Loading UIView transform & center from settings gives different position - iphone

Question

I'm using pan, pinch, and rotate UIGestureRecognizers to allow the user to put certain UI elements exactly where they want them. Using the code from here http://www.raywenderlich.com/6567/uigesturerecognizer-tutorial-in-ios-5-pinches-pans-and-more (or similar code from here http://mobile.tutsplus.com/tutorials/iphone/uigesturerecognizer/) both give me what I need for the user to place these UI elements as they desire.
When the user exits "UI layout" mode, I save the UIView's transform and center like so:
NSString *transformString = NSStringFromCGAffineTransform(self.transform);
[[NSUserDefaults standardUserDefaults] setObject:transformString forKey:#"UItransform", suffix]];
NSString *centerString = NSStringFromCGPoint(self.center);
[[NSUserDefaults standardUserDefaults] setObject:centerString forKey:#"UIcenter"];
When I reload the app, I read the UIView's transform and center like so:
NSString *centerString = [[NSUserDefaults standardUserDefaults] objectForKey:#"UIcenter"];
if( centerString != nil )
self.center = CGPointFromString(centerString);
NSString *transformString = [[NSUserDefaults standardUserDefaults] objectForKey:#"UItransform"];
if( transformString != nil )
self.transform = CGAffineTransformFromString(transformString);
And the UIView ends up rotated and scaled correctly, but in the wrong place. Further, upon entering "UI layout" mode again, I can't always grab the view with the various gestures (as though the view as displayed is not the view as understood by the gesture recognizer?)
I also have a reset button that sets the UIView's transform to the identity and its center to whatever it is when it loads from the NIB. But after loading the altered UIView center and transform, even the reset doesn't work. The UIView's position is wrong.
My first thought was that since those gesture code examples alter center, that rotations must be happening around different centers (assuming some unpredictable sequence of moves, rotations, and scales). As I don't want to save the entire sequence of edits (though that might be handy if I want to have some undo feature in the layout mode), I altered the UIPanGestureRecognizer handler to use the transform to move it. Once I got that working, I figured just saving the transform would get me the current location and orientation, regardless of in what order things happened. But no such luck. I still get a wacky position this way.
So I'm at a loss. If a UIView has been moved and rotated to a new position, how can I save that location and orientation in a way that I can load it later and get the UIView back to where it should be?
Apologies in advance if I didn't tag this right or didn't lay it out correctly or committed some other stackoverflow sin. It's the first time I've posted here.
EDIT
I'm trying the two suggestions so far. I think they're effectively the same thing (one suggests saving the frame and the other suggests saving the origin, which I think is the frame.origin).
So now the save/load from prefs code includes the following.
Save:
NSString *originString = NSStringFromCGPoint(self.frame.origin);
[[NSUserDefaults standardUserDefaults] setObject:originString forKey:#"UIorigin"];
Load (before loading the transform):
NSString *originString = [[NSUserDefaults standardUserDefaults] objectForKey:#"UIorigin"];
if( originString ) {
CGPoint origin = CGPointFromString(originString);
self.frame = CGRectMake(origin.x, origin.y, self.frame.size.width, self.frame.size.height);
}
I get the same (or similar - it's hard to tell) result. In fact, I added a button to just reload the prefs, and once the view is rotated, that "reload" button will move the UIView by some offset repeatedly (as though the frame or transform are relative to itself - which I'm sure is a clue, but I'm not sure what it's pointing to).
EDIT #2
This makes me wonder about depending on the view's frame. From Apple http://developer.apple.com/library/ios/#documentation/WindowsViews/Conceptual/ViewPG_iPhoneOS/WindowsandViews/WindowsandViews.html#//apple_ref/doc/uid/TP40009503-CH2-SW6 (emphasis mine):
The value in the center property is always valid, even if scaling or rotation factors have been added to the view’s transform. The same is not true for the value in the frame property, which is considered invalid if the view’s transform is not equal to the identity transform.
EDIT #3
Okay, so when I'm loading the prefs in, everything looks fine. The UI panel's bounds rect is {{0, 0}, {506, 254}}. At the end of my VC's viewDidLoad method, all still seems okay. But by the time things actually are displayed, bounds is something else. For example: {{0, 0}, {488.321, 435.981}} (which looks like how big it is within its superview once rotated and scaled). If I reset bounds to what it's supposed to be, it moves back into place.
It's easy enough to reset the bounds to what they're supposed to be programatically, but I'm actually not sure when to do it! I would've thought to do it at the end of viewDidLoad, but bounds is still correct at that point.
EDIT #4
I tried capturing self.bounds in initWithCoder (as it's coming from a NIB), and then in layoutSubviews, resetting self.bounds to that captured CGRect. And that works.
But it seems horribly hacky and fraught with peril. This can't really be the right way to do this. (Can it?) skram's answer below seems so straightforward, but doesn't work for me when the app reloads.

