Class DraggingTool

GoDiagram®
v10.0.12
by Northwoods Software®

The DraggingTool is used to move or copy selected parts with the mouse. This sets the Location property; you may want to save the location to the model by using a TwoWay Binding on the "Location" property in your Parts/Nodes/Groups templates.

Inheritance

object

Tool

DraggingTool

GuidedDraggingTool

NonRealtimeDraggingTool

Namespace: Northwoods.Go.Tools

Assembly: Northwoods.GoDiagram.Avalonia.dll

Syntax

public class DraggingTool : Tool

Remarks

Dragging the selection moves parts for which CanMove() is true. If the user holds down the Control key (Option key on Mac), this tool will make a copy of the parts being dragged, for those parts for which CanCopy() is true.

When the drag starts it calls ComputeEffectiveCollection(IEnumerable<Part>, DraggingOptions) to find the actual collection of Parts to be dragged. Normally this collection includes not only the Selection, but also parts that belong to those selected parts, such as members of groups. If DragsTree is true, the effective collection also includes all of the nodes and links that constitute the subtree starting from selected nodes. The result of ComputeEffectiveCollection(IEnumerable<Part>, DraggingOptions) is a dictionary which remembers the original Location for all of the dragged parts. This dictionary is saved as the value of DraggedParts.

During the drag if the user holds down the Control/Option key this tool makes a copy of the DraggedParts and proceeds to drag it around. (It only copies the Selection, not the whole effective collection, if CopiesEffectiveCollection is false.) The collection of copied parts is held by CopiedParts. It too is a dictionary remembering the original locations of the parts. CopiedParts will be null when this tool is moving (not copying) at the moment.

Each Part's movement is limited by the ComputeMove(Part, Point, DraggingOptions) method. By default it limits the Location to be within the bounds given by MinLocation and MaxLocation. (Those default to double.NegativeInfinity to double.PositiveInfinity.) As a further convenience, the value of NaN in MinLocation and MaxLocation cause ComputeMove(Part, Point, DraggingOptions) to use the part's current location. So, for example, an easy way to declare that the user may only drag a node horizontally is to just set:

new Node {
  . . .
  MinLocation: new Point(double.NegativeInfinity, double.NaN), MaxLocation: new Point(double.PositiveInfinity, double.NaN) }
  . . .
}

If you set IsGridSnapEnabled to true, dragged or copied parts will be snapped to points on a grid. The snapping occurs continuously during a drag unless you set IsGridSnapRealtime to false. Normally the grid points come from the Grid, even if that grid is not Visible. However you can override those grid's properties for the snapping grid cell size and offset by setting the properties here: GridSnapCellSize and GridSnapOrigin. This computes the point to snap to for each dragged part. The resulting point is used as the new Location.

For the most general control over where a part may be dragged, either set the DragComputation property or override ComputeMove(Part, Point, DraggingOptions). For the common case of wanting to keep member nodes within the Group that they are members of, you can do something like:

// this is a Part.DragComputation function for limiting where a Node may be dragged
static Point stayInGroup(Part part, Point pt, Point gridpt) {
  // don't constrain top-level nodes
  var grp = part.ContainingGroup;
  if (grp == null) return pt;
  // try to stay within the background Shape of the Group
  var back = grp.ResizeElement;
  if (back == null) return pt;
  // allow dragging a Node out of a Group if the Shift key is down
  if (part.Diagram.LastInput.Shift) return pt;
  var p1 = back.GetDocumentPoint(Spot.TopLeft);
  var p2 = back.GetDocumentPoint(Spot.BottomRight);
  var b = part.ActualBounds;
  var loc = part.Location;
  // find the padding inside the group's placeholder that is around the member parts
  var m = grp.Placeholder.Padding;
  // now limit the location appropriately, assuming no grid-snapping
  var x = Math.Max(p1.X + m.Left, Math.Min(pt.X, p2.X - m.Right - b.Width - 1)) + (loc.X - b.X);
  var y = Math.Max(p1.Y + m.Top, Math.Min(pt.Y, p2.Y - m.Bottom - b.Height - 1)) + (loc.Y - b.Y);
  return new Point(x, y);
}

