Stage 2: Linking to C#

This stage isn't too hard once you understand the tricks behind it. Let's hook our new MCML file up to C#.

Because of the Model-View seperation that is part of the basic design of Media Center Markup Language projects (see my post on Model-View Seperation), you should carefully plan out exactly what sort of communication you will need between your model (The C# code) and your view (The MCML code).

I'd suggest drawing these interactions, perhaps as use-case diagrams or similar simple drawings to show the sort of information that flows between your C# and your MCML.

In this example, we will want to set the text that appears in the background of our screen - and we want to be able to change it from our code.

First step is to create a C# class we are going to use as our 'main' class for interacting with Media Center. Although you can use several if you want, I've found it much easier to try to stick with a single primary class.

In this case, the class is going to encapsulate everything about our trivia game. It is going to manage questions, answers, keep score etc. But for starters, it is only going to hold one thing - the name of the program as it appears in the top right corner, in our BackgroundText object.

On The C# Side

If you take a quick look at the Stage 1 sample code, you'll notice that I have created a file called TriviaGame.cs. This is where we will create our class, called 'TriviaGame'.

First, set up the class itself...

namespace TriviaCenter
{
    public class TriviaGame
    {
 
    }
}
 
OK, so our 'TriviaCenter' namespace now includes a class called TriviaGame.

Now - we are going to need somewhere to keep the title of the program. Why not create a string member to hold this data? (NOTE: Something will come up in the future to make us need to change this - but for now, let's ignore that and just use strings).

    String _GameName;

You may notice that we didn't specify a protection level for this particular variable, which means it defaults to being a private variable. Surely, you'd think, for Media Center to be able to access it, it would need to be declared 'public'?

The truth is that MCML can't read values directly out of members like _GameName. It needs to read information out of properties, not members.

So to access this game name, we are going to need a property. Since we don't anticipate that your MCML file will ever have to change the value, we should only need to provide a get function.

public String GameName
{
    get
    {
        return _GameName;
    }
}
 

There. This defines a property called 'GameName' which can be accessed publically - meaning that Media Center should be able to get to it. This is also the reason I used an underscore (_) key under the name of the member variable _GameName...it avoids confusing the internal object (the member functions) with the properties.

All we need to do now on the C# front is set a default value for GameName. The easiest way to do this is simply to create a constructor and set the value of _GameName to 'triviacenter'.

On The MCML Side

In our MCML, we only need a couple of changes.

The first step is to actually import the assembly containing all of the 'TriviaCenter' objects, allowing us to use our new TriviaGame object. We do this the same way we added the con namespace in the previous version.