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How can I share LiveData between multiple ViewModels?

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1

I've tried extracting the value into a base class and having the ViewModels extend it. When I do that, however, the Observer isn't sticking to the LiveData. For instance, when I have a parent class with LiveData:

class Base : ViewModel() 
 private val _ data = MutableLiveData()
 val data: LiveData = _data

 fun someEvent(foo: Foo) // update _data 


class Derived : Base()

class Derived1 : Base()

Then get one of those ViewModels and observe data:

class Frag : Fragment 
 onViewCreated() 
 // get Derived, ViewModelProviders.of ...etc
 derived.data.observe // Doesn't observe changes 
 

Calling Base.someEvent(foo) doesn't notify the LiveData in the Fragment.

I want to avoid getting a reference to both subclasses and invoking someEvent on each. One thing to note is that I'm using a single Activity approach and all ViewModels are Activity scoped.

android kotlin android-architecture-components android-livedata

share|improve this question

asked Mar 27 at 0:34

Jerum Jerum

3611 silver badge88 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The // update _data is kind of the critical piece of code. What exactly are you doing there?
  
  – ianhanniballake
  Mar 27 at 1:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Please see this stackoverflow.com/questions/56521969/…
  
  – Levon Petrosyan
  Jun 10 at 16:11
  

  
  
  
  

add a comment | 

1

I've tried extracting the value into a base class and having the ViewModels extend it. When I do that, however, the Observer isn't sticking to the LiveData. For instance, when I have a parent class with LiveData:

class Base : ViewModel() 
 private val _ data = MutableLiveData()
 val data: LiveData = _data

 fun someEvent(foo: Foo) // update _data 


class Derived : Base()

class Derived1 : Base()

Then get one of those ViewModels and observe data:

class Frag : Fragment 
 onViewCreated() 
 // get Derived, ViewModelProviders.of ...etc
 derived.data.observe // Doesn't observe changes 
 

Calling Base.someEvent(foo) doesn't notify the LiveData in the Fragment.

I want to avoid getting a reference to both subclasses and invoking someEvent on each. One thing to note is that I'm using a single Activity approach and all ViewModels are Activity scoped.

android kotlin android-architecture-components android-livedata

share|improve this question

asked Mar 27 at 0:34

Jerum Jerum

3611 silver badge88 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The // update _data is kind of the critical piece of code. What exactly are you doing there?
  
  – ianhanniballake
  Mar 27 at 1:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Please see this stackoverflow.com/questions/56521969/…
  
  – Levon Petrosyan
  Jun 10 at 16:11
  

  
  
  
  

add a comment | 

I've tried extracting the value into a base class and having the ViewModels extend it. When I do that, however, the Observer isn't sticking to the LiveData. For instance, when I have a parent class with LiveData:

class Base : ViewModel() 
 private val _ data = MutableLiveData()
 val data: LiveData = _data

 fun someEvent(foo: Foo) // update _data 


class Derived : Base()

class Derived1 : Base()

Then get one of those ViewModels and observe data:

class Frag : Fragment 
 onViewCreated() 
 // get Derived, ViewModelProviders.of ...etc
 derived.data.observe // Doesn't observe changes 
 

Calling Base.someEvent(foo) doesn't notify the LiveData in the Fragment.

I want to avoid getting a reference to both subclasses and invoking someEvent on each. One thing to note is that I'm using a single Activity approach and all ViewModels are Activity scoped.

android kotlin android-architecture-components android-livedata

share|improve this question

asked Mar 27 at 0:34

Jerum Jerum

3611 silver badge88 bronze badges

class Base : ViewModel() 
 private val _ data = MutableLiveData()
 val data: LiveData = _data

 fun someEvent(foo: Foo) // update _data 


class Derived : Base()

class Derived1 : Base()

class Frag : Fragment 
 onViewCreated() 
 // get Derived, ViewModelProviders.of ...etc
 derived.data.observe // Doesn't observe changes 
 

android kotlin android-architecture-components android-livedata

android kotlin android-architecture-components android-livedata

share|improve this question

asked Mar 27 at 0:34

Jerum Jerum

3611 silver badge88 bronze badges

share|improve this question

asked Mar 27 at 0:34

Jerum Jerum

3611 silver badge88 bronze badges

asked Mar 27 at 0:34

Jerum Jerum

3611 silver badge88 bronze badges

asked Mar 27 at 0:34

Jerum Jerum

3611 silver badge88 bronze badges

1 Answer
1

active

oldest

votes

1

class Derived : Base()

and

class Derived1 : Base()

have their own instance of:

private val _ data = MutableLiveData()
val data: LiveData = _data

that means you need to

derived.data.observe // do something 
derived1.data.observer // do something 
derived.someEvent(someFoo)
derived1.someEvent(someFoo)

You are trying to achieve something in a wrong way.

share|improve this answer

answered Mar 27 at 1:21

Archie G. QuiñonesArchie G. Quiñones

1,3181010 silver badges2525 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have a floating action button on multiple(but not all) fragments. It would be ideal to simply dispatch a single click listener with the current location to all relevant fragments instead of setting a click listener for each.
  
