WPF

myMediaElement.Source = new Uri(myListBox.SelectedItem.ToString());

System.NullReferenceException was unhandled by user code
  Message="Object reference not set to an instance of an object."
  Source="Bleach Player"
  StackTrace:
       at WpfApplication1.Window1.ListBoxItem_Selected(Object sender, RoutedEventArgs e) in C:\Documents and Settings\Nick\My Documents\Visual Studio 2008\Projects\Bleach Player\Bleach Player\Window1.xaml.cs:line 61
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.RaiseEventImpl(RoutedEventArgs args)
       at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
       at System.Windows.Controls.ListBoxItem.OnSelected(RoutedEventArgs e)
       at System.Windows.Controls.ListBoxItem.OnIsSelectedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
       at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, OperationType operationType)
       at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, OperationType operationType, Boolean isInternal)
       at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
       at System.Windows.Markup.BamlRecordReader.SetDependencyValueCore(DependencyObject dependencyObject, DependencyProperty dependencyProperty, Object value)
       at System.Windows.Markup.BamlRecordReader.SetDependencyValue(DependencyObject dependencyObject, DependencyProperty dependencyProperty, Object value)
       at System.Windows.Markup.BamlRecordReader.ReadPropertyCustomRecord(BamlPropertyCustomRecord bamlPropertyRecord)
       at System.Windows.Markup.BamlRecordReader.ReadRecord(BamlRecord bamlRecord)
  InnerException: 

string myFilePath = @"C:\myMp3\Soundgarden - Some Song.mp3";
myListBox.Items.Add(myFilePath);

private void myListBox_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    if (myListBox.SelectedItems.Count > 0) //Make sure there is at least one selected item
    {
        string mySelectedFilePath = myListBox.SelectedItem.ToString();  //Get the selected file path from the listbox
        myMediaElement.Source = new Uri(mySelectedFilePath); //add it to the media element source
    }
}

C# Beginner Nick wrote:

Still not getting this to work out right, i figured out I'm missing the mySelectedFilePath. And if i leave as is, no song plays/it adds the same thing into the list over and over and over (if you keep selecting it)

C# Beginner Nick wrote:

Trying to switch things around to see if it works but still has been giving the same errors as before.

C# Beginner Nick wrote:

And i can't show you the code to what i had before, i switched it to see if it would work as you said you would do. Accidentally saved after changes (habit)