What are some advantages to using an interface in C#?

Question

I was forced into a software project at work a few years ago, and was forced to learn C# quickly. My programming background is weak (Classic ASP).

I\'ve learned qui

Answer 1

An example. Consider an MDI application that shows reports, there's basically 2 different report types. A chart, and a grid. I need to Save these reports as PDF and I need to mail them to someone. The event handler for the menu the user clicks to save a report to PDF could do this:

void ExportPDF_Clicked(...) {
   if(currentDocument is ChartReport) {
      ChartReport r = currentDocument as ChartReport;
      r.SavePDF();
   } else if(currentDocument is GridReport) {
     GridReport r = currentDocument as GridReport;
      r.SavePDF();
   }
}

I'll rather make my ChartReport and GridReport implement this interface:

public interface Report {
  void MailTo();
  void SavePDF();
}

Now I can do:

void ExportPDF_Clicked(...) {
   Report r = currentDocument as Report;
   r.SavePDF();
}

Similar for other code that need to do the same operation(save it to a file,zoom in,print,etc.) on the different report types. The above code will still work fine when I add a PivotTableReport also impelmenting Rpoert the next week.