Reuse a filestream in silverlight

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C#

Silverlight4

FileStream

I actually need to implement Word like functionality of re-writing an already saved file in my Silverlight application without SaveFileDialog prompting again for the name of the file.

I open up SaveFileDialog box when I want to save the file for the first time. After that I want that fileStream should be preserved so that after I make changes in my contenr, I can simply save that file again without SaveFileDialog prompting again to save file with a name, just like we do in word or notepad, i.e. I want to overwrite the already opened file.

Can anyone please suggest how it can be done so, since I am not able to save the full file path due to security reasons..??