Adding subview center of screen

Question

I am trying to add a small icon in the center of my iPhone app screen. Below is the code I think should work, but it isn't centering it. The position regarding the width is fine, but the height is way off, about 100 pixels off?

UIImage *pinMarker = [UIImage imageNamed:@"red_pen_marker.png"];
UIImageView *pinMarkerView = [[UIImageView alloc] initWithImage:pinMarker];
pinMarkerView.frame = CGRectMake(self.view.frame.size.width/2 - 9, self.view.frame.size.height/2 - 36, 18, 36);


[self.view addSubview:pinMarkerView];

Any suggestions? Maybe placing it according to the entire app window size instead of this screens view?

Answer 1

It should be self.view.frame.size.height/2 - 18. A simpler way is to just set it like this:

pinMarkerView.center = self.view.center;

But without knowing what the parent view is it is impossible to tell how to bring the imageView to the center of the screen.

Answer 2

I think NSLayoutConstraint should solve your problem

UIView *superview = self.view;

UIImage *pinMarker = [UIImage imageNamed:@"red_pen_marker.png"];
UIImageView *pinMarkerView = [[UIImageView alloc] initWithImage:pinMarker];
pinMarkerView.frame = CGRectMake(self.view.frame.size.width/2 - 9, self.view.frame.size.height/2 - 36, 18, 36);

[pinMarkerView setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.view addSubview:pinMarkerView];

NSLayoutConstraint *myConstraint =[NSLayoutConstraint
                                   constraintWithItem:pinMarkerView
                                   attribute:NSLayoutAttributeCenterX
                                   relatedBy:NSLayoutRelationEqual
                                   toItem:superview
                                   attribute:NSLayoutAttributeCenterX
                                   multiplier:1.0
                                   constant:0];
NSLayoutConstraint *myConstraint2 =[NSLayoutConstraint
                                   constraintWithItem:pinMarkerView
                                   attribute:NSLayoutAttributeCenterY
                                   relatedBy:NSLayoutRelationEqual
                                   toItem:superview
                                   attribute:NSLayoutAttributeCenterY
                                   multiplier:1.0
                                   constant:0];

[superview addConstraint:myConstraint];
[superview addConstraint:myConstraint2];