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junior
Asked: 2022-06-06 08:06:49 +0800 CST 2022-06-06 08:06:49 +0800 CST

How to send the position when observing an array in a Viewmodel?

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I have implemented the entire structure of an MVVM architecture with jetpack but I don't know how to observe each position of an array, to observe a property it is only done like this:

var normales=""
    @Bindable get
    set(v){
        field=v
        notifyPropertyChanged(BR.normales)
    }

With an array of type map<String, String> I would need the index because it would not be convenient to go through the entire array to know which change, to observe the change I have it like this:

inner class ArrayWrapper(vararg pairs: Pair<String, String>) :LinkedHashMap<String, String>(pairs.size) {
    override fun put(key: String, value: String): String {
        notifyPropertyChanged(BR.calibre)
        return super.put(key,value)!!
    }
}

var calibre= ArrayWrapper("C2" to "", "C3" to "", "C4" to "", "C5" to "", "C6+" to "")
    @Bindable get

This works very well but currently I have the observer like this:

viewModel.addOnPropertyChangedCallback(object: Observable.OnPropertyChangedCallback(){
        override fun onPropertyChanged(sender: Observable?, propertyId: Int) {
            when(propertyId){
                BR.calibre-> Log.i("cambio calibres","asi "+ viewModel.calibre.toString())
                else-> Log.i("hola","notificaron")
            }
        }
    })

and the output gives me:

I/cambio calibres: asi {C2=56, C3=4, C4=, C5=, C6+=}
I/cambio calibres: asi {C2=56, C3=4, C4=, C5=5, C6+=}

So how can I know which index changed?

android-studio

1 Answers

  1. Best Answer

    Before I answer, I'm going to show you how to improve the way you create observables because you're writing a lot of unnecessary code. Your programming sense should be able to detect that your solution is too complex for such a simple problem.

    Unnecessary things you are doing:

    • create aArrayWrapper
    • notify every time the value of a property changes
    • add the annotation@Bindable
    • implement the interfaceObservable

    So what is the correct way to implement it? The answer is in the documentation

    There are multiple ways to implement observability. You can use observable classes, observable fields, or, the preferred way, LiveData.

    All you have to do is wrap LiveDatawhatever object you want to observe in a

    val calibre = MutableLiveData(
    mapOf(
        "C2" to "",
        "C3" to "",
        "C4" to "",
        "C5" to "",
        "C6+" to ""
    )
)

    Now the solution to know which index changed is to add another observable property

    class ExampleViewModel : ViewModel() {
    
    val calibre = MutableLiveData(
        mapOf(
            "C2" to "",
            "C3" to "",
            "C4" to "",
            "C5" to "",
            "C6+" to ""
        )
    )
    val keyChanged = MutableLiveData<String>()
    
    fun updateCalibre(key: String, value: String) {
        calibre.value?.let { currentMap ->
            calibre.value = currentMap + Pair(key, value) //concat array
            keyChanged.value = key
        }
    }
    
}

    Then in your activity you see it like this

    viewModel.calibre.observe(this) { calibres ->
    Log.i("cambio calibres", "asi $calibres")
}
viewModel.keyChanged.observe(this) { indice ->
    Log.i("cambio calibres", "cambió índice $indice")
}
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