Develop Reference

Click Handling on Views in Clean Architecture

I have to implement click listener using binding and ViewModel as per clean architecture.
I have two button to select language like English and Chinese.
LanguageActivity.kt
#AndroidEntryPoint
class LanguageActivity : PBActivity(R.layout.activity_language) {
private val mViewModel:LanguageViewModel by viewModels()
private val mBinding:ActivityLanguageBinding by viewbind()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
mBinding.apply {
lifecycleOwner = this#LanguageActivity
viewModel = mViewModel
}
collectFlow(mViewModel.uiState){
Toast.makeText(this, it.name, Toast.LENGTH_SHORT).show()
when(it){
LanguageSelected.ENGLISH -> {
}
LanguageSelected.CHINESE -> {
}
LanguageSelected.NONE -> {
}
}
}
}
}
enum class LanguageSelected{
ENGLISH,CHINESE,NONE
}
LanguageViewModel.kt
#HiltViewModel
class LanguageViewModel #Inject constructor(
private val pbPrefs: PBPrefs
): ViewModel(){
// Backing property to avoid state updates from other classes
private val _uiState = MutableStateFlow(LanguageSelected.NONE)
// The UI collects from this StateFlow to get its state updates
val uiState: StateFlow<LanguageSelected> = _uiState
fun englishSelected()= viewModelScope.launch {
_uiState.value = LanguageSelected.ENGLISH
pbPrefs.setLanguageSelect()
}
fun urduSelected() = viewModelScope.launch {
_uiState.value = LanguageSelected.URDU
pbPrefs.setLanguageSelect()
}
}
activity_language.xml
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="viewModel"
type="uk.co.planetbeyond.telenorbluecollar.ui.language.LanguageViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ui.language.LanguageActivity">
<androidx.constraintlayout.widget.Guideline
android:id="#+id/center_vertical_gl"
android:layout_width="match_parent"
android:layout_height="1dp"
android:orientation="vertical"
app:layout_constraintGuide_percent="0.5" />
<Button
android:id="#+id/englishTv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="English "
android:onClick="#{() -> viewModel.englishSelected()}"
android:layout_marginEnd="8dp"
app:layout_constraintEnd_toStartOf="#id/center_vertical_gl"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/urduTv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Urdu"
android:onClick="#{() -> viewModel.urduSelected()}"
android:layout_marginStart="8dp"
app:layout_constraintStart_toEndOf="#id/center_vertical_gl"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
I have to select language on click of a button. What's the best approach as per clean architecture to implement
I have created an interface LanguageSelected but for that I have to created multiple methods in viewModel, As languages increase I have to create more methods in viewmodel.
How could I make it short or I mean extensible?

How can I set a ConstraintLayout Group's visibility via DataBinding?

I have 2 Groups in my layout which control the visibility of my Views.
However, I cannot set their visibility via DataBinding:
<layout>
<data>
<import type="android.view.View"/>
<variable
name="viewModel"
type="co.aresid.book13.fragments.trackinglist.TrackingListViewModel"
/>
</data>
<androidx.constraintlayout.widget.ConstraintLayout>
...
<androidx.constraintlayout.widget.Group
android:id="#+id/content_group"
android:layout_width="0dp"
android:layout_height="0dp"
android:visibility="#{viewModel.hideLoadingAndShowContent ? View.VISIBLE : View.GONE, default=gone}"
app:constraint_referenced_ids="tracking_list_recycler_view"
/>
<androidx.constraintlayout.widget.Group
android:id="#+id/loading_group"
android:layout_width="0dp"
android:layout_height="0dp"
android:visibility="#{viewModel.hideLoadingAndShowContent ? View.GONE : View.VISIBLE, default=visible}"
app:constraint_referenced_ids="progress_circular"
/>
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
The hideLoadingAndShowContent variable is a LiveData which gets its value from a corresponding MutableLiveData in my ViewModel:
private val _hideLoadingAndShowContent = MutableLiveData<Boolean>()
val hideLoadingAndShowContent: LiveData<Boolean>
get() = _hideLoadingAndShowContent
This LiveData is only set in the ViewModel and does not occur in the Fragment class.
In the Fragment class, I have also set the binding.lifecycleOwner:
binding.lifecycleOwner = viewLifecycleOwner
What detail am I missing out?

