C＃Excel interop - 如何测试互操作对象是否仍在工作并执行任务？

I am looping through a directory of several hundered excel files and trying to refresh the excel files one at a time. I keep getting this error which indicates that the refresh operation is still running on File A, for example, and FileB is trying to start a refresh operation. The loop is to fast and somehow I have to wait for the prior refresh operation on File A to complete before starting to refresh File B.I am looping through a directory of several hun