When I want to grab the whole window, I can only grab what is drawed with OpenGL in centralWidget.
QPixmap my_pixmap = QPixmap::grabWidget(ui->OpenGLWidget, 0, 0, frameto264.iWidth, frameto264.iHeigth);
What I have draw with QT, like QPixmap or QPainter(or even in statusBar), cant not be showed in grabWidget.
Can anyone tell me how to grab the whole mainwindow, or was the ui->OpenGLWidget using wrong?
It is my first time asking question on stackoverflow. If there is something wrong with my statement, please be free to correct it.
You are capturing the opengl only because that is what you are giving as parameter to the method grabWidget here:
QPixmap::grabWidget(ui->OpenGLWidget....
Instead of doing
grabWidget(ui->OpenGLWidget,...
repalce the pointer to your openGl widget by a pointer to the mainWindow
Related
In my Qt widget I sometimes get this error:
malloc(): smallbin double linked list corrupted
It does not happen all the time but I think I have narrowed it down to when it starts.
I have a QGraphicsView and QGraphicsScene and there I'm drawing lines whos points are stored in a vector. Reason for this is I need to pass this points to another library. Once I draw the points I have an option if I click on a line I'm prompted to another window where I can change the coordinates of a line.
ResizeDialog *dialog = new ResizeDialog(this);
dialog->exec();
delete dialog;
The above code is the code I use to open a new QDialog. I know if I use this->close() the
qt malloc(): smallbin double linked list corrupted does not appear but then I lose the instance of QGraphicsView. Reason I need to keep the QGraphicsView window open if I need to chose to add further lines.
Any advice on how I can eliminate this issue wold be helpful.
Rather than using delete dialog;, use dialog->deleteLater();. I assume the small code portion is inside a slot of the object referenced by "this", and direct deletion is source of trouble as ResizeDialog *dialog = new ResizeDialog(this); affect the parent object this.
So I'm trying to use QPropertyAnimation on a QWidget that has been added to a QGraphicsScene and it's not working. I can't really copy and paste the code as it's intertwined with a somewhat complicated system but the summary is basically this:
A custom widget is created
CustomWidget widget;
Widget is added to a graphics scene
graphicsScene,addWidget(widget);
at some later point, one of the widget's member functions tries to create and start a QPropertyAnimation
QPropertyAnimation *anim = new QPropertyAnimation(this, "_opacity");
anim->setDuration(5000);
anim->setKeyValueAt(0, 0);
anim->setKeyValueAt(1, 1);
anim->start();
instead of a smooth animation, the property changes to the second value and stays there.
I've looked online at some related problems and their solutions, but none seem to match my situation. Does anyone know how to accomplish this?
EDIT: I discovered I just needed to make the WRITE function for _opacity call update()
I guess you are allocating QPropertyAnimation and friends on the stack instead of the heap.
Note that the QPropertyAnimation object will be destructed at the end of the scope, hence no properties are changed later on.
You most likely wanted to create that object on the heap. Also see the example at: http://doc.qt.digia.com/4.7/qpropertyanimation.html
I'm a beginner to Qt and am making (or at least trying to make) a basic calculator. If I understand correctly, when doing this:
connect(my_button_4, SIGNAL(clicked()), this, SLOT(writeNumberLbl("4")));
The "4" is not accessible (rather, only its type is) in writeNumberLbl. Basically, I would like so that when the button is clicked, the label sets its text to "4". However, I have the numbers 0 to 9, so I wanted to do:
connect(my_button_0, SIGNAL(clicked()), this, SLOT(writeNumberLbl("0")));
connect(my_button_1, SIGNAL(clicked()), this, SLOT(writeNumberLbl("1")));
...
connect(my_button_9, SIGNAL(clicked()), this, SLOT(writeNumberLbl("9")));
My writeNumberLbl function is:
void Calculator::preWriteVal(QChar val)
{
QString curVal = ui.lbl_output->text();
curVal += val;
ui.lbl_output->setText(curVal);
}
However, I can see that this will not work due to the parameter, 'val'. Could someone please point me in the right direction? Thank you. I did look to see if this question had already been answered and couldn't find anything. If it has, please provide me a link.
Also, is it possible, using Qt Designer 4, to connect a widget to a custom slot?
Thank you.
As far as I know,Qt's signal/slot system requires that the number of parameters of signal function is not less than that of slots function.
In your example,the signal function click() have zero parameters and slot function writeNumberLbl("4") have one parameter,this will not be accepted by the Qt's signal/slot system and if you run your program in debug mode of Qt creator,the qDebug will show you a message like 'Incompatiable signal/slot' blalbalba~. To solve this problem, just read the article given by Arnold Spence. It is quite clear.
There are a number of ways to tackle this problem and they are outlined very nicely here. Although that page is a bit old, I think it is still quite valid. I would recommend using a signal mapper.
For your second question, yes. You can connect signals and slots using Qt Designer by setting the designer in "Edit Signals/Slots" mode. Once in this mode, for example, you can drag a connection line from a button to the form. A dialog will open up allowing you to choose the signal and slot to connect. If you haven't already implemented a slot in code, you can specify the name of a slot and then add the code for it afterward.
The number of parameters in Slot can not exit those in Signal? and pressed() has none. You have two choices (three, counting the dumb one):
Use QSignalMapper. Its help is self-explanatory.
Connect all your buttons to single slot. In it, find out what button has been pressed. QObject::sender() function helps.
There are even more ways, but more complicated.
Hi I have a problem, in my program I have several QLabel and QTextbrowser, at times, I want each of them to display something, but I want to do this through another function called NewMessage. So NewMessage will receive message from QLabel or QTextbrowser, and process them, then display it. But the problem is I don't want to have overloading function for QLabel and QTextBrowser, I want only 1 NewMessage function that can handle message pass in by either QLabel or QTextBrowser(the objects have to pass themselves in as well), how should I do that? Does it has to do with something called casting? Thank you !
I'm not sure I fully understand what you want to achieve. May be you could start by reading Qt documentation about QObject and qobject_cast :
http://doc.qt.io/qt-5/qobject.html#qobject_cast
I have some Qt application with QPlainTextEdit in Tab widget. When try to make a pointer on it
QPlainTextEdit *w = (QPlainTextEdit*)ui->tabWidget->widget(0)
and call a document() method
w->document()
I get a segfault.
But if i call document directly, e.g. ui->mainEdit->document(), then everything works fine.
Can anybody explain me why it happens?
You want to do:
QPlainTextEdit *w = ui->mainEdit;
Then w->document() will return what you want. You are getting the segmentation fault because when you cast ui->tabWidget->widget(0); gives a pointer to a tab page object. When you cast this to QPlainTextEdit* are telling your program to treat a part of memory that does not represent a QPlainTextEdit as a QPlainTextEdit. This causes trouble at the time that you call w->document() because that is in the memory location that it tries to access is not what it would expect from memory which belongs to QPlainTextEdit.
i'm almost sure, that ui->tabWidget->widget(0) return container widget inside of tabWidget. Try qDebug() << ui->tabWidget->widget(0)->metaObject()->className() and see what is printed. It's probably just "QWidget" not "QPlainTextEdit". Your edit is inside of layout of this widget
You can use qobject_cast to make sure that it returns the right type.
QPlainTextEdit *w = qobject_cast<QPlainTextEdit*>(ui->tabWidget->widget(0));
if (w)
{
...
}
It'll return 0 if the type is not of QPlainTextEdit*.
As stated, widget(0) is probably not returning what you wanted - and probably contains a container or some other item, and is probably not the way you want to be accessing your widgets unless there is no other way.