No custom widgets in Qt Designer for QGIS 3
The environment and path needs to be set for Qt Designer to access the QGIS Custom widgets. These can be set by running the "qgis-designer.bat" file that comes with a QGIS installation. For a network installation, this file is located in: ...\OSGEO4W64\bin\qgis-designer.bat
The contents of this batch file are:
@echo off
call "%~dp0\o4w_env.bat"
call qt5_env.bat
call py3_env.bat
path %OSGEO4W_ROOT%\apps\qgis\bin;%PATH%
set QGIS_PREFIX_PATH=%OSGEO4W_ROOT:\=/%/apps/qgis
set QT_PLUGIN_PATH=%OSGEO4W_ROOT%\apps\qgis\qtplugins;%OSGEO4W_ROOT%\apps\qt5\plugins
start "Qt Designer with QGIS custom widgets" /B designer.exe %*
In QGIS 3.2.0, custom widgets seem to be available:
Tested on Windows 7 64-bit.
Edit:
I used the QGIS Standalone Installer Version 3.2 (64 bit) and following the simple on-screen instructions. Once installed, I simply ran
Qt Designer with QGIS 3.2.0 custom widgets.exewhich was found in the Start menu.I also tested QGIS Standalone Installer Version 3.2 (32 bit) on a 32-bit computer and the custom widgets were also available.