Brief introduction of DrawRect and Setneedsdisplay

1 -(void) DrawRect: (cgrect) rect {2     3 }

1.rect default is your own bounds

2.drawRect call ?

- called once when the view is first displayed to the screen

- when calling this method, the system will help us create the graphical context, so we just need to get the graphics context to

- After the display is complete, this method is no longer called

3. How to call the DrawRect method

Apple rules that programmers are not allowed to call this method directly

Indirect call !

You can use the following two methods to let the system help us execute the drawrect method !

-(void) setneedsdisplay; It 's common !

redraw within the specified area !

-(void) Setneedsdisplayinrect: (cgrect) rect;

the benefit of indirect invocation:----- can guarantee that the system will then help us create the graphics context !

Brief introduction of DrawRect and Setneedsdisplay