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Thread: QPushButton invoking setText fails

  1. #1
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    Default QPushButton invoking setText fails

    I'm trying to set text of a push button by invoking its method via QMetaObject::invokeMethod but failing to achieve any successful results. I have tried it with some other widgets and they seem to work fine. Would appropriate any suggestions, kinda stuck here and googling is not helping. Here is the code:

    Qt Code:
    1. // w is QMainWindow
    2.  
    3. QWidget* label = w.findChild<QLabel*>("label");
    4. ((QLabel*)label)->setText("text old"); // works fine
    5. bool res_label = QMetaObject::invokeMethod(label, "setText", Q_ARG(QString, "text new")); // works fine, returns true
    6.  
    7. QWidget* lineEdit = w.findChild<QLineEdit*>("lineEdit");
    8. ((QLineEdit*)lineEdit)->setText("text old"); // works fine
    9. bool res_line_edit = QMetaObject::invokeMethod(lineEdit, "setText", Q_ARG(QString, "text new")); // works fine, returns true
    10.  
    11. QWidget* textBrowser = w.findChild<QTextBrowser*>("textBrowser");
    12. ((QTextBrowser*)textBrowser)->setText("text old"); // works fine
    13. bool res_text_browser = QMetaObject::invokeMethod(textBrowser, "setText", Q_ARG(QString, "text new")); // works fine, returns true
    14.  
    15. QWidget* pushButton = w.findChild<QPushButton*>("pushButton");
    16. ((QPushButton*)pushButton)->setText("text old"); // works fine
    17. bool res_push_button = QMetaObject::invokeMethod(pushButton, "setText", Q_ARG(QString, "text new")); // NOT WORKING, RETURNS FALSE
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    I tried all connection types (Qt::DirectConnection, Qt::QueuedConnection, Qt::BlockingQueuedConnection, Qt::AutoConnection). Also setText is defined as a public slot in the first three widgets but is defined as a public function in the QPushButton, is it possible that it might be the cause of the problem?

  2. #2
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    Default Re: QPushButton invoking setText fails

    That is right, QMetaObject::invokeMethod() works on signals, slots and invokable methods, not on properties (such as text for QPushButton). For the latter you can use a combination of QMetaObject::indexOfProperty(), QMetaObject::property(), and QMetaProperty::write().

  3. The following user says thank you to yeye_olive for this useful post:

    bokadam (25th June 2012)

  4. #3
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    Default Re: QPushButton invoking setText fails

    Thanks yeye, it worked like a charm. Here is the working code:

    Qt Code:
    1. QWidget* pushButton = w.findChild<QPushButton*>("pushButton");
    2. int propertyIndex = pushButton->metaObject()->indexOfProperty("text");
    3. QMetaProperty property = pushButton->metaObject()->property(propertyIndex);
    4. bool res = property.write(pushButton, "text new 2"); // works fine, returns true
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  5. #4
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    Default Re: QPushButton invoking setText fails

    Quote Originally Posted by yeye_olive View Post
    That is right, QMetaObject::invokeMethod() works on signals, slots and invokable methods, not on properties (such as text for QPushButton). For the latter you can use a combination of QMetaObject::indexOfProperty(), QMetaObject:roperty(), and QMetaProperty::write().
    Or just QObject::setProperty()
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  6. #5

    Default Re: QPushButton invoking setText fails

    HI ,
    Facing an issue for passing a pointer as QARG in invokeMethod :

    I am calling the api void CAppManager::launchUrl(const int f_iXcoord,const int f_iYcoord,const int f_iHeight, const int f_iWidth,const QString f_cobjUrl,unsigned long *f_ulRenHandle,bool bSetupURL) as

    QMetaObject::invokeMethod(this,"launchUrl",Qt::Que uedConnection,
    Q_ARG(int,0),Q_ARG(int,0),Q_ARG(int,480),Q_ARG(int ,800),Q_ARG(QString,sSetUpURL),Q_ARG(unsigned long*,handle),Q_ARG(bool,true));

    The issue seems to be with ARG f_ulRenHandle . As when the function had this argument only as pass by value and in InvokeMethod I had passed just Q_ARG(unsigned long,handle) instead of Q_ARG(unsigned long*,handle).It worked.
    handle here has to be pointer or refrence as its getting modified in launchURL API .Here I am using pointer as we can't use Refrences with Q_ARG.Here invoke method is always returning 0.
    I am initializing/declaring handle as follows :
    unsigned long dummyHandle=0;
    unsigned long * handle = &dummyHandle;
    Please let me know what measure should i take to solve this issue ?

  7. #6
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    Default Re: QPushButton invoking setText fails

    You should not be passing pointers or references. It is better to use a signal-slot connection that will give you the result.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

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