Zoom a UIScrollview on Objective-C - iphone

Question

In one of the projects I'm working on, I have a UIScrollView that has a lot of buttons and labels that resemble movie theater seats that the user can tap to select seats for them to buy. Is it possible to zoom the UIScrollView? I have already declared the UIScrollViewDelegate, set the delegate to self, set the minimum and maximum zoom scale but I'm having issues with the viewForZoomingInScrollView and scrollViewDidEndZooming methods. I tried to return my scrollview on the viewForZoomingInScrollView method but it crashes.
Here's some of the code:
- (void) renderSeatMapOnScreen
{
int x_offset_row = 10;
int y_offset_row = 25;
int x_offset_col = 30;
int y_offset_col = 0;
int scrollview_w = 0;
int scrollview_h = 0;
NSString *row_name = #"";
int tag_index = 0;
NSMutableArray *seat_map_table = [seat_map_xml seats_map];
NSString *seat_available_str = [seat_avail_xml seat_available];
HideNetworkActivityIndicator();
NSLog(#"Seats available = %#", seat_available_str);
NSArray *seats_avail = [seat_available_str componentsSeparatedByString:#";"];
int ROW_COL_OFFSET = 25;
for (int row = 0; row < [seat_map_table count]; row++)
{
UILabel * rowlabel = [[UILabel alloc] init];
rowlabel.frame = CGRectMake(x_offset_row , y_offset_row, 22, 22);
SeatMapDeclaration *rowmap = [seat_map_table objectAtIndex:row];
rowlabel.text = rowmap.rows;
[scrollview addSubview:rowlabel];
row_name = [NSString stringWithFormat:#"%#", rowmap.rows];
NSArray *seat = [rowmap.rowmap componentsSeparatedByString:#";"];
NSLog(#"row[%i] = %#", row, rowmap.rowmap);
if (row == 0)
{
scrollview_w = [seat count] * ROW_COL_OFFSET + y_offset_row;
total_column = [seat count];
total_row = [seat_map_table count];
}
x_offset_col = 30 ;
y_offset_col = y_offset_row ;
for (int column = 0; column < [seat count]; column++)
{
if (([[seat objectAtIndex:column] rangeOfString:#"a("].location != NSNotFound)
|| ([[seat objectAtIndex:column] isEqualToString:#""]))
{
CGRect myImageRect = CGRectMake(x_offset_col, y_offset_col, 22, 22);
UIImageView *imageView = [[UIImageView alloc] initWithFrame:myImageRect];
[imageView setImage:[UIImage imageNamed:#"noseat.png"]];
[scrollview addSubview:imageView];
}
else if ([[seat objectAtIndex:column] rangeOfString:#"b("].location != NSNotFound)
{
CGRect myImageRect = CGRectMake(x_offset_col, y_offset_col, 22, 22);
UIImageView *imageView = [[UIImageView alloc] initWithFrame:myImageRect];
imageView.image = [UIImage imageNamed:#"noseat.png"];
[scrollview addSubview:imageView];
}
else
{
NSString *status = [NSString stringWithFormat:#"%#%#", row_name, [seat objectAtIndex:column]];
BOOL matchedFound = NO;
for (int i = 0; i < [seats_avail count]; i++)
{
if ([[seats_avail objectAtIndex:i] isEqualToString:status])
{
matchedFound = YES ;
break ;
}
}
if (matchedFound == YES)
{
UIButton * seat_btn = [UIButton buttonWithType:UIButtonTypeCustom];
[seat_btn setBackgroundImage:[UIImage imageNamed:#"seatavailable.png"] forState:UIControlStateNormal];
[seat_btn setBackgroundImage:[UIImage imageNamed:#"seatactive.png"] forState:UIControlStateSelected];
seat_btn.frame = CGRectMake(x_offset_col, y_offset_col, 22, 22);
tag_index = [[seat objectAtIndex:column] intValue];
[seat_btn setTitle:[seat objectAtIndex:column] forState:UIControlStateNormal];
seat_btn.titleLabel.font = [UIFont fontWithName:#"Helvetica" size:12.0];
seat_btn.tag = tag_index + row * 100;
[seat_btn addTarget:self
action:#selector(checkboxButton:)
forControlEvents:UIControlEventTouchUpInside];
[scrollview addSubview:seat_btn];
}
else
{
CGRect myImageRect = CGRectMake(x_offset_col, y_offset_col, 22, 22);
UIImageView *imageView = [[UIImageView alloc] initWithFrame:myImageRect];
imageView.image = [UIImage imageNamed:#"seat_not_available.png"];
[scrollview addSubview:imageView];
}
}
x_offset_col += ROW_COL_OFFSET ;
NSString *data = #"";
[seatControl addObject:data];
}
y_offset_row += ROW_COL_OFFSET;
}
UILabel *screenlabel = [[UILabel alloc] init];
screenlabel.frame = CGRectMake((scrollview_w-300)/2, 3, 300, 15);
screenlabel.text = #"Screen";
screenlabel.backgroundColor = [UIColor blackColor];
screenlabel.textColor = [UIColor whiteColor] ;
screenlabel.font = [UIFont fontWithName:#"Helvetica" size:10.0];
screenlabel.textAlignment = UITextAlignmentCenter;
[scrollview addSubview:screenlabel];
scrollview_h = y_offset_row + ROW_COL_OFFSET;
// Adjust scroll view
[scrollview setContentSize:CGSizeMake(scrollview_w, scrollview_h )];
}
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
NSLog(#"1");
return scrollview;
}
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale
{
NSLog(#"2");
}

Answer 1

In:
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
NSLog(#"1");
return scrollview;
}
you are not supposed to return the UIScrollView itself, rather its subview that you would like to scroll/zoom.
If you have many subviews, I would suggest creating a container view for all of them that you return from viewForZoomingInScrollView; instead of adding your seats to the scrollview itself you would then add them to the container view.

Answer 2

If you want to zoom to a certain seat in the UIScrollView, you should use zoomToRect: animated:. You can specify a certain rectangle (i.e. the seat) to which you would like to zoom in on.

Answer 3

Zooming only works when you implement the viewForZoomingInScrollView: delegate callback.
UIImageView *tempImage = [[UIImageView alloc]initWithImage:[UIImage imageWithData:data]];
self.imageView = tempImage;
scrollView.contentSize = CGSizeMake(imageView.frame.size.width , imageView.frame.size.height);
scrollView.maximumZoomScale = 1;
scrollView.minimumZoomScale = .37;
scrollView.clipsToBounds = YES;
scrollView.delegate = self;
[scrollView addSubview:imageView];
scrollView.zoomScale = .37;
-(UIView *) viewForZoomingInScrollView:(UIScrollView *)inScroll {
return imageView;
}