GraphSelection

Description

Provides methods for implementing selection history handling in a GraphView.

Selection in a graph view is based on selecting GraphElement objects (for example, nodes or edges). GraphElement objects aren't regular Unity Object classes, so they are not recorded in the regular Selection history.

Use this helper class with the Selection.RegisterCustomHandler and Selection.SetCustomSelection to implement selection history handling in a graph view.

The GraphSelection class contains a list of selected graph elements, typically their VisualElement.viewDataKey. The GraphSelection class is serializable, so you can use it with EditorJsonUtility to serialize to and from a JSON representation.

Use the ApplyToGraphView method to apply the list of selected elements to a graph view.

// Example of implementing selection history handling in a graph view.
// The graph below does not do anything useful, and it
// does not survive script recompilation (for simplicity purposes, the graph
// view edits a transient graph object, not an asset).
using UnityEngine;
using UnityEngine.UIElements;
using UnityEditor;
using UnityEditor.Experimental.GraphView;
using System.Collections.Generic;

public class SampleGraphView : GraphView
{
    const string kSelectionKey = "GraphViewSelectionHistoryExample";

    public SampleGraphView()
    {
        // Register a function that applies a stored selection
        // back to the graph view.
        Selection.RegisterCustomHandler(kSelectionKey, ApplySelection);
    }

    static void ApplySelection(string data, EntityId[] selectedEntityIDs)
    {
        // Deserialize selection from a JSON string.
        var info = GraphSelection.FromJson(data);
        if (info == null)
            return;

        // Selection history code focuses the relevant Editor window
        // before applying the selection history entry.
        // We'll want to apply selection to the graph view in that window.
        var window = EditorWindow.focusedWindow as GraphViewSelectionHistory;
        var gv = window?.graphView;
        if (gv == null)
            return;

        // Apply selection to the graph view.
        info.ApplyToGraphView(gv, null);
    }

    // Override selection related graph view methods, to record
    // the selection history entry.
    public override void AddToSelection(ISelectable selectable)
    {
        base.AddToSelection(selectable);
        UpdateSelectionHistory();
    }
    public override void RemoveFromSelection(ISelectable selectable)
    {
        base.RemoveFromSelection(selectable);
        UpdateSelectionHistory();
    }
    public override void ClearSelection()
    {
        base.ClearSelection();
        UpdateSelectionHistory();
    }

    // Record graph view selection into the selection history.
    void UpdateSelectionHistory()
    {
        var sel = new GraphSelection();
        foreach (var s in selection)
        {
            if (s is SampleNode node)
            {
                // Add view data key (which uniquely identifies a graph element)
                // into the selection object.
                sel.elements.Add(node.viewDataKey);
            }
        }
        if (sel.isEmpty)
            return;

        // Record the selection by serializing it into JSON.
        Selection.SetCustomSelection(kSelectionKey, EditorJsonUtility.ToJson(sel));
    }
}

// A simple node that only has a title.
public class SampleNode : Node
{
    public void InitializeNode(string text, float x, float y)
    {
        UseDefaultStyling();
        title = text;
        SetPosition(new Rect(x, y, 0, 0));
        MarkDirtyRepaint();
    }
}

// Editor window with the graph view. This does not do anything
// related to selection handling. This sets up the graph view
// and creates some nodes.
public class GraphViewSelectionHistory : EditorWindow
{
    [MenuItem("Window/GraphView Selection Example")]
    static void Init()
    {
        var window = EditorWindow.GetWindow<GraphViewSelectionHistory>();
        window.InitGraph();
        window.Show();
    }

    public GraphView graphView;

    void InitGraph()
    {
        rootVisualElement.Clear();

        graphView = new SampleGraphView();
        graphView.AddManipulator(new ContentDragger());
        graphView.AddManipulator(new SelectionDragger());
        graphView.AddManipulator(new RectangleSelector());
        graphView.AddManipulator(new ClickSelector());

        rootVisualElement.Add(graphView);
        graphView.StretchToParentSize();

        CreateNode("One", 20, 20);
        CreateNode("Two", 120, 20);
        CreateNode("Three", 20, 100);

        rootVisualElement.MarkDirtyRepaint();
    }

    void CreateNode(string text, float x, float y)
    {
        var node = new SampleNode();
        node.InitializeNode(text, x, y);
        graphView.AddElement(node);
    }
}

Properties

Constructors

Public Methods

Static Methods