code></pre>    <h2> </h2>    <p>来自：http://www.cnblogs.com/jpush88/p/6670724.html</p>    <p> </p>