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Xamarin.Android Calendar

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Calendar API

A new set of calendar APIs introduced in Android 4 supports applications that are designed to read or write data to the calendar provider. These APIs support a wealth of interaction options with calendar data, including the ability to read and write events, attendees, and reminders. By using the calendar provider in your application, data you add through the API will appear in the built-in calendar app that comes with Android 4.

Adding Permissions

When working with the new calendar APIs in your application, the first thing you need to do is add the appropriate permissions to the Android manifest. The permissions you need to add are android.permisson.READ_CALENDAR and android.permission.WRITE_CALENDAR, depending on whether you are reading and/or writing calendar data.

Using the Calendar Contract

Once you set the permissions, you can interact with calendar data by using the CalendarContract class. This class provides a data model that applications can use when they interact with the calendar provider. The CalendarContract allows applications to resolve the Uris to calendar entities, such as calendars and events. It also provides a way to interact with various fields in each entity, such as a calendar's name and ID, or an event's start and end date.

Let's look at an example that uses the Calendar API. In this example, we'll examine how to enumerate calendars and their events, as well as how to add a new event to a calendar.

Listing Calendars

First, let's examine how to enumerate the calendars that have been registered in the calendar app. To do this, we can instantiate a CursorLoader. Introduced in Android 3.0 (API 11), CursorLoader is the preferred way to consume a ContentProvider. At a minimum, we'll need to specify the content Uri for calendars and the columns we want to return; this column specification is known as a projection.

Calling the CursorLoader.LoadInBackground method allows us to query a content provider for data, such as the calendar provider. LoadInBackground performs the actual load operation and returns a Cursor with the results of the query.

The CalendarContract assists us in specifying both the content Uri and the projection. To get the content Uri for querying calendars, we can simply use the CalendarContract.Calendars.ContentUri property like this:

var calendarsUri = CalendarContract.Calendars.ContentUri;

Using the CalendarContract to specify which calendar columns we want is equally simple. We just add fields in the CalendarContract.Calendars.InterfaceConsts class to an array. For example, the following code includes the calendar's ID, display name, and account name:

string[] calendarsProjection = {
    CalendarContract.Calendars.InterfaceConsts.Id,
    CalendarContract.Calendars.InterfaceConsts.CalendarDisplayName,
    CalendarContract.Calendars.InterfaceConsts.AccountName
};

The Id is important to include if you are using a SimpleCursorAdapter to bind the data to the UI, as we will see shortly. With the content Uri and projection in place, we instantiate the CursorLoader and call the CursorLoader.LoadInBackground method to return a cursor with the calendar data as shown below:

var loader = new CursorLoader(this, calendarsUri, calendarsProjection, null, null, null);
var cursor = (ICursor)loader.LoadInBackground();

The UI for this example contains a ListView, with each item in the list representing a single calendar. The following XML shows the markup that includes the ListView:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
  <ListView
    android:id="@android:id/android:list"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content" />
</LinearLayout>

Also, we need to specify the UI for each list item, which we place in a separate XML file as follows:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
  <TextView android:id="@+id/calDisplayName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textSize="16dip" />
  <TextView android:id="@+id/calAccountName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textSize="12dip" />
</LinearLayout>

From this point on, it's just normal Android code to bind the data from the cursor to the UI. We'll use a SimpleCursorAdapter as follows:

string[] sourceColumns = {
    CalendarContract.Calendars.InterfaceConsts.CalendarDisplayName,
    CalendarContract.Calendars.InterfaceConsts.AccountName };

int[] targetResources = {
    Resource.Id.calDisplayName, Resource.Id.calAccountName };      

SimpleCursorAdapter adapter = new SimpleCursorAdapter (this,
    Resource.Layout.CalListItem, cursor, sourceColumns, targetResources);

ListAdapter = adapter;

In the above code, the adapter takes the columns specified in the sourceColumns array and writes them to the user interface elements in the targetResources array for each calendar entry in the cursor. The Activity used here is a subclass of ListActivity; it includes the ListAdapter property to which we set the adapter.

Here's a screenshot showing the end result, with the calendar info displayed in the ListView:

CalendarDemo running in emulator, displaying two calendar entries

Listing Calendar Events

Next let's look at how to enumerate the events for a given calendar. Building upon the example above, we'll present a list of events when the user selects one of the calendars. Therefore, we'll need to handle the item selection in the previous code:

ListView.ItemClick += (sender, e) => {
    int i = (e as ItemEventArgs).Position;

    cursor.MoveToPosition(i);
    int calId =
        cursor.GetInt (cursor.GetColumnIndex (calendarsProjection [0]));

    var showEvents = new Intent(this, typeof(EventListActivity));
    showEvents.PutExtra("calId", calId);
    StartActivity(showEvents);
};

In this code, we're creating an Intent to open an Activity of type EventListActivity, passing the calendar's ID in the Intent. We will need the ID to know which calendar to query for events. In the EventListActivity's OnCreate method, we can retrieve the ID from the Intent as shown below:

_calId = Intent.GetIntExtra ("calId", -1);

