CameraX PreviewView转换为位图而不是文件

dependencies {
    implementation "androidx.camera:camera-core:1.1.0"
    implementation "androidx.camera:camera-camera2:1.1.0"
    implementation "androidx.camera:camera-lifecycle:1.1.0"
    implementation "androidx.camera:camera-view:1.0.0-alpha27"
}

<androidx.camera.view.PreviewView
    android:id="@+id/previewView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

private val previewView: PreviewView by lazy {
    findViewById<PreviewView>(R.id.previewView)
}

private fun startCameraPreview() {
    val previewConfig = PreviewConfig.Builder().build()
    val preview = Preview(previewConfig)

    preview.setOnPreviewOutputUpdateListener { previewOutput ->
        val parent = previewView.parent as ViewGroup
        parent.removeView(previewView)
        parent.addView(previewView, 0)

        previewView.surfaceTexture = previewOutput.surfaceTexture
    }

    CameraX.bindToLifecycle(this, preview)
}

private fun previewToBitmap(): Bitmap? {
    val bitmap = Bitmap.createBitmap(previewView.width, previewView.height, Bitmap.Config.ARGB_8888)
    val surfaceTexture = SurfaceTexture(false)
    surfaceTexture.setDefaultBufferSize(previewView.width, previewView.height)
    val surface = Surface(surfaceTexture)

    val previewConfig = PreviewConfig.Builder().build()
    val preview = Preview(previewConfig)
    preview.setSurfaceProvider { request ->
        try {
            request.provideSurface(surface, Executors.newSingleThreadExecutor(), Consumer { })
        } catch (e: Exception) {
            Log.e(TAG, "Error: ${e.message}")
        }
    }

    CameraX.bindToLifecycle(this, preview)

    surfaceTexture.setOnFrameAvailableListener {
        surfaceTexture.updateTexImage()
        bitmap.copyPixelsFromBuffer(surfaceTexture.getTransformMatrix())
    }

    return bitmap
}