title: -[__NSDictionaryI setObject:forKey:]: unrecognized selector sent to instance 0x91da0f0
body: <p>when i set the value in nsmutabledictionary then given error show in image below....</p>
  
  <p><img src="https://i.stack.imgur.com/x19ir.png" alt="enter image description here"></p>
  
  <p>here my code for setvalue in nsmutabledictionary</p>
  
  <pre><code>NSMutableArray *countArray=[[NSMutableArray alloc] init];
  for (int i=0;i&lt;artistName.count;i++)
  {
      int count=0;
      NSMutableDictionary *dir1=[artistName objectAtIndex:i];
      NSString *artist1=[dir1 objectForKey:@"SONG_ARTIST"];
  
      for (int j=0;j&lt;CurrentPlayingSong.count;j++)
      {
          NSDictionary *dir2=[CurrentPlayingSong objectAtIndex:j];
          NSString *artist2=[dir2 objectForKey:@"SONG_ARTIST"];
  
          if ([artist2 isEqualToString:artist1])
          {
              count++;
          }
      }
  
      NSString *Size=[[NSString alloc] initWithFormat:@"%d",count];
      [dir1 setObject:Size forKey:@"SIZE"];
  
      [countArray addObject:dir1];
  }
  return countArray;
  </code></pre>