StorageLibraryLastChangeId.Unknown 屬性

定義

命名空間:

Windows.Storage

當 USN 日誌溢位且服務無法跟上變更，或因無法計算變更識別碼的另一個原因而傳回。

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 ULong

屬性值

UInt64

unsigned long long

uint64_t

唯讀的唯一識別碼，表示無法計算變更識別碼。

範例

// 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();
    }
}
}

另請參閱

• StorageLibraryLastChangeId