ComboBox internal state not consistent when inserting at SelectedIndex and IsHandleCreated == false

[jbhensley]

• .NET Core Version: 6.0.101

• Have you experienced this same bug with .NET Framework?:
  Yes

Problem description:

Add items to the ComboBox and select one:

comboBox1.Items.Add("Item 1");
comboBox1.Items.Add("Item 2");
comboBox1.Items.Add("Item 3");

comboBox1.SelectedIndex = 1;

Now insert at the selected index: comboBox1.Items.Insert(1, "Test");

If the handle has been created:

• Item will be inserted into collection
• SelectedIndex will increment
• SelectedItem and Text remain consistent

If the handle has not been created:

• Item will be inserted into collection
• SelectedIndex will remain the same
• SelectedItem will be the newly inserted item
• Text will match the old SelectedItem

Issue discovered while adding events to Items collection (#6673)

Expected behavior:

• Internal state of control should remain consistent
• Behavior when handle has not yet been created should match that of when it has been

Minimal repro:

• Create new WinForms project
• Add the following to Main just after ApplicationConfiguration.Initialize();

var comboBox = new ComboBox();

comboBox.Items.Add("Item 1");
comboBox.Items.Add("Item 2");
comboBox.Items.Add("Item 3");
comboBox.SelectedIndex = 1;

comboBox.Items.Insert(1, "Test");

• Set a breakpoint on comboBox.Items.Insert(1, "Test");
• Observe the values of SelectedIndex, SelectedItem and Text before and after that line executes

[merriemcgaw]

It would be a breaking change if we adjusted this behavior. The question we have is exactly how breaking this change is going to be. This seems to be another one of those cases where we probably ought to document this issue and a workaround would be to create the handle before trying to add something in the list.

[RussKie]

I suggest updating the docs https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.Windows.Forms/ComboBox.xml

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Happy Coding!