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Thread: Connect lambda, sender argument must be string from array

  1. #1
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    Default Connect lambda, sender argument must be string from array

    How can I send a string from an array with connect using the lambda-notation? I want to send btnTest[pagecounter-1] as the first argument of the connect, but the compiler says 'no matching function for call to ...'

    Qt Code:
    1. btnTest = new QPushButton[pagecounter];//("G", this);
    2. btnTest[pagecounter-1].setMaximumSize(QSize(20,20));
    3.  
    4. btnTest[pagecounter-1].setObjectName(QString::number(pagecounter-1));
    5.  
    6. top->addWidget(groupBox);
    7. top->addWidget(btnTest, pagecounter-1);
    8. top->maximumSize();
    9.  
    10. mainLayout->addLayout(top);
    11.  
    12. QVBoxLayout *vbox = new QVBoxLayout;
    13. groupBox->setLayout(vbox);
    14.  
    15. connect(btnTest[pagecounter-1], &QPushButton::clicked, [=] {
    16. emit systembutton_clicked(btnTest[pagecounter-1].objectName().toInt(), 1, vbox);
    17. });
    To copy to clipboard, switch view to plain text mode 
    Last edited by bchinfosieeuw; 24th December 2016 at 22:52.

  2. #2
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    Default Re: Connect lambda, sender argument must be string from array

    Ok, second attempt at replying.

    Is your intent to emit another signal from your slot (that is lambda)?

    If so, I would create local variables for the ones you want to use (capture) in the body of the lambda. Warning: with [=] you are capturing by value!!

  3. #3
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    Default Re: Connect lambda, sender argument must be string from array

    Your lambda syntax is wrong. It needs to be a functor:

    Qt Code:
    1. connect(btnTest[pagecounter-1], &QPushButton::clicked, [=] () {
    2. emit systembutton_clicked(btnTest[pagecounter-1]->objectName().toInt(), 1, vbox);
    To copy to clipboard, switch view to plain text mode 

    Note the parentheses following the [=]. And btnTest[pagecounter-1] is a pointer to QPushButton so needs to be dereferenced with pointer syntax.

    Warning: with [=] you are capturing by value!!
    Should not matter in this case, since the arguments in the lambda are pointers.
    <=== The Great Pumpkin says ===>
    Please use CODE tags when posting source code so it is more readable. Click "Go Advanced" and then the "#" icon to insert the tags. Paste your code between them.

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    Default Re: Connect lambda, sender argument must be string from array

    Good point! Missed the pointer aspect with my quick perusal.

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    Default Re: Connect lambda, sender argument must be string from array

    Also, from the previous thread, you don't need the emit, systembutton_clicked() is a method.

    And, again also from the previous thread, are you sure you want to create an array every time the slot is called and only initialize the last entry?

    Cheers,
    _

  6. #6
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    Default Re: Connect lambda, sender argument must be string from array

    I would like to initialize all the arrays in the for loop. Can you tell me how to do that?

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    Default Re: Connect lambda, sender argument must be string from array

    Maybe something like:

    Qt Code:
    1. for ( int i = 0; i < pagecounter; i++ )
    2. {
    3. // initialize btnTest[i]
    4. }
    To copy to clipboard, switch view to plain text mode 

    You should have learned that in the first couple of weeks of your C++ class...
    <=== The Great Pumpkin says ===>
    Please use CODE tags when posting source code so it is more readable. Click "Go Advanced" and then the "#" icon to insert the tags. Paste your code between them.

  8. #8
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    Default Re: Connect lambda, sender argument must be string from array

    What I really want to do is disable the btnTest buttons when they are clicked a couple of times. But after invoking
    Qt Code:
    1. void MyWidget::onaddbutton_clicked()
    2. {
    To copy to clipboard, switch view to plain text mode 
    a second time, and then clicking on the old btnTest button of the first time, they do not get disabled. Any ideas of how to do this?

    The disabling methods are placed here:
    Qt Code:
    1. void MyWidget::systembutton_clicked(int j, int k, QVBoxLayout *vbox)
    2. {
    3. ...
    4. if(...){
    5. btnTest[j].setEnabled(false);
    To copy to clipboard, switch view to plain text mode 

  9. #9
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    Default Re: Connect lambda, sender argument must be string from array

    According to the btnTest2[i].isEnabled() function the button is disabled, but in the program the btnTest2[i] remains clickable.

  10. #10
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    Default Re: Connect lambda, sender argument must be string from array

    You onaddbutton_clicked() creates a new array of buttons every time, maybe you disabled only one of these sets.

    Cheers,
    _

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