Develop Reference

Attribute to mark as "internal use"

I made a class which requires the public default constructor but
that is never called; instead another constructor is used at DataGrid.AddingNewItem.
I'd like to tell developers that the default constructor is not for their use.
Is there an attribute which suits the purpose?
I had checked DebuggerNonUserCode and MethodImplAttribute with MethodImplAttributes.InternalCall but not sure that's the proper approach.
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.dataGrid1.CanUserAddRows = true;
var list = new List<RowX>();
this.dataGrid1.ItemsSource = CollectionViewSource.GetDefaultView(list);
this.dataGrid1.AddingNewItem += (s, e) => e.NewItem = new RowX("ABC");
}
}
public class RowX
{
public RowX()
{
//this is not used. but CollectionView require this to be public or
//CanUserAddRows doesn't work.
}
public RowX(object o)
{
//this is the actual ctor.
}
public string Text { get; set; }
}

Mark it private
class Foo
{
private Foo() {}
}

You can give your constructor an access modifier.
private This means it can only be called from another constructor in that class.
public class PrivateClass
{
//Only from inside this class:
private PrivateClass()
{
}
public static PrivateClass GetPrivateClass()
{
//This calls the private constructor so you can control exactly what happens
return new PrivateClass();
}
}
internal This means only code in the same assembly (i.e. from inside your library) can access it.
public class InternalClass
{
//Only from within the same assembly
internal InternalClass(string foo)
{
}
}

Seemann's Dependency Injection, "Three Calls Pattern" vs Service Locator Anit-Pattern

