Beginners: signal slot help
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hello guys,
I ve a class and in this class I create a new QWidget to show an image. I want to get the signal when this QWidget is closed, or even the possibility to know if it is open or closed.
here is how I build it from inside my class. the connect has a mistake.
myclass.h
@
private:
QWidget *blub;
@@myclass.cpp
QWidget *blub = new QWidget(); blub->resize(250,230); blub->setWindowFlags((windowFlags() | Qt::CustomizeWindowHint) & ~Qt::WindowMaximizeButtonHint); //no resize connect(blub,SIGNAL(destroyed(blub)),this,SLOT(handwindowcloseevent()));
@
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The connect() should read:
@connect(blub,SIGNAL(destroyed()),this,SLOT(handwindowcloseevent()));
@However, there is a difference between closed, as in hidden, and destroyed where the object is being torn down (after a delete or going out of scope). QWidget::visible() will tell you if the widget is visible. You can use the QWidget::closeEvent() (in the blub object) to do pre-close processing if that suits your purposes.
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Use a QPointer instead of a naked pointer. This will save you later on. The QPointer will null itself when the Widget is freed.
Then call
setAttribute( Qt::WA_DeleteOnClose, true );
on your widget it will delete itself when closed.
And because you use a QPointer the pointer will be null as well. -
What is QPointer can you give me an example?
I tried the connect as stated above but it did not work, unfortunately, do i miss something else? Should I create it as a class?
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@
QPointer<QWidget> blub;
blub = new QWidget():
@A QPointer is just Qt's class wrapper for Qt dynamic memory.
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is it possible say to get keyboard events from the main widget irregardless which (it or blub) has focus.
can i put in the main widget @this->grabkeyboard();@ ?
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hello m usind qt designer for first time.. i need to create a calculator using three line edits and two pushbutoons for addition and equality.
cn anyone help me with the code using signals and slots?? -
see this video to learn more about signal and slots
https://www.youtube.com/watch?v=GxlB34Cn0zw -
hello hav to design a calculator in which if a value becomes more than 10 color of button changes to red otherwise green..
plzzz help me with the code -
You can connect the textChanged() signal of the lineEdit to a slot where you can check the count using
lineEdit->text().length() you can also set the maxlengh like lineEdit->setMaxLength().