From 87723e508147c96f121cf2a9b544fd435810adc8 Mon Sep 17 00:00:00 2001
From: Oliver <480930+rivo@users.noreply.github.com>
Date: Sat, 25 Mar 2023 22:05:32 +0100
Subject: [PATCH] Fixed the logic for triggering a TreeView's "changed"
 callback, allowing it to be triggered for calls to SetCurrentNode(), too.

---
 treeview.go | 48 +++++++++++++++++++++++++-----------------------
 1 file changed, 25 insertions(+), 23 deletions(-)

diff --git a/treeview.go b/treeview.go
index 77bce5b..ae937ad 100644
--- a/treeview.go
+++ b/treeview.go
@@ -274,6 +274,9 @@ type TreeView struct {
 	// The currently selected node or nil if no node is selected.
 	currentNode *TreeNode
 
+	// The last note that was selected or nil of there is no such node.
+	lastNode *TreeNode
+
 	// The movement to be performed during the call to Draw(), one of the
 	// constants defined above.
 	movement int
@@ -346,8 +349,8 @@ func (t *TreeView) GetRoot() *TreeNode {
 // selection will be changed to the top-most selectable and visible node.
 //
 // This function does NOT trigger the "changed" callback because the actual node
-// that will be selected is not known until the tree is drawn. That is also when
-// the "changed" callback will be triggered.
+// that will be selected is not known until the tree is drawn. Triggering the
+// "changed" callback is thus deferred until the next call to [TreeView.Draw].
 func (t *TreeView) SetCurrentNode(node *TreeNode) *TreeView {
 	t.currentNode = node
 	return t
@@ -404,8 +407,8 @@ func (t *TreeView) SetGraphicsColor(color tcell.Color) *TreeView {
 	return t
 }
 
-// SetChangedFunc sets the function which is called when the user navigates to
-// a new tree node.
+// SetChangedFunc sets the function which is called when the currently selected
+// node changes, for example when the user navigates to a new tree node.
 func (t *TreeView) SetChangedFunc(handler func(node *TreeNode)) *TreeView {
 	t.changed = handler
 	return t
@@ -458,9 +461,9 @@ func (t *TreeView) Move(offset int) *TreeView {
 }
 
 // process builds the visible tree, populates the "nodes" slice, and processes
-// pending movement actions. Set "drawingAfter" to true if you know that [Draw]
-// will be called immediately after this function (to avoid having [Draw] call
-// it again).
+// pending movement actions. Set "drawingAfter" to true if you know that
+// [TreeView.Draw] will be called immediately after this function (to avoid
+// having [TreeView.Draw] call it again).
 func (t *TreeView) process(drawingAfter bool) {
 	t.stableNodes = drawingAfter
 	_, _, _, height := t.GetInnerRect()
@@ -544,26 +547,25 @@ func (t *TreeView) process(drawingAfter bool) {
 	// Process selection. (Also trigger events if necessary.)
 	if selectedIndex >= 0 {
 		// Move the selection.
-		newSelectedIndex := selectedIndex
 		switch t.movement {
 		case treeMove:
 			for t.step < 0 { // Going up.
-				index := newSelectedIndex
+				index := selectedIndex
 				for index > 0 {
 					index--
 					if t.nodes[index].selectable {
-						newSelectedIndex = index
+						selectedIndex = index
 						break
 					}
 				}
 				t.step++
 			}
 			for t.step > 0 { // Going down.
-				index := newSelectedIndex
+				index := selectedIndex
 				for index < len(t.nodes)-1 {
 					index++
 					if t.nodes[index].selectable {
-						newSelectedIndex = index
+						selectedIndex = index
 						break
 					}
 				}
@@ -571,26 +573,20 @@ func (t *TreeView) process(drawingAfter bool) {
 			}
 		case treeParent:
 			if parentSelectedIndex >= 0 {
-				newSelectedIndex = parentSelectedIndex
+				selectedIndex = parentSelectedIndex
 			}
 		case treeChild:
-			index := newSelectedIndex
+			index := selectedIndex
 			for index < len(t.nodes)-1 {
 				index++
 				if t.nodes[index].selectable && t.nodes[index].parent == t.nodes[selectedIndex] {
-					newSelectedIndex = index
+					selectedIndex = index
 				}
 			}
 		}
 		t.step = 0
-		t.currentNode = t.nodes[newSelectedIndex]
-		if newSelectedIndex != selectedIndex {
-			t.movement = treeNone
-			if t.changed != nil {
-				t.changed(t.currentNode)
-			}
-		}
-		selectedIndex = newSelectedIndex
+		t.currentNode = t.nodes[selectedIndex]
+		t.movement = treeNone
 
 		// Move selection into viewport.
 		if t.movement != treeScroll {
@@ -616,6 +612,12 @@ func (t *TreeView) process(drawingAfter bool) {
 			t.currentNode = nil
 		}
 	}
+
+	// Trigger "changed" callback.
+	if t.changed != nil && t.currentNode != nil && t.currentNode != t.lastNode {
+		t.changed(t.currentNode)
+	}
+	t.lastNode = t.currentNode
 }
 
 // Draw draws this primitive onto the screen.