How can I do databinding with livedata?
activity_user_detail.xml:
<data>
<variable
name="viewModel"
type="com.test.viewmodel.UserViewModel" />
</data>
<TextView
android:id="@+id/tv_amount"
android:layout_width="match_parent"
android:text="@{viewModel.age}"
....
UserViewModel.java:
public class UserViewModel extends ViewModel {
public LiveData<User> user;
public void getUserById(UserDao userDao, String userId){
transaction = UserDao .load(userId);
}
}
UserDao.java:
@Query("SELECT * FROM `user` WHERE id = :userId")
LiveData<User> load(String userId);
UserDetailActivity.java:
private ActivityUserDetailBinding binding;
binding = DataBindingUtil.setContentView(this, R.layout.activity_user_detail);
viewModel = ViewModelProviders.of(this).get(UserViewModel.class);
viewModel.getUserById(userDao, userId);
viewModel.user.observe(this, user -> binding.setViewModel(user)); // How to bind livedata?
I have tried this also:
binding.setViewModel(viewModel);
Why use Data binding with Mvp? Combining Databinding along wih MVP pattern can result in a very clean structure and maintainable project. Databinding saves u a lot of stress and uneccesary long lines of code. Your UI is updated eaily and gone are those days where you need "findViewById" and onclick listeners and so on.
View binding doesn't support layout variables or layout expressions, so it can't be used to declare dynamic UI content straight from XML layout files. View binding doesn't support two-way data binding.
Data Binding allows you to effortlessly communicate across views and data sources. This pattern is important for many Android designs, including model view ViewModel (MVVM), which is currently one of the most common Android architecture patterns.
Data Binding with LiveData. Data Binding with LiveData makes our code more concise. It allows layouts to directly communicate with ViewModels. We created a simple code example during our LIveData tutorial.
LiveData always need a lifecycle. But, in this code LiveData directly work with data binding. So, we should set the activity (this activity) as the lifecycle owner to the data binding instance. Here is the final MainActivity.kt code.
To understand that, you should be good with the basics. In simple terms, LiveData is an observable data holder class. This means it can hold a set of data that can be observed from other Android components like Activities, Fragments, and Services. It’s lifecycle-aware and mostly used to update UI from the ViewModel in MVVM architecture projects.
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. Show activity on this post.
This is a sample to figure out how LiveData and ObservableField works. You need to change T object and setValue() with LiveData, or set(T) with ObservableField. Changing properties of object T does not update UI.
<?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">
<data>
<variable
name="viewModel"
type="com.example.tutorial3livedata_databinding2objects.UserViewModel" />
</data>
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/user_info"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text='@{viewModel.userMutableLiveData.name+ ", email " + viewModel.userMutableLiveData.email}'
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.501"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.1" />
<EditText
android:id="@+id/et_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="48dp"
android:text="@={viewModel.userMutableLiveData.name}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.501"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/user_info" />
<EditText
android:id="@+id/et_email"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="28dp"
android:text="@={viewModel.userMutableLiveData.email}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.501"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/et_name" />
<Button
android:id="@+id/button_change_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="32dp"
android:onClick="@{() -> viewModel.changeUserName()}"
android:text="Change Name"
app:layout_constraintEnd_toStartOf="@+id/button_change_user"
app:layout_constraintHorizontal_chainStyle="spread"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/et_email" />
<Button
android:id="@+id/button_change_user"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="@{() -> viewModel.changeUser()}"
android:text="Change User"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/button_change_name"
app:layout_constraintTop_toTopOf="@+id/button_change_name" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="56dp"
android:text="Display User"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/button_change_name" />
</android.support.constraint.ConstraintLayout>
</layout>
ViewModel
public class UserViewModel extends ViewModel {
public MutableLiveData<User> userMutableLiveData = new MutableLiveData<>();
private User mUser;
public UserViewModel() {
mUser = new User("User", "[email protected]");
userMutableLiveData.setValue(mUser);
}
public void changeUserName() {
// Both updates LiveData but does not update UI
mUser.setName("Name is Changed");
// userMutableLiveData.getValue().setName("Updated Name");
// This one Updates UI
// userMutableLiveData.setValue(userMutableLiveData.getValue());
}
public void changeUser() {
mUser = new User("New User Name", "[email protected]");
// Without setting new value UI is not updated and observe is not called
userMutableLiveData.setValue(mUser);
}
}
MainActivity
/*
Without binding.setLifecycleOwner(this), liveData.setValue() does not update UI
liveData.setValue() updates UI
EditText changes LiveData but does not update UI
*/
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
UserViewModel userViewModel = ViewModelProviders.of(this).get(UserViewModel.class);
// LiveData should call setValue() to update UI via binding
binding.setViewModel(userViewModel);
// Required to update UI with LiveData
binding.setLifecycleOwner(this);
}
}
This code is for learning purposes.
Results you can get from this code:
1- Changing user name with changeUserName() updates the name of existing User of LiveData but does not update UI. UI gets updated when you rotate the device.
2- When you change User of LiveData and setValue() data-binding works.
3- Changing User properties using EditText 2-way binding android:text="@={viewModel.userMutableLiveData.name}"
changes LiveData's User's name but does not update UI until device is rotated since User is still same.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With