ReactiveUI:将CanExecute与ReactiveCommand一起使用 [英] ReactiveUI: Using CanExecute with a ReactiveCommand

问题描述

我开始在Silverlight项目上使用ReactiveUI框架，并且需要一些使用ReactiveCommands的帮助.

I'm starting to work with the ReactiveUI framework on a Silverlight project and need some help working with ReactiveCommands.

在我的视图模型中，我大致看起来像这样(这只是一个简化的示例):

In my view model, I have something that looks roughly like this (this is just a simplified example):

public class MyViewModel : ReactiveObject
{
  private int MaxRecords = 5;

  public ReactiveCommand AddNewRecord { get; protected set; }

  private ObservableCollection<string> _myCollection = new ObservableCollection<string>();
  public ObservableCollection<string> MyCollection
  {
    get
    {
      return _myCollection;
    }

    set
    {
      _myCollection = value;
      raiseCollectionChanged("MyCollection");
    }
  }

  MyViewModel()
  {
    var canAddRecords = Observable.Return<bool>(MyCollection.Count < MaxRecords);
    AddNewRecord = new ReactiveCommand(canAddRecords);

    AddNewRecord.Subscribe(x => 
    {
       MyCollection.Add("foo");
    }
  }
}

第一次创建ReactiveCommand时将对canAddRecords函数进行评估，但是将项目添加到MyCollection中时不会对其进行重新评估.谁能给我展示一个很好的示例，说明如何绑定ReactiveCommand的canExecute属性，以便在这种情况下自动重新评估它?

The canAddRecords function is getting evaluated the first time the ReactiveCommand is created, but it's not getting re-evaluated when items are added to MyCollection. Can anyone show me a good example of how to bind the canExecute property of a ReactiveCommand so that it gets automatically re-evaluated in this situation?

推荐答案

实际上，有一种更好的方法，将ObservableCollection更改为ReactiveCollection(继承自ObservableCollection，但添加了一些额外的属性):

Actually, there's a better way to do this, change your ObservableCollection to ReactiveCollection (which inherits from ObservableCollection but adds some extra properties):

MyCollection = new ReactiveCollection<string>();

AddNewRecord = new ReactiveCommand(
    MyCollection.CollectionCountChanged.Select(count => count < MaxRecords));

虽然现在的问题是，您不能覆盖 MyCollection，只能重新填充它(即Clear()+ Add()).让我知道这是否是一个破坏交易的方法，尽管还有很多工作要做，但是也有一种解决方法.

The catch here now is though, you can't overwrite the MyCollection, only repopulate it (i.e. Clear() + Add()). Let me know if that's a dealbreaker, there's a way to get around that too though it's a bit more work.

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