I have a UIImageView inside a UIScrollView which I use for zooming and scrolling. If the image / content of the scroll view is bigger than the scroll view, everything works fine. However, when the image becomes smaller than the scroll view, it sticks to the top left corner of the scroll view. I would like to keep it centered, like the Photos app.
Any ideas or examples about keeping the content of the UIScrollView centered when it's smaller?
I am working with iPhone 3.0.
The following code almost works. The image returns to the top left corner if I pinch it after reaching the minimum zoom level.
- (void)loadView {
[super loadView];
// set up main scroll view
imageScrollView = [[UIScrollView alloc] initWithFrame:[[self view] bounds]];
[imageScrollView setBackgroundColor:[UIColor blackColor]];
[imageScrollView setDelegate:self];
[imageScrollView setBouncesZoom:YES];
[[self view] addSubview:imageScrollView];
UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"WeCanDoIt.png"]];
[imageView setTag:ZOOM_VIEW_TAG];
[imageScrollView setContentSize:[imageView frame].size];
[imageScrollView addSubview:imageView];
CGSize imageSize = imageView.image.size;
[imageView release];
CGSize maxSize = imageScrollView.frame.size;
CGFloat widthRatio = maxSize.width / imageSize.width;
CGFloat heightRatio = maxSize.height / imageSize.height;
CGFloat initialZoom = (widthRatio > heightRatio) ? heightRatio : widthRatio;
[imageScrollView setMinimumZoomScale:initialZoom];
[imageScrollView setZoomScale:1];
float topInset = (maxSize.height - imageSize.height) / 2.0;
float sideInset = (maxSize.width - imageSize.width) / 2.0;
if (topInset < 0.0) topInset = 0.0;
if (sideInset < 0.0) sideInset = 0.0;
[imageScrollView setContentInset:UIEdgeInsetsMake(topInset, sideInset, -topInset, -sideInset)];
}
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
return [imageScrollView viewWithTag:ZOOM_VIEW_TAG];
}
/************************************** NOTE **************************************/
/* The following delegate method works around a known bug in zoomToRect:animated: */
/* In the next release after 3.0 this workaround will no longer be necessary */
/**********************************************************************************/
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
[scrollView setZoomScale:scale+0.01 animated:NO];
[scrollView setZoomScale:scale animated:NO];
// END Bug workaround
CGSize maxSize = imageScrollView.frame.size;
CGSize viewSize = view.frame.size;
float topInset = (maxSize.height - viewSize.height) / 2.0;
float sideInset = (maxSize.width - viewSize.width) / 2.0;
if (topInset < 0.0) topInset = 0.0;
if (sideInset < 0.0) sideInset = 0.0;
[imageScrollView setContentInset:UIEdgeInsetsMake(topInset, sideInset, -topInset, -sideInset)];
}
I've got very simple solution!
All you need is to update the center of your subview (imageview) while zooming in the ScrollViewDelegate.
If zoomed image is smaller than scrollview then adjust subview.center else center is (0,0).
- (void)scrollViewDidZoom:(UIScrollView *)scrollView
{
UIView *subView = [scrollView.subviews objectAtIndex:0];
CGFloat offsetX = MAX((scrollView.bounds.size.width - scrollView.contentSize.width) * 0.5, 0.0);
CGFloat offsetY = MAX((scrollView.bounds.size.height - scrollView.contentSize.height) * 0.5, 0.0);
subView.center = CGPointMake(scrollView.contentSize.width * 0.5 + offsetX,
scrollView.contentSize.height * 0.5 + offsetY);
}
#EvelynCordner's answer was the one that worked best in my app. A lot less code than the other options too.
Here's the Swift version if anyone needs it:
func scrollViewDidZoom(_ scrollView: UIScrollView) {
let offsetX = max((scrollView.bounds.width - scrollView.contentSize.width) * 0.5, 0)
let offsetY = max((scrollView.bounds.height - scrollView.contentSize.height) * 0.5, 0)
scrollView.contentInset = UIEdgeInsets(top: offsetY, left: offsetX, bottom: 0, right: 0)
}
Okay, I've been fighting this for the past two days on and off and having finally come to a pretty reliable (so far...) solution I thought I should share it and save others some pain. :) If you do find a problem with this solution please shout!
