如何确定NSString的第一个字符是否为字母 [英] How to determine if the first character of a NSString is a letter

问题描述

在我的应用中

我需要知道字符串的第一个字符是否是字母

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

我正在得到这样的字符串的第一个字符

Im getting first character of the string like this

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

我可以通过与a，b，c，.**进行比较来了解它.

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

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

但是还有其他方法要知道吗?

But is there any other method to know?

我需要为字母和符号显示不同的颜色.

I need to display different colors for letters and symbols.

我如何以简单的方式实现它?

How can i achieve it in simple way?

推荐答案

首先，您的一行:

NSString *firstLetter = [codeString substringFromIndex:1];

没有得到第一个字母.这为您提供了一个新字符串，其中包含除第一个字符以外的所有原始字符串.这与您想要的相反.您想要:

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];

但是有一种更好的方法来查看第一个字符是否是字母.

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
}

但是，由于iOS应用程序可与国际用户打交道，因此仅查找字母A-Z中的字符并不是理想的选择.更好的方法是:

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
}

在某些情况下，此操作无法按预期进行. unichar仅包含16位字符.但是NSString值实际上可以包含一些32位字符.示例包括许多表情符号字符.因此，这段代码可能会产生误报.理想情况下，您想这样做:

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
}        

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