I'm trying to do this:
public string LangofUser
{
get
{
return string.IsNullOrEmpty("how to get value?") ? "English" : "how to get value?";
}
set;
}
do I have to do this?
string _LangofUser
public string LangofUser
{
get
{
return string.IsNullOrEmpty(_LangofUser) ? "English" : _LangofUser;
}
set { _LangofUser = value};
}
This mixing of auto-implement and not-auto-implemented properties in C# is not possible. A property must be fully auto-implemented or a normal property.
Note: Even with a fully auto-implemented property there is no way to reference the backing field from C# source in a strongly typed manner. It is possible via reflection but that's depending on implementation details of the compiler.
As others have said, don't try to mix automatic and regular properties. Just write a regular property.
If you want to know what secret names we generate behind the scenes for hidden compiler magic, see
Where to learn about VS debugger 'magic names'
but do not rely on that; it can change at any time at our whim.
If you provide your own implementation of the property, it's not automatic any more. So yes, you need to do create the instance.
Check this question
What's the difference between encapsulating a private member as a property and defining a property without a private member?
If you want to keep the automatic property and still have a default value, why don't you initialize it in your constructor?
public class MyClass
{
public MyClass() { LangOfUser = "English"; }
public string LangOfUser { get; set; }
}
Since C# 6, you can also set a default value for a property as follows:
public class MyClass
{
public string LangOfUser { get; set; } = "English";
}
Related
Note: I know how to accomplish this without using auto-implemented properties, but I'm wondering if C# has a built-in way to do this.
Let's say I have this simple example of an auto-implemented property (a.k.a. auto backing field):
public class MyClass
{
public MyClass(){}
public string MyString { get; private set; }
}
Now, I would like to return a custom exception in the getter if the auto backing field is null:
public class MyClass
{
public MyClass(){}
public string MyString
{
get
{
return [backing field] ?? throw new Exception("MyString is null");
}
private set;
} = null;
}
Do newer C# versions support something like this? Perhaps there is some syntactic sugar that I can use in place of [backing field] to access the backing field that is automatically created by the compiler?
Note on putting an exception in the getter: I know it shouldn't be a habit. But Microsoft does it occasionally; for example, the property HttpContext.Request.Form will throw an exception if the request is not of the proper content-type.
No, you can not access to backing field in this way.
You must define backing field and validate it.
public class MyClass
{
public MyClass(){}
private string? _myString
public string MyString
{
get
{
return _myString ?? throw new Exception("MyString is null");
}
private set => _myString = value;
} = null;
}
As Fred said, its better to validate it outside of property.
I'm surprised noone mentioned the field keyword, it is exactly what you are asking for (what you would use instead of [backing field] in your example). It was supposed to be shipped with C# 10. It seems it is going to be shipped with C# 11 instead (?)
Search for Field Keyword here.
Put validation in the setter and/or ensure that the constructor sets a valid/non-null default value.
Or make the property nullable to hint to the customer that they have to account for a null value possibility.
Alternatively (but less optimally for multiple reasons), make the property private and add a method for accessing it.
Strongly advise against a property get directly throwing an exception. You or the consumer will dislike the results at some point.
In C#, can you use a property without a field?
Edit for clarification:
private string _name;
public string Name
{
get { return _name; }
set { _name value; }
}
It seem's like they are always paired, is there a circumstance where we don't use the field at all?
All properties must have a field, assuming they are simple properties to store a value (*). However, the language (as of version 3.0) offers a way to declare the field implicitly. For example:
public int Value { get; set; }
That would declare a property named Value with an implicit field backing it and the getter and setter both public. You can include an accessibility keyword on either the getter or setter to restrict access to the property. For example:
public int Value { get; private set; }
In this case, only the owning type may call the setter, but any class can call the getter.
The next version of C# will have additional features for dealing with these "automatic properties", allowing you to provide a concise initialization syntax for them. For now, you have to initialize them in a constructor.
EDIT: based on your edited question, it seems worthwhile to address this specific question: "is there a circumstance where we don't use the field at all?"
The answer to that is, it's not common for no field to be involved at all. But it is possible, and it's not uncommon for a property to not use a field as storage for the property. For example, imagine a Rectangle object with an Area property:
class Rectangle
{
public double Width { get; private set; }
public double Height { get; private set; }
public double Area { get { return Width * Height; } }
}
Obviously there are fields involved (two of them), but there is not a field specifically dedicated to the Area property.
Another example would be where the property delegates. For example, in a WinForms Form subclass, it's common to expose specific control values via a property:
class MyForm : Form
{
public string EditText
{
get { return textBox1.Text; }
set { textBox1.Text = value; }
}
}
Again, the textBox1 field is being used here. But it actually represents something other than the property itself. The property is using a member of the object that field references.
