iPhone Multi touch interactive to CorePlot

Question

I\'m developing an iPhone application with core-plot chart. With the help of some tutorials, i managed to do it with single touch and drag. How can I make it with multiple touch

Answer 1

I came across the same problem recently and couldn't find any solution. After some time researching and coding I found some solutions and want to share one, quite easy one, so it may help you get an idea how to approach this.

I have created transparent UIView, which I've put on top of CPTGraphHostingView. This view was handling needed touch events. Let's name it TestView

TestView.h file looks like

@protocol TestViewDelegate 
- (void)myTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;
- (void)myTouchesMoved:(NSSet *)touches withEvent:(UIEvent *)event;
- (void)myTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event;

@end

@interface TestView : UIView
@property (nonatomic, weak) id delegate;
@end

TestView.m

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
    }
    return self;
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    [self.delegate myTouchesBegan:touches withEvent:event];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    [self.delegate myTouchesMoved:touches withEvent:event];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
    [self.delegate myTouchesEnded:touches withEvent:event];
}

TestView delegate, in my case viewController, which includes corePlot hosting view, will implement those methods and see the sample of the code below

- (void)myTouchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    if (touches.count == 1) {
        UITouch *touch = (UITouch *)[[touches allObjects] objectAtIndex:0];
        CGPoint point = [touch locationInView:nil];
        [self plotSpace:self.plotSpace shouldHandlePointingDeviceDraggedEvent:event atPoint:point];
    }
    if (touches.count == 2) {
        UITouch *touch = (UITouch *)[[touches allObjects] objectAtIndex:1];
        CGPoint point = [touch locationInView:nil];
        [self plotSpace:self.plotSpace shouldHandlePointingDeviceDraggedEvent:event atPoint:point];
    }
}

CPTPlotSpace delegate method in viewController will look like

- (BOOL)plotSpace:(CPTPlotSpace *)space shouldHandlePointingDeviceDraggedEvent:(id)event atPoint:(CGPoint)point{
    NSSet *allTouches = [event allTouches];
    if ([allTouches count] >0 ) {
        UITouch *touch1 = [[allTouches allObjects] objectAtIndex:0];
        if (touch1){
            CGPoint pointInPlotArea = [self.graph convertPoint:[touch1 locationInView:self.view] toLayer:self.graph.plotAreaFrame];
//              padding
            pointInPlotArea.x -=10;
            NSDecimal newPoint[2];
            [self.graph.defaultPlotSpace plotPoint:newPoint forPlotAreaViewPoint:pointInPlotArea];
            NSDecimalRound(&newPoint[0], &newPoint[0], 0, NSRoundPlain);
            int x = [[NSDecimalNumber decimalNumberWithDecimal:newPoint[0]] intValue];
            x--;

            if (x <= 0)
                x = 0;
            else if (x >= [self.currentDatapoints count])
                x = [self.currentDatapoints count] - 1;

            selectedCoordination = x;
            self.label.text = [NSString stringWithFormat:@"%@", [self.currentDatapoints objectAtIndex:x]];
            self.differenceLabel.text = @"";
            [touchPlot reloadData];
        }
        if ([allTouches count] > 1){
            secondTouchPlot.hidden = NO;
            UITouch *touch2 = [[allTouches allObjects] objectAtIndex:1];
            if (touch2) {
                CGPoint pointInPlotArea = [self.graph convertPoint:[touch2 locationInView:self.view] toLayer:self.graph.plotAreaFrame];
                pointInPlotArea.x -= 10;
                NSDecimal newPoint[2];
                [self.graph.defaultPlotSpace plotPoint:newPoint forPlotAreaViewPoint:pointInPlotArea];
                NSDecimalRound(&newPoint[0], &newPoint[0], 0, NSRoundPlain);
                int x = [[NSDecimalNumber decimalNumberWithDecimal:newPoint[0]] intValue];
                x--;
                if (x <= 0)
                    x = 0;
                else if (x >= [self.currentDatapoints count])
                    x = [self.currentDatapoints count] - 1;

                selectedCoordination2 = x;
                self.secondLabel.text = [NSString stringWithFormat:@"%@", [self.currentDatapoints objectAtIndex:x]];
                [secondTouchPlot reloadData];
                float first = [self.label.text floatValue];
                float second = [[self.currentDatapoints objectAtIndex:x] floatValue];
                self.differenceLabel.textColor = (first - second) > 0 ? [UIColor greenColor] : [UIColor redColor];
                self.differenceLabel.text = [NSString stringWithFormat:@"%f", first - second];

            }
        }
    }
    return YES;
}

And that's the result...

This is not optimized code, it's just the idea, as I mentioned above, how to approach this problem.

Hope it helps...