如何在Interface Builder文件中使用自定义iOS视图（位于引用的类库中）？

Question

I have two projects. The first one is the iOS-App which is referencing a class library with the target framework Xamarin.iOS . In that class library I implemented a CustomView which inherits from UIView . I also registered it with the "Register" attribute.

So in the interface designer I get the prefilled information to use this class as custom class after I dragged the UIView to my ViewController . But when I run the app I get the following information:

"Unknown class MyCustomView in Interface Builder file."  

If I move the my CustomView from the class library project into my first project then it will run as expected.

Does someone know how to use a CustomView , which is located in a referenced class library, in an Interface Builder file?

Answer 1

I don't think it's possible to Register accross project boundaries. In my tests, even when you use the exact same namespace, you still end up with an error.

What is possible, on the other hand, is to use a proxy class and make use of inheritance to bring the desired behaviour to the proxy.

Basically, it boils down to this:

1) In your library, you define your Custom UIView and implement any behaviour you want to share:

public class MyCustomUIView : UIView
{
    public MyCustomUIView(IntPtr ptr) : base (ptr)
    {
    }

    public override void AwakeFromNib()
    {
        // Do something beautiful here...
        AddSubview(new UILabel(new CGRect(0,0,200,30)) { Text = "I live in the library"});
        BackgroundColor = UIColor.Green;
    }
}

Note that we don't Register this class, because it won't work anyway.

2) Now in your app project, open up the storyboard in interface designer or XCode and assign a completely new name to your placeholder UIView . In my case, I chose MyCustomUIViewProxy . Xamarin studio will create two files for you: MyCustomUIViewProxy.cs and MyCustomUIViewProxy2.designer.cs. Note that in the designer.cs file, Xamarin automatically Register ed your proxy class.

3) Now all we have to do is use inheritance, to make the proxy act like the original: In MyCustomUIViewProxy.cs, we change the base class from UIView to MyCustomUIView , and we're good to go:

partial class MyCustomUIViewProxy : MyCustomUIView
{
    public MyCustomUIViewProxy (IntPtr handle) : base (handle)
    {
    }
}

That's it: