如何在 Android 平台上打开“前置摄像头”？

As of Android 2.1, Android only supports a single camera in its SDK. It is likely that this will be added in a future Android release.

public void surfaceCreated(SurfaceHolder holder) {
try {
mCamera = Camera.open();
mCamera.setDisplayOrientation(90);
mCamera.setPreviewDisplay(holder);


Camera.Parameters p = mCamera.getParameters();
p.set("camera-id",2);
mCamera.setParameters(p);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

With the release of Android 2.3 (Gingerbread), you can now use the android.hardware.Camera class to get the number of cameras, information about a specific camera, and get a reference to a specific Camera. Check out the new Camera APIs here.

private Camera openFrontFacingCameraGingerbread() {
int cameraCount = 0;
Camera cam = null;
Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
cameraCount = Camera.getNumberOfCameras();
for (int camIdx = 0; camIdx < cameraCount; camIdx++) {
Camera.getCameraInfo(camIdx, cameraInfo);
if (cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
try {
cam = Camera.open(camIdx);
} catch (RuntimeException e) {
Log.e(TAG, "Camera failed to open: " + e.getLocalizedMessage());
}
}
}


return cam;
}

Add the following permissions in the AndroidManifest.xml file:

<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" android:required="false" />
<uses-feature android:name="android.hardware.camera.front" android:required="false" />

Note: This feature is available in Gingerbread(2.3) and Up Android Version.

Camera camera;
if (Camera.getNumberOfCameras() >= 2) {


//if you want to open front facing camera use this line
camera = Camera.open(CameraInfo.CAMERA_FACING_FRONT);


//if you want to use the back facing camera
camera = Camera.open(CameraInfo.CAMERA_FACING_BACK);
}


try {
camera.setPreviewDisplay("your surface holder here");
camera.startPreview();
} catch (Exception e) {
camera.release();
}

/* This is not the proper way, this is a solution for older devices that run Android 4.0 or older. This can be used for testing purposes, but not recommended for main development. This solution can be considered as a temporary solution only. But this solution has helped many so I don't intend to delete this answer*/

All older answers' methods are deprecated by Google (supposedly because of troubles like this), since API 21 you need to use the Camera 2 API:

This class was deprecated in API level 21. We recommend using the new android.hardware.camera2 API for new applications.

In the newer API you have almost complete power over the Android device camera and documentation explicitly advice to

String[] getCameraIdList()

and then use obtained CameraId to open the camera:

void openCamera(String cameraId, CameraDevice.StateCallback callback, Handler handler)

99% of the frontal cameras have id = "1", and the back camera id = "0" according to this:

Non-removable cameras use integers starting at 0 for their identifiers, while removable cameras have a unique identifier for each individual device, even if they are the same model.

However, this means if device situation is rare like just 1-frontal -camera tablet you need to count how many embedded cameras you have, and place the order of the camera by its importance ("0"). So CAMERA_FACING_FRONT == 1 CAMERA_FACING_BACK == 0, which implies that the back camera is more important than frontal.

I don't know about a uniform method to identify the frontal camera on all Android devices. Simply said, the Android OS inside the device can't really find out which camera is exactly where for some reasons: maybe the only camera hardcoded id is an integer representing its importance or maybe on some devices whichever side you turn will be .. "back".

Documentation: https://developer.android.com/reference/android/hardware/camera2/package-summary.html

Explicit Examples: https://github.com/googlesamples/android-Camera2Basic

For the older API (it is not recommended, because it will not work on modern phones newer Android version and transfer is a pain-in-the-arse). Just use the same Integer CameraID (1) to open frontal camera like in this answer:

cam = Camera.open(1);

If you trust OpenCV to do the camera part:

Inside

    <org.opencv.android.JavaCameraView
../>

use the following for the frontal camera:

        opencv:camera_id="1"

For API 21 (5.0) and later you can use the CameraManager API's

try {
String desiredCameraId = null;
for(String cameraId : mCameraIDsList) {
CameraCharacteristics chars =  mCameraManager.getCameraCharacteristics(cameraId);
List<CameraCharacteristics.Key<?>> keys = chars.getKeys();
try {
if(CameraCharacteristics.LENS_FACING_FRONT == chars.get(CameraCharacteristics.LENS_FACING)) {
// This is the one we want.
desiredCameraId = cameraId;
break;
}
} catch(IllegalArgumentException e) {
// This key not implemented, which is a bit of a pain. Either guess - assume the first one
// is rear, second one is front, or give up.
}
}
}

build.gradle

 dependencies {
compile 'com.google.android.gms:play-services-vision:9.4.0+'
}

Set View

CameraSourcePreview mPreview = (CameraSourcePreview) findViewById(R.id.preview);


GraphicOverlay mGraphicOverlay = (GraphicOverlay) findViewById(R.id.faceOverlay);


CameraSource mCameraSource = new CameraSource.Builder(context, detector)
.setRequestedPreviewSize(640, 480)
.setFacing(CameraSource.CAMERA_FACING_FRONT)
.setRequestedFps(30.0f)
.build();


mPreview.start(mCameraSource, mGraphicOverlay);

To open the back camera:-

val cameraIntent = Intent(MediaStore.ACTION_IMAGE_CAPTURE)
startActivityForResult(cameraIntent, REQUEST_CODE_CAMERA)

To open the front camera:-

val cameraIntent = Intent(MediaStore.ACTION_IMAGE_CAPTURE)
when {
Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP_MR1 && Build.VERSION.SDK_INT < Build.VERSION_CODES.O -> {
cameraIntent.putExtra("android.intent.extras.CAMERA_FACING", CameraCharacteristics.LENS_FACING_FRONT)  // Tested on API 24 Android version 7.0(Samsung S6)
}
Build.VERSION.SDK_INT >= Build.VERSION_CODES.O -> {
cameraIntent.putExtra("android.intent.extras.CAMERA_FACING", CameraCharacteristics.LENS_FACING_FRONT) // Tested on API 27 Android version 8.0(Nexus 6P)
cameraIntent.putExtra("android.intent.extra.USE_FRONT_CAMERA", true)
}
else -> cameraIntent.putExtra("android.intent.extras.CAMERA_FACING", 1)  // Tested API 21 Android version 5.0.1(Samsung S4)
}
startActivityForResult(cameraIntent, REQUEST_CODE_CAMERA)

I could not make it work for API 28 and above. Also, opening the front camera directly is not possible in some devices(depends on the manufacturer).

I found this works nicely.

fun frontCamera(context: Context): Int {
val cameraManager = context.getSystemService(Context.CAMERA_SERVICE) as CameraManager
return cameraManager.cameraIdList
.find { id ->
cameraManager.getCameraCharacteristics(id)[LENS_FACING] == LENS_FACING_FRONT
}?.toInt() ?: 0
}