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Image.FromStream does not hold a ref to the underlying stream

Answer 1

+1 A:

There isn't a way to do it without changing your code somewhat. The Remarks section for the documentation for the static FromStream method on the Image class states:

You must keep the stream open for the lifetime of the Image.

That being said, you have to make sure that while the Image is accessing the Stream, the stream is open. It would also appear (looking through Reflector) that the FromImage method doesn't actually cause the Image instance to hold onto a reference to the Stream the image was loaded from.

That being said, you to somehow link the image and the MemoryStream (or Stream) together so that it doesn't get GCed. If don't really retain "ownership" of the image (it is passed around), then I recommend that you create a data structure which will hold the reference to the Image and to the Stream and pass the two around in tandem.

casperOne 2010-02-26 06:38:30

I don't get it. If the image requires the stream to be open, then it must hold a reference to it, right?

Isaac Cambron 2010-02-26 06:46:07

@Issac Cambron: Yes, and that's fine, but it's referring to the Stream being open, not the reference being valid. To that end, if you are passing the Image around and don't have control over when it is closed (or maybe you are closing it yourself somewhere else when the Image still needs it). I'm updating the answer to reflect this.

casperOne 2010-02-26 06:55:46

@Sam Saffron: If you clone the image, I would assume you have to still keep the stream around. The documentation for the Clone method isn't too explicit, saying it produces an "exact copy" which can be interpreted a number of different ways. I wouldn't dobut if the clone requires the original stream to be open as well.

casperOne 2010-02-26 07:06:28

Answer 2

+1 A:

This seems highly unlikely to me - it would cause a problem for almost any use of Image.FromStream.

It seems more likely to me that something's disposing of your MemoryStream, which it shouldn't.

Could you provide a short but complete program which demonstrates the problem? Forcing garbage collection should make it relatively easy to reproduce - you could even create your own class deriving from MemoryStream with a finalizer to show whether or not it really is being collected (well, finalized at least).

Jon Skeet 2010-02-26 07:11:36

@Sam: `read` should always be greater than **0** if there's more data in the stream - but it can easily be less than `buffer.Length`, even if there's more data still in the stream afterwards.

Jon Skeet 2010-02-26 08:16:01

yeah, it all turned out to be this: http://stackoverflow.com/questions/2340337/how-can-i-get-net-to-open-this-image

Sam Saffron 2010-02-26 08:31:24

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Image.FromStream does not hold a ref to the underlying stream

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