android 双向绑定/w LiveData 使用 Java

Question

I try to implement two way databinding in Java and I cant get it to work. There seems to be not much material about that mostly Kotlin. What I have now:

A simple ViewModel

I had to make the MutableLiveData properties public when I reference them via @={dashBoardViewModel.text} , otherwise the compiler complained that it could not find FragmentDashBoardDataBindingImpl.

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class DashboardViewModel extends ViewModel {

    public MutableLiveData<String> text;
    public MutableLiveData<String> name;

    public DashboardViewModel() {
        text = new MutableLiveData<>();
        name = new MutableLiveData<>();
        text.setValue("This is the dashboard");
    }

    public void onSave() {
        String oldValue = text.getValue();
        String newValue = "new value " + name.getValue();
        text.setValue(newValue);
    }
}

A simple layout in a fragment:

<?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="dashBoardViewModel"
            type="example.com.ui.dashboard.DashboardViewModel" />

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        ...
        tools:context=".ui.dashboard.DashboardFragment">

        <TextView
            android:id="@+id/text_dashboard"
            ...
            android:text="@={dashBoardViewModel.text}"
            ... />

        <EditText
            ...
            android:inputType="textPersonName"
            android:text="@={dashBoardViewModel.name}"
            ... />

        <Button
            ...
            android:onClick="@{() -> dashBoardViewModel.onSave()}"
            ...
        />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

In the constructor I call text.setValue("This is the dashboard") which works fine and the value is displayed nicely.

In the click listener dashBoardViewModel.onSave() I can call text.setValue(newValue) and it assigns the correct value but the value never gets displayed.

So text.setValue() seems to work differently in the same class / same instance.

Any hints would be very much appreciated.

Answer 1

You may forgot to give lifecycleowner to your databinding . You should check this one