expressappframework-devexpress-dot-expressapp-dot-viewvariantsmodule-db316607.md
Implemented by objects that provide a list of view variants available for the specific View, and stores the variant selected by the user.
Namespace : DevExpress.ExpressApp.ViewVariantsModule
Assembly : DevExpress.ExpressApp.ViewVariantsModule.v25.2.dll
NuGet Package : DevExpress.ExpressApp.ViewVariantsModule
public interface IVariantsProvider
Public Interface IVariantsProvider
The following members return IVariantsProvider objects:
The default implementation of the IVariantsProvider interface used by the View Variants Module is ModelVariantsProvider, that stores view variants in the Application Model. You can create a custom IVariantsProvider implementation and pass it to the ViewVariantsModule.VariantsProvider property.
The following snippet illustrates how to implement an IVariantsProvider that stores View Variants in the database.
public class DatabaseViewVariantsProvider : IVariantsProvider {
XafApplication application;
public DatabaseViewVariantsProvider(XafApplication application) {
Guard.ArgumentNotNull(application, nameof(application));
this.application = application;
}
public VariantsInfo GetVariants(string rootVariantViewId) {
VariantsInfo result = null;
if(application.Security.IsAuthenticated) {
using(IObjectSpace os = application.CreateObjectSpace(typeof(ViewVariantsObject))) {
ViewVariantsObject variants = os.FirstOrDefault<ViewVariantsObject>(obj => obj.RootViewId == rootVariantViewId);
if(variants != null && (variants.Items.Count >= 2)) {
List<VariantInfo> items = new List<VariantInfo>();
foreach(ViewVariantObject variant in variants.Items) {
items.Add(new VariantInfo(variant.ID.ToString(), variant.ViewId, variant.Caption));
}
string currentVariantId;
if(variants.CurrentVariant != null) {
currentVariantId = variants.CurrentVariant.ID.ToString();
}
else {
currentVariantId = variants.Items[0].ID.ToString();
}
result = new VariantsInfo(variants.RootViewId, currentVariantId, items);
}
}
}
return result;
}
public void SaveCurrentVariantId(string rootViewId, string currentVariantId) {
using(IObjectSpace os = application.CreateObjectSpace(typeof(ViewVariantsObject))) {
ViewVariantObject variant = os.GetObjectByKey<ViewVariantObject>(Guid.Parse(currentVariantId));
if((variant == null) || (variant.Owner == null)) {
throw new InvalidOperationException();
}
variant.Owner.CurrentVariant = variant;
os.CommitChanges();
}
}
}
The following code illustrates persistent objects used by DatabaseViewVariantsProvider to store View Variants:
[Index(nameof(RootViewId), IsUnique = true)]
[DefaultClassOptions,XafDefaultProperty(nameof(RootViewId))]
public class ViewVariantsObject : BaseObject {
[RuleUniqueValue]
public virtual string RootViewId { get; set; }
public virtual ViewVariantObject CurrentVariant { get; set; }
public virtual IList<ViewVariantObject> Items { get; set; } = new ObservableCollection<ViewVariantObject>();
}
[XafDefaultProperty(nameof(Caption))]
public class ViewVariantObject : BaseObject {
[InverseProperty(nameof(ViewVariantsObject.Items))]
public virtual ViewVariantsObject Owner { get; set; }
public virtual string ViewId { get; set; }
public virtual string Caption { get; set; }
}
// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.
[DefaultClassOptions, XafDefaultProperty(nameof(RootViewId))]
public class ViewVariantsObject : BaseObject {
public ViewVariantsObject(Session session) : base(session) { }
[Indexed(Unique = true), RuleUniqueValue]
public string RootViewId {
get { return GetPropertyValue<string>(nameof(RootViewId)); }
set { SetPropertyValue<string>(nameof(RootViewId), value); }
}
public ViewVariantObject CurrentVariant {
get { return GetPropertyValue<ViewVariantObject>(nameof(CurrentVariant)); }
set { SetPropertyValue<ViewVariantObject>(nameof(CurrentVariant), value); }
}
[Association]
public XPCollection<ViewVariantObject> Items {
get { return GetCollection<ViewVariantObject>(nameof(Items)); }
}
}
[XafDefaultProperty(nameof(Caption))]
public class ViewVariantObject : BaseObject {
public ViewVariantObject(Session session) : base(session) { }
[Association]
public ViewVariantsObject Owner {
get { return GetPropertyValue<ViewVariantsObject>(nameof(Owner)); }
set { SetPropertyValue<ViewVariantsObject>(nameof(Owner), value); }
}
public string ViewId {
get { return GetPropertyValue<string>(nameof(ViewId)); }
set { SetPropertyValue<string>(nameof(ViewId), value); }
}
public string Caption {
get { return GetPropertyValue<string>(nameof(Caption)); }
set { SetPropertyValue<string>(nameof(Caption), value); }
}
}
See Also