Can anyone explain me when should i use Property, Private or both? When i create class what is good practice choose between them. I always see in many examples people used to do it diffrent way.
Some of them doing like this:
Private _name as string
Private _age as Integer
Other people does:
Property Name as string
Property Age as Integer
and other people:
Private _name As String
Private _age As Integer
Public Property name() As String
Get
Return _name
End Get
Set
_name = value
End Set
End Property
Public Property age() As Integer
Get
Return _age
End Get
Set
_age = value
End Set
End Property
in this case what is a sense to use private as Property already hiding private variable so in this case we could call it: _name and _age without specifying it as here.
You use fields (variables) when you want to only store value in memory. You use properties when you want to do more, for example validating it. Property is basically two methods for getting value (Get) and setting value (Set).
Related
Having a bit of a brain fart, right before bed. But i have the need to remap a ReadOnly Property from one name to a specified name i want.
I figured i could do
Public Readonly Property DocName as String
Get
Return Mybase.Name
End Get
End Property
And yes i am trying to remap the Name Property for an XMLDocument object. Just want to make sure that as long as i declare this property and then type:
Public Overrides ReadOnly Property Name As String
Get
Return SomeValue
End Get
End Property
I will be good togo? I know i will get the method has multiple definitions with identical signatures message, which brings me to my 2nd Question:
How do i prevent the Multiple Signatures error message from popping up with this type of declaration?
Unless i am missing some declaration attribute for this type of override.
You can use Shadows to accomplish this:
Public Class A
Public ReadOnly Property Name As String
Get
Return "Name"
End Get
End Property
End Class
Public Class B
Inherits A
Public ReadOnly Property DocName As String
Get
Return MyBase.Name
End Get
End Property
Public Shadows ReadOnly Property Name As String
Get
Return "SomeValue"
End Get
End Property
End Class
Greetins,
I am programmer from some time only, I have certain doubts in fundamentals, could you please clarify on the following:
Case 1:
Public Class BillItems
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged
Private Sub NotifyPropertyChanged(ByVal info As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
End Sub
Private _BillIdValue As String
Property BillId As String
Get
Return _BillIdValue
End Get
Set(ByVal value As String)
If Not _BillIdValue = value Then
_BillIdValue = value
End If
End Set
End Property
End Class
Case 2:
Public Class BillItems
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged
Private Sub NotifyPropertyChanged(ByVal info As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
End Sub
Property BillId As String
Get
Return BillId
End Get
Set(ByVal value As String)
If Not BillId = value Then
BillId = value
End If
End Set
End Property
End Case
Does case 1 and case 2 yield same result, I mean is a private value necessarily in there?, can we use property itself to use its own value in its Set and get statements?
Thank you.
I can't imagine that Case 2 is going to run without causing a stack-overflow exception. You are essentially making an infinite loop that is going to constantly call itself.
Case 1 would be the right way to do it.
If you are using .Net 4 you could just do this (without the further Get/Set code):
Property BillId As String
This will generate the private member variable (_BillId) for you.
Edit:
You could try this to raise the event:
Property BillId As String
Get
Return _BillIdValue
End Get
Set(ByVal value As String)
If Not _BillIdValue = value Then
_BillIdValue = value
NotifyPropertyChanged("BillId")
End If
End Set
End Property
In this article on MSDN about Auto-Implemented Properties you can read that a property requires a standard syntax when you
Add code to the Get or Set procedure of a property, such as code to validate incoming values in the Set procedure. For example, you might want to verify that a string that represents a telephone number contains the required number of numerals before setting the property value.
Therefore, because you implement IPropertyChanged interface, you need to add code to the setter.
and write something like this.
Property BillId As String
Get
Return _BillIdValue
End Get
Set(ByVal value As String)
If Not _BillIdValue = value Then
_BillIdValue = value
NotifyPropertyChanged("BillID")
End If
End Set
End Property
The second case is clearly wrong. (Infinite loop as someone else has already said)
How to pass a object that is initialized from a derived class to a method that has Interface as the parameter? Below is the example of what I'm trying. Is it possible? Please suggest any better way of doing.
