如何创建通用类类型的属性？

Question

I have this code:

public class SelectionList<T> : ObservableCollection<SelectionItem<T>> where T : IComparable<T>
{
  // Code 
}

public class SelectionItem<T> : INotifyPropertyChanged
{
// Code
}

I need to create a property which is of the type SelectionList as follows:

public SelectionList<string> Sports { get; set; }

But when I replace string with DataRowView, as

 public SelectionList<DataRowView> Sports { get; set; }`

I am getting an error. Why doesn't this work?

Answer 1

Your problem is that string implements IComparable<string> and DataRowView doesn't.

SelectionList<T> has a constraint that T must implement IComparable<T> , hence the error.

public class SelectionList<T> : ObservableCollection<SelectionItem<T>> where T : IComparable<T>
{
  // Code 
}

One solution would be to subclass DataRowView and implement IComparable :

public class MyDataRowView : DataRowView, IComparable<DataRowView>{
  int CompareTo(DataRowView other) {
    //quick and dirty comparison, assume that GetHashCode is properly implemented
    return this.GetHashCode() - (other ? other.GetHashCode() : 0);
  }
}

Then SelectionList<MyDataRowView> should compile fine.

Answer 2

You have a constraint on your class where T : IComparable<T> . DataRowView does not implement IComparable<DataRowView> and therefore cannot be used in this case.

See here for more information about Generic Constraints: http://msdn.microsoft.com/en-us/library/d5x73970.aspx