Question

I’ve been wrestling with this for a few days – I have a custom protocol that is supposed to get the data from one of my models (via it’s controller) to a view that graphs it.

Here’s how I am doing this – step by step:

In graphing view, I declare the protocol as follows:

@class GraphView;

@protocol GraphViewDataSource <NSObject>

-(CGFloat)yValueForGraphView:(GraphView *)sender usingXval:(CGFloat)xVal;

@end

I then declare a property in view.h

@interface GraphView : UIView

@property (nonatomic, weak) IBOutlet id <GraphViewDataSource> dataSource;

@end

I synthesize the property in view.m:

@synthesize dataSource=_dataSource;

Then in my drawRect, I am calling this method to bring me back a CGFloat from another controller’s model:

-(void) drawRect:(CGRect)rect
{
//context stuff, setting line width, etc

CGPoint startPoint=CGPointMake(5.0, 6.0);

NSLog(@"first, y value is: %f", startPoint.y);

startPoint.y=[self.dataSource yValueForGraphView:self usingXval:startPoint.x]; //accessing delegate via property

NSLog(@"now the y value now is: %f", startPoint.y);

//other code..
}

Now in my other view controller, I am importing the view.h file and declaring that it conforms to the protocol:

#import "GraphView.h"

@interface CalculatorViewController () <GraphViewDataSource>

Creating a property for the GraphView:

@property (nonatomic, strong) GraphView *theGraphView;

Synthesize:

@synthesize theGraphView=_theGraphView;

Now in the setter, I set the current controller as the dataSource (aka the delegate):

-(void) setTheGraphView:(GraphView *)theGraphView
{
    _theGraphView=theGraphView;
    self.theGraphView.dataSource=self;

}

I also set the controller as the delegate in prepareForSegue (one of the things I tried while looking for a fix):

-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"GraphViewController"])
    {
        self.theGraphView.dataSource=self;
    }
}

Finally, I implement the required method:

-(CGFloat)yValueForGraphView:(GraphView *)sender usingXval:(CGFloat)xVal
{
    CGFloat test=51.40; //just to test
    return test;
}

And the output I’m getting from my test NSLog in graphView’s drawRect is:

2012-10-25 20:56:36.352 ..[2494:c07] first, y value is: 6.000000
2012-10-25 20:56:36.354 ..[2494:c07] now the y value now is: 0.000000

This should be returning 51.40 via the dataSource, but it is not. I can’t figure out why! Driving me crazy, it seems like I’ve done everything right. But the delegate method is not getting called.

Is there some silly thing I am missing?

---

Additional info – diagram of controllers & GraphView:

Answer 1

The way I solved this was chaining some delegates, my GraphView declares a protocol GraphViewDelegate with the following methods:

-(float)ordinateForAbscissa:(float)abscissa forGraph:(GraphView *)requestor;
-(float)scaleForGraph(GraphView *)requestor;

This protocol is implemented by the GraphViewController and he sets himself as a delegate of the GraphView when the controller loads in viewDidLoad.

Now I have another delegate that is CalculatorControllerDelegate that implements yCoordinateForX that is called from ordinateForAbscissa. CalculatorViewController implements this protocol and when segueing sets itself up as the GraphViewController‘s delegate.

Hope this helps.