Android Camera2 實現(xiàn)預(yù)覽功能

更新時間：2018年11月21日 16:19:48 作者：Lightweh

最近在做一些關(guān)于人臉識別的項目，需要用到 Android 相機的預(yù)覽功能。今天小編通過本文給大家分享Android Camera2 實現(xiàn)預(yù)覽功能，感興趣的朋友跟隨小編一起看看吧

1. 概述

最近在做一些關(guān)于人臉識別的項目，需要用到 Android 相機的預(yù)覽功能。網(wǎng)上查閱相關(guān)資料后，發(fā)現(xiàn) Android 5.0 及以后的版本中，原有的 Camera API 已經(jīng)被 Camera2 API 所取代。

全新的 Camera2 在 Camera 的基礎(chǔ)上進行了改造，大幅提升了 Android 系統(tǒng)的拍照功能。它通過以下幾個類與方法來實現(xiàn)相機預(yù)覽時的工作過程：

•CameraManager ：攝像頭管理器，主要用于檢測系統(tǒng)攝像頭、打開系統(tǒng)攝像頭等；
•CameraDevice : 用于描述系統(tǒng)攝像頭，可用于關(guān)閉相機、創(chuàng)建相機會話、發(fā)送拍照請求等；
•CameraCharacteristics ：用于描述攝像頭所支持的各種特性；
•CameraCaptureSession ：當(dāng)程序需要預(yù)覽、拍照時，都需要先通過 CameraCaptureSession 來實現(xiàn)。該會話通過調(diào)用方法 setRepeatingRequest() 實現(xiàn)預(yù)覽；
•CameraRequest ：代表一次捕獲請求，用于描述捕獲圖片的各種參數(shù)設(shè)置；
•CameraRequest.Builder ：負責(zé)生成 CameraRequest 對象。

2. 相機預(yù)覽

下面通過源碼來講解如何使用 Camera2 來實現(xiàn)相機的預(yù)覽功能。

2.1 相機權(quán)限設(shè)置

<uses-permission android:name="android.permission.CAMERA" />

2.2 App 布局

•activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/container"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:background="#000"
 tools:context=".MainActivity">
</FrameLayout>
•fragment_camera.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context=".CameraFragment">
 <com.lightweh.camera2preview.AutoFitTextureView
 android:id="@+id/textureView"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_centerVertical="true"
 android:layout_centerHorizontal="true" />
</RelativeLayout>

2.3 相機自定義View

public class AutoFitTextureView extends TextureView {
 private int mRatioWidth = 0;
 private int mRatioHeight = 0;
 public AutoFitTextureView(Context context) {
 this(context, null);
 }
 public AutoFitTextureView(Context context, AttributeSet attrs) {
 this(context, attrs, 0);
 }
 public AutoFitTextureView(Context context, AttributeSet attrs, int defStyle) {
 super(context, attrs, defStyle);
 }
 public void setAspectRatio(int width, int height) {
 if (width < 0 || height < 0) {
 throw new IllegalArgumentException("Size cannot be negative.");
 }
 mRatioWidth = width;
 mRatioHeight = height;
 requestLayout();
 }
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 super.onMeasure(widthMeasureSpec, heightMeasureSpec);
 int width = MeasureSpec.getSize(widthMeasureSpec);
 int height = MeasureSpec.getSize(heightMeasureSpec);
 if (0 == mRatioWidth || 0 == mRatioHeight) {
 setMeasuredDimension(width, height);
 } else {
 if (width < height * mRatioWidth / mRatioHeight) {
 setMeasuredDimension(width, width * mRatioHeight / mRatioWidth);
 } else {
 setMeasuredDimension(height * mRatioWidth / mRatioHeight, height);
 }
 }
 }
}

2.4 動態(tài)申請相機權(quán)限

public class MainActivity extends AppCompatActivity {
 private static final int REQUEST_PERMISSION = 1;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 if (hasPermission()) {
 if (null == savedInstanceState) {
 setFragment();
 }
 } else {
 requestPermission();
 }
 }
 @Override
 public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
 if (requestCode == REQUEST_PERMISSION) {
 if (grantResults.length == 1 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
 setFragment();
 } else {
 requestPermission();
 }
 } else {
 super.onRequestPermissionsResult(requestCode, permissions, grantResults);
 }
 }
 // 權(quán)限判斷，當(dāng)系統(tǒng)版本大于23時，才有必要判斷是否獲取權(quán)限
 private boolean hasPermission() {
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
 return checkSelfPermission(Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED;
 } else {
 return true;
 }
 }
 // 請求相機權(quán)限
 private void requestPermission() {
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
 if (shouldShowRequestPermissionRationale(Manifest.permission.CAMERA)) {
 Toast.makeText(MainActivity.this, "Camera permission are required for this demo", Toast.LENGTH_LONG).show();
 }
 requestPermissions(new String[]{Manifest.permission.CAMERA}, REQUEST_PERMISSION);
 }
 }
 // 啟動相機Fragment
 private void setFragment() {
 getSupportFragmentManager()
 .beginTransaction()
 .replace(R.id.container, CameraFragment.newInstance())
 .commitNowAllowingStateLoss();
 }
}

2.5 開啟相機預(yù)覽

首先，在onResume()中，我們需要開啟一個 HandlerThread，然后利用該線程的 Looper 對象構(gòu)建一個 Handler 用于相機回調(diào)。

