Download Pro WPF and Silverlight MVVM : Effective Application De - bertarenurti33 - opurelit.tk
WPF and Silverlight are Microsoft technologies that facilitate the development of rich user interfaces. They are analogous to Windows Forms and Adobe Flash, respectively. The view provides two services to the user: presenting data and interacting with data. The former involves reading data and displaying it in a certain format, whereas the latter implies editing existing or adding new data. In a software product there are two distinct modules whose responsibilities are well-defined and should be clearly demarcated. The model is a software representation of a solution to a known problem whereas the view allows the user to interact with the model to solve a specific problem.
In Chapter 3, we looked at the reasons for splitting model and view responsibilities and implementing a ViewModel to mediate between these layers. An event is a programming construct that reacts to a change in state, notifying any endpoints that have registered for notification. They are ubiquitous in. Primarily, events are used to inform of user input via the mouse and keyboard, but their utility is not limited to that.
Whenever a state change is detected, perhaps when an object has been loaded or initialized, an event can be fired to alert any interested third parties. Data integrity is a very important part of developing a software product. The view model may also define logical states the view can use to provide visual changes in the UI. The view may define layout or styling changes that reflect the state of the view model.
For example, the view model may define a state that indicates that data is being submitted asynchronously to a web service. The view can display an animation during this state to provide visual feedback to the user. Typically, the view model will define commands or actions that can be represented in the UI and that the user can invoke. A common example is when the view model provides a Submit command that allows the user submit data to a web service or to a data repository. The view may choose to represent that command with a button so that the user can click the button to submit the data.
Typically, when the command becomes unavailable, its associated UI representation becomes disabled. Commands provide a way to encapsulate user actions and to cleanly separate them from their visual representation in the UI.
Effective Application Development with Model-View-ViewModel
To summarize, the view model has the following key characteristics:. It encapsulates the presentation logic required to support a use case or user task in the application. The view model is testable independently of the view and the model. It implements properties and commands to which the view can data bind. It may convert or manipulate data so that it can be easily consumed by the view and may implement additional properties that may not be present on the model. The view model may define logical states that the view can represent visually to the user.
Pro WPF and Silverlight MVVM
The Model Class. The model in the MVVM pattern encapsulates business logic and data. Business logic is defined as any application logic that is concerned with the retrieval and management of application data and for making sure that any business rules that ensure data consistency and validity are imposed. To maximize re-use opportunities, models should not contain any use case—specific or user task—specific behavior or application logic.
Typically, the model represents the client-side domain model for the application. It can define data structures based on the application's data model and any supporting business and validation logic.
The model may also include the code to support data access and caching, though typically a separate data repository or service is employed for this. Often, the model and data access layer are generated as part of a data access or service strategy, such as the ADO. Typically, the model implements the facilities that make it easy to bind to the view. This usually means it supports property and collection changed notification through the INotifyPropertyChanged and INotifyCollectionChanged interfaces. These interfaces allow WPF and Silverlight data binding to be notified when values change so that the UI can be updated.
They also enable support for data validation and error reporting in the UI layer. The model has the following key characteristics:.
They are responsible for managing the application's data and for ensuring its consistency and validity by encapsulating the required business rules and data validation logic. This allows them to be easily data bound in the view. The MVVM pattern provides a clean separation between your application's user interface, its presentation logic, and its business logic and data by separating each into separate classes. Therefore, when you implement MVVM, it is important to factor in your application's code to the correct classes, as described in the previous section. Well-designed view, view model, and model classes will not only encapsulate the correct type of code and behavior; they will also be designed so that they can easily interact with each other via data binding, commands, and data validation interfaces.
The interactions between the view and its view model are perhaps the most important to consider, but the interactions between the model classes and the view model are also important. The following sections describe the various patterns for these interactions and describe how to design for them when implementing the MVVM pattern in your applications. Data Binding. Data binding plays a very important role in the MVVM pattern.
WPF and Silverlight both provide powerful data binding capabilities. Your view model and ideally your model classes should be designed to support data binding so that they can take advantage of these capabilities.
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Typically, this means that they must implement the correct interfaces. Silverlight and WPF data binding supports multiple data binding modes. With one-way data binding, UI controls can be bound to a view model so that they reflect the value of the underlying data when the display is rendered. Two-way data binding will also automatically update the underlying data when the user modifies it in the UI. To ensure that the UI is kept up to date when the data changes in the view model, it should implement the appropriate change notification interface.
If it defines properties that can be data bound, it should implement the INotifyPropertyChanged interface.
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