带有 Click 事件的 RecyclerView

此示例显示如何在 Xamarin.Android RecyclerView 中设置 Click EventHandlers。

在 Android Java 中，为 Click 设置侦听器的方法是使用 onClickListener 来查看将被单击的视图，如下所示：

ImageView picture = findViewById(R.id.item_picture);
picture.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        // do stuff
    }
});

但是，在 Xamarin.Android 中，为 Click 事件设置侦听器的方法是通过以下方式添加 EventHandler：

1

ImageView picture = FindViewById<ImageView>(Resource.Id.item_picture);
picture.Click += delegate {
    // do stuff
};

2

ImageView picture = FindViewById<ImageView>(Resource.Id.item_picture);
picture.Click += async delegate {
    // await DoAsyncMethod();
    // do async stuff
};

3

ImageView picture = FindViewById<ImageView>(Resource.Id.item_picture);
picture.Click += Picture_Click;
... // rest of your method

private void Picture_Click(object sender, EventArgs e)
{
    // do stuff
}

请注意，**添加了 EventHandler，而不是设置。**如果在 GridView / ListView 适配器的 GetView 方法中添加 Click EventHandler，或者从 RecyclerView.Adapter 添加 OnBindViewHolder 方法，则每次创建项目视图时都会添加新的 EventHandler。滚动几次后，将添加多个 EventHandler，当单击视图时，将触发所有这些事件。

为了避免这种麻烦，必须取消订阅 EventHandlers 并随后在 GetView 或 OnBindViewHolder 方法中进行订阅。此外，他们必须使用数字 3. 方式来设置 EventHandler，否则将无法取消订阅 EventHandler。

具有 Click 事件的 RecyclerView.Adapter 示例如下所示：

public class ViewHolderPerson : Android.Support.V7.Widget.RecyclerView.ViewHolder
{
    public View Item { get; private set; }
    public ImageView Picture { get; private set; }
    public TextView Name { get; private set; }

    public ViewHolderPerson(View itemView) : base(itemView)
    {
        this.Item = itemView;
        this.Picture = itemView.FindViewById<ImageView>(Resource.Id.Item_Person_Picture);
        this.Name = itemView.FindViewById<TextView>(Resource.Id.Item_Person_Name);
    }
}

public class AdapterPersons : Android.Support.V7.Widget.RecyclerView.Adapter
{
    private Context context;
    private Android.Support.V7.Widget.RecyclerView recyclerView;
    private List<Person> persons;

    public AdapterPersons(Context context, Android.Support.V7.Widget.RecyclerView recyclerView, List<Person> persons)
    {
        this.context = context;
        this.recyclerView = recyclerView;
        this.persons = persons;
    }

    public override int ItemCount => persons.Count;

    public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
    {
        Person person = this.persons[position];
        ((ViewHolderPerson)holder).Name.Text = person.Name;
        ((ViewHolderPerson)holder).Picture.SetImageBitmap(person.Picture);

        // Unsubscribe and subscribe the method, to avoid setting multiple times.
        ((ViewHolderPerson)holder).Item.Click -= Person_Click;
        ((ViewHolderPerson)holder).Item.Click += Person_Click;
    }

    private void Person_Click(object sender, EventArgs e)
    {
        int position = this.recyclerView.GetChildAdapterPosition((View)sender);
        Person personClicked = this.persons[position];
        if(personClicked.Gender == Gender.Female)
        {
            Toast.MakeText(this.context, "The person clicked is a female!", ToastLength.Long).Show();
        }
        else if(personClicked.Gender == Gender.Male)
        {
            Toast.MakeText(this.context, "The person clicked is a male!", ToastLength.Long).Show();
        }
    }

    public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
    {
        View itemView = LayoutInflater.From(parent.Context).Inflate(Resource.Layout.item_person, parent, false);
        return new ViewHolderPerson(itemView);
    }

}