I have created a WinForms MVC application using Dependency Injection (DI) and Ninject as the DI Container. The basic architecture is as follows
Program.cs (the main entry point of the WinForms application):
static class Program
{
[STAThread]
static void Main()
{
...
CompositionRoot.Initialize(new DependencyModule());
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(CompositionRoot.Resolve<ApplicationShellView>());
}
}
DependencyModule.cs
public class DependencyModule : NinjectModule
{
public override void Load()
{
Bind<IApplicationShellView>().To<ApplicationShellView>();
Bind<IDocumentController>().To<SpreadsheetController>();
Bind<ISpreadsheetView>().To<SpreadsheetView>();
}
}
CompositionRoot.cs
public class CompositionRoot
{
private static IKernel ninjectKernel;
public static void Initialize(INinjectModule module)
{
ninjectKernel = new StandardKernel(module);
}
public static T Resolve<T>()
{
return ninjectKernel.Get<T>();
}
public static IEnumerable<T> ResolveAll<T>()
{
return ninjectKernel.GetAll<T>();
}
}
ApplicationShellView.cs (the main form of the application)
public partial class ApplicationShellView : C1RibbonForm, IApplicationShellView
{
private ApplicationShellController controller;
public ApplicationShellView()
{
this.controller = new ApplicationShellController(this);
InitializeComponent();
}
public void InitializeView()
{
dockPanel.Extender.FloatWindowFactory = new CustomFloatWindowFactory();
dockPanel.Theme = vS2012LightTheme;
}
private void ribbonButtonTest_Click(object sender, EventArgs e)
{
controller.OpenNewSpreadsheet();
}
public DockPanel DockPanel
{
get { return dockPanel; }
}
}
where
public interface IApplicationShellView
{
void InitializeView();
DockPanel DockPanel { get; }
}
ApplicationShellController.cs
public class ApplicationShellController
{
private IApplicationShellView shellView;
public ApplicationShellController(IApplicationShellView view)
{
this.shellView = view;
}
public void OpenNewSpreadsheet(DockState dockState = DockState.Document)
{
SpreadsheetController controller = (SpreadsheetController)GetDocumentController("new.xlsx");
SpreadsheetView view = (SpreadsheetView)controller.New("new.xlsx");
view.Show(shellView.DockPanel, dockState);
}
private IDocumentController GetDocumentController(string path)
{
return CompositionRoot.ResolveAll<IDocumentController>()
.SingleOrDefault(provider => provider.Handles(path));
}
public IApplicationShellView ShellView { get { return shellView; } }
}
SpreadsheetController.cs
public class SpreadsheetController : IDocumentController
{
private ISpreadsheetView view;
public SpreadsheetController(ISpreadsheetView view)
{
this.view = view;
this.view.SetController(this);
}
public bool Handles(string path)
{
string extension = Path.GetExtension(path);
if (!String.IsNullOrEmpty(extension))
{
if (FileTypes.Any(ft => ft.FileExtension.CompareNoCase(extension)))
return true;
}
return false;
}
public void SetViewActive(bool isActive)
{
((SpreadsheetView)view).ShowIcon = isActive;
}
public IDocumentView New(string fileName)
{
// Opens a new file correctly.
}
public IDocumentView Open(string path)
{
// Opens an Excel file correctly.
}
public IEnumerable<DocumentFileType> FileTypes
{
get
{
return new List<DocumentFileType>()
{
new DocumentFileType("CSV", ".csv" ),
new DocumentFileType("Excel", ".xls"),
new DocumentFileType("Excel10", ".xlsx")
};
}
}
}
where the implemented interface is
public interface IDocumentController
{
bool Handles(string path);
void SetViewActive(bool isActive);
IDocumentView New(string fileName);
IDocumentView Open(string path);
IEnumerable<DocumentFileType> FileTypes { get; }
}
Now the view ascociated with this controller is
public partial class SpreadsheetView : DockContent, ISpreadsheetView
{
private IDocumentController controller;
public SpreadsheetView()
{
InitializeComponent();
}
private void SpreadsheetView_Activated(object sender, EventArgs e)
{
controller.SetViewActive(true);
}
private void SpreadsheetView_Deactivate(object sender, EventArgs e)
{
controller.SetViewActive(false);
}
public void SetController(IDocumentController controller)
{
this.controller = controller;
Log.Trace("SpreadsheetView.SetController(): Controller set successfully");
}
public string DisplayName
{
get { return Text; }
set { Text = value; }
}
public WorkbookView WorkbookView
{
get { return workbookView; }
set { workbookView = value; }
}
...
}
Finally the view interfaces are
public interface ISpreadsheetView : IDocumentView
{
WorkbookView WorkbookView { get; set; }
}
and
public interface IDocumentView
{
void SetController(IDocumentController controller);
string DisplayName { get; set; }
bool StatusBarVisible { get; set; }
}
Now for my questions. In Seemann's book "Dependency Injection in .NET" he talks about the "Three Calls Pattern" and this is what I have attempted to implement in the above. The code works, the shell view displays and via the MVC pattern my controllers correctly open views etc. However, I am confused as the above definately has the flavour of the "Service Locator Anti-Pattern". In chapter 3 of Seemann's book he states
The COMPOSITION ROOT pattern describes where you should use a DI CONTAINER. However,
it doesn’t state how to use it. The REGISTER RESOLVE RELEASE pattern addresses
this question [...] A DI CONTAINER should be used in three successive
phases called Register, Resolve, and Release.
In its pure form, the REGISTER RESOLVE RELEASE pattern states that you should only
make a single method call in each phase. Krzysztof Kozimic calls this the Three Calls Pattern.
Configuring a DI CONTAINER in a single method call requires more explanation. The
reason that registration of components should happen in a single method call is
because you should regard configuration of a DI CONTAINER as a single, atomic action.
Once configuration is completed, the container should be regarded as read-only.
This sounds like the dredded "Service locator", why is this not deemed service location?
In order to adjust my code to instead use Contstructor Injection, I changed my entry code to
[STAThread]
static void Main()
{
var kernel = new StandardKernel();
kernel.Bind(t => t.FromThisAssembly()
.SelectAllClasses()
.BindAllInterfaces());
FileLogHandler fileLogHandler = new FileLogHandler(Utils.GetLogFilePath());
Log.LogHandler = fileLogHandler;
Log.Trace("Program.Main(): Logging initialized");
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(kernel.Get<ApplicationShellView>());
}
using Ninject.Extensions.Conventions, I then changed ApplicationShellController in order to correct my code to inject the IDocumentControllers via ctor injection:
public class ApplicationShellController
{
private IApplicationShellView shellView;
private IEnumerable<IDocumentController> controllers;
public ApplicationShellController(IApplicationShellView shellView, IEnumerable<IDocumentController> controllers)
{
this.shellView = shellView;
this.controllers = controllers;
Log.Trace("ApplicationShellController.Ctor(): Shell initialized successfully");
}
...
}
where
public class SpreadsheetController : IDocumentController
{
private ISpreadsheetView view;
public SpreadsheetController(ISpreadsheetView view)
{
this.view = view;
this.view.SetController(this);
}
...
}
but this leads to a circular dependency, how do I handle this?
Question Summary:
Why is my initial use of Ninject using "Thee Calls Pattern" and CompositionRoot.Resolve<T>() bad or different to the Service Locator Anti-Pattern?
How can I resolve the circular dependency issue above if I want to switch to pure ctor injection?
Thanks very much for your time.

At some point in the process, you have to use service location. However, the difference between DI and SL is that in SL, you are resolving your services at the point they are requested, whereas in DI you resolve them in some kind of factory (such as a controller factory) and then construct your objects and pass the reference in.
You should create some kind of infrastructure that dispatches your commands and uses a factory of some kind to locate the dependencies used by the created objects.
In this way, the rest of your code doesn't have dependency resolution, and you are following a DI pattern except at the construction point.

