How do you send a refresh message to a WPF grid or canvas?

How do you send a refresh message to a WPF grid or canvas?

In other words, I have noticed while in debug mode, I can write code that sends a line to the display and then, if that line is not right, I can adjust it -- but the previous line is still there.
Now, the code I am writing sends information to the display based on what the user clicks. So this must mean that the display is not refreshed each time a new set of lines and boxes and text goes to the grid or canvas in WPF.

Using C# code, how do you send a refresh/repaint message to a WPF grid or canvas?

If I have drawn lines on a canvas in my C# code (instead of in the XAML code) how do I remove them?

In general, if you are using data binding correctly it isn't required to have to 'refresh' anything.

Can you zip up a sample of what your approach is? We might be able to offer something different.