how can you get the default value of a property?

[MrPolite]

lets say you declare a property and set its defaultValue attribute to something. Is there a way to get this value using code?

[Pirate]

Did you check this method in Attribute class !!

DefaultValueAttribute

[Edneeis]

I think you'd have to create a new instance of the container of the property and then find its value.

[MrPolite]

Originally posted by Edneeis
I think you'd have to create a new instance of the container of the property and then find its value.

hmm what's the container of the property?

Pirate how can you get the value using that thing?

[Edneeis]

What is the container of the property? What is housing it?

Is it in a Class? Form? Module? Or it doesn't really matter as long as you have a reference to the container or know the strong type of the container.

Here is an example using a private field in a class:

Public Class Test
 
    Private _name As String = "Test"
 
    Public Property Name() As String
        Get
            Return _name
        End Get
        Set(ByVal Value As String)
            _name = Value
        End Set
    End Property
 
    'this doesn't have to by in the class I just didn't know where to put it for the example
    Public Shared Function GetDefault(ByVal type As Type, ByVal member As String) As Object
        'get new instance
        Dim newInst As Object = Activator.CreateInstance(type)
        'get member
        Dim bf As Reflection.BindingFlags = Reflection.BindingFlags.IgnoreCase Or _
            Reflection.BindingFlags.Instance Or Reflection.BindingFlags.Public Or _
            Reflection.BindingFlags.NonPublic
        Dim minfo As Reflection.MemberInfo() = type.GetMember(member, bf)
        If minfo.Length > 0 Then
            'now get the value
            If minfo(0).MemberType = Reflection.MemberTypes.Field Then
                Return CType(minfo(0), Reflection.FieldInfo).GetValue(newInst)
            ElseIf minfo(0).MemberType = Reflection.MemberTypes.Property Then
                Return CType(minfo(0), Reflection.PropertyInfo).GetValue(newInst, Nothing)
            Else
                Throw New ArgumentException("Member is the wrong type!")
            End If
        Else
            Throw New ArgumentException("Member not found!")
        End If
 
    End Function
 
End Class
 
'syntax
        Dim t As New Test
        t.Name = "Ed"
 
        MsgBox(String.Format("Original: {1}{0}Default: {2}", ControlChars.NewLine, t.Name, Test.GetDefault(t.GetType, "_name").ToString))

[MrPolite]

thanks a lot Edneeis.... I'll have to think on that one. its in a class btw. I dont have a good understanding of all these reflections and such

[Pirate]

Originally posted by MrPolite
Pirate how can you get the value using that thing?

private bool myVal=false;

[DefaultValue(false)]
 public bool MyProperty {
    get {
       return myVal;
    }
    set {
       myVal=value;
    }
 }




// Gets the attributes for the property.
 AttributeCollection attributes = 
    TypeDescriptor.GetProperties(this)["MyProperty"].Attributes;
 
 /* Prints the default value by retrieving the DefaultValueAttribute 
  * from the AttributeCollection. */
 DefaultValueAttribute myAttribute = 
    (DefaultValueAttribute)attributes[typeof(DefaultValueAttribute)];
 Console.WriteLine("The default value is: " + myAttribute.Value.ToString());

[MrPolite]

Originally posted by Pirate

private bool myVal=false;

[DefaultValue(false)]
 public bool MyProperty {
    get {
       return myVal;
    }
    set {
       myVal=value;
    }
 }




// Gets the attributes for the property.
 AttributeCollection attributes = 
    TypeDescriptor.GetProperties(this)["MyProperty"].Attributes;
 
 /* Prints the default value by retrieving the DefaultValueAttribute 
  * from the AttributeCollection. */
 DefaultValueAttribute myAttribute = 
    (DefaultValueAttribute)attributes[typeof(DefaultValueAttribute)];
 Console.WriteLine("The default value is: " + myAttribute.Value.ToString());

w00t works a bit simpler than Edneeis'version but still what a mess both of them are I dont understand any of it. Where did you learn all that ha? hehe


edit: btw what does typeof do in vb.net? I know you're supposed to use getType instead of the C# typeOf() but still if you type "typeOf" in VB it highlights it in blue so I'm wondering if it really means anything in vb or if its just reserved

[Pirate]

Originally posted by MrPolite
w00t works a bit simpler than Edneeis'version but still what a mess both of them are I dont understand any of it. Where did you learn all that ha? hehe

Always consult your MSDN in your area .

edit: btw what does typeof do in vb.net? I know you're supposed to use getType instead of the C# typeOf() but still if you type "typeOf" in VB it highlights it in blue so I'm wondering if it really means anything in vb or if its just reserved

It seems to be only for comparsion issues. Ex .

Sub TypeOfEx()
        Dim c As New TextBox
        If TypeOf c Is TextBox Then
            MessageBox.Show("textbox")
        ElseIf TypeOf c Is ComboBox Then
            MessageBox.Show("whatever")
        Else
            MessageBox.Show("go home")
        End If
 
    End Sub

[MrPolite]

thanks... I know I shouldnt be making posts like THIS one but its hard to resist: you have 6000 posts now congrats

[Pirate]

Originally posted by MrPolite
thanks... I know I shouldnt be making posts like THIS one but its hard to resist:

If it didn't help you , then I'm sure it would be useful for some other guys who ever wanted to do something like this .

you have 6000 posts now congrats

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