我的ComboBox SelectionChangedEvent发送先前选择的项目

Question

So, whenever I change the selections I need to call a method, that compares the new selection with different options. Problem is, that it always sends the object selected before that

Initially I thought I could just invert the selection, but that would only work with 2 options.

// Create the Combobox
ComboBox selectType = new ComboBox();
selectType.Text = "Select Type";
selectType.SelectionChanged += CallChange;

ComboBoxItem sortingAlgorithm = new ComboBoxItem();
sortingAlgorithm.Content = "Sorting Algorithm";

ComboBoxItem searchingAlgorithm = new ComboBoxItem();
searchingAlgorithm.Content = "Searching Algorithm";

// add the items to ComboBox

// Call on new selection
void CallChange(object sender, SelectionChangedEventArgs args)
{
   _controller.ChangeType((string)selectType.SelectionBoxItem);
}

I'd think that it just sends the new selection. Do I have any thinking mistakes or did I mix anything up? Also I know that using Strings to compare selections is very bad practice, I am currently changing it all to dictionaries

Answer 1

The selected item is only propagated after the changed event was handled. This allows to manipulate the selected value before it is visible as selected. Therefore the moment the SelectionChanged event occurred, the SelectionBoxItem hasn't changed yet. You have to reference the selected item from the args object instead:

// Call on new selection
void CallChange(object sender, SelectionChangedEventArgs args)
{
  _controller.ChangeType(args.AddedItems.OfType<string>().FirstOrDefault() ?? string.Empty);
}