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===Implementing the Slot===
===Implementing the Slot===
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|Note: This page deals with content related to KDE 3. If you are developing for KDE 4, this information might not be valid anymore.|
To get us started doing something useful with Qt Designer, we are going to build a simple program that will show you the power of Qt Designer and KDevelop. I hope that this will help you to create your first "real" KDE application.
KDevelop will help you to build a complete KDE application. The KDE project uses the autoconf and automake tools for KDE 3.x, and KDevelop will provide you with all the necessary files (admin directory, Makefile.cvs, Makefile.am,...).
Qt Designer is part of the qt-3.2.x package and above. If you have an older Qt on your system, you should get at least this version. At the time of writing, Qt latest version is 3.3.2.
Please remember to check if you have all the qt-related packages installed. You need the qt headers in order to compile this tutorial application. These headers usually come in the devel package. You also need to be sure you have designer. In some distributions, it comes in a separate package.
To check if you have everything, do a:
If you get something like /usr/lib/qt3/include/qstring.h then you can set your QTDIR variable to /usr/lib/qt3/. In bash environment, this is done by typing:
export QTDIR= /usr/lib/qt3
For an explanation for how to use anonymous SVN, get the qt-copy and kde modules and compile them, please see a great documentation at Using Subversion with KDE.
You must then set the QTDIR environment variable. This should point to the directory into which you installed Qt. In bash, for example, you would type:
export QTDIR= /usr/local/qt
provided that /usr/local/qt is the directory into which you installed Qt. Please read the INSTALL file for more details.
You then compile by issuing the following commands, here is the recommended compile line:
./configure -system-zlib -qt-gif -system-libpng -system-libjpeg \
-plugin-imgfmt-mng -thread -no-exceptions -debug -fast
The command make install is not needed.
Qt Designer is located in the bin directory of your Qt installation directory. You can run it by typing:
in a console.
KDevelop 3 should be part of your distribution. Pre 3 versions of KDevelop were nicknamed Gideon, but they are obsolete now.
KDevelop can be downloaded from the KDevelop website, under the Quick download heading.
To compile KDevelop 3, you need qt-3.1.0 or higher and kdelibs-3.1.0 or higher. The environment variables QTDIR and KDEDIR should point to those directories.
Don't forget to set up the KDE and Qt paths. The most common errors while using KDevelop come from the environment variables not set up properly. Check in a console by issuing the command set to see all your environment variables. You should set your PATH variable as follow as well as your LD_LIBRARY_PATH:
If you have any problem getting KDevelop running, please refer to the KDevelop Forum to find the answer to your problem.
If you never used KDevelop before, try to create a new project and to compile it to get used to the interface and the icons.
The framework in which our program will sit in (i.e. the main window) can be done easily and quickly by using KDevelop. Start KDevelop and select New Project in the Project menu. The Application Wizard appears then. Choose a C++ -> KDE -> Simple KDE Application. Fill in the blank lines with the project name SigCreate, your name as author, and your email. Refer to this screen shot as a reference.
Click on Next. Have a look to the CVS option and the header templates. Then click on Finish on the last screen. KDevelop creates all the files that you need to compile your project. You can use the file selector to view the code of the 3 files which are main.cpp, sigcreate.cpp and sigcreate.h, as shown here.
Once the Application Wizard has created your application, compile it to ensure that everything is fine. To do that, select Build -> Run automake & friends then Build -> Run configure. The Messages output window should say
" Good - your configure finished. Start make now
so you can run make with Build -> Build Project (or using the F8 shortcut). Then Build -> Install. Then Build -> Execute program (or F9). The result is shown here.
Qt Designer is a tool for designing and implementing user interfaces. It helps you arranging your widgets on a form and adding a proper layout so your interface can be resized properly. I recommend that you read the Qt Designer manual to know everything about Qt Designer. Qt Designer includes a code editor but we'll use KDevelop to edit and modify all code.