I hope that clarifies the relationship between fields and properties adequately for you. Please feel free to ask for further clarifications if needed.
(*) Note that the only real rule for properties is that they have at least one of the getter or setter, and those methods can do whatever you want. I assume we are talking about simple value-based properties here.
A property is not required to have a field
public string Version
{
get
{
return "1.3.Awesome";
}
}
If you're asking what I think you are, the answer is yes, you just put get; set; inside the property declaration. C# encapsulates a variable for you.
EDIT: example
//no need for field declaration
public string Name
{
get;
set;
}
New to C#, and I understand that encapsulation is just a way of "protecting data". But I am still unclear. I thought that the point of get and set accessors were to add tests within those methods to check to see if parameters meet certain criteria, before allowing an external function to get and set anything, like this:
private string myName;
public string MyName;// this is a property, speical to c#, which sets the backing field.
private string myName = "mary";// the backing field.
public string MyName // this is a property, which sets/gets the backing field.
{
get
{
return myName;
}
set
{
if (value != "Silly Woman"){
myName = value;
}
}
}
But I've been seeing code in c# which just looks like this:
public string MyName { get; set; }
Why would you just have a get and set with nothing in there, - isn't that the same as just declaring your private backing field public? If you can just get and set it from outside, why wouldn't you just do it directly?
Indeed, creating an auto-property as follows:
public string Name { get; set; }
is identical to building a property backed by a field:
private string _name;
public string Name {
get { return _name; }
set { _name = value; }
}
The point of these properties is not to hide data. As you observed, they don't do this. Instead, these properties can do other stuff instead of just working with a field:
public string Name {
get { return _name; }
set { if (value == null) throw new Exception("GTFO!"); _name = value; }
}
Another thing is, you can make properties virtual:
public virtual string Name { get; set; }
which, if overridden, can provide different results and behaviours in a derived class.
By using public string MyName { get; set; }, you leave an ability to change its logic later without the need to recompile/change other code that uses your property.
For example, if you are making a library and v1 uses a field and v2 uses a property, applications that work with v1 will not work with v2 without recompilation (and, potentially, code changes if they are written in some .NET language that has different syntax for accessing fields).
Another important difference is in serialization scenarios -- a lot of them do not support fields. Also any interface that requires a property can not be implemented without using one, but depending on interface it may not be required to do any additional checks/logic in it.
It makes it easier to add logic later. If you have a class that has a public field that you want to change to a property, you have to recompile everything that uses your class. That's a key point that I didn't understand initially.
If you have a class:
public class MyClass
{
public string MyString;
}
You could access the value like this:
var myClass = new MyClass();
string s = myClass.MyString;
Now change that to a property:
public class MyClass
{
public string MyString { get; set; }
}
How is it accessed? The exact same way:
var myClass = new MyClass();
string s = myClass.MyString;
So no big deal, right? Well, actually....
Properties are actually compiled into getter and setter methods:
get_MyString() and set_MyString(string value)
So the two methods do produce different compiled code. Now if all your code that uses this class is in the same project, is not as big a deal, because it will all be compiled together. But if you have an API library that you've distributed, it can be a much bigger deal to update.
Because it is easier to change the Code if you want to add the checks/tests later on.
Especially if you have many inheritance and many classes in your code it is very hard to change the implementation from a public variable to a public Property.
Moreover you can add to the get and set within the property different attributes, e.g. if you are using reflection. The get and set of the property are internally different methods. If you have just a public variable /field it is not possible to added different properties to the different access ways.
Yeah, but you can easily change it to:
public string MyName { get; private set; }
Plus, properties are used in other scenarios, like DataContracts and Serialization... so, this is a nice feature... (Mostly, syntactic sugar. I think) EDIT: I take that back.. you can apply virtual to it, so it's not the same
Why are we able to write
public int RetInt
{
get;set;
}
instead of
public int RetInt
{
get{return someInt;}set{someInt=value;}
}
What is the difference between the two?
This feature is called Auto implemented properties and introduced with C# 3.0
In C# 3.0 and later, auto-implemented properties make
property-declaration more concise when no additional logic is required
in the property accessors. They also enable client code to create
objects. When you declare a property as shown in the following
example, the compiler creates a private, anonymous backing field
that can only be accessed through the property's get and set
accessors.
class Customer
{
// Auto-Impl Properties for trivial get and set
public double TotalPurchases { get; set; }
public string Name { get; set; }
public int CustomerID { get; set; }
For your question
What is the difference between the two?
