How to draw text in UIView after -drawRect has been called - objective-c

Question

I have an iPad app, XCode 4.5, iOS 6.1 and Storyboards. I have a UIView, with two (2) UIViews embedded in it. The first UIView (called Calendar) is on the top half, and the second UIView (called Schedule) is on the bottom half. I create a calendar on the top half, and draw a grid to display a schedule on the bottom half.
The sequence of events is the user is presented with the scene with the Calendar (completely filled in for current month) and Schedule (an empty grid is displayed). When a day is tapped on the Calendar, the schedule for that day will be displayed in the Schedule view.
The problem is -drawRect is called when the scene is initially displayed, before the user has the ability to choose a date to display for the schedule. Since I have to do the drawing from within -drawRect, I can't figure out how to fill in the schedule outside of -drawRect. I was wondering if using setNeedsDisplayInRect:, would accomplish what I need to do?
I have looked at SO and Google for several days now, and found nothing that would answer this particular question. This is NOT a duplicate of this question, but rather a follow-on since the project has been redefined. Any ideas would be gratefully appreciated.
UPDATE: here is my code using setNeedsDisplayInRect:
- (void) drawSchedule {
const float rectWidth = 120.0;
// draw detail for selected day for each staff member
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGContextSetLineWidth(context, 1.0);
CGContextSetRGBFillColor(context, 0, 0, 1, 0.3);
UIGraphicsBeginImageContext(self.bounds.size);
// draw customer name using bounds from CGRectMake
const float nameFontSize = 12;
UIFont *hourfont=[UIFont systemFontOfSize: nameFontSize];
[[UIColor blackColor] set];
[self setNeedsDisplayInRect: CGRectMake(160.0, 150.0, 120.0, 50.0)]; // mark as needs to be redrawn
// customer for this time slot
[#"John Doe" drawAtPoint:CGPointMake(114, 40) withFont:hourfont];
}

Answer 1

When a day is tapped on the Calendar, the schedule for that day will be displayed in the Schedule view.
When you user taps the a day on the calendar, tell the Schedule to change:
[self.calendarView displayDate: thatDay];
The Schedule, in turn, gets the message, figures out what it needs to do, and tells itself to redisplay when its time to draw.
- (void) displayDate: (YourDateObject*) thatDay
{
self.date=thatDay;
[self setNeedsDisplay: YES]
}
Now, the system will call the Schedule's drawRect: at the appropriate time, and you'll display the new schedule.
The general rule is simply this: set the state of the view when you know it, and let the view redisplay itself when asked. Don't try to say, "Draw this"; instead, say, "Here is what you should draw next time. As soon as you're ready, raise your hand; the teacher will call on you."

Answer 2

Perhaps you can use UIView's method: setNeedsDisplay. This will cause drawRect: to be called again. Or, if you only want to redraw a portion of the view you could use setNeedsDisplayInRect:, as you mentioned.
You should never call drawRect: yourself.
UIGraphicsBeginImageContext(self.bounds.size)
[#"John Doe" drawAtPoint:CGPointMake(114,40) withFont:hourFont];
UIimage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
Then you can use imageView to add it as a sub-view to your view.

Answer 3

Typically, you should do all of your drawing within the drawRect: method. When a user taps on a date in the calendar, you only need to send the setNeedsUpdate message to the schedule view. Then the schedule view will automatically redraw and call its own drawRect: method.
Calling setNeedsDisplayInRect: (or setNeedsDisplay) simply notifies the system that the receiver needs to be redrawn. Your drawRect: method will be invoked at some point later, when it is appropriate to perform the actual drawing.

Answer 4

This question is moot; you can't clear the drawing on a UIView, which makes this design not viable.
I am now considering using UITableViews or a UIView sub-view on top of the schedule grid, which brings up new issues.
Thank you everybody for your comments.