Now let's query events for this calendar ID. The process to query for events is similar to the way we queried for a list of calendars earlier, only this time we'll work with the CalendarContract.Events class. The following code creates a query to retrieve events:

var eventsUri = CalendarContract.Events.ContentUri;

string[] eventsProjection = {
    CalendarContract.Events.InterfaceConsts.Id,
    CalendarContract.Events.InterfaceConsts.Title,
    CalendarContract.Events.InterfaceConsts.Dtstart
};

var loader = new CursorLoader(this, eventsUri, eventsProjection,
                   String.Format ("calendar_id={0}", _calId), null, "dtstart ASC");
var cursor = (ICursor)loader.LoadInBackground();

In this code, we first get the content Uri for events from the CalendarContract.Events.ContentUri property. Then we specify the event columns we want to retrieve in the eventsProjection array. Finally, we instantiate a CursorLoader with this information and call the loader's LoadInBackground method to return a Cursor with the event data.

To display the event data in the UI, we can use markup and code just like we did before to display the list of calendars. Again, we use SimpleCursorAdapter to bind the data to a ListView as shown in the following code:

string[] sourceColumns = {
    CalendarContract.Events.InterfaceConsts.Title,
    CalendarContract.Events.InterfaceConsts.Dtstart };

int[] targetResources = {
    Resource.Id.eventTitle,
    Resource.Id.eventStartDate };

var adapter = new SimpleCursorAdapter (this, Resource.Layout.EventListItem,
    cursor, sourceColumns, targetResources);

adapter.ViewBinder = new ViewBinder ();       
ListAdapter = adapter;

The main difference between this code and the code that we used earlier to show the calendar list is the use of a ViewBinder, which is set on the line:

adapter.ViewBinder = new ViewBinder ();

The ViewBinder class allows us to further control how we bind values to views. In this case, we use it to convert the event start time from milliseconds to a date string, as shown in the following implementation:

class ViewBinder : Java.Lang.Object, SimpleCursorAdapter.IViewBinder
{    
    public bool SetViewValue (View view, Android.Database.ICursor cursor,
        int columnIndex)
    {
        if (columnIndex == 2) {
            long ms = cursor.GetLong (columnIndex);

            DateTime date = new DateTime (1970, 1, 1, 0, 0, 0,
                DateTimeKind.Utc).AddMilliseconds (ms).ToLocalTime ();

            TextView textView = (TextView)view;
            textView.Text = date.ToLongDateString ();

            return true;
        }
        return false;
    }    
}

This displays a list of events as shown below:

Screenshot of example app displaying three calendar events

Adding a Calendar Event

We've seen how to read calendar data. Now let's see how to add an event to a calendar. For this to work, be sure to include the android.permission.WRITE_CALENDAR permission we mentioned earlier. To add an event to a calendar, we will:

  1. Create a ContentValues instance.
  2. Use keys from the CalendarContract.Events.InterfaceConsts class to populate the ContentValues instance.
  3. Set the time zones for the event start and end times.
  4. Use a ContentResolver to insert the event data into the calendar.

The code below illustrates these steps:

ContentValues eventValues = new ContentValues ();

eventValues.Put (CalendarContract.Events.InterfaceConsts.CalendarId,
    _calId);
eventValues.Put (CalendarContract.Events.InterfaceConsts.Title,
    "Test Event from M4A");
eventValues.Put (CalendarContract.Events.InterfaceConsts.Description,
    "This is an event created from Xamarin.Android");
eventValues.Put (CalendarContract.Events.InterfaceConsts.Dtstart,
    GetDateTimeMS (2011, 12, 15, 10, 0));
eventValues.Put (CalendarContract.Events.InterfaceConsts.Dtend,
    GetDateTimeMS (2011, 12, 15, 11, 0));

eventValues.Put(CalendarContract.Events.InterfaceConsts.EventTimezone,
    "UTC");
eventValues.Put(CalendarContract.Events.InterfaceConsts.EventEndTimezone,
    "UTC");

var uri = ContentResolver.Insert (CalendarContract.Events.ContentUri,
    eventValues);

Note that if we do not set the time zone, an exception of type Java.Lang.IllegalArgumentException will be thrown. Because event time values must be expressed in milliseconds since epoch, we create a GetDateTimeMS method (in EventListActivity) to convert our date specifications into millisecond format:

long GetDateTimeMS (int yr, int month, int day, int hr, int min)
{
    Calendar c = Calendar.GetInstance (Java.Util.TimeZone.Default);

    c.Set (Java.Util.CalendarField.DayOfMonth, 15);
    c.Set (Java.Util.CalendarField.HourOfDay, hr);
    c.Set (Java.Util.CalendarField.Minute, min);
    c.Set (Java.Util.CalendarField.Month, Calendar.December);
    c.Set (Java.Util.CalendarField.Year, 2011);

    return c.TimeInMillis;
}

If we add a button to the event list UI and run the above code in the button's click event handler, the event is added to the calendar and updated in our list as shown below:

Screenshot of example app with calendar events followed by Add Sample Event button

If we open the calendar app, then we will see that the event is written there as well:

Screenshot of calendar app displaying the selected calendar event

As you can see, Android allows powerful and easy access to retrieve and persist calendar data, allowing applications to seamlessly integrate calendar capabilities.