In your case, none. Since you are not doing anything while setting or retrieving the value, but suppose you have want to do some validation or want to perform other types of check then :
private int someInt;
public int RetInt
{
get
{
if (someInt > 0)
return someInt;
else
return -1;
}
set { someInt = value; } // same kind of check /validation can be done here
}
The above can't be done with Auto implemented properties.
One other thing where you can see the difference is when initializing a custom class type property.
If you have list of MyClass
Then in case of Normal property, its backing field can be initialized/instantiated other than the constructor.
private List<MyClass> list = new List<MyClass>();
public List<MyClass> List
{
get { return list; }
set { list = value; }
}
In case of Auto implemented property,
public List<MyClass> SomeOtherList { get; set; }
You can only initialize SomeOtherList in constructor, you can't do that at Field level.
How are these two different ?
There are different at least by 2 points:
In normal property you have to define a field before (someInt in your case)
In normal property you can set a breakpoint into the set/get modifiers, instead in auto property can not do that.
In other words: if you need "just property", use auto-properties, if you need more control over workflow (raise an event on set, debug, run other stuff inside), use "normal" properties.
These are auto implemented properties. Please see http://msdn.microsoft.com/en-us/library/bb384054.aspx for more info.
Basic reason why these were introduced was to reduce the overhead of programmer of creating a private variable like someInt which had little use than being used in a property.
Actually these aren't really different, in both cases you have a private field that corresponds to your property, but in the first case it is generated by the compiler and hidden.
If you need to use the variable behind the property quite often in your class, I think it's better to declare your property the old way (2nd one), because each time you will access it this will call the getter if you do it the "new" way.
If you only need it to be used from outside your class (or in most of cases), then you can go with the "new" way (1st one)
In C# do properties need to reference private member variables, or can I just declare the properties and use them directly in the class code?
If the former is the best practice, then does that rule out using C# property short-hand? I.e.
public string FirstName { get; set; }
Properties, when implemented like this:
public string FirstName { get; set; }
Automatically create a private member variable (the compiler does this for you), so you don't have to worry about it. This will behave exactly the same as if you do:
private string firstName;
public string FirstName {
get { return firstName; }
set { firstName = value; }
}
There is no reason not to use the automatic properties ( { get; set; } ). The provide the same advantages as making your own private member variable.
In addition, if you later decide you need to do extra processing (for example, if you decide to implement INotifyPropertyChanged in your property setter), you can add this without changing your public API, but putting a backing field in manually.
You don't need properties to access private fields but in general it is considered best practice.
And you can use auto-properties (short hand) untill you need to add more functionality to a property, like validation. Changing it to a 'real' property is always a non-breaking change.
Properties created like this
public String Caption{ get; set; }
this will be compiled as
[CompilerGenerated]
private string <Caption>k__BackingField;
public string Caption
{
[CompilerGenerated]
get
{
return this.<Caption>k__BackingField;
}
[CompilerGenerated]
set
{
this.<Caption>k__BackingField = value;
}
}
The above code is extracted after compilation using reflector tool.
They do not need to reference private member variables. You can use them directly in the class.
Properties do not need to reference private member variables. It is best practice, though, to have them do so. You can think of properties as methods if it makes it easier to understand. You can run code inside of them. You can return whatever you want. You can call methods and use private member variables. You can even simply return a constant.
I use private member variables in almost all cases. It allows me to create a readonly property, or to provide some rules to those outside my class of getting or setting properties that my class doesn't have to follow.
To add on to Reed's answer, inside of your code (within the class itself) the member functions should adhere to this and actually use the Property rather then the actual private member. For instance if you had this:
public string FirstName { get; set; }
And you had a strange method called public char GetFirstLetter() that returned the first letter in a person's first name you'd want to do it like this:
public char GetFirstLetter()
{
return FirstName[0];
}
Instead of actually using your private variable. When you set a property a programmer may have written code to set it in a particular manner. So it only makes sense to simply use that property within your class methods.
C# can reference private variables as in:
public class A
{
private string _b;
public string B
{
get { return _b; }
set { _b = value; }
}
}
The get;set; designation is automatic properties which when compiled will generate the private variable for you, as a way to make it easy to setup your code.
Using properties is the best way to provide a method of control and security to the attributes in a class, always keep the attributes private if possible.
if you use like
public string FirstName { get; set; }
compiler will automatically adds getters and setters for this property automatically.it not a bad practice.
Here is the proof
if you declare
private string firstName;
public string FirstName
{
get { return firstName; }
set { firstName = value; }
}
like this also compiler will takes it as
so its not ruled out... :)