Develop Reference

Why would my initialized static property be null when I access it?

I have the following code ( extracted from the real code )
public static class AssemblyLogger {
public static Lazy<Window> Window { get; } = new Lazy<Window>(NewWindowHandler);
public static IScheduler Scheduler =>
new DispatcherScheduler( Window.Value.Dispatcher );
}
When I call Scheduler I get a NullReferenceException. Stopping with the debugger I see
As far as I know this should be impossible. Window is statically initialized and read only and so any further access to it should be get only and it should never be null.
I have set a breakpoint against the initializer but it never gets hit
I have also tried a static readonly field and still the same problem
public static readonly Lazy<Window> Window = new Lazy<Window>(NewWindowHandler);
Is it possible to have a race condition against the static initialization?
Attempts to make an MCVE so far are not successful. The below spec tests my minimal postable code and the real code. The MCVE one passes :( and the real one fails. I am missing some context and need further work to isolate the issue.
public class Tester
{
public static class AssemblyLoggerMCVE
{
public static Lazy<Window> Window { get; } = new Lazy<Window>(NewWindowHandler);
private static Window NewWindowHandler() => new Window();
public static IScheduler Scheduler =>
new DispatcherScheduler(Window.Value.Dispatcher);
}
/// This passes
[StaFact]
public void AssemblyLoggerMCVEShouldWork()
{
AssemblyLoggerMCVE.Scheduler.Should().NotBeNull();
}
/// This fails
[StaFact]
public void AssemblyLoggerShouldWork()
{
AssemblyLogger.Scheduler.Should().NotBeNull();
}
}

The error can be clearly replicated by the following test case which has more context than the question suggested was necessary.
public class Tester
{
public class AssemblyLoggerControlModel
{
public static IScheduler S = AssemblyLoggerMCVE.Scheduler;
}
public class AssemblyLogger
{
public static AssemblyLoggerControlModel ModelInstance { get; } =
new AssemblyLoggerControlModel();
public static readonly Lazy<Window> Window =
new Lazy<Window>(NewWindowHandler);
private static Window NewWindowHandler() => new Window();
public static IScheduler Scheduler =>
new DispatcherScheduler(Window.Value.Dispatcher);
}
}
There is a circular dependency between static initializers. Static initialization of static property AssemblyLogger.ModelInstance causes static property AssemblyLoggerControlModel.S to be intitialized which then tries to call the static AssemblyLogger.Scheduler method which in turn tries to access Window which because the static initialization for AssemblyLogger is not complete is still null.
Basically my code is pure evil and the best thing to do is

How to pass parameter to static class constructor?

I have a static class with a static constructor. I need to pass a parameter somehow to this static class but I'm not sure how the best way is.
What would you recommend?
public static class MyClass {
static MyClass() {
DoStuff("HardCodedParameter")
}
}

Don't use a static constructor, but a static initialization method:
public class A
{
private static string ParamA { get; set; }
public static void Init(string paramA)
{
ParamA = paramA;
}
}
In C#, static constructors are parameterless, and there're few approaches to overcome this limitation. One is what I've suggested you above.

As per MSDN, A static constructor is called automatically to initialize the class before the first instance is created. Therefore you can't send any parameters.
CLR must call a static constructor, how will it know which parameters to pass it?
So don't use a static constructor.
Here's the work around for your requirement.
public class StaticClass
{
private int bar;
private static StaticClass _foo;
private StaticClass() {}
static StaticClass Create(int initialBar)
{
_foo = new StaticClass();
_foo.bar = initialBar;
return _foo;
}
}
Static constructors have the following properties:
A static constructor does not take access modifiers or have parameters. A static constructor is called automatically to
initialize the class before the first instance is created or any
static members are referenced.
A static constructor cannot be called directly.
The user has no control on when the static constructor is executed in the program.
A typical use of static constructors is when the class is using a log file and the constructor is used to write entries to this file.
Static constructors are also useful when creating wrapper classes for unmanaged code, when the constructor can call the LoadLibrary
method.
If a static constructor throws an exception, the runtime will not invoke it a second time, and the type will remain uninitialized for
the lifetime of the application domain in which your program is
running.

