Sometimes you would like to be able to display an image or view that is larger than the iPhone or iPod screen. UIScrollView gives you this ability plus the feature of zooming using the pinch gesture. This video will show you how to implement this in your own iPhone app. Source Code follows video.
Implementing UIScrollView in Cocoa-Touch
This example starts with a View Based Application with the image already in the Resources group. You can create this yourself using XCode’s “New Project” menu item.
Add IBOutlets
Select the view controller interface file and add the scroll view IBOutlet and the image view property:
#import <UIKit/UIKit.h>
@interface UseScrollViewViewController : UIViewController { IBOutlet UIScrollView *scrollView; UIImageView *imageView; }
@property (nonatomic, retain) UIScrollView *scrollView; @property (nonatomic, retain) UIImageView *imageView;
@end
Finish implementing the IBOutlet and property in the implementation file.
#import "UseScrollViewViewController.h"
@implementation UseScrollViewViewController @synthesize scrollView, imageView;
- (void)dealloc { [super dealloc]; [imageView release]; [scrollView release]; }
@end
Adopt the Delegate Protocol
To use UIScrollView we must adopt the UIScrollViewDelegate protocol. Once we do our view controller may act on behalf of our scroll view. Simple add this after the UIViewController sublcass: <UIScrollViewDelegate>.
#import <UIKit/UIKit.h>
@interface UseScrollViewViewController : UIViewController<UIScrollViewDelegate> { IBOutlet UIScrollView *scrollView; UIImageView *imageView; }
@property (nonatomic, retain) UIScrollView *scrollView; @property (nonatomic, retain) UIImageView *imageView;
@end
Implement the Delegate Method viewForZoomingInScrollView
Implementing this method will allow the scroll view to provide the pinching and zooming behavior demonstrated in the video.
#import "UseScrollViewViewController.h" @implementation UseScrollViewViewController
...
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{ return imageView; }
...
@end
Create the Image View
The image view will be used to display the image on the view. This is pretty straightforward: you will simple create the object and set it to the property we defined earlier in the viewDidLoad method.
- (void)viewDidLoad { [super viewDidLoad]; UIImageView *tempImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Beer-Sign-On-Wall.jpg"]]; self.imageView = tempImageView; [tempImageView release];
}
Set the UIScrollView Properties
Since we are using Interface Builder to add the scroll view we do not need to create it here. But, we will be setting some of the scroll view properties. Note that we add the image view to the scroll view’s subview collection.
- (void)viewDidLoad {
...
scrollView.contentSize = CGSizeMake(imageView.frame.size.width, imageView.frame.size.height); scrollView.maximumZoomScale = 4.0; scrollView.minimumZoomScale = 0.75; scrollView.clipsToBounds = YES; scrollView.delegate = self; [scrollView addSubview:imageView]; }
Add Scroll View in Interface Builder
Now all you need to do is add your scroll view in interface builder and hook it up to the IBOutlet you defined in the view controller!
Discuss in the comments below!
Hi,
Is there a specific reason for not using IB to add your image view with the image to the scrollview?
I tried to add an imageview to the scrollview, added an image using attributes inspector to the image view, connected the file’s owner using an outlet. Then I changed the ViewDidLoad method to remove image view creation and addition statements. But my example doesn’t work. Can you suggest other changes that I may have to make?
Thank you.
This is an AWESOME tutorial. Very easy to understand and EXACTLY what I was looking for. One thing. When the image loads into the UIScrollview, is there a way to make it look to fit the screen? I would like the image loaded to by default zoom to the size of the window it is in. Then allow zooming in. I don’t want to start zoomed in.
Does that make sense?
Hi
Great tutorial, really easy to follow.
I have built this “UIscrollview” and one other – “UIpopover” tutorial as separate files but would like to combine both, but I’m running into a spot of bother though combining these to files into one app. Basically would like a scroll view to one side of the interface and a pop up on the other. Just cant seem to get them to work together. Im sure its something to do with the views or delegate, but hoping you could point me in the right direction please?
thanks
nice tutorial but do one things is that list line code change there
[scrollView addSubview:imageView];
not imageview;
[[scrollView addSubview:tempImageView];