Static members can't be called with instance, like instance.myStaticProperty.
Is there any way, that I can have an instance variable that will be an alias of static self class? like:
class myClass
{
public string a ="hello";
public static string b ="world";
public myClass myVariable = global::myClass; // <--- phseudo code
}
and i could call:
myClass instance= new myClass();
instance.myVariable.b; //
No, there is not. The closest you get is using a using.
Your static class definition:
class ClassA
{
public static string A = "A";
}
And to use it:
using StaticClassA = ConsoleApp1.ClassA;
class Program
{
static void Main(string[] args)
{
string a = StaticClassA.A;
}
}
Not too much to gain though, but it might ease your naming a little.
Another (somewhat cooler) option is a static using:
using static ConsoleApp1.StaticClassA;
class Program
{
static void Main(string[] args)
{
string a = A;
}
}
You're attempting to do an anti-pattern there.
Static properties are properties not defined in an instance (object) of that class, but by the class itself. And as such, you can access and modify them whenever you choose to, provided you have the required scopes to do so.
I don't see the problem in calling MyClass.StaticProperty = <some expression>, if indeed the functions the static property do, are static. If it's something part of the object, something you don't connect with the class itself, i.e it might be different for each instanced object of that class, then just turn it into a regular property instead.
Example of some static properties and methods:
public class DoMath
{
public static string Pi { get; private set; } = "3.14";
public static double X {get; set;}
public static double Y {get; set;}
public static double Sum() => X + Y;
}
DoMath.X = 3.5;
DoMath.Y = 4;
double result = DoMath.Sum();
Console.WriteLine($"Pi is equal to {DoMath.Pi}.");
If you truly wish something to be static, then don't try to make it non-static. Simply declare it as such.
Static members are shared across all instances of the class or all instances of Class Of T of same T.
So you can access static properties outside of class by using the ClassName.VarName or directly by the VarName from within the class.
You can access static fields and properties and methods from all non static methods.
You can also add an instance member mapping a static member.
Instances of a static thing can't exist in addition to the static existence itself.
So you can write this:
class myClass
{
public string a = "hello";
static public string b = "world";
public string B { get { return b; } set { b = value; } }
public void DoSomething()
{
b = "new world";
}
}
And use it like that:
myClass instance= new myClass();
instance.DoSomething();
myClass.b = "another world";
instance.B = "C# world";
Related
Consider the following classes
class A
{
public static int i;
}
class B
{
public static A a{get;}=new A(); // without new A(), B.A will be null
}
now,
B.a gives a new instance of A and since the variable "i" of class A is static, I can not access "i" through B.a i.e B.a.i is compile time error.
I understand that if I do like below,
class B
{
static class A
{
static int i;
}
}
then I could do B.A.i.
So my question is how could I access static members of a static member of a class? Is it possible at all and is there any other pattern that I can use.
Also note that making class "A" as static and having class "B" as
class B
{
public static A a{get;}
}
gives a compile time error that "static type cannot be used as return type".
Since i is static member of A you can access it directly like
class B
{
public static A a {get;} = new A();
public int ii{get;} = A.i;
}
how could I access static members of a static member of a class?
If something is a member of a class -- static or not static -- that means it's either a value or a reference to an instance of something. Therefore, if you know you have an instance of a class but that class has static members itself, then just access those members statically:
class MyClass
{
public static string Value { get; }
}
string x = MyClass.Value;
You don't need to instantiate a class to access it's static members.
Simply you can try :
int value = A.i;
If you need, you can add a static class too :
public static class A
{
public static int i;
}
and you can use anywhere in your code like :
int value = A.i;
I have a few classes. Lets say:
public class A
{
public void SomeAction()
{
Debug.Write("I was declared in class: and my name is:");
}
}
And
public class B
{
public static A myClass = new A();
}
public class C
{
public static A myClass = new A();
}
public class D
{
public static A myClass = new A();
}
What I want "SomeAction" in class A to do is to print out which class it was initialized in.
So that for example in another class I called C.myClass.SomeAction(); it would print out "I was declared in class C my name is myClass"
I hope this makes sense.
The reasons im doing this is for debugging within automated testing. I understand its not the best way to do things but its a requirement of the business.
This requirement can be satisfied without inheritance or passing the object; we can get the name of the class that calls the constructor from within the body of the constructor by examining the stack.
public class A
{
private string _createdBy;
public void SomeAction()
{
Console.WriteLine("I was declared in class [{0}]", _createdBy);
}
public A()
{
var stackFrame = new StackFrame(1);
var method = stackFrame.GetMethod();
_createdBy = method.DeclaringType.Name;
}
}
In terms of performance, I am assuming that you are not creating many instances of these objects. You could also predicate this on whether you are doing a DEBUG build or on some other setting, so that this stuff is skipped entirely in your production executables.
