CODEWITHSUNDEEP
iosobjective-crotation
fs_tigre
fs_tigre

Reputation: 10738

Why does a view changes position when rotating it using CGAffineTransformMakeRotation

I have the following super simple animation, I'm basically rotating a view 2 radians from its original angle/center, it rotates fine my only misunderstanding is why does the view move from its original position when the rotation occurs.

[UIView animateWithDuration:1.0 animations:^{
        self.someView.transform = CGAffineTransformMakeRotation( 2 );
    }];

Why does the view moves when rotated with the code above?

enter image description here

I'm currently trying to discern the information in the CGAffineTransform Reference.

Understanding the anchor point.

I found this threads but it doesn't show a concrete answer. Why rotating imageView, it changes position?

Thanks a lot

Upvotes: 21

Views: 11115

Answers (3)

Basheer_CAD
Basheer_CAD

Reputation: 4919

I am adding another answer due to @fs_tigre request. The problem is with the auto layouts in your xib file, unfortunately is it unknown why that affects the transform.
Now here is the steps I did to solve the issue:

1- first you need to get rid off your auto layout (yes, you have to)
uncheck Use Autolayout
uncheck Use Autolayout

2- remove all constraints and autoresizing masks for your view that will be rotated, as in the screenshot (Here I have my blue box, see on the right autoresizing, nothing is selected)
enter image description here

I have made some changes for your rotation's code

self.someView.layer.anchorPoint = CGPointMake(0.5, 0.5);
    // one degree = pi/180. so...
    // rotate by 90
    CGFloat radians = (M_PI/180) * 90;
    [UIView animateWithDuration:1.0 animations:^{
        self.someView.transform = CGAffineTransformRotate(self.someView.transform, radians);
    }];

Click rotate and see the magic :)

Upvotes: 7

Basheer_CAD
Basheer_CAD

Reputation: 4919

You need to set the anchor point of your view to rotate around. 

self.somview.layer.anchorPoint = CGPointMake(0.5, 0.5);

Then start the rotation.
From Apple documentations

@property(nonatomic) CGAffineTransform transform
Changes to this property can be animated. Use the beginAnimations:context: class method to begin and the commitAnimations class method to end an animation block. The default is whatever the center value is (or anchor point if changed) Link: https://developer.apple.com/library/ios/documentation/GraphicsImaging/Reference/CALayer_class/Introduction/Introduction.html#//apple_ref/occ/instp/CALayer/anchorPoint

enter image description here
image from here http://www.raywenderlich.com/9864/how-to-create-a-rotating-wheel-control-with-uikit
- As you see the anchor point is the point with the value from 0.0 - 1.0 for X and Y when you rotate the rotation will be around these points
NOTE: you need to import QuartzCore

Upvotes: 10

Aviel Gross
Aviel Gross

Reputation: 9965

The "anchor" of CGAffineTransformMakeRotation is the X,Y of the view. You can try this:

CGPoint center = self.someView.center;
[UIView animateWithDuration:1.0 animations:^{
    self.someView.transform = CGAffineTransformMakeRotation( 2 );
    self.someView.center = center;
}];

Upvotes: 3

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