I am trying to make a property in my class. What would I need to do where once the property is initialized, it cannot be changed?
These are the actual instructions:
Create a class in the existing namespace, either in an existing code
file or in a new file, to represent the amount in pounds of dirt
sample. In this class (a) do not create constructors. (b) inherit the
sand class (to make use of the sand property). (c) add a property to
represent the sample name. This property may not be changed once
initialized. (d) add a property to represent and process assignments
the quantity of clay, with a minimum value of 0. (e) add methods to
return the weight of the sample, the percentage of sand in the sample
and the percentage of clay in the sample.
I am on part (c). I have tried to exclude setters. Then, I've tried to use readonly, but it cannot work because my class cannot have constructors.
public class AmountSand //parent class
{
public class AmountSand {
private double quantity;
public double Sand {
get {
return quantity;
}
set {
if (value >= 0) quantity = value;
}
}
}
public class AmountDirt: AmountSand { //part (b): inherited the parent class, AmountSand
private string name = null;
private double clay;
public string Name { //here is where the specific property starts
get {
return name;
}
set {
if (name == null)
name = value;
}
} //ends
public double Clay {
get {
return clay;
}
set {
if (value >= 0) clay = value;
}
}
Depends on from where you would like it to be initialized.
EDIT: sorry, i didn't read that your class could have ctors, but i'll keep this in for completeness. It seems kinda weird that your class can't have ctors. May I ask why?
From the ctor:
class MyClass
{
public MyClass()
{
Name = "Muhammed";
}
public MyClass(string newName)
{
Name = newName;
}
public string Name{get;}
}
If you'd like it to be initialized from outside the class, your code is not too far off. You could even remove the backing property. I'd use
if(string.IsNullOrEmpty(Name))
rather than comparing to null.
if you'd like it to be set from a method inside your class:
public string Name{get; private set;}
Strings are already immutable by nature, so you need to clarify what you're trying to accomplish.
However, if you simply don't want anything else to be able to set the value other than the class itself, then you can make the set accessor private.
I am asking a beginner level question. Though I am working in MVC but I am really confused with a simple concept and that is "Properties". There are lot of questions that
I have already gone through but there is surely a doubt in mind and did'nt able to clear it up.
Actually c# properties used for getting and setting the value to the private fields.
Like
Public class MyClass
{
private int number;
public int Number{
get{ return this.number;}
set{ number=Value }
}
}
class Program
{
static void Main()
{
MyClass example = new MyClass();
example.Number = 5; // set { }
Console.WriteLine(example.Number); // get { }
}
}
Now , the value is assigned to property also and to the variable also. Right?
Now , here is my doubt::
When we create property in model for MVc structure, we only have
public int Number{get;set;}
If this is okay to work with then why we are creating unnecessorily one more field of private access specifier. If encapsulation is the reason for that or hiding the data then why not in model in MVC?
Actually, in the above class example can I only use
Console.WriteLine(example.number);
after declaring it public?
Then what's the use of creating property over here?
Properties can be used to a store and retrieve values from a backing field (number in your case) directly as in your first sample. But property getters and setters are ordinary blocks of code that you can use as you want. So you don't have to assign a backing field, but can derive the value of a property also from another property in a getter, e.g.
public int NumberTimesTwo
{
get
{
return Number * 2;
}
}
However, as a common scenario is to have a property retrieve and assign the value of a backing field, there is a shortcut that you can use:
public int Number { get; set; }
In this case, the compiler automatically creates a private backing field that the property retrieves in the getter and assigns in the setter, so the code is equivalent to the following, but less to type:
private int _number;
public into Number
{
get
{
return _number;
}
set
{
_number = value;
}
}
As the backing field is also private, you cannot access it from outside of the class directly.
private int myVar;
public int MyProperty
{
get { return myVar; }
set { myVar = value; }
}
You are implementing Encapsulation by using MyProperty, which is public to access myVar which is private and is accessible only in the block where defined, that is, your class and not outside it.
Btw, in what way does this QA not answer your question? Try going through this for further reference.
