如何获取xcassets中的启动图片

NSDictionary *dic = @{@"320×480"：@"LaunchImage-700", @"320×568":@"LaunchImage-700-568h", @"375×667":@"LaunchImage-800-667h", @"414×736", @"launchImage-800-Portrait-736h"};NSString *key = [NSString stringWithFormat:@"%d×%d", (int)[UIScreen mainScreen].bounds.size.width], (int)[UIScreen mainScreen].bounds.size.height];UIImage launchImage = [UIImage imageName:dic[key]];