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- Herausgeber: Packt Publishing
- Sprache: Englisch
- Veröffentlichungsjahr: 2012
Windows Presentation Foundation (WPF) provides developers with a unified programming model for building rich Windows smart client user experiences that incorporate UI, media, and documents.WPF has become the leading technology for developing rich client applications on the Windows platform, packed with features and capabilities. However, WPF is big; in fact, it's huge, causing a steep learning curve for the beginner and even for those already using some WPF features.Windows Presentation Foundation 4.5 Cookbook provides clear recipes for common WPF tasks. It includes detailed explanations and code examples for customizing and enhancing the basic scenarios, while gaining a deep understanding of WPF mechanics and capabilities.WPF is different and requires a different mind-set and approach. This book provides recipes and insights not only in its design but also its practical implementation details.Starting from the foundations of WPF, such as dependency properties and XAML, the book touches on all major WPF aspects, such as controls and layout, resources, and digs deep into its unprecedented data binding capabilities.The book shows data and control templates in action, which allow full customizations of displayed data and controls in a declarative way. Supported by styles and resources makes data binding all the more powerful. The Model View View-Model pattern is presented as an effective way of maximizing decoupling of components, while providing an elegant way of expanding applications while maintaining a tight grip on complexity.The later parts discuss custom elements and controls ñ the ultimate customization mechanism, and looks at multithreading issues, and how .NET 4.5 task parallelism features can enhance application performance.
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Table of Contents
Windows Presentation Foundation 4.5 Cookbook
Windows Presentation Foundation 4.5 Cookbook
Copyright © 2012 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: September 2012
Production Reference: 1150912
Published by Packt Publishing Ltd.
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Cover Image by Mark Holland (<[email protected]>)
Credits
Author
Pavel Yosifovich
Reviewers
Alon Fliess
Ariel Ben Horesh
Stas Shteinbook
Dan Vestergaard
Acquisition Editor
Rukshana Khambatta
Lead Technical Editor
Kedar Bhat
Technical Editor
Madhuri Das
Project Coordinator
Yashodhan Dere
Proofreaders
Aaron Nash
Maria Gould
Indexer
Rekha Nair
Graphics
Aditi Gajjar
Production Coordinator
Shantanu Zagade
Cover Work
Shantanu Zagade
About the Author
Pavel Yosifovich is the CTO of CodeValue (http://www.codevalue.net), a software development, consulting, and training company, based in Israel. He writes, consults, and trains developers on various software development topics, from Windows internals, to .NET enterprise systems, and almost everything in between. He’s a Microsoft MVP and a frequent speaker at national events, such as Tech-Ed and DevAcademy.
In the past, he co-founded the startup company Quiksee that was acquired by Google in September 2010.
Writing a book is a tremendous effort, even if you know what you want to write (and I didn’t some of the time). It wasn’t possible without the support of my family: my wife Idit, and my kids, Daniel and Amit, and the latest recruit, Yoav. Thank you for the making the time and more than that – thank you for the support and encouragement along the way. It’s certainly easy to give up, but you wouldn’t let me – so thank you again!
About the Reviewers
Alon Fliess is the chief architect and founder of CodeValue. CodeValue is the home of software experts. CodeValue builds software tools, foundations, and products for the software industry and offers mentoring, consulting, and project development services.
Alon got his BSc degree in Electrical and Computer Engineering from the Technion, the Israel Institute of Technology. He is an expert on many Microsoft technologies, be it Windows client and server programming using C#/C++/.NET, Windows Azure Cloud Computing, or Windows internals. Microsoft has recognized his expertise and community activities and granted him two awards: Microsoft Regional Director (MRD) and a VC++ MVP.
Alon has deep knowledge and understanding of Windows and Windows Internals. He is a co-author of Windows 7 Microsoft Training Program as well as a co-author of the Introducing Windows 7 for Developers book (ISBN-10: 0735626820)
Alon delivers courses and lectures in many seminars and conferences around the world, such as TechEd Europe, TechEd USA, NDC, and in Israel. Alon is a senior Software Architect; he deals with vast and complex projects. Alon architected and designed the software for the revolutionary new line of industrial printing machine of Landa Labs. He is also the architect of one of the largest software project of the Israeli Air Force. Alon is responsible for several open-source projects.
Many thanks to Pavel and Yashodhan, who gave me the opportunity to take part in the creation of this book.
Ariel Ben Horesh is a well-known .NET expert, team leader, and community leader.
With more than 10 years of experience in the software industry, Ariel now works at CodeValue, a company he co-founded, where he creates products for developers, and consults and conducts courses around the world on UI development: WPF/SL, Web, Mobile, and UI architecture.
