Pro WPF and Silverlight MVVM effective Application Development

this print for content only—size & color not accurate 7.5 x 9.25 spine = 0.75" 272 page count 360 PPI Hall WPF and Silverlight MVVM

THE EXPERT’S VOICE® IN WPF

Pro

WPF and Silverlight

MVVM

Effective Application Development with

Model-View-ViewModel

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Gary McLean Hall

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Harness the power of WPF and Silverlight to

produce clean, testable, maintainable code

BOOKS FOR PROFESSIONALS BY PROFESSIONALS®

Pro WPF and Silverlight MVVM

WPF and Silverlight are unlike any other user interface technologies. They have

been built to a new paradigm that—if harnessed correctly—can yield unprec￾edented power and performance. This book shows you how to control that

power to produce clean, testable, maintainable code.

Design and development experts now recognize that any non-trivial WPF

or Silverlight application needs to be designed around the Model-View￾ViewModel (MVVM) design pattern in order to unlock the technology’s full

data-binding potential. But many coders still rely solely on programmatic

interaction between controls, because it's been hard for many to trust the WPF

data-binding technologies.

Pro WPF and Silverlight MVVM shows you why that trust has been earned.

Inside, discover how to create fast, scalable, and maintainable applications

using Silverlight and WPF. With this book, you’ll learn how to:

• Split view and model code apart to achieve a separation of concerns

• Implement a ViewModel layer that mediates between the view and model

• Apply automated unit tests to verify the quality of production code

• Validate user input with a variety of techniques

• Integrate a data access layer for persistently storing objects

Gary McLean Hall

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Pro

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Pro WPF and

Silverlight MVVM

Effective Application Development with

Model-View-ViewModel

■ ■ ■

Gary McLean Hall

ii

Pro WPF and Silverlight MVVM: Effective Application Development with Model-View-ViewModel

Copyright © 2010 by Gary McLean Hall

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iii

For my wife, Victoria

iv

Contents at a Glance

■Contents ................................................................................................................ v

■About the Author ................................................................................................... x

■About the Technical Reviewer .............................................................................. xi

■Acknowledgments ............................................................................................... xii

■Introduction ....................................................................................................... xiii

■Chapter 1: Overview of WPF and Silverlight ......................................................... 1

■Chapter 2: DataBinding ....................................................................................... 21

■Chapter 3: Model-View Separation ..................................................................... 55

■Chapter 4: The ViewModel .................................................................................. 81

■Chapter 5: Events and Commands .................................................................... 111

■Chapter 6: Validation ......................................................................................... 129

■Chapter 7: Unit Testing ...................................................................................... 145

■Chapter 8: Data Access Layer ........................................................................... 163

■Chapter 9: Application Support ......................................................................... 185

■Chapter 10: Sample Application ........................................................................ 205

■Index ................................................................................................................. 243

v

Contents

■Contents at a Glance ............................................................................................ iv

■About the Author ................................................................................................... x

■About the Technical Reviewer .............................................................................. xi

■Acknowledgments ............................................................................................... xii

■Introduction ........................................................................................................ xiii

■Chapter 1: Overview of WPF and Silverlight ......................................................... 1

WPF and Silverlight ......................................................................................................... 1

What Is WPF? ......................................................................................................................................... 1

What Is Silverlight? ................................................................................................................................ 5

Differences Between WPF and Silverlight .............................................................................................. 7

Multi-Target Platforms ........................................................................................................................... 9

XAML ............................................................................................................................. 13

Declarative User Interfaces .................................................................................................................. 13

XAML Elements .................................................................................................................................... 14

XAML Features ..................................................................................................................................... 16

User Experience vs. User Interface ............................................................................... 18

Summary ....................................................................................................................... 19

■Chapter 2: DataBinding ....................................................................................... 21

The Power of DataBinding with XAML .......................................................................... 21

Dependency Objects ............................................................................................................................ 21

Dependency Properties ........................................................................................................................ 23

Binding Sources ................................................................................................................................... 26

■ CONTENTS

vi

Binding Modes ..................................................................................................................................... 28

The DataContext ................................................................................................................................... 30

Advanced DataBinding .................................................................................................. 31

