How To Use Choosers in Your Windows Phone 7 Applications

Introduction

As we saw in an earlier article
describing Launchers
, the Windows Phone
7 platform does not provide any application direct access to the contacts, send
email or take pictures features of the phone. This is done to provide
sandboxing. However when applications have a legitimate need for doing so, they
can access these features via some helper APIs. When there is a need for output
from such platform specific tasks, we use Chooser APIs, which are provided by
the Windows Phone 7 platform.

Choosers Defined

Choosers are a set of APIs that launche one of the built-in
applications by which users can complete a task for which the Windows Phone 7
platform provides a native application. In addition to doing the task, a
Chooser API also returns a value, which is used by the application to determine
business logic. An example would be selecting a phone number.

Developers will author their applications such that their
application code calls the Chooser API with the required information and the Choosers
API will do the specified task. For example, you can call a Chooser API to
select a contact’s phone number to populate a field in the current application.
When the user selects a contact, the Chooser API returns the phone number of
the chosen contact to the originally executing application.

Types of Choosers

There are various Choosers available with Windows Phone 7:

  • For camera capture
  • For choosing email address
  • For choosing phone number
  • For choosing photo
  • For saving email address
  • For saving phone number

Let’s look at how we can use these Choosers in an
application.

Hands-On

Let us start by creating a new Silverlight C# project for
Windows Phone. Let’s call it ChooserDemo.

Create a new Silverlight C# project
Figure 1: Create a new Silverlight C# project

Add a button with the text “Choose Phone number”. Also add a
text box on the MainPage.

In the MainPage.xaml.cs, add a reference directive for
Microsoft.Phone.Tasks namespace.

In the class for the MainPage, declare an object of type
PhoneNumberChooserTask.

PhoneNumberChooserTask phoneNumberChooserTask;

In the constructor for MainPage class, instantiate the
PhoneNumberChooserTask.

Wire a method called phoneNumberChooserTask_Completed on its Completed
Event.

        public MainPage()
        {
            InitializeComponent();

            phoneNumberChooserTask = new PhoneNumberChooserTask();
            phoneNumberChooserTask.Completed += new EventHandler<PhoneNumberResult>(phoneNumberChooserTask_Completed);
 
        }

On the button click event, add the following code.

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            phoneNumberChooserTask.Show();

        }

Now, lay out the phoneNumberChooserTask method. In
this method, update the textbox to show the phone number ifB a contact is
selected.

void phoneNumberChooserTask_Completed(object sender, PhoneNumberResult e)
        {
            if (e.TaskResult == TaskResult.OK)
            {
                // if successfully chose a number, show it.
                textBox1.Text = e.PhoneNumber;
            }
        }

We are all set. Go ahead and launch the application. If you
are having issues compiling, you can grab the source code of the demo, which is
referenced in the resources section of this article.

When you click the “Choose Phone number” button, the address
book opens up and once you choose a contact from that, it automatically fills
the textbox on the MainPage with that contact’s phone number.

You have successfully used the Chooser feature of Windows
Phone 7 platform. As simple as that.

Summary

In this article, we learned how to use Choosers API.B

About the author

Vipul Patel is a Software Engineer currently working at
Microsoft Corporation. He is currently working in the Office Communications
Group and has worked in the .NET team earlier in the Base Class libraries and
the Debugging and Profiling team. He can be reached at [email protected]

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