android-jetpack-composeviewmodelandroid-viewmodel

How do I create an instance of a view model with input parameters

I have the following view model which is taking a Context input parameter.

class MyViewModel(val context: Context): ViewModel() {

}

When my app tries to create an instance of this view model, I get an error saying an instance cannot be created. This is clearly because I've not given it the input context parameter, but how do I do this?

val myViewModel: MyViewModel = viewModel()
Solution

  • Disclaimer:

    Please be aware that using a Context in a ViewModel is discouraged.

    Documentation Hint

    Answer:

    You can use an AndroidViewModel for this. It is basically a ViewModel that holds a reference to the Application and thus also to the Context. You can declare it as follows:

    class MyViewModel(application: Application) : AndroidViewModel(application) {
    val someString by mutableStateOf("HELLO")

    // below function needs a Context to fetch a String resource
    fun getResourceString(): String {
        return getApplication<Application>().getString(R.string.world)
    }
}

    Then, in your Composable, you can invoke it like this:

    import androidx.lifecycle.viewmodel.compose.viewModel

@Composable
fun AndroidViewModelSample(myViewModel: MyViewModel = viewModel()) {
    Column {
        Text(text = myViewModel.someString)
        Text(text = myViewModel.getResourceString())
    }
}

    Make sure that you have the needed dependencies added to your build.gradle file:

    implementation 'androidx.lifecycle:lifecycle-viewmodel-compose:2.6.1'

    Output:

    Screenshot