How to show a text for 3 sec?

MasterBlade

I want to show a qlabel for 3 sec and used the following code. The label is initially hidden.

ui->qlabel->show();
QThread::sleep(3);
ui->qlabel->hide();

But the label didn't show up at all. I tried to comment ui->qlabel->hide(); and the label appeared after 3 sec waiting. What's wrong with these steps?

Gojir4

Hi,
By using QThread::sleep(), you are blocking the event loop, which can cause the effect you are describing.

Do that instead:

ui->qlabel->show();
QTimer::singleShot(3000, ui->qlabel, &QWidget::hide);

You should avoid as much as possible usage of QThread::sleep(), QThread::msleep() or QThread::usleep() from the GUI (main) thread, try to use signal & slots or QTimer to make this kind of behavior to keep you application responsive and avoid "freezing" of the window.

MasterBlade

@Gojir4 said in How to show a text for 3 sec?:

Hi,
By using QThread::sleep(), you are blocking the event loop, which can cause the effect you are describing.

Do that instead:
ui->qlabel->show();
QTimer::singleShot(3000, ui->qlabel, &QWidget::hide);
You should avoid as much as possible usage of QThread::sleep(), QThread::msleep() or QThread::usleep() from the GUI (main) thread, try to use signal & slots or QTimer to make this kind of behavior to keep you application responsive and avoid "freezing" of the window.

This worked perfectly. Thanks so much!

I have another question. Is it possible to set a fade effect when the label is hiding or showing?

jsulm

@MasterBlade See http://doc.qt.io/qt-5/animation-overview.html

Gojir4

I think this should do the job (not tested and compiled):

//mywidget.h
QPropertyAnimation *m_animation;

//mywidget.cpp
//Constructor
void MyWidget::MyWidget(QWidget *parent) 
    : QWidget(parent), ui(new Ui::MyWidget)
{
    //...    
    m_animation = new QPropertyAnimation(ui->qlabel, "windowOpacity", this);    
    //See QPropertyAnimation documentation for more parameters
    m_animation->setDuration(1000);    
    m_animation->setStartValue(0.0);
    m_animation->setEndValue(1.0);
    //...
}

void MyWidget::showLabel(int duration)
{   
    ui->qlabel->setWindowOpacity(0.0);
    ui->qlabel->show();
    m_animation->setDirection(QPropertyAnimation::Forward);
    m_animation->start();    
    //Ensure it's visible with 100% opacity at least 1 sec. 
    QTimer::singleShot(qMax(2000, duration), this, &MyWidget::hideLabel);
}

void MyWidget::hideLabel()
{
    m_animation->setDirection(QPropertyAnimation::Backward);
    m_animation->start();
    QTimer::singleShot(m_animation.duration(), ui->qlabel, &QWidget::hide);
}