view offset by Custom navigationBar setBackgroundImage - ios

Question

I set Custom navigationBar by KVO in iOS8,and the custom navigationBar setBackgroundImage.
I found that the viewContoller.view.frame.origin.y is 64 and viewController is Navigation's rootViewController.
why viewContoller.view.frame.origin.y is 64 in iOS 8?
the following is demo code:
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
UINavigationBar *temp = [[UINavigationBar alloc]init];
[temp setBackgroundImage:[UIImage imageNamed:#"navbar_bg"] forBarMetrics:UIBarMetricsDefault];
[self.navigationController setValue:temp forKey:#"navigationBar"];
}
- (void)viewDidAppear:(BOOL)animated
{
NSLog(#"view : %#",self.view); // print :<UIView: 0x7ff8fa72cfa0; frame = (0 64; 375 603); autoresize = RM+BM; layer = <CALayer: 0x7ff8fa72b2b0>>
}
If I cancel [temp setBackgroundImage:[UIImage imageNamed:#"navbar_bg"] forBarMetrics:UIBarMetricsDefault]; , the view.origin.y is 0 correctly.
what i should do correctly to set custom navigationBar which setBackgroundImage and keep self.view.orgin is (0,0)?

Answer 1

Please check the image assets.
The image "navbar_bg#2x" should exists in the assets, If you are tested on device or simulators ,which has UIKit Scale factor 2.0, such as a iPhone 8 .
The image "navbar_bg#3x" should exists in the assets, if tested on iPhone 8 Plus. And so on.
It should be OK, according to Apple's Demo Code Customizing Your App’s Navigation Bar.
Two cases , your issue happens.
In my case , It does not work, when converting color to image.
Firstly I thought it is image size issue.
Accoring to Debug View Hierarchy, I got the BackgroundImageView's size, 414 X 88.Tested in simulator of iPhone XR.
When debugging, I think maybe the image should be smaller than imageView'size.
Still not work, after many times of adjusting the image size.
the code of converting color to image:
public static func color(_ color: UIColor, width w: CGFloat, height h: CGFloat) -> UIImage {
let rect = CGRect(x: 0.0, y: 0.0, width: w, height: h)
UIGraphicsBeginImageContextWithOptions(rect.size, false, UIScreen.main.scale)
let ctx = UIGraphicsGetCurrentContext()
ctx?.setFillColor(color.cgColor)
ctx?.fill(rect)
var image = UIGraphicsGetImageFromCurrentImageContext()!
UIGraphicsEndImageContext()
let imageData = UIImageJPEGRepresentation(image, 1.0)!
image = UIImage(data: imageData)!
return image
}
case two: image#2x ("navbar_bg#2x") doesn't exist in assets when tested in simulator of iPhone XR, which has UIKit Scale factor 2.0.
Then it doesn't work either in my experiment.

Answer 2

You can set title of navigationController.navigationItem instead of setting up UINavigationBar and providing with KVO.
- (void)viewDidLoad {
[super viewDidLoad];
UIImageView *img = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"navbar_bg"]];
//Here you can create your own Custom View and provide as title of self.navigationController.navigationItem
[self.navigationController.navigationItem setTitleView:img];
}
- (void)viewDidAppear:(BOOL)animated
{
NSLog(#"view : %#",self.view); // print :<UIView: 0x79ea0a30; frame = (0 0; 375 603); autoresize = W+H; layer = <CALayer: 0x79ea0ac0>>
}

Answer 3

I did an experiment too.
I think the problem is caused by color space.
According to the answer above, I created three images of white with imageMagick.
And use white image#2x with simulator iPhone XR .
The issue happens too.
The example image of Apple's Demo Code Customizing Your App’s Navigation Bar is of SRBG, my color image is simply gray scale.
I think it is the difference.
from image magick community
-colorspace changes the way the image is stored in memory
-set colorspace just sets the colorsapce of the image without conversion
Many image formats (like JPG) do not use difference colorspaces
without using some time of color profile, as such the image is
converted back to RGB colorspace unless a color profile has been
defined.
That is why you don't see a difference. It is only different IN
MEMORY!
Maybe iOS did some optimization because of this.