Implemented accessible objects for TreeView and TreeNode. Added needed automation events and unit tests.

Implements part of #3421

Proposed changes

• Switched on SupportsUiaProviders property of TreeView class.
• Implemented accessible objects for TreeView and TreeNode classes.
• Added needed automation events and unit tests.

Customer Impact

• Improving development experience for TreeView control accessibility.

Regression?

• No

Risk

• Minimal

Screenshots

Inspect

TreeView before and after

Default TreeNode before and after

Expanded TreeNode before and after

Leaf TreeNode before and after

CheckBox TreeNode before and after

Invisible TreeNode before and after

Editable TreeNode before and after

Accessibility Insights

There is no specific errors. You can see errors on next image, but they are not about accessibility changes were created in this PR.

Narrator

Expand and collapse default node before and after

Check and uncheck node before and after

Edit default node before and after

ScrollIntoView method comparison

ScrollIntoView method before

ScrollIntoView method after

This realization sets calling node as TopNode of TreeView if the node is invisible. Looks like it works the same.

Focus on TreeView issue

By default, when we focus on a TreeView control, Inspect and Narrator highlight the SelectedNode of
this control. As I know it takes raise an events for a selected node accessible object to notify it was focused. But calling AccessibilityObject forces creation the object. It takes accessible object of the tree, so forces creating the object if it doesn't exist yet.
To avoid force creation if this is not needed should use check IsAccessibilityObjectCreated. But I found next problem when I try to add this check. Highlight after focus doesn't work for the first time if the control has first TabIndex on form. You can see this issue behavior below.

Focus on the control with check IsAccessibilityObjectCreated

It works incorrect.

Focus on the control without check IsAccessibilityObjectCreated

It works great, but not safety due to forcing the object creating.

It was not so easy for me to resolve it in the fix. So I skipped this problem and took implementation without the check. I guess this problem needs to be investigated and resolved in out of scope issue.

Additional note

I take it if node is check box it has DefaultAction equals Check or Uncheck but before the fix DoDefaultAction does nothing in this case. I configured this method, so it performs Toggle method of TreeNodeAccessibleObject in this case.

Test methodology

• Manually
• Unit testing
• CTI

Accessibility testing

• Inspect
• Accessibility Insights
• Narrator

Test environment(s)

• .Net version: 6.0.100
• OS version: 10.0.19044

Microsoft Reviewers: Open in CodeFlow