You can visit his blog at: http://arielbh.com
Stas Shteinbook is a senior development leader and solution architect who works at CodeValue. He has a long history in developing large enterprise applications, guiding their architecture and developing process, and creating end-to-end solutions involving rich user experience interfaces using WPF technology.
I would like to thank my family, my mother Ludmila and my father Zinoviy, for all the help and support.
Dan Vestergaard is currently working as a software engineer, with primary focus on .NET, and in particular, developing user interfaces using WPF.
He has worked in the consultant business and for several years in financial and industrial businesses. He is now a software engineer in a large world-wide industrial company, writing WPF applications for factory quality control systems.
He started working with WPF in the early beta days, back in 2006, and has loved it ever since.
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Preface
Windows Presentation Foundation has been in release since late 2006, as a part of the then .NET 3.0 Framework, also preinstalled on Windows Vista at the time. It promised to change the way rich client applications are written, and eventually replace the old, Win32-based Windows Forms.
WPF gained traction slowly because of its enormous breadth and the different kind of thinking that was required—using XAML, data binding, templates, and styles was very different from the classic WinForms way of working. The power of WPF was evident, but it was difficult to master, and had a steep learning curve.
Over the years things changed; developers started to get used to and appreciate the new way of doing things. XAML began to look convenient and powerful and not just an extra thing to learn with little benefit. Still, for the newcomer, with or without WinForms experience, WPF looks daunting and uncontrollable.
Patterns have emerged, most notably the Model-View-View Model (MVVM), a variant of other existing view-data separation patterns (MVC and MVP), that made life easier (most of the time) but more importantly set a standard way of interaction of view and data; and although many implementations are possible (this is just a pattern, after all), it does let an application be built in more confidence, piece by piece.
This book holds a set of recipes that show how to do common tasks. But don’t just look at the recipes; instead, look at the other sections to deepen your understanding of WPF. No matter the number of recipes, there will always be other things an application needs that no book can cover; by understanding the foundations well, it’s possible to tackle any problem. This is why I have tried to emphasise the why, and not just the how.
WPF led to a bunch of other technologies being built on similar principles, namely Silverlight (cross browser web client development in .NET), Windows Phone 7.x (Microsoft’s Phone OS that uses a Silverlight variant), and lately Windows 8 and Windows Phone 8—all built around similar concepts such as XAML, dependency properties, templates, styles, and bindings—this shows the power and impact of WPF.
What this book covers
Chapter 1, Foundations, introduces the most important concepts in WPF. From the XAML language, to dependency properties, to attached events.
Chapter 2, Resources, discusses WPF’s unique resource system that allows any object to be placed as a resource and consequently shared in an efficient and flexible way.
Chapter 3, Layout and Panels, discusses how WPF manages layout of elements, including looking at the standard layout panels, how they work, and how they can be combined to produce complex and flexible interfaces.
Chapter 4, Using Standard Controls, looks at the major controls in WPF and how they are typically used. The content model is also discussed, along with other control families.
Chapter 5, Application and Windows, takes a look at a WPF application from a higher perspective, including application level resources and the way windows are used and managed.
Chapter 6, Data Binding, discusses the powerful and important concept of data binding and the way it’s used in WPF, including leveraging data templates, converters, and other ideas that make WPF so powerful.
Chapter 7, Commands and MVVM, looks at the way a moderately complex application might be built, by leveraging higher level abstractions known as commands (as opposed to raw events). The MVVM pattern is introduced with some implementation to show how commands, data binding and some extra ingredients can produce a complex, yet manageable, application.
Chapter 8, Styles, Triggers, and Control Templates, shows some of the ways controls can be customized in XAML only, without the need to derive new types for the sake of appearance only.
Chapter 9, Graphics and Animation, provides a tour of the major graphic and animation capabilities of WPF and how they integrate with other mechanisms such as styles and triggers.
Chapter 10, Custom Elements, shows what is required to create custom elements with the considerations that lead to a particular implementation path.
Chapter 11, Threading, discusses WPF’s support for asynchronous operations, so that the UI is responsive at all times, including the support provided in C# 5.0 for performing asynchronous operations more easily.
What you need for this book
The books assumes the reader is a .NET developer working with C# (at least version 2.0, but 3.0 is preferred), and is comfortable working with generics, virtual methods, delegates, and lambdas (C# 3.0). Some WPF exposure is assumed. Visual Studio 2010 as well as Visual Studio 2012 for some features of .NET 4.5.
Who this book is for
The book is intended for developers who are relatively new to WPF, or those who have been working with WPF for a while, but want to a get a deeper understanding of its mechanisms and concepts.
