Selection and Hit Testing

• Aug 16, 2019
• 5 minutes to read

The Selection allows end-users to select single or multiple points or series.

How to: Handle chart selection changes

The code snippet below shows how to handle chart selection changes.

Objective C

-(void) viewDidLoad { 
// ...
    self.chart.delegate = [ChartDelegate delegateWithOwner: self];
}
// ...

@interface ChartDelegate : NSObject <DXChartDelegate>
    +(id) delegateWithOwner: (ViewController *)owner;
@end

@implementation ChartDelegate {
    ViewController *owner;
}

+(id) delegateWithOwner: (ViewController *)owner {
    ChartDelegate *delegate = [[ChartDelegate alloc] init];
    delegate->owner = owner;
    return delegate;
}

- (void)chart:(DXChartBase*) chart seriesDidSelect:(NSInteger) seriesIndex {
    [self showAlertWithMessage: [NSString stringWithFormat: @"Series with index %ld was selected.", seriesIndex]];
}

- (void)chart:(DXChartBase*) chart seriesDidDeselect:(NSInteger) seriesIndex {
    [self showAlertWithMessage: [NSString stringWithFormat: @"Series with index %ld was deselected.", seriesIndex]];
}

-(void)showAlertWithMessage: (NSString *)message {
    UIAlertAction *okAction = [UIAlertAction actionWithTitle: @"OK"
                                                       style: UIAlertActionStyleDefault
                                                     handler: nil];

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle: @"Series selection"
                                                                             message: message
                                                                      preferredStyle: UIAlertControllerStyleAlert];
    [alertController addAction:okAction];

    [owner presentViewController: alertController
                        animated: YES
                      completion: nil];
}
@end

Swift

override func viewDidLoad() { 
// ...
    self.chart.delegate = ChartController(self);
}
// ...

class ChartDelegate : DXChartDelegate {
    let owner: ViewController;

    required init(_ owner: ViewController) {
        self.owner = owner;
    }

    func chart(_ chart: DXChartBase!, seriesDidSelect seriesIndex: Int) {
        showAlert(message: String.init(format: "Series with index %d was selected.", seriesIndex));
    }

    func chart(_ chart: DXChartBase!, seriesDidDeselect seriesIndex: Int) {
        showAlert(message: String.init(format: "Series with index %d was selected.", seriesIndex));
    }

    private func showAlert(_ message: String) {
        let alertController = UIAlertController(
            title: "Series selection",
            message: message,
            preferredStyle: UIAlertControllerStyle.alert);
        alertController.addAction(UIAlertAction(
            title: "OK",
            style: UIAlertActionStyle.default,
            handler: nil));
        owner.present(alertController, animated: true, completion: nil);
    }
}

C#

override func viewDidLoad() { 
// ...
    this.chart.Delegate = new ChartDelegate(this);
}
// ...

class ChartDelegate : DXChartDelegate {
    ViewController owner;
    public ChartDelegate(ViewController owner) {
        this.owner = owner;
    }

    public override void SeriesDidSelect(DXChartBase chart,long seriesIndex) {
        showAllert(String.Format("Series with index {0} was selected.",seriesIndex));
    }

    public override void SeriesDidDeselect(DXChartBase chart,long seriesIndex) {
        showAllert(String.Format("Series with index {0} was deselected.",seriesIndex));
    }

    void showAllert(String message) {
        UIAlertController alertController = UIAlertController.Create(
            title: "Series selection",
            message: message,
            preferredStyle: UIAlertControllerStyle.Alert);
        alertController.AddAction(
            UIAlertAction.Create(
                title: "OK",
                style: UIAlertActionStyle.Default,
                handler: null
            )
        );

        owner.PresentViewController(
            viewControllerToPresent: alertController,
            animated: true,
            completionHandler: null
        );
    }
}

The following symbols allow you to configure the selection:

Symbols	Description
delegate	Gets or sets the chart delegate.
DXChartDelegate	A protocol that a class should adopt to handle selection changes.

How to: Select an individual point or whole series

The Charts’ selection mechanism allows you to specify a type of chart elements which should be selected - a series or a point.

The following code demonstrates how to do this:

Objective C

self.chart.selectionKind = DXChartSelectionKindSeries;

Swift

self.chart.selectionKind = DXChartSelectionKind.series;

C#

this.chart.SelectionKind = DXChartSelectionKind.Series;

The following classes and methods allow you to specify what chart element should be selected:

Symbols	Description
DXChartBase.selectionKind	Gets or sets the value indicating a type of chart elements which should be selected.
DXChartSelectionKind	Lists all values indicating what chart element should be selected.

