在iOS应用中，即使没有添加主自定义UIView，我仍然可以将其他视图对象添加为子视图吗？

Question

It is quite strange that in some other iOS apps, I created a Single View app, and then added MainView.h and MainView.m that is the subclass of UIView , but then in another program, I didn't add such class, but could immediately do:

ShapeView *sv;

sv = [[ShapeView alloc] initWithFrame:CGRectMake(10, 170, 140, 140)];
[self.view addSubview:sv];

inside of ViewController.m . Of course, ShapeView.m has to implement drawRect to properly draw the shape. But how come we don't need to add a MainView.h and MainView.m first this time and still draw on some main view?

Answer 1

You don't have to add MainView.h and .m for any app. That is necessary only when you want your own customized UIView named "MainView". If you don't need to draw the view or part of the view yourself, view controller + XIB/NIB work well.

The main UIViewController in your app (which is created from Single View App template as you mentioned) creates a default UIView which is loaded from the default NIB/XIB. It is available as self.view in your UIViewController code after the view is loaded.

In fact MainView is nothing special compared with ShapeView . They are both customized UIView subclasses.