Can I set the newly created object equal to the supplied object in the constructor of the class?
I want to do something like this:
public MyClass
{
public MyClass(MyClassDto myClassDto)
{
MyClass convertedMyClassObj = AutoMapper.LoadEntityFromDto<MyProject.DTO.MyClassDto, MyClass>(myClassDto);
//Assign the new object being created here equal to convertedMyClassObj:
this = convertedMyClassObj; //I want to reference the current object in place of 'this'.
}
public int MyProperty1 { get; set;}
public int MyProperty2 { get; set;}
public int MyProperty3 { get; set;}
}
I don't want to do it property by property. Do I have to use a a singleton like procedure to return the copied instance in a GetInstance() method. Because constructor has no return parameter. I just want to know if this is possible or not.
You won't be able to do that because this can't be set. But you are already using AutoMapper which creates your object from your DTO. You could just use a static method if you want a shorthand.
public MyClass
{
public static MyClass FromDto(MyClassDto myClassDto)
{
return AutoMapper.LoadEntityFromDto<MyProject.DTO.MyClassDto, MyClass>(myClassDto);
}
//Properties
}
Then you would just use it with
var myClass = MyClass.FromDto(myClassDto);
There is an overload of AutoMapper.Map that takes a reference to an existing destination object.
public static TDestination Map<TSource, TDestination>(TSource source, TDestination destination);
You can use it with this to set the properties based on the DTO:
class MyClass
{
public MyClass(MyClassDTO dto)
{
AutoMapper.Mapper.Map(dto, this);
}
}
The problem with this approach is that MyClass gets coupled to Automapper and MyClassDTO. It might be better to move the responsibility of converting MyClassDTO to MyClass to a separate class.
You're essentially talking about creating a factory, and if you look at the factory pattern, the key is a static class that does the work of instantiating the new "thing". So, no, you can't really do this like you're trying to, but if you want to encapsulate the AutoMapper logic, then you can simply do something like:
public static class MyClassFactory
{
public static MyClass FromMyClassDto(MyClassDto myClassDto)
{
return AutoMapper.LoadEntityFromDto<MyProject.DTO.MyClassDto, MyClass>(myClassDto);
}
}
Then:
var myClassInstance = MyClassFactory.FromMyClassDto(myClassDto);
You cannot assign a value to this in a class. You'll need to copy the values over.
Related
I have a class with several attributes that have getters and setters. I want to make the objects of this class immutable. I thought of giving the setters a return type instead of void like is done to the functions in System.Collections.Immutable classes. For now I did it like this:
MyImmutableClass
{
public int MyAttribute { get; }
public MyImmutableClass SetMyAttribute(int attribute)
{
return new MyImmutableClass(attribute, ...);
}
...
public MyImmutableClass(int attribute, ...)
{
MyAttribute = attribute;
...
}
}
Is this how it should be done or is there a better/nicer way? Can I moddify a normal setter for instance?
You should rather use a static factory method and use a private constructor, properties aren't made for this (because creating an object may be a lot of work -> use a method). You do everything in the create method, which gives you back an object that you can't modify anymore, by having readonly properties like you do:
public class MyImmutableClass
{
public int MyAttribute { get; }
private MyImmutableClass(int attribute, ...)
{
MyAttribute = attribute;
...
}
public static MyImmutableClass Create(int attribute)
{
return new MyImmutableClass(attribute, ...);
}
}
Then use it:
var myClass = MyImmutableClass.Create(2);
I am looking to get a child class instantiated using a parent instance to set all of the inherited variables.
For example:
public class Foo
{
//Variables
}
public class bar : Foo
{
public int ID { get; set; }
public bar(Foo instance)
{
base = instance; // Doesn't work but is generally the idea I'm looking for
}
}
Just add a constructor to your parent Foo class that accepts a Foo instance and takes care of copying the fields. The Bar class can then invoke that as the base constructor.
public class Foo
{
private string var1;
private string var2;
public Foo() { }
public Foo(Foo otherFoo)
{
this.var1 = otherFoo.var1;
this.var2 = otherFoo.var2;
}
}
public class Bar : Foo
{
public int ID { get; set; }
public Bar(Foo instance)
: base(instance)
{
}
}
You would have to make all your members public inside Foo that would need to be set from the constructor. Then, set the properties you need to.
I think you are looking for some kind of mapper that maps from one object to another.