Public Interface IFruit
Property Name As String
Property Color As String
End Interface
Public Class Fruit
Implements IFruit
Private _Name As String
Private _Color As String
Public Property Color As String Implements IFruit.Color
Get
Return _Color
End Get
Set(value As String)
_Color = value
End Set
End Property
Public Property Name As String Implements IFruit.Name
Get
Return _Name
End Get
Set(value As String)
_Name = value
End Set
End Property
End Class
Public Class FruitExtended
Inherits Fruit
Private _Taste As String
Public Property Taste() As String
Get
Return _Taste
End Get
Set(ByVal value As String)
_Taste = value
End Set
End Property
End Class
Public Class A
Public Sub ProcessFruit(F as IFruit)
'...
'Do something
End Sub
will the below code work? or how to achieve this in other ways?
Public Sub Test()
Dim F1 as new FruitExtended()
ProcessFruit(F1)
End sub
End Class
I didn't try your code, but - in general - interfaces are good because they define a behaviuor rather than a state (properties). So maybe you could rethink your design and ask yourself what the ProcessFruit is supposed to do with a IFruit.
Some languages even disallow to declare properties in interfaces, other than constants. Java is an example.
In VB6, there used to be a Collection data type that would allow retrieval of an item in the collection by either its key or its ordinal. However, it wasn't strongly typed.
Now, with VB.Net, I am looking for a suitable replacement that is strongly type and could be used with a generic collection.
This is a simple example of what I want to do. The only problem is that the underlying collection class, BindingList, does not support efficient retrieval of an item by an alpha key, so I have to loop through the elements to get the item I am looking for. For large collections, this is not efficient.
I have looked though the various Collection type classes and have found no suitable replacement.
This is what I want to do, except for the looping that is done with the Item property.
Rather than just saying "Use Hash tables" or something like that, if you could, please include the detailed out as I have done for the short example below.
Public Class Car
Public Sub New(ByVal keyName As String, ByVal property1 As String)
_KeyName = keyName
_Property1 = property1
End Sub
Dim _KeyName As String
Public Property KeyName() As String
Get
Return _KeyName
End Get
Set(ByVal value As String)
_KeyName = value
End Set
End Property
Public _Property1 As String
Public Property Property1() As String
Get
Return _Property1
End Get
Set(ByVal value As String)
_Property1 = value
End Set
End Property
End Class
Public Class Cars
Inherits System.ComponentModel.BindingList(Of Car)
Public Overloads ReadOnly Property Item(ByVal key As String) As Car
Get
For Each CurrentCar As Car In Me.Items
If CurrentCar.KeyName = key Then
Return CurrentCar
End If
Next
Return Nothing
End Get
End Property
End Class
I believe you're looking for Dictionary<TKey, TValue>. In fact, if you do want your own collection class that's strongly typed and isn't (itself) generic, if you change your parent class to Dictionary<string, Car>, you should be all set. This all does, of course, assume that you add the cars to the collection with an explicit string key. If you want the lookup to be based on the value of a property in the collection, you'd do better either using or inheriting from List<Car> and using LINQ to query the list. You could then have...
Public Overloads ReadOnly Property Item(ByVal key As String) As Car
Get
Return (from c in Me where c.KeyName = key select c).SingleOrDefault()
End Get
End Property
Do you really need both access by key AND index?
If you do not, then use a Dictionary(Of String, Car), and use
- MyCol.Items("XXX") to retrieve an item by key (or the shorthand MyCol("XXX"))
- MyCol.ContainsKey("XXX") to test if a key exists in the collection
- For Each Entry as KeyValuePair(Of String, Car) in MyCol if you want to enumerate all objects AND their key
- For Each Entry as Car in MyCol.Values if you want to enumerate the entries without consideration for the key
If you need both access by index and key, I'm afraid your best bet is to use a List(of Car) and a Dictionary(of Car) rolled into one custom collection class, because I believe they went away from that kind of collection which is not really all that useful for most problems.
