[Qt-interest] Adding widget to QGraphicsView

[John McClurkin]

Yuvaraj R wrote:
>  
>  
> Thanks for your reply..
>  
> I ran my program in  Debugger.. It was hunging.. and complier went to 
> Qlineedit .h line number 268...
>  
> I have used lineedit in my program.. and used properly
>  
> But i don't understand the bug.
>  
> Could explain me.please
The compiler went to Qlineedit.h 268? I assume you mean that the 
debugger went to qlineedit.h 268. If this is a stack trace, then this 
line just the last entry of the trace. Since this is a Qt src file, I 
double strongly that the error is here. The error was triggered by your 
code. You need to examine the stack trace to find the entries that 
identify your code. That said, I would guess that, since the debugger 
stops in qlineedit.h, you are using an invalid pointer to a QLineEdit 
widget.

>  
>  
> Thanks
>  
> Yuvaraj R
> 
> On Wed, Jul 22, 2009 at 5:15 PM, John McClurkin <jwm at nei.nih.gov 
> <mailto:jwm at nei.nih.gov>> wrote:
> 
>     Yuvaraj R wrote:
>      >
>      > What mistake below code.
>      >
>      >  QGraphicsScene *scene= new QGraphicsScene(this);
>      >
>      > ui->graphicsView->setScene(scene);
>      >
>      > ui->graphicsView->setCacheMode(QGraphicsView::CacheBackground);
>      >
>      > Ui_Form *m_ui = new Ui_Form;
>      >
>      > QWidget *wid = new QWidget;
>      >
>      > m_ui->setupUi(wid);
>      >
>      > QGraphicsProxyWidget *proxy = new QGraphicsProxyWidget;
>      >
>      > QLabel *label = new QLabel;
>      >
>      > label->setText("Hello World !!!");
>      >
>      > QPushButton *button = new QPushButton;
>      >
>      > button->setText("dfgdfgdsg");
>      >
>      > label->setGeometry(30,30,40,20);
>      >
>      > QLineEdit *line = new QLineEdit;
>      >
>      > line->setGeometry(0,0,50,50);
>      >
>      > line->setFocus();
>      >
>      > proxy =scene->addWidget(line);
>      >
>      > label->setScaledContents(true);
>      >
>      >
>     QObject::connect(button,SIGNAL(clicked()),this,SLOT(show_message1()));
>      >
>      > proxy = scene->addWidget(button);
>      >
>      > proxy = scene->addWidget(label);
>      >
>      > ui->graphicsView->setBackgroundBrush(Qt::darkCyan);
>      >
>      > ui->graphicsView->setScene(scene);
>      >
>      > void Widget::show_message1()
>      >
>      > {
>      >
>      > QMessageBox::information(0,"",QString(line->text()));
>      >
>      > }
>      >
>      >
>      > When i pressing the button ,application is crashing. if use the base
>      > class slots,it is working..any mistake in above code...
>      >
>      > And one more thing  i want to design the login page ,2 label,2
>     line edit
>      > ,one push button..
>      >
>      > Functionality wise i am strong..But i am struggling with GUi.. I
>     have to
>      > do get rich GUi..
>      >
>      > What are things  i have to use.Good Gui based examples are Welcome
>      >
>      > Please Guide me..
>      >
>      > Thanks
>      >
>      > Yuvaraj R
> 
>     I see this a lot on this news group. Some one has a program that
>     crashes, so they post some code and ask what is wrong with the code. The
>     first thing any one should do when their program crashes is run it in a
>     debugger to get, at the very least, a stack trace. Most often this will
>     show what the problem is. This is much quicker than posting to a news
>     group. So, Yuvaraj, run your program in a debugger, make it crash, and
>     examine the stack trace. Most program crashes are caused by trying to
>     dereference a NULL pointer or trying to access invalid memory.
> 
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>