Description
This article provides an introduction to building Windows Vista codename Longhorn applications. I intend to touch upon several new things that are available to the developers for consideration before and during the application development on Longhorn.
Introduction
Application development has till now taken a lot of various shapes, from the old days of using the MFC, win32 programming model, ATL , COM , the not so old .NET managed framework and now the latest Winfx Framework. (Winfx Framework is the new framework which is a managed environment for the operating system. In other words the .NET framework has been taken to the next level of integrating in to the operating system). While one should not forget that a new operating system would also need to have backward compatibility to the various applications that were build in the previous programming model. Longhorn promises to provide the execution environment for the various (previously used) technologies in addition to the whole new programming model.
One of the most glaring trends in windows longhorn environment is a direction towards declarative programming. (In other words, An xml declaration is used to build applications). Though, declarative programming is newly introduced in longhorn it is not the only way to build winfx applications. Now, Longhorn tries the narrow the gap between the application building paradigms of web and windows development.
Avalon, One of the pillars of Longhorn which is responsible for the presentation in longhorn. The word presentation encompasses the width and breadth of the kind of applications you can think of. When I say presentation I include presentation as in a web and windows form scenario. Avalon provides a framework using which the developer can build applications that can be built as either web applications or client based windows application. The build environment setting in winfx will either build your application which could be hosted in your browser or can be hosted in a windowed environment. The attribute called HostInBrowser which is part of the application object will build your application suitable to the intended environment.
Types of applications in Longhorn
There are three types of applications that can be build in winfx (or on longhorn). These applications are classified based on the different programming models used to accomplish the application. These applications are written using the "XAML" (The language of Longhorn) or/and a language like C# or VB (presently, may be other .NET languages in the future.). The types of applications are
1. Multipage Applications
Longhorn applications are built using a set of XAML (Pronounced as XAMAL) pages. In a multipage application there are a set of XAML pages that are tied together to fulfill a business functionality. In other words Multipage applications are similar to the web applications that we see today. Each page of the multipage application controls a specific functionality. Each of these pages can have controls and content such as labels or list box etc.
A multipage application uses a NavigationApplication model. An application using this programming model has multiple XAML pages. The event handling for these pages can either be embedded in the CDATA section of the XAML file or be enclosed in a code behind file for the XAML file.
2. Windows Form Applications
This kind of application is similar to the win 32 application. In these applications the application is hosted in a window. This window is treated as a canvas which is painted and this window handles all the events generated. This kind of applications use the Application Object. An application object is a light weight object than compared to the navigationapplication object.
In these kind of applications use a programming model which is similar to the familiar .NET object model. In these applications the objects are created and inserted in a hierarchy as it would be represented in XAML. These applications are inherited from the Application object. The respective objects (either content or control ) are created and their properties are set programatically.
3. Document Containers.
Document containers are basically a kind of navigationapplication. These applications are containers for content. The object model available for such applications is very limited compared to the others application models. These applications have additional features such as digital rights management (DRM) or digital signing. These applications are meant to be used to deliver graphics and content. Using DRM such containers can prevent unauthorized use of the container. For example if an important document needs to be protected for unauthorized printing such logic can be embedded in to these containers.
UI hierarchy
The various elements in the avalon interface are needed to be used in a specific hierarchy. The three different types of elements are
1. Window
A window is usually the topmost parent. It contains all the other elements in the applications. And an window can have only one child.
2. Panel
A panel is the only element that can be a child to a Window. Panels in avalon help in the layout of the applications elements. A panel can contain other panels or can contain content and controls. There a few types of panels such as Canvas, Dock Panel, Flow Panel, Grid Panel and Text panel. Each of these panels have different properties. Using a canvas a developer can explicitly position the controls of his choice by fixing the positions using coordinates with respect to the canvas area.
A Dock panel allows the controls and content to be docked to any side of the window. A Flow panel is a panel where the controls flow horizontally or vertically and can arranged by line braking. A Grid panel is a panel which is consisted of rows and columns which can take in controls or content. Text panel can take in text and formats/sizes or draws text per specification.
3. Content and Controls
Content and controls are elements part of avalon which are used to interact with the users of the application. Controls much like the controls we are familiar can be programmed. While the content elements are used to display content, the content can either be text, graphics, audio etc.
Styling
Styling in avalon is a new way to control the look and feel of your applications in longhorn. A developer can style the look of each of the control by setting a set of properties. A style can be applied broadly to the whole application. Styling offers a very rich presentation for the applications. Styles can be applied to data or controls.
Annotations
Annotations is a way in longhorn to add comments to documents. Annotations are just like writing a postit note and pasting on your document. Annotations can be of several types such as Sticky Notes, Margin Notes, Book Marks, Callouts, Rollups or related topics.
Summary
There are significant changes to the way we build applications in longhorn, having said that does not mean that old existing applications will not work. Longhorn has great flexibility for application developers when it comes to building applications. This article is intended to give an idea to the user on what things he can expect.