CorePlot学习 点击scatterPlot中的symbol点时弹出相应的注释

首先要引用委托方法：CPTScatterPlotDelegate、CPTPlotSpaceDelegate

完成如下:

#pragma mark -
#pragma mark CPTPlotSpaceDelegate methods
-(BOOL)plotSpace:(CPTPlotSpace *)space shouldHandlePointingDeviceCancelledEvent:(UIEvent *)event
{
    return YES;
}
-(BOOL)plotSpace:(CPTPlotSpace *)space shouldHandlePointingDeviceUpEvent:(UIEvent *)event atPoint:(CGPoint)point
{
    return YES;
}
-(BOOL)plotSpace:(CPTPlotSpace *)space shouldHandlePointingDeviceDownEvent:(UIEvent *)event atPoint:(CGPoint)point
{
    NSLog(@"you putdown at point:%@",[NSValue valueWithCGPoint:point]
);
    return YES;
}
-(BOOL)plotSpace:(CPTPlotSpace *)space shouldHandlePointingDeviceDraggedEvent:(UIEvent *)event atPoint:(CGPoint)point
{
    return YES;
}  

#pragma mark -
#pragma mark CPTScatterPlotDelegate
//当我们选择相应的点时，弹出注释：
-(void)scatterPlot:(CPTScatterPlot *)plot plotSymbolWasSelectedAtRecordIndex:(NSUInteger)idx withEvent:(UIEvent *)event
{  

    if ( symbolTextAnnotation ) {
        [xyGraph.plotAreaFrame.plotArea removeAnnotation:symbolTextAnnotation];
        symbolTextAnnotation = nil;
    }
    // Setup a style for the annotation
    CPTMutableTextStyle *hitAnnotationTextStyle = [CPTMutableTextStyle textStyle];
    hitAnnotationTextStyle.color    = [CPTColor greenColor];
    hitAnnotationTextStyle.fontSize = 10.0f;
    hitAnnotationTextStyle.fontName = @"Helvetica-Bold";  

    // Determine point of symbol in plot coordinates
    NSNumber *x          =
    [[datasForPlot objectAtIndex:idx] valueForKey:@"x"];
    NSNumber *y          = [[datasForPlot objectAtIndex:idx] valueForKey:@"y"];
    NSString *date = [[datasForPlot objectAtIndex:idx]valueForKey:@"date"];  

    NSArray *anchorPoint = [NSArray arrayWithObjects:x, y, nil nil];
    // Add annotation
    // First make a string for the y value
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
    [formatter setMaximumFractionDigits:2];
    NSString *yString = [formatter stringFromNumber:y];
    NSString *myString = [NSString stringWithFormat:@"温度：%@\n日期：%@\n事件：%@",yString,date,nil];  

    // Now add the annotation to the plot area
    CPTTextLayer *textLayer = [[CPTTextLayer alloc] initWithText:myString/*yString*/ style:hitAnnotationTextStyle];
    symbolTextAnnotation              = [[CPTPlotSpaceAnnotation alloc] initWithPlotSpace:xyGraph.defaultPlotSpace anchorPlotPoint:anchorPoint];
    symbolTextAnnotation.contentLayer = textLayer;
    symbolTextAnnotation.displacement = CGPointMake(0.0, 20.0);
    [xyGraph.plotAreaFrame.plotArea addAnnotation:symbolTextAnnotation];  

   // NSLog(@"index:%lu,event:%@",(unsigned long)idx,event);
}  

千万别忘记了根据自己定义的设置相应的delegate = self；

红色标注的就是我们实现该功能的重点

对了，忘记说一点，该点非常重要，不然你手指点击不灵活。我们的symbol那么小，还要点击到它的中心才能触发下面的方法，这多难啊，有个参数设置一下就搞定了，设置它的触发范围：

    CPTScatterPlot *boundLinePlot = [[CPTScatterPlot alloc]init];
    boundLinePlot.plotSymbolMarginForHitDetection = 5.0f;//设置symbol点的外沿范围，以用来检测手指的触摸