How can I zoom a UIScrollview to a fixed point?

Question

I am creating a control for showing the timeline. Initially , it should show the year. When zooming in and the zoomScale reached a specific value, it will show the value of the individual months, and In the next zoom level, it should show the real values for the individual days.

I have creatd a scrollview and added the layers (for showing the month/year values) to this. After overriding the pinch guesture, I am able to do the zooming (Normal UIScrollview zooming). But I need to zoom it to a particular point. ie, Suppose i am zooming January, I need to keep it in the same position(for creating an effect like moving inside of January). Any suggestions to achieve this?

Is my way is currect? else please help me to start this.

u mean scrollView zoom at specific size ??? – iPatel Feb 04 '13 at 10:51 — iPatel, Feb 04 '13 at 10:51
why don't you try the `-zoomToRect:animated:` method? – holex Feb 04 '13 at 11:54 — holex, Feb 04 '13 at 11:54

score 3 · Answer 1 · answered Feb 04 '13 at 11:50

3

Use This bellow method for your requirement,

- (void)zoomToRect:(CGRect)rect animated:(BOOL)animated

just call this above method with your selected frame or point , like if select January then just take the point ( position) of january button or view and just call above method with that frame..

for more information see this link UIScrollView_Class

i hope this helpful to you...

answered Feb 04 '13 at 11:50

Paras Joshi

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I am not using the default UIScrollview zoom. I am resizing the layers in pinch guesture for reatsining the clarity of the text.Please see the code below for zooming. [CATransaction begin]; [CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions]; tmpLayer.frame = 'CGRectMake(i*layerWidthOnPinch*recognizer.scale,tmpLayer.frame.origin.y,layerWidthOnPinch*recognizer.scale, tmpLayer.frame.size.height); [tmpLayer setNeedsDisplay]; [CATransaction commit]; eventScroll.contentOffset = CGPointMake(500, 0); – user2039257 Feb 04 '13 at 11:57
try this may be you get some idea from that http://stackoverflow.com/questions/11536555/i-would-like-to-implement-only-zoom-in-feature-on-uiscrollview-in-iphone-sdk-is – Paras Joshi Feb 04 '13 at 12:04
and this one is also.. http://stackoverflow.com/questions/5150642/max-min-scale-of-pinch-zoom-in-uipinchgesturerecognizer-iphone-ios i just get some idea from this at one time for PichGesture.. http://stackoverflow.com/questions/5150642/max-min-scale-of-pinch-zoom-in-uipinchgesturerecognizer-iphone-ios – Paras Joshi Feb 04 '13 at 12:06

score 2 · Answer 2 · edited Mar 14 '13 at 12:32

Here’s what it looks like:

@implementation UIScrollView (ZoomToPoint)

- (void)zoomToPoint:(CGPoint)zoomPoint withScale: (CGFloat)scale animated: (BOOL)animated
{
    //Normalize current content size back to content scale of 1.0f
    CGSize contentSize;
    contentSize.width = (self.contentSize.width / self.zoomScale);
    contentSize.height = (self.contentSize.height / self.zoomScale);

    //translate the zoom point to relative to the content rect
    zoomPoint.x = (zoomPoint.x / self.bounds.size.width) * contentSize.width;
    zoomPoint.y = (zoomPoint.y / self.bounds.size.height) * contentSize.height;

    //derive the size of the region to zoom to
    CGSize zoomSize;
    zoomSize.width = self.bounds.size.width / scale;
    zoomSize.height = self.bounds.size.height / scale;

    //offset the zoom rect so the actual zoom point is in the middle of the rectangle
    CGRect zoomRect;
    zoomRect.origin.x = zoomPoint.x - zoomSize.width / 2.0f;
    zoomRect.origin.y = zoomPoint.y - zoomSize.height / 2.0f;
    zoomRect.size.width = zoomSize.width;
    zoomRect.size.height = zoomSize.height;

    //apply the resize
    [self zoomToRect: zoomRect animated: animated];
}

@end

Looking at it, it should be pretty straightforward to figure out how it works. If you see anything wrong with it, let me know in the comments.
Thanks :)

source: http://www.tim-oliver.com/2012/01/14/zooming-to-a-point-in-uiscrollview/

I am not using the default UIScrollview zoom. I am resizing the layer in pich guester for retain the text clarity. — user2039257, Feb 04 '13 at 11:54
I'm working with this code. It works, but something works incorrect. I have Scale 3.0, and when i`m trying to zoomToRect - the center of content rect is wrong. — Arthur, Mar 20 '13 at 10:42
Oh wow! That's my blog post there! Thank you so much for crediting me! However, Nicolas is correct. When I was trying to do some more complex zooming with it, I discovered the origin calculation is off if you're not zooming in from the minimum scale value. As a result, I just finished implementing a new version of this category. See if this one helps! :) https://gist.github.com/TimOliver/71be0a8048af4bd86ede — TiM, Feb 08 '15 at 06:43

score 1 · Answer 3 · answered Dec 10 '14 at 09:47

I had same problem,
I was having a world map image, & i wanted to zoom the map to certain location, India
This is how i fixed it.
I found out the position of India, in terms of CGRect(X,Y) [CGRect(500,300)]
& following code in DidLoad

    [self.scrollViewForMap setZoomScale:2.0 animated:YES]; //for zooming
    _scrollViewForMap.contentOffset = CGPointMake(500,300); //for location

This solved my problem. :)

score 0 · Answer 4 · answered Feb 18 '15 at 07:58

- (void)pinchDetected:(UIPinchGestureRecognizer *)gestureRecognizer {

if([gestureRecognizer state] == UIGestureRecognizerStateBegan) {
    // Reset the last scale, necessary if there are multiple objects with different scales
    lastScale = [gestureRecognizer scale];
}

if ([gestureRecognizer state] == UIGestureRecognizerStateBegan ||
    [gestureRecognizer state] == UIGestureRecognizerStateChanged) {

    CGFloat currentScale = [[[gestureRecognizer view].layer valueForKeyPath:@"transform.scale"] floatValue];

    // Constants to adjust the max/min values of zoom
    const CGFloat kMaxScale = 2.2;
    const CGFloat kMinScale = 0.64;

    CGFloat newScale = 1 -  (lastScale - [gestureRecognizer scale]);
    newScale = MIN(newScale, kMaxScale / currentScale);
    newScale = MAX(newScale, kMinScale / currentScale);
    CGAffineTransform transform = CGAffineTransformScale([[gestureRecognizer view] transform], newScale, newScale);
    [gestureRecognizer view].transform = transform;

    [gestureRecognizer setScale:1.0];

    lastScale = [gestureRecognizer scale];  // Store the previous scale factor for the next pinch gesture call
}
}

score 0 · Answer 5 · answered May 16 '18 at 12:24

What worked for me (Swift 4):

func zoomIn(with gestureRecognizer: UIGestureRecognizer?) {
    guard let location = gestureRecognizer?.location(in: gestureRecognizer?.view)

    let rect = CGRect(x: location.x, y: location.y, width: 0, height: 0)
    scrollView.zoom(to: rect, animated: true)
}

Or in other words creating a CGRect with zero width and height will cause the UIScrollView to zoom to the rects origin at maximumZoomScale

How can I zoom a UIScrollview to a fixed point?

5 Answers5