I am using SharePoint 2013.
I am using a modal dialog with the SP.UI.ModalDialog.showModalDialog method.
I also have a Ribbon in the custom application page.
This all worked in SharePoint 2010, but in 2013 it doesn't work. The ribbon is no longer showing.
How can I resovle this?
In the SharePoint 2013 masterpage the elements that shouldn't be visible in the dialog mode (IsDlg=1) have the "s4-notdlg" CSS class applied. To solve your problem you have the following options: