CODEWITHSUNDEEP
qtqwidgetqlabel
Laurent Crivello
Laurent Crivello

Reputation: 3931

QLabel does not display in QWidget

I have the following hierarchy in my Qt Application: QMainWindow > QWidget (centralWidget) > QWidget (subclassed) > QLabel

Initialization code in my QMainWindow code:

centralWidget = new QWidget();
centralWidget->setGeometry(0,0,width,height);
chatWidget=new ChatWidget(this); // the subclassed QWidget
setCentralWidget(centralWidget);

In my subclassed QWidget initialization (which happens at the same time than the Qt App initialization) I have the following code:

ChatWidget::ChatWidget(QWidget *parent):QWidget(parent)
{
    QLabel  *lbl;
    lbl=new QLabel(this);
    lbl->setText("Hello World 1"); <-- Is properly Display
}

void ChatWidget::displayChatAfterButtonPressed()
{
    QLabel *lbl;
    lbl=new QLabel(this);
    lbl->setText("Hello World 2"); <-- Does NOT appear
}

When the QLabel is added from the class initialization then the message is well displayed in the widget.

However when I launch the same code after a button pressed (via a function in the same QWidget subclass), then the text does not appear on screen.

I don't want to use layouts as I need to exactly position my labels.

Tried to repaint, but didn't help neither.

How can I properly and dynamically display a label after the initialization is done ?

Upvotes: 3

Views: 9024

Answers (2)

Mohammad Kanan
Mohammad Kanan

Reputation: 4582

We need to show the label created by button click, cause centralwidget was already painted. Here is a working example, I added this as answer also I noticed better adding chatWidget as child to centralWidget where in your original code its added to the UI .. this is your choice.

Mainwindow:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    //
    ui->setupUi(this);
    centralWidget = new QWidget();
    centralWidget->setGeometry(width,height);
    chatWidget=new ChatWidget(centralWidget); // the subclassed QWidget
    setCentralWidget(centralWidget);

    // added testing
    QPushButton *btn = new QPushButton("MyButton",centralWidget);
    btn->setGeometry(100,100,100,100);
    btn->setMaximumSize(100,100);
    connect(btn,&QPushButton::clicked, chatWidget, &ChatWidget::displayChatAfterButtonPressed);
 }

and chatWidget:

ChatWidget::ChatWidget(QWidget *parent):QWidget(parent)
{
    QLabel  *lbl;
    lbl=new QLabel(this);
    lbl->setText("Hello World 1");
}

void ChatWidget::displayChatAfterButtonPressed()
{
    QLabel *lbl;
    lbl=new QLabel(this);
    lbl->setText("Hello World 2");
    lbl->show();
}

Upvotes: 1

eyllanesc
eyllanesc

Reputation: 243897

Widgets when they are visible for the first time call to be visible to their children, but since you are creating it afterwards they probably are not calling that method, a possible solution is to call the show method.

void ChatWidget::displayChatAfterButtonPressed()
{
    QLabel *lbl;
    lbl=new QLabel(this);
    lbl->setText("Hello World 2");
    lbl->show();
}

comment: it seems strange to me that the QMainWindow you set a central widget and then create the chatWidget as a parent to the QMainWindow, it is generally not recommended to add children to the QMainWindow because it has a given structure, what should be done is to place it inside the centralwidget.

Upvotes: 6

Related Questions