Since you only reference an instance of class A in your other classes, I think there is no other way then setting a reference to the type which created class A, like eddie_cat already mentioned. You could do something like this:
public class B
{
public static A myClass = new A(typeof(B));
}
And then your class A would look like:
public class A
{
// store the parent type
private Type mParentClass;
// provide parent type during construction of A
public A(Type parentClass)
{
mParentClass = parentClass;
}
// note that method cannot be static anymore, since every instance of A might
// have a different parent
public void SomeAction()
{
// access field where parent type is stored.
Debug.Write("I was declared in class: {0} and my name is:",mParentClass.Name);
}
}
I think you have two choices. Either set a property in A, or inherit from A. Personally, I prefer inheriting from A, because then A could just use GetType().
public class A
{
public void SomeMethod()
{
Debug.Write(string.Format("I was declared in class: {0}",this.GetType()));
}
}
public class B : A
{
}
var instanceOfB = new B();
instanceOfB.SomeMethod();
Hello,
I'm trying to call the double paying from within the class "Wallet"
but when i try to do this it gives this error:
Member'Mc_DOnalds.Program.Paying' cannot be accessed with an instance reference; qualify it with a type name instead.
This is in the class Wallet.
class Wallet
{
public double WalletCustomer = 100;
Program Betalen = new Program();
public void Pay()
{
WalletCustomer = (WalletCustomer - Betalen.Paying);
}
}
}
This is in the Program.cs
public static double Paying = 0;
Because Paying is static, you don't need to create an instance of the class to access the property. Try this (take a look on how I access the Program.Paying):
class Wallet
{
public double WalletCustomer = 100;
public void Pay()
{
WalletCustomer = (WalletCustomer - Program.Paying);
}
}
}
For static member you need to use class name instead of instance
WalletCustomer = (WalletCustomer - Program.Paying);
You access the members of a static class by using the class name
itself. For example, if you have a static class that is named
UtilityClass that has a public method named MethodA, you call the
method as give below, MSDN.
UtilityClass.MethodA();
This error is coming because you are trying to access your non static member from static class.
Solution: Either mark your member as static or change your Calling function to Non-Static.
or access your Non-Static Member with Class Name
Here is how?
class Wallet
{
public static double WalletCustomer = 100;
Program Betalen = new Program();
public void Pay()
{
WalletCustomer = (WalletCustomer - Betalen.Paying);
}
}
Or
class Wallet
{
public double WalletCustomer = 100;
Program Betalen = new Program();
public void Pay()
{
WalletCustomer = (WalletCustomer - Betalen.Paying);
}
}
In your Main Program
Program.Paying = 0;
According to LeakyCode, in C#, unlike VB.NET and Java, you can't access static members with instance syntax. You should do:
MyClass.MyItem.Property1
To refer to that property or remove the static modifier from Property1 (which is what you probably want to do). For a conceptual idea about what static is, see my other answer.
Poom
I've got a class which looks like this
class MyClass
{
string myData;
//.....
//other fields
public static implicit operator string(MyClass c)
{
return c.myData;
}
}
Now when I assign the value of the class to a string, I get myData's value. But in microsoft's example, to do implicit convection from MyClass to string, I'd have to create a new instance of MyClass in a static method. I don't want to do this, instead I want to simply assign the string's value to myData field.
Is this possible to do in c#, and if it is, how do I do it?
Sounds like there is no direct solution to what you need. I would suggest to try operator overloading and this would allow to perform some of the things I think you need with the understanding that = (equal) cannot be overloaded probably you would like to try += You can find additional help here:
http://msdn.microsoft.com/en-us/library/6fbs5e2h.aspx
This is a sample version:
namespace ConsoleApplication1
{
public struct MyClass
{
public string MyData {get;set;}
// Constructor.
public MyClass(string obj1):this()
{
this.MyData = obj1;
}
public static MyClass operator +(MyClass c1, string var3)
{
return new MyClass(var3);
}
public override string ToString()
{
return (System.String.Format("{0} ", this.MyData));
}
}
[System.Runtime.InteropServices.GuidAttribute("D36900FE-8902-4ED8-B961-DE5B3F3273AC")]
class Program
{
static void Main(string[] args)
{
MyClass obj1 = new MyClass();
obj1 += "Hello";
Console.ReadKey();
}
}
}
As far as I know you can can't pass parameters to a static constructor in C#.
