IN VB.NET you can change the name of this variable. Can you do this in C# too or is it always called value?
Example:
Private _SomeVariable As String
Public Property SomeValue() As String
Get
Return _SomeVariable
End Get
Set(ByVal foo As String) ' This is what I mean
_SomeVariable = foo
End Set
End Property
I'm used to write code in VB.NET, but want to change to C# eventually and trying to learn all the differences and peculiarities of C#.
I know this is no big deal, but Telerik for example isn't aware of it while converting VB.NET to C#, which could lead to a missbehaviour in case you have a class variable named foo too (for the above-mentioned example).
The set parameter is always named value, and you cannot change it. If you happen to have a conflicting name in your code, you can use the fully-qualified name in order to use it:
class MyClass
{
private string value;
public string Value
{
get { return value; }
set { this.value = value; } // this.value is the private field
}
}
In C#, the new value is always accessed via value. There is no syntax to write a setter to accept a custom name.
See Using Properties (C# Programming Guide).
The set accessor resembles a method whose return type is void. It uses an implicit parameter called value, whose type is the type of the property ..
The value is keyword, so it cannot be changed
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In C# what does this code with “get” mean?
I'm using open source project. In this project there is function.
public virtual ICollection<Customer> AffiliatedCustomers
{
get
{
return _affiliatedCustomers ?? (_affiliatedCustomers = new List<Customer>());
}
protected set { _affiliatedCustomers = value; }
}
I don't understand what is the meaning of "get".
Can you please explain this function.
AffiliatedCustomers is a property.
The get defines the property getter, which is a method used internally to return the value by the property. It allows you to use this given an instance of the class like so:
var customers = theClass.AffiliatedCustomers; // Looks like a field, but is a property
Properties can also have a set section, as well, as this one does (protected set { _affiliatedCustomers = value; }), which gives you control over what happens when you set the value via the Property.
For details, see Properties in C#.
This is not a function. It is a property. A property is basically a fancy wrapper for some variable. For example, declaring the following property:
public string SomeProperty { get; set; }
will actually compile to something like this:
private string backing_SomeProperty;
public void set_SomeProperty(string value)
{
backing_SomeProperty = value;
}
public int get_SomeProperty()
{
return backing_SomeProperty;
}
That's an example of an automatic property. Of course, you can also define the getter and setter methods yourself like this:
public string SomeProperty
{
get
{
// some logic code here
// then return some value
}
set
{
// some logic code here
// then set some value
}
}
This is a property,
Quoted by msdn:
Properties are members that provide a flexible mechanism to read, write, or compute the values of private fields. Properties can be used as though they are public data members, but they are actually special methods called accessors. This enables data to be accessed easily while still providing the safety and flexibility of methods.
Please refer to this link for more:
http://msdn.microsoft.com/en-us/library/x9fsa0sw(v=vs.80).aspx
Properties have a getter and a setter - their purpose is obvious (to get and set the value of the property).
When you use auto properties, there is still a get and a set, but the backing variable is automatically implemented for you. In the example you have given the author of the code has chosen to have their own implementation of the get - in this case to automatically initialise the member variable the first time the property is accessed.
Just wondering in the below function
public Dictionary<string, List<TrainingItem>> TrainingItems
{
set
{
trainingItems = SanitizeTrainingItems(value);
Results_Repeater.DataSource = trainingItems;
Results_Repeater.DataBind();
}
}
How does the value of (value) get past here and what is it. I mean there is no parameters to function but yet I am still passing a value in function I just don't understand where it comes from ?
A property in C# simulates a data member when in reality it's a set of accessor methods, specifically a get accessor and a set accessor (unless the property is read-only). In most cases, a property is used to read, write or compute the value of a private field.
A common use for a property would be:
private string _firstName;
public int FirstName
{
get { return _firstName; }
set { _firstName = value; }
}
The get and set blocks within the property definition represent the accessor method bodies that either read or write the value of _firstName. In the set accessor, value is a contextual keyword representing the parameter of the set_FirstName accessor method generated by the compiler.
Without properties, you would have to write these methods yourself, i.e., you'd have a public string getFirstName(); and a public void setFirstName(string value); and you would call each method accordingly. A C# property is just a shortcut and gives you an easy to use mechanism to invoke the correct accessor.
set accessor uses implicit parameter called value, whose type is the type of the property. In the following example, a set accessor is added to the TrainingItems property
When you assign a value to the property, the set accessor is invoked by using an argument that provides the new value.
See it here - http://msdn.microsoft.com/en-us/library/w86s7x04(v=vs.90).aspx
Automatic properties were added to the language in about .net 3 which create a 'private' field, anyway, using the code:
public string foo {get;set;}
Is it possible to actually get any sort of reference to this private field?
