TodoListViewModel

The TodoListViewModel constructor accepts an IDeviceProperties instance and an ITodoService instance, which, as you saw in Chapter 32, is used for storage and retrieval of to-do items. See the following excerpt:

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public TodoListViewModel(
    ITodoService todoService, IDeviceProperties deviceProperties)
{
...
    backupDatabaseCommand = new DelegateCommand(obj => BackupDatabase());
    restoreDatabaseCommand = new DelegateCommand(obj => RestoreDatabase());

    Load();
}

The viewmodel contains a method that leverages the IDeviceProperties instance to create a unique ID to use to identify itself to calls to a WCF service.

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string GetUserId()
{
    string id= deviceProperties.WindowsLiveAnonymousId;
    if (string.IsNullOrWhiteSpace(id))
    {
        id= "Emulator";
    }
    return id;
}

The anonymous ID is passed to the WCF service when backing up the local database file and used as part of the URL when restoring it.