通过

StorageLibraryLastChangeId 类

  • 参考

定义

命名空间:
Windows.Storage
编辑

允许基于唯一值跟踪更改，该值代表由给定 StorageFolder 或 StorageLibrary 的索引服务处理的最后一个更改。

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
继承
Object Platform::Object IInspectable StorageLibraryLastChangeId
属性
ContractVersionAttribute MarshalingBehaviorAttribute ThreadingAttribute

Windows 要求

设备系列
Windows 10, version 2104 (在 10.0.20348.0 中引入)
API contract
Windows.Foundation.UniversalApiContract (在 v12.0 中引入)

示例

// 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();
    }
}
}

属性

Unknown

当 USN 日记溢出且服务无法跟上更改，或者有另一个原因无法计算更改 ID 时返回。

适用于

另请参阅