Core-Plot graph not showing any data points

Question

I've been able to get the axes for a standard core-plot graph to show up, but I'm having some trouble actually adding points to it.

I have these two methods declared in the .m file (found from another question on this site):

-(NSUInteger)numberOfRecordsForPlot:(CPTPlot *)plot;


-(NSNumber *)numberForPlot:(CPTPlot *)plot field:(NSUInteger)fieldEnum recordIndex:

So, at the top of that controller.m file, I have this:

NSArray *myDataArray;

Lastly, in the viewDidLoad method (still .m file), near the end (after creating the graph), I have an array with points set up.

When I build and run, XCode gives 0 errors or warnings, but the points do not show up on the graph.

Would appreciate any help, thanks!

Do you have the delegate protocols declared in the header file? For example, if you are using a bar graph, you should have CPBarPlotDelegate and CPPlotDataSource in the header. Otherwise, those methods above do not get called. Hopefully that's the problem. Otherwise, we'll have to do a little more digging — justin

justin justin · Accepted Answer · 2011-09-20T17:21:53

I thought this would be too confusing to read in the comments, so I'm moving to an answer.

In your numberForPlot method, try something like the following:

- (NSNumber *)numberForPlot:(CPPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index { 
    if (fieldEnum == CPScatterPlotFieldX) {
        // should return data for x axis point;
        return [[myDataArray objectAtIndex:index] objectAtIndex:index];
    }
    else {
        // y axis point;
        return [NSDecimalNumber numberWithInt:index];
    }
}

I apologize if it's pretty crude. I just rewrote a bit from a bar graph to scatter plot. But this should do the trick. I think the issue was that you were calling objectAtIndex:fieldEnum. This had me confused for a while also when I first started using CorePlot. Again, if this doesn't do the trick, just say so and we'll try something new. But I believe this should do it, or something very similar.

EDIT: In the example code provided with CorePlot, here is the code for the data itself:

-(NSNumber *)numberForPlot:(CPPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index {
    NSDecimalNumber *num = nil;
    if ( [plot isKindOfClass:[CPPieChart class]] ) {
        if ( index >= [self.dataForChart count] ) return nil;

        if ( fieldEnum == CPPieChartFieldSliceWidth ) {
            num = [self.dataForChart objectAtIndex:index];
        }
        else {
            num = (NSDecimalNumber *)[NSDecimalNumber numberWithUnsignedInteger:index];
        }
    }
    else if ( [plot isKindOfClass:[CPBarPlot class]] ) {
        switch ( fieldEnum ) {
        case CPBarPlotFieldBarLocation:
            if ( index == 4 ) {
                num = [NSDecimalNumber notANumber];
            }
            else {
                num = (NSDecimalNumber *)[NSDecimalNumber numberWithUnsignedInteger:index];
            }
            break;
        case CPBarPlotFieldBarTip:
            if ( index == 8 ) {
                num = [NSDecimalNumber notANumber];
            }
            else {
                num = (NSDecimalNumber *)[NSDecimalNumber numberWithUnsignedInteger:(index+1)*(index+1)];
                if ( [plot.identifier isEqual:@"Bar Plot 2"] ) {
                    num = [num decimalNumberBySubtracting:[NSDecimalNumber decimalNumberWithString:@"10"]];
                }
            }
            break;
        }
    }
    else {
        if ( index % 8 ) {
            num = [[dataForPlot objectAtIndex:index] valueForKey:(fieldEnum == CPScatterPlotFieldX ? @"x" : @"y")];
            // Green plot gets shifted above the blue
            if ( [(NSString *)plot.identifier isEqualToString:@"Green Plot"] ) {
                if ( fieldEnum == CPScatterPlotFieldY ) {
                    num = (NSDecimalNumber *)[NSDecimalNumber numberWithDouble:[num doubleValue] + 1.0];
                }
            }
        }
        else {
            num = [NSDecimalNumber notANumber];
        }
    }
    return num;
}

Sorry for including all of it, but I thought it might make it easier to look at all of the types to better differentiate how to approach the scatter plot. Creating their data, it looks like this:

NSMutableArray *contentArray = [NSMutableArray arrayWithCapacity:100];
NSUInteger i;
for ( i = 0; i < 60; i++ ) {
    id x = [NSNumber numberWithFloat:1+i*0.05];
    id y = [NSNumber numberWithFloat:1.2*rand()/(float)RAND_MAX + 1.2];
    [contentArray addObject:[NSMutableDictionary dictionaryWithObjectsAndKeys:x, @"x", y, @"y", nil]];
}
self.dataForPlot = contentArray;

So maybe if you try a format like that, it could work. If that doesn't do the trick, then we know it's an issue with the graph creation itself and not the data

Core-Plot graph not showing any data points

1 Answers