  – Jerum
  Mar 27 at 1:34
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don't understand can you explain that further?
  
  – Archie G. Quiñones
  Mar 27 at 1:56
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  My activity has multiple fragments and some have a FAB. When the FAB is clicked I want some contextual action to occur (will largely be screen dependant but there are other factors too). I feel that doing activity.fab.onclick() in each of those fragments would break encapsulation.
  
  – Jerum
  Mar 27 at 3:14
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  then delegate the onClick to the Fragments. I dont understand why you can't place the onClick logic inside the fragment.
  
  – Archie G. Quiñones
  Mar 27 at 3:58
  

  
  
  
  

add a comment | 

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1

class Derived : Base()

and

class Derived1 : Base()

have their own instance of:

private val _ data = MutableLiveData()
val data: LiveData = _data

that means you need to

derived.data.observe // do something 
derived1.data.observer // do something 
derived.someEvent(someFoo)
derived1.someEvent(someFoo)

You are trying to achieve something in a wrong way.

share|improve this answer

answered Mar 27 at 1:21

Archie G. QuiñonesArchie G. Quiñones

1,3181010 silver badges2525 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have a floating action button on multiple(but not all) fragments. It would be ideal to simply dispatch a single click listener with the current location to all relevant fragments instead of setting a click listener for each.
  
  – Jerum
  Mar 27 at 1:34
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don't understand can you explain that further?
  
  – Archie G. Quiñones
  Mar 27 at 1:56
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  My activity has multiple fragments and some have a FAB. When the FAB is clicked I want some contextual action to occur (will largely be screen dependant but there are other factors too). I feel that doing activity.fab.onclick() in each of those fragments would break encapsulation.
  
  – Jerum
  Mar 27 at 3:14
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  then delegate the onClick to the Fragments. I dont understand why you can't place the onClick logic inside the fragment.
  
  – Archie G. Quiñones
  Mar 27 at 3:58
  

  
  
  
  

add a comment | 

1

class Derived : Base()

and

class Derived1 : Base()

have their own instance of:

private val _ data = MutableLiveData()
val data: LiveData = _data

that means you need to

derived.data.observe // do something 
derived1.data.observer // do something 
derived.someEvent(someFoo)
derived1.someEvent(someFoo)

You are trying to achieve something in a wrong way.

share|improve this answer

answered Mar 27 at 1:21

Archie G. QuiñonesArchie G. Quiñones

1,3181010 silver badges2525 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have a floating action button on multiple(but not all) fragments. It would be ideal to simply dispatch a single click listener with the current location to all relevant fragments instead of setting a click listener for each.
  
  – Jerum
  Mar 27 at 1:34
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don't understand can you explain that further?
  
  – Archie G. Quiñones
  Mar 27 at 1:56
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  My activity has multiple fragments and some have a FAB. When the FAB is clicked I want some contextual action to occur (will largely be screen dependant but there are other factors too). I feel that doing activity.fab.onclick() in each of those fragments would break encapsulation.
  
  – Jerum
  Mar 27 at 3:14
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  then delegate the onClick to the Fragments. I dont understand why you can't place the onClick logic inside the fragment.
  
  – Archie G. Quiñones
  Mar 27 at 3:58
  

  
  
  
  

add a comment | 

class Derived : Base()

and

class Derived1 : Base()

have their own instance of:

private val _ data = MutableLiveData()
val data: LiveData = _data

that means you need to

derived.data.observe // do something 
derived1.data.observer // do something 
derived.someEvent(someFoo)
derived1.someEvent(someFoo)

You are trying to achieve something in a wrong way.

share|improve this answer

answered Mar 27 at 1:21

Archie G. QuiñonesArchie G. Quiñones

1,3181010 silver badges2525 bronze badges

class Derived : Base()

class Derived1 : Base()

private val _ data = MutableLiveData()
val data: LiveData = _data

derived.data.observe // do something 
derived1.data.observer // do something 
derived.someEvent(someFoo)
derived1.someEvent(someFoo)

share|improve this answer

answered Mar 27 at 1:21

Archie G. QuiñonesArchie G. Quiñones

1,3181010 silver badges2525 bronze badges

answered Mar 27 at 1:21

Archie G. QuiñonesArchie G. Quiñones

1,3181010 silver badges2525 bronze badges

answered Mar 27 at 1:21

Archie G. QuiñonesArchie G. Quiñones

1,3181010 silver badges2525 bronze badges