View Models

• Aug 12, 2022
• 3 minutes to read

The View Model is a part of an MVVM application responsible for the interaction between the two other parts: Model and View.

Base View Models

The DevExpress MVVM Framework contains base classes that you can use to create your View Models:

BindableBase

Implements the INotifyPropertyChanged interface and allows you to implement bindable properties.

ViewModelBase

A BindableBase descendant that offers commands, services, and interaction between View Models.

Generated View Models

The MVVM Framework allows you to produce boilerplate code for your View Models, so that you do not need to implement each command or property:

Runtime-generated POCO View Models

Use the ViewModelSource.Create method to create a descendant of your View Model class. The mechanism is based on the Reflection Emit and produces code at runtime.

View Models Generated at Compile Time

Use attributes to generate a View Model. The mechanism is based on the Source Generators and produces code at compile time.

You can find the requirements for both techniques in the table below:

	POCO View Models generated at runtime	View Models generated at compile time
C#	v6+	v9+
.NET Framework	v4.5.2+	v4.6.1+
.NET Core	v3.0+	v3.0+

Note

C# 9 is officially supported in .NET 5 and newer. You may encounter issues when you use earlier versions of .NET and .NET Framework.

The following table summarizes the differences between View Models generated at runtime and compile time:

	POCO View Models generated at runtime	View Models generated at compile time
Execution time	Runtime	Compile time
Generated class	Descendant class	Partial class
Generated code access		Read-only .cs file
Debug access
VB support

Dependency Injection

To bind a view to a view model, create a MarkupExtension that resolves the correct ViewModel type:

C#

public class DISource : MarkupExtension {
    public static Func<Type, object, string, object> Resolver { get; set; }

    public Type Type { get; set; }
    public object Key { get; set; }
    public string Name { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider) => Resolver?.Invoke(Type, Key, Name);
}

Register the resolver at application startup:

C#

protected override void OnStartup(StartupEventArgs e) {
    base.OnStartup(e);
    DISource.Resolver = Resolve;
}
object Resolve(Type type, object key, string name) {
    if(type == null)
        return null;
    if(key != null)
        return Container.ResolveKeyed(key, type);
    if(name != null)
        return Container.ResolveNamed(name, type);
    return Container.Resolve(type);
}

Specify the DataContext in XAML in the following manner:

XAML

DataContext="{common:DISource Type=common:CollectionViewModel}"

Examples

• Services:

  View Example

• POCO:

  View Example

View Model Interaction

• Interaction of ViewModels
• Passing Data Between ViewModels (ISupportParameter)
• ViewModel Relationships (ISupportParentViewModel)
• Messenger