Xamarin-将集合设置为XAML中的自定义可绑定属性 [英] Xamarin - setting a collection to custom bindable property in XAML

问题描述

我有一个具有定义的可绑定属性的自定义ContentView:

I have a custom ContentView with a defined bindable property:

    public IEnumerable<SomeItem> Items
    {
        get => (IEnumerable<SomeItem>)GetValue(ItemsProperty);
        set => SetValue(ItemsProperty, value);
    }

    public static readonly BindableProperty ItemsProperty = BindableProperty.Create(
        nameof(Items),
        typeof(IEnumerable<SomeItem>),
        typeof(MyControl),
        propertyChanged: (bObj, oldValue, newValue) =>
        {
        }
    );

如何在XAML中为此设置一个值?

How can I set a value to this in XAML?

我尝试过:

<c:MyControl>
   <c:MyControl.Items>
      <x:Array Type="{x:Type c:SomeItem}">
           <c:SomeItem />
           <c:SomeItem />
           <c:SomeItem />
      </x:Array>
   </c:MyControl.Items>
</c:MyControl>

但是会不时出现编译错误:

But getting from time to time following compilation error:

error : Value cannot be null.
error : Parameter name: fieldType

我做错了什么?有其他方法吗?

I'm doing something wrong? Is there a different way?

推荐答案

将ContentView更改为以下内容:

Change your ContentView to something like this:

public partial class MyControl : ContentView
{
    public ObservableCollection<SomeItem> Items { get; } = new ObservableCollection<SomeItem>();

    public MyControl()
    {
        InitializeComponent();

        Items.CollectionChanged += Items_CollectionChanged;
    }

    public static readonly BindableProperty ItemsProperty = BindableProperty.Create(
        nameof(Items),
        typeof(ObservableCollection<SomeItem>),
        typeof(MyControl)
    );

    void Items_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
       //Here do what you need to do when the collection change
    }
}

您的IEnumerable属性将其更改为ObservableCollection并订阅CollectionChanged事件.

Your IEnumerable property change it for an ObservableCollection and subscribe for the CollectionChanged event.

还对BindableProperty进行了一些更改.

Also do some changes in the BindableProperty.

因此，现在您可以在XAML中添加以下项目:

So now in your XAML you can add the items like this:

<c:MyControl>
   <c:MyControl.Items>
        <c:SomeItem />
        <c:SomeItem />
        <c:SomeItem />
        <c:SomeItem />
    </c:MyControl.Items> 
</c:MyControl>

希望这会有所帮助.-

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