@Override
public void onResume() {
 super.onResume();
 startBackgroundThread();

 // When the screen is turned off and turned back on, the SurfaceTexture is 
 // already available, and "onSurfaceTextureAvailable" will not be called. In 
 // that case, we can open a camera and start preview from here (otherwise, we 
 // wait until the surface is ready in the SurfaceTextureListener).
 if (mTextureView.isAvailable()) {
 openCamera(mTextureView.getWidth(), mTextureView.getHeight());
 } else {
 mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);
 }
}
private void startBackgroundThread() {
 mBackgroundThread = new HandlerThread("CameraBackground");
 mBackgroundThread.start();
 mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
}

同時，在 onPause() 中有對應(yīng)的 HandlerThread 關(guān)閉方法。

當(dāng)屏幕關(guān)閉后重新開啟，SurfaceTexture 已經(jīng)就緒，此時不會觸發(fā) onSurfaceTextureAvailable 回調(diào)。因此，我們判斷 mTextureView 如果可用，則直接打開相機，否則等待 SurfaceTexture 回調(diào)就緒后再開啟相機。

private void openCamera(int width, int height) {
 if (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.CAMERA)
 != PackageManager.PERMISSION_GRANTED) {
 return;
 }
 setUpCameraOutputs(width, height);
 configureTransform(width, height);
 Activity activity = getActivity();
 CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);
 try {
 if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {
 throw new RuntimeException("Time out waiting to lock camera opening.");
 }
 manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);
 } catch (CameraAccessException e) {
 e.printStackTrace();
 } catch (InterruptedException e) {
 throw new RuntimeException("Interrupted while trying to lock camera opening.", e);
 }
}

開啟相機時，我們首先判斷是否具備相機權(quán)限，然后調(diào)用 setUpCameraOutputs 函數(shù)對相機參數(shù)進行設(shè)置（包括指定攝像頭、相機預(yù)覽方向以及預(yù)覽尺寸的設(shè)定等），接下來調(diào)用 configureTransform 函數(shù)對預(yù)覽圖片的大小和方向進行調(diào)整，最后獲取 CameraManager 對象開啟相機。因為相機有可能會被其他進程同時訪問，所以在開啟相機時需要加鎖。

private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {
 @Override
 public void onOpened(@NonNull CameraDevice cameraDevice) {
 mCameraOpenCloseLock.release();
 mCameraDevice = cameraDevice;
 createCameraPreviewSession();
 }
 @Override
 public void onDisconnected(@NonNull CameraDevice cameraDevice) {
 mCameraOpenCloseLock.release();
 cameraDevice.close();
 mCameraDevice = null;
 }
 @Override
 public void onError(@NonNull CameraDevice cameraDevice, int error) {
 mCameraOpenCloseLock.release();
 cameraDevice.close();
 mCameraDevice = null;
 Activity activity = getActivity();
 if (null != activity) {
 activity.finish();
 }
 }
};

相機開啟時還會指定相機的狀態(tài)變化回調(diào)函數(shù) mStateCallback，如果相機成功開啟，則開始創(chuàng)建相機預(yù)覽會話。

private void createCameraPreviewSession() {
 try {
 // 獲取 texture 實例
 SurfaceTexture texture = mTextureView.getSurfaceTexture();
 assert texture != null;
 // 設(shè)置 TextureView 緩沖區(qū)大小
 texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
 // 獲取 Surface 顯示預(yù)覽數(shù)據(jù)
 Surface surface = new Surface(texture);
 // 構(gòu)建適合相機預(yù)覽的請求
 mPreviewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
 // 設(shè)置 surface 作為預(yù)覽數(shù)據(jù)的顯示界面
 mPreviewRequestBuilder.addTarget(surface);
 // 創(chuàng)建相機捕獲會話用于預(yù)覽
 mCameraDevice.createCaptureSession(Arrays.asList(surface),
 new CameraCaptureSession.StateCallback() {
  @Override
  public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
  // 如果相機關(guān)閉則返回
  if (null == mCameraDevice) {
  return;
  }
  // 如果會話準備好則開啟預(yù)覽
  mCaptureSession = cameraCaptureSession;
  try {
  // 自動對焦
  mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
   CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
  mPreviewRequest = mPreviewRequestBuilder.build();
  // 設(shè)置反復(fù)捕獲數(shù)據(jù)的請求，預(yù)覽界面一直顯示畫面
  mCaptureSession.setRepeatingRequest(mPreviewRequest,
   null, mBackgroundHandler);
  } catch (CameraAccessException e) {
  e.printStackTrace();
  }
  }
  @Override
  public void onConfigureFailed(
  @NonNull CameraCaptureSession cameraCaptureSession) {
  showToast("Failed");
  }
 }, null
 );
 } catch (CameraAccessException e) {
 e.printStackTrace();
 }
}

以上便是 Camera2 API 實現(xiàn)相機預(yù)覽的主要過程。

3. Demo 源碼

Github：Camera2Preview

4. 參考

• https://github.com/googlesamples/android-Camera2Basic

總結(jié)

以上所述是小編給大家介紹的Android Camera2 實現(xiàn)預(yù)覽功能，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復(fù)大家的。在此也非常感謝大家對腳本之家網(wǎng)站的支持！

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