从ViewModel启动DialogFragment的推荐方法是什么？

问题描述：

我在 Recyclerview 中有一个列表对象。当长按一个项目时，我想显示一个对话框，其中包含点击该项目的数据。

I have a list objects in a Recyclerview. When long-pressing an item I want to show a dialog with data from the item clicked.

Recyclerview 是使用每个项目的数据绑定，我可以在长按时使用Log显示所选项目中的数据。

The Recyclerview is using data binding for each item and I am able to display data from the selected item using Log when long-pressing.

但是，当您尝试显示对话框时，您需要进入活动，不建议在 ViewModel 对象中使用。

When trying to show a dialog, however, you need to get to the Activity, which is not recommended to use in the ViewModel object.

那么如何显示对话框呢？

So how can I show the dialog?

谢谢，Ove

答

从概念上讲，一个ViewModel让我觉得从一个错误的地方发起一个Dialog。为了更清楚地做到这一点，我将RecyclerView.ViewHolder传递到布局中，并在ViewHolder上有一个方法，触发RecyclerView.Adapter上的自定义侦听器。然后，任何订阅该侦听器（Activity / Fragment）的人都可以启动Dialog。可能看起来有点迂回，但我不认为列表项的ViewModel应该知道或控制其环境。

Conceptually a ViewModel strikes me as the wrong place to launch a Dialog from. To do it more cleanly I would pass the RecyclerView.ViewHolder into the layout, and have a method on the ViewHolder that triggers a custom listener on your RecyclerView.Adapter. Then whoever subscribes to that listener (Activity/Fragment) can launch the Dialog. May seem a little roundabout, but I don't think a ViewModel of a list item should have knowledge or control of its environment.

这是一个例子。这是使用数据绑定和ViewModel处理RecyclerView项目点击的一般模式。这不是一个完整的例子，只是突出显示这种特定模式的代码。

Here is an example. This is a general pattern for handling RecyclerView item clicks with data binding and a ViewModel. This is not a complete example, just the code to highlight this specific pattern.

布局：

<layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    >
    <data>
    <variable
        name="viewHolder"
        type="com.example.ViewHolder"
        />
    <variable
        name="viewModel"
        type="com.example.ViewModel"
        />
    </data>

    <com.example.View
        android:layout_width="match_parent"
        android:layout_height="24dp"
        android:onClick="@{() -> viewHolder.onClick(viewModel)}"
        />
</layout>

适配器：

class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    public interface SelectionListener {
        void onSelectionChanged(int newPosition, ViewModel viewModel);
    }

    private @NonNull WeakReference<SelectionListener> selectionListener =
            new WeakReference<>(null);

    public void setSelectionListener(@Nullable SelectionListener listener) {
        selectionListener = new WeakReference<>(listener);
    }

    public class ViewHolder extends RecyclerView.ViewHolder<ViewBinding> {
        ViewHolder(ViewBinding binding) {
            super(binding.getRoot());

            binding.setViewHolder(this);
            binding.setViewModel(new ViewModel());
        }

        public void onClick(ViewModel viewModel) {
            SelectionListener listener = selectionListener.get();
            if (listener != null) {
                listener.onSelectionChanged(getAdapterPosition(), viewModel);
            }
        }
    }
}

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