Make Custom WinForms Control Work with Narrator (Accessibility)

Question

I have a custom list control derived from Control class.

I need to make it accessible to people with disabilities through MSAA (Microsoft Active Accessibility).

So far I understand that I need to create class that inherits from ControlAccessibleObject and then return its instance in Control.CreateAccessibilityInstance method override.

The problem is that I have implemented this and it seems not work with Windows Narrator tool.

For example, when I click on an item in standard ListView, the Narrator speaks out the selected item text.

But when I click on item in my control, nothing happens (although the item text is requested in my ControlAccessibleObject implementation)

I thought I need to implement IAccessible as well, but I looked on .NET refrence source code and the ListView does not implement this interface. I thought maybe this is implemented in the wrapped Win32 control, so I took a look on similar control - DataGridView - but this does not implement IAccessible as well.

DataGridView have accessibility support, but although I copied all the important code of DataGridViewAccessibleObject, it still does not work in my control.

Do anyone have more experience with custom control accessibility in WinForms?

Answer 1

Okay, I found it: The Control.AccessibilityNotifyClients method does the magic. One have to override this method in a derived control.

However, to make screen readers speak the text, I had to call:

AccessibilityNotifyClients(AccessibleEvents.Focus, index);
AccessibilityNotifyClients(AccessibleEvents.Selection, index);

Here the index is an index of newly selected item.

I found this code in the .NET reference source of CheckedListBox. When I used Focus or Selection event solely, the screen reader have not reacted. The spoken text also depend on the AccessibleObject state that corresponds to a newly selected item.