Customizing Appearance and Behavior of TAdvTreeComboBox

Troubleshooting Common TAdvTreeComboBox Issues and FixesTAdvTreeComboBox (part of TMS Software’s component suites for Delphi/C++Builder) combines a tree view with a combo box, offering hierarchical selection inside a compact dropdown. Its flexibility makes it powerful, but also introduces several common issues developers may face during implementation. This article covers frequent problems, diagnostic steps, and practical fixes to get your TAdvTreeComboBox behaving reliably.

---

Table of contents

• Common symptoms and quick checks
• Initialization and population problems
• Display and painting issues
• Selection, focus, and keyboard behavior
• Data binding and value retrieval
• Performance with large trees
• Styling, themes, and alignment problems
• Event handling pitfalls
• Debugging tips and tools
• Example fixes and sample code snippets

---

Common symptoms and quick checks

If you see unexpected behavior, run these quick checks first:

• Ensure you’re using a supported TMS/TAdvTreeComboBox version compatible with your Delphi/C++Builder IDE version.
• Check component properties (AutoDropDown, ReadOnly, ShowButtons, ShowLines, etc.) — many “mysteries” are property settings.
• Confirm event handlers aren’t unintentionally consuming events (e.g., OnKeyDown with Key := 0).
• Reproduce the issue in a minimal project to isolate it from other components or project-specific settings.

---

Initialization and population problems

Symptoms: empty dropdown, nodes not visible, or nodes disappear after runtime changes.

Causes & fixes:

• Nodes not added before the component is shown:
  • Add nodes during FormCreate or before the component is visible. If populating dynamically, call BeginUpdate/EndUpdate to avoid flicker and partial states:

    
    AdvTreeComboBox1.BeginUpdate; try AdvTreeComboBox1.Clear; // add nodes AdvTreeComboBox1.Items.AddChild(nil, 'Root'); // ... finally AdvTreeComboBox1.EndUpdate; end; 

• Using wrong collection/API:
  • Use the component’s Items/Nodes API (e.g., AdvTreeComboBox1.Items or AdvTreeComboBox1.Nodes) rather than VCL TTreeView methods.
• Nodes added from a background thread:
  • VCL is not thread-safe. Marshal node creation to the main thread (use Synchronize or TThread.Queue).

---

Display and painting issues

Symptoms: flicker, blank area in dropdown, clipped text, or incorrect icons.

Causes & fixes:

• Flicker or slow paint:
  • Ensure DoubleBuffered is enabled on the form or component where appropriate. Use BeginUpdate/EndUpdate around bulk changes.
• Clipped text or wrong row height:
  • Adjust RowHeight/ItemHeight or Font size to match custom fonts.
• Icons not shown:
  • Verify ImageList is assigned and contains indexed images. Check Transparent color settings and that the component’s ShowImages property is enabled.
• High-DPI scaling issues:
  • Ensure your application manifest supports Per-Monitor DPI aware mode (Delphi settings) and that the TAdvTreeComboBox version supports High-DPI. If not, use scaling code to adjust font and image sizes at runtime.

---

Selection, focus, and keyboard behavior

Symptoms: selection doesn’t update text, keyboard navigation unpredictable, focus lost when dropdown opens.

Causes & fixes:

• Text not updating after selecting node:
  • Confirm DropDownSelect or similar property is set to update the edit portion on selection. Use code in OnNodeClick or OnNodeChecked to set Text explicitly:

    
    procedure TForm1.AdvTreeComboBox1NodeClick(Sender: TObject; Node: TAdvTreeViewItem); begin AdvTreeComboBox1.Text := Node.Text; end; 

• Keyboard navigation issues:
  • Ensure KeyPreview on the form isn’t swallowing keys. If you intercept keys globally, forward relevant keystrokes to the component when focused.
• Focus lost on dropdown open:
  • Some focus issues stem from modal dialogs or other controls reclaiming focus in events triggered on dropdown. Avoid long-running logic in OnDropDown or OnOpen events; defer with TThread.Queue if necessary.

---

Data binding and value retrieval

Symptoms: getting wrong node, Value property not reflecting selection, problems integrating with data-aware controls.

