我想从给定索引处的 NSString 中提取一个子字符串。例子:
NSString = @"Hello, welcome to the jungle";
int index = 9;
索引点“9”位于“欢迎”这个词的中间,我希望能够将“欢迎”这个词提取为子字符串。谁能告诉我如何实现这一目标?用正则表达式?
这是 NSString 上的一个类别的解决方案:
- (NSString *) wordAtIndex:(NSInteger) index {
__block NSString *result = nil;
[self enumerateSubstringsInRange:NSMakeRange(0, self.length)
options:NSStringEnumerationByWords
usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
if (NSLocationInRange(index, enclosingRange)) {
result = substring;
*stop = YES;
}
}];
return result;
}
另一个更复杂,但可以让您准确指定所需的单词字符:
- (NSString *) wordAtIndex:(NSInteger) index {
if (index < 0 || index >= self.length)
[NSException raise:NSInvalidArgumentException
format:@"Index out of range"];
// This definition considers all punctuation as word characters, but you
// can define the set exactly how you like
NSCharacterSet *wordCharacterSet =
[[NSCharacterSet whitespaceAndNewlineCharacterSet] invertedSet];
// 1. If [self characterAtIndex:index] is not a word character, find
// the previous word. If there is no previous word, find the next word.
// If there are no words at all, return nil.
NSInteger adjustedIndex = index;
while (adjustedIndex < self.length &&
![wordCharacterSet characterIsMember:
[self characterAtIndex:adjustedIndex]])
++adjustedIndex;
if (adjustedIndex == self.length) {
do
--adjustedIndex;
while (adjustedIndex >= 0 &&
![wordCharacterSet characterIsMember:
[self characterAtIndex:adjustedIndex]]);
if (adjustedIndex == -1)
return nil;
}
// 2. Starting at adjustedIndex which is a word character, find the
// beginning and end of the word
NSInteger beforeBeginning = adjustedIndex;
while (beforeBeginning >= 0 &&
[wordCharacterSet characterIsMember:
[self characterAtIndex:beforeBeginning]])
--beforeBeginning;
NSInteger afterEnd = adjustedIndex;
while (afterEnd < self.length &&
[wordCharacterSet characterIsMember:
[self characterAtIndex:afterEnd]])
++afterEnd;
NSRange range = NSMakeRange(beforeBeginning + 1,
afterEnd - beforeBeginning - 1);
return [self substringWithRange:range];
}
假设单词很短,第二个版本对于长字符串也更有效。
这是一种相当老套的方法,但它会起作用:
NSString 有一个方法:
- (NSArray *)componentsSeparatedByString:(NSString *)separator;
所以你可以这样做:
NSString *myString = @"Blah blah blah";
NSString *output = @"";
int index = 9;
NSArray* myArray = [myString componentsSeparatedByString:@" "]; // <-- note the space in the parenthesis
for(NSString *str in myArray) {
if(index > [str length]) index -= [str length] + 1; // don't forget the space that *was* there
else output = str;
}