Note that this expects there to be a "SHAPE" object within the Group's visual tree that delimits where the part may be dragged within the group. This also expects that ComputesBoundsIncludingLinks is false. Then in your node template(s), just set:

new Node {
  . . .
  DragComputation = stayInGroup
  . . .
}

This tool does not utilize any Adornments or tool handles. If the drag is successful, it raises the "SelectionMoved" or "SelectionCopied" DiagramEvent and produces a "Move" or a "Copy" transaction.

If you want to programmatically start a new user's dragging of a particular existing node, you can make sure that node is selected, set the CurrentPart property, and then start and activate the tool.

var node = ...;
myDiagram.Select(node);        // in this case the only selected node
var tool = myDiagram.ToolManager.DraggingTool;
tool.CurrentPart = node;       // the DraggingTool will not call StandardMouseSelect
myDiagram.CurrentTool = tool;  // starts the DraggingTool
tool.DoActivate();             // activates the DraggingTool

Constructors

DraggingTool()

You do not normally need to create an instance of this tool because one already exists as the DraggingTool, which you can modify.

The Name of this tool is "Dragging".

Declaration

public DraggingTool()

Properties

CopiedParts

Gets or sets the collection of Parts that this tool has copied.

Declaration

public IDictionary<Part, DraggingInfo> CopiedParts { get; set; }

Property Value

Type	Description
IDictionary<Part, DraggingInfo>

Remarks

The value is a dictionary mapping Parts to DraggingInfo Objects that have a "Point" property remembering the original location of that Part. The value is null when moving instead of copying.

DraggedParts provides the dictionary of Parts that are being moved and from which this collection was copied.

CopiesEffectiveCollection

Gets or sets whether for a copying operation the extended selection is copied or only the selected parts.

Declaration

public bool CopiesEffectiveCollection { get; set; }

Property Value

Type	Description
bool

Remarks

The default value is true. Setting this property does not raise any events.

The CopiesConnectedLinks property serves a similar role for the CopySelection() command, when the user types control-C to copy the currently selected parts.

CopyCursor

The cursor to show when a drop is allowed and will result in a copy.

Declaration

public string CopyCursor { get; set; }

Property Value

Type	Description
string

Remarks

This defaults to "copy".

CurrentPart

Gets or sets the Part found at the mouse point.

Declaration

public Part CurrentPart { get; set; }

Property Value

Type	Description
Part

Remarks

This is normally set by a call to StandardMouseSelect().

Delay

On touch gestures only, this property gets or sets the TimeSpan for which the mouse must be stationary before this tool can be started.

Declaration

public TimeSpan Delay { get; set; }

Property Value

Type	Description
TimeSpan

Remarks

The default value is 100 milliseconds. Setting this property does not raise any events.

DraggedParts

Gets or sets the collection of Parts being moved.

Declaration

public IDictionary<Part, DraggingInfo> DraggedParts { get; set; }

Property Value

Type	Description
IDictionary<Part, DraggingInfo>

Remarks

The value is a dictionary mapping Parts to DraggingInfo Objects that have a "Point" property remembering the original location of that Part.

CopiedParts provides the dictionary of Parts that have been copied during a copying operation, if any.

DragOptions

Gets or sets the DraggingTool's DraggingOptions instance, which controls several dragging properties.

Declaration

public DraggingOptions DragOptions { get; set; }

Property Value

Type	Description
DraggingOptions

Remarks

Several DraggingTool properties are just convenience properties:

• IsGridSnapEnabled
• IsGridSnapRealtime
• GridSnapCellSize
• GridSnapCellSpot
• GridSnapOrigin
• DragsLink
• DragsTree

Setting any of these properties really sets the corresponding dragOptions property.

Setting this property does not raise any events.

DragsLink

Gets or sets whether the user can drag a single Link, disconnecting it from its connected nodes and possibly connecting it to valid ports when the link is dropped.

