Flet Visual Builder

Flet Visual Builder (FVB) is a drag-and-drop UI builder for Flet apps.

⚠️ Disclaimer: This project is currently experimental and can be very buggy.
Some widgets and preview behavior may break depending on the installed Flet version.

⚠️ Vibe Code Alert: This project was 99% vibe coded as a fun long weekend hack.

Current MVP foundation

This repository includes the core architecture required by the TDD:

• Widget tree model (WidgetNode) with slot-aware children
• Widget registry and centralized enum mapping
• Tree operations (insert/delete/move/reorder/wrap) with cycle prevention
• Validation engine for export safety (including slot checking)
• Code generation (WidgetNode → runnable Flet Python)
• Project serialization, migrations, save/load with auto-backup
• App state with snapshot-based undo/redo
• Canvas hit-test engine with drop-zone detection
• Unit test suite (42 tests) covering all core engine modules

Run

pip install -r requirements.txt
python main.py

Test

pytest -q

Design tab

Preview tab

Code tab

Changelog (from Codex baseline)

Bug fixes

• Code generator: event handlers quoted as strings — on_click='handler' now correctly renders as on_click=handler (bare function reference)
• Code generator: handler stubs after main() — stubs now defined before main() so names are in scope when the control tree is built
• Code generator: bool/int type ambiguity — isinstance(True, int) is True in Python; bool check now runs before int check
• Validator: wrong slot not detected — children assigned to undeclared slots (e.g. slot="controls" under Container) now raise ValidationError
• tree_ops.move_node: no cycle detection — moving a node into its own descendant now returns False instead of corrupting the tree
• WidgetNode.clone: duplicate IDs — clone() now generates fresh unique IDs by default for copy-paste safety; clone(deep_new_ids=False) preserves IDs for undo snapshots

Improvements

• tree_renderer: removed eval() — replaced with safe getattr chain on the flet module
• tree_renderer: slot-aware child assignment — uses registry slot definitions instead of hasattr heuristics
• tree_renderer: skips event props — event handler name strings are not passed to Flet constructors in preview
• serializer: removed redundant asdict() — node_to_dict now builds dicts manually instead of calling dataclasses.asdict then overwriting children
• hit_test: drop zone detection — added DropZone enum (BEFORE/INSIDE/AFTER) based on TDD spec (top 25%/middle 50%/bottom 25%)
• hit_test: accepts_children flag — leaf nodes fall back to AFTER when pointer is in the middle zone
• Test suite expanded — 9 tests → 42 tests covering all bug fixes and edge cases