Fix datagrid memory leak - selection and clear

[singhashish-wpf]

Fixes #6983 and partially fixes 6087

Description

Clear properties which were holding references related to selection and focused info, once the datagrid is cleared.

Customer Impact

Huge memory consumption.

Regression

No

Testing

Local testing with sample app for memory leak fix.
WPF CTP testing.

Risk

Low

Microsoft Reviewers: Open in CodeFlow

[singhashish-wpf]

cc: @KirillOsenkov

[Symbai]

In the original issue people reported that it also happens on ItemsControl and ListView etc. I only see a fix for Datagrid here. So its just a partial fix? If so a merge should not close the original issue.

[KirillOsenkov]

It's a good idea to fix this for other controls as well, but I think it's better to do it in separate PRs, one per control. This way if we break anything we can roll back just that one PR.

[Symbai]

It's a good idea to fix this for other controls as well, but I think it's better to do it in separate PRs, one per control. This way if we break anything we can roll back just that one PR.

I don't disagree but to my knowledge if the first post contains Fixes #number then the issue gets automatically closed once the PR has been merged. And since the original issue contains useful information including repros I think it should be left open.

[h3xds1nz]

I don't disagree but to my knowledge if the first post contains Fixes #number then the issue gets automatically closed once the PR has been merged. And since the original issue contains useful information including repros I think it should be left open.

You know how good it feels to close an issue? Eitherway there's also #6983, so that one could be considered for DataGrid and the currently linked one renamed appropriately if the issue is in those controls.

[Symbai]

You know how good it feels to close an issue?

Yes. But I also know how insanely frustrating it feels for users if repo owners are closing an issue which isn't (fully) fixed. You have to create a new one, posting all the information again. Repo owners asking for a repro again, etc.

Eitherway there's also #6983, so that one could be considered for DataGrid and the currently linked one renamed appropriately if the issue is in those controls.

Sounds good 👍

[h3xds1nz]

Yes. But I also know how insanely frustrating it feels for users if repo owners are closing an issue which isn't (fully) fixed. You have to create a new one, posting all the information again. Repo owners asking for a repro again, etc.

Of course, I was joking, was most likely an oversight.

[singhashish-wpf]

Thanks @KirillOsenkov for the suggestion and the review.
Thanks @Symbai and @h3xds1nz
Updated the description to remove the link to the other issue which contains lot more information, such that it doesn't get closed automatically with this PR.

[h3xds1nz]

@singhashish-wpf No worries.

By the way, a very tiny nit: Most of the codebase has space between // and the actual comment text, I believe we should follow it when we can.