Improvements in the LongListSelector Selection with Nov `11 release of WP Toolkit

published on: 11/22/2011 | Views: N/A | Tags: WP7Toolkit

by WindowsPhoneGeek

In this article I am going to talk about some improvements that have been made to the LongListSelector control in the latest official release of Windows Phone Toolkit Nov `11.

Here is a common question that our readers have been asking about the LongListSelector:

"How to get Selected Item and Group info in the LongListSelector SelectionChaged event? "

The problem was that this was not possible until the Nov`11 release of the toolkit, because the arguments of the SelectionChanged event were practically useless since the type of the objects representing the selected items was private.

In the November update of the Toolkit this issue is already fixed and here is the official release note:

"ItemTuple is now refactored to be the public type LongListSelectorItem to provide users better access to the values in selection changed handlers"

Before you begin: For more information about how to use the LongListSelector control take a look at our FREE eBook: "Silverlight for Windows Phone Toolkit In Depth".

In this article we will use the example from our previous post: "WP7 LongListSelector in depth | Part2: Data binding scenarios". In short here is the data source should look like and how we should subscribe to the SelectionChanged event:

public MainPage()
{
    InitializeComponent();

    List<City> source = new List<City>();
    //   ...
    source.Add(new City() { Name = "Roma", Country = "IT", Language = "Italian" });
    source.Add(new City() { Name = "Paris", Country = "FR", Language = "French" });


    var cityByCountry = from city in source
                        group city by city.Country into c
                        orderby c.Key
                        select new Group<City>(c.Key, c);

    this.longListSelector.ItemsSource = cityByCountry;

    this.longListSelector.SelectionChanged += new SelectionChangedEventHandler(longListSelector_SelectionChanged);
}

Next we will add the following code inside the LongListSelectro SelectionChanged handler:

void longListSelector_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    IList addedItems = e.AddedItems;
    if (addedItems == null || addedItems.Count < 1)
    {
        return;
    }

    // get first selected item
    LongListSelectorItem selectedItem = addedItems[0] as LongListSelectorItem;
    if (selectedItem == null)
    {
        return;
    }

    StringBuilder message = new StringBuilder();
    message.AppendLine("Selected item:");
    message.AppendLine(string.Format("Type: {0}", selectedItem.ItemType));
    message.AppendLine(string.Format("Group: {0}", selectedItem.Group));
    message.AppendLine(string.Format("Item: {0}", selectedItem.Item));
    MessageBox.Show(message.ToString());
}

Items of type LongListSelectorItem are used to represent selected items. This type has the following important properties:

ItemType: the type of the selected item.
Group: holds a reference to the group of the selected item (in our case this will be an object of type Group<City>)
Item: holds a reference to the selected item (in our case this will be an object of type City)

Here is the final result: