Text is not updated in qwidget.



  • I created qwidget in qmainwindow, and then qwidget on it.
    However, Text is not updated in the top QWidget.

    I have done a great deal of effort to solve this problem, but it has not been solved.
    I've tried everything, including repaint, update, processEvents, but I still have problems.
    Also, I tried with other widgets such as qlabel, lcd number, text edit,
    The text was not updated.

    Label_SetVal->setText(SetValue);
    /*
    qApp->processEvents();
    qApp->sendPostedEvents();
    qApp->processEvents(QEventLoop::ExcludeUserInput);
    Label_SetVal->repaint();
    Label_SetVal->parentWidget()->repaint();
    Label_SetVal->update();
    Label_SetVal->parentWidget()->update();
    */


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    Can you show how you initialise Label_SetVal ?
    Where exactly are you calling setText on it ?



  • @SGaist said in Text is not updated in qwidget.:

    Can you show how you initialise Label_SetVal ?
    Where exactly are you calling setText on it ?

    Thank you for your reply.
    source code---------------------------------------------------------------------------
    char keypadBuf[30] = {0,};
    QLabel* Label_SetVal ;

    Label_SetVal = ui->lb_NetSetVal;

    sprintf((char *)keypadBuf, "%s.%d", QByteArray(Label_SetVal ->text().toLocal8Bit()).data(),val);
    SetValue = QString(keypadBuf);
    Label_SetVal ->setText(SetValue);

    //qApp->processEvents();
    //qApp->sendPostedEvents();
    //qApp->processEvents(QEventLoop::ExcludeUserInput);
    //LB_SetVal->repaint();
    //LB_SetVal->parentWidget()->repaint();
    //LB_SetVal->update();
    //LB_SetVal->parentWidget()->update();

  • Moderators

    @sootoo23 said in Text is not updated in qwidget.:

    sprintf((char *)keypadBuf, "%s.%d", QByteArray(Label_SetVal ->text().toLocal8Bit()).data(),val);

    Wow, this looks really complicated.
    Why not just use QString::arg(...)?

    SetValue = QString("%1.%2").arg(Label_SetVal ->text()).arg(val);
    


  • @jsulm

    I need to pass the char buffer of "keypadBuf" to the C library.
    It can not pass in the type of QString.


  • Moderators

    @sootoo23

    keypadBuf = SetValue.toLocal8Bit().data();
    


  • @jsulm
    Thank you for your feedback.
    Is there a solution to my problem?


  • Moderators

    @sootoo23 Is this label visible? Does it already have any text? Also, what are you doing after setting the text - do you maybe block the event loop with a loop?
    Did you check what SetValue contains?



  • @jsulm said in Text is not updated in qwidget.:

    Is this label visible? Does it already have any text? Also, what are you doing after setting the text - do you maybe block the event loop with a loop?
    Did you check what SetValue contains?

    yes, it is visible.

    The default text is displayed when you load the initial QWidget.
    The problem is that if you change the value by the number of characters, it will not update.

    "printf("%s (%s)\n", keypadBuf, SetValue.toLocal8Bit().data());"
    data is output well.


  • Moderators

    @sootoo23 Do you block the event loop somewhere?



  • @jsulm

    I do not know what blocking an event loop is.


  • Moderators

    @sootoo23 Do you have any endless loops?



  • @jsulm
    Yes, i have endless loop.
    I’m using tow QTimers.


  • Moderators

    @sootoo23 Endless loops are a bad idea when using event driven frameworks like Qt...



  • @jsulm
    Instead of a regular endless loop,
    Is it also a problem when using QTimer?

    Also, how does the endless loop relate to the problem of not updating the text?



  • @jsulm

    I tried to remove the endless loop,
    but The problem was not solved.


  • Moderators

    @sootoo23 Endless loops block the Qt event loop. If this event loop is blocked no signals are emitted and no events are handled - the UI is not updated. I don't know what the problem with your code is as I don't have it.


  • Lifetime Qt Champion

    Can you show the latest complete version of that part of your code ?

    With only I removed something and it still doesn't work, there's no way to debug your problem.



