On iOS, we can create an Outlet by code easily -- what about Actions?

Question

On iOS, if we use Interface Builder, we can create Outlet and Action easily.

If we use Objective-C code instead of Interface Builder, we can create outlet quite easily too, it seems, by just

datePicker = [[UIDatePicker alloc] initWithFrame:CGRectMake(200, 200, 200, 200)];
[self.view addSubview:datePicker];

and that we define an instance variable in the .h file.

UIDatePicker *datePicker;

And I think this is exactly like an Outlet?

How about for Actions -- how do we create Actions purely using Objective-C code (without using Interface Builder) for the different types of user interaction?

score 3 · Accepted Answer · answered May 25 '12 at 03:15

3

Just like this:

- (void)someMethod {
  //...
  [button_ addTarget:self
              action:@selector(buttonAction:)
    forControlEvents:UIControlEventTouchUpInside];
  //...
}

//...

// Either |IBAction| or |void| is okay,
//   the former one is just used to be shown in Interface Builder
- (void)buttonAction:(id)sender {
  // your action code here
}

Note: IBOutlet & IBAction are just for IB (short for Interface Builder). You can forget it if you don't want to use Interface Builder to manage your views & actions.

answered May 25 '12 at 03:15

Kjuly

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how come your button variable is `button_` (with underscore)? I also see some code such as ViewController having `_view` as an instance variable but the underscore is in front – nonopolarity May 25 '12 at 03:24
2

He chose to define his matching iVars with an underscore. It's just traditional, in fact, `@Synthesize button =hrighaohfunaksifh___` would work just as well. – CodaFi May 25 '12 at 03:25
1

@動靜能量 CodaFi is right. You can refer it [HERE](http://stackoverflow.com/questions/8832091/ivar-vs-ivar-for-variable-naming) if you're interested in. :) – Kjuly May 25 '12 at 03:29
so the convention is, if it is iOS framework code, use `_foo` for ivar names, and if it is our own app's code, use `foo_` for ivar names... and that's to distinguish between ivars and local vars... sort of like Ruby's `@foo` for ivars. – nonopolarity May 25 '12 at 03:43
@動靜能量 use `_foo` is fine, just be careful on naming. :) – Kjuly May 25 '12 at 03:59

score 1 · Answer 2 · answered May 25 '12 at 02:48

1

Using the IBAction macro:

 // in .h
 -(IBAction) myAction:(id) sender;

answered May 25 '12 at 02:48

Richard J. Ross III

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I'm sure he means `addTarget:action:forControlEvents:` from the `UIControl` class, although his question really is quite ambiguous. – JustSid May 25 '12 at 02:56
I mean, we can have the event handler and change the property of the control using Interface Builder's outlet and action. What if we do it purely by Objective-C (without Interface Builder)? – nonopolarity May 25 '12 at 02:58

On iOS, we can create an Outlet by code easily -- what about Actions?

2 Answers2