I've basically gone through what everyone else has: searching StackOverflow, the Apple Developer Forums, looked at the code for three20, ScrollingMadness, ScrollTestSuite, etc. I've tried enlarging the UIImageView frame, playing with the UIScrollView's offset and/or insets from the ViewController, etc. but nothing worked great (as everyone else has found out too).
After sleeping on it, I tried a couple of alternative angles:
Subclassing the UIImageView so it alters it's own size dynamically - this didn't work well at all.
Subclassing the UIScrollView so it alters it's own contentOffset dynamically - this is the one that seems to be a winner for me.
With this subclassing UIScrollView method I'm overriding the contentOffset mutator so it isn't setting {0,0} when the image is scaled smaller than the viewport - instead it's setting the offset such that the image will be kept centred in the viewport. So far, it always seems to work. I've checked it with wide, tall, tiny & large images and doesn't have the "works but pinch at minimum zoom breaks it" issue.
I've uploaded an example project to github that uses this solution, you can find it here: http://github.com/nyoron/NYOBetterZoom
For a solution better suited for scroll views that use autolayout, use content insets of the scroll view rather than updating the frames of your scroll view's subviews.
- (void)scrollViewDidZoom:(UIScrollView *)scrollView
{
CGFloat offsetX = MAX((scrollView.bounds.size.width - scrollView.contentSize.width) * 0.5, 0.0);
CGFloat offsetY = MAX((scrollView.bounds.size.height - scrollView.contentSize.height) * 0.5, 0.0);
self.scrollView.contentInset = UIEdgeInsetsMake(offsetY, offsetX, 0.f, 0.f);
}
This code should work on most versions of iOS (and has been tested to work on 3.1 upwards).
It's based on the Apple WWDC code for the photoscoller.
Add the below to your subclass of UIScrollView, and replace tileContainerView with the view containing your image or tiles:
- (void)layoutSubviews {
[super layoutSubviews];
// center the image as it becomes smaller than the size of the screen
CGSize boundsSize = self.bounds.size;
CGRect frameToCenter = tileContainerView.frame;
// center horizontally
if (frameToCenter.size.width < boundsSize.width)
frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
else
frameToCenter.origin.x = 0;
// center vertically
if (frameToCenter.size.height < boundsSize.height)
frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
else
frameToCenter.origin.y = 0;
tileContainerView.frame = frameToCenter;
}
Currently I'm subclassing UIScrollView and overriding setContentOffset: to adjust the offset based on contentSize. It works both with pinch and programatic zooming.
#implementation HPCenteringScrollView
- (void)setContentOffset:(CGPoint)contentOffset
{
const CGSize contentSize = self.contentSize;
const CGSize scrollViewSize = self.bounds.size;
if (contentSize.width < scrollViewSize.width)
{
contentOffset.x = -(scrollViewSize.width - contentSize.width) / 2.0;
}
if (contentSize.height < scrollViewSize.height)
{
contentOffset.y = -(scrollViewSize.height - contentSize.height) / 2.0;
}
[super setContentOffset:contentOffset];
}
#end
In addition to being short and sweet, this code produces a much smoother zoom than #Erdemus solution. You can see it in action in the RMGallery demo.
I've spent a day fighting with this issue, and ended up implementing the scrollViewDidEndZooming:withView:atScale: as follows:
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
CGFloat screenWidth = [[UIScreen mainScreen] bounds].size.width;
CGFloat screenHeight = [[UIScreen mainScreen] bounds].size.height;
CGFloat viewWidth = view.frame.size.width;
CGFloat viewHeight = view.frame.size.height;
CGFloat x = 0;
CGFloat y = 0;
if(viewWidth < screenWidth) {
x = screenWidth / 2;
}
if(viewHeight < screenHeight) {
y = screenHeight / 2 ;
}
self.scrollView.contentInset = UIEdgeInsetsMake(y, x, y, x);
}
This ensures that when the image is smaller than the screen, there's still adequate space around it so you can position it to the exact place you want.
