I have an IBAction like:
- (IBAction)thisThing:(id)sender {
[self doSomething];
}
I would like do this (manually call the IBAction):
[self thisThing];
However I obviously need to do [self thisThing:...];. <- (what the heck goes after the colon?)
I'm not sure what (id)sender is supposed to be. How do call it manually without needing to click the button that it's tied to? I searched for anything about IBAction (id)sender and the results came up completely empty.
what the heck goes after the colon?
Well it depends on how you have written code inside the IBAction. Say for a calculator app, if all buttons are hooked up with the same IBAction then you would need sender (in this case NSButton) to identify which button got touched/clicked.
-(IBAction) buttonClicked:(id) sender {
// sender's identifier or Tag will let us know the number clicked here
[self doSomeThing];
}
But if you had IBActions for each and every button you would not need to be dependent on sender.
-(IBAction) firstButtonClicked:(id)sender;
-(IBAction) secondButtonClicked:(id)sender;
and so on ...
So in the first case if I want to programatically invoke the action I would pass the sender with appropriate attributes set to make sure the correct button got clicked. In second case just pass nil as it does not depend upon sender's value.
While popeye's comment answers your question, here's another perspective.
You have complete control over the action method. If you aren't using the sender parameter for anything in that method, then you do not have to supply it when calling it manually. By not supply it I mean pass nil as the value of the parameter.
Normally, it will contain a pointer to the control that is wired up to the action. If you did want to use if for something, they you would simply cast sender to the type of the control and do whatever with it.
- (IBAction)thisThing:(id)sender
In here,
- denotes the start of a instance method, whereas + means class(static) method.
( .. ) indicate return type. IBAction is actually void. Using IBAction instead of void tells that this method will be associated with UI(.nib) events.
thisThing is the name of the method, followed by parameter list.
In C view point, actual function names is something like thisThing:. That is, number of parameter modifies function name (external linkage).
If you meant to call thisThing: but write [self thisThing], you are calling different (not existing) method.
So, you must write :. What actual value to pass? One can decide this by looking at the method implementation.
If you have the IBOutlet of the button, you can pass that like [self thisThing:btn];
Or simply pass nil, [self thisThing:nil]; (if you are not using sender inside the IBAction)
- (IBAction)thisThing:(id)sender {
}
Is an event handler. That means that it is called when an event is sent by someone. A typical example of an event is a click on a button, it that case, the button sends the event (that means the button, a NSButton instance, is the sender).
Having the sender as a parameter is useful when you use the same event handler for events coming from different sources, e.g.
- (IBAction)buttonTapped:(id)sender {
if (sender == self.myButton1) {
//button 1 was tapped
}
else if (sender == self.myButton2) {
//button 2 was tapped
}
}
If this case, if you want to call the event handler manually, you just call
[self buttonTapped:self.myButton1];
If you don't use the sender parameter, then you can simply call
[self buttonTapped:nil];
However, the parameter is completely optional, so you can eliminate it:
- (IBAction)buttonTapped {
// ...
}
[self buttonTapped];
On a separate note, it's never good to call event handlers manually. Event handlers serve to handle events. If you need to perform the same action manually, separate it from the event handler, e.g.
- (IBAction)buttonTapped {
[self doSomething];
}
instead of calling [self buttonTapped], call [self doSomething]
Related
The following code works good for me:
In the init method of a menu layer:
CCMenuItemFont *item1 = [CCMenuItemFont itemWithString:#"Level 1" target: self selector: #selector(startLevel:)];
item1.userData = (__bridge void*) ([NSNumber numberWithInt:1]);
...//create menu and add in the item1
-(void)startLevel: (CCMenuItem *)sender
{
NSNumber *number = sender.userData;
...
}
My questions are:
I didn't pass item1 when call the method startLevel: how does it know that the sender is item1?
is it written into selector? or is it written in cocoa?
CCMenuItem passes itself as parameter to this selector. Details are in CCMenuItem source code.
Regarding omitting passing itself as a parameter, do you mean like...
- (void) pushedStart : (id) sender
{
//start game
}
but you can't do
[self pushedStart];
because it needs a parameter? If so, what you can do this:
id junkID;
[self pushedStart: junkID];
JunkID will initialize to whatever the hell it is an unassigned ID assigns to, so you pass it as a reference and just don't use it for anything, which is good if you want to have a "start game" button but have the game automatically start inside of a timer or whatever else you're doing with your buttons
As a side note, and getting more into the guts of cocoa, the way it KNOWS (and what YOU must not forget) is that colon. When you call a function you put the variable after a colon [self eat: food];
When you put together the menu item you set it up with target:self, which makes the button use itself (not the layer "self" you use when you call [self eatABanana]) as a target. The button push of
menuButton = target:self selector:#selector(pushButton:)
is represented like
[self pushButton:menuButton]
If you forgot that colon, it's the same as calling a function and not passing the variable, which doesn't give a very helpful error message insofar as it doesn't help you locate where the problem is occurring. I've spent hours upon hours chasing down memory crashes resulting from writing #selector(startGame) instead of #selector(startGame:) in those damn menu buttons. I always feel stupid when I finally figure it out.