How to: Select several points (series) simultaneously

The Chart selection mechanism allows you to select one or more chart elements simultaneously.

The following code demonstrates how to configure the selection mechanism to accomplish this:

Objective C

self.chart.selectionMode = DXChartSelectionModeMultiple;

Swift

self.chart.selectionMode = DXChartSelectionMode.multiple;

C#

this.chart.SelectionMode = DXChartSelectionMode.Multiple;

The following classes and methods allow you to specify the selection mode:

Symbols	Description
DXChartBase.selectionMode	Gets or sets the value indicating how many chart elements can be selected simultaneously.
DXChartSelectionMode	Lists all values indicating how many chart elements can be selected simultaneously.

How to: Get information about chart elements under the specified point

The Hit testing allows you to recognize which element is at the specified screen coordinates. For example, determining which chart element has been tapped by an end-user. The following example shows how to perform hit testing:

Objective C

-(void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView: self.chart];
    DXChartHitInfo *hitInfo = [self.chart calcHitInfo:location];

    BOOL useComma = NO;
    NSMutableString *text = [NSMutableString stringWithString: @"You tap"];

    if (hitInfo.inSeries){
        [text appendString:@" in a series"];
        useComma = YES;
    }
    if (hitInfo.inPoint){
        if (useComma) {
            [text appendString:@","];
        }
        [text appendString:@" in a point"];
        useComma = YES;
    }
    if (hitInfo.inLegend){
        if (useComma) {
            [text appendString:@","];
        }
        [text appendString:@" in the legend"];
    }
    [text appendString:@"."];

    UIAlertAction *okAction = [UIAlertAction actionWithTitle: @"OK"
                                                       style: UIAlertActionStyleDefault
                                                     handler: ^(UIAlertAction* action){ }];

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle: @"Series hit-testing"
                                                                             message: text
                                                                      preferredStyle: UIAlertControllerStyleAlert];
    [alertController addAction:okAction];

    [self presentViewController:alertController
                       animated: YES
                     completion: nil];
}

Swift

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    let touch = touches.first!;
    let location = touch.location(in: self.chart);
    let hitInfo = self.chart.calcHitInfo(location);

    var useComma: Bool = false; 
    var text: String = "You tap";

    if (hitInfo.inSeries){
        text.append(" in a series");
        useComma = true;
    }
    if (hitInfo.inPoint){
        if (useComma) {
            text.append(",");
        }
        text.append(" in a point");
        useComma = true;
    }
    if (hitInfo.inLegend){
        if (useComma) {
            text.append(",")
        }
        text.append(" in the legend");
    }
    text.append(".");

    let okAction = UIAlertAction(title: "OK", style: UIAlertActionStyle.default);

    let alertController = UIAlertController(title: "Series hit-testing",
                                          message: text,
                                   preferredStyle: UIAlertControllerStyle.alert);
    alertController.addAction(okAction);

    self.present(alertController, animated: true, completion: nil);
}

C#

public override void TouchesEnded(Foundation.NSSet touches,UIEvent evt) {
    UITouch touch = (UITouch)touches.AnyObject;
    CGPoint location = touch.LocationInView(this.chart);
    DXChartHitInfo hitInfo = this.chart.CalcHitInfo(location);

    bool useComma = false;
    StringBuilder textBuilder = new StringBuilder("You tap");

    if (hitInfo.InSeries) {
        textBuilder.Append(" in a series");
        useComma = true;
    }
    if (hitInfo.InPoint) {
        if (useComma) {
            textBuilder.Append(",");
        }
        textBuilder.Append(" in a point");
        useComma = true;
    }
    if (hitInfo.InLegend) {
        if (useComma) {
            textBuilder.Append(",");
        }
        textBuilder.Append(" in the legend");
    }
    textBuilder.Append(".");

    UIAlertController alertController = UIAlertController.Create(
        title: "Series hit-testing",
        message: textBuilder.ToString(),
        preferredStyle: UIAlertControllerStyle.Alert
    );
    alertController.AddAction(
        UIAlertAction.Create(
            title: "OK",
            style: UIAlertActionStyle.Default,
            handler: null
        )
    );

    this.PresentViewController(
        viewControllerToPresent: alertController,
        animated: true,
        completionHandler: null
    );
}

The following methods and classes allows you to perform hit testing.

Symbols	Description
DXChartBase::calcHitInfo:	Returns information about chart elements at the specified point.
DXChartHitInfo	The information about chart elements located in a specific point.