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Windows Phone 8 : Scheduled Tasks - To-Do List Scheduled Task Sample (part 1) - TodoItem,TodoDataContext

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This section looks at creating a to-do list app that uses periodic tasks in conjunction with a scheduled task agent. The app allows the user to enter a to-do item, which is stored in a local database, and which can be pinned as a live tile on the start experience. We look at using a periodic task to update the status of the to-do item live tiles.

TodoItem

To-do items are represented by the TodoItem class, which contains three properties: Id, Description, and DueDate. DueDate is of type DateTime and indicates when the to-do item should be considered overdue. TodoItem objects are persisted using LINQ to SQL. The TodoItem class is decorated with a Table attribute, and its properties with Column attributes (see Listing 1).

LISTING 1. TodoItem Class


[Table]
public class TodoItem : NotifyPropertyChangeBase
{
    int id;

    [Column(
        IsPrimaryKey = true,
        DbType = "INT IDENTITY NOT NULL",
        IsDbGenerated = true,
        UpdateCheck = UpdateCheck.Never)]
    public int Id
    {
        get
        {
            return id;
        }
        set
        {
            Assign(ref id, value);
        }
    }

    string description;

    [Column]
    public string Description
    {
        ...
    }

    DateTime dueDate;

    [Column]
    public DateTime DueDate
    {
        ...
    }
}


We now look briefly at the app’s data layer, before moving on to its viewmodels. Persistence of TodoItem objects is performed using a LINQ to SQL DataContext instance, and an intermediary service that decouples the data context from the app’s viewmodels.

TodoDataContext

To retrieve and store TodoItem objects in a database, we use a custom DataContext class called TodoDataContext. This class allows TodoItem objects to be retrieved via its TodoItems property (see Listing 2).

LISTING 2. TodoDataContext Class


public class TodoDataContext : DataContext
{
    public TodoDataContext(string connection)
        : base(connection)
    {
    }

    public Table<TodoItem> TodoItems
    {
        get
        {
            return GetTable<TodoItem>();
        }
    }
}


In the sample app, viewmodels do not directly interact with the TodoDataContext, but perform all CRUD operations via a to-do service. This decouples the data context from the viewmodels, allowing you to replace the to-do service with an implementation that could, for example, use a cloud service rather than a local database. Decoupling the data context also means that you have the flexibility to unit test the code outside an emulator, perhaps on a build server.

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