This is what I am thinking is my best solution. I welcome comments for a better way!
Imports Microsoft.VisualBasic
Public Class Car
Implements Xs(Of Car).IKeyName
Private _KeyName As String
Public Sub New(ByVal keyName As String, ByVal property1 As String)
_KeyName = keyName
_Property1 = property1
End Sub
Public Property KeyName() As String Implements Xs(Of Car).IKeyName.KeyName
Get
Return _KeyName
End Get
Set(ByVal value As String)
_KeyName = value
End Set
End Property
Public _Property1 As String
Public Property Property1() As String
Get
Return _Property1
End Get
Set(ByVal value As String)
_Property1 = value
End Set
End Property
End Class
Public Class Cars
Inherits System.ComponentModel.BindingList(Of Car)
Public Overloads ReadOnly Property Item(ByVal key As String) As Car
Get
For Each CurrentCar As Car In Me.Items
If CurrentCar.KeyName = key Then
Return CurrentCar
End If
Next
Return Nothing
End Get
End Property
End Class
Public Class X
Private _KeyName As String
Public Property KeyName() As String
Get
Return _Keyname
End Get
Set(ByVal value As String)
_Keyname = value
End Set
End Property
End Class
Public Class Xs(Of X)
Inherits Hashtable
Interface IKeyName
Property KeyName() As String
End Interface
Public Shadows Sub Add(ByVal item As IKeyName)
MyBase.Add(item.KeyName, item)
End Sub
Public Shadows ReadOnly Property Item(ByVal key As String) As x
Get
If Me.ContainsKey(key) Then
Return MyBase.Item(key)
Else
'If I mispell a key, I don't want to end up creating a new mispelled version, I want an error
Throw New Exception("Element with key " & key & " is not found")
End If
End Get
End Property
End Class
Public Class Cars2
Inherits Xs(Of Car)
End Class
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim MyCar As New Car("key1", "prop1")
'First approach
Dim MyCars As New Cars
MyCars.Add(MyCar)
Dim RetrievedCar As Car = MyCars.Item("key1") 'Inefficient retrieval by key (uses looping)
'Second approach
Dim Cars2 As New Cars2
Cars2.Add(MyCar)
Dim RetrievedCar2 As Car = Cars2.Item("key1") 'Can now efficiently retreive an item by its key
End Sub
The OrderedDictionary in the System.Collections.Specialized namespace can be accessed by index and by key, if you ever need that. But looking at your solution, it looks like a standard Dictionary, but less efficient because it forces a string type for keys.
Is there any reason you can't use the Dictionary .NET provides you, or another collection type that's already in .NET like OrderedDictionary?
I figured I would ask... but is there a way to have the Get part of a property available as public, but keep the set as private?
Otherwise I am thinking I need two properties or a property and a method, just figured this would be cleaner.
Yes, quite straight forward:
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Private Set(ByVal value As String)
_name = value
End Set
End Property
I'm not sure what the minimum required version of Visual Studio is, but in VS2015 you can use
Public ReadOnly Property Name As String
It is read-only for public access but can be privately modified using _Name
Public Property Name() As String
Get
Return _name
End Get
Private Set(ByVal value As String)
_name = value
End Set
End Property
One additional tweak worth mentioning: I'm not sure if this is a .NET 4.0 or Visual Studio 2010 feature, but if you're using both you don't need to declare the value parameter for the setter/mutator block of code:
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Private Set
_name = value
End Set
End Property
I find marking the property as readonly cleaner than the above answers. I believe vb14 is required.
Private _Name As String
Public ReadOnly Property Name() As String
Get
Return _Name
End Get
End Property
This can be condensed to
Public ReadOnly Property Name As String
https://msdn.microsoft.com/en-us/library/dd293589.aspx?f=255&MSPPError=-2147217396
If you are using VS2010 or later it is even easier than that
Public Property Name as String
You get the private properties and Get/Set completely for free!
see this blog post: Scott Gu's Blog