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- Herausgeber: Packt Publishing
- Kategorie: Fachliteratur
- Sprache: Englisch
Windows Presentation Foundation is rich in possibilities when it comes to delivering an excellent user experience. This book will show you how to build professional-grade applications that look great and work smoothly.
We start by providing you with a foundation of knowledge to improve your workflow – this includes teaching you how to build the base layer of the application, which will support all that comes after it. We’ll also cover the useful details of data binding. Next, we cover the user interface and show you how to get the most out of the built-in and custom WPF controls.
The final section of the book demonstrates ways to polish your applications, from adding practical animations and data validation to improving application performance. The book ends with a tutorial on how to deploy your applications and outlines potential ways to apply your new-found knowledge so you can put it to use right away.
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Table of Contents
Mastering Windows Presentation Foundation
Mastering Windows Presentation Foundation
Copyright © 2017 Packt Publishing
All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.
Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.
Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.
First published: February 2017
Production reference: 1130217
Published by Packt Publishing Ltd.
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ISBN 978-1-78588-300-2
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Credits
Author
Sheridan Yuen
Copy Editor
Pranjali Chury
Reviewer
Alex Golesh
Project Coordinator
Vaidehi Sawant
Commissioning Editor
Edward Gordon
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About the Author
Sheridan Yuen is a Microsoft .NET MCTS and Oracle Java SCJP certified software developer, living in London, England. His passion for coding made him stand out from the crowd right from the start. From his second year onward at university, he was employed to be a teaching assistant for the first year student coding workshops and has since returned as a guest lecturer.
Among other prestigious positions, he was the primary software developer for the Ministry of Sound group for four years, working on their main music business application, responsible for creating their multi award winning albums. This application managed to increase its users’ productivity by up to 80% in some cases.
In addition to this, he architected a unique ticket scanning application for their award winning nightclub, making it the first club in the world to introduce scanned ticket entry across all streams for their clients. Coming from a musical background and being a qualified audio engineer, with experience of record production and digital audio, this post was a perfect union.
He soon became a popular figure in the C# and WPF sections of the Stack Overflow, “question and answer” website, being awarded enough reputation by the community members to raise him to well within the top half percent of all users. While authoring this book and other projects have kept him away for some time, he is keen to return to continue to help new users to get to grips with WPF.
I would like to thank my long suffering girlfriend Jemma, who has regularly had to make do without my company for the best part of a year, for her patience while I was composing and writing this book and the many examples in it. I’d also like to thank Chaitanya from Packt Publishing for convincing me to write this book in the first place and without who, this book would not have been written.
Finally, I would like to thank Mary Thomson, Professor Sarah Barman and Professor James Orwell in particular, from Kingston University, London, who inspired me to change the direction of my previous career and planted the seed of curiosity that has taken me so far. I would also like to thank James for encouraging me to move from the Bachelor’s Degree course to the integrated Master’s Degree that I ended up gaining and for all of the benefits that this brought with it.
About the Reviewer
Alex Golesh is an international expert in XAML-based technologies such as Universal Windows Platform (Windows, Windows Phone, HoloLens, Xbox One), Xamarin.Forms, WPF, and Silverlight. Also, Alex specializes in cloud-based solutions such as Microsoft Azure. Alex developed training solutions for Microsoft Learning on Windows Phone and Windows 8 and delivers workshops for developers and enterprises. Alex leads the architecture and development process in multiple projects for his clients.
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Preface
While it can be easy to construct a basic form using WPF, it takes a lot more to fully understand what WPF can do for us and how best to use it. It has a steep learning curve and it can be difficult to comprehend this very different way of working. This book aims to help you to get over that initial hill and continue to fully enable you to implement any given requirement.
This book will start by providing you the foundation knowledge on how to improve your workflow and what to do when you have problems. It will build upon this foundation by introducing the base layer of the application that will serve all that comes after it. We will then take a detour to cover data binding in detail.
The book will then turn to the User Interface (UI) and how to get the most out of the built-in and custom WPF controls. It will make clear which customization methods are best to utilize in a wide range of scenarios, avoiding the need to rewrite existing functionality. Other tips and tricks will also be provided to enable you to create your own visually stunning UIs.
The final section of the book will introduce the concluding ways for you to polish your applications, from adding practical animations and data validation, to improving application performance. The book will end by explaining how to deploy the applications that you have been working so hard on and discuss other things that you can now achieve with your new found knowledge.
What this book covers
Chapter 1, A Smarter Way of Working with WPF, introduces the Model, View, View Model (MVVM) software architectural pattern and the benefits of using it with WPF.
Chapter 2, Debugging WPF Applications, provides essential tips on various methods of debugging WPF applications, ensuring the ability to iron out any problems that may occur.
