1. How to find whether a string is matching particular regular expression.
I will illustrate this with an example, Email validator. Assume, we want to check whether email
entered by user is following certain pattern or not. For this we are creating a regular expression
@"[A-Z0-9a-z._]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}"
|--User Name --|---HostName --| -- Domain---------|
This regular expression checks for:
a. Having at least a character before @
b. Having at least a character between @ and .(dot)
c. Domain name should be between 2 to 4 characters.
Now in objective-C we can use following method to check email validation,
-(BOOL)validateEmail:(NSString *)email {
NSString * regex = @"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}"; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex];
return [predicate evaluateWithObject: email];
}
2. How to replace occurrence of a pattern with replacement string in a given text string.
Assume we have some patterns and replacement strings like
Pattern Replacement string
:A GOTA
:B GOTB
:C GOTC
:D GOTD
:E GOTE
:F GOTF
:G GOTG
Text string : @"this is pattern1 :A and this is pattern2 :B and again :A"
after replacement we want result like this : @"this is pattern1 GOTA and this is pattern2 GOTB and
again GOTA"
It can be done by following lines of code:
-(NSString*)replaceStringWithRegularExpression:(NSRegularExpression*)regex dictionary:(NSDictionary*)dict string:(NSString*)string
{
NSArray *matches = [regex matchesInString:string options:0 range:NSMakeRange(0, [string length])];
for (NSTextCheckingResult* b in matches) // Loop through matches
{
NSString* url = [string substringWithRange:b.range]; // get the actual pattern matched
if([dict valueForKey:url]) // check if value present in dictionary
{
string=[string stringByReplacingOccurrencesOfString:url withString:[dict valueForKey:url]];
return [self replaceStringWithRegularExpression:regex dictionary:dict string:string];
// using recursion to avoid iteration when text contains same pattern multiple times
}
}
return string;
}
Call above method like this:
NSDictionary * dict=[[NSDictionary alloc] initWithObjectsAndKeys:@"GOTA",@":A", @"GOTB",@":B",@"GOTC",@":C",@"GOTD",@":D",@"GOTE",@":E",@"GOTF",@":F",nil]; //Create dictionary of patters and replacement strings
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@":A|:B|:C|:D|:E|:F" options:0 error:NULL]; //create regular expression
NSString *str = @"this is pattern1 :A and this is pattern2 :B and again :A"; //Text string which needs to be replaced NSString * result=[self replaceStringWithRegularExpression:regex dictionary:dict string:str]; NSLog(@"result:%@",result);
