How to Customize TSectionListBox: A Step-by-Step Guide

How to Customize TSectionListBox: A Step-by-Step Guide

This guide shows practical steps to customize a TSectionListBox (Delphi/Lazarus-style component) for appearance and behavior: grouping, headers, item styles, selection, and dynamic updates. Assumes a VCL/FMX environment where TSectionListBox supports sections and items (adjust names if using a different framework).

1. Create the basic list and sections

1. Drop a TSectionListBox onto your form (or create in code).
2. Add sections and items at design time: right-click → Add Section → add ListBoxItems under each section.
3. Create in code example:

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var
Sec: TListBoxGroupHeader;
  It: TListBoxItem;
begin
  Sec := TListBoxGroupHeader.Create(SectionListBox1);
  Sec.Parent := SectionListBox1;
  Sec.Text := ‘Group A’;

  It := TListBoxItem.Create(SectionListBox1);
  It.Parent := SectionListBox1;
  It.Text := ‘Item 1’;
  It.GroupIndex := Sec.Index; // if supported by your framework
end;

2. Customize section headers

• Change text and font

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  Sec.Text := ‘New Header’;
  Sec.Font.Size := 14;
  Sec.Font.Style := [TFontStyle.fsBold];
  

• Background and padding

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  Sec.StyleLookup := ‘groupheaderstyle’; // use a custom style name
  // Or set appearance properties directly if available:
  Sec.Fill.Color := TAlphaColorRec.Lightgray;
  Sec.Padding.Rect := RectF(8,4,8,4);
  

3. Style list items

• Item templates: Use custom styles or add controls to items.

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  var
    Img: TImage;
  begin
    Img := TImage.Create(It);
    Img.Parent := It;
    Img.Align := TAlignLayout.Left;
    Img.Width := 40;
    Img.Bitmap.LoadFromFile(‘icon.png’);
  end;
  

• Alternate row colors

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  if (Index mod 2) = 0 then
    It.StyleLookup := ‘evenitemstyle’
  else
    It.StyleLookup := ‘odditemstyle’;
  

• Custom fonts and colors

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  It.TextSettings.Font.Size := 12;
  It.TextSettings.FontColor := TAlphaColorRec.Navy;
  

4. Handle selection and tapping

• Single selection handling

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  procedure TForm1.SectionListBox1Click(Sender: TObject);
  begin
    ShowMessage(‘Selected: ‘ + SectionListBox1.Selected.Text);
  end;
  

• Custom selection visuals: define styles for the selected state (e.g., “listboxitemstyleselected”) and assign via Item.StyleLookup or global stylebook.

5. Dynamic updates (add/remove/refresh)

• Add item at runtime

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  var It: TListBoxItem;
  begin
    It := TListBoxItem.Create(SectionListBox1);
    It.Parent := SectionListBox1;
    It.Text := ‘New dynamic item’;
  end;
  

• Remove item

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  SectionListBox1.Items.Remove(It); // or It.Free;
  

• Refresh visual state

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  SectionListBox1.Repaint;
  

6. Performance tips for large lists

• Use virtualizing list if available (TVirtualListBox or virtualization property).
• Reuse item controls where possible; create minimal visual trees.
• Load images lazily; use thumbnails rather than full-size bitmaps.

7. Accessibility and RTL

• Ensure TextAlign and ReadingDirection follow user locale.
• Provide meaningful text for screen readers in Item.Hint or AccessibleName.

8. Example: fully customized item with checkbox and subtitle

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var
  Item: TListBoxItem;
  Cb: TCheckBox;
  Sub: TLabel;
begin
  Item := TListBoxItem.Create(SectionListBox1);
  Item.Parent := SectionListBox1;
  Item.Text := ‘Main title’;

  Cb := TCheckBox.Create(Item);
  Cb.Parent := Item;
  Cb.Align := TAlignLayout.Right;
  Cb.Width := 44;

  Sub := TLabel.Create(Item);
  Sub.Parent := Item;
  Sub.Text := ‘Subtitle or description’;
  Sub.Margins.Top := 18;
  Sub.TextSettings.Font.Size := 10;
end;

9. Debugging common issues

• Items not visible: verify Parent and Align settings.
• Styles not applied: ensure StyleLookup names match those in the active StyleBook.
• Slow scrolling: reduce embedded controls and large images.

10. Quick checklist before shipping

• Consistent header and item typography
• Responsive selection feedback
• Lazy image loading and virtualization enabled
• Proper accessibility labels
• Tested on target platforms and DPI settings

This step-by-step approach covers typical customizations for TSectionListBox. Adjust code snippets to match your framework (VCL vs FMX) and component versions.