Conventions
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Code words in text are shown as follows: "the typical Window class is declared as partial, meaning there may be more source files describing the same class".
A block of code is set as follows:
When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:
New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "right-click on the project node and select Add and then Class…".
Note
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Tip
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Chapter 1. Foundations
In this chapter we will cover the following:
Introduction
Any attempt at mastering a technology, any technology, requires a good understanding of its foundations. This understanding makes it possible to grasp the more complex aspects of that technology; Windows Presentation Foundation (WPF) is no different.
In this first chapter, we'll discuss recipes concerning the very foundations of WPF – what makes it tick—and also along the way, what makes it unique.
XAML
The first noticeable facet of WPF is XAML (eXtensible Markup Language). XAML is an XML based language used in WPF to declaratively create user interfaces. Actually, XAML has nothing to do with UI. It's merely a declarative way of constructing objects and setting their properties. In fact, it's leveraged in other technologies, such as the Windows Workflow Foundation (WF), where it's used as a way of constructing workflows. To create objects in XAML, they must be "XAML friendly" – meaning they must have the following:
The second item is not strictly a requirement, but the lack of settable properties would make the object a bit dull. Note that starting with .NET 4, XAML is in fact capable of handling parameterized constructors, but WPF's XAML parser currently does not leverage that capability.
XAML is not an absolute requirement. In fact, you can create an entire application using C# or VB (or whichever .NET language you fancy) without a single XAML tag. However, that would be much more difficult and error prone with high maintenance costs, not to mention the difficulty of integration with your fellow designers.
XAML is about the what, not the how. This declarative style makes things easier (granted, after some getting used to), and is a paradigm shift in software development in general (the classic example in .NET being the LINQ-based technologies). XAML is neutral—it's not C# or anything like that—so other, non-developer tools can create or manipulate it. Microsoft provides the Expression Blend tool, which at its core, is a glorified XAML producer/consumer.
XAML and compilation
What happens to a XAML file? How is it tied to the code behind file created by Visual Studio? A XAML file is compiled by a XAML compiler that produces a binary version of the XAML, known as BAML. This BAML is stored as a resource inside the assembly and is parsed at runtime in the InitializeComponent call to create the actual objects. The result is bundled with the code behind file (the typical Window class is declared as partial, meaning there may be more source files describing the same class) to produce the final code for that class.
Browsing a typical WPF application, we won't find the canonical Main method, because it's generated by WPF. It constructs the singleton Application object instance and creates the first window specified by the Application.StartupUri property (if not null). We can find that code in the file App.g.cs (g stands for generated) inside the Obj\x86\Debug sub-folder.
Dependency properties
.NET properties are nothing more than syntactic sugar over set and get methods. What those methods do is up to the property's developer. More often than not, a property is a thin wrapper over a private field, perhaps adding some validation logic in its setter.
WPF requires more out of its properties. Specifically, WPF's dependency properties provide the following:
These features provide the basis of some of WPF's strong features, such as data binding and animation.
On the surface, these properties look the same as any other property—a getter and a setter. But no private fields are involved, as we'll see in the following recipes.
Creating custom type instances in XAML
Sometimes there's a need to create instances of your own types, or other .NET Framework, non-WPF types within XAML. A classic example is a data binding value converter (which we'll explore in Chapter 6, Data Binding, but other scenarios might call for it).
Getting ready
Make sure you have Visual Studio 2010 up and running.
How to do it...
We'll create a simple application that creates an instance of a custom type in XAML to demonstrate the entire procedure:
Tip
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How it works...
The XAML compiler needs to be able to resolve type names such as Button or Book. A simple name like Button is not necessarily unique, not in the XML sense and certainly not in the .NET sense (there are at least four Button types in .NET, naturally in diffrent namespaces) .
A mapping is required between an XML namespace and a .NET namespace, so that the XAML compiler can reference the correct type. By default, two XML namespaces are declared by a typical XAML file: the first, which is the default XML namespace, is mapped to the normal WPF namespaces (System.Windows, System.Windows.Controls, and so on). The other, typically with the x prefix, is mapped to the XAML namespace (System.Windows.Markup).
For our own types, we need to do similar mapping (but with a different syntax) means map the XML namespace prefix local to the .NET namespace CH01.CustomTypes. The following line:
This allows our Book class to be recognized and used within the XAML.
