不幸的是，stringByAddingPercentEscapesUsingEncoding 并不总是 100% 有效.它对非 URL 字符进行编码，但保留保留字符(如斜线 / 和 & 符号 &)单独.显然这是 Apple 知道的一个 错误，但由于他们还没有修复它，我一直在使用这个类别对字符串进行 url 编码:

Unfortunately, stringByAddingPercentEscapesUsingEncoding doesn't always work 100%. It encodes non-URL characters but leaves the reserved characters (like slash / and ampersand &) alone. Apparently this is a bug that Apple is aware of, but since they have not fixed it yet, I have been using this category to url-encode a string:

@implementation NSString (NSString_Extended)

- (NSString *)urlencode {
    NSMutableString *output = [NSMutableString string];
    const unsigned char *source = (const unsigned char *)[self UTF8String];
    int sourceLen = strlen((const char *)source);
    for (int i = 0; i < sourceLen; ++i) {
        const unsigned char thisChar = source[i];
        if (thisChar == ' '){
            [output appendString:@"+"];
        } else if (thisChar == '.' || thisChar == '-' || thisChar == '_' || thisChar == '~' || 
                   (thisChar >= 'a' && thisChar <= 'z') ||
                   (thisChar >= 'A' && thisChar <= 'Z') ||
                   (thisChar >= '0' && thisChar <= '9')) {
            [output appendFormat:@"%c", thisChar];
        } else {
            [output appendFormat:@"%%%02X", thisChar];
        }
    }
    return output;
}

这样使用:

NSString *urlEncodedString = [@"SOME_URL_GOES_HERE" urlencode];

// Or, with an already existing string:
NSString *someUrlString = @"someURL";
NSString *encodedUrlStr = [someUrlString urlencode];

这也有效:

This also works:

NSString *encodedString = (NSString *)CFURLCreateStringByAddingPercentEscapes(
                            NULL,
                            (CFStringRef)unencodedString,
                            NULL,
                            (CFStringRef)@"!*'();:@&=+$,/?%#[]",
                            kCFStringEncodingUTF8 );

一些关于这个主题的好读物:

Some good reading about the subject:

Objective-c iPhone 百分比编码字符串?
Objective-C 和 Swift URL 编码

http://cybersam.com/programming/proper-url-ios 中的百分比编码
https://devforums.apple.com/message/15674#15674http://simonwoodside.com/weblog/2009/4/22/how_to_really_url_encode/一个>