Causes & fixes:

• Using Text vs Value:
  • TAdvTreeComboBox may expose both display text and an associated Value (ID). Use the Value property for programmatic identification, and Text for display. Assign Node.Data or Node.Tag if you need custom payloads, but manage types carefully.
• Data-aware binding:
  • For DB-aware scenarios, ensure the component’s DataBinding properties (if applicable) are correctly mapped and that DataSet events (OnNewRecord, AfterScroll) synchronize the control explicitly.

---

Performance with large trees

Symptoms: slow dropdown open, UI lag while expanding nodes, long startup times.

Causes & fixes:

• Loading too many nodes at once:
  • Implement lazy-loading (load children on node expansion). Use a placeholder child node to indicate expandable nodes and replace it when expansion occurs.
• Heavy image lists or custom drawing:
  • Cache scaled images, minimize OnDraw events, and avoid complex operations during paint. Use BeginUpdate/EndUpdate around large modifications.
• Excessive event processing:
  • Temporarily disable event handlers (set a boolean guard) during bulk updates to avoid repeated heavy processing.

---

Styling, themes, and alignment problems

Symptoms: inconsistent look under different Windows themes, misaligned text or caret, background differences.

Causes & fixes:

• VCL Themes / Styles incompatibility:
  • Modern versions of TAdvTreeComboBox are usually compatible with VCL styles, but custom drawing might need adaptation. Check component updates or set OwnerDraw properties to false if default styling is preferable.
• Caret or text alignment off:
  • Adjust margins, Indent, and alignment properties. For RTL layouts, confirm the component’s BiDiMode and alignment settings are correctly set.

---

Event handling pitfalls

Symptoms: unexpected behavior after implementing event handlers, recursive calls, or missed updates.

Causes & fixes:

• Recursive events:

  • Changing properties inside an event handler that fire the same event can cause recursion. Use a guard flag: “`pascal var FUpdating: Boolean;

  procedure TForm1.AdvTreeComboBox1Change(Sender: TObject); begin if FUpdating then Exit; FUpdating := True; try

  // change properties 

  finally

  FUpdating := False; 

  end; end; “`

• Missing OnChange after programmatic set:

  • Some changes made in code bypass events. Manually call the appropriate event method or trigger notification after programmatic updates if needed.

---

Debugging tips and tools

• Reproduce in a minimal test project to isolate variables.
• Use logging inside event handlers to trace sequence/order of operations.
• Temporarily disable StyleHook or custom draw code to see if visuals are from styling.
• Use the Delphi CPU profiler or sampling profiler when performance issues appear.
• Keep TMS component versions and Delphi patches updated; many issues are resolved in newer builds.

---

Example fixes and sample code snippets

1. Populate safely and update text on selection: “`pascal procedure TForm1.FormCreate(Sender: TObject); begin AdvTreeComboBox1.BeginUpdate; try AdvTreeComboBox1.Clear; with AdvTreeComboBox1.Items.AddChild(nil, ‘Fruits’) do AddChild(‘Apple’); AdvTreeComboBox1.Items.AddChild(nil, ‘Vegetables’); finally AdvTreeComboBox1.EndUpdate; end; end;

procedure TForm1.AdvTreeComboBox1NodeClick(Sender: TObject; Node: TAdvTreeViewItem); begin AdvTreeComboBox1.Text := Node.Text; end;

2) Lazy-load children on expansion: ```pascal procedure TForm1.AdvTreeComboBox1NodeExpanding(Sender: TObject; Node: TAdvTreeViewItem); begin   if Node.HasChildren and (Node.ChildCount = 1) and (Node.Children[0].Text = 'Loading') then   begin     Node.Children[0].Free;     // add real children     Node.AddChild('Child 1');     Node.AddChild('Child 2');   end; end; 

1. Guard against recursive change events:

   
   procedure TForm1.AdvTreeComboBox1Change(Sender: TObject); begin if FUpdating then Exit; FUpdating := True; try // handle change finally FUpdating := False; end; end; 

---

When to contact TMS support or check release notes

If you’ve verified common causes, reproduced the problem in a minimal project, and updated to the latest TMS/TAdvTreeComboBox build but still see issues, contact TMS support. Provide:

• Delphi/C++Builder version and update pack
• TMS component version
• A minimal reproducible project or code snippets
• Steps to reproduce and screenshots or logs

---

Troubleshooting TAdvTreeComboBox often comes down to lifecycle (when you populate/setup), threading, event recursion, and property settings. Use incremental testing, guard flags for events, and lazy-loading for performance to resolve most issues.