(assuming that your UIScrollView contains an UIImageView to hold the image)
Essentially, what this does is check whether your image view's width / height is smaller that the screen's width / height, and if so, create an inset of half the screen's width / height (you could probably make this larger if you want the image to go out of the screen bounds).
Note that since this is a UIScrollViewDelegate method, don't forget to add it to your view controller's declaration, so to avoid getting a build issue.
If contentInset is not needed for anything else, it can be used to center scrollview's content.
class ContentCenteringScrollView: UIScrollView {
override var bounds: CGRect {
didSet { updateContentInset() }
}
override var contentSize: CGSize {
didSet { updateContentInset() }
}
private func updateContentInset() {
var top = CGFloat(0)
var left = CGFloat(0)
if contentSize.width < bounds.width {
left = (bounds.width - contentSize.width) / 2
}
if contentSize.height < bounds.height {
top = (bounds.height - contentSize.height) / 2
}
contentInset = UIEdgeInsets(top: top, left: left, bottom: top, right: left)
}
}
Advantage if this approach is that you can still use contentLayoutGuide to place content inside scrollview
scrollView.addSubview(imageView)
imageView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
imageView.leadingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leadingAnchor),
imageView.trailingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.trailingAnchor),
imageView.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor),
imageView.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor)
])
or just drag and drop the content in Xcode's Interface Builder.
Apple has released the 2010 WWDC session videos to all members of the iphone developer program. One of the topics discussed is how they created the photos app!!! They build a very similar app step by step and have made all the code available for free.
It does not use private api either. I can't put any of the code here because of the non disclosure agreement, but here is a link to the sample code download. You will probably need to login to gain access.
http://connect.apple.com/cgi-bin/WebObjects/MemberSite.woa/wa/getSoftware?code=y&source=x&bundleID=20645
And, here is a link to the iTunes WWDC page:
http://insideapple.apple.com/redir/cbx-cgi.do?v=2&la=en&lc=&a=kGSol9sgPHP%2BtlWtLp%2BEP%2FnxnZarjWJglPBZRHd3oDbACudP51JNGS8KlsFgxZto9X%2BTsnqSbeUSWX0doe%2Fzv%2FN5XV55%2FomsyfRgFBysOnIVggO%2Fn2p%2BiweDK%2F%2FmsIXj
Ok, this solution is working for me. I have a subclass of UIScrollView with a reference to the UIImageView it is displaying. Whenever the UIScrollView zooms, the contentSize property is adjusted. It is in the setter that I scale the UIImageView appropriately and also adjust its center position.
-(void) setContentSize:(CGSize) size{
CGSize lSelfSize = self.frame.size;
CGPoint mid;
if(self.zoomScale >= self.minimumZoomScale){
CGSize lImageSize = cachedImageView.initialSize;
float newHeight = lImageSize.height * self.zoomScale;
if (newHeight < lSelfSize.height ) {
newHeight = lSelfSize.height;
}
size.height = newHeight;
float newWidth = lImageSize.width * self.zoomScale;
if (newWidth < lSelfSize.width ) {
newWidth = lSelfSize.width;
}
size.width = newWidth;
mid = CGPointMake(size.width/2, size.height/2);
}
else {
mid = CGPointMake(lSelfSize.width/2, lSelfSize.height/2);
}
cachedImageView.center = mid;
[super setContentSize:size];
[self printLocations];
NSLog(#"zoom %f setting size %f x %f",self.zoomScale,size.width,size.height);
}
Evertime I set the image on the UIScrollView I resize it. The UIScrollView in the scrollview is also a custom class I created.
-(void) resetSize{
if (!scrollView){//scroll view is view containing imageview
return;
}
CGSize lSize = scrollView.frame.size;
CGSize lSelfSize = self.image.size;
float lWidth = lSize.width/lSelfSize.width;
float lHeight = lSize.height/lSelfSize.height;
// choose minimum scale so image width fits screen
float factor = (lWidth<lHeight)?lWidth:lHeight;
initialSize.height = lSelfSize.height * factor;
initialSize.width = lSelfSize.width * factor;
[scrollView setContentSize:lSize];
[scrollView setContentOffset:CGPointZero];
scrollView.userInteractionEnabled = YES;
}
With these two methods I am able to have a view that behaves just like the photos app.
The way I've done this is to add an extra view into the hierarchy:
UIScrollView -> UIView -> UIImageView
Give your UIView the same aspect ratio as your UIScrollView, and centre your UIImageView into that.
Just the approved answer in swift, but without subclassing using the delegate
func centerScrollViewContents(scrollView: UIScrollView) {
let contentSize = scrollView.contentSize
let scrollViewSize = scrollView.frame.size;
var contentOffset = scrollView.contentOffset;
if (contentSize.width < scrollViewSize.width) {
contentOffset.x = -(scrollViewSize.width - contentSize.width) / 2.0
}
if (contentSize.height < scrollViewSize.height) {
contentOffset.y = -(scrollViewSize.height - contentSize.height) / 2.0
}
scrollView.setContentOffset(contentOffset, animated: false)
}
// UIScrollViewDelegate
func scrollViewDidZoom(scrollView: UIScrollView) {
centerScrollViewContents(scrollView)
}
I know some answers above are right, but I just want to give my answer with some explanation, the comments will make you understand why we do like this.
When I load the scrollView for the first time, I write the following code to make it center, please notice we set contentOffset first, then contentInset
scrollView.maximumZoomScale = 8
scrollView.minimumZoomScale = 1
// set vContent frame
vContent.frame = CGRect(x: 0,
y: 0 ,
width: vContentWidth,
height: vContentWidth)
// set scrollView.contentSize
scrollView.contentSize = vContent.frame.size
//on the X direction, if contentSize.width > scrollView.bounds.with, move scrollView from 0 to offsetX to make it center(using `scrollView.contentOffset`)
// if not, don't need to set offset, but we need to set contentInset to make it center.(using `scrollView.contentInset`)
// so does the Y direction.
let offsetX = max((scrollView.contentSize.width - scrollView.bounds.width) * 0.5, 0)
let offsetY = max((scrollView.contentSize.height - scrollView.bounds.height) * 0.5, 0)
scrollView.contentOffset = CGPoint(x: offsetX, y: offsetY)
let topX = max((scrollView.bounds.width - scrollView.contentSize.width) * 0.5, 0)
let topY = max((scrollView.bounds.height - scrollView.contentSize.height) * 0.5, 0)
scrollView.contentInset = UIEdgeInsets(top: topY, left: topX, bottom: 0, right: 0)
Then, when I pinch vContent, I write the following code to make it center.
func scrollViewDidZoom(_ scrollView: UIScrollView) {
//we just need to ensure that the content is in the center when the contentSize is less than scrollView.size.
let topX = max((scrollView.bounds.width - scrollView.contentSize.width) * 0.5, 0)
let topY = max((scrollView.bounds.height - scrollView.contentSize.height) * 0.5, 0)
scrollView.contentInset = UIEdgeInsets(top: topY, left: topX, bottom: 0, right: 0)
}
You could watch the contentSize property of the UIScrollView (using key-value observing or similar), and automatically adjust the contentInset whenever the contentSize changes to be less than the size of the scroll view.
One elegant way to center the content of UISCrollView is this.
Add one observer to the contentSize of your UIScrollView, so this method will be called everytime the content change...
[myScrollView addObserver:delegate
forKeyPath:#"contentSize"
options:(NSKeyValueObservingOptionNew)
context:NULL];
Now on your observer method:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
// Correct Object Class.
UIScrollView *pointer = object;
// Calculate Center.
CGFloat topCorrect = ([pointer bounds].size.height - [pointer viewWithTag:100].bounds.size.height * [pointer zoomScale]) / 2.0 ;
topCorrect = ( topCorrect < 0.0 ? 0.0 : topCorrect );
topCorrect = topCorrect - ( pointer.frame.origin.y - imageGallery.frame.origin.y );
// Apply Correct Center.
pointer.center = CGPointMake(pointer.center.x,
pointer.center.y + topCorrect ); }
You should change the [pointer
viewWithTag:100]. Replace by your
content view UIView.
Also change imageGallery pointing to your window size.
This will correct the center of the content everytime his size change.
NOTE: The only way this content don't works very well is with standard zoom functionality of the UIScrollView.
