在开发Android应用时，经常需要处理列表视图，而RecyclerView是处理列表数据的首选方式。本文将介绍如何在Xamarin Android中创建RecyclerView，并在每个列表项中添加Spinner控件，以及如何根据用户选择的Spinner下拉值动态更新列表项。
首先，需要创建一个ViewHolder类，用于引用视图对象。ViewHolder类中包含Spinner对象，并在构造函数中为Spinner对象分配事件监听器。
public class VegeViewHolder : RecyclerView.ViewHolder
{
public ImageView Image { get; set; }
public TextView Name { get; set; }
public Spinner Quantity { get; set; }
public TextView Price { get; set; }
public TextView TotalAmount { get; set; }
public VegeViewHolder(View itemView, Action itemlistner, Action spinnerItemSelected)
: base(itemView)
{
Image = itemView.FindViewById(Resource.Id.list_image);
Name = itemView.FindViewById(Resource.Id.Name);
Price = itemView.FindViewById(Resource.Id.Price);
Quantity = itemView.FindViewById(Resource.Id.spinner1);
TotalAmount = itemView.FindViewById(Resource.Id.total);
itemView.Click += (sender, e) => itemlistner(base.Position);
Quantity.ItemSelected += new EventHandler(spinnerItemSelected);
}
}
接下来，需要创建一个自定义适配器类。RecyclerView需要提供一个适配器，用于访问数据源并填充每个列表项。在适配器类中，创建了一个事件处理器，用于处理Spinner控件的事件。
public event EventHandler ItemClick;
public event EventHandler SpinnerItemSelectionChanged;
public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
{
View itemView = LayoutInflater.From(parent.Context).Inflate(Resource.Layout.list_items, parent, false);
VegeViewHolder vh = new VegeViewHolder(itemView, OnClick, spinner_ItemSelected);
return vh;
}
void OnClick(int position)
{
if (ItemClick != null)
ItemClick(this, position);
}
void spinner_ItemSelected(object sender, AdapterView.ItemSelectedEventArgs e)
{
if (SpinnerItemSelectionChanged != null)
SpinnerItemSelectionChanged(sender, e);
}
当布局管理器准备在RecyclerView的可见屏幕区域显示特定视图时，它会调用适配器的OnBindViewHolder方法，以从数据源填充指定行位置的项目。
public override void OnBindViewHolder(RecyclerView.ViewHolder viewHolder, int position)
{
var item = Items[position];
var vh = viewHolder as VegeViewHolder;
var spinnerPos = 0;
var adapter = new ArrayAdapter(Context, Android.Resource.Layout.SimpleSpinnerItem, _quantity);
adapter.SetDropDownViewResource(Android.Resource.Layout.SimpleSpinnerDropDownItem);
vh.Name.Text = item.Name;
vh.Price.Text = string.Format("Price: ${0}", item.Price);
vh.ItemView.Tag = position;
if (item.Quantity > 0)
{
spinnerPos = adapter.GetPosition(item.Quantity.ToString());
vh.TotalAmount.Text = string.Format("${0}", item.Price * item.Quantity);
}
else
{
vh.TotalAmount.Text = "";
}
vh.Quantity.Tag = position;
vh.Quantity.Adapter = adapter;
vh.Quantity.SetSelection(spinnerPos);
vh.Image.SetImageResource(item.ImageId);
}
最后，需要在MainActivity类中处理事件。当用户触摸或更改Spinner值时，这些事件将在活动类级别处理。
void OnItemClick(object sender, int position)
{
int itemPosition = position + 1;
Toast.MakeText(this, "Vegetable Item " + itemPosition, ToastLength.Short).Show();
}
void SpinnerItemSelectionChangedEvent(object sender, AdapterView.ItemSelectedEventArgs e)
{
Spinner spinner = (Spinner)sender;
var itemPosition = Convert.ToInt32(spinner.Tag);
var currentquantity = vegeList[itemPosition].Quantity;
var selectedQuantity = Convert.ToInt32(spinner.GetItemAtPosition(e.Position).ToString());
if (currentquantity != selectedQuantity)
{
vegeList[itemPosition].Quantity = selectedQuantity;
mAdapter.NotifyItemChanged(itemPosition);
}
}