I want to do something like
public string foo {get{/*some code to check foo for nulls etc*/};set;}
Without losing this automatic property feature and writing something like
private string _foo = null;
public string foo{get{_foo==null?_foo="hello"; return _foo;}set{_foo=value;}}
The backing field of an automatic property is anonymous; you can't access it from within its getter or setter.
If you need to implement your own logic in your getter or setter, your property isn't considered automatic anymore anyway.
Auto properties are simply there to save the tedium of typing, and eyesore of seeing, multitudes of these:
private object _x;
public object X
{
get { return _x; }
set { _x = value; }
}
You can't have a an "automatic" get and a "manual" set (or a "manual" get with an "automatic" set). You must have both "manual" or both "automatic".
why do we do this:
private string StatusText
{
set { toolStripStatusLabel1.Text = value; }
}
instead of just this?
private string StatusText
{
toolStripStatusLabel1.Text = value;
}
i do not understand the point of using set?
These are two completely different things.
This is a method:
private string StatusText()
{
toolStripStatusLabel1.Text = value;
}
which is called like this:
StatusText();
(and which will not compile, because the local variable value cannot be found). To make it work, you would need to write it like this:
private string StatusText(string value)
{
toolStripStatusLabel1.Text = value;
}
and call it like this:
StatusText("bla");
On the other hand, this is the definition of a property:
private string StatusText
{
set { toolStripStatusLabel1.Text = value; }
}
whose setter (hence the keyword set) is called like this:
StatusText = "bla";
Because there could also be a get:
get { return toolStripStatusLabel1.Text; }
Properties are syntactic sugar. When compiled you will have two methods get_[property name] and set_[property name]. If you only have the set method, only the set_[propety name] will be in the IL.
In a little more detail, since the OP has said she doesn't understand gets and sets:
The get and set keywords are used to define a "property". A property is a pair of methods - a "getter" and "setter" - that are used behind the scenes when the property is used or written to by other code. The advantage of a property over explicitly defining getter and setter methods is that you can use the property as if it were a "field" (a simple, publicly-visible member variable). The advantage of using a property instead of a field is that a property allows you to customize the behavior of assigning or using a variable. You can create "calculated fields" that are evaluated when needed based on other data in the object, or include basic validation or other business logic when reading or writing a value.
To define a property, you start by declaring it like you would a field, but then add a code block with get and set sub-blocks. You then define its read behavior in the get block, and the write behavior in the set block. You can choose to define only one accessor (making a "read-only" or "write-only" property), or you can define more limited visibility for one function or the other; for instance, you can make the getter public but the setter protected, so everyone can examine the property's value but only the class's other members and derived types can set its value.
The most common property implementation uses a "backing field", a private variable that acts as the store for the value exposed by the property. To streamline this implementation, .NET 3.0 included the concept of an "auto-property"; if you didn't define the code bodies of the getter and setter, the compiler would generate a basic implementation using a backing field.
First will not compile for value isn't valid unless you have set.
private string StatusText
{
toolStripStatusLabel1.Text = value;
}
Check out MSDN on Accessors here.
Setting and Getting fields and properties...
Example:
private string statusText;
public string StatusText
{
get { return this.statusText;}
set { this.statusText = value;
toolStripStatusLabel1.Text = this.statusText;
}
}
private String StatusText
{
get { ... }
set { ... }
}
The get/set tokens are to distinguish between the get and set accessors.
The latter wouldn't compile. The set part shows that it's the setter part of a property.
An alternative is to just write a method:
private void SetStatusText(string value)
{
toolStripStatusLabel1.Text = value;
}
To enable you to apply more complex logic, when the need will arise.
I'd like to do the same in C#. Is there anyway of using properties in C# with parameters in the same way I've done with the parameter 'Key' in this VB.NET example?
Private Shared m_Dictionary As IDictionary(Of String, Object) = New Dictionary(Of String, Object)
Public Shared Property DictionaryElement(ByVal Key As String) As Object
Get
If m_Dictionary.ContainsKey(Key) Then
Return m_Dictionary(Key)
Else
Return [String].Empty
End If
End Get
Set(ByVal value As Object)
If m_Dictionary.ContainsKey(Key) Then
m_Dictionary(Key) = value
Else
m_Dictionary.Add(Key, value)
End If
End Set
End Property
Thanks
Is there anyway of using properties in C# with parameters
No. You only can provide the default property in C# with an argument, to model indexed access (as in a dictionary):
public T this[string key] {
get { return m_Dictionary[key]; }
set { m_Dictionary[key] = value; }
}
Other properties can't have arguments. Use a function instead. By the way, it's recommented to do the same in VB so other .NET languages (C# …) can use your code.