If the type was defined in a referenced assembly (not our own assembly), then the mapping would continue to something like the following:
For example, suppose we want the ability to create instances of the System.Random type. Here's how we'd map an XML namespace to the .NET namespace and assembly where Sysem.Random resides:
Now, we could create an instance of anything in the System namespace (that is XAML friendly) and the mscorlib assembly (such as Random):
In this case, it's hosted in a ResourceDictionary (which is a kind of dictionary, meaning every value requires a key; we'll discuss these in more detail in the next chapter).
There's more...
It's possible to map a single XML namespace to multiple .NET namespaces. This is the same technique used by the WPF assemblies itself: a single XML namespace maps to multiple WPF namespaces, such as System.Windows, System.Windows.Controls, and System.Windws.Media.
The trick is to use the XmlnsDefinition attribute within the assembly where the exported types reside. This only works for referenced assemblies; that is, it's typically used in class library assemblies.
For example, suppose we create a MyClassLibrary class library assembly, with a type like the Book introduced earlier:
We can make all types within this assembly and the MyClassLibrary namespace part of an XML namespace by adding the following attribute:
The first argument to the attribute is the XML namespace name. This can be anything, but is typically some form of fictitious URL (usually a variation on the company's URL), so as to lower chances of collisions (this is exactly the same idea used by WPF). The second string is the .NET namespace mapped by this XML namespace.
Now, suppose we have another .NET namespace within that same assembly with some types declared within it:
We can add another attribute to map the same XML namespace to the new .NET namespace:
This means that a single XML prefix (in some client application) can now map to multiple .NET namespaces:
This scheme can save multiple distinct XML prefix declarations. One consequence of this idea is that all public type names must be unique across the mapped .NET namespaces (as they are indeed within WPF itself).
Using an attached property
Attached properties are curious beings. There is no direct analogue to anything else in the .NET framework. The closest may be extension methods, introduced in C# 3.0. Extension methods are a way of extending a type without inheriting from it (even if that type is sealed). Attached properties are dependency properties that are defined by some type, but can be used by (almost) any other typed object. That is, they can extend a type's properties without code derivation. In this recipe, we'll see how to use an existing attached property, and in the next one we'll learn how to create a new attached property.
Getting ready
Make sure Visual Studio is up and running.
How to do it...
We'll create an application that creates a rectangle and places it inside a canvas at exact coordinates using attached properties:
How it works...
An attached property is first and foremost a dependency property, meaning it supports all the capabilities of dependency properties. However, as an attached property is "attached" to an object that did not define it, a simple property like syntax is not possible – as C# does not support the concept of attached properties natively. Instead, the declaring class provides two static methods, named DeclaringType.SetPropertyName and DeclaringType.GetPropertyName, that provide a way to set or get the property value for some object passed in as the first argument (as demonstrated in the last code snippet).
In XAML, things are simpler, as the XAML parser is aware of attached properties, and converts the simpler DeclaringType.PropertyName attribute to the aforementioned Set method.
There's more...
The actual implementation of the Set/Get static methods mentioned above is to call the regular DependencyObject.SetValue/GetValue as for a regular dependency property. This means that the code to move the rectangle could have been written as follows:
Why an attached property?
One may wonder why to go to all this trouble for the Left and Top properties. Would it not be simpler to define the Left and Top properties on the (for example) UIElement class and be done with it? These properties could have been normal dependency properties and enjoy the simpler syntax they carry.
The reason is, that a Left or Top property may not always make sense. In fact, it only makes sense when the element is placed within a Canvas. What if the rectangle is inside a Grid? Or a StackPanel? The Left/Top properties wouldn't make sense. This leads to the conclusion that attached properties are a kind of contextual property – they are relevant under particular circumstances, so they can be "attached" if and when actually needed.
Does the declaring type "own" the property?
The previous example may lead to a wrong conclusion. It seems Canvas.Left and the like are only relevant when the element is inside a Canvas. Similarly, the Grid.Row and Grid.Column attached properties only make sense for elements placed inside a Grid. Is this somehow necessary from an attached property point of view?
Not at all. This is just coincidence. The above properties in fact make sense only for elements placed inside their respective declaring type, but that does not have to be the case. For example, suppose we have a button with a tool tip defined:
If the button is disabled (IsEnabled set to true), the tool tip does not appear at runtime. To make it appear even if the control is disabled, we must set the ToolTipService.ShowOnDisabled attached property to true:
We set the property on the button, but it's defined in the ToolTipService class. This class is not an element (unlike the Canvas for example). In fact, it's a static class (instances of it cannot be created). So, there is no relationship between the button and the ToolTipService class, or between the ToolTip and ToolTipService classes, for that matter. The way this connection is established (so it can have some effect) will be revealed in the next recipe in this chapter.
See also
To create your own attached properties, refer to the next recipe, Creating an attached property.
