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ReadOnlyAttribute Class

Specifies whether the property this attribute is bound to is read-only or read/write at design time.

For a list of all members of this type, see ReadOnlyAttribute Members.

System.Object
   System.Attribute
      System.ComponentModel.ReadOnlyAttribute

[Visual Basic]
<AttributeUsage(AttributeTargets.All)>
NotInheritable Public Class ReadOnlyAttribute
   Inherits Attribute
[C#]
[AttributeUsage(AttributeTargets.All)]
public sealed class ReadOnlyAttribute : Attribute
[C++]
[AttributeUsage(AttributeTargets::All)]
public __gc __sealed class ReadOnlyAttribute : public Attribute
[JScript]
public
   AttributeUsage(AttributeTargets.All)
class ReadOnlyAttribute extends Attribute

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Remarks

Members that are marked with the ReadOnlyAttribute constructor of the value true or that do not have a Set method cannot be changed. Members that do not have this attribute or that are marked with the ReadOnlyAttribute constructor of the value false are read/write, and they can be changed. The default is No.

Note   When you mark a property with the ReadOnlyAttribute constructor of the value true, the value of this attribute is set to the constant member Yes. For a property marked with the ReadOnlyAttribute constructor of the value false, the value is No. Therefore, when you want to check the value of this attribute in your code, you must specify the attribute as ReadOnlyAttribute.Yes or ReadOnlyAttribute.No.

For more information, see Attributes Overview and Extending Metadata Using Attributes.

Example

[Visual Basic, C#, C++] The following example marks a property as read-only.

[Visual Basic] 
Public ReadOnly Property MyProperty() As Integer
    Get
        ' Insert code here.
        Return 0
    End Get
End Property


[C#] 
[ReadOnly(true)]
 public int MyProperty {
    get {
       // Insert code here.
       return 0;
    }
}

[C++] 
public:
    [ReadOnly(true)]
     __property int get_MyProperty() {
           // Insert code here.
           return 0;
        }
    

[Visual Basic, C#, C++] The next example shows how to check the value of the ReadOnlyAttribute for MyProperty. First the code gets a PropertyDescriptorCollection with all the properties for the object. Next it indexes into the PropertyDescriptorCollection to get MyProperty. Then it returns the attributes for this property and saves them in the attributes variable.

[Visual Basic, C#, C++] The example presents two different ways of checking the value of the ReadOnlyAttribute. In the second code fragment, the example calls the Equals method. In the last code fragment, the example uses the IsReadOnly property to check the value.

[Visual Basic] 
' Gets the attributes for the property.
Dim attributes As AttributeCollection = _
    TypeDescriptor.GetProperties(Me)("MyProperty").Attributes

' Checks to see whether the value of the ReadOnlyAttribute is Yes.
If attributes(GetType(ReadOnlyAttribute)).Equals(ReadOnlyAttribute.Yes) Then
    ' Insert code here.
End If 

' This is another way to see whether the property is read-only.
Dim myAttribute As ReadOnlyAttribute = _
    CType(attributes(GetType(ReadOnlyAttribute)), ReadOnlyAttribute)
    
If myAttribute.IsReadOnly Then
    ' Insert code here.
End If 

[C#] 
// Gets the attributes for the property.
AttributeCollection attributes = 
   TypeDescriptor.GetProperties(this)["MyProperty"].Attributes;
 
// Checks to see whether the value of the ReadOnlyAttribute is Yes.
if(attributes[typeof(ReadOnlyAttribute)].Equals(ReadOnlyAttribute.Yes)) {
   // Insert code here.
}
 
// This is another way to see whether the property is read-only.
ReadOnlyAttribute myAttribute = 
   (ReadOnlyAttribute)attributes[typeof(ReadOnlyAttribute)];
if(myAttribute.IsReadOnly) {
   // Insert code here.
}

[C++] 
// Gets the attributes for the property.
AttributeCollection* attributes = 
   TypeDescriptor::GetProperties(this)->Item[S"MyProperty"]->Attributes;
 
// Checks to see whether the value of the ReadOnlyAttribute is Yes.
if(attributes->Item[__typeof(ReadOnlyAttribute)]->Equals(ReadOnlyAttribute::Yes)) {
   // Insert code here.
}
 
// This is another way to see whether the property is read-only.
ReadOnlyAttribute* myAttribute = 
   dynamic_cast<ReadOnlyAttribute*>(attributes->Item[__typeof(ReadOnlyAttribute)]);
if(myAttribute->IsReadOnly) {
   // Insert code here.
}

[Visual Basic, C#, C++] If you marked a class with the ReadOnlyAttribute, use the following code example to check the value.

[Visual Basic] 
Dim attributes As AttributeCollection = TypeDescriptor.GetAttributes(MyProperty)
If attributes(GetType(ReadOnlyAttribute)).Equals(ReadOnlyAttribute.Yes) Then
    ' Insert code here.
End If 

[C#] 
AttributeCollection attributes = 
   TypeDescriptor.GetAttributes(MyProperty);
if(attributes[typeof(ReadOnlyAttribute)].Equals(ReadOnlyAttribute.Yes)) {
   // Insert code here.
}

[C++] 
AttributeCollection* attributes = 
   TypeDescriptor::GetAttributes( __box(MyProperty));
if(attributes->Item[__typeof(ReadOnlyAttribute)]->Equals(ReadOnlyAttribute::Yes)) {
   // Insert code here.
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Namespace: System.ComponentModel

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

Assembly: System (in System.dll)

See Also

ReadOnlyAttribute Members | System.ComponentModel Namespace | Attribute | PropertyDescriptor | AttributeCollection | PropertyDescriptorCollection

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