Constraints

23 Sep 20205 minutes to read

Constraints are used to enable/disable certain behaviors of the diagram, node and connector. Constraints are provided as flagged enumerations, so that multiple behaviors can be enabled/disabled with bitwise operators (&, |, ~, <<, etc.).
To know more about bitwise operators, refer to Bitwise Operations

DiagramConstraints

Diagram constraints allow to enable or disable the following behaviors.

  • Page Editing
  • Line Bridging
  • Zoom and Pan
  • Undo Redo

For more information about Diagram constraints, refer to Diagram Constraints.

Example

The following example illustrates how to disable page editing.

<ej:Diagram ClientIDMode="Static" ID="Diagram" runat="server" Height="600px" Width="100%" >
  </ej:Diagram>
protected void Page_Load(object sender, EventArgs e)
	{
		if (!IsPostBack)
		{
			//Set Diagram in read-only mode
			Diagram.Model.Constraints = DiagramConstraints.Default &~ DiagramConstraints.PageEditable;
		}
	}

NodeConstraints

NodeConstraints allows to enable or disable the following behaviors of node.

  • Selection
  • Deletion
  • Drag
  • Resize
  • Rotate
  • Connect
  • Drop shadow
  • Drag label
  • Define tooltip

For more information about node constraints, refer to Node Constraints

Example

The following code illustrates how to disable rotation.

  • C#
    • protected void Page_Load(object sender, EventArgs e)
	{
		if (!IsPostBack)
		{
			//Disables rotation
			Node node = new Node(){ Constraints = NodeConstraints.Default &~ NodeConstraints.Rotate };
        	Diagram.Model.Nodes.Add(node);
		}
	}

    ConnectorConstraints

    ConnectorConstraints allow to enable or disable certain behaviors of Connectors. They are as follows.

    • Selection
    • Deletion
    • Drag
    • Segment editing
    • Define tooltip
    • Bridging
    • Label dragging

    For more information about connector constraints, refer to Connector Constraints

    Example

    The following code illustrates how to disable selection.

  • C#
    • //Disables selection
	Connector connector = new Connector(){
		Name = "name",
		Constraints = ConnectorConstraints.Default &~ ConnectorConstraints.Select
	};
    Diagram.Model.Connectors.Add(connector);

    PortConstraints

    You can enable or disable certain behaviors of Port. They are as follows.

    • Connect

    For more information about port constraints, refer to Port Constraints

    Example

    The following code illustrates how to disable creating connections with a port.

  • C#
    • Node node = new Node(){ Name = "Node1"};
	node.Ports.Add(new Port() { Constraints = PortConstraints.None });
	Diagram.Model.Nodes.Add(node);

    SelectorConstraints

    Selector visually represents the selected elements with certain editable thumbs. The visibility of the thumbs can be controlled with selector constraints. The part of selector is categorized as follows.

    • Resizer
    • Rotator
    • User handles

    For more information about Selector constraints, refer to Selector Constraints

    Example

    The following code illustrates how to hide rotator.

  • C#
    • //Hides rotator
	Diagram.Model.SelectedItems = new SelectedItems(){
		Constraints = SelectorConstraints.All &~ SelectorConstraints.Rotator
	};

    SnapConstraints

    Snap Constraints control the visibility of gridlines and enable/disable snapping. Snap constraints allow to set the following behaviors.

    • Show only horizontal or vertical gridlines
    • Show both horizontal and vertical gridlines
    • Snap to either horizontal or vertical gridlines
    • Snap to both horizontal and vertical gridlines

    For more information about snap constraints, refer to Snap Constraints

    Example

    The following code illustrates how to show only horizontal gridlines.

  • C#
    • Diagram.Model.SnapSettings = new SnapSettings(){
		//Shows horizontal gridlines
		SnapConstraints = SnapConstraints.ShowHorizontalLines
	};

    Inherit behaviors

    Some of the behaviors can be defined through both the specific object(node/connector) and Diagram. When the behaviors are contradictorily defined through both, the actual behavior is set through inherit options.

    The following code example illustrates how to inherit the line bridging behavior from the Diagram model.

  • C#
    • //Enables/disables line bridging based on the Diagram constraints
	Connector connector = new Connector() { Name = "Connector", SourcePoint = new DiagramPoint(100f, 100f), TargetPoint = new DiagramPoint(200f, 200f) };
	//Sets to inherit bridging from model
	connector.Constraints = ConnectorConstraints.Default | ConnectorConstraints.InheritBridging;
	Diagram.Model.Connectors.Add(connector);
	
	//Enables line bridging for all connectors
	Diagram.Model.Constraints = DiagramConstraints.Default | DiagramConstraints.Bridging;

    Bitwise Operations

    Bitwise Operations are used to manipulate the flagged enumerations [enum]. In this section, Bitwise Operations are illustrated by using node Constraints. The same is applicable while working with Node Constraints, Connector Constraints, or Port Constraints.

    Add Operation

    You can add or enable multiple values at a time by using Bitwise ‘|’ (OR) operator.

  • C#
    • node.Constraints = NodeConstraints.Select | NodeConstraints.Rotate;

    In the above example, you can do both the selection and rotation.

    Remove Operation

    You can remove or disable values by using Bitwise ‘&~’ (XOR) operator.

  • C#
    • node.Constraints = node.Constraints & ~(NodeConstraints.Rotate);

    In the above example, Rotation is disabled but other constraints are enabled.

    Check Operation

    You can check any value by using Bitwise ‘&’ (AND) operator.

  • C#
    • if ((node.Constraints & (NodeConstraints.Rotate)) == (NodeConstraints.Rotate))

    In the above example, you can check whether the rotate constraints are enabled in a Node. When Node constraints have rotate constraints, the expression returns a rotate constraint.