[SOLVED] QLayout does not work -> experimental Graph like widget

jjan

Currently I try to add buttons (here nodes) to an widget. My code looks like this:

GraphWidget::GraphWidget(QWidget *parent)
				: QWidget(parent)
	{
		/* Load style */
		QFile stylefile(":/styles/src/nitro/node_graph/style.qss");
		stylefile.open(QFile::ReadOnly);
		QString stylestring = QLatin1String(stylefile.readAll());
		setStyleSheet(stylestring);
		/* Set context menu */
		setContextMenuPolicy(Qt::CustomContextMenu);
		connect(this, SIGNAL(customContextMenuRequested(QPoint)), SLOT(customMenuRequested(QPoint)));
		/* Set layout */
		layout = new QLayout(this);
		setLayout(layout);
	}

and for adding the "node":

void GraphWidget::addEmptyEntry(QString *NITRO_OBJECT_NAME)
	{
		Node *n = new Node();
		n->setText(*NITRO_OBJECT_NAME);
		n->move(click_pos);
		layout->addWidget(n);
	}

But what I get is an error I do not really understand (because Qt documentation means I need to insert my widget there):

../src/nitro/node_graph/graph_widget.cpp:46:28: error: invalid new-expression of abstract class type 'QLayout'
   layout = new QLayout(this);
                            ^

How can I fix this (and I don't want to use an NodeGraph library, I want to build it as my own)?

~jan

Chris Kawa

As the error says QLayout is an abstract base class. You can't instantiate it.
Use one of the derived sub-classes like QHBoxLayout, QGridLayout etc.

jjan

@Chris-Kawa

Thanks for this. I understand now what the problem is, but is there an other widget where I can get something like this (adding Buttons to an widget, position is random so no HBox or centralWidget)?

Chris Kawa

If you want to position children within a widget manually then don't use layouts at all. Also move() does nothing when widget is managed by a layout.
So just add a child and set its geometry manually:

...
   /* DON'T set layout */
   //layout = new QLayout(this);
   //setLayout(layout);
}

void GraphWidget::addEmptyEntry(const QString& WHATS_WITH_THE_CAPS) { //don't pass QString as pointer
   Node* n = new Node(this); //important to pass "this" as parent
   n->setText(WHATS_WITH_THE_CAPS);
   n->move(click_pos); // is click_pos some sort of global? better make that function argument
   n->show(); // widgets not managed by layout are not shown by default so this is required
}

jjan

@Chris-Kawa click_pos is global because an other void will set the point of it (when User makes right click the position will saved). But does show()really works here? I tried it sometimes but it shows the button in a new window.

Chris Kawa

show() will make a widget a new top level window when it has no parent or has a dialog flag set. That's why I marked setting parent ("this") as important.
As for the click_pos- still. It would make the function reusable and more maintainable if you passed the position as an argument, and not rely on a piece of outside state. For example if later you would like to add entries "from code" and not by user interaction you could pass a position to the function. Right now you would have to "simulate click" by writing to click_pos before you call addEmptyEntry, which can have other side effects if you use it somewhere else. Bad practice.

jjan

@Chris-Kawa
Sorry that was my problem didn't have seen the comment^^ Thank you :)