BLOB Image Properties in XPO

• Oct 17, 2023
• 3 minutes to read

You can declare image properties as byte arrays or MediaDataObject type reference properties (this type is available in the Business Class Library).

Image as a Byte Array

The example below illustrates how to implement byte array type image properties in an XPO persistent class by declaring a byte array property and applying the ImageEditorAttribute to it. You can also customize the image editor using the attribute’s parameters.

C#

[VisibleInListView(true)]
[ImageEditor(ListViewImageEditorMode = ImageEditorMode.PictureEdit, 
    DetailViewImageEditorMode = ImageEditorMode.PictureEdit, 
    ListViewImageEditorCustomHeight = 40)]
public byte[] ImageProperty {
    get { return GetPropertyValue<byte[]>(nameof(ImageProperty)); }
    set { SetPropertyValue<byte[]>(nameof(ImageProperty), value); }
}
[Delayed(), VisibleInListViewAttribute(true)]
[ImageEditor(ListViewImageEditorMode = ImageEditorMode.PopupPictureEdit, DetailViewImageEditorMode = ImageEditorMode.DropDownPictureEdit)]
public byte[] ImageDelayedProperty {
    get { return GetDelayedPropertyValue<byte[]>(nameof(ImageDelayedProperty)); }
    set { SetDelayedPropertyValue<byte[]>(nameof(ImageDelayedProperty), value); }
}

VB.NET

<VisibleInListViewAttribute(True), _
ImageEditor(ListViewImageEditorMode := ImageEditorMode.PictureEdit, _
DetailViewImageEditorMode := ImageEditorMode.PictureEdit, ListViewImageEditorCustomHeight := 40)>
Public Property ImageProperty() As Byte()
    Get
        Return GetPropertyValue(Of Byte())(NameOf(ImageProperty))
    End Get
    Set(ByVal value As Byte())
        SetPropertyValue(Of Byte())(NameOf(ImageProperty), value)
    End Set
End Property

<Delayed(), VisibleInListView(True), _
ImageEditor(ListViewImageEditorMode := ImageEditorMode.PopupPictureEdit, _
DetailViewImageEditorMode := ImageEditorMode.DropDownPictureEdit)>
Public Property ImageDelayedProperty() As Byte()
    Get
        Return GetDelayedPropertyValue(Of Byte())(NameOf(ImageDelayedProperty))
    End Get
    Set(ByVal value As Byte())
        SetDelayedPropertyValue(Of Byte())(NameOf(ImageDelayedProperty), value)
    End Set
End Property

Refer to the ImageEditorAttribute topic for details on parameters passed to the ImageEditor attribute in the code above. You can also specify image options using the following properties in the Model Editor:

• IModelCommonMemberViewItem.ImageSizeMode
• IModelMember.DetailViewImageEditorMode
• IModelMember.DetailViewImageEditorFixedWidth
• IModelMember.DetailViewImageEditorFixedHeight
• IModelMember.ListViewImageEditorMode
• IModelMember.ListViewImageEditorCustomHeight

Tip

When an application displays a lot of large images in a List View, it may consume much memory. This applies to ASP.NET Web Forms applications with many simultaneously connected clients. To improve the performance, you can use lazy loading.

Image as a MediaDataObject

The example below illustrates how to implement MediaDataObject type’s image properties (available in the Business Class Library) in an XPO persistent class. Image Property Editors are used automatically for MediaDataObject type’s properties; no attributes are required (however, you still can apply the ImageEditorAttribute to customize the editor’s options, as it is demonstrated above for byte arrays). Using this type reduces traffic because images are cached in the browser cache (compared to byte[] type images). Delayed loading is always used for MediaDataObject properties.

C#

using DevExpress.Xpo;
using DevExpress.Persistent.BaseImpl;
// ...
[DefaultClassOptions]
public class Contact : BaseObject {
    public Contact(Session session) : base(session) { }
    private string name;
    public string Name {
        get { return name; }
        set { SetPropertyValue(nameof(Name), ref name, value); }
    }
    private MediaDataObject image;
    public MediaDataObject Image {
        get { return image; }
        set { SetPropertyValue(nameof(Image), ref image, value); }
    }
}

VB.NET

Imports DevExpress.Xpo
Imports DevExpress.Persistent.BaseImpl
' ...
<DefaultClassOptions> _
Public Class Contact
    Inherits BaseObject

    Public Sub New(ByVal session As Session)
        MyBase.New(session)
    End Sub
    Private _name As String
    Public Property Name() As String
        Get
            Return _name
        End Get
        Set(ByVal value As String)
            SetPropertyValue(NameOf(Name), _name, value)
        End Set
    End Property
    Private _image As MediaDataObject
    Public Property Image() As MediaDataObject
        Get
            Return _image
        End Get
        Set(ByVal value As MediaDataObject)
            SetPropertyValue(NameOf(Image), _image, value)
        End Set
    End Property
End Class