Simple GUI tasks (Well I need help!)

aaronjlaw

Hello, I am using the latest 5.01 version at home whilst my university has an older version which is causing issues when opening and compiling. That is a separate issue though.

I have a task which is to create a GUI application which displays a label marked “Size”, a lineEdit with the default value 50, and two buttons marked “Display” and “Step”. I have managed to do this:
!http://img.photobucket.com/albums/v334/Klaus5000/1gui_zps39dd3e4a.png()!

"These should be placed in a vertical layout on the left. Use a spacer to stop the label getting too big.":
!http://img.photobucket.com/albums/v334/Klaus5000/blahhh_zps24f24e55.png()!

The bit I am stuck on is this: (I am guessing it is to do with signals and slots but I am not sure how to reset the text value?)
"Change the label text to “Hello world” when you click the “Display” button."

Any pointers?

Chris Kawa

Take a look at step 9 "here":http://doc.qt.digia.com/qtcreator-2.4/creator-writing-program.html#designing-the-user-interface and then "here":http://qt-project.org/doc/qt-5.0/qtwidgets/qlabel.html#text-prop

aaronjlaw

Hello there,

I am a bit confused by the second link.... I have done something like this.

void MainWindow::on_displayButton_clicked()
{
QLabel::setText("Hello World");
}

It is an update() function too. ?

Chris Kawa

That's "almost" right ;) Think about it. If you had a couple of labels which would get updated if it worked like you wrote it?
You need to call setText on a specific instance, not on a class in general. Check in the properties panel what is the object name of your label and call setText on it.

aaronjlaw

It gives me a couple of errors.

EDIT:
void MainWindow::on_displayButton_clicked()
{
sizeLabel::setText("Hello World");
}

Chris Kawa

:: is for when you call a static method on a class or in method definition or when you use namespaces. In case of class instance you use . (dot) and for pointers -> (this is your case).

I'd suggest going through a good C++ book and learning some language basics before you dive into Qt and UI programming. It would save you a lot of time and you could concentrate on the task instead of fighting with the syntax.

aaronjlaw

Oh I have done a year and a half of C++ dont worry about that haha... I know the basics. Never used Qt before this week though so have to get used to it.
Just getting confused by it. Havent used different class/function files for a while properly.

Still not quite working, not picking up my sizeLabel still... Undeclared, but I have changed it in the GUI view.

aaronjlaw

Still having issues. (Not looked since last night though)

void MainWindow::on_displayButton_clicked()
{
sizeLabel->setText("Hello World");
}

Following errors ( I am not sure what is going on here as the properties name is sizeLabel so that should be it?)

!http://i49.tinypic.com/2v3ljpg.png()!

Chris Kawa

Qt puts all the widgets created in designer as a children of the ui object, so it should be ui.sizeLabel->setText

aaronjlaw

Ahhhhh I see now. I think I will get used to the design view and code switch over after a bit more practise.
This was only a first task.

Thanks very much for your help. I am sure this forum will prove useful over the next few weeks.