What is the difference, if any, between
public int x;
and
public int x { get; set; }
?
The first one is called a field. The second one is a property, in this case an auto-implemented property.
Properties act like fields but use a getter and a setter function to retrive and set the value. Another way of writing the above property is as follows:
private int _x;
public int X
{
get
{
return _x;
}
set
{
_x = value;
}
}
The variable _x in this case is called a backing field. With an auto-implemented property you can't access the backing field or customize code in the getter/setter, but if you don't need to than it's shorter and more succinct.
As a rule in C# most of the time any public member should be exposed as a property instead of a field.
The difference between thise two is that a property can do something more than just get / set a variable.
take this example:
private int _x;
public int x
{
get
{
//do something
return _x;
}
set
{
if(_x != value)
PropertyChanged("x");
_X = value;
}
}
when we set the property - we notify something ( PropertyChanged()) that the value has changed. It would be very hard to do with just the field
The first one is public variable which can be accessed from anywhere.
The second one is public property
Check Properties tutorial for details.
Properties have many uses: they can validate data before allowing a
change; they can transparently expose data on a class where that data
is actually retrieved from some other source, such as a database; they
can take an action when data is changed, such as raising an event, or
changing the value of other fields.
Do I need to declare a class-level variable to hold a property, or can I just refer to self.{propertyname} in the getter/setter?
In other words, can I do this? (where I haven't defined mongoFormId anywhere):
public string mongoFormId
{
get
{
return this.mongoFormId;
}
set
{
this.mongoFormId = value;
revalidateTransformation();
}
}
You can either use automatic accessors or implement your own. If you use automatic accessors, the C# compiler will generate a backing field for you, but if you implement your own you must manually provide a backing field (or handle the value some other way).
private string _mongoFormId;
public string mongoFormId
{
get { return this._mongoFormId; }
set
{
this._mongoFormId = value;
revalidateTransformation();
}
}
UPDATE: Since this question was asked, C# 6.0 has been released. However, even with the new syntax options, there is still no way to provide a custom setter body without the need to explicitly declare a backing field.
You need to set a field variable and store the value there, if you're going to use custom getter and setter.
With the code you have right now you will be running into a stack overflow exception. When you assign something to mongoFormId, you'll execute the line this.MongoFormId = value;. This is an assignment to mongoFormId, resulting in executing the line this.MongoFormId = value;, and so on. It won't ever stop.
The correct way is a field:
private string _mongoFormId;
public string mongoFormId {
get { return this._mongoFormId; }
set {
this._mongoFormId = value;
revalidateTransformation();
}
}
You should have a backing variable. Take a closer look:
get { return this.mongoFormId; }
Is going to call the getter on mongoFormId, which will call that code again, and again, and again! Defining a backing variable will avoid the infinite recursive call.
Check MSDN Properties Overview
While a property definition generally includes a private data member,
this is not required. The get accessor could return a value without
accessing a private data member. One example is a property whose get
method returns the system time. Properties enable data hiding, the
accessor methods hide the implementation of the property.
You can do it both the ways.
If you want to have a class level member variable then do it this way -
public class sampleClass
{
private string _mongoFormId;
public string mongoFormId {
get { return _mongoFormId; }
set {
_mongoFormId = value;
revalidateTransformation();
}
}
}
Or do this simple in class, if no need for revalidateTransformation() execution call there
public class sampleClass
{
public string mongoFormId {get; set;}
}
This won't work since you get a recursive call to the property.
If I'm not mistaken, the result will be a StackOverflowException.
You must use a variable.
private string mongoFormId;
public string MongoFormId
{
get
{
return this.mongoFormId;
}
set
{
this.mongoFormId = value;
revalidateTransformation();
}
}
If you don't have to execute revalidateTransformation, you can use the auto-property.
This will create a backingfiled for you behind the scene.
public string MongoFormId { get; set; }
With the code you wrote, you are creating a recursive endless loop on both the get and set. The this keyword refer to the current class, not the property you are in.
