Core Plot: Should I add CPTPlotSpaceAnnotation for plotting so the whole plot is redrawn?
I am using Core Plot to display price time series. When the user taps the graph, I show a draggable vertical line at that point. Both the time series and the drag line are CPTScatterPlot
objects within CPTXYGraph
. This works pretty well - the performance when dragging a line across the time series plot is acceptable.
The next step is to display the price and date at the point chosen by the user. The Yahoo Stocks app has a nice feature that displays the price in a label that moves as if it's attached to the top of a dragged line. I tried to reproduce this using the text displayed in CPTPlotSpaceAnnotation
. It works, but it has a huge performance impact. After some digging, I found that it CPTLayer drawInContext:
gets called multiple times - it looks like the entire graph is redrawn every time I redraw the text label (actually my logs imply it is redrawn twice).
Here is the code that draws the label (work in progress). It is called plotSpace:shouldHandlePointingDeviceDraggedEvent:atPoint:
.
- (void)displayPriceAndDateForIndex:(NSUInteger)index atPoint:(CGPoint)pointInPlotArea
{
NSNumber * theValue = [[self.graphDataSource.timeSeries objectAtIndex:index] observationValue];
// if the annotations already exist, remove them
if ( self.valueTextAnnotation ) {
[self.graph.plotAreaFrame.plotArea removeAnnotation:self.valueTextAnnotation];
self.valueTextAnnotation = nil;
}
// Setup a style for the annotation
CPTMutableTextStyle *annotationTextStyle = [CPTMutableTextStyle textStyle];
annotationTextStyle.color = [CPTColor whiteColor];
annotationTextStyle.fontSize = 14.0f;
annotationTextStyle.fontName = @"Helvetica-Bold";
// Add annotation
// First make a string for the y value
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setMaximumFractionDigits:2];
NSString *currentValue = [formatter stringFromNumber:theValue];
NSNumber *x = [NSNumber numberWithDouble:[theDate timeIntervalSince1970]];
NSNumber *y = [NSNumber numberWithFloat:self.graphDataSource.maxValue];
NSArray *anchorPoint = [NSArray arrayWithObjects:x, y, nil];
// Then add the value annotation to the plot area
float valueLayerWidth = 50.0f;
float valueLayerHeight = 20.0f;
CPTTextLayer *valueLayer = [[CPTTextLayer alloc] initWithFrame:CGRectMake(0,0,valueLayerWidth,valueLayerHeight)];
valueLayer.text = currentValue;
valueLayer.textStyle = annotationTextStyle;
valueLayer.backgroundColor = [UIColor blueColor].CGColor;
self.valueTextAnnotation = [[CPTPlotSpaceAnnotation alloc] initWithPlotSpace:self.graph.defaultPlotSpace anchorPlotPoint:anchorPoint];
self.valueTextAnnotation.contentLayer = valueLayer;
// modify the displacement if we are close to either edge
float xDisplacement = 0.0;
...
self.valueTextAnnotation.displacement = CGPointMake(xDisplacement, 8.0f);
[self.graph.plotAreaFrame.plotArea addAnnotation:self.valueTextAnnotation];
// now do the date field
...
}
Is the expected full redraw behavior? And is there a better way to manage the annotation without destroying it and recreating it every time the method is called?
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