Color Properties in XPO

• Mar 12, 2021
• 3 minutes to read

This topic demonstrates two approaches to store a System.Drawing.Color property value in the database managed by the eXpressPersistent Objects ORM.

1. The first approach is to implement a Value Converter.

   C#

   using System;
   using System.Drawing;
   using DevExpress.Xpo.Metadata;
   // ...
   public class ColorValueConverter : ValueConverter {
       public override Type StorageType {
           get { return typeof(Int32); }
       }
       public override object ConvertToStorageType(object value) {
           if(!(value is Color)) return null;
           Color color = (Color)value;
           return color.IsEmpty ? -1 : color.ToArgb();
       }
       public override object ConvertFromStorageType(object value) {
           if(!(value is Int32)) return null;
           Int32 argbCode = Convert.ToInt32(value);
           return argbCode == -1 ? Color.Empty : Color.FromArgb(argbCode);
       }
   }
   

   VB.NET

   Imports System
   Imports System.Drawing
   Imports DevExpress.Xpo.Metadata
   ' ...
   Public Class ColorValueConverter
       Inherits ValueConverter
       Public Overrides ReadOnly Property StorageType() As Type
           Get
               Return GetType(Int32)
           End Get
       End Property
       Public Overrides Function ConvertToStorageType(ByVal value As Object) As Object
           If Not(TypeOf value Is Color) Then
               Return Nothing
           End If
           Dim color As Color = CType(value, Color)
           Return If(color.IsEmpty, -1, color.ToArgb())
       End Function
       Public Overrides Function ConvertFromStorageType(ByVal value As Object) As Object
           If Not(TypeOf value Is Int32) Then
               Return Nothing
           End If
           Dim argbCode As Int32 = Convert.ToInt32(value)
           Return If(argbCode = -1, Color.Empty, Color.FromArgb(argbCode))
       End Function
   End Class
   

   After that, decorate properties that need to be converted with the ValueConverterAttribute and the converter will be called on each attempt to store or acquire a value of the System.Drawing.Color type.

   C#

   using DevExpress.Xpo;
   using System.Drawing;
   //...
   private Color color;
   [ValueConverter(typeof(ColorValueConverter))]
   public Color Color {
       get { return color; }
       set { SetPropertyValue("Color", ref color, value); }
   }
   

   VB.NET

   Imports DevExpress.Xpo
   Imports System.Drawing
   '...
   Private color_ As Color
   <ValueConverter(GetType(ColorValueConverter))> _
   Public Property Color() As Color
       Get
           Return color_
       End Get
       Set(ByVal value As Color)
           SetPropertyValue("Color", color_, value)
       End Set
   End Property
   

2. Another approach is to convert the System.Drawing.Color type to System.Int32 on property implementation using get and set accessors, as shown below. Mobile applications do not support this approach.

   C#

   using DevExpress.Xpo;
   using System.Drawing;
   //...
   [Persistent("Color")]
   private Int32 color;
   [NonPersistent]
   public Color Color {
       get { return Color.FromArgb(color); }
       set {
           color = value.ToArgb();
           OnChanged("Color");
       }
   }
   

   VB.NET

   Imports DevExpress.Xpo
   Imports System.Drawing
   '...
   <Persistent("Color")> _
   Private color_ As Int32
   <NonPersistent> _
   Public Property Color() As Color
       Get
           Return Color.FromArgb(color_)
       End Get
       Set(ByVal value As Color)
           color_ = value.ToArgb()
           OnChanged("Color")
       End Set
   End Property
   

   Note

   If the type’s class does not have an appropriate conversion method (Color.ToArgb in this case), implement a Type Converter and use it any time you need a value conversion between the type you need to store and an ORM-friendly type.