How to determine if the first character of a NSString is a letter

问题

In my app

i need to know if the first character of a string is a letter or not

Im getting first character of the string like this

NSString *codeString;
 NSString *firstLetter = [codeString substringFromIndex:1];

I can know it by comparing with a, b, c, .**.

if([firstLetter isEqualToString "a"] || ([firstLetter isEqualToString "A"] || ([firstLetter isEqualToString "b"] ......)

But is there any other method to know?

I need to display different colors for letters and symbols.

How can i achieve it in simple way?

回答1:

First off, your line:

NSString *firstLetter = [codeString substringFromIndex:1];

does not get the first letter. This gives you a new string the contains all of the original string EXCEPT the first character. This is the opposite of what you want. You want:

NSString *firstLetter = [codeString substringToIndex:1];

But there is a better way to see if the first character is a letter or not.

unichar firstChar = [[codeString uppercaseString] characterAtIndex:0];
if (firstChar >= 'A' && firstChar <= 'Z') {
    // The first character is a letter from A-Z or a-z
}

However, since iOS apps deal with international users, it is far from ideal to simply look for the character being in the letters A-Z. A better approach would be:

unichar firstChar = [codeString characterAtIndex:0];
NSCharacterSet *letters = [NSCharacterSet letterCharacterSet];
if ([letters characterIsMember:firstChar]) {
    // The first character is a letter in some alphabet
}

There are a few cases where this doesn't work as expected. unichar only holds 16-bit characters. But NSString values can actually have some 32-bit characters in them. Examples include many Emoji characters. So it's possible this code can give a false positive. Ideally you would want to do this:

NSRange first = [codeString rangeOfComposedCharacterSequenceAtIndex:0];
NSRange match = [codeString rangeOfCharacterFromSet:[NSCharacterSet letterCharacterSet] options:0 range:first];
if (match.location != NSNotFound) {
    // codeString starts with a letter
}

来源：https://stackoverflow.com/questions/16860108/how-to-determine-if-the-first-character-of-a-nsstring-is-a-letter

标签

objective-c

nsstring