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Introducing the Model Thread View Thread Pattern

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1 May 2010BSD14 min read 163K   862   172  
Reduce threading code, and increase UI responsiveness with a new pattern extending MVVM.
//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation.  All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious.  No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System.ComponentModel;
using System.Windows;

namespace Microsoft.Practices.Composite.Presentation
{
    /// <summary>
    /// Class that wraps an object, so that other classes can notify for Change events. Typically, this class is set as 
    /// a Dependency Property on DependencyObjects, and allows other classes to observe any changes in the Value. 
    /// </summary>
    /// <remarks>
    /// This class is required, because in Silverlight, it's not possible to receive Change notifications for Dependency properties that you do not own. 
    /// </remarks>
    /// <typeparam name="T">The type of the property that's wrapped in the Observable object</typeparam>
    public class ObservableObject<T> : FrameworkElement, INotifyPropertyChanged
    {
        /// <summary>
        /// Identifies the Value property of the ObservableObject
        /// </summary>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1000:DoNotDeclareStaticMembersOnGenericTypes", Justification = "This is the pattern for WPF dependency properties")]
        public static readonly DependencyProperty ValueProperty =
                DependencyProperty.Register("Value", typeof(T), typeof(ObservableObject<T>), new PropertyMetadata(ValueChangedCallback));

        /// <summary>
        /// Event that gets invoked when the Value property changes. 
        /// </summary>
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// The value that's wrapped inside the ObservableObject.
        /// </summary>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1721:PropertyNamesShouldNotMatchGetMethods")]
        public T Value
        {
            get { return (T)this.GetValue(ValueProperty); }
            set { this.SetValue(ValueProperty, value); }
        }

        private static void ValueChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ObservableObject<T> thisInstance = ((ObservableObject<T>)d);
            PropertyChangedEventHandler eventHandler = thisInstance.PropertyChanged;
            if (eventHandler != null)
            {
                eventHandler(thisInstance, new PropertyChangedEventArgs("Value"));
            }
        }
    }
}

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License

This article, along with any associated source code and files, is licensed under The BSD License


Written By
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Switzerland Switzerland
Daniel is a former senior engineer in Technology and Research at the Office of the CTO at Microsoft, working on next generation systems.

Previously Daniel was a nine-time Microsoft MVP and co-founder of Outcoder, a Swiss software and consulting company.

Daniel is the author of Windows Phone 8 Unleashed and Windows Phone 7.5 Unleashed, both published by SAMS.

Daniel is the developer behind several acclaimed mobile apps including Surfy Browser for Android and Windows Phone. Daniel is the creator of a number of popular open-source projects, most notably Codon.

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