This is my solution to that problem which works pretty fine for any kind of view inside a scrollview.
-(void)scrollViewDidZoom:(__unused UIScrollView *)scrollView
{
CGFloat top;
CGFloat left;
CGFloat bottom;
CGFloat right;
if (_scrollView.contentSize.width < scrollView.bounds.size.width) {
DDLogInfo(#"contentSize %#",NSStringFromCGSize(_scrollView.contentSize));
CGFloat width = (_scrollView.bounds.size.width-_scrollView.contentSize.width)/2.0;
left = width;
right = width;
}else {
left = kInset;
right = kInset;
}
if (_scrollView.contentSize.height < scrollView.bounds.size.height) {
CGFloat height = (_scrollView.bounds.size.height-_scrollView.contentSize.height)/2.0;
top = height;
bottom = height;
}else {
top = kInset;
right = kInset;
}
_scrollView.contentInset = UIEdgeInsetsMake(top, left, bottom, right);
if ([self.tiledScrollViewDelegate respondsToSelector:#selector(tiledScrollViewDidZoom:)])
{
[self.tiledScrollViewDelegate tiledScrollViewDidZoom:self];
}
}
There are a plenty of solutions here, but I'd risk putting here my own. It's good for two reasons: it doesn't mess zooming experience, as would do updating image view frame in progress, and also it respects original scroll view insets (say, defined in xib or storyboard for graceful handling of semi-transparent toolbars etc).
First, define a small helper:
CGSize CGSizeWithAspectFit(CGSize containerSize, CGSize contentSize) {
CGFloat containerAspect = containerSize.width / containerSize.height,
contentAspect = contentSize.width / contentSize.height;
CGFloat scale = containerAspect > contentAspect
? containerSize.height / contentSize.height
: containerSize.width / contentSize.width;
return CGSizeMake(contentSize.width * scale, contentSize.height * scale);
}
To retain original insets, defined field:
UIEdgeInsets originalScrollViewInsets;
And somewhere in viewDidLoad fill it:
originalScrollViewInsets = self.scrollView.contentInset;
To place UIImageView into UIScrollView (assuming UIImage itself is in loadedImage var):
CGSize containerSize = self.scrollView.bounds.size;
containerSize.height -= originalScrollViewInsets.top + originalScrollViewInsets.bottom;
containerSize.width -= originalScrollViewInsets.left + originalScrollViewInsets.right;
CGSize contentSize = CGSizeWithAspectFit(containerSize, loadedImage.size);
UIImageView *imageView = [[UIImageView alloc] initWithFrame:(CGRect) { CGPointZero, contentSize }];
imageView.autoresizingMask = UIViewAutoresizingNone;
imageView.contentMode = UIViewContentModeScaleAspectFit;
imageView.image = loadedImage;
[self.scrollView addSubview:imageView];
self.scrollView.contentSize = contentSize;
[self centerImageViewInScrollView];
scrollViewDidZoom: from UIScrollViewDelegate for that scroll view:
- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
if (scrollView == self.scrollView) {
[self centerImageViewInScrollView];
}
}
An finally, centering itself:
- (void)centerImageViewInScrollView {
CGFloat excessiveWidth = MAX(0.0, self.scrollView.bounds.size.width - self.scrollView.contentSize.width),
excessiveHeight = MAX(0.0, self.scrollView.bounds.size.height - self.scrollView.contentSize.height),
insetX = excessiveWidth / 2.0,
insetY = excessiveHeight / 2.0;
self.scrollView.contentInset = UIEdgeInsetsMake(
MAX(insetY, originalScrollViewInsets.top),
MAX(insetX, originalScrollViewInsets.left),
MAX(insetY, originalScrollViewInsets.bottom),
MAX(insetX, originalScrollViewInsets.right)
);
}
I didn't test orientation change yet (i.e. proper reaction for resizing UIScrollView itself), but fix for that should be relatively easy.
You'll find that the solution posted by Erdemus does work, but… There are some cases where the scrollViewDidZoom method does not get invoked & your image is stuck to the top left corner. A simple solution is to explicitly invoke the method when you initially display an image, like this:
[self scrollViewDidZoom: scrollView];
In many cases, you may be invoking this method twice, but this is a cleaner solution than some of the other answers in this topic.
