title: How to get a class's property from a string?
body: <p>I want to get a class's property from a string.
  For example:</p>
  
  <pre><code>    NSString * propertyStr = @"propertyStr";
      if ([class haveProperty:propertyStr]) {
          class.propertyStr = @"avalue";
      }
  </code></pre>
  
  <p>I don't know if i have say it clear.</p>