Chapter 3, Writing Custom Application Frameworks, introduces the indispensable concept of application frameworks, with early examples that will be built upon as the book progresses. By the end of the book, you will have a fully functioning Framework with which to build your applications upon.
Chapter 4, Becoming Proficient with Data Binding, demystifies data binding and clearly demonstrates how to use it in a practical application. A plethora of examples will help you to understand which binding syntax to use in any given situation and to be confident that their bindings will work as expected.
Chapter 5, Using The Right Controls for The Job, explains which controls to use in particular situations and describes the various ways to modify them when required. It clearly outlines how to customize existing controls and how to create custom controls when required.
Chapter 6, Mastering Practical Animations, explains the ins and outs of WPF Animations, detailing lesser known functionality. It concludes with a number of ideas for practical animations and continues to build upon the custom application framework.
Chapter 7, Creating Visually Stunning User Interfaces, offers advice for getting the most out of the WPF visuals, while remaining practical, and provides handy tips on making applications stand out from the crowd.
Chapter 8, Implementing Responsive Data Validation, presents a number of methods of data validation to suit every situation and continues to build upon the custom application framework. It covers full, partial, instant, and delayed validation and a variety of different ways to display validation errors.
Chapter 9, Completing That Great User Experience, provides tips for creating applications with a great user experience. Concepts introduced here, such as asynchronous data access and keeping the end users well informed, will substantially improve the existing custom application framework.
Chapter 10, Improving Application Performance, lists a number of ways to increase the performance of WPF applications from freezing resources to implementing virtualization. Readers that follow these tips and tricks can rest assured that their WPF applications will perform as optimally as they can.
Chapter 11, Deploying Your Masterpiece Application, covers the final requirement for all professional applications—deployment. It includes the older method of using the Windows Installer software, along with the more common and up-to-date method of using ClickOnce functionality.
Chapter 12, What Next?, summarizes what you have learned from this book and suggests what you can do with many of your various new skills. It provides you with further ideas on extending the application framework.
What you need for this book
As with all WPF development, you'll need to have the .NET Framework and a version of Microsoft's Visual Studio integrated development environment software installed on your computer.
You'll be able to use versions as old as 2010, but in order to use the code in the book that takes advantage of the latest .NET Framework improvements, you'll need to use one of the newer versions. Note that any edition of Visual Studio can be used, from the top of the line Enterprise edition to the free Community (2015) edition.
Who this book is for
This book is for working developers with a basic to moderate level of knowledge about Windows Presentation Foundation and for those interested in improving their practical day to day WPF skills. It will also be of special interest to individuals wanting to know more about application architecture and those wanting to improve the look of their user interfaces.
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Chapter 1. A Smarter Way of Working with WPF
When Windows Presentation Foundation (WPF) was first released as part of the .NET Framework version 3.0 in 2006, it was billed as the future of desktop application Graphical User Interface (GUI) languages and supporters claimed that it would put an end to the previous GUI technology, Windows Forms. However, as time passed, it has fallen far short of this claim.
There are three main reasons that WPF has not taken off as widely as previously expected. The first reason has nothing to do with WPF and stems from the recent push to host everything in the cloud and having web interfaces rather than desktop applications. The second reason relates to the very steep learning curve and the very different way of working that is required to master WPF.
The last reason is that it is not a very efficient language and if a WPF application has lots of 'bells and whistles' in, then either the client computers will need to have additional RAM and/or graphics cards installed, or they could face a slow and stuttering user experience.
This explains why many companies that make use of WPF today are in the finance industry, where they can afford to upgrade all users' computers to be able to run their applications optimally. This book will aim to make WPF more accessible to the rest of us by providing practical tips and tricks to help build our real-world applications more easily and more efficiently.
One of the simplest changes with the biggest workflow improvements that we can make to improve the way we work with WPF is to follow the MVVM software architectural pattern. It describes how we can organize our classes to make our applications more maintainable, testable, and generally simpler to understand. In this chapter, we will take a closer look at this pattern and discover how it can help us to improve our applications.
After discovering what MVVM is and what its benefits are, we'll learn several new ways to communicate between the various components in this new environment. We'll then focus on the physical structure of the code base in a typical MVVM application and investigate a variety of alternative arrangements.
What is MVVM and how does it help?
Model-View-View Model (MVVM) is a software architectural pattern that was famously introduced by John Gossman on his blog back in 2005 and is now commonly used when developing WPF applications. Its main purpose is to provide a Separation of Concerns between the business model, the User Interface (UI), and the business logic. It does this by dividing them into three distinct types of core components: Models, Views, and View Models. Let's take a look at how they are arranged and what each of these components represent.
As we can see here, the View Models component sits between the Models and the Views and provides two-way access to each of them. It should be noted at this point that there should be no direct relationship between the Views and Models components and only loose connections between the other components. Let's now take a closer look at what each of these components represent.
