title: Defining a property in iOS class extension
body: <p>I would like to add a property to UITableView in a Class Extension:</p>
  
  <pre><code>@interface UITableViewController ()
  
  @property NSString *entityString;
  
  @end
  </code></pre>
  
  <p>Then I import the extension and then I use entityString property in a subclass of UITableViewController:</p>
  
  <pre><code>@implementation CustomerTableViewController
  
  - (void)viewDidLoad {
      self.entityString = @"Customer";
      ...
      [super viewDidLoad];
  }
  ...
  </code></pre>
  
  <p><a href="https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/CustomizingExistingClasses/CustomizingExistingClasses.html#//apple_ref/doc/uid/TP40011210-CH6-SW1" rel="noreferrer">Apple documentation</a> says: </p>
  
  <blockquote>
    <p>the compiler will automatically synthesize the relevant accessor
    methods (...) inside the primary class
    implementation.</p>
  </blockquote>
  
  <p>But when I try to execute it I get this error: </p>
  
  <blockquote>
    <p>-[CustomerTableViewController setEntityString:]: unrecognized selector sent to instance 0x737b670</p>
  </blockquote>
  
  <p>What am I doing wrong? maybe the property cannot be accessed by subclasses?</p>