iOS & macOS Charting Documentation - SciChart iOS & macOS Charts SDK v4.x

SCIExtendedLineCreationModifier

The SCIExtendedLineCreationModifier is a custom gesture modifier used for interactive creation of Extended Line annotations on a SciChart surface. It enables users to define a line with two anchor points using a pan gesture workflow, with options to extend the line forward, backward, or both directions beyond its anchors.

Overview

The modifier manages the full lifecycle of extended line creation:

Two-step gesture interaction (A → B)
Real-time rendering while dragging points
Automatic annotation finalization after point B is set
Immediate reset for continuous creation of multiple extended lines
Configurable line extension behavior (both directions, forward, backward, or none)

Once completed, the annotation is added to the chart and a completion callback is triggered.

Interaction Behavior

The creation flow is split into two sequential pan gestures.

Gesture Flow (A → B)

Gesture	Behavior
Touch Down	Locks point A at touch location
Drag	Dynamically updates point B
Touch Up	Finalizes A and B, transitions to waiting state

Completion

After point B is set, a SCIExtendedLineAnnotation is created
The annotationCreationCompletionListener callback is invoked
The modifier automatically resets to Idle and is ready for the next line

Retrieving Annotation Data

After completion, the resulting SCIExtendedLineAnnotation provides direct access to its defining anchor points in data space.

Point Accessors

-[ISCIAnnotation getX1] / -[ISCIAnnotation getY1] and [ISCIAnnotation getX2] / -[ISCIAnnotation getY2] Returns the first anchor point (A) and the second anchor point (B) in data coordinates. Values correspond to the chart’s X‑Axis and Y‑Axis units.

API Reference

Field	Description
`SCIExtendedLineCreationModifier.stroke`	Pen style used to draw the extended line.
`SCIExtendedLineCreationModifier.extendStart`	Boolean flag controlling backward extension of the line.
`SCIExtendedLineCreationModifier.extendEnd`	Boolean flag controlling forward extension of the line.
`-[SCIExtendedLineCreationModifier reset]`	Cancels any in‑progress gesture and returns the modifier to Idle.

NOTE: The xAxisId and yAxisId must be supplied if you have axis with non-default Axis Ids, e.g. in multi-axis scenario.

Usage Example

// Create extended line creation modifier
SCIExtendedLineCreationModifier *modifier = [SCIExtendedLineCreationModifier new];

// Configure extension behavior
modifier.extendStart = YES;
modifier.extendEnd = YES; 

// Set the stroke style
modifier.stroke = [[SCISolidPenStyle alloc] initWithColorCode:0xFFE97064 thickness:2];

// Handle completion
modifier.annotationCreationCompletionListener = ^(id _Nonnull createdAnnotation, SCIAnnotationCreationType type) {         
  __strong typeof(weakSelf) strongSelf = weakSelf;
  if (!strongSelf) return;
            
  NSLog(@“ExtendedLine annotation created: %@ type %@”, createdAnnotation, SCIAnnotationTypeName(type));
     
  if (![createdAnnotation isKindOfClass:[SCIExtendedLineAnnotation class]]) return;
  SCIExtendedLineAnnotation *annotation = (SCIExtendedLineAnnotation *)createdAnnotation;
            
  double x1Point = annotation.x1.toDouble;
  double x2Point = annotation.x2.toDouble;
  double y1Point = annotation.y1.toDouble;
  double y2Point = annotation.y1.toDouble;
  NSLog(@“Point A: %f, %f”, x1Point, y1Point);
  NSLog(@“Point B: %f, %f”, x2Point, y2Point);
};
        
// Add to chart
[self.surface.chartModifiers add:modifier];

// Create extended line creation modifier
let modifier = SCIExtendedLineCreationModifier()
            
// Configure extension behavior
modifier.extendStart = true
modifier.extendEnd = true
            
// Set the stroke style
modifier.stroke = SCISolidPenStyle(color: 0xFFE97064, thickness: 2)
                        
// Handle completion
modifier.annotationCreationCompletionListener  = { [weak self] createdAnnotation, type in
  guard self != nil else { return }
                
  print(“Annotation created: \(createdAnnotation), type: \(SCIAnnotationTypeName(type))”)
                
  guard let annotation = createdAnnotation as? SCIExtendedLineAnnotation else { return }
  let x1Point: Double = annotation.getX1()
  let y1Point: Double = annotation.getY1()
  let x2Point: Double = annotation.getX2()
  let y2Point: Double = annotation.getY2()
                
  print(“point =\(x1Point)  \(x2Point)”)
  print(“point =\(y1Point)  \(y2Point)”)
}

Best Practices

Disable conflicting gesture modifiers during extended line creation for smoother interaction
Use SCIAnnotationCreationModifierBase.annotationCreationCompletionListener to persist or analyze completed annotations
Call -[SCIExtendedLineCreationModifier reset] when switching tools or exiting drawing mode
Configure extendStart and extendEnd to match the desired line extension behavior