android_settings_permission_observation.kt

import android.app.AppOpsManager
import android.app.AppOpsManager.OnOpChangedListener
import android.content.Context
import android.os.Build
import android.os.Process
import androidx.core.content.getSystemService
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.channels.awaitClose
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.callbackFlow
import kotlinx.coroutines.flow.conflate
import kotlinx.coroutines.flow.distinctUntilChanged
import kotlinx.coroutines.flow.flowOn
import kotlinx.coroutines.flow.map
import kotlinx.coroutines.flow.onStart

/**
 * Credits: [Detecting when the usage access changes](https://stackoverflow.com/a/54838247).
 * Observe the status of a permission.
 *
 * @param targetOp The target op to observe. See [AppOpsManager].
 */
fun Context.observePermissionStatus(targetOp: String): Flow<Boolean> {
  val appOpsManager = getSystemService<AppOpsManager>()!!

  return callbackFlow<Unit> {
    val usageOpListener = OnOpChangedListener { op: String?, packageName: String? ->
      // Android sometimes sets packageName to null
      if (packageName == null || this@observePermissionStatus.packageName == packageName) {
        // Android actually notifies us of changes to ops other than the one we registered for, so filtering them out
        if (targetOp == op) {
          // We're not in main thread, so post to main thread queue
          trySend(Unit)
        }
      }
    }

    appOpsManager.startWatchingMode(targetOp, packageName, usageOpListener)
    awaitClose { appOpsManager.stopWatchingMode(usageOpListener) }
  }
    .conflate()
    .onStart { emit(Unit) }
    .map {
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
        appOpsManager.unsafeCheckOpNoThrow(targetOp, Process.myUid(), packageName) == AppOpsManager.MODE_ALLOWED
      } else {
        @Suppress("DEPRECATION")
        appOpsManager.checkOpNoThrow(targetOp, Process.myUid(), packageName) == AppOpsManager.MODE_ALLOWED
      }
    }
    .flowOn(Dispatchers.Main)
    .distinctUntilChanged()
}

class MainActivity : ComponentActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    setContent {
      ComposeSlideTheme {
        // A surface container using the 'background' color from the theme
        Surface(modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background) {
          Greeting("Android")
        }
      }
    }

    observePermissionStatus(targetOp = AppOpsManager.OPSTR_SYSTEM_ALERT_WINDOW)
      .onEach { Log.d("MainActivity", "-->: $it") }
      .launchIn(lifecycleScope)

    val intent = Intent(
      Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
      Uri.parse("package:$packageName")
    ).apply {
      addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
    }
    startActivity(intent)
  }
}