title: @protocol implementation in @interface in Objective-C
body: <p>I need to develop an application which has a interface which implements methods of 3 protocols.
  Assume protocol A extends protocol B and protocol C, and interface implements protocol A.
  This is how my code looks,</p>
  
  <pre><code>// This is in MyClass.h file
  
  #import &lt;Foundation/Foundation.h&gt;
  #import &lt;UIKit/UIKit.h&gt;
  #import "protocol_A"
  @interface MyClass : NSObject &lt;protocol_A&gt;
  {
  }
  @end
  
  //This is MyClass.m file
  #import "MyClass.h"
  
  @implementation myClass
  
  -(void)methodinA
  {
  NSLog(@"I'm in protocol_A");
  }
  }
  -(void)methodinB
  {
  NSLog(@"I'm in protocol_B");
  }
  
  -(void)methodinC
  {
  NSLog(@"I'm in protocol_C");
  }
  
  @end
  
  //This is protocol_A.h file
  #import &lt;Foundation/Foundation.h&gt;
  #import &lt;UIKit/UIKit.h&gt;
  #import "protocol_B.h"
  #import "protocol_C.h"
  
  @protocol protocol_A &lt;protocol_B, protocol_C&gt;
  
  -(void)methodinA;
  @end
  
  //This is in protocol_B.h file
  #import &lt;Foundation/Foundation.h&gt;
  #import &lt;UIKit/UIKit.h&gt;
  @protocol protocol_B
     -(void)methodinB;
  @end
  
  //This is in protocol_C.h file
  
  #import &lt;Foundation/Foundation.h&gt;
  #import &lt;UIKit/UIKit.h&gt;
  @protocol protocol_C
     -(void)methodinC;
  @end
  </code></pre>
  
  <p>i'm getting an exception , and my app is getting crashed...</p>
  
  <pre><code>***Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[&lt;MyClass 0X323nm31&gt;setvalue:forundefinedKey:]:this class is not key value coding-compilant for the key window'.
  </code></pre>
  
  <p>Plz Tel me how to solve this problem??</p>