Problem in use of SortDescription in WPF - int and string are not IComparable?

I have a problem in using SortDescription. I've found some thread about the problem, like if you want to sort by a type that doesn't implement IComparable, like a user defined class, but it's not my case.

I have a class, that has two properties: string ID, and int Value. Let's call it Item! And I have a view:

<UserControl> <!-- ... -->
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>

        <Button Click="Button_Click"
                Content="Sort by ID"
                Grid.Row="0"/>
        <Button Click="Button_Click1"
                Content="Sort by Value"
                Grid.Row="1"/>
        <DockPanel Grid.Row="2">
            <ItemsControl x:Name="mItemsControl"
                          ItemsSource="{Binding Items}"><!-- The type of Items is ObservableCollection<Item> -->
                <!-- ... -->
            </ItemsControl>
        </DockPanel>
    &l开发者_高级运维t;/Grid>
</GroupBox>

EventHandlers are like these:

private void Button_Click(object sender, RoutedEventArgs e)
    {
        mItemsControl.Items.SortDescriptions.Add(new SortDescription("ID", ListSortDirection.Ascending); //Exception here
    }
private void Button_Click1(object sender, RoutedEventArgs e)
    {
        mItemsControl.Items.SortDescriptions.Add(new SortDescription("Value", ListSortDirection.Ascending); //...and here as well
    }

I get InvalidOperationException because it "Failed to compare two elements in the array.", and it is because neither of the elements implement IComparable. And that is, what I can't understand, as I can compare ints, as well as strings.

Thanks for any idea!

This works fine for me so you are doing something wrong in other parts of your code. Compare what you do with below sample.

XAML:

<Window x:Class="SortDemo.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <StackPanel>
        <Button Click="OnSort" Content="Sort by ID" Tag="ID"/>
        <Button Click="OnSort" Content="Sort by Value" Tag="Value"/>
        <ItemsControl Name="_itemsControl" ItemsSource="{Binding Path=Items}" />
    </StackPanel>
</Window>

Code behind:

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows;

namespace SortDemo
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            Items = new ObservableCollection<Item>();
            Items.Add(new Item() { ID = "AAA", Value = 2 });
            Items.Add(new Item() { ID = "BBB", Value = 1 });

            DataContext = this;
        }

        public ObservableCollection<Item> Items { get; private set; }

        private void OnSort(object sender, RoutedEventArgs e)
        {
            string sortProperty = (sender as FrameworkElement).Tag as string;
            _itemsControl.Items.SortDescriptions.Clear();
            _itemsControl.Items.SortDescriptions.Add(new SortDescription(sortProperty, ListSortDirection.Ascending)); 
        }
    }

    public class Item
    {
        public string ID { get; set;}
        public int Value { get; set; }

        public override string ToString()
        {
            return ID + " " + Value;
        }
    }
}

I don't know if this is relevant, but I received the same error on a DataGridView when trying to sort a colum and this was the reason:

The value of the cell must by of the same type for it to be compared. If you have three rows and in two of the row you have values of the same type but the other row does not have a value it cannot compare it if the two rows which have value have been set to an object as the value for the cell in the row which has not value will be an empty string. In order to sort you will have to set the Value as string value for all the cell in the column that you are sorting.

Its in the runtime type of the items in the columns you are sorting by. The properties ID and Value must both be types deriving IComparable.

I am assuming you are not trying to do something clever and putting different runtime types all with properties named ID and Value into the Items list. You can use WPF to do dynamic things like that, but this is one example of where it will fall down.

String implement IComparable http://msdn.microsoft.com/en-us/library/system.string.aspx