I have the following, seemingly simple piece of code handling button taps in an iOS application:
- (IBAction)tapKeypadButton:(UIButton *)sender {
NSString *buttonLabel = sender.titleLabel.text;
if ([buttonLabel isEqualToString:#"<"]) {
[self _tapBackButton];
} else {
[self _tapDigitButton:buttonLabel];
}
}
To completely follow the Clean Code principles by Robert C. Martin, would I need a ButtonTapFactory or something in the same line?
You have two types of buttons, with different behaviors (back button and digit button). To make this code clean, you should have two actions for each type. The type should not be determined by the contents of the text inside the button, but through a semantically meaningful way. (i.e. subclass).
Further, an action method should only contain a call to another method that does the actual logic. Everything else is not testable. In code:
- (IBAction) tapBackButton:(id) sender
{
[self _tapBackButton:sender];
}
- (IBAction) tapDigitButton:(id) sender
{
[self _tapDigitButton:sender];
}
This way you can have unit tests calling your methods without your UI code interfering. Please also note that I removed the label from the call to _tapDigitButton. The digit should not be parsed from the label, but be passed in a more semantically stable way, for example using the tag property.
I have an IBAction called keyboardResponse associated with a text field called myTextFieldIBOutlet via the "Editting Changed" event handler in the xib:
- (IBAction)keyboardResponse:(id)sender
{
// process this single character - function I wrote else where that works fine.
[self processSingleCharacter:myTextFieldIBOutlet.text];
// clear input text
myTextFieldIBOutlet.text = #"";
}
It's supposed to clear the input after the user types something into it.
I get a run time error with this code in iOS Simulator:
Thread 1: EXC_BAD_ACCESS (code=2, address=0xbf7fff0c)
Why? I had synthesized the IBOutlet myTextFieldIBOutlet already.
if myTextFieldIBOutlet is synthesized, you should change the last line to:
self.myTextFieldIBOutlet.text = #"";
If the textfield you want to clear is the same control that calls this action, you can also use the sender variable you are sending
[sender setText:#""];
I implemented the following delegate method for NSTextField to add autocompletion support:
- (NSArray *)control:(NSControl *)control
textView:(NSTextView *)textView
completions:(NSArray *)words
forPartialWordRange:(NSRange)charRange
indexOfSelectedItem:(NSInteger *)index
The issue is that this method never gets called. I can verify that the delegate of the NSTextField is set properly because the other delegate methods function as they should.
You'll need to get complete: called on the text field's field editor at some point. That's what triggers the completions menu, but it doesn't get called automatically. If you don't have F5 bound to anything, try typing in your field and hit that. Completion should trigger then; Option-Esc may also work.
If you want auto completion, it takes some work. You could start with something like this:
- (void)controlTextDidChange:(NSNotification *)note {
if( amDoingAutoComplete ){
return;
} else {
amDoingAutoComplete = YES;
[[[note userInfo] objectForKey:#"NSFieldEditor"] complete:nil];
}
}
Some kind of flag is necessary because triggering completion will make NSControlTextDidChangeNotification be posted again, which causes this to be called, triggering completion, which changes the control text, which...
Obviously, you'll need to unset the flag at some point. This will depend on how you want to handle the user's interaction with autocompletion -- is there likely to only be one completion for a given start string, or will the user need to keep typing to narrow down possibilities (in which case you'll need to trigger autocompletion again)?
A simple flag might not quite do it, either; it seems that although the notification is re-posted, the field editor's string won't have changed -- it will only change in response to direct keyboard input. In my implementation of autocomplete, I found that I had to keep a copy of the "last typed string" and compare that each time to the field editor's contents.
When I use the code -(IBAction) onClick1: (id) sender;, what will be passed as sender? I tried to use the sender as the object id and fails (I mean I used the code sender.tag and it didn't return).
I am sure that when I am using - (void)buttonTouched1:(UIButton *)sender; here the sender should act as an object id.
The sender is usually the object that will invoke the onClick1 message. For example if you have a button and you associate your -(IBAction)onClick1:(id)sender message with the "touch up inside" event of the button, then when you tap on the button, the object representing the button will be passed to onClick1:
-(IBAction)onClick1:(id)sender
{
UIButton *button = (UIButton*)sender;
NSLog(#"%#", button);
}
The sender variable is normally the object that sent the action message (this isn't exactly guaranteed — for example, you can send an action message yourself and pass anything you want — but that's how it's supposed to work).
You can't just write sender.tag in those methods because dot notation requires the object to have a static type so the compiler knows what message the property corresponds to. If you write [sender tag] instead, it will work.