I have an Interface
interface IPerson
{
PersonInformation PersonInfo { get; set; }
}
And this class
public class PersonInformation
{
public string Name{ get; set; }
}
When I implement the interface it's giving me a null error and I can't determine why. My get/set looks correct
class Employee: MyStore, IPerson
{
private PersonInformation _perInfo;
public override void Execute()
{
PersonInfo.Name = "Bill";
}
public PersonInformation PersonInfo
{
get
{
return _perInfo;
}
set
{
_perInfo = value;
}
}
}
Everything compiles but when I try to set PersonInfo.Name it's saying the object isn't set. I've played around with the get/set in the interface but that didn't change anything. I'm thinking I'm missing something so obvious...any ideas???
Just declaring a reference variable member does not create an object for that variable. You must set the variable to refer to an actual object instance.
So you either want this:
myEmployee.PersonInfo = new PersonInformation();
myEmployee.PersonInfo.Name = "Some Name";
or this in the class definition:
private PersonInformation _perInfo = new PersonInformation();
// ...
myEmployee.PersonInfo.Name = "Some Name";
As a further note, in the latter case you probably would be better off having the set be private, or not even defining it at all. (Note the interface definition will require otherwise, but I expect you can change that, too).
This is because setting a mere property like .Name is still a get operation on the parent object: first you get the reference to the entire PersonInformation object, and then use the set on the object's .Name property to set the field.
You only need to use a set for this property if you want to replace the entire object with a different one (see, for example, the first line in my sample above).
Related
I would like to know if there is any way to implement a get method inside a class?
public class Element: IWebElement
{
IWebElement realElement;
//Question point is this get{}
//Everytime I access the instance of this class this get would be called
get
{
//This 'realElement' is not present yet
//So I cannot initialize it
//But when the properties of this class are accessed
//I'm telling the get method that it's time to initialize 'realElement'
realElement = webDriver.FindElement(...);
Visible = element.Visible;
return this;
}
public bool Visible {get; set;}
}
public class AnotherClass()
{
public void AccessElement()
{
Element element = new Element();
if(element.Visible) // At this point the 'element'
{
}
}
}
Usage:
I cannot initialize every property with their own get, because they are too many
Everytime I access the instance of this class this get would be called
If that could be done you'd be in trouble returning this since that would then access the instance, which would call the method, which would then access the instance, which would call the method… and so on until you get a StackOverflowException (or if it got tail-call optimised, forever).
More generally the question doesn't make sense.
A get method is a method identified as being the getter of a property. When C# is compiled to CIL then properties with getters are compiled so that there is a .property declaration with a .get declaration that refers to that method. If C# decided to change the rules to have getters on classes, it wouldn't have any corresponding CIL to compile it to.
The closest thing to a getter on a class in .NET is a default property, which in C# you can only have (and will always have) on a property called this (it becomes what is visible to other .NET languages or reflection property called Item), but it must have an indexer, and it does still exist as a property rather than with the getter directly applied to the class.
You could use the constructor, so it will be called everytime instance of object will be created.
public class Element()
{
public Element(){
AnyProperty = ""; //some value initialize
}
}
Added this new answer with my old answer because I got downvoted for trying to answer your original code which is now really different. Sheesh.
Usage: I cannot initialize every property with their own get, because
they are too many
So, this is actually not how you usually use get. Get is used mostly for access to a private method, or with a little logic, and oftentimes for data-binding such as in MVVM, etc.
I think your wording is not accurate. You said
Everytime I access the instance of this class this get would be called
But based on your code, what you mean is "Everytime I instantiate a class". The only thing you really need is a constructor.
public class Element: IWebElement
{
IWebElement realElement;
public bool Visible {get; set;}
public Element()
{
realElement = webDriver.FindElement(...);
Visible = element.Visible;
}
}
Old answer:
You're probably thinking of the Singleton Pattern
EDIT: This originally answered original question's code, seen below.
public class Element()
{
//Question point is this get{}
//Everytime I access the instance of this class this get would be called
get{
return this;
}
public string AnyProperty {get; set;}
}
public class AnotherClass()
{
public void AccessElement()
{
Element element = new Element();
element.AnyProperty = "";
}
}
It seems weird that you can define a class that has a member field that is of that class.
public class Person
{
public string Name { get; set; }
public Person Spouse { get; set; }
}
Now if I call that class:
var jane = new Person();
var jim = new Person();
jane.Spouse = jim;
jim.Spouse.Spouse = jane;
The last line causes an error. But I'm having a bit of trouble imaging what what the jim.Spouse.Spouse call is doing. It should evaluate jim.spouse first which is null so it causes an error right? If I assert jim.Spouse = jane first then it should work? But then I'm essentially saying jane.spouse = jane.