How do I use this singleton example

This page does a good job of describing how to create c# singletons, but it doesn't seem to explain how you actually use them.
http://msdn.microsoft.com/en-us/library/ff650316.aspx
So if I were to create this singleton below, how do I kick things off (I don't think I can instantiate it directly) and if I don't have an instance object how to I access it - e.g. how do I read and write to property prop1
public sealed class Singleton
{
private static readonly Singleton instance = new Singleton();
private Singleton(){}
public static Singleton Instance
{
get
{
return instance;
}
}
public int prop1 {get; set;}
}

To use a singleton class, you simply call it's public static instance property. For example, suppose that you have a logger, and you don't want other developers to always instantiating it:
public class Logger
{
private static Logger logger = new Logger();
private Logger() { }
public static Logger Instance
{
get
{
return logger;
}
}
public void Log(text)
{
// Logging text
}
public int Mode { get; set; }
}
You should log this way:
Logger.Instance.Log("some text here");
In your case, to read/write Mode property, you should write:
Logger.Instance.Mode = 1;
int mode = Logger.Instance.Mode;

You can access the instance by using
Singleton.Instance

You only create the instance once, So you will have something like this
public sealed class Singleton
{
private static readonly Singleton instance;
private bool initialised = false;
private Singleton(){}
public static Singleton Instance
{
get
{
if(initialised)
return instance;
else {
initialsed = true;
instance = new Singleton();
return instance;
}
}
}
public int prop1 {get; set;}
}

Singleton.Instance.prop1 = 12;

How to initialize a static property before initializing a static class?

Below Class2 has a property that needs to be set before GetSomething is called, however because I access Class2 at the top of Class1 the property is always null when it gets to Something class. I can't seem to figure out how to change my code to set the property before it's used. Anyone?
EDIT
I want to pass the dependency from form1's constructor, not hardcode it further up the chain.
public partial class form1
{
private static readonly ISomeConstructedClass someConstructedClass = Class1.SomeConstructedClass;
public form1()
{
someConstructedClass.SomeDependency = new SomeDependency();
someConstructedClass.Whatever();
}
}
public static class Class1
{
public static readonly ISomething something = (ISomething)Class2.GetSomething("something");
public static ISomeConstructedClass SomeConstructedClass
{
get
{
return something.SomeConstructedClass;
}
}
}
....
}
public class Class2
{
public static ISomeDependency SomeDependency
{
get;
set;
}
public static GetSomething(string something)
{
switch(something)
{
case "something":
return new Something( SomeDependency );
}
}
}
public class Something : ISomething
{
public ISomeDependency SomeDependency
{
get;
set;
}
public Something(ISomeDependency someDependency)
{
SomeDependency = someDependency;
}
}

[Re]Edit:
I was confused about what you were trying to do before, you just need to create the dependency first.
public partial class form1
{
private static /*readonly*/ ISomeConstructedClass someConstructedClass;
public form1()
{
Class2.SomeDependency = new SomeDependency();
someConstructedClass = Class1.SomeConstructedClass;
someConstructedClass.Whatever();
}
}
I would also move the creation of something into the property just to make sure it is not initialized too soon (before the form1 constructor is called).
public static class Class1
{
public static ISomething something;
public static ISomeConstructedClass SomeConstructedClass
{
get
{
if (something == null) {
something = (ISomething)Class2.GetSomething("something");
}
return something.SomeConstructedClass;
}
}
}
You can use a static constructor. This is called before any static (or instance for that matter) fields or methods are called/accessed.
Something like:
static Class2() {
SomeDependency = SomeDependencyYouNeed;
}

Why are you using static methods? It looks like you're attempting a sort of Dependency Injection. Either create an instance of Class2 and pass the dependency in the constructor (and don't use static methods), or pass the dependency as a parameter of the GetSomething() method.
public static GetSomething(string something, ISomeDependency dependency).

How can I make one class solely responsible for creating and providing access to another class

This is how I understand I can implement the singleton pattern in C#:
public class ChesneyHawkes{
private static ChesneyHawkes _instance = new ChesneyHawkes();
public ChesneyHawkes Instance {get{return _instance;}}
private ChesneyHawkes()
{
}
}
What if I want to provide a single instance of an object, so that there can only ever be one, make the access to it public, but only allow it to be created or replaced by another singleton.
// The PuppetMaster should be the only class that
// can create the only existing Puppet instance.
public class PuppetMaster{
private static PuppetMaster_instance = new PuppetMaster();
public static PuppetMaster Instance {get{return _instance;}}
// Like a singleton but can be replaced at the whim of PuppetMaster.Instance
public static Puppet PuppetInstance {get {return Puppet;}}
private PuppetMaster()
{
}
public class Puppet{
// Please excuse the pseudo-access-modifier
puppetmasteronly Puppet(){
}
}
}
// To be accessed like so.
PuppetMaster.Puppet puppet = PuppetMaster.Instance.PuppetInstance;

You don't really need more than one singleton for that. Look at this example:
using System;
// interface for the "inner singleton"
interface IPuppet {
void DoSomething();
}
class MasterOfPuppets {
// private class: only MasterOfPuppets can create
private class PuppetImpl : IPuppet {
public void DoSomething() {
}
}
static MasterOfPuppets _instance = new MasterOfPuppets();
public static MasterOfPuppets Instance {
get { return _instance; }
}
// private set accessor: only MasterOfPuppets can replace instance
public IPuppet Puppet {
get;
private set;
}
}
class Program {
public static void Main(params string[] args) {
// access singleton and then inner instance
MasterOfPuppets.Instance.Puppet.DoSomething();
}
}