You could use a open source project like AutoMapper or ValueInjecter which can be found on NuGet.
Here is also a nice article:
Copy values from one object to another
Demo with ValueInjecter:
static void Main(string[] args)
{
var foo = new Foo()
{
Property1 = "Value1",
Property2 = "Value2"
};
var bar = Mapper.Map<Bar>(foo);
bar.Id = 3;
Console.WriteLine(bar.Id); //3
Console.WriteLine(bar.Property1); //Value1
Console.WriteLine(bar.Property2); //Value2
}
Why can't you get it done through a public auto property like below. BTW, what you are trying to have is Composition wherein bar object is composed of foo object. Not sure why you are still inheriting from foo then?
public class bar : Foo
{
public int ID { get; set; }
public Foo baseinstance { get; set;}
public bar(Foo instance)
{
baseinstance = instance;
}
}
I am not absolutely sure but from your posted code (specifically the below part) it feels like you are trying to call the base class constructor or constructor initializer since you said
I am looking to get a child class instantiated using a parent instance
to set all of the inherited variables.
public bar(Foo instance)
{
base = instance;
}
Which should actually be
public bar(Foo instance) : base()
{
//child instance initialization
}
But that's not needed for a parameterless constructor cause when you instantiate child object constructor initializer will get invoked and base class will gets initialize first in-order to have the base member initialized before child initialization.
If you have parameterized constructor in base and in child then you can explicitly call base constructor
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();
This is a followup to a previous question. There was a mistake in that question (I actually posted my current solution instead of the better one I'm looking for).
I have 3 classes, ParentClass,ClassA,ClassB. Both ClassA and ClassB are subclasses of ParentClass. I wanna try to create objects of type ClassA or ClassB using some kind of enumeration to identify a type, and then instantiate the object cast as the parent type. How can I do that dynamically? Please take a look at the code below, and the part that says //what do I put here?. Thanks for reading!
public enum ClassType
{
ClassA,
ClassB
};
public abstract class ParentClass
{
public static readonly Dictionary<ClassType, Type> Types =
new Dictionary<ClassType, Type>{
{ClassType.ClassA, typeof(ClassA) },
{ClassType.ClassB, typeof(ClassB) }
};
public ParentClass()
{
//....
}
public static ParentClass GetNewObjectOfType(ClassType type)
{
//What do I put here?
}
}
public class ClassA:ParentClass
{
//....
}
public class ClassB:ParentClass
{
//.......
}
You can do it easily with the Activator class, especially if there aren't any arguments to the constructors:
return Activator.CreateInstance(Types[type]);
To restate your question: you're looking for advice on how to code a static factory method.
I don't think you need a separate enumeration to accomplish this. This is a LINQPad script I threw together (EDIT: added static constants, demo creation using them)
void Main()
{
var a = ParentClass.Create(typeof(ClassA));
var b = ParentClass.Create(typeof(ClassB));
var c = ParentClass.Create(ParentClass.ClassAType);
a.Dump();
b.Dump();
c.Dump();
}
public abstract class ParentClass
{
public static readonly Type ClassAType = typeof(ClassA);
public static readonly Type ClassBType = typeof(ClassB);
public string SomeProp { get; set; }
protected ParentClass() {}
public static ParentClass Create(Type typeToCreate)
{
// validate that type is derived from ParentClass
return (ParentClass)Activator.CreateInstance(typeToCreate);
}
}
public class ClassA:ParentClass {
public ClassA()
{
SomeProp = "ClassA~";
}
}
public class ClassB:ParentClass
{
public ClassB()
{
SomeProp = "ClassB~";
}
}
As stated in the previous question:
Reflection is slow and is often used where it isn't needed
Activator.CreateInstance uses reflection to track down a parameter-less constructor. To solve this problem - that isn't needed. The parent class already knows all of the types it is responsible for creating.
One of the reasons to use a static factory method, is that there may be substantial work, or different kinds of work involved in creating the child classes. I think if you beef up your map some, you'll have a easier time coding that static factory:
public static readonly Dictionary<ClassType, Func<ParentClass>> Types =
new Dictionary<ClassType, Func<ParentClass>>{
{ClassType.ClassA, () => new ClassA(1, 2, 3) },
{ClassType.ClassB, () => new ClassB("1") }
};
public static ParentClass GetNewObjectOfType(ClassType type)
{
Func<ParentClass> maker = Types[type];
ParentClass result = maker();
return result;
}
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.