问题
Can someone explain the difference between the Graphics object that is passed as pevent.Graphics and the one that is returned by a call to this.CreateGraphics()?
回答1:
Whenever a Paint event is raised, you are given a Graphics object to draw into. This is passed as pevent.Graphics. Drawing into this Graphics object is how you paint the element.
CreateGraphics should basically never be used. It creates a new Graphics object on-the-fly from a window handle. You can draw into the Graphics object it returns, but anything you draw into it will be obliterated the next time that a Paint event is raised.
The only time you might want to use CreateGraphics is for special effects, like showing real-time feedback during a drag. You want that to be erased the next time that the element is repainted, so you go ahead and use CreateGraphics to get a temporary canvas to draw onto while the drag event is in progress.
You will never use CreateGraphics inside of a Paint event handler method. There is no point—you are given a Graphics object to draw into already!
来源：https://stackoverflow.com/questions/25301743/what-is-the-difference-between-creategraphics-and-a-paint-events-graphics-objec