Question

Whats the best way to ensure the user has entered a valid time string such as:

5:24
5.4

102:30
102.5

It will be entered into a UITextField therefore will be in a NSString.

I want to allow the user to enter the time in either hours and minutes (hh:mm) or hours and decimal minutes (hh.m).

In the hours minutes example they should be able to enter as many hours as the like but only between 0 – 59 minutes. With the hours decimal minutes I want them to only be able to enter again as many hours as the like but decimal minutes can only be 0 – 9.

Many Thanks

Answer 1

If you are using the latest non beta SDK (3.2), you can use regular expressions for this.

NSString *myString = @"5:24";
NSString *myRegex = @"^\\d+(?:[:](?:[0-5]?\\d)|\\.\\d)$";
NSRange myRange = [myString rangeOfString:myRegex options:NSRegularExpressionSearch];
if (myRange.location != NSNotFound)
  // the string is valid
else
  // the string is invalid

Matches:

5:12
5:1
5:01
5:0
5:00
1234567:12
0:0
5.1
5.0
0.1
0.0
1234567.1

Non-matches:

5     // symbol required (i.e. ":" or ".")
5:    // minutes are required
5:123 // too many minutes, max is 2 digits
5:67  // minutes can only be up to 59
-5:12 // negative numbers aren't allowed
5.    // minutes are required
5.12  // too many minutes, max is 1 digit
:12   // hours are required
.12   // hours are required
5.1a  // string must not contain "a"
 5.1  // string must not contain whitespace " "