Question

I am Using CorePlot in my app, and I want to display a annotation over the plotSymbol. I haven’t found any code in the sample projects of the latest 0.9 version of CorePlot. After some research i have come to this point:

- (void)scatterPlot:(CPTScatterPlot *)plot plotSymbolWasSelectedAtRecordIndex:(NSUInteger)index
{
    CPTLayerAnnotation *annot = [[CPTLayerAnnotation alloc]initWithAnchorLayer:graph];
    CPTBorderedLayer * logoLayer = [[(CPTBorderedLayer *) [CPTBorderedLayer alloc] initWithFrame:CGRectMake(10,10,100,50)] autorelease]; 
    CPTFill *fillImage = [CPTFill fillWithImage:[CPTImage imageForPNGFile:@"whatEver!"]]; 
    logoLayer.fill = fillImage; 
    annot.contentLayer = logoLayer; 
    annot.rectAnchor=CPTRectAnchorTop;
    [graph addAnnotation:annot];
}

But its obviously not working…. Can anybody help me?

My goal is to get an annotation over the selected plot symbol, similar to annotations in MKMapView.

Update

It is a DatePlot, just to clarify things and it is working with time intervals since 2001 on the x-axis.

Answer 1

There are several examples of this in the Core Plot example apps. The gradient scatter plot in the Plot Gallery app (and several other apps as well) use this method to attach a text label to the selected point. The point selection demo in the Mac version of CPTTestApp uses a second scatter plot to draw a crosshairs over the selected point.

Remember to set the plotSymbolMarginForHitDetection property on the scatter plot, too. The default is 0, which means you have to hit the center of the point exactly to register a touch.

There are two types of annotation in Core Plot. A CPTLayerAnnotation is anchored to a given Core Animation layer (the graph in your case). A CPTPlotSpaceAnnotation is anchored to a plot space coordinate (== data coordinate). Your comment below makes it sound like you want to use a plot space annotation instead of a layer annotation.