Encode NSString for XML/HTML

Question

Is there a way to HTML encode a string (NSString) in Objective-C, something along the lines of Server.HtmlEncode in .NET?

Answer 1

There isn't an NSString method that does that. You'll have to write your own function that does string replacements. It is sufficient to do the following replacements:

• '&' => "&"
• '"' => """
• '\'' => "'"
• '>' => ">"
• '<' => "&lt;"

Something like this should do (haven't tried):

[[[[[myStr stringByReplacingOccurrencesOfString: @"&" withString: @"&"]
 stringByReplacingOccurrencesOfString: @"\"" withString: @"""]
 stringByReplacingOccurrencesOfString: @"'" withString: @"'"]
 stringByReplacingOccurrencesOfString: @">" withString: @">"]
 stringByReplacingOccurrencesOfString: @"<" withString: @"&lt;"];

Answer 2

I took Mike's work and turn it into a category for NSMutableString and NSString

Make a Category for NSMutableString with:

- (NSMutableString *)xmlSimpleUnescape
{
    [self replaceOccurrencesOfString:@"&"  withString:@"&"  options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@""" withString:@"\"" options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@"'" withString:@"'"  options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@"'"  withString:@"'"  options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@"’" withString:@"'"  options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@"–" withString:@"-"  options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@">"   withString:@">"  options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@"&lt;"   withString:@"<"  options:NSLiteralSearch range:NSMakeRange(0, [self length])];

    return self;
}

- (NSMutableString *)xmlSimpleEscape
{
    [self replaceOccurrencesOfString:@"&"  withString:@"&amp;"  options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@"\"" withString:@"&quot;" options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@"'"  withString:@"&#x27;" options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@">"  withString:@"&gt;"   options:NSLiteralSearch range:NSMakeRange(0, [self length])];
    [self replaceOccurrencesOfString:@"<"  withString:@"&lt;"   options:NSLiteralSearch range:NSMakeRange(0, [self length])];

    return self;
}

Make a Category for NSString with:

- (NSString *)xmlSimpleUnescapeString
{
    NSMutableString *unescapeStr = [NSMutableString stringWithString:self];

    return [unescapeStr xmlSimpleUnescape];
}


- (NSString *)xmlSimpleEscapeString
{
    NSMutableString *escapeStr = [NSMutableString stringWithString:self];

    return [escapeStr xmlSimpleEscape];
}

* A Swift 2.0 Version *

The Objective-C version is a little more efficient as it does mutable operations on the string. However, this is a swift way to do simple escaping:

extension String
{
    typealias SimpleToFromRepalceList = [(fromSubString:String,toSubString:String)]

    // See http://stackoverflow.com/questions/24200888/any-way-to-replace-characters-on-swift-string
    //
    func simpleReplace( mapList:SimpleToFromRepalceList ) -> String
    {
        var string = self

        for (fromStr, toStr) in mapList {
            let separatedList = string.componentsSeparatedByString(fromStr)
            if separatedList.count > 1 {
                string = separatedList.joinWithSeparator(toStr)
            }
        }

        return string
    }

    func xmlSimpleUnescape() -> String
    {
        let mapList : SimpleToFromRepalceList = [
            ("&",  "&"),
            (""", "\""),
            ("'", "'"),
            ("'",  "'"),
            ("’", "'"),
            ("–", "-"),
            (">",   ">"),
            ("&lt;",   "<")]

        return self.simpleReplace(mapList)
    }

    func xmlSimpleEscape() -> String
    {
        let mapList : SimpleToFromRepalceList = [
            ("&",  "&amp;"),
            ("\"", "&quot;"),
            ("'",  "&#x27;"),
            (">",  "&gt;"),
            ("<",  "&lt;")]

        return self.simpleReplace(mapList)
    }
}

I could have used the NSString bridging capabilities to write something very similar to the NSString version, but I decided to do it more swifty.

Answer 3

I use Google Toolbox for Mac (works on iPhone). In particular, see the additions to NSString in GTMNSString+HTML.h and GTMNSString+XML.h.