Assume i have a class:
public class Products
{
public string ID { get; set; }
public string Name { get; set; }
public string GetItemName() { ... }
public void SetItemName() { ... }
public string GetItemID() { ... }
public void SetItemID() { ... }
//...
}
It is any way to make all the properties or method inherits the parent class's access modifiers,so i don't have to assign [public] to each of properties/method.
public string Name { get; set; }
public string GetItemName() { ... }
public void SetItemName() { ... }
That's not C# code, that's C++. A language that doesn't support properties, but does support this:
public:
string GetItemName();
void SetItemName();
Which is probably what you are really asking for. No, never make the mistake of comparing C# to C++, it resembles the language only in passing. The accessor keyword must be applied to every member. Good thing is, you'll have a lot less of them. Delete the GetItemName and SetItemName methods, the Name property is all you need.
Here's an old magazine article that might be useful to you, "C++ -> C#: What You Need to Know to Move from C++ to C#"
There is no way to do this with class. It's how C# syntax is defined. If you skip access modifier then the default value is applied, for classes it would be internal modifier and for their members private.
Other default values according to specification are:
Interfaces, like classes, can be declared as public or internal types. Unlike classes, interfaces default to internal access. Interface members are always public, and no access modifiers can be applied.
Namespaces and enumeration members are always public, and no access modifiers can be applied.
Delegates have internal access by default.
Any types declared within a namespace or at the top level of a compilation unit (for example, not within a namespace, class, or struct) are internal by default, but can be made public.
No, the language specs say that if you don't specify the access modifier, a default one will be used:
Members in classes and structs are private by default.
Types (classes, structs, delegates, interfaces and enums) are internal by default, unless they are placed within another type (nested classes) when they default to private..
Interface members, enum members and namespaces have no concept of accessibility modifiers, but can be thought of as always being public.
Related
Interface:
interface IMyInterface{
internal int Property {get; set;}
}
Class:
public class MyClass: IMyInterface{
internal int Property {get; set;}
}
Result:
CS8704 Error: MyClass doesnot implement interface member Property.get MyClass cannot implicitly implement a non-public member.
Why I have to implement the interface explicitly?
The simple answer to "why is a language like this" is "because that's how the language designers specified it".
Now, why did they design it that way? Some of the official notes I found were these. It seems the main question was about what kind of access the implementor must have:
Would we allow non-public interface members to be implemented implicitly? If so, what is required of the accessibility of the implementing method? Some options:
Must be public
Must be the exact same accessibility
Must be at least as accessible
They decided:
For now, let's simply not allow it. Only public interface members can be implicitly implemented (and only by public members).
The "for now" never changed, so as of C# 8 an interface can have non-public virtual members but a class may only implement them explicitly.
I can speculate on a couple of reasons they may have decided against implicit overrides like this:
Non-public virtual methods in interfaces may have been considered a "rare" feature (after all, aren't interfaces supposed to document the public behavior of a class?), not worth putting a lot of resources into in terms of the semantics of implicit overrides.
Unlike with method overridding in class-to-class inheritance, an class method implementing an interface method doesn't use the override keyword. It might have been considered confusing to see a protected and/or internal method and not realize that it's fulfilling an interface contract. (Public methods are presumably considered exempt from this concern because that's the way they've always worked, and public methods are part of the class' public contract anyway so modifying / removing them would already be cause the reader to think about other parts of code that depend on it.)
Interfaces can only override other interface methods explicitly, possibly again because allowing interface-to-interface implicit implementation would be too expensive for the compiler and tooling teams and too confusing for C# users. (Especially since interface-to-interface inheritance is multiple-inheritance.) Since both this and non-public interface methods were introduced in general in C# 8, it may have made sense to make the two features match syntactically.
See also the notes on this question in the default interface method proposal.
Interface members don't have scopes like public or internal. What you have here is a default interface implementation.
So you need to remove the scope on the interface:
interface IMyInterface{
int Property {get; set;}
}
The internal property forces the implementation to be explicit such that the internal members of the interfaces will remain internal to the assembly.
It helps you to keep implementations internal (to an assembly) so that you can update code without breaking changes e.g. renaming the property.
interface IMyInterface
{
internal int Property { get; set; }
}
public class MyClass : IMyInterface
{
int IMyInterface.Property { get; set; }
}
by default is a class:
private ?
internal ?
sealed ?
The default for non-nested types is internal.
The default for nested types is private.
In both cases the default (for classes) is unsealed.
