How to decide between C# static and non-static methods?

Question

[Edit]

My original-question was \"Why to decide between static and non-static? Both do the same...\"

Unfortunately it was edited to a C#-specific question wh

Answer 1

If you use any other objects then you shokld default to instance level methods so that you can configure those dependencies using Dependancy Injection.

For example, if one of those images was an SVG image then you may have a dependency on an XML parser which (in Java at least) have many implementations, likewise for SVG renderers I imagine and many other constituent image types may require similar arrangements that evolve as the state of the object evolves or which must be changed in different usage scenarios (e.g. test, production, different projects re-using your code).

The blinking amber warning light is that you may be using classes that are not part of your framework's default libraries, so you've made a choice of a third party component and if using statics you are not well placed to modify that decision.

A useful "redline" is that if you touch another process (database server, web service etc) then I'd regard a static method as bad 100% of the time as this makes unit testing more dificult.