Gsemac.Common/src/Gsemac.Forms/TreeViewUtilities.cs at master · gsemac/Gsemac.Common · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Windows.Forms;

namespace Gsemac.Forms {

    public static class TreeViewUtilities {

        // Public members

        public static IEnumerable<TreeNode> GetVisibleNodes(TreeView treeView) {

            return treeView.Nodes.Cast<TreeNode>()
                .SelectMany(node => GetVisibleNodes(node));

        }

        public static void SetAlternatingNodeColorsEnabled(TreeView treeView, bool value) {

            // When we set the back color of TreeNodes to a custom color, selection turns the node white, making it look like it's flickering.
            // The following event handlers help to reduce the appearance of flicker.

            if (value) {

                treeView.AfterExpand += AlternatingNodeColorsAfterExpandEventHandler;
                treeView.AfterCollapse += AlternatingNodeColorsAfterExpandEventHandler;
                treeView.MouseDown += AlternatingNodeColorsMouseDownEventHandler;
                treeView.MouseUp += AlternatingNodeColorsMouseUpEventHandler;


            }
            else {

                treeView.AfterExpand -= AlternatingNodeColorsAfterExpandEventHandler;
                treeView.AfterCollapse -= AlternatingNodeColorsAfterExpandEventHandler;
                treeView.MouseDown -= AlternatingNodeColorsMouseDownEventHandler;
                treeView.MouseUp -= AlternatingNodeColorsMouseUpEventHandler;

            }

            ApplyAlternatingNodeColors(treeView);

        }

        // Private members

        private static IEnumerable<TreeNode> GetVisibleNodes(TreeNode node) {

            if (node.Parent == null || node.Parent.IsExpanded)
                yield return node;

            foreach (TreeNode childNode in node.Nodes)
                foreach (TreeNode visibleNode in GetVisibleNodes(childNode))
                    yield return visibleNode;

        }

        private static void ApplyAlternatingNodeColors(TreeView treeView) {

            treeView.BeginUpdate();

            bool even = true;

            foreach (TreeNode node in GetVisibleNodes(treeView)) {

                node.BackColor = even ? default : SystemColors.Control;

                even = !even;

            }

            treeView.EndUpdate();

        }

        private static void AlternatingNodeColorsAfterExpandEventHandler(object sender, TreeViewEventArgs e) {

            if (sender is TreeView treeView)
                ApplyAlternatingNodeColors(treeView);

        }
        private static void AlternatingNodeColorsMouseDownEventHandler(object sender, MouseEventArgs e) {

            if (sender is TreeView treeView) {

                treeView.SelectedNode = null;

                ApplyAlternatingNodeColors(treeView);

                TreeViewHitTestInfo hitTestInfo = treeView.HitTest(e.Location);

                if (hitTestInfo.Node != null)
                    hitTestInfo.Node.BackColor = default;

            }

        }
        private static void AlternatingNodeColorsMouseUpEventHandler(object sender, MouseEventArgs e) {

            if (sender is TreeView treeView)
                ApplyAlternatingNodeColors(treeView);

        }

    }

}