VB.NET vs C# – Event handling
Basic concept of the events is simple:
Class can raise an event. User of the class can subscribe to the event and react to it using delegate functions.
For example, handling the click event of a button. Button is named btnOK, delegate function is named btnOK_Click.
Subscribing:
//C# btnOK.Click += new EventHandler(btnOK_Click);
'VB.NET AddHandler btnOK.Click, AddressOf btnOK_Click
That’s very similar but this is also where similarities end. Now for the differences:
VB – Syntactic sugar:
Instead of manually attaching to the event, you can decorate the handler function with Handles keyword:
Private Sub btnOK_Click(...) Handles btnOK.Click
With that you don’t have to worry about adding or removing the handler and it’s obvious what this method is doing and what it handles. One method can handle multiple events of the same signature.
Private Sub txt_Validating(...) Handles txtName.Validating, txtNumber.Validating, txtDate.Validating
C# – IDE feature:
After writing “btnOK.Click +=” IDE will offer you to complete the statement for you (press TAB to insert “new EventHandler(btnOK_Click)”). Even better, after that it will offer you to create delegate sub if you press another TAB. Useful and unobtrusive, great feature.
VB – IDE feature:
If a variable is declared with WithEvents keyword (all UI controls created in designer are), you can select it from pull-down menu above the code and all events will be offered in another pull-down menu next to it. Clicking on the event automatically creates a delegate sub with Handles keyword.
C# – IDE problem:
Lack of handles keyword is problematic in C# when you create the event handler from UI designer. Double clicking a button automatically creates the delegate and attaches the event to it. Problem is that attacher code is hidden in autogenerated part of the code and you can’t see if handler is really attached which can lead to duplicate attachment or no attachment at all.
VB – feature:
You can just raise an event, if somebody will handle it, great, if not, no worries.
C# – feature:
You can check if any event is attached and raise only if there is.
VB.NET vs C#
I have been working in VB.NET at work and C# at home for some time now. Sometimes I get puzzled when they differ in unexpected places. They are very different in syntax, sure, but that isn’t the issue for me.
- Are brackets better then End… keywords?
- Is For i as integer = 1 to 10 … Next better then for(int i = 1; i <= 10; i++){…}?
- Case sensitive or not?
I can’t say for some, for others I just accept the differences. You learn one way or another. Or both.
That said, it is interesting that although they are product of the same company and compiled to the same intermediate language, using them is very different experience. After the syntax which is, as I said, just the way it is, the next big difference is made by IDE. That’s what puzzles me. One product, Visual Studio, behaves very different for each language. It doesn’t just accommodate the differences, it expands them.
Under VB vs C# tag I’m collecting puzzling differences I stumbled upon. It’s not about syntactic differences – that is just fodder for religious wars. Some syntax differences are mentioned only when they result in big advantage for one or another language. But what I want to express here are different experiences which come combined from IDE, syntax, available tools and community.