If by "HardCodedParameter" you really mean hard coded, you can use constants.
public static class YoursClass
{
public const string AnotherHardCodedParam = "Foo";
}
public static class MyClass
{
private const string HardCodedParam = "FooBar";
static MyClass()
{
DoStuff(MyClass.HardCodedParam);
DoStuff(YoursClass.AnotherHardCodedParam);
}
}
Also, you can use static readonly properties.

Constructors on non-static class have have the benefit to ensure they're properly initialized before they're actually being used.
Since static classes don't have this benefit, you have to make ensure that yourself.
Use a static constructor with an obvious name, then in the relevant portion of your static procedures check to make sure the initialization has been performed.
The example below assumes your want to "initialize" your static class with a Form object.
public static class MyClass
{
private static Form FormMain { get; set; }
public static void Init(Form initForm)
{
FormMain = initForm;
}
private static bool InitCheck()
{
return FormMain != null ? true: false;
}
public static void DoStuff()
{
if (InitCheck())
{
// Do your things
}
else
{
throw new Exception("Object reference not set to an instance of an object");
}
}
}

How is the method called in static class

My code is as follows
class MyStaticClass
{
static MyStaticClass{};
public static readonly MyStaticClass Instance = CreateMe();
public static int GetSomeValue = GetValue();
private static int GetValue()
{
return 0;
}
private static MyStaticClass CreateMe()
{
Console.WriteLine("This method was called");
return new MyStaticClass();
}
}
public class Program
{
public static void Main()
{
int val=MyStaticClass.GetSomeValue;
}
}
O/p:
This method was called
When I call val why does the debugger accesses CreateMe method ? Is it that any static method I access it will access all the static methods in the class ?

The method CreateMe() is called because you are calling in when you create object Instance in the following statement.
public static readonly MyStaticClass Instance = CreateMe();
This is static object in your class and is created as you access the class which you did by MyStaticClass.GetSomeValue.
Dubugging the code will give you clear view of the order of the statements get executed. You can go through this detailed article on MSDN regarding debugging Debugger Roadmap

You have a static initializer for a static field. As part of program startup, all static fields are evaluated.
Edit: small clarification here:
The static fields in a particular class are evaluated in declaration order, but there in no particular order for which class has it's static fields initialized first.
Now, if you had a static property, that would be different.
MSDN link

Both fields have been initialized using the static methods. So, in that case, all the static methods will be evaluated.

Risk by using a static property in a multi-threading (or web) c# project

i am a little confused by multi-thread access risk on a static property in C#.
public class MyClass
{
public static MyClass Static
{
get
{
var c = new MyClass();
c.SomeProperty = "12345";
c.OtherProperty = DateTime.Now.ToString();
return c;
}
}
}
This example class provides a static property that create a new instance of MyClass,
like a method:
public class MyClass
{
public static MyClass Static()
{
var c = new MyClass();
c.SomeProperty = "12345";
c.OtherProperty = DateTime.Now.ToString();
return c;
}
}
Obviously, this property is not a "storage" box for an instance of MyClass, but it behaves like a static method (that, if i reading good a msdn article, is completely thread-safe).
My question is: i risk something with using this concept ?
Especially in a web or multi-thread enviroinment ?
There is a no particular utility in using it, only for simple reading and cleaning code:
MyClass.Static.SomeProperty = "Something";
is more clear than
MyClass.Static().SomeProperty = "Something";
All help will be appreciated
Thanks

