为什么我的 RecyclerView 没有响应我的自定义 Click-Event？

Question

I am using the this tutorial.

I am using API 27 and Xamarin Android without Forms.

The basic usage of a RecyclerView is explained in the previous step of this tutorial and the next step is to extend the sample by Click-Handlers.

I have extended my Adapter with this code public event EventHandler<int> ItemClick; and created a callback function like this:

void OnItemClick (object sender, int position)
{
    Console.WriteLine("I've done it!");
}

and added it to the Adapter like this:

mAdapter = new CustomObjectAdapter(mCustomObject);
mAdapter.ItemClick += OnItemClick;

Once the app shows up I have set a Breckpoint on the Console.WriteLine -Part and touched/clicked the shown image. But the event doesn't fire.

This is my adapter-class:

class ModuleClassContainerAdapter : RecyclerView.Adapter
    {
        public event EventHandler<int> ItemClick;
        public ModuleClassContainer mModuleClassContainer;

        public ModuleClassContainerAdapter(ModuleClassContainer moduleClassContainer)
        {
            mModuleClassContainer = moduleClassContainer;
        }

        public override int ItemCount
        {
            get { return mModuleClassContainer.NumModules; }
        }

        public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
        {
            ModuleViewHolder vh = holder as ModuleViewHolder;

            var imageBitmap = BitmapFactory.DecodeByteArray(mModuleClassContainer[position].ImageBytes, 0, mModuleClassContainer[position].ImageBytes.Length);

            // Load the photo image resource from the photo album:
            vh.Image.SetImageBitmap(imageBitmap);

            // Load the photo caption from the photo album:
            vh.Caption.Text = mModuleClassContainer[position].ModuleName;
        }

        public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
        {
            // Inflate the CardView for the photo:
            View itemView = LayoutInflater.From(parent.Context).
                        Inflate(Resource.Layout.ModuleCardView, parent, false);

            // Create a ViewHolder to hold view references inside the CardView:
            ModuleViewHolder vh = new ModuleViewHolder(itemView);
            return vh;
        }
    }

And this is how I set-up my adapter:

private void SetupView()
        {
            RunOnUiThread(() =>
            {
                mModuleClassContainerAdapter = new ModuleClassContainerAdapter(mModuleClassContainer);
                mModuleClassContainerAdapter.ItemClick += MModuleClassContainerAdapter_ItemClick;
                mRecyclerView.SetAdapter(mModuleClassContainerAdapter);
                mModuleClassContainerAdapter.NotifyDataSetChanged();
            });
        }

Why gets my event not fired?

Answer 1

In your adapter, declare the eventHandler, and pass it to the ViewHolder

public class ModuleClassContainerAdapter  : RecyclerView.Adapter
    {
        // Event handler for item clicks:
        public event EventHandler<int> ItemClick;

// Create a new photo CardView (invoked by the layout manager): 
        public override RecyclerView.ViewHolder 
            OnCreateViewHolder (ViewGroup parent, int viewType)
        {
            // You need to pass the event 
            ModuleViewHolder vh = new ModuleViewHolder (itemView, OnClick); 
            return vh;
        }

        // Raise an event when the item-click takes place:
        void OnClick (int position)
        {
            if (ItemClick != null)
                ItemClick (this, position);
        }

In your ViewHolder

    public class ModuleViewHolder : RecyclerView.ViewHolder
    {
        // Get references to the views defined in the CardView layout.
        public ModuleViewHolder (View itemView, Action<int> listener) 
            : base (itemView)
        {
 on the item view and report which item
            // was clicked (by layout position) to the listener:
            itemView.Click += (sender, e) => listener (base.LayoutPosition);
        }
    }