Extract Method

I m going to extract the code that talks to the TextBox from the KeyDownHandler. I think I ll begin with just the last few lines that set the TextBox. I plan two steps, more for purposes of explaining than anything else. First, let s make a new method:

 public void PutText() { 
 textbox.Lines = model.LinesArray(); 
 textbox.SelectionStart = model.SelectionStart; 
 textbox.ScrollToCaret(); // keep cursor on screen. no test. 
 } 

And we ll call it from the handler, replacing the last three lines. I removed the debugging stuff as well, so the new handler looks like this:

 void XMLKeyDownHandler(object objSender, KeyEventArgs kea) { 
 model.SetLines(textbox.Lines); 
 model.SelectionStart = textbox.SelectionStart; 
 if (kea.KeyCode == Keys.Enter) { 
 model.Enter(); 
 kea.Handled = true; 
 } 
 PutText(); 
 } 

Normally, I d just compile now and run the tests. But my tests don t test this! I ll have to test it manually. This is awful ! But it seems to work. Now for the second step.

The PutText method refers to the instance variable textbox. I want to pass it in as a parameter instead. This may seem odd at first, but remember that I want to use this thing with my Mock Object.

However, thinking about this tells me that I don t have a clear picture of what my test will look like, so I m speculating about what I want. And surely so are you. I should be writing the test first. So I ll do that now.