Passing UITextField Value to Function Within View - ios

Question

I'm just beginning with XCode and coding for iOS, have the following problem. I want to add a function that sets UITextField values in the ViewController based around the value from a UIStepper. The code actually handles formatting three UITextFields, cut it to one to shorten the example. This code works fine:
- (IBAction)Temp_Stepper_Changed:(UIStepper *)sender {
integer_t stepperValue = (integer_t) sender.value;
NSString *temp_format = [[NSString alloc]
initWithFormat: #"%%.%df",stepperValue];
double fahrenheit = [_TempF_Text.text doubleValue];
NSString *FresultString = [[NSString alloc]
initWithFormat: temp_format,fahrenheit];
_TempF_Text.text = FresultString;
}
I have several places I want to do this, so want to create a function to call, and so I put this function into the view controller's .m file:
void Temp_Text_Update (double F_Temp){
NSString *FresultString = [[NSString alloc]
initWithFormat: #"%.2f",F_Temp];
_TempF_Text.text = FresultString;
}
The function won't compile, results in error:
use of undeclared identifier '_TempF_Text'
Without the line, it compiles fine, can call the function, pass values, etc. I had assumed (remember, beginning at this) as the UIStepper had _TempF_Text in it's scope, the function being in the same .m file would as well. Is there some magic happening behind the scenes that allows the IBAction type calls to access any value from the ViewController items, but my function is missing said magic? I'll also need the UIStepper value to complete the function. This was built using Storyboard, control-drag for outlets and actions, header file is:
#interface TemperatureViewController : UIViewController
#property (weak, nonatomic) IBOutlet UITextField *TempF_Text;
#property (weak, nonatomic) IBOutlet UIStepper *Temp_Stepper;
- (IBAction)TempF_CnvButton:(id)sender;
- (IBAction)Temp_Stepper_Changed:(UIStepper *)sender;
I've spent a few hours searching, including this site, found references from one ViewController to another and so forth, but doesn't really match; tried a few things anyway, but nothing worked (though some yielded extra errors). I suspect it is so obvious and simple as to not be asked, but I've run out of ideas and any help would be appreciated.

Answer 1

To answer the specific question, the correct syntax for the signature you're trying to write would look like this:
- (void)Temp_Text_Update:(double)F_Temp {
This says we have a method named Temp_Text_Update: that takes a double parameter called F_Temp and doesn't return anything.
A more general solution would be to use NSNumberFormatter to go between strings and doubles in a locale sensitive way, something like this:
// get a double from a string
- (double)doubleFromString:(NSString *)string {
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setNumberStyle:NSNumberFormatterDecimalStyle];
NSNumber *number = [formatter numberFromString:string];
return [number doubleValue];
}
// get a string from a double:
- (NSString *)stringFromDouble:(double)aDouble {
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setNumberStyle:NSNumberFormatterDecimalStyle];
return [formatter stringFromNumber:[NSNumber numberWithDouble:aDouble]];
}
Then your computing functions would look like this:
NSString *text = self.someControlView.text;
double aDouble = [self doubleFromString:text];
// do computation on aDouble, resulting in
double result = // whatever
[self setOutputTextWithResult:result];
Finally, your method (better named):
- (void) setOutputTextWithResult:(double)result {
self.someControlView.text = [self stringFromDouble:result];
}
It's so short now, it almost doesn't need it's own method.