Models
Unlike the other MVVM components, the Model constituent comprises of a number of elements. It encompasses the business data model along with its related validation logic and also the Data Access Layer (DAL), or data repositories, that provide the application with data access and persistence.
The data model represents the classes that hold the data in the application. They typically mirror the columns in the database more or less, although it is common that they are hierarchical in form, and so may require joins to be performed in the data source in order to fully populate them. One alternative would be to design the data model classes to fit the requirements in the UI, but either way, the business logic or validation rules will typically reside in the same project as the data model.
The code that is used to interface with whatever data persistence technology is used in our application is also included within the Models component of the pattern. Care should be taken when it comes to organizing this component in the code base, as there are a number of issues to take into consideration. We'll investigate this further in a while, but for now, let's continue to find out more about the components in this pattern.
View Models
The View Models can be explained easily; each View Model provides its associated View with all of the data and functionality that it requires. In some ways, they can be considered to be similar to the old Windows Forms code behind files, except that they have no direct relationship with the View that they are serving. A better analogy, if you're familiar with MVC, would be that they are similar to the Controllers in the Model-View-Controller (MVC) software architectural pattern. In fact, in his blog, John describes the MVVM pattern as being a variation of the MVC pattern.
They have two-way connections with the Model component in order to access and update the data that the Views require, and often, they transform that data in some way to make it easier to display and interact with in the UI. They also have two-way connections with the Views through data binding and property change notification. In short, View Models form the bridge between the Model and the View, which otherwise have no connection to each other.
However, it should be noted that the View Models are only loosely connected to the Views and Model components through their data binding and interfaces. The beauty of this pattern enables each element to be able to function independently from each other.
To maintain the separation between the View Models and the View, we avoid declaring any properties of UI-related types in the View Model. We don't want any references to UI-related DLLs in our View Models project, and so we make use of custom IValueConverter implementations to convert them to primitive types. For example, we might convert Visibility objects from the UI to plain bool values or convert the selection of some colored Brush objects to an Enum instance that is safe to use in the View Model.
Views
The Views define the appearance and layout of the UI. They typically connect with a View Model through the use of their DataContext property and display the data that it supplies. They expose the functionality provided by the View Model by connecting its commands to the UI controls that the users interact with.
In general, the basic rule of thumb is that each View has one associated View Model. This does not mean that a View cannot data bind to more than one data source or that we cannot reuse View Models. It simply means that, in general, if we have a class called SecurityView, it is more than likely that we'll also have an instance of a class named SecurityViewModel that will be set as the value of that View's DataContext property.
Data binding
One often overlooked aspect of the MVVM pattern is its requirement for data binding. We could not have the full Separation of Concerns without it, as there would be no easy way of communicating between the Views and View Models. The XAML markup, data binding classes, and ICommand and INotifyPropertyChanged interfaces are the main tools in WPF that provide this functionality.
The ICommand interface is how commanding is implemented in the .NET Framework. It provides behavior that implements and even extends the ever useful Command pattern, in which an object encapsulates everything needed to perform an action. Most of the UI controls in WPF have Command properties that we can use to connect them to the functionality that the commands provide.
The INotifyPropertyChanged interface is used to notify binding clients that property values have been changed. For example, if we had a User object and it had a Name property, then our User class would be responsible for raising the PropertyChanged event of the INotifyPropertyChanged interface, specifying the name of the property each time its value was changed. We'll look much deeper into all of this later, but now let's see how the arrangement of these components help us.
So how does MVVM help?
One major benefit of adopting MVVM is that it provides the crucial Separation of Concerns between the business model, the UI, and the business logic. This enables us to do several things. It frees the View Models from the Models, both the business model and the data persistence technology. This in turn enables us to reuse the business model in other applications and swap out the DAL and replace it with a mock data layer so that we can effectively test the functionality in our view models without requiring any kind of real data connection.
It also disconnects the Views from the View logic that they require, as this is provided by the View Models. This allows us to run each component independently, which has the advantage of enabling one team to work on designing the Views, while another team works on the View Models. Having parallel work streams enables companies to benefit from vastly reduced production times.
Furthermore, this separation also makes it easier for us to swap the Views for a different technology without needing to change our Model code. We may well need to change some aspects of the View Models, for example, the new technology used for the Views may not support the ICommand interface, but in principal, the amount of code that we would need to change would be fairly minimal.
The simplicity of the MVVM pattern also makes WPF easier to comprehend. Knowing that each View has a View Model that provides it with all the data and functionality that it requires means that we always know where to look when we want to find where our data bound properties have been declared.
Is there a downside?
There are, however, a few drawbacks to using MVVM, and it will not help us in every situation. The main downside to implementing MVVM is that it adds a certain level of complexity to our applications. First, there's the data binding, which can take some time to master. Also, depending on your version of Visual Studio, data binding errors may only appear at runtime and can be very tricky to track down.