Apple's Photo Scroller Example does exactly what you are looking for. Put this in your UIScrollView Subclass and change _zoomView to be your UIImageView.
-(void)layoutSubviews{
[super layoutSubviews];
// center the zoom view as it becomes smaller than the size of the screen
CGSize boundsSize = self.bounds.size;
CGRect frameToCenter = self.imageView.frame;
// center horizontally
if (frameToCenter.size.width < boundsSize.width){
frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
}else{
frameToCenter.origin.x = 0;
}
// center vertically
if (frameToCenter.size.height < boundsSize.height){
frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
}else{
frameToCenter.origin.y = 0;
}
self.imageView.frame = frameToCenter;
}
Apple's Photo Scroller Sample Code
To make the animation flow nicely, set
self.scrollview.bouncesZoom = NO;
and use this function (finding the center using the method at this answer)
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale {
[UIView animateWithDuration:0.2 animations:^{
float offsetX = MAX((scrollView.bounds.size.width-scrollView.contentSize.width)/2, 0);
float offsetY = MAX((scrollView.bounds.size.height-scrollView.contentSize.height)/2, 0);
self.imageCoverView.center = CGPointMake(scrollView.contentSize.width*0.5+offsetX, scrollView.contentSize.height*0.5+offsetY);
}];
}
This creates the bouncing effect but doesn't involve any sudden movements beforehand.
In case your inner imageView has initial specific width(eg 300) and you just want to center its width only on zoom smaller than its initial width this might help you also.
func scrollViewDidZoom(scrollView: UIScrollView){
if imageView.frame.size.width < 300{
imageView.center.x = self.view.frame.width/2
}
}
Here's the current way I'm making this work. It's better but still not perfect. Try setting:
myScrollView.bouncesZoom = YES;
to fix the problem with the view not centering when at minZoomScale.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
CGSize screenSize = [[self view] bounds].size;//[[UIScreen mainScreen] bounds].size;//
CGSize photoSize = [yourImage size];
CGFloat topInset = (screenSize.height - photoSize.height * [myScrollView zoomScale]) / 2.0;
CGFloat sideInset = (screenSize.width - photoSize.width * [myScrollView zoomScale]) / 2.0;
if (topInset < 0.0)
{ topInset = 0.0; }
if (sideInset < 0.0)
{ sideInset = 0.0; }
[myScrollView setContentInset:UIEdgeInsetsMake(topInset, sideInset, -topInset, -sideInset)];
ApplicationDelegate *appDelegate = (ApplicationDelegate *)[[UIApplication sharedApplication] delegate];
CGFloat scrollViewHeight; //Used later to calculate the height of the scrollView
if (appDelegate.navigationController.navigationBar.hidden == YES) //If the NavBar is Hidden, set scrollViewHeight to 480
{ scrollViewHeight = 480; }
if (appDelegate.navigationController.navigationBar.hidden == NO) //If the NavBar not Hidden, set scrollViewHeight to 360
{ scrollViewHeight = 368; }
imageView.frame = CGRectMake(0, 0, CGImageGetWidth(yourImage)* [myScrollView zoomScale], CGImageGetHeight(yourImage)* [myScrollView zoomScale]);
[imageView setContentMode:UIViewContentModeCenter];
}
Also, I do the following to prevent the image from sticking a the side after zooming out.
- (void) scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
myScrollView.frame = CGRectMake(0, 0, 320, 420);
//put the correct parameters for your scroll view width and height above
}
Okay, I think I've found a pretty good solution to this problem. The trick is to constantly readjust the imageView's frame. I find this works much better than constantly adjusting the contentInsets or contentOffSets. I had to add a bit of extra code to accommodate both portrait and landscape images.
Here's the code:
- (void) scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
CGSize screenSize = [[self view] bounds].size;
if (myScrollView.zoomScale <= initialZoom +0.01) //This resolves a problem with the code not working correctly when zooming all the way out.
