First, we need to make sure that our project has a settings file. It is usually under the Properties node of the project. If it is not, right click on the solution and Add | New Item… | Visual C# Items | General | Settings File and name it Settings.settings. Next, drag it and drop it in your project’s Properties folder.

Next, you need to add a bool User setting called UpgradeRequired and default it to true. Next, at the very beginning of your Main, you check if UpgradeRequired is true, and if it is, upgrade the settings, set UpgradeRequired to false and save out the settings. This will pull in the settings from previous versions of your application.

Your settings should look like this,

The code should look like this,

static void Main( string[] args )
{
   // Upgrade settings if required
   if ( Properties.Settings.Default.UpgradeRequired )
   {
      Properties.Settings.Default.Upgrade();
      Properties.Settings.Default.UpgradeRequired = false;
      Properties.Settings.Default.Save();
   }

   // Do work...

   // At the end of main, save out any changes to settings
   Properties.Settings.Default.Save();
}

Now you just need to create new settings and use them in your application. Any setting with Application scope will be set in your app.config and will be read-only. This is often used for connection strings and other information that is unlikely to change. User scoped settings also have their default values in app.config, but any changes are written out to an XML file in the user’s AppData folder.

Also, notice that code gets generated for any setting that you create and you access it through a property on Properties.Settings.Default. You can use any complex type for a setting, including classes in your application, as long as they are Serializable.

In the fine, time honored tradition, I have continued to update with each new Visual Studio release and have finally done so for Visual Studio 2010.

To install, download, unzip and right click and install the INF file, it will add a “VS 2010 Cmd Prompt Here” menu item when you right click on a folder in Explorer. Clicking on the menu item will launch a DOS prompt in that directory with all of the Visual Studio and .NET paths set correctly.

• Visual Studio 2010 Command Prompt Here (x86)
• Visual Studio 2010 Command Prompt Here (x64)

This assumes that you have installed Visual Studio to the default directory on the C drive. If that is not the case, edit the INF file and change line 38 to the correct path for your installation.

return max( eRetVal, GetNumber() );

While debugging, he noticed that he was stepping into the GetNumber() method twice, and in his code, it had side-effects. We both puzzled over it for awhile. We looked at the disassembly and sure enough, it was getting called twice, but why? Then it hit me, max is a macro, not a function. If you go to the definition of max, you find;

#ifndef max
#define max(a,b)            (((a) > (b)) ? (a) : (b))
#endif

So, if you expand that macro out, the original code gets compiles as;

return (((eRetVal) > (GetNumber()) ? (eRetVal) : (GetNumber());

Once the macro is expanded, it is easy to see why the method is called twice. Obviously I have not being doing enough C++ lately. There was a time when I would have seen that immediately as it is the classic example, but I have been working in .NET so long now that I am forgetting all of the little ways that C++ can bite you.

Copier<ICustomer>.Copy( customer ).To<ICustomerView>( view );

Today, I am going to use extension methods to simplify the above code even further. I want to be able to write

customer.CopyTo<ICustomerView>( view );

or if we want to rely on type inferencing with the generic CopyTo method, you could write it as simply as

customer.CopyTo( view );

How is this done? Using extension methods, it was actually much simpler than yesterday’s Copier class. In fact, it just ended up being one line of code for the CopyTo method and for the CopyFrom method. I simply wrapped the CopyHelper class like this.

public static class CopierExtensions
{
    public static void CopyTo<T>( this object from, T to ) where T : class
    {
        CopyHelper.Copy( from.GetType(), from, typeof( T ), to );
    }

    public static void CopyFrom<T>( this object to, T from ) where T : class
    {
        CopyHelper.Copy( typeof( T ), from, to.GetType(), to );
    }
}

The only problem I have with this is that the class that the extension methods are applied to are not constrained by an interface, so all matching properties are copied. Does anyone have any ideas on that?

I have uploaded a copy of the solution for this project along with an NUnit test project. Take a look, use it if you like and feel free to give me suggestions for improvements.

In the next few posts I was thinking of extending these classes even further. I might add attributes that allow you to ignore certain properties, maybe add an attribute that specifies interfaces that you are allowed to copy to, possibly an attribute that allows properties to automatically be converted between types. What would you find useful or like to see? Would you like to see a post on the performance using these methods?

// Copy the data from the customer to the view
view.Address = customer.Address;
view.Country = customer.Country;
view.FirstName = customer.FirstName;
view.LastName = customer.LastName;
view.PostalCode = customer.PostalCode;
view.Province = customer.Province;

The newly created CopyHelper class allows me to shorten that to this.

// Copy the data from the customer to the view (using reflection in .NET 1.x)
CopyHelper.Copy( typeof(ICustomer), customer, typeof(ICustomerView), view );

Today, I want to extend that code using Generics and a fluent interface so that I can write code like this.

// Copy the data from the customer to the view (using reflection and generics in .NET 2.0)
Copier<ICustomer>.Copy( customer ).To<ICustomerView>( view );

Internally, I use my CopyHelper class from my last post. I extend that by creating a generic Copier class. I make the constructor private so that it can only be created as a part of the fluent interface, in this case the static copy method. Using the instance of the Copier class that was returned from that method, you can then copy To or From another class instance.

Here is the code.

public sealed class Copier<T1> where T1 : class
{
    #region Private Members

    private readonly T1 _subject;

    #endregion

    #region Public Interface

    /// <summary>
    /// Begin the copying process.
    /// </summary>
    /// <param name="interface1">The object you are copying from or to</param>
    /// <returns>An instance of the Copier class so that you can
    /// continue with the copy to/from in a fluent interface.</returns>
    public static Copier<T1> Copy( T1 interface1 )
    {
        return new Copier<T1>( interface1 );
    }

    #endregion

    #region Construction

    /// <summary>
    /// Private constructor so that it can only be created as a part of a fluent interface.
    /// </summary>
    /// <param name="subject"></param>
    private Copier( T1 subject )
    {
        _subject = subject;
    }

    #endregion

    #region Copier Methods

    /// <summary>
    /// Copies properties from the subject to the passed in object.
    /// </summary>
    /// <typeparam name="T2">The type of object you are copying into.</typeparam>
    /// <param name="to">The object to copy into.</param>
    /// <returns>The modified object that you passed in.</returns>
    public T2 To<T2>( T2 to ) where T2 : class
    {
        CopyHelper.Copy( typeof( T1 ), _subject, typeof( T2 ), to );
        return to;
    }

    /// <summary>
    /// Copies properties from the passed in object into the subject.
    /// </summary>
    /// <typeparam name="T2">The type of object you are copying from.</typeparam>
    /// <param name="from">The object to copy from.</param>
    /// <returns>The modified subject that you originally passed in the Copy method.</returns>
    public T1 From<T2>( T2 from ) where T2 : class
    {
        CopyHelper.Copy( typeof( T2 ), from, typeof( T1 ), _subject );
        return _subject;
    }

    #endregion
}

I would like to constrain T1 and T2 to interfaces at compile time, but I am not sure if that can be done. If you have ideas, please post them in the comments. I thought of using reflection to check if T1 and T2 are interfaces at run time, but I am a big believer in favouring compile time errors over run time errors.

In my next post, I am going to use C# 3.0 extension methods to further simplify copying allowing you to write code like this.

// Copy the data from the customer to the view (using extension methods in C# 3.0)
customer.CopyTo<ICustomerView>( view );

I am very interested in hearing your feedback on this, so be sure to post to the comments. Do you think this is a good idea? Do you have suggestions for improvements? Let me know.