how can you get the default value of a property?

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

Did you check this method in Attribute class !!

VB Code:

DefaultValueAttribute

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

Quote:

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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.

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hmm what's the container of the property?:D

Pirate how can you get the value using that thing?:confused:

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:

VB Code:

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))

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:(

Quote:

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

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Code:

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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());

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Quote:

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Originally posted by Pirate

Code:

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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());

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w00t works:D a bit simpler than Edneeis'version but still what a mess both of them are:D 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

Quote:

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

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Always consult your MSDN in your area . :)

Quote:

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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

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It seems to be only for comparsion issues. Ex .

VB Code:

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

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

Quote:

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

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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 .

Quote:

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you have 6000 posts now:D:D:D congrats;)

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:D ----------:p