So yes, you need to declare a private field. And to avoid confusion, create properties following the MSDN Naming Guideline (Use Pascal case for properties, camel case for private fields). And please do the same for your methods, it should be RevalidateTransformation instead of revalidateTransformation if you follow the C# convention instead of java's.
private string mongoFormId;
public string MongoFormId
{
get
{
return mongoFormId;
}
set
{
mongoFormId = value;
RevalidateTransformation();
}
}
public string mongoFormId {
get {
return this.mongoFormId;
}
set {
this.mongoFormId = value;
revalidateTransformation();
}
}
this way you have the Function recursive on all paths
The only way i see is to use a private data member. As other boys tells.
I am learning ASP.NET MVC and I can read English documents, but I don't really understand what is happening in this code:
public class Genre
{
public string Name { get; set; }
}
What does this mean: { get; set; }?
It's a so-called auto property, and is essentially a shorthand for the following (similar code will be generated by the compiler):
private string name;
public string Name
{
get
{
return this.name;
}
set
{
this.name = value;
}
}
So as I understand it { get; set; } is an "auto property" which just like #Klaus and #Brandon said is shorthand for writing a property with a "backing field." So in this case:
public class Genre
{
private string name; // This is the backing field
public string Name // This is your property
{
get => name;
set => name = value;
}
}
However if you're like me - about an hour or so ago - you don't really understand what properties and accessors are, and you don't have the best understanding of some basic terminologies either. MSDN is a great tool for learning stuff like this but it's not always easy to understand for beginners. So I'm gonna try to explain this more in-depth here.
get and set are accessors, meaning they're able to access data and info in private fields (usually from a backing field) and usually do so from public properties (as you can see in the above example).
There's no denying that the above statement is pretty confusing, so let's go into some examples. Let's say this code is referring to genres of music. So within the class Genre, we're going to want different genres of music. Let's say we want to have 3 genres: Hip Hop, Rock, and Country. To do this we would use the name of the Class to create new instances of that class.
Genre g1 = new Genre(); //Here we're creating a new instance of the class "Genre"
//called g1. We'll create as many as we need (3)
Genre g2 = new Genre();
Genre g3 = new Genre();
//Note the () following new Genre. I believe that's essential since we're creating a
//new instance of a class (Like I said, I'm a beginner so I can't tell you exactly why
//it's there but I do know it's essential)
Now that we've created the instances of the Genre class we can set the genre names using the 'Name' property that was set way up above.
public string Name //Again, this is the 'Name' property
{ get; set; } //And this is the shorthand version the process we're doing right now
We can set the name of 'g1' to Hip Hop by writing the following
g1.Name = "Hip Hop";
What's happening here is sort of complex. Like I said before, get and set access information from private fields that you otherwise wouldn't be able to access. get can only read information from that private field and return it. set can only write information in that private field. But by having a property with both get and set we're able do both of those functions. And by writing g1.Name = "Hip Hop"; we are specifically using the set function from our Name property
set uses an implicit variable called value. Basically what this means is any time you see "value" within set, it's referring to a variable; the "value" variable. When we write g1.Name = we're using the = to pass in the value variable which in this case is "Hip Hop". So you can essentially think of it like this:
public class g1 //We've created an instance of the Genre Class called "g1"
{
private string name;
public string Name
{
get => name;
set => name = "Hip Hop"; //instead of 'value', "Hip Hop" is written because
//'value' in 'g1' was set to "Hip Hop" by previously
//writing 'g1.Name = "Hip Hop"'
}
}
It's Important to note that the above example isn't actually written in the code. It's more of a hypothetical code that represents what's going on in the background.
So now that we've set the Name of the g1 instance of Genre, I believe we can get the name by writing
console.WriteLine (g1.Name); //This uses the 'get' function from our 'Name' Property
//and returns the field 'name' which we just set to
//"Hip Hop"
and if we ran this we would get "Hip Hop" in our console.
