// problem · 11 august 2026 · 1 min

Discovering that my Qt UI is QML rather than Widgets

Qt Designer would not edit the screen. The file was never a .ui form.

Time wasted: 1 hour

Problem

I opened Qt Designer expecting to drag widgets. The screen did not appear as an editable form.

Qt 6.x Qt Creator QML project

Designer empty or refusing the file. A .qml file in the project. Confusion about where main.cpp was.

The Qt Designer / form editor workflow I had read about for Widgets.

Looked at the project files. Found .qml. Read just enough CMakeLists to see Qt Quick.

Reopening Designer. Looking for a missing .ui file. Searching the web for “Qt Designer blank”.

The UI is QML (Qt Quick), not Widgets. Designer is the wrong tool for that file. Qt Design Studio / the QML editor are the right family.

Stopped forcing Designer. Edited QML as QML. Treated C++ as the engine, not the layout.

Two UI toolkits live under the Qt umbrella. The file extension was the clue I ignored.

If Designer cannot see your screen, check whether you have a .ui file at all.

I am learning this. The confusion is the point of writing it down.

Found something wrong?

These notes can be incomplete, or wrong in a different environment. Suggest a correction on GitHub or email me at me@t4mer.net.

// til

TIL: QML describes the UI tree. C++ still runs the process.

Designer not editing your screen is often the first clue that you are not in a Widgets project.

// learning

main.cpp is not index.php

A Qt process starts once. There is no front controller. I was looking for the wrong kind of door.

// til

TIL: Qt is the toolkit. C++ is the language.

Search results get worse when you ask the toolkit to be a language.