{
imageView.frame = [[self view] bounds];
[myScrollView setZoomScale:myScrollView.zoomScale +0.01];
}
if (myScrollView.zoomScale > initialZoom)
{
if (CGImageGetWidth(temporaryImage.CGImage) > CGImageGetHeight(temporaryImage.CGImage)) //If the image is wider than tall, do the following...
{
if (screenSize.height >= CGImageGetHeight(temporaryImage.CGImage) * [myScrollView zoomScale]) //If the height of the screen is greater than the zoomed height of the image do the following...
{
imageView.frame = CGRectMake(0, 0, 320*(myScrollView.zoomScale), 368);
}
if (screenSize.height < CGImageGetHeight(temporaryImage.CGImage) * [myScrollView zoomScale]) //If the height of the screen is less than the zoomed height of the image do the following...
{
imageView.frame = CGRectMake(0, 0, 320*(myScrollView.zoomScale), CGImageGetHeight(temporaryImage.CGImage) * [myScrollView zoomScale]);
}
}
if (CGImageGetWidth(temporaryImage.CGImage) < CGImageGetHeight(temporaryImage.CGImage)) //If the image is taller than wide, do the following...
{
CGFloat portraitHeight;
if (CGImageGetHeight(temporaryImage.CGImage) * [myScrollView zoomScale] < 368)
{ portraitHeight = 368;}
else {portraitHeight = CGImageGetHeight(temporaryImage.CGImage) * [myScrollView zoomScale];}
if (screenSize.width >= CGImageGetWidth(temporaryImage.CGImage) * [myScrollView zoomScale]) //If the width of the screen is greater than the zoomed width of the image do the following...
{
imageView.frame = CGRectMake(0, 0, 320, portraitHeight);
}
if (screenSize.width < CGImageGetWidth (temporaryImage.CGImage) * [myScrollView zoomScale]) //If the width of the screen is less than the zoomed width of the image do the following...
{
imageView.frame = CGRectMake(0, 0, CGImageGetWidth(temporaryImage.CGImage) * [myScrollView zoomScale], portraitHeight);
}
}
[myScrollView setZoomScale:myScrollView.zoomScale -0.01];
}
Just disable the pagination, so it'll work fine:
scrollview.pagingEnabled = NO;
I had the exact same problem. Here is how I solved
This code should get called as the result of scrollView:DidScroll:
CGFloat imageHeight = self.imageView.frame.size.width * self.imageView.image.size.height / self.imageView.image.size.width;
BOOL imageSmallerThanContent = (imageHeight < self.scrollview.frame.size.height) ? YES : NO;
CGFloat topOffset = (self.imageView.frame.size.height - imageHeight) / 2;
// If image is not large enough setup content offset in a way that image is centered and not vertically scrollable
if (imageSmallerThanContent) {
topOffset = topOffset - ((self.scrollview.frame.size.height - imageHeight)/2);
}
self.scrollview.contentInset = UIEdgeInsetsMake(topOffset * -1, 0, topOffset * -1, 0);
Although the question is a bit old yet the problem still exists. I solved it in Xcode 7 by making the vertical space constraint of the uppermost item (in this case the topLabel) to the superViews (the scrollView) top an IBOutlet and then recalculating its constant every time the content changes depending on the height of the scrollView's subviews (topLabel and bottomLabel).
class MyViewController: UIViewController {
#IBOutlet weak var scrollView: UIScrollView!
#IBOutlet weak var topLabel: UILabel!
#IBOutlet weak var bottomLabel: UILabel!
#IBOutlet weak var toTopConstraint: NSLayoutConstraint!
override func viewDidLayoutSubviews() {
let heightOfScrollViewContents = (topLabel.frame.origin.y + topLabel.frame.size.height - bottomLabel.frame.origin.y)
// In my case abs() delivers the perfect result, but you could also check if the heightOfScrollViewContents is greater than 0.
toTopConstraint.constant = abs((scrollView.frame.height - heightOfScrollViewContents) / 2)
}
func refreshContents() {
// Set the label's text …
self.view.layoutIfNeeded()
}
}
A Swift version to just subclass UIScrollView and lauout the subview by yourself. It works pretty smooth.
