Formatting UITextField as a time hh:mm - objective-c

Question

I want a UITextField to correctly format an inputted number as a time, adding minutes using "shouldChangeCharactersInRange" to obtain this result every time a new number is pressed:
i.e.:
00:00
00:08 = 8 pressed
01:23 = 8 -> 3 pressed
08:30 = 8 -> 3 -> 0 pressed
The UITextField is a subview into a Custom UITableViewCell.
I can't figure out, thanks in advance.

Answer 1

Simple
in the H declare:
#interface ViewController : UIViewController
{
int hh;
int mm;
int ss;
}
#property (strong, nonatomic) IBOutlet UILabel *outputLabel;
#end
In the M
-(void)generateText
{
NSString *hhString;
NSString *mmString;
NSString *ssString;
if (hh < 10){
hhString = [NSString stringWithFormat:#"0%d",hh];
} else {
hhString = [NSString stringWithFormat:#"%d",hh];
}
//
if (mm < 10){
mmString = [NSString stringWithFormat:#"0%d",mm];
} else {
mmString = [NSString stringWithFormat:#"%d",mm];
}
if (ss < 10){
ssString = [NSString stringWithFormat:#"0%d",ss];
} else {
ssString = [NSString stringWithFormat:#"%d",ss];
}
NSString *outputText = [NSString stringWithFormat:#"%#:%#:%#",hhString,mmString,ssString];
NSLog(#"output string = %#",outputText);
outputLabel.text = outputText;
}
-(IBAction)addHH:(id)sender
{
hh = hh +1;
[self generateText];
}
-(IBAction)addMM:(id)sender
{
mm = mm +1;
[self generateText];
}
-(IBAction)addSS:(id)sender
{
ss = ss +1;
[self generateText];
}
In Interface builder use 3 buttons to activate the appropriate IBActions

Answer 2

http://developer.apple.com/library/ios/#documentation/uikit/reference/UITextFieldDelegate_Protocol/UITextFieldDelegate/UITextFieldDelegate.html
Use this delegate method to change the text field accordingly
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
// You should already have set some string in the text field
if (/*user input is between 0-9*/) {
NSString *text = /* Format your text */
textFiled.text = text;
// Return NO to disable editing done by the user
// Not required to return here if you always return NO;
return NO;
}
// Return NO if you do not want to let user make any changes, otherwise YES
return YES;
}
I have tested it, but changing the textField.text inside this method may call this recursively and fail. If this is the case, use a flag to keep track of what changes are made by you and what by the user. Return YES if the flag is ON and NO otherwise.