So for the purpose of this explanation I'll complete the example with outputs as well
using System;
public class Genre
{
public string Name { get; set; }
}
public class MainClass
{
public static void Main()
{
Genre g1 = new Genre();
Genre g2 = new Genre();
Genre g3 = new Genre();
g1.Name = "Hip Hop";
g2.Name = "Rock";
g3.Name = "Country";
Console.WriteLine ("Genres: {0}, {1}, {2}", g1.Name, g2.Name, g3.Name);
}
}
Output:
"Genres: Hip Hop, Rock, Country"
Those are automatic properties
Basically another way of writing a property with a backing field.
public class Genre
{
private string _name;
public string Name
{
get => _name;
set => _name = value;
}
}
It is a shortcut to expose data members as public so that you don't need to explicitly create a private data members. C# will creates a private data member for you.
You could just make your data members public without using this shortcut but then if you decided to change the implementation of the data member to have some logic then you would need to break the interface. So in short it is a shortcut to create more flexible code.
This is the short way of doing this:
public class Genre
{
private string _name;
public string Name
{
get => _name;
set => _name = value;
}
}
Basically, it's a shortcut of:
class Genre{
private string genre;
public string getGenre() {
return this.genre;
}
public void setGenre(string theGenre) {
this.genre = theGenre;
}
}
//In Main method
genre g1 = new Genre();
g1.setGenre("Female");
g1.getGenre(); //Female
Basically it helps to protect your data. Consider this example without setters and getter and the same one with them.
Without setters and getters
Class Student
using System;
using System.Collections.Generic;
using System.Text;
namespace MyFirstProject
{
class Student
{
public string name;
public string gender;
public Student(string cName, string cGender)
{
name = cName;
gender= cGender;
}
}
}
In Main
Student s = new Student("Some name", "Superman"); //Gender is superman, It works but it is meaningless
Console.WriteLine(s.Gender);
With setters and getters
using System;
using System.Collections.Generic;
using System.Text;
namespace MyFirstProject
{
class Student
{
public string name;
private string gender;
public Student(string cName, string cGender)
{
name = cName;
Gender = cGender;
}
public string Gender
{
get { return gender; }
set
{
if (value == "Male" || value == "Female" || value == "Other")
{
gender = value;
}
else
{
throw new ArgumentException("Invalid value supplied");
}
}
}
}
}
In Main:
Student s = new Student("somename", "Other"); // Here you can set only those three values otherwise it throws ArgumentException.
Console.WriteLine(s.Gender);
Its an auto-implemented property for C#.
The get/set pattern provides a structure that allows logic to be added during the setting ('set') or retrieval ('get') of a property instance of an instantiated class, which can be useful when some instantiation logic is required for the property.
A property can have a 'get' accessor only, which is done in order to make that property read-only
When implementing a get/set pattern, an intermediate variable is used as a container into which a value can be placed and a value extracted. The intermediate variable is usually prefixed with an underscore.
this intermediate variable is private in order to ensure that it can only be accessed via its get/set calls. See the answer from Brandon, as his answer demonstrates the most commonly used syntax conventions for implementing get/set.
They are the accessors for the public property Name.
You would use them to get/set the value of that property in an instance of Genre.
That is an Auto-Implemented Property. It's basically a shorthand way of creating properties for a class in C#, without having to define private variables for them. They are normally used when no extra logic is required when getting or setting the value of a variable.
You can read more on MSDN's Auto-Implemented Properties Programming Guide.
This mean that if you create a variable of type Genre, you will be able to access the variable as a property
Genre oG = new Genre();
oG.Name = "Test";
In the Visual Studio, if you define a property X in a class and you want to use this class only as a type, after building your project you will get a warning that says "Field X is never assigned to, and will always has its default value".
By adding a { get; set; } to X property, you will not get this warning.
In addition in Visual Studio 2013 and upper versions, by adding { get; set; } you are able to see all references to that property.
Its basically a shorthand. You can write public string Name { get; set; } like in many examples, but you can also write it:
private string _name;
public string Name
{
get { return _name; }
set { _name = value ; } // value is a special keyword here
}
Why it is used? It can be used to filter access to a property, for example you don't want names to include numbers.
