How can I obtain data from a server (HTTP POST) during class construction without putting the HTTP POST in the constructor itself?

Question

I have a class that in order to have all its properties fully populated it needs to obtain some data from the server.

Currently I have a call to the server in its constructor like so:

public class GeometryObject
{
    public GeometryObject(string partName, CADFileType partType)
    {
        InitializeTransformParameters(); 
        CreateDefaultInternalParameters(); 
        CADFile = Server.GetCADFileAsync(partName, partType).Result; // not great having a time consuming action in the constructor but not sure how else to do this.                             
    } 
}

Server.GetCADFileAsync() is essentially a wrapper for HttpClient.PostAsync().

Although this works (provided the call succeeds!!), it smells a bit like a bad design. How is this kind of thing usually approached? I'm using C# 6.

Answer 1

I've seen it done, but it's not exactly good. A more common approach uses a Factory Method, like this:

public class MyClass
{
    // private constructor
    private MyClass() {}

    // public static method to wrap the constructor. 
    // "Create" is also a common name here,
    // but I prefer "Load" when I *know* it's gonna take a while
    public static MyClass Load()
    {
        // We can call the constructor here, because it's a member of the class
        var result = new MyClass();
        
        // populate required fields here

        
        return result;       
    }
}

Then, instead of new MyClass() you'd use the type like this:

var myVariable = MyClass.Load();

And so we would adapt the code in the question like this:

public class GeometryObject
{
    private GeometryObject() 
    {
        // normal/fast initialization can still go here (but doesn't have to)
        InitializeTransformParameters(); 
        CreateDefaultInternalParameters(); 
    }

    public static GeometryObject Load(string partName, CADFileType partType)
    {
        var result = new GeometryObject();
        result.CADFile = Server.GetCADFileAsync(partName, partType).Result;
        return result;                            
    }         
}