使用Android数据绑定动态切换布局元素的可见性.

Question

我正在构建一个Android应用程序,我想根据按钮点击切换一些视图元素的可见性.我试图用数据绑定而不是使用findViewById()来存档它,但是直到现在我发现的所有解决方案都不会在更改变量时更新布局.

这是我到目前为止所拥有的.(我简化了代码,专注于问题)

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();
        }
    });
}
}

助手班

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;
}

布局

<?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>

Answer 1

我强烈推荐阅读 George Mount关于 Android 数据绑定的帖子，它们非常有用。

为了解决这个问题，我将辅助类扩展为BaseObservable ，如文档中所述。

助手类

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;
}

Activity 中的binding.notifyChange();不是必需的，可以删除。

现在，当单击按钮时，应用程序会根据需要删除 TextView。

一件奇怪的事情是 Android Studio（2.1.2，Ubuntu）给了我一个Cannot resolve symbol 'BR'警告，但应用程序按预期编译和运行。