Let me give you an example:
private class Person {
private int _age; // Person._age = 25; will throw an error
public int Age{
get { return _age; } // example: Console.WriteLine(Person.Age);
set {
if ( value >= 0) {
_age = value; } // valid example: Person.Age = 25;
}
}
}
Officially its called Auto-Implemented Properties and its good habit to read the (programming guide).
I would also recommend tutorial video C# Properties: Why use "get" and "set".
Such { get; set; } syntax is called automatic properties, C# 3.0 syntax
You must use Visual C# 2008 / csc v3.5 or above to compile.
But you can compile output that targets as low as .NET Framework 2.0 (no runtime or classes required to support this feature).
Get set are access modifiers to property.
Get reads the property field.
Set sets the property value.
Get is like Read-only access.
Set is like Write-only access.
To use the property as read write both get and set must be used.
Get is invoked when the property appears on the right-hand side (RHS)
Set is invoked when the property appears on the left-hand side (LHS)
of '=' symbol
For an auto-implemented property, the backing field works behind the scene and not visible.
Example:
public string Log { get; set; }
Whereas for a non auto-implemented property the backing field is upfront, visible as a private scoped variable.
Example:
private string log;
public string Log
{
get => log;
set => log = value;
}
Also, it is worth noted here is the 'getter' and 'setter' can use the different 'backing field'
A property is a like a layer that separates the private variable from other members of a class. From outside world it feels like a property is just a field, a property can be accessed using .Property
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string FullName => $"{FirstName} {LastName}";
}
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string FullName { get { return $"{FirstName} {LastName}"; } }
}
FullName is a Property. The one with arrow is a shortcut. From outside world, we can access FullName like this:
var person = new Person();
Console.WriteLine(person.FullName);
Callers do not care about how you implemented the FullName. But inside the class you can change FullName whatever you want.
Check out Microsoft Documentation for more detailed explanation:
https://learn.microsoft.com/en-us/dotnet/csharp/properties
Define the Private variables
Inside the Constructor and load the data
I have created Constant and load the data from constant to Selected List class.
public class GridModel
{
private IEnumerable<SelectList> selectList;
private IEnumerable<SelectList> Roles;
public GridModel()
{
selectList = from PageSizes e in Enum.GetValues(typeof(PageSizes))
select( new SelectList()
{
Id = (int)e,
Name = e.ToString()
});
Roles= from Userroles e in Enum.GetValues(typeof(Userroles))
select (new SelectList()
{
Id = (int)e,
Name = e.ToString()
});
}
public IEnumerable<SelectList> Pagesizelist { get { return this.selectList; } set { this.selectList = value; } }
public IEnumerable<SelectList> RoleList { get { return this.Roles; } set { this.Roles = value; } }
public IEnumerable<SelectList> StatusList { get; set; }
}
Properties are functions that are used to encapsulate data, and allow additional code to be executed every time a value is retrieved or modified.
C# unlike C++, VB.Net or Objective-C doesn’t have a single keyword for declaring properties, instead it uses two keywords (get/set) to give a much abbreviated syntax for declaring the functions.
But it is quite common to have properties, not because you want to run additional code when data is retrieved or modified, but because either you MIGHT want to do so in the future or there is a contract saying this value has to be a exposed as a property (C# does not allow exposing data as fields via interfaces). Which means that even the abbreviated syntax for the functions is more verbose than needed. Realizing this, the language designers decided to shorten the syntax even further for this typical use case, and added “auto” properties that don’t require anything more than the bare minimum, to wit, the enclosing braces, and either of the two keywords (separated by a semicolon when using both).
In VB.Net, the syntax for these “auto” properties is the same length as in c# —- Property X as String vs string X {get; set;}, 20 characters in both cases. It achieves such succinctness because it actually requires 3 keyword under the normal case, and in the case of auto properties can do without 2 of them.
Removing any more from either, and either a new keyword would have had to be added, or significance attached to symbols or white space.