ComboBox与ComboBoxItem名称为空及消息列表按其选项排序问题咨询

Let's break down your two problems and fix them step by step:

1. Fixing Null Names for ComboBox and ComboBoxItem #

If your named elements (sort_dropdown, time_sort, etc.) are coming up null, here are the most common fixes:

• Wait for the UI to fully load: Don't try accessing these elements in your window/user control's constructor. The XAML elements haven't finished initializing yet at that point. Instead, hook into the Loaded event:

  public YourWindow()
  {
      InitializeComponent();
      this.Loaded += YourWindow_Loaded;
  }
  
  private void YourWindow_Loaded(object sender, RoutedEventArgs e)
  {
      // Now you can safely access sort_dropdown, time_sort, etc.
      if (sort_dropdown != null)
      {
          // Do something with the ComboBox
      }
  }
  

• Check for template nesting: If your ComboBox is inside a DataTemplate or ControlTemplate, direct access via x:Name won't work. You'll need to use FindName() on the template's parent to retrieve the element. But based on your XAML snippet, this probably isn't the case here.

• Validate XAML syntax: Ensure all your ComboBoxItem elements are properly closed (your snippet cuts off at "g...", so double-check the last item's closing tag). Typos in x:Name can also cause null references.

2. Sorting Your Message List by ComboBox Selection #

Instead of handling the Selected event on each individual ComboBoxItem, it's cleaner to use the ComboBox's SelectionChanged event. Here's how to implement it:

Step 1: Update Your XAML #

Remove the individual Selected events from each item and add a single SelectionChanged event to the ComboBox:

<ComboBox x:Name="sort_dropdown" HorizontalAlignment="Left" Margin="828,219,0,0" VerticalAlignment="Top" Width="120" SelectedIndex="0" SelectionChanged="sort_dropdown_SelectionChanged">
    <ComboBoxItem x:Name="time_sort" Content="Time"/>
    <ComboBoxItem x:Name="nickname_sort" Content="Nickname"/>
    <ComboBoxItem x:Name="groupid_sort" Content="Group ID"/>
</ComboBox>

Step 2: Implement the Sort Logic in Code-Behind #

Assume your message list is an ObservableCollection<Message> where Message has properties like Timestamp, Nickname, and GroupId. Use a CollectionViewSource to sort without recreating the collection:

private void sort_dropdown_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    var selectedItem = sort_dropdown.SelectedItem as ComboBoxItem;
    if (selectedItem == null) return;

    // Get the view of your message collection
    var messageView = CollectionViewSource.GetDefaultView(YourMessageCollection);
    if (messageView == null) return;

    // Clear existing sort rules
    messageView.SortDescriptions.Clear();

    // Apply new sort based on selection
    switch (selectedItem.Content.ToString())
    {
        case "Time":
            messageView.SortDescriptions.Add(new SortDescription("Timestamp", ListSortDirection.Ascending));
            break;
        case "Nickname":
            messageView.SortDescriptions.Add(new SortDescription("Nickname", ListSortDirection.Ascending));
            break;
        case "Group ID":
            messageView.SortDescriptions.Add(new SortDescription("GroupId", ListSortDirection.Ascending));
            break;
    }
}

This approach keeps your original collection intact and just updates the sorting order, which is more efficient than creating a new collection each time.

内容的提问来源于stack exchange，提问作者D. Ziegler