This is an extension and not part of the main GoJS library. Note that the API for this class may change at any time. If you intend to use an extension in production, you should copy the code to your own source directory. Extensions can be found in the GoJS kit under the `extensions` or `extensionsTS` folders. See the Extensions intro page for more information.

### Hierarchy

- Tool
  - LinkLabelOnPathDraggingTool

The LinkLabelOnPathDraggingTool class lets the user move a label on a Link while keeping the label on the link's path. This tool only works when the Link has a label marked by the "_isLinkLabel" property.

If you want to experiment with this extension, try the Link Label On Path Dragging sample.

## Index

### Constructors

- constructor

### Properties

- label

### Methods

- canStart
- doActivate
- doCancel
- doDeactivate
- doMouseMove
- doMouseUp
- doStop
- findLabel
- updateSegmentOffset

## Constructors

### constructor

- new LinkLabelOnPathDraggingTool(): LinkLabelOnPathDraggingTool

- Constructs a LinkLabelOnPathDraggingTool and sets the name for the tool.

  #### Returns LinkLabelOnPathDraggingTool

## Properties

### label : GraphObject | null

The label being dragged.

## Methods

### Override canStart

- canStart(): boolean

- This tool can only start if the mouse has moved enough so that it is not a click, and if the mouse down point is on a GraphObject "label" in a Link Panel, as determined by findLabel.

  #### Returns boolean

### Override doActivate

- doActivate(): void

- Start a transaction, call findLabel and remember it as the "label" property, and remember the original values for the label's segment properties.

  #### Returns void

### Override doCancel

- doCancel(): void

- Restore the label's original value for GraphObject.segment... properties.

  #### Returns void

### Override doDeactivate

- doDeactivate(): void

- Stop any ongoing transaction.

  #### Returns void

### Override doMouseMove

- doMouseMove(): void

- During the drag, call updateSegmentOffset in order to set the segment... properties of the label.

  #### Returns void

### Override doMouseUp

- doMouseUp(): void

- At the end of the drag, update the segment properties of the label and finish the tool, completing a transaction.

  #### Returns void

### Override doStop

- doStop(): void

- Clear any reference to a label element.

  #### Returns void

### findLabel

- findLabel(): GraphObject | null

- From the GraphObject at the mouse point, search up the visual tree until we get to an object that has the "_isLinkLabel" property set to true and that is an immediate child of a Link Panel.

  #### Returns GraphObject | null

  This returns null if no such label is at the mouse down point.

### updateSegmentOffset

- updateSegmentOffset(): void

- Save the label's GraphObject.segmentIndex and GraphObject.segmentFraction at the closest point to the mouse.

  #### Returns void

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