By the way, your code is unnecessarily complicated. Four things:
You don't need to escape the String identifier. Use the keyword directly.
Why not use ""?
Use TryGetValue, it's faster. You query the dictionary twice.
Your setter doesn't have to test whether the value already exists.
Public Shared Property DictionaryElement(ByVal Key As String) As Object
Get
Dim ret As String
If m_Dictionary.TryGetValue(Key, ret) Then Return ret
Return "" ' Same as String.Empty! '
End Get
Set(ByVal value As Object)
m_Dictionary(Key) = value
End Set
End Property
The "proper" way to do it in C# is to create child class specifically to access the collection. It should either hold the collection itself or have internal linkages to the parent class.
A more general-purpose, safer, and reusable solution to your problem might be implementing a generic, "parameterized" property class, like this:
// Generic, parameterized (indexed) "property" template
public class Property<T>
{
// The internal property value
private T PropVal = default(T);
// The indexed property get/set accessor
// (Property<T>[index] = newvalue; value = Property<T>[index];)
public T this[object key]
{
get { return PropVal; } // Get the value
set { PropVal = value; } // Set the value
}
}
You could then implement any number of properties within your public class so that clients could set/get the properties with an index, descriptor, security key, or whatever, like this:
public class ParameterizedProperties
{
// Parameterized properties
private Property<int> m_IntProp = new Property<int>();
private Property<string> m_StringProp = new Property<string>();
// Parameterized int property accessor for client access
// (ex: ParameterizedProperties.PublicIntProp[index])
public Property<int> PublicIntProp
{
get { return m_IntProp; }
}
// Parameterized string property accessor
// (ex: ParameterizedProperties.PublicStringProp[index])
public Property<string> PublicStringProp
{
get { return m_StringProp; }
}
}
Finally, client code would access your public class's "parameterized" properties like this:
ParameterizedProperties parmProperties = new ParameterizedProperties();
parmProperties.PublicIntProp[1] = 100;
parmProperties.PublicStringProp[1] = "whatever";
int ival = parmProperties.PublicIntProp[1];
string strVal = parmProperties.PublicStringProp[1];
Sure, this seems weird, but it definitely does the trick. Besides, from a client-code perspective, it's not weird at all -- it's simple and intuitive and acts just like real properties. It doesn't break any C# rules, nor is it incompatible with other .NET managed languages. And from the class-implementer's perspective, creating a reusable, generic, "parameterized" property template class makes component coding a relative breeze, as shown here.
NOTE: You can always override the generic property class to provide custom processing, such as indexed lookup, security-controlled property access, or whatever-the-heck you want.
Cheers!
Mark Jones
Here is a sample for you (with changes along the lines of Grauenwolf's suggestions):
using System;
using System.Collections.Generic;
public class Test
{
public FakeIndexedPropertyInCSharp DictionaryElement { get; set; }
public Test()
{
DictionaryElement = new FakeIndexedPropertyInCSharp();
}
public class FakeIndexedPropertyInCSharp
{
private Dictionary<string, object> m_Dictionary = new Dictionary<string, object>();
public object this[string index]
{
get
{
object result;
return m_Dictionary.TryGetValue(index, out result) ? result : null;
}
set
{
m_Dictionary[index] = value;
}
}
}
}
class Program
{
static void Main(string[] args)
{
Test t = new Test();
t.DictionaryElement["hello"] = "world";
Console.WriteLine(t.DictionaryElement["hello"]);
}
}
Your code sample strikes me as a very strange design and an abuse of what properties are intended for. Why not just an instance method AddOrUpdateKey:
Public Sub AddOrUpdateKey(ByVal Key As String, ByVal Value as Object)
If m_Dictionary.ContainsKey(Key) Then
m_Dictionary(Key) = Value
Else
m_Dictionary.Add(Key, Value)
End If
End Sub
Your property also returns String.Empty if the key does not exist, but claims to return an Object, nor a String.
Thanks Konrad, Alan, Grauenwolf,
In conclusion, I can't use C# properties exactly in the same way that in VB.NET... :_( Anyway, your answers has been very usefull to me, and I´ll probably take this ideas to my C# code.
In addition to the answers to the properties question, there are other good points. For example,
Use TryGetValue, it's faster. You query the dictionary twice.
Your setter doesn't have to test whether the value already exists.
Thanks Sören, too, using a method don't fits well in my initial aims, but thanks very much.