MvxSpinner selecteditem在项目源更改中未更新 [英] MvxSpinner selecteditem not updated on itemssource change

问题描述

我正在构建一个涉及从列表中添加项目的表单，但是向用户显示的列表取决于从另一个列表中进行选择.为此，我有两个MvxSpinners，每个MvxSpinners具有绑定的ItemsSource和SelectedItem.

I am building a form that involves adding items from a list, but the list that is being shown to the user depends on the selection from another list. To do this I have two MvxSpinners each with a bound ItemsSource and SelectedItem.

<MvxSpinner
   android:layout_width="300dp"
   android:layout_height="50dp"
   local:MvxBind="ItemsSource item_source_one; SelectedItem selected_item_one;"/>
<MvxSpinner
   android:layout_width="300dp"
   android:layout_height="50dp"
   local:MvxBind="ItemsSource item_source_two; SelectedItem selected_item_two;"/>

selected_item_one更改时，item_source_two更改为新列表.所有这些工作均有效，但更改item_source_two时selected_item_two保持与更改前相同.我希望selected_item_two匹配item_source_two更改时在视觉上显示的内容.

When selected_item_one changes item_source_two changes to a new list. All of this works, except when item_source_two is changed selected_item_two remains the same as it was before the change. I would like for the selected_item_two to match what is visually shown when item_source_two changes.

推荐答案

微调器绑定在MvvmCross中并不完美-特别是，必须在ItemsSource更改后发送SelectedItem更改.

The spinner binding isn't perfect in MvvmCross - in particular, the SelectedItem change must be sent after the ItemsSource change.

要解决此问题，您可以在ItemsSource之后 处发出伪造的SelectedItem更改信号-例如像这样:

To work around this, you could signal a fake SelectedItem change after the ItemsSource - e.g. something like:

 RaisePropertyChanged(() => item_source_two);
 RaisePropertyChanged(() => selected_item_two);

如果您想更全面地解决此问题，还可以考虑覆盖MvxSpinner-遗憾的是，由于我们错过了虚拟，因此您无法轻易继承，但是您可以执行以下操作:

If you wanted to fix this more fully, you could also consider overriding MvxSpinner - sadly you can't easily inherit because we missed virtual, but you do something like:

public class MySpinner : MvxSpinner
{
    public MySpinner(Context context, IAttributeSet attrs)
        : base(context, attrs)
    {
    }

    [MvxSetToNullAfterBinding]
    public new IEnumerable ItemsSource
    {
        get { return base.ItemsSource; }
        set 
        { 
            // TODO - work out what the current selection and store it in a local variable
            base.ItemsSource = value; 
            // TODO - reset the current selection here from the local variable
        }
    }
}

继承自 https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Binding.Droid/Views/MvxSpinner.cs

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