I forgot to pass the ViewModel to the layout binding in my Fragment class:
binding.viewModel = viewModel

Because that android:visibility does not support binding variable observation,
You can create BindingAdapter this way
#BindingAdapter("mutableVisibility")
fun setMutableVisibility(view: View, visibility: MutableLiveData<Boolean>) {
val owner = (view.getParentActivity() ?: view.context) as LifecycleOwner
if (owner != null) {
visibility.observe(
owner,
Observer { value ->
view.visibility = if(value) View.VISIBLE else View.GONE
})
}
}
Utility function for getting activity from view.
fun View.getParentActivity(): AppCompatActivity?{
var context = this.context
while (context is ContextWrapper) {
if (context is AppCompatActivity) {
return context
}
context = context.baseContext
}
return null
}
Then in your XML you can do it like
<androidx.constraintlayout.widget.Group
android:id="#+id/content_group"
android:layout_width="0dp"
android:layout_height="0dp"
android:visibility="#{viewModel.hideLoadingAndShowContent}"
app:constraint_referenced_ids="tracking_list_recycler_view"
/>

Android : Kotlin : MVVM : Why viewModel.onButtonClicked() causes the app crash?

Logcat Message :
java.lang.IllegalStateException: Could not find method #={() -> viewModel.onBtnClicked()(View) in a parent or ancestor Context for android:onClick attribute defined on view class androidx.appcompat.widget.AppCompatButton with id 'button'
File1 : activity_main.xml
<data>
<variable
name="viewModel"
type="com.wingsquare.databindingdemo.MainViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:onClick = "#={() -> viewModel.onBtnClicked()"
/>
</androidx.constraintlayout.widget.ConstraintLayout>
File 2 : MainActivity.kt
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val binding: ActivityMainBinding = DataBindingUtil.setContentView(this,R.layout.activity_main)
// val binding = ActivityMainBinding.inflate(layoutInflater)
val mainViewModel = ViewModelProvider(this).get(MainViewModel::class.java)
binding.viewModel = mainViewModel
binding.lifecycleOwner = this
}
}
File 3 : MainViewModel.kt
class MainViewModel : ViewModel() {
fun onBtnClicked() {
Log.d("MainViewModel", "MainViewModel")
}
}

The Logcat Message is some how misleading.
I was facing the same error for couple of hours checking everything else I thought it be the root cause. But for this particular error, all you have to do is to keep an eye on "{ }". This is one of the drawbacks of data binding in android. lots of the times you don't get any error on compile times, And if you do! that's not really helpful !
and another thing to consider is that '=' in
android:onClick = "#={() -> viewModel.onBtnClicked()}"
is used for a two way binding.
you don't need it in this case.
you can read about it here on android official docs

android:onClick="#{() -> viewModel.onBtnClicked()}"
Add a parenthesis at the end.
also you may want to remove the equal sign after the #

UI not updated when ViewModel value changed

I have created sample app to demo my question:
A TextView and a Button, text view visibility is bound to viewModel.bar
I want the button to switch the value of viewModel.bar when clicked and the UI to get updated as well.
However, this is not happening. The value is changed but the UI is not updated.
Layout File:
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<import type="android.view.View"/>
<variable name="viewModel"
type="com.example.bindingone.MainViewModel"/>
</data>
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="#+id/text_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World"
android:visibility="#{viewModel.bar ? View.VISIBLE : View.GONE}"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<Button
android:text="Update UI"
android:onClick="clicked"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</android.support.constraint.ConstraintLayout>
</layout>
MainActivity File:
class MainActivity : AppCompatActivity() {
private val viewModel = MainViewModel()
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
binding = DataBindingUtil.setContentView(this, R.layout.activity_main)
binding.viewModel = viewModel
}
fun clicked(v: View) {
viewModel.bar.value = viewModel.bar.value?.not() ?: false
}
}
MainViewModel file:
class MainViewModel : ViewModel() {
var bar = MutableLiveData<Boolean>()
}

After creating binding, add this line binding.setLifecycleOwner(this).
/**
* Sets the {#link LifecycleOwner} that should be used for observing changes of
* LiveData in this binding. If a {#link LiveData} is in one of the binding expressions
* and no LifecycleOwner is set, the LiveData will not be observed and updates to it
* will not be propagated to the UI.
*
* #param lifecycleOwner The LifecycleOwner that should be used for observing changes of
* LiveData in this binding.
*/
#MainThread
public void setLifecycleOwner(#Nullable LifecycleOwner lifecycleOwner)

