Android：实现手机前后摄像头预览双开

效果展示

一.概述

本博文讲解如何实现手机前后两颗摄像头同时预览并显示

我之前博文《OpenGLES：GLSurfaceView实现Android Camera预览》对单颗摄像头预览做过详细讲解，而前后双摄实现原理其实也并不复杂，粗糙点说就是把单摄像头预览流程写两遍。

与之前博文中使用GLSurfaceView实现相机预览不同，这次前后双摄使用TextureView来完成

二.变量定义

2.1 公共变量

//权限
public static final int REQUEST_CAMERA_PERMISSION = 1;private String mCameraId;
private Size mPreviewSize;
public final int mMaxImages = 5;//相机状态信号量
private Semaphore mCameraOpenCloseLock = new Semaphore(1);

2.2 摄像头相关变量

...private TextureView mFrontTextureView;
private CameraCaptureSession mFrontCaptureSession;private TextureView mBackTextureView;
private CameraCaptureSession mBackCaptureSession;...

两个CaptureSession、两个TextureView(也就是同时两个Surface)

三.OpenCamera()

在 onResume() 中先判断 TextureView 状态是否 Available()

• 如果是就 OpenCamera()
• 如果不是就设置 SurfaceTexture 监听，在 onSurfaceTextureAvailable() 监听回调中再OpenCamera()

onResume()代码：

@Override
public void onResume() {super.onResume();if (mBackTextureView.isAvailable()) {openCamera(true, mBackTextureView.getWidth(), mBackTextureView.getHeight());} else {mBackTextureView.setSurfaceTextureListener(mBackSurfaceTextureListener);}if (mFrontTextureView.isAvailable()) {openCamera(false, mFrontTextureView.getWidth(), mFrontTextureView.getHeight());} else {mFrontTextureView.setSurfaceTextureListener(mFrontSurfaceTextureListener);}startBackgroundThread();
}

OpenCamera()时需要判断当前打开的是哪颗摄像头，然后走各自对应的流程

OpenCamera()代码：

private void openCamera(boolean isBack, int width, int height) {...if (isBack) {mCameraId = manager.getCameraIdList()[0];//预览size先写成固定值mPreviewSize = new Size(1440, 1080);mBackImageReader = ImageReader.newInstance(mPreviewSize.getWidth(), mPreviewSize.getHeight(), ImageFormat.YUV_420_888, mMaxImages);mBackImageReader.setOnImageAvailableListener(mOnImageAvailableListenerBack, mBackgroundHandler);Log.v(TAG, "openCamera mCameraId=" + mCameraId);manager.openCamera(mCameraId, mStateCallBack, mBackgroundHandler);} else {mCameraId = manager.getCameraIdList()[1];//预览size先写成固定值mPreviewSize = new Size(1080, 720);mFrontImageReader = ImageReader.newInstance(mPreviewSize.getWidth(), mPreviewSize.getHeight(), ImageFormat.YUV_420_888, mMaxImages);mFrontImageReader.setOnImageAvailableListener(mOnImageAvailableListenerFront, mFrontgroundHandler);Log.v(TAG, "openCamera mCameraId=" + mCameraId);manager.openCamera(mCameraId, mStateCallFront, mFrontgroundHandler);}...}

四.createCaptureSession()

OpenCamera()之后，分别为前后摄创建CaptureSession

private void createCameraPreviewSession(boolean isBack) {try {if (isBack) {SurfaceTexture texture = mBackTextureView.getSurfaceTexture();assert texture != null;texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());ArrayList<Surface> surfaces = new ArrayList<Surface>();Surface surface = new Surface(texture);surfaces.add(surface);surfaces.add(mBackImageReader.getSurface());...mCameraDeviceBack.createCaptureSession(surfaces, mBackStateCallback, mBackgroundHandler);} else {SurfaceTexture texture = mFrontTextureView.getSurfaceTexture();assert texture != null;texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());ArrayList<Surface> surfaces = new ArrayList<Surface>();Surface surface = new Surface(texture);surfaces.add(surface);surfaces.add(mFrontImageReader.getSurface());...mCameraDeviceFront.createCaptureSession(surfaces, mFrontStateCallback, mFrontgroundHandler);}} catch (CameraAccessException e) {e.printStackTrace();}
}

五.setRepeatingRequest()

createCaptureSession()之后，在前后摄各自的状态回调StatCallback中调用setRepeatingRequest()启动预览。

前摄：

CameraCaptureSession.StateCallback mFrontStateCallback = new CameraCaptureSession.StateCallback() {@Overridepublic void onConfigured(CameraCaptureSession session) {Log.v(TAG, "CameraCaptureSession onConfigured");...mFrontCaptureSession = session;try {...mFrontCaptureSession.setRepeatingRequest(mFrontPreviewRequest,mPreviewBackCallback, mBackgroundHandler);} catch (CameraAccessException e) {e.printStackTrace();}}@Overridepublic void onConfigureFailed(CameraCaptureSession session) {Log.v(TAG, "onConfigureFailed");showToast("onConfigureFailed");}
};

后摄：

CameraCaptureSession.StateCallback mBackStateCallback = new CameraCaptureSession.StateCallback() {@Overridepublic void onConfigured(CameraCaptureSession session) {Log.v(TAG, "CameraCaptureSession onConfigured");...mBackCaptureSession = session;try {...mBackCaptureSession.setRepeatingRequest(mBackPreviewRequest,mPreviewFrontCallback, mFrontgroundHandler);} catch (CameraAccessException e) {e.printStackTrace();}}@Overridepublic void onConfigureFailed(CameraCaptureSession session) {Log.v(TAG, "onConfigureFailed");showToast("onConfigureFailed");}
};

六.注意

1.布局优化

本篇博文最开始，展示了两种前后双摄效果

第一种是分屏显示，前后摄预览各占1/2，但是画面有压缩

第二种是重合显示，前后摄预览重合在一起，画面没有压缩，但是有部分区域重叠覆盖

两种不同的显示方式，其实只是两个TextureView在布局文件中不同的配置

(1).第一种是在两个TextureView控件外加了一层LinearLayout控件

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"><LinearLayoutandroid:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"><TextureViewandroid:id="@+id/texture_back"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"/><TextureViewandroid:id="@+id/texture_front"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"/></LinearLayout></androidx.constraintlayout.widget.ConstraintLayout>

(2).第二种去掉了LinearLayout，且在源生TextureView基础上略微封装了一个自定义的AutoFitTextureView，自动适配传入的显示区域宽高

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"><ImageViewandroid:id="@+id/iv_background"android:layout_width="match_parent"android:layout_height="match_parent" /><com.android.cameraapp.UiUtil.AutoFitTextureViewandroid:id="@+id/texture_back"android:layout_width="wrap_content"android:layout_height="wrap_content"tools:ignore="MissingConstraints" /><com.android.cameraapp.UiUtil.AutoFitTextureViewandroid:id="@+id/texture_front"android:layout_width="wrap_content"android:layout_height="wrap_content"tools:ignore="MissingConstraints" /></androidx.constraintlayout.widget.ConstraintLayout>

2.代码优化

如果看到这里，证明你已经跟随博文实现了前后双摄，回过头来看代码，会发现比较简单粗糙，就是博文开始时所述，将单个摄像头预览开启流程重复了一遍。

这样的代码不简洁也不美观，且不易于扩展，可以使用工厂模式将功能代码抽象成一个Camera2Proxy，这一过程就不在此复述了。

七.结束语

前后双摄的实现过程和关键代码讲解到此结束