I've made my first qt window. Now I'd like to make my first dialog, using qt. I have just finished creating the dialog, which is basically made of a QDialogButtonBox, and now I'd like to connect it to the window. I have two beginner's questions:
How can I retrieve how the dialog was closed (ok pressed or cancel pressed) from the window.cpp, which creates a new dialog, and then calls dialog->show() ?
Where and how to destroy the dialog pointer ?
If you use dialog->show() then I assume it's non-modal dialog.
If you have created QDialogButtonBox and connected its signals with accept() and reject() slots of your dialog as documentation shows, then your dialog will emit finished(int) and additionally accepted() or rejected() signals by which you can determine how it was closed.
If you need more customized behavior, then you can reimplement closeEvent(QCloseEvent *event) or create your own singnals.
If you need to delete your dialog you can use setAttribute(Qt::WA_DeleteOnClose, true);, which will delete instance on close.
you can use one flag, and signal and slot.
when put OK flag=1 , and when put cancel then flag=-1; and then use signal.
in in the window.h write code how to handle that flags with 1 simple slot.
for destroying the pointer you can use signal and slot in your Dialog and tell when user push
Ok, or Cancel , or exit (up- right (red cross)) go to slot in call the Destructer of dialog
and also you that you better set parent of dialog to window.
First Question:
When you want to show the dialog,just construct it,using myDialog *d = new myDialog(this)(the this pointer will make sure that you havn't to delete the pointer you created 'cause Qt will handle this if you specified the dialog's parent). And use d->exec() if you need a modal dialog, or d->show() to make it non-modal;
Second Question:
Once your specified the dialog's parent object, all u need is just use it and leave alone the memory managent,Qt will do this for you. Also you can use d->setAttribute(Qt::WA_DeleteOnClose,true) to make it destroy itself when it is closed.
Remember to link the QDialogButtonBox to your dialog's actions.
Related
What is the difference between hide,close and show of pushbutton or any widget in terms of memory?
Which is better if I don't want to use widget again?
First as said #Hayt, read the documentation.
For the actual answer:
hide() is the same as setVisible(false).
show() is the same as setVisible(true).
close() attempts to close the widget by triggering a QCloseEvent, if the event is accepted the result is:
The same as calling hide() if Qt::WA_DeleteOnClose attribute is not set on the widget which is the default.
The same as calling deleteLater() if Qt::WA_DeleteOnClose is set.
In term of memory, any of the 3 will not change anything (except for close() if you have set Qt::WA_DeleteOnClose). If you do not want to use the widget ever, the best is to delete it:
delete pointerToMyWidget;
or
pointerToMyWidget->deleteLater();
The second form is generally safer as the 1st one can be dangerous depending on where your write it. (e.g you delete it in a slot called by a signal emitted by the widget you delete).
According to Qt, you can read this :
CLOSE :
Closes this widget. Returns true if the widget was closed; otherwise
returns false.
First it sends the widget a QCloseEvent. The widget is hidden if it
accepts the close event. If it ignores the event, nothing happens. The
default implementation of QWidget::closeEvent() accepts the close
event.
If the widget has the Qt::WA_DeleteOnClose flag, the widget is also
deleted. A close events is delivered to the widget no matter if the
widget is visible or not.
The QApplication::lastWindowClosed() signal is emitted when the last
visible primary window (i.e. window with no parent) with the
Qt::WA_QuitOnClose attribute set is closed. By default this attribute
is set for all widgets except transient windows such as splash
screens, tool windows, and popup menus.
.
HIDE : Hides the widget. This function is equivalent to
setVisible(false).
Note: If you are working with QDialog or its subclasses and you invoke
the show() function after this function, the dialog will be displayed
in its original position.
.
SHOW : Shows the widget and its child widgets. This function is
equivalent to setVisible(true).
If you don't need to use your widget, call close(). You can manage the event to destroy your widget.
hide() only hides. It's only graphical, you can't see your widget but you don't destroy it.
But I think that the name fo the function are enough explicit to understand!