  • @SGaist

    ------------mainwindow.cpp------------
    MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
    {
    ...
    ...
    #if (0)
    //Removed endless loop timer
    Hometimer = new QTimer(this);
    connect(Hometimer, SIGNAL(timeout()),this,SLOT(HomeInfo_Update()));
    Hometimer->start(1000);
    #endif
    }
    void MainWindow::HomeInfo_Update()
    {
    ...
    ...
    ui->lb_HomeClk->setText(QString(TimeBuf));
    ...
    }

    ------------menuQwidget.cpp------------
    wnd_menu::wnd_menu(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::wnd_menu)
    {
    ...
    ...
    #if (0)
    //Removed endless loop timer
    Menu_Timer = new QTimer;
    connect(Menu_Timer, SIGNAL (timeout()), this, SLOT(MenuInfo_Update()));
    Menu_Timer->start(1000);
    Menu_Timer->blockSignals(true);
    #endif
    }

    void wnd_menu::MenuInfo_Update()
    {
    ...
    ...
    ui->lb_MenuClk->setText(QString(TimeBuf));
    ...
    ...
    }


  • Moderators

    @sootoo23

    • Are the slots you connected to the timers called?
    • Is TimeBuf set when these slots are called?

    //Removed endless loop timer - this is not the kind of endless loop I mentioned. It is fine to use timers this way. The problem is somewhere else. You need to debug your app or upload the code to somewhere so we can take a look.



  • @sootoo23 Both, setText functions does not get called at all. Hence, text is not displayed.

    And I don't know why 'blocksignals' function is used here.



  • This post is deleted!

  • Moderators

    @kumararajas said in Text is not updated in qwidget.:

    And I don't know why 'blocksignals' function is used here.

    Wow, I didn't notice at all!

    @sootoo23 Why do you block the timer signals? This way you cannot expect the signals to be emitted and the slots called!

    Menu_Timer->blockSignals(true); // WHY?
    


  • @jsulm @kumararajas
    The main problem is not a block signal.
    The Timer is already blocked from use.

    Timer has nothing to do with the problem.

    The code that I uploaded is the code that removed the infinite loop (timer).

    Mainwindow.cpp -> menuQwidget->show();
    menuQwidget.cpp -> Dialog_Keypad->exec();

    ------------DialogKeypad.cpp------------
    my problem... not updated >>>>> LB_SetVal->setText(SetValue);



  • @jsulm @kumararajas
    ------------mainwindow.cpp------------
    MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
    {
    ...
    ...
    #if (0)
    //Removed endless loop timer
    Hometimer = new QTimer(this);
    connect(Hometimer, SIGNAL(timeout()),this,SLOT(HomeInfo_Update()));
    Hometimer->start(1000);
    #endif
    }
    void MainWindow::HomeInfo_Update()
    {
    ...
    ...
    ui->lb_HomeClk->setText(QString(TimeBuf));
    ...
    }

    ------------menuQwidget.cpp------------
    wnd_menu::wnd_menu(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::wnd_menu)
    {
    ...
    ...
    #if (0)
    //Removed endless loop timer
    Menu_Timer = new QTimer;
    connect(Menu_Timer, SIGNAL (timeout()), this, SLOT(MenuInfo_Update()));
    Menu_Timer->start(1000);
    Menu_Timer->blockSignals(true);
    #endif
    }

    void wnd_menu::MenuInfo_Update()
    {
    ...
    ...
    ui->lb_MenuClk->setText(QString(TimeBuf));
    ...
    ...
    }

    ------------DialogKeypad.cpp------------
    Dialog_Keypad::Dialog_Keypad(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog_Keypad)
    {
    ui->setupUi(this);

    QString img_path = "/images/Keypad.jpg";
    QImage img(img_path);    
    QPixmap buf = QPixmap::fromImage(img);    
    QGraphicsScene* MenuScene = new QGraphicsScene;
    
    ui->KeypadFrame->setScene(MenuScene);
    MenuScene->addPixmap(buf);
    
    //text color setting
    QPalette* palette = new QPalette();
    palette->setColor(QPalette::WindowText,Qt::yellow);
    ui->lb_SettingValue->setPalette(*palette);	
    
    
    connect(ui->Keypad_Num0, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num1, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num2, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num3, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num4, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num5, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num6, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num7, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num8, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num9, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Dot,  SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    
    KeyPadMapper.setMapping(ui->Keypad_Num0, 0);
    KeyPadMapper.setMapping(ui->Keypad_Num1, 1);
    KeyPadMapper.setMapping(ui->Keypad_Num2, 2);
    KeyPadMapper.setMapping(ui->Keypad_Num3, 3);
    KeyPadMapper.setMapping(ui->Keypad_Num4, 4);
    KeyPadMapper.setMapping(ui->Keypad_Num5, 5);
    KeyPadMapper.setMapping(ui->Keypad_Num6, 6);
    KeyPadMapper.setMapping(ui->Keypad_Num7, 7);
    KeyPadMapper.setMapping(ui->Keypad_Num8, 8);
    KeyPadMapper.setMapping(ui->Keypad_Num9, 9);
    KeyPadMapper.setMapping(ui->Keypad_Dot, 100);
    
    connect(&KeyPadMapper, SIGNAL(mapped(int)), this, SLOT(SetKeypadData(int)));
    

    }

    void Dialog_Keypad::SetKeypadData(int val)
    {
    char keypadBuf[30] = {0,};
    QLabel* LB_SetVal;

    if(CurKeypadType == KEYPAD_NORMAL)
    	LB_SetVal = ui->lb_SettingValue;
    else if(CurKeypadType == KEYPAD_NETWORK)
    	LB_SetVal = ui->lb_NetSetVal;
    else if(CurKeypadType == KEYPAD_PASSWORD)
    	LB_SetVal = ui->lb_PWSetVal;
    else 
    	LB_SetVal = ui->lb_SettingValue;
    
    if(CurKeypadType == KEYPAD_PASSWORD)
    {
    	if(LB_SetVal->text().size() > 3)
    	{
    		printf("[%s] Password Length Over. :%s \n", __FUNCTION__, QByteArray(LB_SetVal->text().toLocal8Bit()).data());
    		return;
    	}
    	
    	SetValue = SetValue + QString::number(val);
    	sprintf((char *)keypadBuf, "%s%s", QByteArray(LB_SetVal->text().toLocal8Bit()).data(), "*");
    	LB_SetVal->setText(QString(keypadBuf));
    	return;
    }
    else if(CurKeypadType == KEYPAD_NETWORK)
    {
    	if(LB_SetVal->text().size() > 14)
    	{
    		printf("[%s] Network Setting Str Length Over.\n", __FUNCTION__);
    		return;
    	}
    	
    	if(val == 100) //dot.
    		sprintf((char *)keypadBuf, "%s%s", QByteArray(LB_SetVal->text().toLocal8Bit()).data(),".");
    	else if((LB_SetVal->text().size() == 3)
    			|| (LB_SetVal->text().size() == 7)
    			|| (LB_SetVal->text().size() == 11))
    		sprintf((char *)keypadBuf, "%s.%d", QByteArray(LB_SetVal->text().toLocal8Bit()).data(),val);
    	else
    		sprintf((char *)keypadBuf, "%s%d", QByteArray(LB_SetVal->text().toLocal8Bit()).data(),val);
    }
    else
    {		
    	if(val == 100) //dot.
    		sprintf((char *)keypadBuf, "%s%s", QByteArray(LB_SetVal->text().toLocal8Bit()).data(),".");
    	else
    		sprintf((char *)keypadBuf, "%s%d", QByteArray(LB_SetVal->text().toLocal8Bit()).data(),val);
    }
    
    SetValue = QString(keypadBuf);
     My Problem >> LB_SetVal->setText(SetValue);
    
    //qApp->processEvents();
    //qApp->sendPostedEvents();
    //qApp->processEvents(QEventLoop::ExcludeUserInput);
    //LB_SetVal->repaint();
    //LB_SetVal->parentWidget()->repaint();
    //LB_SetVal->update();
    //LB_SetVal->parentWidget()->update();
    
    printf("[%s] %s\n", __FUNCTION__, keypadBuf);
    

    }



  • @sootoo23 Maybe you're doing the mapping wrong? I don't use it often, once in years I believe. So I'm not sure.