We will now create the interface of our application using Qt Designer. A form from Qt Designer is saved with a .ui extension because it is then processed by the uic program to generate a .h and .cpp files. KDevelop takes care of that, the only thing we need to do is to create the form.
In KDevelop, click on File -> New and fill the dialog window that appears. First write the file name: sigcreatedlg and select what new file you want in the combobox: here we want a Widget (.ui). Please be sure that Add to project is checked, this ensures that the Makefile.am is updated. Refer to this screen shot.
Click the OK button. The Automake manager dialog then pops up. Click the OK button for this dialog as well.
If the new file sigcreatedlg.ui is not open in Qt Designer, open the Automake Manager, right-click on the file and select Open With, then Qt Designer. Qt Designer will open.
The Qt Designer interface is essentially split into three areas. On the left is the toolbox, where you can select your widgets. On the right, several dialogs can be selected. I'll keep only the Property Editor dialog (I close the 2 others). Your widgets can be fine tuned to behave how you want them to. You can choose the size of the widget, its background color (palette), and so on. Between those 2 windows is the Form, your program window, within which you will design your user interface.
Each time you want to use Qt Designer, you should have a precise visual idea of the design of your interface. You can see in this picture what the program will be like. It is a window with a number of different items (or widgets) on it, designed so that the user puts the right information in the right boxes. You should always design your program from the user's point of view, as it must be easy to use.
This application creates an email signature, which is then displayed on the screen. The user should enter her/his name, email address, and then select one of three comments. When you click the Create! button, the generated signature is shown in a MultiLineEdit. When you click Cancel, the program quits.
Go back to the Qt Designer window with the new dialog open. You will see that the property editor has been filled with details about the form you have created. The first line in the Property Editor shows the name of the form which is Form1. Click on the field with this name to change it and type SigCreateDlg. This will form the class name of the dialog so you should name it something useful.
To change properties, select the property you wish to change, then alter its setting on the right. Change the Caption property to "SigCreateDlg v.01". We will now begin to add widgets on our dialog.
To start, we will insert the text at the top of the program window, which can be seen here. This text tells the user how to operate the program. This type of widget is called a Label and you can put one on your program like this:
You follow pretty much the same procedure for embedding any type of widget that is supported by Qt Designer; select it, drag it, and finally, change its properties and size.
An interesting concept in Qt Designer is that widgets can act as containers for other widgets. This will be demonstrated in our next task, which is to create the input fields inside the frame. You can see that in Picture 8 we have a bunch of labels and text boxes inside a frame. This frame is called a Group Box and acts as a container for the labels and text boxes inside it. Let's first create the frame by selecting the GroupBox in the Toolbox dialog->Containers or Tools->Containers->GroupBox from the menubar. You can drag the mouse to create the box just below the Label you put before. In the Property Editor you can change the title property to alter the text in the frame. Put Details in the title text field. You may notice a + symbol in this entry in the Property Editor. This indicates that the property has subproperties that can also be changed.
Once you have created the frame (i.e the GroupBox), create three more labels as before but when you draw them, draw them inside the GroupBox frame. You can then see in the Object Explorer box (Windows menu -> Views -> Object Explorer) to the right that the labels have become children of the GroupBox frame. See this image.
Change the text of labels by double-clicking on it.
Once you have done this you can then create the text boxes. They will allow the user to type in text like his(her) name and email address. We use the simplest type of text boxes: a widget called QLineEdit which allows the user to enter one line of text only. You have to create two QLineEdit widgets for the name and the email address. You choose the menu Tools then the entry Input then LineEdit and you draw it beside the 'Your Name' Label. Do the same below for the address.
The witty comment will be selected by the user. We use a ComboBox which will present the user with three comments. Click on the ComboBox icon or select it via the Tools-> Input-> ComboBox menu. Draw it beside the Witty Comment label. Then double-click on it. You will be presented with a box into which you can add the contents of the combo box. Click on the 'New Item' button and type in your comment in the text box at the right. Then click again on 'New Item' for the second and third comments. Click on OK when you have finished.