Declaration

public bool DragsLink { get; set; }

Property Value

Type	Description
bool

Remarks

The default value is false. Setting this property does not raise any events.

In order to avoid too many cases of having both ends of a dragged Link connect to the same node (if allowed), it is commonplace to decrease the PortGravity to a smaller value such as 10 or 20.

This property is a convenience getter/setter, and sets a value on DragOptions.

DragsTree

Gets or sets whether moving or copying a node also includes all of the node's tree children and their descendants, along with the links to those additional nodes.

Declaration

public bool DragsTree { get; set; }

Property Value

Type	Description
bool

Remarks

The default value is false. Setting this property does not raise any events.

The CopiesTree property serves a similar role for the CopySelection() command, when the user types control-C to copy the currently selected parts.

This property is a convenience getter/setter, and sets a value on DragOptions.

GridSnapCellSize

Gets or sets the size of the grid cell used when snapping during a drag if the value of IsGridSnapEnabled is true.

Declaration

public Size GridSnapCellSize { get; set; }

Property Value

Type	Description
Size

Remarks

By default this property is the Size(NaN, NaN), which causes this tool to use the GridCellSize value of the Grid. Setting this property does not raise any events.

This property is a convenience getter/setter, and sets a value on DragOptions.

GridSnapCellSpot

Gets or sets the Spot that specifies what point in the grid cell dragged parts snap to, if the value of IsGridSnapEnabled is true.

Declaration

public Spot GridSnapCellSpot { get; set; }

Property Value

Type	Description
Spot

Remarks

By default this property is TopLeft: node locations will snap exactly to the grid point. Setting this property does not raise any events.

This property is a convenience getter/setter, and sets a value on DragOptions.

GridSnapOrigin

Gets or sets the snapping grid's origin point, in document coordinates, if the value of IsGridSnapEnabled is true.

Declaration

public Point GridSnapOrigin { get; set; }

Property Value

Type	Description
Point

Remarks

By default this property is the Point(NaN, NaN), which causes this tool to use the GridOrigin value from the Grid. Setting this property does not raise any events.

This property is a convenience getter/setter, and sets a value on DragOptions.

IsComplexRoutingRealtime

Gets or sets whether link routing takes some short-cuts during dragging.

Declaration

public bool IsComplexRoutingRealtime { get; set; }

Property Value

Type	Description
bool

Remarks

When false, Links whose routing is AvoidsNodes are not routed to avoid Nodes, in order to improve dragging performance. The default value is true.

IsCopyEnabled

Gets or sets whether any internal copying operation is permitted by control-drag-and-drop.

Declaration

public bool IsCopyEnabled { get; set; }

Property Value

Type	Description
bool

Remarks

This property affects the behavior of MayCopy(), but does not affect whether copied objects may be dropped into this diagram from a different diagram.

The default value is true. Setting this property does not raise any events.

IsGridSnapEnabled

Gets or sets whether the DraggingTool snaps objects to grid points.

Declaration

public bool IsGridSnapEnabled { get; set; }

Property Value

Type	Description
bool

Remarks

Whether the snapping movement of the dragged parts occurs during the drag or only upon a drop is determined by the value of IsGridSnapRealtime.

This property does not affect dragging disconnected links, but those links to respect the DragComputation, which can be used to snap them.

By default this property is false. Setting this property does not raise any events.

This property is a convenience getter/setter, and sets a value on DragOptions.

IsGridSnapRealtime

Gets or sets whether the DraggingTool snaps objects to grid points during the drag.

Declaration

public bool IsGridSnapRealtime { get; set; }

Property Value

Type	Description
bool

Remarks

This property is ignored unless IsGridSnapEnabled is true. By default this property is true; when false parts are only snapped to grid locations upon the drop (i.e. mouse-up). Setting this property does not raise any events.

This property is a convenience getter/setter, and sets a value on DragOptions.

MoveCursor

The cursor to show when a drop is allowed and will result in a move.

