在RecyclerView适配器中使用自定义视图? [英] Use custom View in a RecyclerView Adapter?

问题描述

我有一个基本的自定义视图，如下所示:

I have a basic custom View which looks like this:

public class CustomView extends RelativeLayout {

    private User user;

    private ImageView profilePicture;

    public CustomView(Context context) {
        super(context);
        init();
    }

    public CustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        inflate(getContext(), R.layout.custom_layout, this);

        profilePicture = (ImageView) findViewById(R.id.profilePicture);

        // ACCESS USER MODEL HERE
        // e.g. user.getUsername()
    }

}

如您所见，我想在视图中访问用户数据(即:user.getUsername()).

As you can see, I'd like to access user data in the View (i.e.: user.getUsername()).

我还需要能够在RecyclerView适配器中使用自定义视图.

I also need to be able to use the custom View in a RecyclerView Adapter.

这是我的适配器当前的外观:

Here is what my Adapter currently looks like:

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

    private Context context;

    private List<User> userData;

    public MyAdapter(Context context, List<User> userData) {
        this.context = context;
        this.userData = userData;
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public ViewHolder(View v) {
            super(v);
        }
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(context);

        // HOW TO INFLATE THE CUSTOM VIEW?

        // ViewHolder viewHolder = new ViewHolder(customView);

        return viewHolder;
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, int position) {
        // ANYTHING HERE?
    }

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

}

如何在适配器中为自定义视图充气?
另外，我应该在onBindViewHolder()中放入任何内容吗?

How can I inflate the custom View in the Adapter?
Also, should I put anything in onBindViewHolder()?

注意:我必须使用自定义视图，因为我在不同的适配器下使用该视图(即:不仅是这个RecyclerView适配器).

Note: I must use a custom View, as I use this View under different Adapters (i.e.: not just this RecyclerView Adapter).

推荐答案

假设一个CustomView类看起来像这样:

Assuming a CustomView class that looks something like this:

public class CustomView extends RelativeLayout {
    private User user;
    private ImageView profilePicture;

    // override all constructors to ensure custom logic runs in all cases
    public CustomView(Context context) {
        this(context, null);
    }
    public CustomView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public CustomView(Context context, AttributeSet attrs, int defStyleAttr) {
        this(context, attrs, defStyleAttr, 0);
    }
    public CustomView(
            Context context,
            AttributeSet attrs,
            int defStyleAttr,
            int defStyleRes
    ) {
        super(context, attrs, defStyleAttr, defStyleRes);

        // put all custom logic in this constructor, which always runs
        inflate(getContext(), R.layout.custom_layout, this);
        profilePicture = (ImageView) findViewById(R.id.profilePicture);
    }

    public void setUser(User newUser) {
        user = newUser;
        // ACCESS USER MODEL HERE
        // e.g. user.getUsername()
    }
}

您的RecyclerView.Adapter和RecyclerView.ViewHolder可能看起来像这样:

Your RecyclerView.Adapter and RecyclerView.ViewHolder could look something like this:

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    // no Context reference needed—can get it from a ViewGroup parameter
    private List<User> userData;

    public MyAdapter(List<User> userData) {
        // make own copy of the list so it can't be edited externally
        this.userData = new ArrayList<User>(userData);
    }

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

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        // no need for a LayoutInflater instance—
        // the custom view inflates itself
        CustomView itemView = new CustomView(parent.getContext());
        // manually set the CustomView's size
        itemView.setLayoutParams(new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.WRAP_CONTENT
        ));
        return new ViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, int position) {
        holder.getCustomView().setUser(userData.get(position));
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        private CustomView customView;

        public ViewHolder(View v) {
            super(v);
            customView = (CustomView) v;
        }

        public CustomView getCustomView() {
            return customView;
        }
    }
}

• CustomView管理自己的设置，该设置发生在其自己的构造函数中，在这种情况下，使用XML文件的填充. (或者，它可以通过编程方式设置其子视图.)
• 因此，RecyclerView.Adapter不需要执行任何充气操作，只需创建一个新的CustomView实例，并让CustomView担心自己的设置即可.
• 在调用其setUser方法之前，CustomView无法获得User实例，因此在构造函数中无法进行用户访问.在任何情况下，在CustomView个生命周期中，RecyclerView都可以要求它在不同时间显示许多不同用户的信息. CustomView需要能够执行此操作.因此，引入了setUser方法.
• 由于CustomView是通过代码而不是XML实例化的，因此无法在XML中定义大小属性.因此，大小是在实例化后以编程方式完成的.
• onBindViewHolder只需在CustomView上调用setUser即可将CustomView与正确的User实例链接.
• ViewHolder类现在只是RecyclerView项目和CustomView之间的链接.
• The CustomView manages its own setup, which occurs in its own constructor and in this case uses inflation of an XML file. (Alternatively, it could set up its child views programmatically.)
• Because of this, the RecyclerView.Adapter doesn't need to perform any inflation—it just creates a new CustomView instance, and lets the CustomView worry about its own setup.
• The CustomView can't get a User instance until its setUser method is called, so user access cannot occur in the constructor. In any case, over one CustomView lifetime, a RecyclerView could ask it to show information for many different users at different times. The CustomView needs to be able to do this. Therefore, a setUser method is introduced.
• Because the CustomView is instantiated by code instead of by XML, attributes for size can't be defined in XML. Therefore, sizing is done programmatically after instantation.
• onBindViewHolder simply calls setUser on the CustomView to link the CustomView with the correct User instance.
• The ViewHolder class is now just a link between a RecyclerView item and a CustomView.

似乎从未讨论过使用RecyclerView内另一个类的预构建自定义视图(即，不夸大RecyclerView.Adapter内的XML).我认为，即使自定义视图仅在RecyclerView中使用，这也是一个好主意，因为它遵守单一责任原则.

Using pre-built custom views from another class within RecyclerViews (i.e. not inflating XML within the RecyclerView.Adapter) never seems to be discussed. I think it's an excellent idea even when the custom view is exclusively used within a RecyclerView, because it promotes separation of concerns and adherence to the Single Responsibility Principle.

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