    Since I'm assuming your running Qt 5.X try it with lambdas

    replace

    connect(ui->Keypad_Num0, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num1, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num2, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num3, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num4, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num5, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num6, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num7, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num8, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Num9, SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    connect(ui->Keypad_Dot,  SIGNAL(clicked()), &KeyPadMapper, SLOT(map()));
    
    KeyPadMapper.setMapping(ui->Keypad_Num0, 0);
    KeyPadMapper.setMapping(ui->Keypad_Num1, 1);
    KeyPadMapper.setMapping(ui->Keypad_Num2, 2);
    KeyPadMapper.setMapping(ui->Keypad_Num3, 3);
    KeyPadMapper.setMapping(ui->Keypad_Num4, 4);
    KeyPadMapper.setMapping(ui->Keypad_Num5, 5);
    KeyPadMapper.setMapping(ui->Keypad_Num6, 6);
    KeyPadMapper.setMapping(ui->Keypad_Num7, 7);
    KeyPadMapper.setMapping(ui->Keypad_Num8, 8);
    KeyPadMapper.setMapping(ui->Keypad_Num9, 9);
    KeyPadMapper.setMapping(ui->Keypad_Dot, 100);
    
    connect(&KeyPadMapper, SIGNAL(mapped(int)), this, SLOT(SetKeypadData(int)));
    

    with

    connect(ui->Keypad_Num0, QPusButton::clicked, this, [=]{SetKeypadData(0);});
    connect(ui->Keypad_Num1, QPusButton::clicked, this, [=]{SetKeypadData(1);});
    connect(ui->Keypad_Num2, QPusButton::clicked, this, [=]{SetKeypadData(2);});
    connect(ui->Keypad_Num3, QPusButton::clicked, this, [=]{SetKeypadData(3);});
    connect(ui->Keypad_Num4, QPusButton::clicked, this, [=]{SetKeypadData(4);});
    connect(ui->Keypad_Num5, QPusButton::clicked, this, [=]{SetKeypadData(5);});
    connect(ui->Keypad_Num6, QPusButton::clicked, this, [=]{SetKeypadData(6);});
    connect(ui->Keypad_Num7, QPusButton::clicked, this, [=]{SetKeypadData(7);});
    connect(ui->Keypad_Num8, QPusButton::clicked, this, [=]{SetKeypadData(8);});
    connect(ui->Keypad_Num9, QPusButton::clicked, this, [=]{SetKeypadData(9);});
    connect(ui->Keypad_Dot,  QPusButton::clicked, this, [=]{SetKeypadData(100);});
    


  • @J.Hilk said in Text is not updated in qwidget.:

    @sootoo23 Maybe you're doing the mapping wrong? I don't use it often, once in years I believe. So I'm not sure.
    Since I'm assuming your running Qt 5.X try it with lambdas
    replace

    mapping is not wrong.
    The function connected is called well and the output from the function is coming out well.



  • @sootoo23 you're going through a loot of loops to create your QString,
    are you sure that QString(keypadBuf) returns a valid QString? and not an empty one for example?

    as a side not this one, for example could be reduced

    {		
    if(val == 100) //dot.
    	sprintf((char *)keypadBuf, "%s%s", QByteArray(LB_SetVal->text().toLocal8Bit()).data(),".");
    else
    	sprintf((char *)keypadBuf, "%s%d", QByteArray(LB_SetVal->text().toLocal8Bit()).data(),val);
    }
    SetValue = QString(keypadBuf);
    LB_SetVal->setText(SetValue);
    
    //to
    QString str = LB_SetVal->text() + val == 100 ? "." : QString::number(val);
    
    LB_SetVal->setText(str);
    


  • @J.Hilk
    The value is always good.
    The problem is that settext can not be updated even if you put any value.



  • @sootoo23 said in Text is not updated in qwidget.:

    @J.Hilk
    The value is always good.
    The problem is that settext can not be updated even if you put any value.

    I'm sorry, but the problem is with 99.9% certainty not the setText function I would say 1 of 4 things is the case:

    • LB_SetVal is invalid or wrong. Doubtful because you say you calculate the correct value
    • SetValue = QString(keypadBuf); returns an invalid or incorrect string. You can test this by setting a breakpoint and debuging, or printing SetValue to the console. e.g qDebug() << SetValue;
    • You're blocking the event loop and your ui doesnt get updated
    • Maybe you have set bool QObject::blockSignals(bool block) to true somewhere that is messing things up

    also, what Qt-Version and compiler is this btw?



  • @J.Hilk

    I found something strange.
     After changing the data to "Settext", execute hide () on the QWidget and show () again.
     I confirmed that it was updated.

    1. LB_SetVal is always good.
      -> printf("LB_SetVal: %s, KeypadBuf: %s \n", QByteArray(LB_SetVal->text().toLocal8Bit()).data(),keypadBuf);
    2. I removed all blockSignals.
      -> The QWidget in problem has no Timer and no BlockSignal.

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