Casting query .Net C#

Question

Can someone please explain why this works:

RibbonTab rt_selecteda = (RibbonTab)MainWindow.Ribbon_Main_Link.SelectedItem;
string a = rt_selecteda.Tag.ToString();

but this fails:

string ab = (RibbonTab)MainWindow.Ribbon_Main_Link.SelectedItem.Tag.ToString();

'object' does not contain a definition for 'Tag' and no extension method 'Tag' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?) W:\Dev_Code\Reporting_App\Core\Ribbon_Common.cs 114 78 Reporting_App

Answer 1

This

string ab = (RibbonTab)MainWindow.Ribbon_Main_Link.SelectedItem.Tag.ToString();

is not the same as (note the brackets)

string ab = ((RibbonTab)MainWindow.Ribbon_Main_Link.SelectedItem).Tag.ToString();

which is the one-line equivalent to your first code

RibbonTab rt_selecteda = (RibbonTab)MainWindow.Ribbon_Main_Link.SelectedItem;
string a = rt_selecteda.Tag.ToString();

Answer 2

(RibbonTab)MainWindow.Ribbon_Main_Link.SelectedItem.Tag.ToString() means:

1. Take MainWindow.Ribbon_Main_Link.SelectedItem

2. Get its Tag property

3. Call the Tag's ToString method

4. Cast the result as an RibbonTab

This fails since a. MainWindow.Ribbon_Main_Link.SelectedItem is of type object and doesn't have a Tag property, and b. even if it had, ToString returns a string and you can't cast a string as a RibbonTab.