main: preload recursive navigation only one layer at a time

main.go

@@ -319,6 +319,29 @@ func (f *TMainForm) OnNavExpanding(sender vcl.IObject, node *vcl.TTreeNode, allo
 	}
 
 	*allowExpansion = node.HasChildren()
+
+	// While we're here - preload one single level deep (not any deeper)
+
+	if node.HasChildren() {
+
+		// This node has children that we haven't processed. Process them now
+		cc := node.GetFirstChild()
+
+		for {
+			ndataChild := (*navData)(cc.Data())
+			if ndataChild.childrenLoaded {
+				break // We always do them together, so if one's done, no need to keep looking
+			}
+
+			f.NavLoadChildren(cc, ndataChild)
+
+			cc = cc.GetNextSibling()
+			if cc == nil {
+				break
+			}
+		}
+
+	}
 }
 
 func (f *TMainForm) NavLoadChildren(node *vcl.TTreeNode, ndata *navData) error {
@@ -345,7 +368,7 @@ func (f *TMainForm) NavLoadChildren(node *vcl.TTreeNode, ndata *navData) error {
 		for _, bucketName := range nextBucketNames {
 
 			node := f.Buckets.Items().AddChild(node, formatUtf8([]byte(bucketName)))
-			// node.SetHasChildren(true) // dynamically populate in OnNavExpanding
+			node.SetHasChildren(true) // dynamically populate in OnNavExpanding
 			node.SetImageIndex(imgTable)
 			node.SetSelectedIndex(imgTable)
 			navData := &navData{
@@ -358,9 +381,6 @@ func (f *TMainForm) NavLoadChildren(node *vcl.TTreeNode, ndata *navData) error {
 			node.SetData(unsafe.Pointer(navData))
 
 			ndata.ld.Keepalive(navData)
-
-			// Recurse to see if it has any children of its own
-			f.NavLoadChildren(node, ndata)
 		}
 	}