StorageLibraryChangeReader.GetLastChangeId 方法
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
取得唯一值，表示指定 StorageFolder 或 StorageLibrary 之索引服務所處理的最後一個變更。
public:
virtual unsigned long long GetLastChangeId() = GetLastChangeId;uint64_t GetLastChangeId();public ulong GetLastChangeId();function getLastChangeId()Public Function GetLastChangeId () As ULong傳回
如果有變更，有效的變更識別碼 (> 0) 。
如果在上次讀取之後沒有變更，或尚未發生任何變更，則傳回 0。
如果變更追蹤器無法計算變更識別碼，或發生太多檔案變更，且此值溢位，則會傳回 StorageLibraryChangeId：：Unknown。
Windows 需求
| 裝置系列 |
Windows 10, version 2104 (已於 10.0.20348.0 引進)
|
| API contract |
Windows.Foundation.UniversalApiContract (已於 v12.0 引進)
|
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();
}
}
}