Qt Designer

Introduction

To be written.

There is a good tutorial on how to use components in your applications at: http://doc.trolltech.com/latest/designer-using-a-ui-file.html

We've compiled some simple working examples on how you can do this. Download Media:Designer-using-a-component.zip to test it out.

This is deeply commented in this article and some other notes are available at this page. But in summary:

A symbol may be missing. Link your dll with a file containing an empty main function and the error will pop up.
The library cannot be located. The plugin must be located in a subfolder named 'designer' inside one the following paths:
- $QTDIR/plugins
- The path where the binary of the plugin host is
- Any path on the QT_PLUGIN_PATH (PATH environment var syntax as it is in your system)
- Any explicitly added path using QCoreApplication::addLibraryPath or QUiLoader::addPluginPath
Another version of the library is placed on a different valid place or with a different name. Remove the library and if you still see the symbols, that's your case.
Your are compiling in either debug/release version of the library and designer or the host is compiled using the other version. Use ldd in Linux to check what's happening.
The initXml() function returns invalid XML. In this case you can load an interface with such plugin but it won't be on the widget toolbox
Missing Q_OBJECT in your widget class. The widget will work properly but will be saved on the ui file as a superclass object missing any specific properties.

A collection of Qt Designer tips and tricks that may be of some use: Qt Designer Tricks