Declaration

public string MoveCursor { get; set; }

Property Value

Type	Description
string

Remarks

This defaults to the empty string, which refers to the DefaultCursor.

NodropCursor

The cursor to show when a drop is not allowed.

Declaration

public string NodropCursor { get; set; }

Property Value

Type	Description
string

Remarks

This defaults to "no-drop".

StartPoint

Gets or sets the mouse point from which parts start to move.

Declaration

public Point StartPoint { get; set; }

Property Value

Type	Description
Point

Remarks

The value is a Point in document coordinates. This property is normally set to the diagram's mouse-down point in DoActivate(), but may be set to a different point if parts are being copied from a different control. Setting this property does not raise any events.

Methods

CanStart()

This tool can run if the diagram allows selection and moves/copies/dragging-out, if the mouse has moved far enough away to be a drag and not a click, and if FindDraggablePart() has found a selectable part at the mouse-down point.

Declaration

public override bool CanStart()

Returns

Type	Description
bool

Overrides

Tool.CanStart()

Remarks

This method may be overridden. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

ComputeEffectiveCollection(IEnumerable<Part>, DraggingOptions)

By default, this just calls ComputeEffectiveCollection(IEnumerable<Part>, DraggingOptions).

Declaration

public virtual IDictionary<Part, DraggingInfo> ComputeEffectiveCollection(IEnumerable<Part> parts, DraggingOptions options)

Parameters

Type	Name	Description
IEnumerable<Part>	parts	A collection of Parts.
DraggingOptions	options	Potential options for the collection computation

Returns

Type	Description
IDictionary<Part, DraggingInfo>	a dictionary mapping Parts to DraggingInfo Objects that have a "Point" property remembering the original location of that Part.

Remarks

This method may be overridden. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

DoActivate()

Start the dragging operation.

Declaration

public override void DoActivate()

Overrides

Tool.DoActivate()

Remarks

This calls ComputeEffectiveCollection(IEnumerable<Part>, DraggingOptions) and saves the result as DraggedParts.

This starts a "Drag" transaction. Depending on what happens, the transaction may be finished as a "Move" or a "Copy" transaction, or it may be rolled-back if the tool is cancelled.

Normally when this method is called the value of CurrentPart will be null, in which case this will call StandardMouseSelect() which will set CurrentPart. But if when this method is called the value of CurrentPart has already been set because the programmer wants the user to start dragging that Part, then this method will not need to call StandardMouseSelect() because the Part(s) to be selected and dragged have already been determined by the caller.

DoCancel()

Abort any dragging operation.

Declaration

public override void DoCancel()

Overrides

Tool.DoCancel()

DoDeactivate()

Stop the dragging operation by stopping the transaction and cleaning up any temporary state.

Declaration

public override void DoDeactivate()

Overrides

Tool.DoDeactivate()

DoDragOver(Point, GraphObject)

Perform any additional side-effects during a drag, whether an internal move or copy or an external drag, that may affect the existing non-moved object(s).

Declaration

public virtual void DoDragOver(Point pt, GraphObject obj)

Parameters

Type	Name	Description
Point	pt	a Point in document coordinates.
GraphObject	obj	the GraphObject at the point, excluding what is being dragged or temporary objects; the argument may be null if the drag is occurring in the background of the diagram. Use Part to get the Node or Part at the root of the visual tree of the stationary object.

Remarks

This method may be overridden. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

DoDropOnto(Point, GraphObject)

Perform any additional side-effects after a drop, whether an internal move or copy or an external drop, that may affect the existing non-moved object(s).

Declaration

public virtual void DoDropOnto(Point pt, GraphObject obj)

Parameters

Type	Name	Description
Point	pt	a Point in document coordinates.
GraphObject	obj	the GraphObject where the drop occurred, excluding what was dropped or temporary objects; the argument may be null if the drop occurred in the background of the diagram. Use Part to get the Node or Part at the root of the visual tree of the stationary object.

