获取对应分辨率的尺寸图片，无需硬编码判断分辨率写图片尺寸获取
CGSize viewSize = self.window.bounds.size;
NSString *viewOrientation = @"Portrait"; //横屏请设置成 @"Landscape"
NSString *launchImage = nil;
NSArray* imagesDict = [[[NSBundle mainBundle] infoDictionary] valueForKey:@"UILaunchImages"];
for (NSDictionary* dict in imagesDict)
{
CGSize imageSize = CGSizeFromString(dict[@"UILaunchImageSize"]);
if (CGSizeEqualToSize(imageSize, viewSize) && [viewOrientation isEqualToString:dict[@"UILaunchImageOrientation"]])
{
launchImage = dict[@"UILaunchImageName"];
}
}
