iOS: Adding pinch-zoom to UIImageView

[Jon Sigman]

I have an iOS iPad app that uses a full screen UIImageView to display some png images. However, this arrangement doesn't allow the user to pinch-zoom the image. It seems to ignore gestures. I've tried embedding the UIImageView within a UIScrollView from IB (using Embed Object in Scroll View), and checking 'Multiple Touch' and 'User Interaction Enabled' for both views, but now I just get a white screen. What's the typical way to add pinch capability to a UIImageView?
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[Fritz Anderson]

On 16 Jan 2012, at 3:57 PM, Jon Sigman wrote:

> What's the typical way to add pinch capability to a UIImageView?

Put it in a UIScrollView.

— F

[Jon Sigman]

Here's what I've tried:

IBOutlet UIScrollView *scrollView;  // created & placed on GUI with IB

@synthesize scrollView;             // hooked up from w/in IB

- (void)viewDidLoad {
    [super viewDidLoad];
    imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"default.png"]];
    [scrollView addSubview:imageView];
    return;
}

The UIScrollView & UIImageView show up on the GUI, with the correct image, but gestures are ignored. What am I overlooking?

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From: Fritz Anderson <fri...@manoverboard.org>
To: Jon Sigman <rf_...@yahoo.com>
Cc: Cocoa- Dev List <coco...@lists.apple.com>
Sent: Tuesday, January 17, 2012 8:11 AM
Subject: Re: iOS: Adding pinch-zoom to UIImageView

[Eric E. Dolecki]

Did you set the contentSize for the scroll view?

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[Jon Sigman]

I just added this:
    [scrollView setContentSize:CGSizeMake(128.0,96.0)];
Now I can move the image about within the UIScrollView, but I can't pinch/zoom it.

________________________________
From: Eric E. Dolecki <edol...@gmail.com>
To: Jon Sigman <rf_...@yahoo.com>
Cc: Fritz Anderson <fri...@manoverboard.org>; Cocoa- Dev List <coco...@lists.apple.com>
Sent: Tuesday, January 17, 2012 11:18 AM

[David Duncan]

You need to set the min/max magnification properties as well. You may also need to implement the delegate protocol to tell the scroll view which view to zoom as well (I'm almost certain this is necessary, but I haven't done this in a little bit).

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--
David Duncan

[Fritz Anderson]

On 17 Jan 2012, at 1:30 PM, Jon Sigman wrote:

> I just added this:
> [scrollView setContentSize:CGSizeMake(128.0,96.0)];
> Now I can move the image about within the UIScrollView, but I can't pinch/zoom it.

There are excellent tutorials about this, and you would profit from a skimming of the UIScrollView class reference.

The properties you are looking for are .minimumZoomScale and .maximumZoomScale.

— F

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[Julius Oklamcak]

You need to implement the -viewForZoomingInScrollView: UIScrollViewDelegate
method and return the image view.

Please have a look at Apple's ScrollViewSuite sample code:

http://developer.apple.com/library/ios/#samplecode/ScrollViewSuite/Introduct
ion/Intro.html

> I just added this:
>    [scrollView setContentSize:CGSizeMake(128.0,96.0)];
> Now I can move the image about within the UIScrollView, but I can't
pinch/zoom it.

_______________________________________________

[Jon Sigman]

Yep, specifying a delegate and implementing -viewForZoomingInScrollView: did the trick! (As a newb, I thought this functionality was innate in UIImageView, but...)

Thanks to everyone for your help!

________________________________
From: Julius Oklamcak <jul...@icodemonks.com>

To: 'Jon Sigman' <rf_...@yahoo.com>
Cc: 'Cocoa- Dev List' <coco...@lists.apple.com>

Sent: Tuesday, January 17, 2012 11:37 AM
Subject: RE: iOS: Adding pinch-zoom to UIImageView