title: use of undeclared identifier collectionView
body: <p>i am trying to create <code>collectionView</code> but it creates error as:
  use of undeclared identifier in <code>collectionView</code>.</p>
  
  <pre><code>- (UICollectionView *)collectionView:(UICollectionView *)collectionView
                 cellForRowAtIndexPath:(NSIndexPath *)indexPath {
  
    UICollectionViewCell *cell =
        [collectionView dequeueReusableCellWithIdentifier:@"MyIdentifier"];
  
    if (cell == nil) {
      cell = [[UICollectionViewCell alloc] init];
  
      [UICollectionView setBackgroundColor:[UIColor redColor]];
    }
  
    [self.view addSubview:__collectionView];
  
    // Do any additional setup after loading the view, typically from a nib.
  }
  </code></pre>