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Attached Property Wizard

Generate the C# code to declare a new attached property declaration

Introduction

In Xamarin.Forms, attached properties are special properties declared on any class that can be consumed in XAML to provide specific, additional behaviour to a XAML element.

One of the best examples of an attached property is the Grid.Row, Grid.RowSpan, Grid.Column and Grid.ColumnSpan properties. These properties allow grid row and column information to be "attached" to any XAML element without the element having knowledge of the Grid layout.

At a minimum, attached properties are composed of three parts:

  • The attached property declaration. This must be a created via the BindableProperty.CreateAttached factory method.
  • The get method for the property. This must be a static method named Get[Name] that returns [Type] with a single parameter of BindableObject.
  • The set method for the property. This must be a static method named Set[Name] that returns void with two parameters of BindableObject, [Type].

Attached Property Example 

public static readonly BindableProperty HasShadowProperty = BindableProperty.CreateAttached("HasShadow", typeof(bool), typeof(MyClass), default(bool));
public static bool GetHasShadow(BindableObject target)
{
    return (bool)target.GetValue(HasShadowProperty);
}
public static void SetHasShadow(BindableObject target, bool value)
{
    target.SetValue(HasShadowProperty, value);
}

Usage Example 

<Label local:MyClass.HasShadow="true"/>

One of the main difficulties with attached properties is remembering the full syntax and correct structure for a new property.

To simplify their creation, the wizard generates the C# code for a new attached property.

Using The Attached Property Wizard

To open the attached property wizard, press Alt+Return within the body any C# class.

In the code actions menu that opens, choose Create an attached property to launch the wizard.

Attached Property Wizard

The attached property wizard in Visual Studio Windows

The attached property wizard consists of the following parts:

  • Name: The name of the new attached property.
  • Type: The fully qualified type name for the attached properties type. Defaults to System.Object, however, the wizard will attempt to infer the desired type based on the Name input. See Automatic Type Inference.
  • Control Type: The type of class that declared this attached property.

On the right hand side of the wizard is a preview of the code that will be created.

To create the new attached property, enter the name and type of the new property and then press Create Attached Property. This will insert the generated code into the class at the location of the caret.

Automatic Type Inference

The attached property wizard supports Automatic Type Inference based on the name that is provided to the wizard.

Please see the Automatic Type Inference documentation for a full breakdown of this feature.

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