The general rule for all members is that if you don't specify an access modifier, it's as private as it can be. The single exception for this is properties which can make one part (i.e. the getter or the setter) more private than the overall property by specifying an access modifier, e.g.
public string Foo { get; private set; }
internal
see:
http://msdn.microsoft.com/en-us/library/ms173121.aspx
Also, it is not sealed by default. I believe nested classes are private by default.
Top-level types, which are not nested into other types, can only have internal or public accessibility. The default accessibility for these types is internal.
Accessibility Levels (C#) on MSDN
(inspired by this comment)
Is there ever a situation in which you need to use the private keyword?
(In other words, a situation in which omitting the keyword would result in different behavior)
public class Foo
{
public int Bar { get; private set; }
}
Omitting the word 'private' would change the accessibility.
a situation in which omitting the keyword [private] would result in different behavior
David Yaw's answer gave the most usual situation. Here is another one:
In Account_generated.cs:
// Generated file. Do not edit!
public partial class Account
{
...
private partial class Helper
{
...
}
...
}
In AccountHandCoded.cs:
public partial class Account
{
...
public partial class Helper
{
...
}
...
}
The above code will not compile. The first "part" of Account requires the nested class Helper to be private. Therefore the attempt by the hand-coder to make Helper public must fail!
However, had the first part of the class simply omitted the private keyword, all would compile.
So for partial classes (and structs, interfaces), the access-level-free declaration
partial class Name
means "the other 'parts' of this class are allowed to decide what the accessibility should be".
Whereas explicitly giving the default accessibility (which is internal for non-nested types and private for nested ones) means "this class must have the most restricted access possible, and the other 'parts' cannot change that fact".
private isn't about the runtime behaviour. It's to make your application maintainable. What's hidden by private can only ever affect the code outside its class through the public or protected members.
So the answer is 'no' for runtime behaviour, 'yes' for developer behaviour!
In C# version 7.2 and later.
The private protected keyword combination is a member access modifier. A private protected member is accessible by types derived from the containing class, but only within its containing assembly.
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/private-protected
Are you able to define class-implementations in an interface?
For instance (pseudo-code alert!)...
interface IClass1
{
String s { get; set; }
// classes implementing this interface has to implement Class2 as "SubClass"
Class2 SubClass;
}
interface IClass2
{
Int32 i { get; set; }
}
class Class1 : IClass1
{
String IClass1.s { get; set; }
class IClass1.Class2 SubClass
{
Int32 IClass2.i { get; set; }
}
}
The purpose of an interface is to define a contract which is separate from any implementation.
What you can do with an interface is defining a property like so:
interface IClass1
{
String S { get; set; }
Class2 SubClass { get; set; }
}
There is no syntax for forcing a class to implement another nested class. What you have effectively defined here is that any IClass1 implementation must have a field of type Class2.
Unfortunately there are two things wrong with this:
Class2 does not resolve to a known accessible type, therefore a compiler error will be generated.
The SubClass member of IClass1 is declared as a field, and interfaces cannot declare fields.
No. Also, Class2 isn't a subclass, it's a nested class or inner class. "Sub-class" is (in this context, there are other contexts that are completely different) another name for a derived class, in which context the base class is called a "super-class" (which is why Java has a keyword super that is analogous to base in C# though with some differences). "Derived" and "base" are the more popular terms in C#, perhaps because they are more popular terms in C++, perhaps because Bjarne Stroustrup says he finds them confusing and even he gets mixed up about which is which (after all, the subclass has a superset of behaviour and vice-versa).
Inner classes are essentially using their containing class as a namespace and nothing else, while interfaces only detail member methods and properties.
First of all, your question was:
"Are you able to define class-implementations in an interface?"
The answer to this is "in a way / no".
You can't include class definitions "inside" the interface definition if that's what you mean.
As mentioned earlier, the implementation of such a thing could happen via interface properties.
You should probably not try to implement your described interface structure unless classes exist that the implementing code's functionality is totally dependent on and if the interface is already deeply integrated into several existing modules. That in it self is a design flaw, and could be swapped with an abstract class implementation.
The CLR does not support multiple inheritance, but it does allow types to implement one or more interfaces in addition to inheriting from a base class. Therefore, interfaces are often used to achieve the effect of multiple inheritance.
Requiring classes to inherit from a single base class would in most cases make the class hierarchy too inflexible. To use a base class internally to simplify library development, public members should delegate work to the base class instead of inheriting from it.
Choose carefully between an abstract class and an interface when designing an abstraction as it can behave like an interface in that it can define members, and it can provide implementation details but are not required to do so, and can add members as needed to support additional functionality...
