Help Please,

I'm new. I've been working on a plotting function that used a draw2D routing I found on line. I need to call the routine from IBAction with a date picker change and want to pass the date in the date picker. So basically I want to combine the IBAction and the plotting on the following two routines. Unsure how to combine them.

-(IBAction)showDate: (id) sender {
//date calculations.....
}

- (id)initWithFrame: (CGRect)frame {
if (self = [super initWithFrame:frame]) {
// Initialization code
}
return self;
}

- (void)drawRect: (CGRect)rect {
//drawing code
}