How to do an on-item-changed for an NSPopUpButton? - objective-c

Question

I'm trying to implement a system that changes a label based on the state of an NSPopUpButton.
So far I've tried to do what's displayed in the code below, but whenever I run it, the code just jumps into the else clause, throwing an alert
- (IBAction)itemChanged:(id)sender {
if([typePopUp.stringValue isEqualToString: #"Price per character"]) {
_currency = [currencyField stringValue];
[additionalLabel setStringValue: _currency];
}
else if([typePopUp.stringValue isEqualToString: #"Percent saved"]) {
_currency = additionalLabel.stringValue = #"%";
}
else alert(#"Error", #"Please select a calculation type!");
}
So does anyone here know what to do to fix this?

Answer 1

#hamstergene is on the right track, but is comparing the title of the menu item rather than, say, the tag, which is wrong for the following reasons:
It means you cannot internationalize the app.
It introduces the possibility of spelling mistakes.
It's an inefficient comparison; comparing every character in a string takes way longer than comparing a single integer value.
Having said all that, NSPopUpButton makes it difficult to insert tags into the menu items, so you need to use the index of the selected item:
Assume you create the menu items using:
[typePopUp removeAllItems];
[typePopUp addItemsWithTitles: [NSArray arrayWithObjects: #"Choose one...", #"Price per character", #"Percent saved", nil]];
Then create an enum that matches the order of the titles in the array:
typedef enum {
ItemChooseOne,
ItemPricePerCharacter,
ItemPercentSaved
} ItemIndexes;
And then compare the selected item index, as follows:
- (IBAction)itemChanged:(id)sender {
NSInteger index = [(NSPopUpButton *)sender indexOfSelectedItem];
switch (index) {
case ItemChooseOne:
// something here
break;
case ItemPricePerCharacter:
_currency = [currencyField stringValue];
[additionalLabel setStringValue: _currency];
break;
case ItemPercentSaved:
_currency = #"%"; // See NOTE, below
additionalLabel.stringValue = #"%";
break;
default:
alert(#"Error", #"Please select a calculation type!");
}
}
NOTE the following line was incorrect in your code:
_currency = additionalLabel.stringValue = #"%";
Multiple assignment works because the result of x = y is y. This is not the case when a setter is involved. The corrected code is above.
EDIT This answer was heavily edited following more info from the OP.

Answer 2

To query the title of currently selected item in NSPopUpButton:
NSMenuItem* selectedItem = [typePopUp selectedItem];
NSString* selectedItemTitle = [selectedItem title];
if ([selectedItemTitle isEqualTo: ... ]) { ... }
Note that comparing UI strings is a very bad idea. A slightest change in UI will immediately break your code, and you are preventing future localization. You should assign numeric or object values to each item using -[NSMenuItem setTag:] or -[NSMenuItem setRepresentedObject:] and use them to identify items instead.