Dynamically toggle visibility of layout elements with Android data-binding.

问题

I am building an Android app, where I want to toggle the visibility of some view elements based on a button click. I am trying to archive it with data-binding instead of using findViewById(), but all the solutions I've have found until now doesn't update the layout, when the variable is changed.

Here is what I have so far. (I've simplified the code, to focus on the problem)

Activicy.java

public class RecipeActivity extends AppCompatActivity {
private Recipe recipe;
private ActivityRecipeBinding binding;
private RecipeBinderHelper rbhelper = new RecipeBinderHelper();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Intent intent = getIntent();
    recipe = intent.getParcelableExtra("recipe");
    binding = DataBindingUtil.setContentView(this, R.layout.activity_recipe);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    toolbar.setTitle(recipe.getName());
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    binding.recipeContent.setRecipe(recipe);
    binding.recipeContent.setHelper(rbhelper);

    binding.Button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //HERE I CHANGE THE VALUE OF THE VARIBLE
            rbhelper.setPresentationViewVisible(false);
            binding.notifyChange();
        }
    });
}
}

Helper class

public class RecipeBinderHelper{
private Boolean presentationElementsVisible;
private Boolean timerElementsVisible;

public RecipeBinderHelper(){
    this.presentationElementsVisible = true;
    this.timerElementsVisible = false;
}
public void setPresentationViewVisible(boolean presentationElementsVisible) {
    this.presentationElementsVisible = presentationElementsVisible;
}
public Boolean getPresentationElementsVisible() {
    return presentationElementsVisible;
}
//getters and setters for private Boolean timerElementsVisible;
}

Layout

<?xml version="1.0" encoding="utf-8"?>
<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="helper"
        type="com.myapps.recipeApp.RecipeBinderHelper"/>
    <variable
        name="recipe"
        type="com.myapps.recipeApp.Recipe"/>
</data>
<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.myapp.recipeApp.RecipeActivity"
    tools:showIn="@layout/activity_recipe">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/r_source"
        android:textStyle="bold"
        android:text="@{recipe.source}"
        android:visibility="@{helper.presentationElementsVisible ? View.VISIBLE : View.GONE}" />
<!-- More TextViews here -->
<!-- Button is located in parret layout -->
</RelativeLayout>
</layout>

回答1:

I highly recommend to read George Mount's posts about Android data-binding, they are very useful.

---

To solve the problem I extended the helper class as an BaseObservable as described in the documentation.

Helper class

public class RecipeBinderHelper{
    private Boolean presentationElementsVisible;
    private Boolean timerElementsVisible;

    public RecipeBinderHelper(){
        this.presentationElementsVisible = true;
        this.timerElementsVisible = false;
    }
    public void setPresentationViewVisible(boolean presentationElementsVisible) {
        this.presentationElementsVisible = presentationElementsVisible;
        //Notifying change in the setter. 
        notifyPropertyChanged(BR.presentationElementsVisible);
    }
    //assigning Bindable annotation to the getter 
    @Bindable
    public Boolean getPresentationElementsVisible() {
        return presentationElementsVisible;
    }
    //getters and setters for private Boolean timerElementsVisible;
}

The binding.notifyChange();in the Activity is not necessary and can be removed.

The app now removes the TextView as desired, when the button is clicked.

---

One peculiar thing is that Android Studio (2.1.2, Ubuntu) gives me a Cannot resolve symbol 'BR' warning, but the app compiles and runs as expected.

来源：https://stackoverflow.com/questions/38240968/dynamically-toggle-visibility-of-layout-elements-with-android-data-binding