Android：实现手机前后摄像头预览同开

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() {
	@Override
	public void onConfigured(CameraCaptureSession session) {
		Log.v(TAG, "CameraCaptureSession onConfigured");

        ...

		mFrontCaptureSession = session;
		try {
		
		    ...
			
			mFrontCaptureSession.setRepeatingRequest(mFrontPreviewRequest,
					mPreviewBackCallback, mBackgroundHandler);
		} catch (CameraAccessException e) {
			e.printStackTrace();
		}
	}

	@Override
	public void onConfigureFailed(CameraCaptureSession session) {
		Log.v(TAG, "onConfigureFailed");
		showToast("onConfigureFailed");
	}
};

后摄：

CameraCaptureSession.StateCallback mBackStateCallback = new CameraCaptureSession.StateCallback() {

	@Override
	public void onConfigured(CameraCaptureSession session) {
		Log.v(TAG, "CameraCaptureSession onConfigured");
        
		...
          
		mBackCaptureSession = session;
		try {
		
		    ...
			
			mBackCaptureSession.setRepeatingRequest(mBackPreviewRequest,
					mPreviewFrontCallback, mFrontgroundHandler);
		} catch (CameraAccessException e) {
			e.printStackTrace();
		}
	}

	@Override
	public 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">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <TextureView
            android:id="@+id/texture_back"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"/>

        <TextureView
            android: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">

    <ImageView
        android:id="@+id/iv_background"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <com.android.cameraapp.UiUtil.AutoFitTextureView
        android:id="@+id/texture_back"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:ignore="MissingConstraints" />

    <com.android.cameraapp.UiUtil.AutoFitTextureView
        android: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