How to use touchesBegan from one UIView in another UIViewController

Question

I have made a graph with data in a UIView called HeartrateGraph. In a UIViewController named HRGraphInfo, I have a connected label that should output values when the graph is touched. The problem is, I don't know how to send a touched event using delegates from the UIView to the UIViewController.

Here is my touch assignment code in the UIView:

UITouch *touch = [touches anyObject];
CGPoint point = [touch locationInView:self];

for (int i = 0; i < kNumberOfPoints; i++)
{
    if (CGRectContainsPoint(touchAreas[i], point))
    {
        graphInfoRF.heartRateGraphString = [NSString stringWithFormat:@"Heart Rate reading #%d at %@ bpm",i+1, dataArray[i]];
        graphInfoRF.touched = YES;

        break;
    }
}

This segment of code is in a touchesBegan and properly stores the data value and number in the object graphInfoRF (I just did not show the declarations of dataArray, kNumberOfPoints, etc).

I am able to access graphInfoRF in the UIViewController using:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{

if (graphInfoRF.touched == YES) {
    self.heartRateLabel.text = graphInfoRF.heartRateGraphString;

}
else {
    self.heartRateLabel.text = @"No data got over to this file";}
}

The label will show the correct string, but only after the data point on the graph is touched AND the label is touched right after. How do I change the touchesBegan so that once I touch the data point on the graph it will fill the label with the data automatically without the need for a second and separate touch on the label?

Answer 1

All ViewControllers comes with a single view it manages once it's initialized. You should be familiar with this view, you see it whenever you use a ViewController in the Interface Builder and you can access it using self.view if you're modifying a subclass.

Since ViewControllers come with a view, it also receives touch events for that view. Implementing touchesBegan in the ViewController will then receive events for that view, and normally any subviews that view is managing. Since you've down your own implementation of 'touchesBegan' in your HeartRateGraph, and since HeartRateGraph is a subview of ViewControllers main view, HeartRateGraph will receive and handle the touch event first before the ViewController ever has a chance to receive and handle the event like it normally would (think of bubbling up).

So what's happening is, the code to change the label in ViewController is only called when the label is touched because the label is a subview of the ViewController's main view... and also label doesn't have its own touches implementation, so ViewController and is able to retrieve and handle the event the way you want only when you click somewhere outside the graph. If you understand then there are two ways to solve this.

Either pass the event up to your superview

[self.superview touchesBegan:touches withEvent:eventargs];

or the proper recommended way of doing it:

Protocols and Delegates where your View makes a delegate call to it ViewController letting it know the graph has been touched and the ViewController needs to update its contents