Data Binding onClick not working

I am getting started for using DataBinding and something is wrong with my onClick.
GameViewModel.java
public void onClickItem(int row, int col){
Log.d("click","row: "+row+" col: "+col);
}
#BindingAdapter("load_image")
public static void loadImage(ImageView view,int imageId) {
view.setImageResource(getDrawable(imageId));
}
GameFragment.java
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
//View view=inflater.inflate(R.layout.fragment_game, container, false);
FragmentGameBinding binding = DataBindingUtil.inflate(inflater, R.layout.fragment_game, container, false);
View view = binding.getRoot();
ButterKnife.bind(this,view);
binding.setGameViewModel(gameViewModel);
gameViewModel= ViewModelProviders.of(getActivity()).get(GameViewModel.class);
gameViewModel.init();
return view;
}
fragment_game.xml
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
tools:context=".view.GameFragment">
<data>
<import type="android.support.v4.app.Fragment"/>
<import type="android.view.View"/>
<variable
name="gameViewModel"
type="harkor.addus.viewmodel.GameViewModel" />
</data>
<android.support.constraint.ConstraintLayout
(...)>
<TextView
(...)>
<android.support.constraint.ConstraintLayout
(...)>
<ImageView
android:id="#+id/image_puzzle11"
android:src="#android:color/holo_green_dark"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginEnd="1dp"
android:layout_marginRight="1dp"
android:onClick="#{() -> gameViewModel.onClickItem(1,1)}"
app:load_image="#{0}"
app:layout_constraintBottom_toTopOf="#+id/image_puzzle21"
app:layout_constraintDimensionRatio="w,1:1"
app:layout_constraintEnd_toStartOf="#+id/image_puzzle12"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
(...)
load_image is working, but onClick do nothing...
No error in compilation, no crash when button is clicking on device, no result in console...

Please check with below code:
You have written as to call on Click of image as :
android:onClick="#{() -> gameViewModel.onClickItem(1,1)}"
Try to write as below and check again :
android:onClick="#{(v) -> gameViewModel.onClickItem(1,1)}"
As per the Guidance This is not the way to achieve the Architecture Principles we can work as below as per the MVVM Architecture:
1. Create an Interface
2. Define Interface as handler inside the Layout File as :
<variable
name="handler"
type="com.cityguide.interfaces.MustVisitItemListener"></variable>
3.Now we are using this handler to define onclick as :
android:onClick="#{(v) ->handler.onGalleryItemClick(v,currentPosition,photo)}"
Implement the Handler with our java Class or Activity class before bind the Handler with View as below:
private MustVisitItemListener mItemListener;
mItemListener = new MustVisitItemListener() { };
5.Set the Interface handler with bind object as below:
mbinding.setHandler(mItemListener);

The easiest way is to set the view model and calling the proper method in the View's onClick from the layout:
Your xml:
<data>
<variable
name="viewModel"
type="co.package.MyViewModel" />
</data>
<com.google.android.material.textfield.TextInputEditText
android:id="#+id/my_id"
android:layout_width="#dimen/full_width"
android:layout_height="wrap_content"
android:onClick="#{() -> viewModel.doSomething()}" />
But if for any reason you need to call a method from your fragment or activity, the best suggestion is to create an interface to handle the method, implement the method and set it to the layout as follows:
Your xml
<data>
<variable
name="myHandlers"
type="co.package.MyHandlersListener" />
</data>
<com.google.android.material.textfield.TextInputEditText
android:id="#+id/my_id"
android:layout_width="#dimen/full_width"
android:layout_height="wrap_content"
android:onClick="#{() -> myHandlers.doSomething()}" />
And within your Fragment or Activity you create the interface and then implement it:
Your activity/fragment:
/* My Handler Methods */
interface MyHandlersListener {
fun doSomething()
}
Then implement the listener, taking into consideration that the method something is defined and implemented within your activity/fragment class:
private val myHandlersListener: MyHandlersListener = object : MyHandlersListener {
override fun doSomething() {
something()
}
}
And using databinding, you can set the handler into your layout class (this can be done within the onCreate or onCreateView method depending if you are using and activity or fragment respectively):
myBinding.myHandlers = myHandlersListener
In this way it works perfectly and you follow the guide given by Android's team:
https://developer.android.com/topic/libraries/data-binding/expressions#method_references