Develop Reference

Databinding via Interface

I have a simple databinding setup:
My ViewModel:
public class MyViewModel {
public ObservableField<Integer> viewVisibility = new ObservableField<>(View.VISIBLE);
public void buttonClicked() {
if (viewVisibility.get() == View.GONE) {
viewVisibility.set(View.VISIBLE);
} else {
viewVisibility.set(View.GONE);
}
}
}
and the layout:
<?xml version="1.0" encoding="utf-8"?>
<layout>
<data>
<variable
name="viewModel"
type="com.example.fweigl.playground.MyViewModel" />
</data>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/root"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="64dp">
<View
android:visibility="#{viewModel.viewVisibility}"
android:layout_width="200dp"
android:layout_height="200dp"
android:background="#00ff00" />
<Button
android:text="click me"
android:onClick="#{() -> viewModel.buttonClicked()}"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
</layout>
As you can see, every click on the button switches the ObservableField<Integer> viewVisibility on the viewmodel, which in turn switches the visibility of a green rectangle. This works fine.
Now I want to do the same but using an interface as a viewmodel:
public interface IMyViewModel {
public void buttonClicked();
public ObservableField<Integer> viewVisibility = new ObservableField<>(View.VISIBLE);
}
the viewmodel:
public class MyViewModel implements IMyViewModel {
#Override
public void buttonClicked() {
if (viewVisibility.get() == View.GONE) {
viewVisibility.set(View.VISIBLE);
} else {
viewVisibility.set(View.GONE);
}
}
}
and in the layout, I import the interface instead of the implementation:
<data>
<variable
name="viewModel"
type="com.example.fweigl.playground.IMyViewModel" />
</data>
What works is the binding for the button click, buttonClicked is called and the value of viewVisibility is changed.
What doesn't work is the changing of the green rectangle view's visibility. Changes of the viewVisibility value are not reflected in the layout.
Am I doing something wrong or does databinding not (fully) work with interfaces as viewmodels?

Id you'd wrap whatever variable you'd like to bind to your view in a LiveData<>, Android will automatically unbox the data and bind it to the view

Data binding needs getter and setter to make work done, it does not access your field directly. So this will also not work without getter setter
public class MyViewModel {
public ObservableField<Integer> viewVisibility = new ObservableField<>(View.VISIBLE);
public void buttonClicked() {
if (viewVisibility.get() == View.GONE) {
viewVisibility.set(View.VISIBLE);
} else {
viewVisibility.set(View.GONE);
}
}
}
So because interface does not have getter setter, so they can not be used as model.

Fixing data binding errors in Android for linking a button with a function

I have a test project where I want to bind the press of a button to trigger a function via the DataBinding Libray and add:command.
Unfortunately, I'm getting the error:
Found data binding errors.
****/ data binding error ****msg:Could not resolve com.example.ckleineidam.testproject.ViewModel.testButton as an accessor or listener on the attribute.
MainActivity:
public class MainActivity extends AppCompatActivity {
ViewModel mModel;
ActivityMainBinding binding;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// setContentView(R.layout.activity_main);
binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
mModel = new ViewModel(this);
binding.setViewModel(mModel);
}
}
ViewModel:
public class ViewModel extends BaseObservable {
private static final String TAG = "VIEW_MODEL";
private Context mActivity;
public ViewModel(Context context) {
this.mActivity=context;
}
public void testButton(){
Log.i(TAG, "Button Click");
}
}
activity_main.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=".MainActivity">
<data>
<variable
name="ViewModel"
type="com.example.ckleineidam.testproject.ViewModel" />
</data>
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="title"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/activation_button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Test Button"
android:background="?android:attr/selectableItemBackground"
app:command="#{ViewModel.testButton}"
app:layout_constraintTop_toBottomOf="#id/title" />
</android.support.constraint.ConstraintLayout >
</layout>
The code is also as an example project at Github.

