共用方式為

StorageLibraryLastChangeId 類別

  • 參考

定義

命名空間:
Windows.Storage
編輯

可讓您根據代表指定 StorageFolder 或 StorageLibrary 之索引服務所處理的最後一個變更的唯一值來追蹤變更。

public ref class StorageLibraryLastChangeId sealed
/// [Windows.Foundation.Metadata.ContractVersion(Windows.Foundation.UniversalApiContract, 720896)]
/// [Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
/// [Windows.Foundation.Metadata.Threading(Windows.Foundation.Metadata.ThreadingModel.Both)]
class StorageLibraryLastChangeId final
[Windows.Foundation.Metadata.ContractVersion(typeof(Windows.Foundation.UniversalApiContract), 720896)]
[Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
[Windows.Foundation.Metadata.Threading(Windows.Foundation.Metadata.ThreadingModel.Both)]
public sealed class StorageLibraryLastChangeId
Public NotInheritable Class StorageLibraryLastChangeId
繼承
Object Platform::Object IInspectable StorageLibraryLastChangeId
屬性
ContractVersionAttribute MarshalingBehaviorAttribute ThreadingAttribute

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();
    }
}
}

屬性

Unknown

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。

適用於

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