通过xib .........很容易迁移iPhone5和iPhone4

UIViewController *viewController3;
if ([[UIScreen mainScreen] bounds].size.height == 568)
{
    UIViewController *viewController3 = [[[mainscreenview alloc] initWithNibName:@"iphone5screen" bundle:nil] autorelease];               
}    
else
{
     UIViewController *viewController3 = [[[mainscreenview alloc] initWithNibName:@"iphone4screen" bundle:nil] autorelease];
}

Download and install latest version of Xcode. Set a Launch Screen File for your app (in the general tab of your target settings). This is how you get to use the full size of any screen, including iPad split view sizes in iOS 9. Test your app, and hopefully do nothing else, since everything should work magically if you had set auto resizing masks properly, or used Auto Layout. If you didn't, adjust your view layouts, preferably with Auto Layout. If there is something you have to do for the larger screens specifically, then it looks like you have to check height of [[UIScreen mainScreen] bounds] as there seems to be no specific API for that. As of iOS 8 there are also size classes that abstract screen sizes into regular or compact vertically and horizontally and are recommended way to adapt your UI.

唯一真正需要做的事情是在应用程序资源中添加一个名为“Default-568h@2x.png”的启动图像，在一般情况下(如果你足够幸运)应用程序将正常工作。

如果应用程序不处理触摸事件，那么确保键窗口有适当的大小。解决方法是设置适当的框架:

[window setFrame:[[UIScreen mainScreen] bounds]]

在迁移到iOS 6时，还有其他与屏幕大小无关的问题。详情请阅读iOS 6.0发布说明。

I never faced such an issue with any device as I've had one codebase for all, without any hardcoded values. What I do is to have the maximum sized image as resource instead of one for each device. For example, I would have one for retina display and show it as aspect fit so it will be views as is on every device. Coming to deciding the frame of button, for instance, at run time. For this I use the % value of the patent view, example , if I want the width to be half of parent view take 50 % of parent and same applies for height and center.

有了这个，我甚至不需要xib。

如果你需要将一个已经存在的应用程序转换为通用，你需要选择相应的xib文件->show Utilities-> show Size inspector。

在大小检查器中，你可以看到自动调整大小，通过使用这个工具你可以转换到现有的iOS应用程序。

你可以手动检查屏幕大小来确定你在哪个设备上:

#define DEVICE_IS_IPHONE5 ([[UIScreen mainScreen] bounds].size.height == 568)

float height = DEVICE_IS_IPHONE5?568:480;
if (height == 568) {
    // 4"

} else {

    // 3"

}