C# AutoCAD选中块获取其位置替换为外部选择的块，其他位置相同的块保留原块不替换为新块

您可以通过以下步骤实现：

1. 获取用户选择的外部块的位置信息。

2. 使用 AutoCAD 的选择集功能选择需要替换的块。

3. 对于每个选择的块，检查其位置信息是否与用户选择的外部块相同。如果是，则替换该块，否则将其保留。

以下是示例代码：

// 获取用户选择的外部块的位置信息
PromptEntityOptions promptOptions = new PromptEntityOptions("\n请选择一个外部块：");
promptOptions.SetRejectMessage("\n请选择一个块！");
promptOptions.AddAllowedClass(typeof(BlockReference), true);
PromptEntityResult promptResult = acDocEd.GetEntity(promptOptions);
if (promptResult.Status != PromptStatus.OK) return;

ObjectId externalBlockId = promptResult.ObjectId;
BlockReference externalBlockRef = acTrans.GetObject(externalBlockId, OpenMode.ForRead) as BlockReference;
Point3d externalPosition = externalBlockRef.Position;

// 选择需要替换的块
SelectionFilter filter = new SelectionFilter(new TypedValue[] { new TypedValue((int)DxfCode.Start, "INSERT") });
PromptSelectionOptions selectionOptions = new PromptSelectionOptions();
selectionOptions.MessageForAdding = "\n请选择需要替换的块：";
PromptSelectionResult selectionResult = acDocEd.GetSelection(selectionOptions, filter);
if (selectionResult.Status != PromptStatus.OK) return;

SelectionSet selectedBlocks = selectionResult.Value;
if (selectedBlocks == null) return;

// 替换块
foreach (SelectedObject selectedObject in selectedBlocks)
{
    BlockReference blockRef = acTrans.GetObject(selectedObject.ObjectId, OpenMode.ForRead) as BlockReference;
    Point3d position = blockRef.Position;

    if (position.Equals(externalPosition))
    {
        using (BlockReference newBlockRef = externalBlockRef.Clone() as BlockReference)
        {
            newBlockRef.Position = position;

            // 复制所有属性
            foreach (DynamicBlockReferenceProperty property in blockRef.DynamicBlockReferencePropertyCollection)
            {
                newBlockRef.SetDynamicBlockProperty(property.PropertyName, blockRef.GetDynamicBlockProperty(property.PropertyName));
            }

            // 替换块
            blockRef.UpgradeOpen();
            blockRef.Erase();
            acTrans.AddNewlyCreatedDBObject(newBlockRef, true);
        }
    }
}