C#: Using Google Data APIs on your application

One way or another your are already using at least one Google Apps or web service. Today I will show you how easy to integrate Google Apps with your client application. In this article I will use Google Calendar Data to store all schedule event entries or migrate existing calendar events to Google Apps.

The Protocol
Google Calendar allows client applications to add, update and view scheduled events in the form of Google Data API feeds. Possible use of Google Calendar API is we can create a calendar front-end that uses Google Calendar as a database or backend. Another use is to synchonize it to your existing outlook calendar events.

.NET Client Libray
Before you can reference the Google Data APIs you need to download and install the latest MSI release of the client library from here. Take note that the MSI package contains samples that you can use as templates for your next application.

Developing your first Google Data application
1. From Visual Studio 2005 or 2008, Create a new project.
2. Right-click on the project then select Add Reference.
3. Click on the Browse tab and navigate to Redist directory in the SDK ("C:\Program Files\Google\Google Data API SDK\Redist")
4. Select the DLL files that will be used by your project such as Google.GData.Client.dll, Google.GData.Calendar and etc.
5. Cut and paste the following codes:

On Namespace include,

using Google.GData.Client;
using Google.GData.Extensions;
using Google.GData.Calendar;

On your windows or web form, place two textboxes for username and password. Then cut & paste the following code to login to Google Apps:

private bool GoogleLogin()
{
bool lreturn = false;

try
{
CalendarService service = new CalendarService("CalendarSample");
if (userName != null && userName.Length > 0)
{
service.setUserCredentials(this.UserName.Text, this.Password.Text);
}
catch(Exception ex)
{
Console.WriteLine("Error encountered: " + ex.Message);
}
}

To retrieve all calendar events:

// Create a CalenderService and authenticate
CalendarService myService = new CalendarService("CalendarSample");
myService.setUserCredentials(this.UserName.Text, this.Password.Text);

CalendarQuery query = new CalendarQuery();
query.Uri = new Uri("http://www.google.com/calendar/feeds/default/allcalendars/full");
CalendarFeed resultFeed = myService.Query(query);
Console.WriteLine("Calendars Entries:\n");
foreach (CalendarEntry entry in resultFeed.Entries)
{
Console.WriteLine(entry.Title.Text + "\n");
}

To create a new calendar entry just follow this code:

CalendarEntry calendar = new CalendarEntry();
calendar.Title.Text = "Sample Event";
calendar.Summary.Text = "This is a sample entry.";
calendar.TimeZone = "Philippines/Manila";
calendar.Hidden = false;
calendar.Color = "#2952A3";
calendar.Location = new Where("", "", "Manila");

Uri postUri = new Uri("http://www.google.com/calendar/feeds/default/owncalendars/full");
CalendarEntry createdCalendar = (CalendarEntry) myService.Insert(postUri, calendar);

Ofcourse you can also update any calendar event:

CalendarQuery query = new CalendarQuery();
query.Uri = new Uri("http://www.google.com/calendar/feeds/default/owncalendars/full");
CalendarFeed resultFeed = myService.Query(query);

//updates the first entry, you can change index
CalendarEntry calendar = (CalendarEntry) resultFeed.Entries[0];
calendar.Title.Text = "Sample Event Again";
calendar.Color = "#A32929";
calendar.Selected = true;
calendar.Update();

To delete an entry, jut call the Delete method.

//this code deletes all entries
CalendarQuery cq = new CalendarQuery();
cq.Uri = new Uri("http://www.google.com/calendar/feeds/default/owncalendars/full");
CalendarFeed rf = myService.Query(query);

foreach (CalendarEntry entry in rf.Entries)
{
Console.WriteLine("Deleting calendar: " + entry.Title.Text + "\n");
try
{
entry.Delete();
}
catch (GDataRequestException)
{
Console.WriteLine("Unable to delete calendar.\n");
}
}

There you have it. These are just basic queries and there are a lot more you can do with Google Data APIs. Visit Google Labs for more details. Good Luck!