StorageLibraryLastChangeId.Unknown Property
Definition
Important
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Returned when the USN journal overflows and the service cannot keep up with changes or there is another reason the change id cannot be computed.
public:
static property unsigned long long Unknown { unsigned long long get(); };static uint64_t Unknown();public static ulong Unknown { get; }var uInt64 = StorageLibraryLastChangeId.unknown;Public Shared ReadOnly Property Unknown As ULongProperty Value
A read-only unique identifier that indicates the change id cannot be computed.
Examples
// applications are expected to persist the previous value
UINT64 appsLastPersistedChangeId = StorageLibraryLastChangeId::Unknown();
StorageFolder folder = StorageFolder::GetFolderFromPathAsync(L"my folder path").get();
StorageLibraryChangeTracker tracker = folder.TryGetChangeTracker();
if (tracker != nullptr)
{
StorageLibraryChangeTrackerOptions ops;
ops.TrackChangeDetails(false);
tracker.Enable(ops);
StorageLibraryChangeReader reader = tracker.GetChangeReader();
if (reader != nullptr)
{
UINT32 changeId = reader.GetLastChangeId();
if ((changeId == StorageLibraryLastChangeId::Unknown())
{
ScanFolderSlow();
}
else if (changeId == 0)
{
// no changes in the storage folder yet, OR nothing has changed
ProcessNormalApplicationStartup();
}
else if (changeId != appsLastPersistedChangeId)
{
// There have been new changes since we’ve last ran, process them
appsLastPersistedChangeId = changeId;
ScanFolderForChanges();
}
else
{
// changeId and our last persisted change id match, also normal application startup
ProcessNormalApplicationStartup();
}
}
}