Core Plot DataSource delegate methods implemented in separate Object are not called

Question

I have two classes, GraphViewController and AppController. AppController (the delegate) implements the datasource protocol of GraphViewController. The problem I have is that those methods are not called by GraphViewController.

However, when I set the datasource of GraphViewController to self and leave the protocol methods in the GraphViewController (like in the CorePlot example provided with CorePlot) everything works fine without any reloadData or setNeedsDisplay methods called.

The problem is not the setup of the view. The theme and the axis are drawn fine, just the plot is missing.

None of the provided answers to very similar questions solved my particular problem. I guess (or hope) that it's just a small thing I'm missing, but I just can't find it.

See the source of the two classes below. Oh, and by the way: this is for OS-X not iOS.

GraphViewController.h:

#import <Cocoa/Cocoa.h>
#import <CorePlot/CorePlot.h>

@interface GraphViewController : NSObject{

    IBOutlet CPTGraphHostingView *graphHostingViewOutlet;
    CPTXYGraph *graph;
}

@property (weak) id<CPTPlotDataSource> delegate;

@end

GraphViewController.m:

#import "GraphViewController.h"

@implementation GraphViewController

@synthesize delegate;

-(void)awakeFromNib {

    [super awakeFromNib];

    // create graph
    graph = [(CPTXYGraph *)[CPTXYGraph alloc] initWithFrame:CGRectZero];

    // apply theme to graph
    [graph applyTheme:[CPTTheme themeNamed:kCPTPlainWhiteTheme]];

    // connect graph to host view
    graphHostingViewOutlet.hostedGraph = graph;

    // get a pointer to the default plot space of the graph
    CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)graph.defaultPlotSpace;

    // setup axes limits
    plotSpace.xRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(-0.2f) length:CPTDecimalFromFloat(1.2f)];
    plotSpace.yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(-0.2f) length:CPTDecimalFromFloat(1.2f)];

    // get a pointer to the axis set of the graph
    CPTXYAxisSet *axisSet = (CPTXYAxisSet *)graph.axisSet;

    // get the x axis element of the axis set and set propertys for x axis
    CPTXYAxis *x = axisSet.xAxis;
    x.majorIntervalLength = CPTDecimalFromFloat(0.2f);

    // get the y axis element of the axis set and set propertys for y axis
    CPTXYAxis *y = axisSet.yAxis;
    y.majorIntervalLength = CPTDecimalFromFloat(0.2f);

    // create a new plot
    CPTScatterPlot *dataSourceLinePlot = [[CPTScatterPlot alloc] init];

    // set the identifier for the plot
    dataSourceLinePlot.identifier = @"ThePlot";

    // set data source for plot
    dataSourceLinePlot.dataSource = delegate;

    // add the plot to the graph
    [graph addPlot:dataSourceLinePlot];

}

@end

AppController.h:

#import <Foundation/Foundation.h>
#import "GraphViewController.h"
#import <CorePlot/CorePlot.h>

@interface AppController : NSObject <CPTPlotDataSource>

@property (weak) GraphViewController *graphViewController;

- (IBAction)doSomething:(id)sender; // connected to a button

@end

AppController.m:

#import "AppController.h"

@implementation AppController{

    NSArray *_plotData;

}

@synthesize graphViewController = _graphViewController;

-(void)awakeFromNib {

    [super awakeFromNib];

    [_graphViewController setDelegate:self];

    // create data array
    NSMutableArray *newData = [NSMutableArray array];

    for (NSUInteger i = 0; i < 20; i++ ) {

        // create random y values
        id y = [NSDecimalNumber numberWithFloat: rand() / (float)RAND_MAX];

        [newData addObject: [NSDictionary dictionaryWithObjectsAndKeys:

                             [NSDecimalNumber  numberWithFloat:0.05 * i],      // x object
                             [NSNumber numberWithInt:CPTScatterPlotFieldX],    // key
                             y,                                                // y object
                             [NSNumber numberWithInt:CPTScatterPlotFieldY],    // key
                             nil]];
    } // end of for

    _plotData = newData;
}

- (IBAction)doSomething:(id)sender{ // connected to a working button

    NSLog(@"Button was pressed.");

    // tell the graphViewController to reload its data from its delegate (me), but how?

    // this does not work: [[NSNotificationCenter defaultCenter] postNotificationName:@"CPTGraphNeedsRedrawNotification" object:nil];

}

// implementation of delegate methods

-(NSNumber *)numberForPlot:(CPTPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index
{
    NSDecimalNumber *num = [[_plotData objectAtIndex:index] objectForKey:[NSNumber numberWithLongLong:fieldEnum]];
    NSLog(@"numberForPlot was called, num is %@",num);
    return num;
}

-(NSUInteger)numberOfRecordsForPlot:(CPTPlot *)plot
{
    NSLog(@"numberForPlot was called.");
    return _plotData.count;
}

@end

I hope the source I posted can serve as a simple prototype for others once the bug was found.

Eric Skroch Eric Skroch · Accepted Answer · 2012-08-01T23:40:46

Check to make sure the delegate has been set in -[GraphViewController awakeFromNib] when you configure the plot. If this class gets initialized before the app controller, it won't be set yet. The fix would be to add a custom setter for the delegate property that sets the new value to the plot datasource, too.

Core Plot DataSource delegate methods implemented in separate Object are not called

2 Answers