Catzie.net Blog

Category: Coding

  • Fix coroutine error: Cannot access database on the main thread // Android Dev Diary

    As I was running a test for a ViewModel function, I encountered the following error:

    [...] Main Thread @coroutine java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time.

    I think it may be caused by the viewModelScope from viewModelScope.launch {} being used by the running test, which may not be accessible during unit tests.

    What I did to fix this error on my unit test was to enable main thread operations in my in-memory Room database test instance. I simply added .allowMainThreadQueries() while building the database instance like so:

    db = Room.inMemoryDatabaseBuilder(
    context, MyRoomDatabase::class.java)
    .allowMainThreadQueries()
    .build()

    Is that the best way to do it? If you got a better suggestion, please comment! I’d love to hear about it.

  • Grant, revoke permissions via Android Studio Terminal (ADB Shell) // Android Dev Diary

    To grant and revoke permissions via Terminal (ADB Shell), run your app on an emulator (I haven’t personally tried on a device but it should work there too).

    Open your Terminal, and then enter the following command:

    adb shell

    Once you’re in, you may use the following syntax for granting or revoking your Android device’s permissions:

    pm grant <package-name> <permission>

    For example, to grant a permission:

    pm grant net.catzie.myapp android.permission.READ_EXTERNAL_STORAGE

    pm grant net.catzie.myapp android.permission.WRITE_EXTERNAL_STORAGE

    And to revoke a permission:

    pm revoke net.catzie.myapp android.permission.READ_EXTERNAL_STORAGE

    pm revoke net.catzie.myapp android.permission.WRITE_EXTERNAL_STORAGE

    Now there’s no need to open the settings screen on your device to play with your Android permissions!

  • Remove room database on app uninstall // Android Dev Diary

    The problem:

    Installing on an Android device that has an old version of an app I’m developing triggers an error:

    Room Database Migration: java.lang.IllegalStateException: Migration didn't properly handle

    Problem persists despite uninstalling the Android app and deleting all app data.

    The solution:

    Very simple. I set allowBackup to false in my AndroidManifest.xml file like so:

    android:allowBackup="false"

    Then I reinstalled the app on the Android device. Error was still triggered on first install, but after one more round of uninstall and reinstall, the error finally went away!

    Side Note / Quick Life Update:

    I have been working on an app, with me as its first user. I tentatively call it “bodymonitor”. It should let me log foods I ate, meds/supplements I took, and body sensations. My brain does not do a good job of monitoring these things so I shall get an app to help me do it. There are existing apps out there that do more or less the same thing, but I want one that caters to my specific needs. Doesn’t hurt to practice Android app development as I make the app, too!

    This weekend I’ll undergo endoscopy again, but this time it’s called a “flexible nasopharyngolaryngoscopy” which will pass through the nose instead of the mouth, to be done under local anesthesia. From the sound of it I don’t expect to be put to sleep, which makes me less anxious, but still anxious. XD It’s gonna be done because of my throat issues.

  • Get Navigation Component destinations in back stack // Android Kotlin Dev Diary

    It’s simple to get the list of destinations that’s currently in your back stack. The only thing you need is a reference to the Navigation Component’s NavController.

    The NavController object has a backQueue property that you can inspect.

    backQueue is an array, and each item’s destination property is what you’re probably looking for!

    To show my current Navigation’s back stack, I use Android Studio’s Debugger, and create watches such as the following:

    Screenshot taking when no frames were available, and thus the texts are red…

    I haven’t literally tried, but logging them programmatically like so should work too:

    for(item in navController.backQueue){
    Log.d("MyNavigationBackStack", "item.destination.displayName: ${item.destination.displayName}")
}
Log.d("MyNavigationBackStack", "navController.backQueue: ${navController.backQueue}")
Log.d("MyNavigationBackStack", "navController.currentBackStackEntry.destination.displayName: ${navController.currentBackStackEntry.destination.displayName}")
Log.d("MyNavigationBackStack", "navController.currentDestination: ${navController.currentDestination}")

    Lemme know if these work, or if you have relevant tips that haven’t been mentioned!

  • A working shared ViewModel between parent and child Fragments //Android Kotlin Dev Diary

    I initially had a problem with the shared ViewModel because the child fragments were creating a new instance from the one held by the parent fragment.

    The ViewModel instantiations below work for me:

    CreateLogFragment.kt (parent)

    CreateLogFoodFragment.kt (child)

    CreateLogNotesFragment.kt (another child)

    by activityViewModels turned things around!

  • Two NavHosts with their own NavControllers and NavGraphs (Navigation Component) //Android Kotlin Dev Diary

    I am trying to make a single-activity app because I’d like to easily share data across screen using, ideally one, or as few as possible ViewModels.

    NavGraph 1

    Host: Layout file of MainActivity

    Destination(s): CreateLogFragment

    NavGraph 2

    Host: Layout file of CreateLogFragment

    Destination(s): CreateLogFoodFragment, CreateLogNotesFragment

    (CreateLogFragment has a BottomNavigationBar that switches between CreateLogFoodFragment and CreateLogNotesFragment)

    The problem was that NavGraph 2 was not getting the correct NavHost and NavController in the CreateLogFragment class.

    And the solution is to retrieve the NavHost in CreateLogFragment like so:

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

        val navHostFragment = childFragmentManager.findFragmentById(R.id.nav_host_create_log) as NavHostFragment
    val navController = navHostFragment.navController

    // Setup Bottom Nav
    val bottomNav: BottomNavigationView = binding.bottomNav
    bottomNav.setupWithNavController(navController)
}

    I’d like to write a full tutorial on how to do this but I’m not sure if I could spare some time. If you’ve been reading my recent posts you’ll notice that I’m not able to put it so much effort in explaining everything. These days I’m always in a hurry to finish stuff. But I’ll still try!!

  • My Fave Android Studio Keyboard Shortcuts

    I have been working on small Android apps, and I just want to share some of my favorite keyboard shortcuts. Some of them were manually added by me.

    Keyboard shortcuts are one of my must-haves for productivity as a programmer, as they let me navigate through code faster, allowing me to focus on creating new modules and solving problems.

    Note: I am using Windows.

    Move between Code, Split, and Design when working on an XML layout file

    Alt + Shift + Left/Right Directional Button
    (If it doesn’t work, click on the layout file’s code/design first, then retry.)

    Run app in test device or emulator

    Shift + F10

    Run app in test device or emulator with Debugger

    Shift + F9

    Navigate between open tabs (no split):

    Navigate between points/screens that you’re viewing:

    Ctrl + Alt + Left/Right

    Show Parameter Info while filling in a function call

    Ctrl + P

    Maximize/minimize editor

    Ctrl + Shift + F12

    Created a custom shortcut for Close All Tabs:

    Ctrl + Alt + Shift + F4

    Created a custom shortcut for Rebuild Project:

    Ctrl + Alt + Shift + F10

    Created a custom shortcut to toggle Distraction-Free Mode on/off:

    Ctrl + Alt + Shift + D

    Created a custom shortcut to toggle ZenMode on/off:

    Ctrl + Alt + Shift + Z

    Other keyboard shortcuts: https://developer.android.com/studio/intro/keyboard-shortcuts