Selecting a Phone Number with the PhoneNumberChooserTask

The phone number chooser task is used to launch the built-in Contacts application and allows the user to select a contact. A phone number for the contact is then returned to your app.

The PhoneNumberChooserTask should be defined as a field in your class, like so:

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readonly PhoneNumberChooserTask phoneNumberChooserTask
                                     = new PhoneNumberChooserTask();

Subscribe to the PhoneNumberChooserTask.Completed event within your class constructor, as shown:

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PhoneNumberChooserTask.Completed
    += new EventHandler<PhoneNumberResult>(
                                   HandlePhoneNumberChooserTaskCompleted);

Use the Show method of the PhoneNumberChooserTask to launch the built-in Contacts app. When the task completes the handler receives a PhoneNumberResult object, as shown:

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void HandlePhoneNumberChooserTaskCompleted(object sender,
                                           PhoneNumberResult e)
{
    if (e.TaskResult == TaskResult.OK)
    {
        PhoneNumber = e.PhoneNumber;
    }
    else if (e.Error != null)
    {
        Message = "Unable to choose number. " + e.ToString();
    }
    else if (e.TaskResult == TaskResult.Cancel)
    {
        Message = "Cancelled";
    }
}

A button in the view is bound to a viewmodel ICommand property named ChooseCommand. The chooseCommand field is instantiated in the PhoneCallViewModel constructor. When executed, the command calls the Show method of the PhoneNumberChooserTask, as shown:

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public PhoneCallViewModel() : base("Phone Call Tasks")
{
    phoneNumberChooserTask.Completed
                += HandlePhoneNumberChooserTaskCompleted;

    chooseCommand = new DelegateCommand(                         obj => phoneNumberChooserTask.Show());
...
}

When the Show method is called, the Contacts application is launched (see Figure 14.16).

FIGURE 14.16 Windows Phone Contacts application.

When the user selects a contact from the Contacts app, the sample app is activated, and the Completed event handler is called, which updates the PhoneNumber property in the viewmodel.