Provide better error messages when opening unsupported formats

[Glenn Thompson]

System.FormatException: Unsupported file format
  at Pinta.Core.WorkspaceManager.OpenFile (System.String file, Gtk.Window parent) <0xaedf0000 + 0x000a3> in <filename unknown>:0

[Sébastien Beaujard (seb-sebandjohn)]

Hi Glenn,
Can you provide the steps to reproduce this exception?

[grofaty (grofaty)]

It looks to me this may appear when opening unsupported file format. For example I tried opening Microsoft Word file *.docx and got very similar error.

Probably the error should be more friendly, without so much technical info and display to the user what kind of file format are supported in Pinta. Also remove the "Bug report" button.

[Nick (thekolian1996)]

I would like to fix this issue, so I wrote some code. Screenshot with a new "Unsupported format" window attached. Is the result fine? Or maybe I should change it somehow?

[Cameron White (cameronwhite91)]

That looks pretty good to me!
I would just change the text slightly to "Pinta supports the following file formats:"

Is the list of formats hardcoded? It's possible to have add-ins for file formats (https://github.com/PintaProject/Pinta/wiki/Writing-a-File-Format-Addin) so maybe it should check all of those formats

[Nick (thekolian1996)]

Changed the text as you mentioned.
The list of formats is not hardcoded. All formats I got from ImageConverterManager.Formats property through LINQ. I can try to write add-in instead. Should I?

[Cameron White (cameronwhite91)]

OK, that sounds like you're doing it correctly!

[Nick (thekolian1996)]

Glad to hear that! It is the first time I'm contributing, so I am not sure about my next step. Can I just send a pull request on GitHub with my code in master branch? Especially interested in code review.

[Cameron White (cameronwhite91)]

Yep, you can just submit a pull request! Typically that's done from a separate branch in your fork, not master (https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/creating-a-pull-request-from-a-fork)

[Nick (thekolian1996)]

Thank you very much for the help! I made a pull request. If something is wrong let me know, I'll try to fix it.

[Cameron White (cameronwhite91)]

Fixed by https://github.com/PintaProject/Pinta/pull/143