So, if used in the way you want, it departs from the concept of C# interfaces, but maybe seem to closer mimic the multiple inheritance model of languages such as C++ in practice, as it it implicitly "forces all implementors of your interface to create an instance of each class that the interface has specified properties for.
You need to think a bit about the reason for wanting to create such a structure (the need to force all implementors of an interface to also create instances of classes that the interface defines as properties).This is more likely a design-flaw in your code than it is a missing language feature.
So even though it is a possible workaround, I wouldn't call it a good way of design things...
Apologies if I've misunderstood but, yes, I do this now (VB 2013 for .NET 4.0 & 4.5). Interfaces can define properties, properties can be complex, the class definition for which can be nested within the interface definition. In your class that implements the interface, you'll can only have a the getter/setter for the complex object as a whole, not for its individual properties. (The getters/setters for those are within the class definition of course). Working example from VB attached, along with untested conversion to C#.
VB:
Interface IPrintable
Property Body As DocBody
Class DocBody
Property Text As String
Property FontSize As Single
End Class
End Interface
Class WordDoc
Implements IPrintable
Public Property WordBody As IPrintable.DocBody Implements IPrintable.Body
End Class
and C#:
interface IPrintable
{
DocBody Body { get; set; }
public class DocBody
{
public string Text { get; set; }
public float FontSize { get; set; }
}
}
class WordDoc : IPrintable
{
public IPrintable.DocBody WordBody { get; set; }
IPrintable.DocBody IPrintable.Body {
get { return WordBody; }
set { WordBody = value; }
}
}
I'm unable to comment, but the accepted answer to this question is no longer accurate.
As of C#8 it is possible to define default implementations for interface methods.
As interfaces have no private member's, this is limited to calling other public members, and so is useful for defining method overrides that call into one another.
This question already has answers here:
Closed 13 years ago.
Possible Duplicate:
C#: Public Fields versus Automatic Properties
Duplicate? I think not:
This question is not the same as "Why
use properties instead of public
field". A property with a specified
getter and setter is far different
than a public field. My question was,
is a property WITHOUT a getter and
setter, any different.
With the somewhat recent ability to have empty getters and setters, what is the benefit of using them instead of just declaring a public member variable?
Example:
public string MyProperty
{
get;
set;
}
versus:
public string MyProperty;
One word: inheritance.
Properties are inheritable while fields are not. You can use fields in an inherited class, but not alter their behavior by making them virtual.
Like so:
public class Foo {
public virtual int MyField = 1; // Nope, this can't
public virtual int Bar {get; set; }
}
public class MyDerive : Foo {
public override MyField; // Nope, this can't
public override int Bar {
get {
//do something;
}
set; }
}
Edit: Besides the fact of inheritance, the points pointed out in the other answers (like visibility) are also a huge benefit of properties over fields.
One thing you can do with properties that you can't do with fields is limit visibility for either setter or getter:
public string MyProperty { get; private set; }
Something I use quite a lot.
And something (more powerful) you can't do with fields is define them inside an interface. Suppose you want an interface that requires implementing classes to have a certain property:
public interface MyInterface
{
string MyProperty { get; }
}
Note that you do not need to have a setter here. It is entirely up to implementing classes to determine how they should set MyProperty.
Fields cannot be exposed in interfaces. And the auto-property can be changed into a "normal" property at any time if needed, without having the signature and interface of the class changing.
In general, fields are considered to be an implementation detail, which may change in future versions of the code. Therefore, you should expose data via methods and properties, leaving the way open for internal changes in the future which do not affect code using the class.
A property gives you several advantages over a simple public field:
you can control whether the property is read-only, write-only, or read/write
you can hide the actual implementation (maybe in the setter you want to do more than just setting a value)
when using databinding (e.g. in ASP.NET), you'll have to use properties (does not work with fields)
Tight coupling comes to mind. Using public fields removes the layer of abstraction made available by the use of properties. Using private fields and properties hides the implementation from other classes and helps to insulate them (external classes) whenever a change is necessary.
Also, keep in mind that you are referring to auto-implemented properties which causes the compiler to create the backing field for you instead of you having to manually create the backing (private) field for each property on your class.
The idea is to manage the values inside of the object, state, avoiding corruption and misuse by calling code.
You can flag properties with attributes that aren't available on members. There are attributes that only apply to fields in the DataContract namespace that affects serialization, the attribute can't be applied to fields, etc.
Admittedly, there isn't anything technically preventing these attributes from being used on members, but nonetheless they only work on properties.