根据Assets.xcassets里的plist文件来动态获取，具体方法如下：

//获取启动图
+ (UIImage *)getLaunchImage{
    
    CGSize viewSize = [UIScreen mainScreen].bounds.size;
    NSString *viewOr = @"Portrait";//垂直
    NSString *launchImage = nil;
    NSArray *launchImages =  [[[NSBundle mainBundle] infoDictionary] valueForKey:@"UILaunchImages"];
    
    for (NSDictionary *dict in launchImages) {
        CGSize imageSize = CGSizeFromString(dict[@"UILaunchImageSize"]);
        
        if (CGSizeEqualToSize(viewSize, imageSize) && [viewOr isEqualToString:dict[@"UILaunchImageOrientation"]]) {
            launchImage = dict[@"UILaunchImageName"];
        }
    }
    return [UIImage imageNamed:launchImage];
}