它也可以用stringByReplacingCharactersInRange:withString替换字符串:

for (int i = 0; i < card.length - 4; i++) {

    if (![[card substringWithRange:NSMakeRange(i, 1)] isEqual:@" "]) {

        NSRange range = NSMakeRange(i, 1);
        card = [card stringByReplacingCharactersInRange:range withString:@"*"];

    }

} //out: **** **** **** 1234

NSString对象是不可变的(他们不能被改变)，但是有一个可变的子类，NSMutableString，它给你一些方法来替换字符串中的字符。这可能是你最好的选择。

如果你想替换多个字符串:

NSString *s = @"foo/bar:baz.foo";
NSCharacterSet *doNotWant = [NSCharacterSet characterSetWithCharactersInString:@"/:."];
s = [[s componentsSeparatedByCharactersInSet: doNotWant] componentsJoinedByString: @""];
NSLog(@"%@", s); // => foobarbazfoo

NSString *stringreplace=[yourString stringByReplacingOccurrencesOfString:@"search" withString:@"new_string"];

你可以用这个方法

- (NSString *)stringByReplacingOccurrencesOfString:(NSString *)target 
                                        withString:(NSString *)replacement

.．.获取一个替换了子字符串的新字符串(其他请参阅NSString文档)

示例使用

NSString *str = @"This is a string";

str = [str stringByReplacingOccurrencesOfString:@"string"
                                     withString:@"duck"];

它也可以用stringByReplacingCharactersInRange:withString替换字符串:

for (int i = 0; i < card.length - 4; i++) {

    if (![[card substringWithRange:NSMakeRange(i, 1)] isEqual:@" "]) {

        NSRange range = NSMakeRange(i, 1);
        card = [card stringByReplacingCharactersInRange:range withString:@"*"];

    }

} //out: **** **** **** 1234