Update Object type LiveData with Databinding

Question

I want to update views via databinding with livedata. Lets have a look at the scenario.

Data Class

data class Movie(var name: String = "", var createdAt: String = "")

ViewModel

class MyViewModel: ViewModel(){
   var pageTitle: MutableLiveData<String>()
   var movie: MutableLiveData<Movie>()

   fun changeTitleAndMovieName()
       pageTitle.value = "Title Changed"
       movie.value.name = "Movie Name Changed"
   } 
}

XML

<layout>
    ...
    <TextView
        ...
        android:text="@{`Title: `+viewmodel.pageTitle `Name: `+viewmodel.movie.name}"/>

    <Button
        ...
        android:onClick="@{() -> viewmodel.changeTitleAndMovieName()}"/>

</layout>

What I want to do?

When the button is pressed, the title and the name of movie should change and reflect to the view.

What is happening now?

Only page title is changing because of String type LiveData.
Movie name is NOT being reflected in the view because of Movie type LiveData and I am changing the property of Movie type LiveData's property.

Is there any way to update Movie type LiveData to the view when any property is changed of the Movie.

I dont want to re-assign the object to the livedata e.g. viewmodel.movie.value = Movie(...)

"I dont want to re-assign the object to the livedata" <- this is the only way to update livedata. If `MutableLiveData.setValue()` is not called, then observers will not be notified. — Sanlok Lee, Jun 24 '19 at 20:48
@SanlokLee see my answer below. Btw Thanks for your appreciated comment on my question. — Amir Raza, Jun 25 '19 at 07:50

Amir Raza · Answer 1 · 2019-06-25T07:56:09.750

0

I have got the answer of my question. A hint from Here

The reference link's answer is a bit long change todo. I have got a very simple solution.

Here's what I did:

Just inherit you Data Class with BaseObservable and just call the method notifyChange() after your Object's property change from anywhere.

i.e. Data Class

  data class Movie(var name: String = "", var createdAt: String = "") : BaseObservable()

ViewModel

class MyViewModel: ViewModel(){
   var pageTitle: MutableLiveData<String>()
   var movie: MutableLiveData<Movie>()

   fun changeTitleAndMovieName()
       pageTitle.value = "Title Changed"
       movie.value.name = "Movie Name Changed"

       //here is the megic
       movie.value.notifyChange()
   } 
}

edited Jun 25 '19 at 07:56

answered Jun 25 '19 at 07:45

Amir Raza

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if it works for you that's great. However there are reasons why people wouldn't recommend this. Your view is not observing the `MutableLiveData`, but it is just observing the `BaseObservable` inside the `MutableLiveData`. Whatever observing `MutableLiveData` is still not notified. Your solution is essentially same as without having `LiveData` at all, just put `var movie: Movie` in `ViewModel` and it will still work. – Sanlok Lee Jun 25 '19 at 20:22
Also, wrapping an observable with another observable is an anti-pattern. As I already mentioned in above comment, sometimes inner observable fires notifications, while outer observable does not, and vice versa. – Sanlok Lee Jun 25 '19 at 20:25
So how do you suggest the best way to update/notify views on changing of Object's property while using LiveData. **P.S. Do not re-assign the object.** @SanlokLee – Amir Raza Jun 27 '19 at 16:27
I would recommend re-assigning the object. In fact having a mutable data object in observer pattern is generally not recommended. I suggest changing every attribute in `Movie` to use `val` instead of `var`. – Sanlok Lee Jun 27 '19 at 18:36
If you must use mutable object, then I suggest just exposing the movie name with `movieName: MutableLiveData()` and then manually update your `movie` and `movieName` object. – Sanlok Lee Jun 27 '19 at 18:37

Update Object type LiveData with Databinding

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