Answer 1

You would save the frame property as well. You can use NSStringFromCGRect() and CGRectFromString().
When loading, set the frame then apply your transform. This is how I do it in one of my apps.
Hope this helps.
UPDATE: In my case, I have Draggable UIViews that rotation and resizing can be applied to. I use NSCoding to save and load my objects, example below.
//encoding
....
[coder encodeCGRect:self.frame forKey:#"rect"];
// you can save with NSStringFromCGRect(self.frame);
[coder encodeObject:NSStringFromCGAffineTransform(self.transform) forKey:#"savedTransform"];
//init-coder
CGRect frame = [coder decodeCGRectForKey:#"rect"];
// you can use frame = CGRectFromString(/*load string*/);
[self setFrame:frame];
self.transform = CGAffineTransformFromString([coder decodeObjectForKey:#"savedTransform"]);
What this does is save my frame and transform, and load them when needed. The same method can be applied with NSStringFromCGRect() and CGRectFromString().
UPDATE 2: In your case. You would do something like this..
[self setFrame:CGRectFromString([[NSUserDefaults standardUserDefaults] valueForKey:#"UIFrame"])];
self.transform = CGAffineTransformFromString([[NSUserDefaults standardUserDefaults] valueForKey:#"transform"]);
Assuming you're saving to NSUserDefaults with UIFrame, and transform keys.

Answer 2

I am having trouble reproducing your issue. I have used the following code, which does the following:
Adds a view
Moves it by changing the centre
Scales it with a transform
Rotates it with another transform, concatenated onto the first
Saves the transform and centre to strings
Adds another view and applies the centre and transform from the string
This results in two views in exactly the same place and position:
- (void)viewDidLoad
{
[super viewDidLoad];
UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
view1.layer.borderWidth = 5.0;
view1.layer.borderColor = [UIColor blackColor].CGColor;
[self.view addSubview:view1];
view1.center = CGPointMake(150,150);
view1.transform = CGAffineTransformMakeScale(1.3, 1.3);
view1.transform = CGAffineTransformRotate(view1.transform, 0.5);
NSString *savedCentre = NSStringFromCGPoint(view1.center);
NSString *savedTransform = NSStringFromCGAffineTransform(view1.transform);
UIView *view2 = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
view2.layer.borderWidth = 2.0;
view2.layer.borderColor = [UIColor greenColor].CGColor;
[self.view addSubview:view2];
view2.center = CGPointFromString(savedCentre);
view2.transform = CGAffineTransformFromString(savedTransform);
}
Giving:
This ties up with what I would expect from the documentation, in that all transforms happen around the centre point and so that is never affected. The only way I can imagine that you're not able to restore items to their previous state is if somehow the superview was different, either with its own transform or a different frame, or a different view altogether. But I can't tell that from your question.
In summary, the original code in your question ought to be working, so there is something else going on! Hopefully this answer will help you narrow it down.

Answer 3

You should the also save the UIView's location,
CGPoint position = CGPointMake(self.view.origin.x, self.view.origin.y)
NSString _position = NSStringFromCGPoint(position);
// Do the saving

Answer 4

I'm not sure of everything that's going on, but here are some ideas that may help.
1- skram's solution seems plausible, but it's the bounds you want to save, not the frame. (Note that, if there's been no rotation, the center and bounds define the frame. So, setting the two is the same as setting the frame.)
From, the View Programming Guide for IOS you linked to:
Important If a view’s transform property is not the identity
transform, the value of that view’s frame property is undefined and
must be ignored. When applying transforms to a view, you must use the
view’s bounds and center properties to get the size and position of
the view. The frame rectangles of any subviews are still valid because
they are relative to the view’s bounds.
2- Another idea. When you reload the app, you could try the following:
First, set the view's transform to the identity transform.
Then, set the view's bounds and center to the saved values.
Finally, set the view's transform to the saved transform.
Depending on where your app is restarting, it may be starting back up with some of the old geometry. I really don't think this will change anything, but it's easy enough to try.
Update: After some testing, it really does seem like this wouldn't have any effect. Changing the transform does not seem to change the bounds or center (although it does change the frame.)
3- Lastly, you may save some trouble by rewriting the pinch gesture recognizer to operate on the bounds rather than the transform. (Again, use bounds, not frame, because an earlier rotation could have rendered the frame invalid.) In this way, the transform is used only for rotations, which, I think, cannot be done any other way without redrawing.
From the same guide, Apple's recommendation is:
You typically modify the transform property of a view when you want to
implement animations. For example, you could use this property to
create an animation of your view rotating around its center point. You
would not use this property to make permanent changes to your view,
such as modifying its position or size a view within its superview’s
coordinate space. For that type of change, you should modify the frame
rectangle of your view instead.

Answer 5

Thanks to all who contributed answers! The sum of them all led me to the following:
The trouble seems to have been that the bounds CGRect was being reset after loading the transform from preferences at startup, but not when updating the preferences while modifying in real time.
I think there are two solutions. One would be to first load the preferences from layoutSubviews instead of from viewDidLoad. Nothing seems to happen to bounds after layoutSubviews is called.
For other reasons in my app, however, it's more convenient to load the preferences from the view controller's viewDidLoad. So the solution I'm using is this:
// UserTransformableView.h
#interface UserTransformableView : UIView {
CGRect defaultBounds;
}
// UserTransformableView.m
- (id)initWithCoder:(NSCoder *)aDecoder {
self = [super initWithCoder:aDecoder];
if( self ) {
defaultBounds = self.bounds;
}
return self;
}
- (void)layoutSubviews {
self.bounds = defaultBounds;
}