I'm trying to search a ListView to see if a certain piece of text has already been added. I've tried using other answers from here, like the code below:

```
ListViewItem item = ListView1.FindItemWithText(txtSearch.Text);
if (item != null)
{
   // you have match
}

```

However, it highlights a problem with "FindItemWithText". The error message is: 

'Windows.UI.Xaml.Controls.ListView' does not contain a definition for 'FindItemWithText' and no extension method 'FindItemWithText' accepting a first argument of type 'Windows.UI.Xaml.Controls.ListView' could be found (are you missing a using directive or an assembly reference?).

I'm using Visual Studio 2013 to create a Windows Phone 8.1 app. 

Any help would be appreciated!