If a class has a field of the same type then what is it doing to the class? Is it just allowing two instances of the class to have a relationship? The class references itself so it's inheriting from itself? I'm kinda confused and also wondering if this is bad practice.
You've asked several things here, but in general it's fine to have a reference to the same type (even the same instance) on an object.
public class Thing {
private string name;
public Thing(string name) {
this.name = name;
}
public Thing Other {
get;
set;
}
public override string ToString() {
return this.name;
}
}
var o = new Thing("Foo");
o.Other = o;
Debug.WriteLine(o.Other.Other.Other.Other.ToString()); // Could go on forever
You're correct in your assertion about the exception. It throws because jim.Spouse is a null reference, so you can't set a property on it.
If you set jim.Spouse = jane;, then you should be able to set a reference. In this case you would want to say jim.Spouse.Spouse = jim;, since jim.Spouse evaluates to jane.
Regarding the fields of the same type, it's no different to anything else. It's just a variable with a type that the class uses. It is not an uncommon pattern for a type to have a reference to something else of the same type. For example, an Employee class might have a reference to a Manager, who is also an Employee. Another common example is tree implementations, in a binary tree a Node will have a reference to a Left/Right Child node.
I have requirement in a custom class where I want to make one of my properties required.
How can I make the following property required?
public string DocumentType
{
get
{
return _documentType;
}
set
{
_documentType = value;
}
}
If you mean "the user must specify a value", then force it via the constructor:
public YourType(string documentType) {
DocumentType = documentType; // TODO validation; can it be null? blank?
}
public string DocumentType {get;private set;}
Now you can't create an instance without specifying the document type, and it can't be removed after that time. You could also allow the set but validate:
public YourType(string documentType) {
DocumentType = documentType;
}
private string documentType;
public string DocumentType {
get { return documentType; }
set {
// TODO: validate
documentType = value;
}
}
.NET 7 or newer
Syntax
public class MyClass
{
public required string Name { get; init; }
}
new MyClass(); // illegal
new MyClass { Name = "Me" }; // works fine
Remarks
The required properties must declare a setter (either init or set).
Access modifiers on properties or setters cannot be less visible than their containing type, as they would make impossible to initialize the class in some cases.
public class MyClass
{
internal required string Name { get; set; } // illegal
}
Documentation
Official documentation here
Feature demo here
.NET 6 or older
See this answer
If you mean you want it always to have been given a value by the client code, then your best bet is to require it as a parameter in the constructor:
class SomeClass
{
private string _documentType;
public string DocumentType
{
get
{
return _documentType;
}
set
{
_documentType = value;
}
}
public SomeClass(string documentType)
{
DocumentType = documentType;
}
}
You can do your validation – if you need it – either in the property's set accessor body or in the constructor.
With the release of .NET 7 and C# 11 in November 2022 you can now use the required modifier this way:
public class Person
{
public Person() { }
[SetsRequiredMembers]
public Person(string firstName) => FirstName = firstName;
public required string FirstName { get; init; }
public int Age { get; set; }
}
And when you don't have the required properties it will throw an error when you try to initialize an object.
For more information refer to:
https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-11#required-members
https://learn.microsoft.com/en-us/dotnet/csharp/properties#init-only
Add a required attribute to the property
Required(ErrorMessage = "DocumentTypeis required.")]
public string DocumentType
{
get
{
return _documentType;
}
set
{
_documentType = value;
}
}
For custom attribute detail Click Here
I used an other solution, not exactly what you want, but worked for me fine because I declare the object first and based on specific situation I have different values. I didnt want to use the constructor because I then had to use dummy data.
My solution was to create Private Sets on the class (public get) and you can only set the values on the object by methods. For example:
public void SetObject(string mandatory, string mandatory2, string optional = "", string optional2 = "")
This one liner works in C# 9:
public record Document(string DocumentType);
new Document(); // compiler error
new Document("csv"); // correct way to construct with required parameter
This explains how it works. In the above code, Document is the name of the class or "record". That first line of code actually defines an entire class. In addition to this solution essentially making a required DocumentType property (required by an auto implemented constructor), because it uses records, there are additional implications. So this may not always be an appropriate solution, and the C# 11 required keyword will still come in handy at times. Just using record types doesn't automatically make properties required. The above code is a special syntax way of using records that essentially has this effect as well as making the property init only and causes a deconstructor to be automatically implemented.
A better example would be using an int property instead of a string since a string could still be empty. Unfortunately I don't know of any good way to do extra validation within the record to make sure the string is not empty or an int is in range, etc. You would have to go deeper down the TOP (type driven development) rabbit hole, which may not be a bad thing. You could create your own type that doesn't allow empty strings or integers outside your accepted range. Unfortunately such an approach would lead to runtime discovery of invalid input instead of compile time. There might be a better way using static analysis and metadata, but I've been away from C# for too long to know anything about that.
I am working on a CSharp code where in constructor i need to access properties of that class. Logically it looks troublesome to me since i will be accessing properties of the object that hasn't is still under construction.
Its an old code using c# version 4.0 and i am kind of refactoring it so that's why can't redesign everything from scratch.
Thanks
class employee
{
employee()
{
int square = count * count;
}
private int count {get;set;}
}
There is nothing wrong with that, except that count will always be 0.
There is (almost) no such thing as a "partially-constructed" object in .Net, except for an object that hasn't set all of its state in the constructor.
If you're constructing the class, and none of the properties have been set previously in the constructor and none of the properties are static and set elsewhere, the values will be default or null, so there's no point getting what they contain. Otherwise, the constructor is the perfect place to set your properties to something.
At construction time you may set a property, but unless it has a static member backing the getting or is a value type, you will get a null value until you set it.
public class WhatClass
{
public WhatClass()
{
int theCount = Count; // This will set theCount to 0 because int is a value type
AProperty = new SomeOtherClass; // This is fine because the setter is totally usable
SomeOtherClass thisProperty = AProperty; // This is completely acceptable because you just gave AProperty a value;
thisProperty = AnotherProperty; // Sets thisProperty to null because you didn't first set the "AnotherProperty" to have a value
}
public int Count { get; set; }
public SomeOtherClass AProperty { get; set; }
public SomeOtherClass AnotherProperty { get; set; }
}
Yes, C# allow this, but sometime better to have private field which is wrapped by public property and in class method work only with field. In your case I would recommend to remove private property and use class field variable instead. If consumers of your class potentially may want to access a property - make it public with a private setter, this kind of autmatic property is an other alternative for privatr field wrapped by a property.
hey i am trying to work with a generic list in C# and for some reason after allocating memory for the list i am getting unhandeledNullException.
//edit
i found out what was my problem i did not use the properties currectly.
if lets say GeoInfo is a private member of my class, how do i do properties to it,
i tried :
private List<GeoInfo> GEOINFOS { get; set; } // edit i forgot to change it back
// but i want to have my geoinfos private and my properties public
thanks in advance for your help
You've made the properties private. If you want them to be public try:
public List<GeoInfo> GeoInfos { get; set; }
The auto-implemented value that is stored locally in the object will be private; but the properties themselves are public.
Because what you are declaring there are the property accessors.
If you want to write everything explicitly, you could do it the old pre 3.0 way
private List<GeoInfo> geoInfos = new List<GeoInfo>;
public List<GeoInfo> GeoInfos {
get { return geoInfos; }
set { geoInfos = value; }
}
This still relies on geoInfos being initialized somewhere (like the constructor) -- or nullPointerException will return.
You could do lazy-evaluation on it right in the getter:
private List<GeoInfo> geoInfos = new List<GeoInfo>;
public List<GeoInfo> GeoInfos {
get { if (geoInfos == null) {
geoInfos = new List<GeoInfo>;
}
return geoInfos;
}
set { geoInfos = value; }
}
This ensures that you don't have to specify a call in the constructor, and you don't have to worry about the execution sequence setting the element explicitly prior to getting it.
But if you use the auto-generated-properties, you will have to explicitly set the reference at some point. AS suggested elsewhere, the best bet is the constructor.
If you want a property to be private, use
private List<GeoInfo> GEOINFOS { get; set; }
However, there's not a lot of reason to use an auto property for a private member variable (and don't forget to initialize that list as well). If you want validation fine, but you're just using that property as a private variable.
Your null reference issue probably comes from not initializing the underlying property variable. That does not get done automatically, so
public MyClass()
{
GEOINFOS = new List<GeoInfo>();
}
One more thing: your naming convension for a property is odd for C#. How about keeping things consistent and sing GeoInfos?