Binding Parameters ............................................................................................................................. 31

Data Conversion ................................................................................................................................... 35

ObjectDataProvider .............................................................................................................................. 42

Debugging DataBindings ...................................................................................................................... 46

Templating ........................................................................................................................................... 49

Summary ....................................................................................................................... 53

■Chapter 3: Model-View Separation ..................................................................... 55

Separation of Concerns ................................................................................................. 55

Dependencies ...................................................................................................................................... 55

MVVM Alternatives ............................................................................................................................... 59

The Model ..................................................................................................................... 66

Encapsulation ....................................................................................................................................... 66

Don’t Repeat Yourself (DRY) ................................................................................................................. 67

You Ain’t Gonna Need It (YAGNI) .......................................................................................................... 69

The Law of Demeter ............................................................................................................................. 70

Test-Driven Development .................................................................................................................... 71

The View ....................................................................................................................... 73

Data Representation ............................................................................................................................ 73

User Input ............................................................................................................................................. 73

Data Binding ......................................................................................................................................... 74

Separating Model from View ......................................................................................... 75

The Mediator Pattern ........................................................................................................................... 75

Other Model-View-X Implementations ................................................................................................. 77

You Gotta Keep ’Em Separated ............................................................................................................ 78

Summary ....................................................................................................................... 79

■Chapter 4: The ViewModel .................................................................................. 81

First ViewModel ............................................................................................................ 81

■ CONTENTS

vii

The MVVM Template Project ................................................................................................................ 81

.NET Framework Interfaces and Classes ...................................................................... 90

Observer Pattern .................................................................................................................................. 90

INotifyPropertyChanged Interface ........................................................................................................ 91

Observable Collections ......................................................................................................................... 92

CollectionViewSource .......................................................................................................................... 94

Constructing ViewModels .................................................................................................................... 96

Handling Concurrency ................................................................................................. 100

Threading ........................................................................................................................................... 100

Threading Problems In WPF and Silverlight ....................................................................................... 104

Updating the UI .................................................................................................................................. 107

Summary ..................................................................................................................... 110

■Chapter 5: Events and Commands .................................................................... 111

Events ......................................................................................................................... 111

Events in .NET .................................................................................................................................... 111

Events in WPF and Silverlight ............................................................................................................ 112

Commands .................................................................................................................. 115

Command Pattern .............................................................................................................................. 116

The RelayCommand ........................................................................................................................... 119

Attached Command Behavior ............................................................................................................. 126

Avoiding Events Using Dependency Injection .................................................................................... 126

Summary ..................................................................................................................... 128

■Chapter 6: Validation ......................................................................................... 129

The Validation Process ................................................................................................ 130

Binding Validation Rules ............................................................................................. 131

ValidationRule Class ........................................................................................................................... 131

Exceptions for Validation .................................................................................................................... 133

A Validation Framework ..................................................................................................................... 135

IDataErrorInfo Interface ...................................................................................................................... 135

DataErrorValidationRule Class ........................................................................................................... 139

■ CONTENTS

viii

Validation in Silverlight ............................................................................................... 139

Visually Formatting Validation Errors .......................................................................... 143

Validation.ErrorTemplate Attached Property ...................................................................................... 143

Validation.HasError Attached Property ............................................................................................... 143

Summary ..................................................................................................................... 144

■Chapter 7: Unit Testing ...................................................................................... 145

The Importance of Testing .......................................................................................... 145

Traditional Testing ............................................................................................................................. 145

What Is Unit Testing? ......................................................................................................................... 149

Why Unit Test? ................................................................................................................................... 151

How to Unit Test .......................................................................................................... 152

Unit Testing with Visual Studio 2010 ................................................................................................. 152

Writing Tests ...................................................................................................................................... 158

Summary ..................................................................................................................... 162

■Chapter 8: Data Access Layer ........................................................................... 163

Object-Relational Dichotomy ...................................................................................... 163

DAL Implementations .................................................................................................. 172

Manual Implementation ..................................................................................................................... 172

Third-Party Implementations ............................................................................................................. 176

Supporting Patterns .................................................................................................... 180

The Repository Pattern ....................................................................................................................... 180

Unit of Work ....................................................................................................................................... 181

