从 ViewModel 启动 DialogFragment 的推荐方法是什么? [英] What is the recommended way to launch a DialogFragment from a ViewModel?

问题描述

我在 Recyclerview 中有一个列表对象.长按某个项目时，我想显示一个对话框，其中包含所点击项目的数据.

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 为每个项目使用数据绑定，我可以在长按时使用 Log 显示所选项目的数据.

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，当尝试显示对话框时，您需要访问 Activity，不推荐在 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?

谢谢欧维

推荐答案

从概念上讲，我认为 ViewModel 是启动 Dialog 的错误位置.为了更干净地做到这一点，我会将 RecyclerView.ViewHolder 传递到布局中，并在 ViewHolder 上有一个方法来触发 RecyclerView.Adapter 上的自定义侦听器.然后订阅该侦听器(活动/片段)的任何人都可以启动对话框.可能看起来有点迂回，但我认为列表项的 ViewModel 不应该了解或控制其环境.

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 项目点击的通用模式.这不是一个完整的示例，只是突出显示此特定模式的代码.

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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