Camera2 API in Kotlin: Guide

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Mastering the Camera2 API in Kotlin involves several steps and understanding key concepts. The Camera2 API, introduced in Android Lollipop (API level 21), offers advanced control over the camera hardware compared to the older Camera API. Kotlin, being a modern and expressive language, is well-suited for working with Camera2 API. Here’s a step-by-step guide with examples:

1. Check and Request Camera Permissions

Before accessing the camera, ensure that the app has the necessary permissions (android.permission.CAMERA and android.permission.WRITE_EXTERNAL_STORAGE).

Example:

if (ContextCompat.checkSelfPermission(thisContext, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(thisActivity, arrayOf(Manifest.permission.CAMERA), MY_CAMERA_PERMISSION_CODE)
}

2. Accessing the Camera Manager

The CameraManager class is used to detect, characterize, and connect to CameraDevice instances.

Example:

val manager = getSystemService(Context.CAMERA_SERVICE) as CameraManager
try {
    val cameraId = manager.cameraIdList[0]
    val characteristics = manager.getCameraCharacteristics(cameraId)
    // Additional setup and configuration...
} catch (e: CameraAccessException) {
    e.printStackTrace()
}

3. Open the Camera

You need to open the camera device. The CameraDevice.StateCallback is used to receive updates about the state of a camera device.

Example:

manager.openCamera(cameraId, object : CameraDevice.StateCallback() {
    override fun onOpened(camera: CameraDevice) {
        // Camera has been opened, you can start camera preview here
    }
    override fun onDisconnected(camera: CameraDevice) {
        camera.close()
    }
    override fun onError(camera: CameraDevice, error: Int) {
        camera.close()
    }
}, null)

4. Create a Capture Session

A CameraCaptureSession is used for capturing images from the camera.

Example:

val captureRequestBuilder = camera.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW)
captureRequestBuilder.addTarget(surfaceHolder.surface)
camera.createCaptureSession(Arrays.asList(surfaceHolder.surface), object : CameraCaptureSession.StateCallback() {
    override fun onConfigured(session: CameraCaptureSession) {
        // The camera is already closed
        if (camera == null) return
        // When the session is ready, we start displaying the preview.
        cameraCaptureSession = session
        try {
            // Auto focus should be continuous for camera preview.
            captureRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE)
            // Finally, we start displaying the camera preview.
            session.setRepeatingRequest(captureRequestBuilder.build(), null, null)
        } catch (e: CameraAccessException) {
            e.printStackTrace()
        }
    }
    override fun onConfigureFailed(session: CameraCaptureSession) {
        Toast.makeText(thisContext, "Configuration change", Toast.LENGTH_SHORT).show()
    }
}, null)

5. Capture a Photo or Start a Preview

You can now start the camera preview or capture a photo using the CaptureRequest.

Example for Preview:

captureRequestBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO)
cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null)

6. Handling Different Camera States

Implement listeners to handle autofocus, zoom, exposure, and other camera states.

Example:

captureRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER, CameraMetadata.CONTROL_AF_TRIGGER_START)

7. Release the Camera

When done, release the camera resources in your Activity's onPause() or onStop() methods.

Example:

cameraCaptureSession?.close()
cameraCaptureSession = null
cameraDevice?.close()
cameraDevice = null

8. Handling Orientation and Screen Size

Make sure the camera preview is displayed correctly according to the device’s orientation and screen size.

9. Adding Advanced Features

Explore more advanced features like face detection, image effects, manual focus, zoom controls, etc.

Closure

Working with the Camera2 API is complex but offers extensive control over the camera hardware. Remember to test your camera app on multiple devices due to differences in camera hardware and capabilities.

Resources for Further Learning

• Official Android Developer Documentation
• Kotlin language documentation

Remember, practical implementation and testing are crucial in mastering Camera2 API in Kotlin. The above examples provide a basic framework, but the implementation can vary based on specific requirements and device capabilities.

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