Creating the Data Schema .......................................................................................... 182

Generate, Not Create .......................................................................................................................... 182

Summary ..................................................................................................................... 183

■Chapter 9: Application Support ......................................................................... 185

Serialization ................................................................................................................ 186

Serializing POCOs ............................................................................................................................... 186

Extensibility ................................................................................................................. 192

■ CONTENTS

ix

Why Extend? ...................................................................................................................................... 192

Using Managed Extensibility Framework ........................................................................................... 193

Extending A WPF Application ............................................................................................................. 197

Limitations ......................................................................................................................................... 202

Summary ..................................................................................................................... 203

■Chapter 10: Sample Application ........................................................................ 205

Requirements .............................................................................................................. 205

The Application .................................................................................................................................. 205

Model and Tests .......................................................................................................... 206

Money ................................................................................................................................................ 206

Account .............................................................................................................................................. 211

ViewModel and Tests .................................................................................................. 220

MainWindowViewModel ..................................................................................................................... 220

View ............................................................................................................................ 228

Summary ..................................................................................................................... 241

■Index ................................................................................................................. 243

■ CONTENTS

x

About the Author

■ Gary McLean Hall lives in Leeds, England, with his wife, Victoria, and their dog,

Isabella. He is the director of Four Minute Mile Ltd, a software development

consultancy specializing in Microsoft technologies.

xi

About the Technical Reviewer

■ Nathan Kannan serves as Director of GIS (Geographic Information System) at Sentinel USA, a

company that specializes in providing GIS services and consulting to the utility industry. Mr. Kannan

provides a wealth of talent and expertise to Sentinel USA and has contributed to the success of several

high-profile development projects in the GIS technology arena. Mr. Kannan holds both a master’s

degree in Geographic Information Systems and Mapping (MS GIS) from The Ohio State University and a

bachelor’s degree in Civil Engineering (BE) from PSG College of Technology, India. His professional

skills and contributions are in the fields of GIS Software and Custom Application Development,

Advanced Spatial Database and Data Structure, Computational Cartography, GPS, and

Photogrammetry. He is the inventor and one of the authors of the patent “Distance Correction for Utility

Damage Prevention System, Publication No: WO/2007/067898, Publication Date: 14.06.2007.”

■ CONTENTS

xii

Acknowledgments

Thanks to my wife, Victoria, for being perfect in every way.

Thanks to my parents, Pam and Les, for funding such an expensive hobby and underwriting the dial-up

Internet bills of the late-90s.

Thanks to my brother, Darryn, for being a constant best friend, his wife, Jo, and their beautiful daughter,

Eleanor.

Thanks to my Granda George for his selfless generosity.

Thanks to my editor, Debra Kelly, whose patience knows no bounds!

Thanks to my dog, Isabella, for her unconditional loyalty.

Thanks to everyone who has taught me, whether they knew it or not.

xiii

Introduction

This book was conceived from a need to explain the MVVM pattern and how it helps structure WPF and

Silverlight applications. I had worked on a number of projects where these technologies were used but

general best practices were ignored because no one had formally explained the MVVM pattern and how

it compared to other patterns such MVP and MVC.

In Chapter 1, WPF and Silverlight will be explored in some detail and their respective features

highlighted.

Chapter 2 introduces the foundation of the MVVM pattern: the databinding model that eclipses the

equivalent functionality of Windows Forms or ASP.NET.

Chapter 3 explains why the model and the view must be separated in an application and provides

various tips and tricks that can help achieve a strict separation of concerns.

Chapter 4 introduces the ViewModel that sits between the model and view layers and mediates between

the two.

Chapter 5 discusses commands and events, weighing up the pros and cons of each.

Chapter 6 examines various options for implementing validation into an application.

Chapter 7 explores the best side effects of the separation of concerns achieved through MVVM:

testability and unit testing.

Chapter 8 outlines how to implement a Data Access Layer into a Silverlight or WPF application and how

the ViewModel can interact with this layer.

Chapter 9 explains how to serialize an object graph using WPF and MVVM, as well as exploring how WPF

and Silverlight applications can be extended.

Chapter 10 ends the book with a sample application that ties together many of the features covered

along the way.