please upgrade to latest Qt Creator 2.8.1 which has an improved QML designer. You can follow our guide how to install it here.
The way I usually use the QML designer is to adjust the positions of items, and wait for changing “more complex” properties like an italic font until the very end when I have set the basic positioning of the items, because QML designer sometimes is not capable of showing a preview for some properties.
What I do in later steps of the game development, is to change the properties while the game is running. You can do that with the following steps:
1.) Go to Projects, then to the Run tab, and select in the Debugger Settings “Enable QML”.
This allows you to change QML properties at runtime and see the effects immediately, while the game is running!
2.) Press the debug button or F5 on Windows to start a debug session.
3.) You can now edit the qml files and change any properties by just saving the file.
This allows for very short turnaround times and you can set up UIs quickly.