import UIKit
class CenteringScrollView: UIScrollView {
override func layoutSubviews() {
super.layoutSubviews()
if zoomScale < 1.0 {
if let subview = self.subviews.first {
subview.center.x = self.center.x
}
}
}
}
I'm using this code to resize an image on the iPhone:
CGRect screenRect = CGRectMake(0, 0, 320.0, 480.0);
UIGraphicsBeginImageContext(screenRect.size);
[value drawInRect:screenRect blendMode:kCGBlendModePlusDarker alpha:1];
UIImage *tmpValue = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Which is working great, as long as the aspect ratio of the image matches that of the new resized image. I'd like to modify this so that it keeps the correct aspect ratio and just puts a black background anywhere the image doesn't show up. So I would still end up with a 320x480 image but with black on the top and bottom or sides, depending on the original image size.
Is there an easy way to do this similar to what I'm doing? Thanks!
After you set your screen rect, do something like the following to decide what rect to draw the image in:
float hfactor = value.bounds.size.width / screenRect.size.width;
float vfactor = value.bounds.size.height / screenRect.size.height;
float factor = fmax(hfactor, vfactor);
// Divide the size by the greater of the vertical or horizontal shrinkage factor
float newWidth = value.bounds.size.width / factor;
float newHeight = value.bounds.size.height / factor;
// Then figure out if you need to offset it to center vertically or horizontally
float leftOffset = (screenRect.size.width - newWidth) / 2;
float topOffset = (screenRect.size.height - newHeight) / 2;
CGRect newRect = CGRectMake(leftOffset, topOffset, newWidth, newHeight);
If you don't want to enlarge images smaller than the screenRect, make sure factor is greater than or equal to one (e.g. factor = fmax(factor, 1)).
To get the black background, you would probably just want to set the context color to black and call fillRect before drawing the image.
I know this is very old, but thanks for that post -- it redirected me from attempting to use scale to drawing the image. In case it is of benefit to anyone, I made an extension class I'll throw in here. It allows you to resize an image like this:
UIImage imgNew = img.Fit(40.0f, 40.0f);
I don't need a fit option, but it could easily be extended to support Fill as well.
using CoreGraphics;
using System;
using UIKit;
namespace SomeApp.iOS.Extensions
{
public static class UIImageExtensions
{
public static CGSize Fit(this CGSize sizeImage,
CGSize sizeTarget)
{
CGSize ret;
float fw;
float fh;
float f;
fw = (float) (sizeTarget.Width / sizeImage.Width);
fh = (float) (sizeTarget.Height / sizeImage.Height);
f = Math.Min(fw, fh);
ret = new CGSize
{
Width = sizeImage.Width * f,
Height = sizeImage.Height * f
};
return ret;
}
public static UIImage Fit(this UIImage image,
float width,
float height,
bool opaque = false,
float scale = 1.0f)
{
UIImage ret;
ret = image.Fit(new CGSize(width, height),
opaque,
scale);
return ret;
}
public static UIImage Fit(this UIImage image,
CGSize sizeTarget,
bool opaque = false,
float scale = 1.0f)
{
CGSize sizeNewImage;
CGSize size;
UIImage ret;
size = image.Size;
sizeNewImage = size.Fit(sizeTarget);
UIGraphics.BeginImageContextWithOptions(sizeNewImage,
opaque,
1.0f);
using (CGContext context = UIGraphics.GetCurrentContext())
{
context.ScaleCTM(1, -1);
context.TranslateCTM(0, -sizeNewImage.Height);
context.DrawImage(new CGRect(CGPoint.Empty, sizeNewImage),
image.CGImage);
ret = UIGraphics.GetImageFromCurrentImageContext();
}
UIGraphics.EndImageContext();
return ret;
}
}
}
As per the post above, it starts a new context for an image, then for that image it figures out aspect and then paints into the image. If you haven't done any Swift xcode dev time, UIGraphics is a bit backwards to most systems I work with but not bad. One issue is that bitmaps by default paint bottom to top. To get around that,
context.ScaleCTM(1, -1);
context.TranslateCTM(0, -sizeNewImage.Height);
Changes the orientation of drawing to the more common top-left to bottom-right... but then you need to move the origin as well hence the TranslateCTM.
Hopefully, it saves someone some time.
Cheers