Suppose I've a Qt app based on QWidget, in which I'd like to obtain a "feedback" everytime I press a QPushButton, I rotate a QDial, I press a mouse button. My question is: how can I set a slot that informs me everytime something happened inside my app built for a touchscreen, in which I need to know when user does something on it.
MousePressEvent partially solves my problem; so when user touches the screen, MousePressEvent warns me about it. Problem is related to widgets as QPushButtons or QDials.
At the moment, I've already arranged my widgets with a lot of subwidgets; number of pushbutton is about 300. How can obtain triggering signal when one of them is pressed without re-edit every single button?
You can use an "event filter" that is installed on QApplication instance. This filter will receive all the events in your application, afterwards you can check event type and object type to pick the events you are interested in. See my answer to another question here for details.
I have a QDialog that was created with Qt::WA_DeleteOnClose flag. When specific event happens I need to hide the dialog and restore it later upon another specific event. If I make a call to QWidget::hide() the dialog object is deleted (due to WA_DeleteOnClose) which doesn't work for me.
Unfortunately I can't unset/reset Qt::WA_DeleteOnClose in runtime for certain technical reasons.
The question is: how do I effectively hide QDialog so that it's not visible but still exists? I tried
QDialog* pDlg = ...;
QSizePolicy newSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
pDlg->setSizePolicy(newSizePolicy);
pDlg->setMinimumSize(0,0);
pDlg->resize(0,0);
but this didn't work. Might it be that I can move the dialog outside the desktop? Or...
I'm solely on Windows if it matters.
Thanks.
I have created a form. I have many 2 push buttons. On clicking on a pushbutton I want to call another custom form. I am using only QtDesigner. I am NOT using QtCreator. Using QtCreator, there are so many examples on how I can do it. But using only QtDesigner 4 there are no examples. I have also tried creating a MainWindow and then having pushbuttons in that. I want to call a new pop up window when I click on a button (which is a custom form). I am using Eclipse CDT as the IDE. I have installed Qt plugin so that I can do both C++ and Qt development. The problem is I cannot use 'Form' to declare my custom form in header file of the mainwindow.
I read in few posts that this is not possible to do using only QtDesigner and also read it can be done using QObject::connect. Please can anyone help me to confirm if we can do it and if yes please can you provide me an example?
Yes, it's definitely possible with C++. You'll need to connect() pushbutton's clicked() signal with a slot in your first form:
connect(pushButton, SIGNAL(clicked()), this, SLOT(show2ndForm()));
The good place to connect is in your first form constructor.
In that slot just show your second form (for example, using QDialog::exec()):
void FirstForm::show2ndForm()
{
static SecondForm *form = 0;
if(!form)
form = new SecondForm(this);
form->exec();
}
You'll probably need to inherit your second form from QDialog to use this method and also create header and source files for your second form.
For modeless form instead of modal, use form->show() instead of exec().
This is not complete possible if you need to customize a slot, but for simple operation where the existing slots are available, you can just use the signal-slot edit as below.
You can select the receiver object and then the correponding slot. I am providing further screenshot to show it is done for customized slots as well.
Right click with your mouse in the middle of the main window and the change signals and slots
Select the change signals and slot option
Use the Add button to add a new slot
Click on the OK button to conirm it once you chose the desired name
In the signal-slot editor double click on the desired object's slot, and it will show the available slots including your new custom slot.
Select your custom slot and you are done from the designer parts. Do not forget to actually implement that in your C++ code.
If you do not need a custom slot, and a built-in will suffice, you can select that off-hand without the previous steps. Those are provided for completeness.
I am developing embedded application for device with touch screen and need to handle separately single clicks and long presses on QTableView items. Single clicks should open editing dialog, long presses should only select item. The problem is that there is only 'pressed' signal in Qt, and I don't know what is the right way to handle long presses. Could anybody suggest how to do it?
Instead of using QTableView directly, subclass it and then implement the virtual functions: -
void mousePressEvent(QMouseEvent *)
void mouseReleaseEvent(QMouseEvent *)
You can then decide how you want to handle the events, creating a timer to see if a certain time has passed before the release event.
Install an event filter on the view's viewport() widget and process its mouse events. Use view->indexAt() to find out which item was clicked. See also Event Filters.