However I do have 2 parameters I need to pass and assign them to static fields before I create an instance of a class. How do I go about it?
This may be a call for ... a Factory Method!
class Foo
{
private int bar;
private static Foo _foo;
private Foo() {}
static Foo Create(int initialBar)
{
_foo = new Foo();
_foo.bar = initialBar;
return _foo;
}
private int quux;
public void Fn1() {}
}
You may want to put a check that 'bar' is already initialized (or not) as appropriate.
You can't pass parameters to a static constructor, but you can pass parameters to the class itself - via generic type parameters.
Slightly crazy this idea, however, I'll just throw it out there anyway.
Make the class generic (with a TypeParam that will provide a parameter type) and place generic constraints on it (details in code example), then derive a new parameter type, which contains virtuals that you can use to read what they want the parameter values to be.
//base parameter type - provides the 'anchor' for our generic constraint later,
//as well as a nice, strong-typed access to our param values.
public class StaticParameterBase
{
public abstract string ParameterString{ get; }
public abstract MyComplexType ParameterComplex { get; }
}
//note the use of the new() generic constraint so we know we can confidently create
//an instance of the type.
public class MyType<TParameter> where TParameter:StaticParameterBase, new()
{
//local copies of parameter values. Could also simply cache an instance of
//TParameter and wrap around that.
private static string ParameterString { get; set; }
private static MyComplexType ParameterComplex { get; set; }
static MyType()
{
var myParams = new TParameter();
ParameterString = myParams.ParameterString;
ParameterComplex = myParams.ParameterComplex;
}
}
//e.g, a parameter type could be like this:
public class MyCustomParameterType : StaticParameterBase
{
public override string ParameterString { get { return "Hello crazy world!"; } }
public override MyComplexType { get {
//or wherever this object would actually be obtained from.
return new MyComplexType() { /*initializers etc */ };
}
}
}
//you can also now derive from MyType<>, specialising for your desired parameter type
//so you can hide the generic bit in the future (there will be limits to this one's
//usefulness - especially if new constructors are added to MyType<>, as they will
//have to be mirrored on this type as well).
public class MyType2 : MyType<MyCustomParameterType> { }
//then you'd use the type like this:
public static void main()
{
var instance = new MyType<MyCustomParameterType>();
//or this:
var instance2 = new MyType2();
}
I did consider a solution that employs custom type attributes applies to a type parameter, however this is easily a better way. However, you'll now be using your class always with a generic parameter type (unless you can use the deriving+specialisation trick) - possibly too clumsy for your liking.
I'd also prefer this over the other solutions presented here as it doesn't require creating any workarounds for the static initialisation - you can still use .Net's guarantee of single-time initialisation.
A word of warning - should you be reviewing your structure?
All that said - remember, though, since you can only parameterise the static once (or in this case, each uniquely parameterised static generic) - I would be asking myself why not just pull the code that is getting the parameters to give to the static, and place it in the static constructor in the first place? That way you don't actually have to resort to strange patterns like this!
I assume you mean static members of a class? In that case, you can do this:
public class MyClass
{
public static int MyInt = 12;
public static MyOtherClass MyOther = new MyOtherClass();
}
Those static members are guaranteed to be instantiated before any class is instantiated.
If you need complex logic, do it in a static constructor:
public class MyClass
{
public static int MyInt;
public static MyOtherClass MyOther;
static MyClass()
{
MyInt = 12;
MyOther = new MyOtherClass();
}
}
Edit
Based on your edit, I'd say just assign the values to what they need to be before you instantiate the class, like so:
public class MyClass
{
public static int MyInt;
public static MyOtherClass MyOther;
}
// elsewhere in code, before you instantiate MyClass:
MyClass.MyInt = 12;
MyClass.MyOther = new MyOtherClass();
MyClass myClass = new MyClass();
That said, this method gives you no guarantee that MyInt and MyOther are set before MyClass is instantiated. It will work, but requires discipline before instantiating MyClass.
One alternative pattern you might follow looks like this:
public class MyClass
{
private static int MyInt;
private static MyOtherClass MyOther;
private static bool IsStaticInitialized = false;
public static InitializeStatic(int myInt, MyOtherClass other)
{
MyInt = myInt;
MyOther = other;
IsStaticInitialized = true;
}
public MyClass()
{
if(!IsStaticInitialized)
{
throw new InvalidOperationException("Static Not Initialized");
}
// other constructor logic here.
}
}
// elsewhere in your code:
MyClass.InitializeStatic(12, new MyOtherClass());
MyClass myClass = new MyClass();
// alternatiavely:
MyClass myClass = new MyClass(); // runtime exception.