Then, there are the different ways to communicate between the Views and View Models that we need to understand. Commanding and handling events in an unusual way takes a while to get used to. Having to discover the optimal arrangement of all the required components in the code base also takes time. So, there is a steep learning curve to climb before we can become competent at implementing MVVM for sure. This book will cover all of these areas in detail and attempt to lessen the gradient of that learning curve.
However, even when we are well practiced at the pattern, there are still occasional situations when it wouldn't make sense to implement MVVM. One example would be if our application was going to be very small, it would be unlikely that we would want to have unit tests for it or swap out any of its components. It would, therefore, be impractical to go through the added complexity of implementing the pattern when the benefits of the Separation of Concerns that it provides were not required.
Structuring the application code base
Now that we have a better understanding of the MVVM pattern, let's look at how we might implement it in a WPF application. What should the folder structure of our application be like? Clearly, we'll need somewhere to put our Models, Views, and View Models; however, how we arrange them will somewhat depend on the overall size of our application.
As we have heard, very small projects do not really suit MVVM because implementing it can involve a lot of preparation and often, the benefits do not apply. For small WPF applications, we would typically have just one project in our WPF application. In these cases, our classes would be separated into different folders within the single project.
With larger scale applications, we arrange our classes in the same basic structure, but as there are more classes and more chance that we want to reuse some of this code, it makes sense to use separate projects instead of folders. Either way, our classes should end up with the same CLR namespaces, as they tend to follow the structure of the application, regardless of whether those classes were separated using folders or projects.
While the CLR namespace in our startup project might be something along the lines of CompanyName.ApplicationName, the namespace of the classes in the Models component would be, or start with, CompanyName.ApplicationName.Models. For the purpose of the remainder of this book, we will assume that we are dealing with a large-scale WPF application and using projects for the separation of our classes.
There is nothing in the MVVM pattern that dictates what structure our code base should have, although there are clues. We will clearly need Views and ViewModels projects, but the Models project is less clearly defined. There are several elements within the Models component of MVVM, but we don't necessarily want to group them all into a single project in our code base. There are other projects that will be required too.
Let's visualize some possible structures so that we can get started with building our application.
These examples offer an insight into what the project structure of an MVVM-based WPF application might look like. However, nothing is set in stone and we are free to rename and to reorganize our application projects as we see fit. The important thing is how the components are connected together rather than the arrangement of the application files.
After we have developed a number of WPF applications, we get a feel for which project names and which structure we prefer, so I'd suggest trying a few variations and seeing which you feel more comfortable working with. Of course, some of us may not have the luxury of being able to create or alter the structure of the application that we work on. Let's first focus on the projects common to both example structures.
We see that the Images and Resources folders reside in the startup project. While this is customary, they can technically reside in any project or even in their own project. However, I prefer to keep them in this project because it provides a marginal performance benefit. Typically, when using MVVM, the only other files in the startup project will be the MainWindow.xaml, App.xaml (and their constituent code behind files), and app.config files.
The Images folder contains the images and icons that are displayed in the UI controls, whereas the Resources folder normally contains any resource files, such as XML schemas or text or data files that are used by the application.
The next project is named Converters and is fairly self-explanatory. It only contains classes that have implemented the IValueConverter interface and are used for converting data bound values in the Views. These classes are all reusable and the DLL from this project should be kept up to date and shared amongst our other applications.
Both examples show an Extensions project, but this is entirely optional and not a requirement of the MVVM pattern. I just happen to find Extension methods to be an essential part of .NET development, having built up a large collection of invaluable helper methods. After getting used to being able to call Add on an IEnumerable instance or ToObservableCollection on a query result for example, I now reuse them in every application. We'll see some examples of these in Chapter 3 , Writing Custom Application Frameworks, Chapter 8, Implementing Responsive Data Validation, and Chapter 9, Completing That Great User Experience.
The next common project that we can see is a project called Managers. Others may prefer to call this Engines, Services, or something similar, but that is just a personal preference, and either way, the content will be the same. In this project, we typically find a number of classes that together provide a wide variety of functionality to the View Models. For example, in this project, we might find classes named ExportManager, FeedbackManager, HardDriveManager, WindowManager, and so on.
It is important to have a project like this, where we have one common place to provide all of the required specialized functionality for our application, rather than having to repeat the code in each View Model that requires that certain functionality. These classes are totally reusable between applications and this arrangement also promotes behavioral consistency throughout the application.
For example, without consolidating all of our functionality in this project, we might be tempted to copy and paste certain bits of code from one View Model to another. If the code then requires a change in the future, we may not remember that it has been copied and only update it in one View Model, thereby breaking the consistency of the application.
