KnowledgeSyncProvider.GetChangeBatch 方法

在派生类中重写时，获取包含某些项的项元数据的变更批，这些项不包含在来自目标提供程序的指定知识中。

命名空间: Microsoft.Synchronization
程序集: Microsoft.Synchronization（在 microsoft.synchronization.dll 中）

语法

声明
Public MustOverride Function GetChangeBatch ( _
    batchSize As UInteger, _
    destinationKnowledge As SyncKnowledge, _
    <OutAttribute> ByRef changeDataRetriever As Object _
) As ChangeBatch
用法
Dim instance As KnowledgeSyncProvider
Dim batchSize As UInteger
Dim destinationKnowledge As SyncKnowledge
Dim changeDataRetriever As Object
Dim returnValue As ChangeBatch

returnValue = instance.GetChangeBatch(batchSize, destinationKnowledge, changeDataRetriever)

public abstract ChangeBatch GetChangeBatch (
    uint batchSize,
    SyncKnowledge destinationKnowledge,
    out Object changeDataRetriever
)

public:
virtual ChangeBatch^ GetChangeBatch (
    unsigned int batchSize, 
    SyncKnowledge^ destinationKnowledge, 
    [OutAttribute] Object^% changeDataRetriever
) abstract

public abstract ChangeBatch GetChangeBatch (
    UInt32 batchSize, 
    SyncKnowledge destinationKnowledge, 
    /** @attribute OutAttribute() */ /** @ref */ Object changeDataRetriever
)

JScript does not support passing value-type arguments by reference.

参数

• batchSize
  要包含在变更批中的变更数。

• destinationKnowledge
  来自目标提供程序的知识。此知识必须先通过调用源知识中的 MapRemoteKnowledgeToLocal 进行映射，然后才能用于变更枚举。

• changeDataRetriever
  返回一个可用于检索变更数据的对象。可以是 IChangeDataRetriever 对象，也可以是提供程序特定的对象。

返回值

包含某些项的项元数据的变更批，这些项不包含在来自目标提供程序的指定知识中。不能是 null 引用（在 Visual Basic 中为 Nothing）。

备注

相同的变更不会出现在多个批中。

如果剩余的变更数小于 batchSize 指定的变更数，则返回较小的批。

如果在已无变更的情况下调用此方法，则引发 InvalidOperationException。

实施者注意事项： 如果在此批之后再无变更要发送，则必须将返回的变更批的 IsLastBatch 设置为 true。否则，Sync Framework 将再次调用 GetChangeBatch 来检索另一个变更批。

示例

以下示例从元数据存储区中获取变更批。

public override ChangeBatch GetChangeBatch(uint batchSize, SyncKnowledge destinationKnowledge, out object changeDataRetriever)
{
    // Return this object as the IChangeDataRetriever object that is called to retrieve item data.
    changeDataRetriever = this;

    // Call the metadata store to get a batch of changes.
    return _itemStore.ContactReplicaMetadata.GetChangeBatch(batchSize, destinationKnowledge);
}

以下示例说明上一个示例中调用的 GetChangeBatch 方法。此示例创建一个 ChangeBatch 对象并启动一个有序组。当某一项不包含在目标知识中时，此示例会将该项添加到有序组。

public override ChangeBatch GetChangeBatch(uint batchSize, SyncKnowledge destinationKnowledge)
{
    // The destination knowledge must be converted to be compatible with the source replica
    // before it can be used.
    SyncKnowledge mappedDestKnowledge = _knowledge.MapRemoteKnowledgeToLocal(destinationKnowledge);

    // Create a new change batch, initialized by using the current knowledge of the source replica
    // and a new ForgottenKnowledge object.
    ChangeBatch changeBatch = new ChangeBatch(IdFormats, GetKnowledge(), new ForgottenKnowledge());

    // Start a group of changes in the change batch. The group is ordered by item ID.
    // _getChangeBatchCurrent is 0 the first time GetChangeBatch is called, and is used to track the
    // position in the metadata store for subsequent calls to GetChangeBatch.
    changeBatch.BeginOrderedGroup(_items.Values[_getChangeBatchCurrent].GlobalId);
    
    // itemsAdded is incremented each time a change is added to the change batch. When itemsAdded
    // is greater than the requested batch size, enumeration stops and the change batch is returned.
    int itemsAdded = 0;
    
    ItemMetadata itemMeta;

    // Enumerate items and add a change to the change batch if it is not contained in the 
    // destination knowledge.
    // _items is a SortedList that contains ItemMetadata objects that are ordered by item ID.
    for (; itemsAdded <= batchSize && _getChangeBatchCurrent < _items.Count; _getChangeBatchCurrent++)
    {
        itemMeta = _items.Values[_getChangeBatchCurrent];
        ChangeKind kind = (itemMeta.IsDeleted) ? ChangeKind.Deleted : ChangeKind.Update;
        ItemChange change = new ItemChange(IdFormats, ReplicaId, itemMeta.GlobalId, kind, itemMeta.CreationVersion, 
            itemMeta.ChangeVersion);

        // If the change is not contained in the destination knowledge, add it to the change batch.
        if (!mappedDestKnowledge.Contains(change))
        {
            changeBatch.AddChange(change);
            itemsAdded++;
        }
    }

    // End the group of changes in the change batch. Pass the current source knowledge.
    changeBatch.EndOrderedGroup(_items.Values[_getChangeBatchCurrent - 1].GlobalId, _knowledge);

    // When all items in the metadata store have been enumerated, set this batch as the
    // last batch.
    if (_getChangeBatchCurrent == _items.Count)
    {
        changeBatch.SetLastBatch();
    }

    return changeBatch;
}

请参阅

参考

KnowledgeSyncProvider 类
KnowledgeSyncProvider 成员
Microsoft.Synchronization 命名空间