You are getting this error because there is no attribute app:command on a button.
If you are trying to achieve an onClick functionality, you can use android:onClick="#{ViewModel.testButton}" and change your function signature to void testButton(View view).
To use custom attributes, you need to define a binding adapter

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

Android - data binding on a property of an LiveData extended object

I currently started to use the Data Binding Library and in my viewmodel I have an extended LiveData object:
public class ScannerViewModel extends AndroidViewModel {
/** MutableLiveData containing the scanner state to notify MainActivity. */
public ScannerLiveData scannerLiveData;
ScannerLiveData:
public class ScannerLiveData extends MutableLiveData<ScannerLiveData> {
public boolean mScanningStarted;
public boolean mBluetoothEnabled;
public boolean mLocationEnabled;
public ScannerLiveData(final boolean bluetoothEnabled, final boolean locationEnabled) {
mScanningStarted = false;
mBluetoothEnabled = bluetoothEnabled;
mLocationEnabled = locationEnabled;
postValue(this);
}
...
}
activity_scanner.xml:
<layout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/layout_test">
<data>
<import type="android.view.View" />
<variable
name="livedata"
type="de.datacollect.ecount.ui.scanner.ScannerLiveData" />
</data>
...
<android.support.constraint.ConstraintLayout
<ProgressBar
android:id="#+id/state_scanning"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="-7dp"
android:layout_marginTop="-8dp"
android:indeterminate="true"
android:indeterminateTint="#android:color/white"
android:visibility="#{livedata.mBluetoothEnabled ? View.VISIBLE : View.INVISIBLE}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="#+id/recycler_view_ble_devices" />
...
ScannerActivity:
#Override
protected void onCreate(#Nullable final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActivityScannerBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_scanner);
// Create view model containing utility methods for scanning
mScannerViewModel = ViewModelProviders.of(this).get(ScannerViewModel.class);
mScannerViewModel.getScannerState().observe(this, this::startScan);
binding.setLifecycleOwner(this);
binding.setLivedata(mScannerViewModel.scannerLiveData);
...
How can I bind to the mBluetoothEnabled property? I get an unclassified error on build. I already used the search but didn't find something about it. Every help would be appreciate.
Btw:
Updates to Data Binding:
You can now use a LiveData object as an observable field in data binding expressions. The ViewDataBinding class now includes a new setLifecycle method that you need to use to use to observe LiveData objects.

Instead of binding the LiveData object bind your viewmodel. So change livedata variable in activity_scanner.xml to
<variable
name="viewModel"
type="de.datacollect.ecount.ui.scanner.ScannerViewModel" />
and in ScannerActivity
binding.setViewModel(mScannerViewModel);
Then your binding expression will become
android:visibility="#{viewModel.scannerLiveData.mBluetoothEnabled ? View.VISIBLE : View.INVISIBLE}"

Replacement for onClick event in xml tag via Databinding

My question is simple but I can't seem to do what I want to.
So In my activity I have this method.
public void performButtonClick(View view)
{
Log.i("INTRO", "OK");
}
Which is called from a button click event defined in xml like so
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="performButtonClick"
android:text="#string/start"/>
Now I've heard that this approach is using reflection which slows down performance so I'm trying to replace the onClick event with databinding.
I tried various combinations like
android:onClick="#{performButtonClick}"
or
android:onClick="#{(v) -> performButtonClick(v)}"
or
android:onClick="#{(v) -> MainActivity::performButtonClick}"
but None of these worked.
Could you help me out?

Ok answering to my own question.
I am new to DataBinding but I do not understand why I have to use copy-pasted solutions which make use of an accessory Handlers class and end up with more boilerplate code than I used to have.
All I wanted is an equivalent to android:onClick="performButtonClick" So here is my solution:
activity_main.xml
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<variable
name="activity"
type="com.example.mydatabinding.MainActivity"/>
</data>
<LinearLayout
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#drawable/bg"
android:orientation="vertical">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="#{activity::performButtonClick}"
android:text="#string/start"/>
</LinearLayout>
MainActivity.java
public final class MainActivity extends AppCompatActivity
{
ActivityMainBinding binding;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
binding.setActivity(this);
}
public void performButtonClick(View view)
{
Log.i("INTRO", "OK");
}
}