Implement filesystem watching via ReadDirectoryChangesW

[lukeblevins]

This requires extensive testing as it may have introduced a few bugs.

[tsvietOK]

Random crash when navigating to a folder still exists and VS can't catch an exception.

Files and folders are not sorted.

After folder creation or renaming there 3 or more folders displaying, fixes by folder refresh. For files the same.

[lukeblevins]

Thanks for the feedback everybody. I'll make it a priority to fix these. Keep up the testing!

[gave92]

@duke7553 Just a curiosity: There is the FileSystemWatcher class which I think is supported in UWP when you use the desktop bridge. It's basically a convenience class that calls ReadDirectoryChagesW internally. Have you considered using this instead of doing the stuff "low level"?

[lukeblevins]

@gave92 Personally, I'm trying to keep as much core functionality as possible outside the Full Trust component. This is because FullTrust components are not supported in Windows 10X.

[gave92]

I meant: I think that FileSystemWatcher is supported in UWP. FileSystemWatcher is part of netstandard 2.0 and uwp supports that.

[lukeblevins]

@gave92 Good thought. Unfortunately, .NET Classes are unable to access brokered filesystem locations which WinRT apps use, which means we have to do it the native way.

[gave92]

@duke7553 thanks for the clarification. I thought that the broadFileSystemAccess capability was enough to bypass this.

[lukeblevins]

@gave92 @tsvietOK If someone could help me understand why there are still duplicate items (after adding one item) I'd be grateful. In my testing, it occurs after quickly refreshing multiple times.

[lukeblevins]

It is clearly because the method is fired twice, but how to prevent that, IDK

[gave92]

@duke7553 I still have to review the code but I had similar issue with the recycle bin functionality: multiple filesystem update events where firing at the same time and I was ending with duplicate items.

I solved it using a semaphore so the refresh function can only be entered after the previous call has ended.

[tsvietOK]

@duke7553 Sometimes displayed(after creation) 4 or more folders/files instead of 1. In my testing this bug is not appears when refreshing items.

[lukeblevins]

@tsvietOK In my testing, it was almost like refreshing multiple times didn't properly cancel the previous watcher.

[lukeblevins]

Refreshing causes the next item add/removal action to be duplicated.

[gave92]

@duke7553 very stupid suggestion: you are not awaiting the call to AddFileOrFolder

[lukeblevins]

@yaichenbaum @tsvietOK @gave92 This is ready for review. If at all possible, we should review this one quickly before the next release.

[yaira2]

[gave92]

@duke7553 refreshing + renaming still has some issues for me:

2020-06-11 07:47:45.2148|ERROR|Files.App|Collection was modified; enumeration operation may not execute.|System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.Collections.Generic.List1.Enumerator.MoveNextRare() at System.Collections.Generic.List1.Enumerator.MoveNext()
at System.Linq.Enumerable.SelectIListIterator2.MoveNext() at System.Linq.Enumerable.Contains[TSource](IEnumerable1 source, TSource value, IEqualityComparer1 comparer) at System.Linq.Enumerable.Contains[TSource](IEnumerable1 source, TSource value)
at Files.Filesystem.ItemViewModel.<>c__DisplayClass72_0.b__0(IAsyncAction x)
--- End of stack trace from previous location where exception was thrown ---
at Files.Filesystem.ItemViewModel.WatchForDirectoryChanges(String path)
at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.b__7_0(Object state)
at System.Threading.WinRTSynchronizationContextBase.Invoker.InvokeCore()