Adjust the size of the different widgets so they are nicely placed.
Up to now, we have not named any of the widgets that are being placed in our program. It is useful to set an internal name for widgets so we can call them after in the program. Labels don't perform any action so they don't need to be named but other widgets do. It is the case now for our text boxes. We'll need to manipulate the data from the three input widgets (i.e. read the text) so we should give them a name. Names should be easily recognized later and they should make sense. The names are assigned via the name property on the top of the Property Editor. We name the top LineEdit nameBox and the second one mailBox. We name the ComboBox commBox. This will allow us to access the comments. So click on each LineEdit and then besides Name in the Property Editor write nameBox and mailBox. Then click on the ComboBox and name it commBox.
We finish the graphical design by adding a label with 'Generated Signature' as text. Below it, we put a TextEdit (Tools->Input->TextEdit') where the generated signature will be displayed. We name it 'sigBox'. And then we add two PushButtons at the bottom ('Create!' and 'Cancel'). They don't need names but you can give them some if you want.
Save your form. You can now have a quick preview by selecting the menu Preview-> Preview Form. This is the form before layout management.
This section describes the layout management. If you resize the preview window you will then notice that the widgets do not adjust appropriately. They are not resized. To improve things, we need to use a feature in Qt called spacers. Spacers are like virtual springs that push the widgets on each side apart.
The use of spacers and layout management is a skill that is developed through trial and error. The main thing to remember when dealing with spacers is that you work horizontally first and then vertically.
We will first use spacers to center the text in the top box. Resize your label so that it only get the size of the text. Then we add two spacers, one at each side. Choose the 'spring' icon or menu Layout-> Add Spacer. You adjust each of the spacers horizontally. Click the space to the left of the text and the blue spacer will appear . Repeat the same procedure for the right. Then add a spacer on the right of the 'Generated Signature' label, and a last one on the left of the the 'Create!' pushbutton. Please use this image as a reference.
Now that we have spacers to fill blank space, we need a proper layout management. This will allow the widgets to be nicely resized whenever the main window is resized. It is really compulsory to have good layout management. Again, try to resize several times to see if everything is in place. We can use Vertical or horizontal layout or grid management. The top row of widget is horizontal (spacer + label + spacer) so we need Horizontal management. We need to select the three widgets alltogether: click on the first spring, then click on the label while holding down Shift, then on the second spring while holding down Shift. Then click on the Horizontal Layout icon or menu Layout-> Lay Out Horizontally. You will then see a resizable red line around the three objects to indicate that their layout is being managed. Resize the red box if it needs to.
We can now repeat this procedure for the three labels inside the GroupBox, this time using vertical layout management. The same vertical management for the two LineEdit and the ComboBox. It is better to use vertical management to keep the object aligned. If we use horizontal management for each label + text box then they will not stay aligned and equally sized. Horizontal management is needed for the label with the spacer and another one for the two pushbuttons and the spacer.
To finish the layout, we need to let the form look after the laid-out boxes. We put everything in a grid. This is done by right clicking the form and selecting "Lay Out in a Grid" from the menu. The final design with layout lines should resemble something similar to this image.
Signals and Slots are used for communication between Qt objects. The signal/slot mechanism is a central feature of Qt and probably the part that differs most from other toolkits which often use callbacks. In Qt, a signal is emitted by a widget when a particular event occurs, very often triggered by the user like for example pressing a button or writing something in a LineEdit. A slot is simply a function that is called in reponse to a particular signal.
Now the widgets are implemented and the layout is arranged the final thing we need to do in the design stage of the form is to create the signal/slot connections. To do this manually requires a connect() function but Qt Designer provides a simple yet effective solution. To create the signal/slot connections we need to use the connecting tool. To do this either select the icon (it looks like a red arrow going into a green square) or select Tools-> Connect Signals/Slots from the menu (or use the F3 shortcut key). To create a connection, click on the form on the widget that is going to be dealing with the slot, drag the line off the form and release the mouse button.
