xcode6 建立 empty application

.新建一个single view application
.打开 Info.plist，删除里面的  Launch screen interface file....以及 Main storyboard file base name...
.删除Main.storyboard以及LaunchScreen.xib
4.打开工程项目属性文件，点击Target下面的第一项，再选择General选项卡，向下找到Use Asset Catalog按钮。点击它。弹出对话框，点击Migrate即可。这样，应用尺寸就能根据屏幕大小进行调整了。
5.在AppDelegate.m修改如下（其中MainViewController是自己新建的 viewController）

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds] ];
    self.window.rootViewController = [[MainViewController alloc]init];
    [self.window makeKeyAndVisible];
    return YES;
}