Question

How does Apple do the iPhone calendar day view transition between dates? When you swipe your finger on the day view it looks a bit like a carousel and when the day view is half way across the screen the date at the top changes.

I have recreated the day view myself but need to figure out how to do the transition between days.

Answer 1

If I had to guess? Using 3 panes in a UIScrollView like this method.

- (void)viewDidLoad 
{
  [super viewDidLoad];

  documentTitles = [[NSMutableArray alloc] init];

  // create our array of documents
  for (int i = 0; i < 10; i++) {
    [documentTitles addObject:[NSString stringWithFormat:@"Document %i",i+1]];
  }

  // create placeholders for each of our documents
  pageOneDoc = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 320, 44)];
  pageTwoDoc = [[UILabel alloc] initWithFrame:CGRectMake(320, 0, 320, 44)];
  pageThreeDoc = [[UILabel alloc] initWithFrame:CGRectMake(640, 0, 320, 44)];

  pageOneDoc.textAlignment = UITextAlignmentCenter;
  pageTwoDoc.textAlignment = UITextAlignmentCenter;
  pageThreeDoc.textAlignment = UITextAlignmentCenter;

  // load all three pages into our scroll view
  [self loadPageWithId:9 onPage:0];
  [self loadPageWithId:0 onPage:1];
  [self loadPageWithId:1 onPage:2];

  [scrollView addSubview:pageOneDoc];
  [scrollView addSubview:pageTwoDoc];
  [scrollView addSubview:pageThreeDoc];

  // adjust content size for three pages of data and reposition to center page
  scrollView.contentSize = CGSizeMake(960, 416);
  [scrollView scrollRectToVisible:CGRectMake(320,0,320,416) animated:NO];
}

- (void)loadPageWithId:(int)index onPage:(int)page 
{
  // load data for page
  switch (page) {
    case 0:
      pageOneDoc.text = [documentTitles objectAtIndex:index];
      break;
    case 1:
      pageTwoDoc.text = [documentTitles objectAtIndex:index];
      break;
    case 2:
      pageThreeDoc.text = [documentTitles objectAtIndex:index];
      break;
  }
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)sender 
{
  // All data for the documents are stored in an array (documentTitles).
  // We keep track of the index that we are scrolling to so that we
  // know what data to load for each page.
  if(scrollView.contentOffset.x > scrollView.frame.size.width) 
  {
    // We are moving forward. Load the current doc data on the first page.
    [self loadPageWithId:currIndex onPage:0];

    // Add one to the currentIndex or reset to 0 if we have reached the end.
    currIndex = (currIndex $gt;= [documentTitles count]-1) ? 0 : currIndex + 1;
    [self loadPageWithId:currIndex onPage:1];

    // Load content on the last page. This is either from the next item in the array
    // or the first if we have reached the end.
    nextIndex = (currIndex $gt;= [documentTitles count]-1) ? 0 : currIndex + 1;

    [self loadPageWithId:nextIndex onPage:2];
  }
  if(scrollView.contentOffset.x $lt; scrollView.frame.size.width) {
    // We are moving backward. Load the current doc data on the last page.
    [self loadPageWithId:currIndex onPage:2];

    // Subtract one from the currentIndex or go to the end if we have reached the beginning.
    currIndex = (currIndex == 0) ? [documentTitles count]-1 : currIndex - 1;
    [self loadPageWithId:currIndex onPage:1];

    // Load content on the first page. This is either from the prev item in the array
    // or the last if we have reached the beginning.
    prevIndex = (currIndex == 0) ? [documentTitles count]-1 : currIndex - 1;

    [self loadPageWithId:prevIndex onPage:0];
  }     

  // Reset offset back to middle page
  [scrollView scrollRectToVisible:CGRectMake(320,0,320,416) animated:NO];
}