ios从html标签内的字符串中转义'<' - Objective-C

Question

我有以下从本地数据库生成的 HTML 字符串：

<div><span>If x < 20 Then y > 20 </span><div> //NSString : dynamically generated

应该怎么做才能从 html 标签内的字符串中转义 '' 符号，以便我们得到以下输出：

<div><span>If x &lt; 20 Then y &gt; 20 </span><div>

更新

NSString *htmlString = @"<td style=\"vertical-align: top; text-align: left; width: 95%;\">\
    <span>$$If\\ \\ f(x) \\ \\ is \\ continuous \\ on \\ [0,8]\\ defined \\ as$$<br>\
    $$f(x) = x^2 +ax + 6 \\ \\ \\ \\ for \\ \\ 0 <x < 2$$<br>\
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; $$= 3x +2 \\ \\ \\ \\ \\ \\ for \\ 2<x<4$$<br>\
            &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; $$= 2ax + 5b \\ \\ \\ \\ \\ \\ \\ for \\ 2<x<8$$<br>\
                Find <em>a</em>&nbsp;and <em>b</em></span>\
    </td>";

这整个字符串是动态生成的，我希望任何 '' 除了带有 HTML 实体的那些被转义。这是使用 MathJax 在 UIWebView 中渲染数学表达式的要求。

Answer 1

- (NSString *) replaceHTMLEntitiesInString:(NSString *) htmlString {
    htmlString = [htmlString stringByReplacingOccurrencesOfString:@" " withString:@" "];
    htmlString = [htmlString stringByReplacingOccurrencesOfString:@""" withString:@"\""];
    htmlString = [htmlString stringByReplacingOccurrencesOfString:@"&lt;" withString:@"<"];
    htmlString = [htmlString stringByReplacingOccurrencesOfString:@"&gt;" withString:@">"];
    return htmlString;
}

拨打htmlString = [self replaceHTMLEntitiesInString:htmlString];