In both your examples you're returning a new instance of MyClass every time the property is accessed. There is no danger that you'll have any concurrency issues when multiple threads access the static property method at the same time, because they're actually modifying the properties of their own instance of MyClass and not sharing it between them.
If you had something like this instead:
public class MyClass
{
private static MyClass _myClass;
public static MyClass Static
{
get
{
return _myClass ?? (_myClass = new MyClass());
}
}
}
...then you'd cause problems when two threads attempted to write/read properties of the resulting MyClass instance, because they're operating on the same MyClass reference _myClass.
Even so, there are two issues with the code you've posted:
You need to change it to a method and rename it, because it's actually creating something, not accessing a static version of anything. Then you can operate on the return value. Something like this:
public class MyClass
{
public static MyClass Create()
{
var c = new MyClass();
c.SomeProperty = "12345";
c.OtherProperty = DateTime.Now.ToString();
return c;
}
}
Then use it like this:
var myClass = MyClass.Create();
myClass.SomeProperty = "Stuff";
The way you're setting properties currently means their values aren't persisted, because a new MyClass is created the next time the Static property is accessed.
If when you set SomeProperty you actually want a static instance to be updated you'll need to lock on a static object to solve the multi threading issue - something like this:
public static class MyClass
{
private static readonly object locker = new object();
private static string someProperty;
public void SetSomeProperty(string val)
{
lock (locker)
{
someProperty = val;
}
}
public void GetSomeProperty()
{
lock (locker)
{
return someProperty;
}
}
}

It seems that you are creating a static factory method that will give you a fully instantiated object.
Threading would not be an issue here because every time you call this method or property you are creating a new object. If 2 threads call the same method at the same time they will each keep on working on the object they are dealing with
Having said that - Perhaps you should reexamine how you are using the class - because if you call this in your code
MyClass.Static.SomeProperty = "Something";
You are basically throwing away the object after it has been instantiated
you would need to assign it to a variable and store it. - the next time you call that function you will receive a new object.

Perhaps I was not able to explain properly, my question was referred multithreaded access on static properties.
I can confirm that they are thread-safe, if the returned object is bound to the current thread.
Here is the example of what I implemented:
public interface IObjectFactory
{
T CreateOrReuse<T>() where T : class, new();
T CreateOrReuse<T>(string key) where T : class, new();
T CreateOrReuse<T>(string key, params object[] args) where T : class;
}
public class ThreadObjectFactory : IObjectFactory
{
// implementation to create and store into the Thread Data
}
public class HttpSessionObjectFactory : IObjectFactory
{
// implementation to create and store into the current session
}
Now the singleton:
public class MyClass
{
public int PageLoadCounter = 0;
public static MyClass Static
{
get
{
IObjectFactory factory = new HttpSessionObjectFactory();
return factory.CreateOrReuse<MyClass>();
}
}
}
And this is the final use:
public class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
MyClass.Static.PageLoadCounter++;
}
}
Thanks for the replies, even if the question was not very clear

Global Static Class with Objects

Ok, so I know you can't have objects in a static class but i need a class that i can hold objects that are accessible from different classes. I am making a dll that will provide extended functionality to another program so i can't just inherit or pass classes around either. if need be i can just maybe make the properties of each object i need to be in the static class which would work but not be as friendly as i would like. anyone have any other ideas on how to accomplish something like this?

Actually, you can have objects in a static class -- they just have to be static objects.
For instance:
public static class SharedObjects
{
private static MyClass obj = new MyClass();
public static MyClass GetObj()
{
return obj;
}
}
And from elsewhere in your program you can call instance methods/properties/etc.:
SharedObjects.GetObj().MyInstanceMethod();

One option is to have a class with the accessors methods accessing a static object (or objects). The other parts of your system can use the class either as static or as a non-static. Here is the code:
public class GlobalInformation {
public static GlobalInformation CreateInstance() {
// Factory method through GlobalInformmation.CreateInstance()
return new GlobalInformation();
}
public GlobalInformation() {
// Regular use through new GlobalInformation()
}
static GlobalInformation() {
// Static initializer called once before class is used.
// e.g. initialize values:
_aString = "The string value";
}
public string AccessAString {
get {
return _aString;
}
}
public Foo AccessAnObject() {
return _anObject;
}
private static string _aString;
private static readonly Foo _anObject = new Foo();
}
Other parts of your system would use it as follows. Option 1:
var globalInfo = GlobalInformation.CreateInstance();
var aString = globalInfo.AssessAString;
var anObj = globalInfo.AccessAnObject();
Option 2:
var globalInfo = new GlobalInformation();
var aString = globalInfo.AssessAString;
var anObj = globalInfo.AccessAnObject();
Option 2 would be my preferred one (I'd remove the static factory method CreateInstance()) as you could change the implementation at any time including making (some of) the fields non-static. It would appear to be a regular class while sharing data.