Let's deal first with the Create! button. Click first on the Connect Signal/Slot icon or select it from the Tools menu or use the F3 key. Then click on the Create! button with the crosshair and drag the line off the form completely. When you have released the mouse button you will see the connections tool shown here.
What we want to do is to create a slot that will create our signature when the user clicks on the Create! button. The signal will be clicked() (you may choose among five signals for a QPushButton) and we need to create the slot then make the connection.
To create the slot we need to click on the Edit Slots button. The slot creation box then appears. See this example. Now click on the New Function button and a slot will appear in the box. Instead of new_slot() rename it to slotCreateSig() and leave the access specifier as public. When you click on OK you will be returned to the connections box and you will see your new slot in the Slots section of the box.
To make a connection you simply select the appropriate signal (which is clicked() in our case) and then select the slot (which is our new slot slotCreateSig()). When you have selected both signal and slot you will see the connection made at the bottom of the screen. After you are finished click OK.
Repeat the procedure for the Cancel button by using the clicked() signal and the close() slot. You are now done with the signals and slots.
In this tutorial, we use KDevelop subclassing tool in Automake Manager. If you have KDevelop version which has not that capability, then please go to Chapter 7 where I explain this step without the subclass tool.
Here we start with the KDE simple project named SigCreate and the sigcreatedlg.ui that we have added in our project. In the Automake Manager, in the section sigcreate (Program in bin) you must have three files: sigcreatedlg.ui, sigcreate.cpp and main.cpp. The project must compile and give the main window as in picture 3 (creating.html).
As the sigcreate class is no use for us, we will remove it and use it for subclassing the sigcreatedlg.ui file. In the Automake Manager, right click on sigcreate.cpp and select Remove and a dialog pops up. Please check 'Also Remove it from disk'. Then do the same with sigcreate.h. This is the way to remove obsolete files from your project and the Makefile.am will be updated. Remember to run automake & friends and configure before compiling your project again. We will not do it right now because we will make other changes. We will now use the class name SigCreate for the subclass.
In the Automake Manager, in sigcreate (program in bin), right click on sigcreatedlg.ui and choose Subclass Widget... from the context menu that appears. Then fill in the subclass name which is SigCreate. Check the box: Reformat source and click on OK. Say No then about adding these files in cvs as we did not enable this in our project. Note You can see that the slot we created in designer is listed here and checked, the method will be implemented in the generated files. If you uncheck it, the code will not be generated in your class.
(The subclass dialog Image)
We have to suppress some lines in main.cpp as the KDE simple project template refers to a KMainWindow which is usually the base class used. But here, SigCreate is based on QWidget. You have to remove all the lines between KApplication app; and return app.exec(); except the ones I keep here:
SigCreate *mainWin = 0;
mainWin = new SigCreate(); app.setMainWidget( mainWin ); mainWin->show();
Then you implement the slot by adding the following lines in the parenthesis of:
to implement the slot
sigBox->append(nameBox->text()); sigBox->append(mailBox->text()); sigBox->append(commBox->currentText());
and also the corresponding headers of course:
#include <qlineedit.h> #include <qcombobox.h> #include <qmultilineedit.h>
</code< Run Build -> Run automake & friends, Build-> Run Configure, Build -> Build Project, Build -> Install (or Build->Install as root user), Build -> Execute Program. That's it! The program is working!
A few more words about signals and slots. The signals and slots mechanism is type safe: the signature of a signal must match the signature of the receiving slot (for example, you will connect valueChanged(int) with a slot having an int as argument). And another thing to keep in mind is that all classes that inherit from QObject or one of its subclasses (e.g. QWidget) can contain signals and slots.
All the strings used in KDE program must be wrapped in the i18n() function (klocale.h as header) because all KDE projects are translated. Please see the KDE Translation HowTo to learn more about i18n to make translations for an application.
==Credits and License==