Check if string is in format dd.mm.yyyy - objective-c

Question

I wanna check if a string is in format dd.mm.yyyy, like
if(myString is in format dd.mm.yyyy) {
NSLog(#"Ok");
}
else{
NSLog(#"No");

Answer 1

You can use a code like this:
NSString *dateString = #"01.01.1970";
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.dateFormat = #"dd.MM.yyyy";
if ([dateFormatter dateFromString:dateString]) {
//YES
}
Why NSDateFormatter: it was created to parse dates. Plus, this way you get an easy way to change date format and as a side effect, get a valid NSDate object that you can work with.
However, if you are intending to use this dateFormatter often (for instance, it is used inside a UITableViewCell), you might encounter performance issues. If you did, and you're sure that NSDateFormatter is what is causing it (Instruments might help you here), you could reuse your dateFormatter. For example, like so:
NSString *dateString = #"01.01.1970";
static NSDateFormatter *dateFormatter = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.dateFormat = #"dd.MM.yyyy";
});
if ([dateFormatter dateFromString:dateString]) {
//YES
}
It seems (it is my guess based on tests that I ran) that the first call to dateFromString triggers lazy initialization inside the dateFormatter, and it takes some time (several tests results are below). If you reuse it, the NSDateFormatter initialization is performed only once.
On my iPhone 5S with iOS 8.4.1 the dispatch_once version works about 10 times faster:
dispatch_once: 0.536 seconds, recreation: 5.475 seconds
(time to parse 10.000 dates)
In the same test #zaph got a 2x performance difference on his iPhone 6S with iOS 9.x:
dispatch_once: 0.57 seconds, recreation: 1.01 seconds
(time to parse 10.000 dates)
So, it depends on the device, the OS version and on how intensively you're going to use that dateFormatter. In some cases the second code fragment might be an overkill. But I encountered situations where it provided a noticeable performance boost.
UPD: Also note that quite often American dates are also written with a dot as a separator, so what seems to be a dd.MM.yyyy date might actually be a MM.dd.yyyy date (e.g. April 5th instead of May 4th). For dates with dd > 12 it's not an issue, but otherwise it is. I don't think there's anything you could do about that without an additional context though, so just be warned.

Answer 2

You can using Regex to check it.
For example this code using Regex to check "mm.dd.yyyy":
NSError *error = NULL;
NSString *expForreg = #"^((((0[13578])|([13578])|(1[02]))[\\.](([1-9])|([0-2][0-9])|(3[01])))|(((0[469])|([469])|(11))[\\.](([1-9])|([0-2][0-9])|(30)))|((2|02)[\\.](([1-9])|([0-2][0-9]))))[\\.]\\d{4}$|^\\d{4}$";
NSRegularExpression *regex = [NSRegularExpression
regularExpressionWithPattern:expForreg
options:NSRegularExpressionCaseInsensitive
error:&error];
NSArray *matches = [regex matchesInString:#"10.30.1989" options:0 range:NSMakeRange(0, [#"10.30.1989" length])];
if(matches && matches.count > 0)
{
NSLog(#"Ok");
}else
{
NSLog(#"No");
}
Hope this help!

Answer 3

You can use a regular expression:
NSString *testString = #"11.22.3333";
NSString *pattern = #"^\\d{2}\\.\\d{2}\\.\\d{4}$";
NSRange range = [testString rangeOfString:pattern options:NSRegularExpressionSearch];
if (range.location != NSNotFound) {
NSLog(#"Ok");
}
else{
NSLog(#"No");
}
Bit that is not really a good date test.