QR Scanning — Programuoki

Code

Create ScanScreen.kt — CameraX + ML Kit

In the code column — ScanScreen.kt. Three parts: (1) request the camera permission at runtime, (2) a CameraX preview via AndroidView, (3) an MlKitAnalyzer that returns the scanned QR and calls onTableScanned(value) — once (the scanned flag). (The real screen also has a decorative instruction overlay — omitted so the mechanics stand out.)

Three environment pieces are needed.

1. Permission and deps in AndroidManifest.xml + build.gradle.kts:

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

implementation(libs.androidx.camera.view)
implementation(libs.androidx.camera.mlkit.vision)
implementation(libs.mlkit.barcode.scanning)

2. Navigation — a new Screen.Scan (lesson-4 Nav3), and once a table is scanned we go to the menu:

@Serializable data object Scan : Screen()

entry<Screen.Scan> {
    ScanScreen(onTableScanned = { raw ->
        tableSession.setTable(raw)
        backStack.add(Screen.Menu)     // scanned → to the menu
    })
}

3. Start at scanning. A logged-in (but not-yet-scanned) user can be routed to Scan — so an order always has a table.

Verify. Generate a test QR with the text table:7 (any online QR generator), and run the app on a real phone (an emulator camera reads QRs poorly):

1. Open Scan → a dialog asks for the camera permission → allow.
2. Point the camera at the QR → the screen jumps to the menu, TableSession = "7".
3. Order → POST /orders with "table_number": "7".

Gotcha (permission). The camera is a runtime permission. If you only put it in the manifest and DON'T request it via rememberLauncherForActivityResult, checkSelfPermission returns DENIED and the preview is black — no error, no dialog, just darkness. That's why ScanScreen checks the permission first and, if it's missing, a LaunchedEffect launches the dialog. Remember: manifest + runtime request — both are required.

ScanScreen.kt CREATE

Create this file in app/src/main/java/eif/viko/lt/pica/feature/scan/presentation/

package eif.viko.lt.pica.feature.scan.presentation

import android.Manifest
import android.content.pm.PackageManager
import androidx.activity.compose.rememberLauncherForActivityResult
import androidx.activity.result.contract.ActivityResultContracts
import androidx.camera.mlkit.vision.MlKitAnalyzer
import androidx.camera.view.CameraController.COORDINATE_SYSTEM_VIEW_REFERENCED
import androidx.camera.view.LifecycleCameraController
import androidx.camera.view.PreviewView
import androidx.compose.foundation.layout.*
import androidx.compose.material3.Text
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.viewinterop.AndroidView
import androidx.core.content.ContextCompat
import androidx.lifecycle.compose.LocalLifecycleOwner
import com.google.mlkit.vision.barcode.BarcodeScannerOptions
import com.google.mlkit.vision.barcode.BarcodeScanning
import com.google.mlkit.vision.barcode.common.Barcode

@Composable
fun ScanScreen(
    onTableScanned: (String) -> Unit
) {
    val context = LocalContext.current
    val lifecycleOwner = LocalLifecycleOwner.current

    // 1) CAMERA is a RUNTIME permission — declaring it in the manifest is not enough.
    var hasPermission by remember {
        mutableStateOf(
            ContextCompat.checkSelfPermission(context, Manifest.permission.CAMERA)
                    == PackageManager.PERMISSION_GRANTED
        )
    }
    val permissionLauncher = rememberLauncherForActivityResult(
        ActivityResultContracts.RequestPermission()
    ) { granted -> hasPermission = granted }

    LaunchedEffect(Unit) {
        if (!hasPermission) permissionLauncher.launch(Manifest.permission.CAMERA)
    }

    if (!hasPermission) {
        Box(Modifier.fillMaxSize(), Alignment.Center) {
            Text("Camera permission needed to scan the table QR")
        }
        return
    }

    // 2) CameraX preview + ML Kit barcode analyzer, embedded in Compose via AndroidView.
    val cameraController = remember { LifecycleCameraController(context) }
    var scanned by remember { mutableStateOf(false) }

    AndroidView(
        modifier = Modifier.fillMaxSize(),
        factory = { ctx ->
            val previewView = PreviewView(ctx)
            val options = BarcodeScannerOptions.Builder()
                .setBarcodeFormats(Barcode.FORMAT_QR_CODE)   // QR only — faster
                .build()
            val scanner = BarcodeScanning.getClient(options)

            cameraController.setImageAnalysisAnalyzer(
                ContextCompat.getMainExecutor(ctx),
                MlKitAnalyzer(
                    listOf(scanner),
                    COORDINATE_SYSTEM_VIEW_REFERENCED,
                    ContextCompat.getMainExecutor(ctx)
                ) { result ->
                    val barcode = result?.getValue(scanner)?.firstOrNull()
                    val value = barcode?.rawValue
                    if (value != null && !scanned) {
                        scanned = true            // 3) fire once, then stop
                        onTableScanned(value)     // → TableSession.setTable(value)
                    }
                }
            )
            cameraController.bindToLifecycle(lifecycleOwner)
            previewView.controller = cameraController
            previewView
        }
    )
}