Remarks

This method may be overridden. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

DoKeyDown()

Handle switching between copying and moving modes as the Control/Option key is pressed or released.

Declaration

public override void DoKeyDown()

Overrides

Tool.DoKeyDown()

DoKeyUp()

Handle switching between copying and moving modes as the Control/Option key is pressed or released.

Declaration

public override void DoKeyUp()

Overrides

Tool.DoKeyUp()

DoMouseMove()

Move the DraggedParts (or if copying, the CopiedParts) to follow the current mouse point.

Declaration

public override void DoMouseMove()

Overrides

Tool.DoMouseMove()

Remarks

If this creates any temporary parts, by default it adds them to the Tool layer.

This calls DoDragOver(Point, GraphObject) for any side-effects on stationary parts.

DoMouseUp()

On a mouse-up, finish moving or copying the effective selection.

Declaration

public override void DoMouseUp()

Overrides

Tool.DoMouseUp()

Remarks

This calls DoDropOnto(Point, GraphObject) for any side-effects on stationary parts.

This also updates the diagram's bounds, raises a "SelectionCopied" or "SelectionMoved" DiagramEvent, and stops this tool.

This method also raises the "ChangingSelection" and "ChangedSelection" diagram events. Changes are performed in a "Drag" transaction, but the "ChangedSelection" event is raised outside the transaction.

FindDraggablePart()

Return the selectable and movable/copyable Part at the mouse-down point.

Declaration

public virtual Part FindDraggablePart()

Returns

Type	Description
Part

Remarks

This is called by CanStart() to decide if this tool is ready to run.

This method may be overridden. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

MayCopy()

This predicate is true when the diagram allows objects to be copied and inserted, and some object in the selection is copyable, and the user is holding down the Control key (Option key on Mac).

Declaration

public virtual bool MayCopy()

Returns

Type	Description
bool

Remarks

This method may be overridden, although in most cases it is easiest to set Copyable. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

MayMove()

This predicate is true when the diagram allows objects to be moved, and some object in the selection is movable.

Declaration

public virtual bool MayMove()

Returns

Type	Description
bool

Remarks

This method may be overridden, although in most cases it is easiest to set Movable. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

MoveParts(IDictionary<Part, DraggingInfo>, Point, bool)

Move a collection Map of Parts by a given offset.

Declaration

public virtual void MoveParts(IDictionary<Part, DraggingInfo> parts, Point offset, bool check = false)

Parameters

Type	Name	Description
IDictionary<Part, DraggingInfo>	parts	a Map mapping Parts to DraggingInfo Objects that have a "Point" property remembering the original location of that Part.
Point	offset	The offset, before snapping, to move parts. This offset reflects the total amount moved during tool operation, based on original Part locations remembered when the DraggingTool activated.
bool	check	Whether to check CanMove() on each part; the default value is false.

Remarks

If check is true this respects the CanMove() predicate for Nodes or simple Parts when this is the CurrentTool. It also respects IsGridSnapEnabled in order to try to automatically snap part locations to a grid. And it also uses the DragComputation function, if any, to determine the new location for each part.

The first argument is a dictionary as produced by ComputeEffectiveCollection(IEnumerable<Part>, DraggingOptions). Call MoveParts(IEnumerable<Part>, Point, bool, DraggingOptions) if you want to move a simple collection of Parts without having to create the argument Map.

StandardMouseSelect()

This override prevents the Control modifier unselecting an already selected part.

Declaration

public override void StandardMouseSelect()

Overrides

Tool.StandardMouseSelect()

Remarks

This also remembers the selectable CurrentPart at the current mouse point.

This method may be overridden. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

StopTransaction()

This calls the base StopTransaction() method, and if the result is true, attempts to optimize the transaction by removing all changes except the first and last by calling Optimize().

Declaration

public override bool StopTransaction()

Returns

Type	Description
bool	the result of the call to rollback or commit the transaction.

Overrides

Tool.StopTransaction()

Remarks

This method may be overridden. Please read the Introduction page on Extensions for how to override methods and how to call this base method.