iOS：使用LaunchImage作为应用程序背景

Question

Is this possible without glitches?

My Xcode project has a launch image defined in the assets (aka Images.xcassets) incl. all supported sizes and orientations. Since I want to use the same image as background in my initial view, I add it in the view controller as background:

    view.layer.contents = UIImage(named:"LaunchImage").CGImage;

However when the launch screen switches to the initial view there's a noticeable glitch since the background image set in the view stretches. Also when I rotate the device, the image stretches.

The stretching occurring when the device is rotated seems plausible since obviously the other image sizes/orientations in the asset catalog image aren't regarded when set as a background image (my guess).

But the stretching that occurs between launch screen and my initial view seems rather strange since the two should have the same size.

Is there any tried and tested procedure to have the bg image always adapt with aspect ratio in mind when the device orientation changes? And is this even possible wit the (multi-sized) launch image?

---

UPDATE:

One possible method to add a bg image is by placing a UIImageView in the background (behind all other views) and load the image into it. That solution takes care of the device orientation issue and would be OK for me but there is another issue: It loads the wrong image size. If I test it on iPad2 emu it should use the image named Default~ipad~nostatusbar.png but if I check the size of the UIImage it is only 320x480 pixels so it obviously used the image named Default.png .

And I can only load the launch image by the name defined in the Images.xcassets. If I try to create a UIImage with physical filename (eg Default.png) the bg will stay black.

So the question is: How do I get iOS to choose the right image size/orientation from LaunchImage in Images.xcassets?

Answer 1

To fully resolve this issue, here's my Swift version of Daij-Djan's code. It also lists the ridiculous amount of different launch image versions in the comment block. there are some calls to my own util lib (EnvUtil) but that's another story and most users can figure out how to get the needed vars.

/**
   Returns the default image (launch image) of the application with regard to the screen size and orientation.

   Default.png                               | LaunchImage.png                       |  320 x 480  | iPhone 4 Low Res.
   Default@2x.png                            | LaunchImage@2x.png                    |  640 x 960  | iPhone 4
   Default@2x.png                            | LaunchImage-700@2x.png                |  640 x 960  | iPhone 4 iOS7
   Default-568h@2x.png                       | LaunchImage-568h@2x.png               |  640 x 1136 | iPhone 5
   Default-568h@2x.png                       | LaunchImage-700-568h@2x.png           |  640 x 1136 | iPhone 5
   Default~ipad.png                          | LaunchImage-Portrait~ipad.png         |  768 x 1004 | iPad Portrait
   Default~ipad~nostatusbar.png              | LaunchImage-700-Portrait~ipad.png     |  768 x 1024 | iPad Portrait FS
   Default~ipad~landscape.png                | LaunchImage-Landscape~ipad.png        | 1024 x 748  | iPad Landscape
   Default~ipad~landscape~nostatusbar.png    | LaunchImage-700-Landscape~ipad.png    | 1024 x 768  | iPad Landscape FS
   Default~ipad@2x.png                       | LaunchImage-Portrait@2x~ipad.png      | 1536 x 2008 | iPad Portrait Retina
   Default~ipad~nostatusbar@2x.png           | LaunchImage-700-Portrait@2x~ipad.png  | 1536 x 2048 | iPad Portrait Retina FS
   Default~ipad~landscape@2x.png             | LaunchImage-Landscape@2x~ipad.png     | 2048 x 1496 | iPad Landscape Retina
   Default~ipad~landscape~nostatusbar@2x.png | LaunchImage-700-Landscape@2x~ipad.png | 2048 x 1536 | iPad Landscape Retina FS
 */
public class func getDefaultImage() -> UIImage
{
    var fileName:String = "LaunchImage";
    let osVersion:String = EnvUtil.systemVersionMajor() > 6 ? "700" : "";
    let scale:String = EnvUtil.isRetina() ? "@2x" : "";
    let div:String = osVersion.length > 0 ? "-" : "";

    if (EnvUtil.isPad())
    {
        let orientation:String = EnvUtil.isPortraitOrientation() ? "Portrait" : "Landscape";
        fileName += "-" + osVersion + div + orientation + scale + "~ipad";
    }
    else
    {
        if (CGRectGetHeight(UIScreen.mainScreen().bounds) > 480.0)
        {
            /* iPhone 5. */
            fileName += "-" + osVersion + div + "568h@2x";
        }
        else
        {
            /* iPhone 4 with iOS7? */
            fileName += div + osVersion + scale;
        }
    }

    fileName += ".png";
    //Log.debug(fileName);

    return UIImage(named: fileName);
}

Answer 2

I have a UIImage+DefaultImage [ios] category in objC that allows this. Should be easy to port to a swift extension

#import <UIKit/UIKit.h>

@interface UIImage (DefaultImage)

// uses statusbar orientation
+ (UIImage *)defaultImage;

//uses given orientation
+ (UIImage *)defaultImageForOrientation:(UIInterfaceOrientation)orient;

@end

---

@implementation UIImage (DefaultImage)

+ (UIImage *)defaultImage {
    return [self defaultImageForOrientation:[[UIApplication sharedApplication] statusBarOrientation]];
}

+ (UIImage  *)defaultImageForOrientation:(UIInterfaceOrientation)orient {
    // choose the correct launch image for orientation, device and scale
    NSMutableString *launchImageName = [[NSMutableString alloc] initWithString:@"Default"];
    BOOL isPad = ( UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad );
    if ( isPad ) {
        BOOL isLandscape = UIInterfaceOrientationIsLandscape(orient);
        NSString *imageOrientation = (isLandscape) ? @"Landscape" : @"Portrait";

        BOOL isRetina = ([[UIScreen mainScreen] respondsToSelector:@selector(scale)] && [[UIScreen mainScreen] scale] == 2.0);
        NSString *scaleString = (isRetina) ? @"@2x" : @"";

        // Default-Landscape~ipad.png
        // Default-Landscape@2x~ipad.png
        // Default-Portrait~ipad.png
        // Default-Portrait@2x~ipad.png
        launchImageName = [NSMutableString stringWithFormat:@"%@-%@%@.png", launchImageName, imageOrientation, scaleString];       
    } else {
        if ( CGRectGetHeight([UIScreen mainScreen].bounds) > 480.f) {
            // Default-568h.png
            launchImageName = [NSMutableString stringWithFormat:@"%@-568h.png", launchImageName];
        } else {
            // Default.png
            // Default@2x.png
            launchImageName = [NSMutableString stringWithFormat:@"%@.png", launchImageName];
        }
    }
    return [UIImage imageNamed:launchImageName];
}

@end

Disclaimer: my own code -- taken from https://github.com/Daij-Djan/DDUtils

Answer 3

启动图像位于应用程序捆绑包中（命名为default ..），因此您只需要将其加载到UIImageView中并将该imageView添加到UIView中即可。