Question

I’m learning some C# and in the tutorials, they usually put most of the code on the button clicks for the sake of teaching. For example, if they were going to show a streamreader, they would do:

StreamReader sr = new StreamReader();

..inside the button’s click function.

Is this a bad programming habit? From javascript, I remember reading a warning on some code I wrote that said something about creating a function inside a timeout event. Should all variables and objects be declared outside of the button click function?

Answer 1

I’m learning some C# and in the tutorials, they usually put most of the code on the button clicks for the sake of teaching

The reason that putting code inside a click handler would be bad is that a click handler is specifically related to the UI, and the rest of your code might not be.

A stream reader reads from a stream. Code that processes a stream should be grouped with it. Code that handles the fact that you clicked on the UI has nothing to do with reading from a stream, so it should be separated.

Generally you should group your code so that parts of your code that are logically similar are together, and that parts of your code that deal with entirely different things are separated. This will give you “high cohesion“. It is related to the Single Responsibility Principle.

Should all variables and objects be declared outside of the button click function?

Absolutely not. If it makes sense to create a specific object when handling a UI event, do so.

However as I mentioned before, if you’re dealing with non-UI things inside a UI click handler you’re doing too many things at once. Split out your streaming code into another method, another set of methods, or into another object. This will make it easier to read your code, it will make your code have a better chance of being reusable, and it will make it easier to edit your code.

UI logic and flow is notorious for being kludgy and requiring a lot of work-arounds and special handling. It is also the area of your app that you will get the most feedback on, so it will undergo the most change. Everyone will have an opinion on how your UI should work, including non-technical users. If you guard yourself against this by separating your UI logic from the logic in the rest of your app, then those changes will be much easier to make.