android - 如何使用 Picasso 设置 @BindingAdapter？

Question

我想使用绑定(bind)创建电影海报图像的 GridView 。

我的 View 模型看起来像这样:

public class PopularMoviesViewModel extends BaseObservable {

    Movie movie;
    Context context;

    MovieServiceComponent movieServiceComponent = DaggerMovieServiceComponent.builder()
            .contextModule(new ContextModule(context))
            .build();

    Picasso getPicasso = movieServiceComponent.getPicasso();

    public PopularMoviesViewModel(Movie movie, Context context) {
        this.movie = movie;
        this.context = context;
    }

    @Bindable
    public String getImageUrl(){
        return movie.posterPath();
    }

    @Bindable
    public String getTitle(){
        return movie.originalTitle();
    }

    @BindingAdapter({"imageUrl"})
    public void setImageUrl(ImageView view, String poserPath){
        getPicasso.with(view.getContext()).load("http://image.tmdb.org/t/p/w185"+ poserPath).into(view);

    }

}

布局:

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <data class="PopularMoviesBinding">
    <variable
        name="pmvm"
        type="com.hartyandi.oviesm.modelviews.PopularMoviesViewModel"></variable>

    </data>

    <LinearLayout


        android:id="@+id/row"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#FFFFFF"
        android:paddingBottom="0dp"
        android:paddingTop="5dp"
        android:paddingRight="2.5dp"
        android:paddingLeft="5dp"
        android:orientation="vertical">

        <ImageView
            app:imageUrl="@{pmvm.imageUrl}"
            android:id="@+id/popular_movies_grid_image"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="0dp"
            android:adjustViewBounds="true"
            android:elevation="20dp">

        </ImageView>

        <TextView
            android:id="@+id/popular_movies_grid_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{pmvm.title}"
            android:textColor="#000000"
            android:textSize="12sp"
            android:background="#FFFFFF"
            >
        </TextView>

    </LinearLayout>
</layout>

适配器:

public class PopularMoviesAdapter extends RecyclerView.Adapter<PopularMoviesAdapter.BindingHolder> {

    private List<Movie> movies;
    private Context context;

    public PopularMoviesAdapter(List<Movie> movies, Context context) {
        this.movies = movies;
        this.context = context;
    }

    public void add(Movie movie){
        movies.add(movie);
    }

    @Override
    public BindingHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        PopularMoviesBinding popularMoviesBinding = DataBindingUtil.inflate(LayoutInflater.from(parent.getContext()),
                R.layout.popular_movies_gridview_row, parent,false);
        return new BindingHolder(popularMoviesBinding);
    }

    @Override
    public void onBindViewHolder(PopularMoviesAdapter.BindingHolder holder, int position) {
        PopularMoviesBinding popularMoviesBinding = holder.popularMoviesBinding;
        popularMoviesBinding.setPmvm(new PopularMoviesViewModel(movies.get(position), context));
    }

    @Override
    public int getItemCount() {
        return movies.size();
    }

    public class BindingHolder extends RecyclerView.ViewHolder{

        private PopularMoviesBinding popularMoviesBinding;

        public BindingHolder(PopularMoviesBinding popularMoviesBinding) {
            super(popularMoviesBinding.getRoot());
            this.popularMoviesBinding = popularMoviesBinding;
        }
 }
}

我收到以下错误:

java.lang.IllegalStateException: Required DataBindingComponent is null in class PopularMoviesBinding.A BindingAdapter in modelviews.PopularMoviesViewModel is not static and requires an object to use, retrieved from the DataBindingComponent. 

I tried to change my implementation just like this stackoverflow post suggest我得到了同样的错误信息。

I also used the following code as example.

谁能解释一下代码的问题是什么，以及如何解决？

Answer 1

您可能不打算为 BindingAdapter 使用实例方法。

如果这样做，您必须提供 DataBindingComponent以便生成的 Binding 类知道要使用哪个实例。

您有两个选择——提供一个 DataBindingComponent 或将所需的上下文作为属性传递给静态绑定(bind)适配器方法。第二个更容易理解，所以我将从它开始:

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <data class="PopularMoviesBinding">
        <variable name="pmvm"
            type="com.hartyandi.oviesm.modelviews.PopularMoviesViewModel"/>
        <variable name="picasso" type="com.whatever.Picasso"/>
    </data>
    <!-- ... -->
    <ImageView
        app:imageUrl="@{pmvm.imageUrl}"
        app:picasso="@{picasso}"
        ... />
    </ImageView>
</layout>

然后在您的 BindingAdapter 中:

@BindingAdapter({"imageUrl", "picasso"})
public static void setImageUrl(ImageView view, String poserPath, Picasso picasso){
    picasso.with(view.getContext()).load("http://image.tmdb.org/t/p/w185"+ poserPath).into(view);
}

请注意，setImageUrl 现在是 static。

或者，由于您的 Picasso 实例也在 ViewModel 上，您可以通过为 picasso 添加一个 getter 来传递该实例:

<ImageView
    app:imageUrl="@{pmvm.imageUrl}"
    app:picasso="@{pmvm.picasso}"
    ... />

以及您的 ViewModel 中的方法:

public Picasso getPicasso() { return this.getPicasso; }

另一种方式意味着您实现了一个DataBindingComponent。当您创建实例 BindingAdapter 方法时，生成的接口(interface)将为您的类提供一个 getter。您需要创建一个类来实现该接口(interface):

public class MyDataBindingComponent implements DataBindingComponent {
    public PopularMoviesViewModel getPopularMoviesViewModel() {
         return whateverIDoToCreateOrGetThisBindingAdapterInstance();
    }
}

然后在膨胀或绑定(bind)时传递实例:

PopularMoviesBinding popularMoviesBinding = 
    DataBindingUtil.inflate(LayoutInflater.from(parent.getContext()),
        R.layout.popular_movies_gridview_row, parent,false,
        new MyDataBindingComponent());