Call WebView page method from referenced WinRT Component with AllowForWeb class - webview

Question

I have a XAML page with WebView inside (for example MainPage.xaml). Also I have WinRT Component with class marked with [AllowForWeb] attribute. This component is referenced from project where MainPage.xaml located and in code-behind AddWebAllowedObject method is used. And I can't reference main project back because of circular dependency.
How to call MainPage.xaml.cs methods from component class? Very usual situation. Is there are some standard way to do it?
For example. I have a method inside RT component that could be called from JavaScript
public void ShowMessage(string message)
{
// I want to call here function from MainPage.xaml.cs
}

Answer 1

How to call MainPage.xaml.cs methods from component class? Very usual situation. Is there are some standard way to do it?
Yes, you can pass the method from MainPage.xaml.cs to Windows Runtime Component through delegate(Currently it's very limited to use delegate in Runtime Component using C#, see this case, so I use C++ as demo).
For Runtime Component Class MyClass.h:
public delegate Platform::String^ MyFunc(int a, int b);
public ref class MyClass sealed
{
public:
MyClass();
static Platform::String^ MyMethod(MyFunc^ func)
{
Platform::String^ abc=func(4, 5);
return abc;
}
};
And you can use the delegate in code behind like below:
using MyComponentCpp;
private void myBtn_Click(object sender, RoutedEventArgs e)
{
String abc=MyClass.MyMethod(MyMethod);
myTb.Text = abc;
}
private String MyMethod(int a, int b)
{
return (a.ToString() + b.ToString());//replace this line with your own logic.
}
And here is the complete Demo: TestProject.

Answer 2

Thankfully to #Elvis Xia who has gived me idea, I has found a solution how to do it without C++.
I have create a third project as Class Library. It doesn't has restrictions to use Action. This library I have referenced from main project and from WinRT component. Code of class inside library:
public class BridgeClass
{
public static event Action<string> MessageReceived;
public static void Broadcast(string message)
{
if (MessageReceived != null) MessageReceived(message);
}
}
Code inside main project with webview is:
// place somewhere
BridgeClass.MessageReceived += ShowMessage;
// ....... and add a method
void ShowMessage(string msg)
{
}
And now i can call this code from WinRT component:
public void ShowMessage(string message)
{
BridgeClass.Broadcast("lalala");
}