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Thread: QTime

  1. #1
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    Default QTime

    Hello anyone,

    I ám a newbie,
    I have a question about QTime and QTimer.
    I have read the posts in the forum about QTime and Qtimer but it gives me not the solution that i want.

    I want to countdown the Time(not the currentTime)in lcdNumber. Example(05:00:00->04:59:59...)
    Is it possible to do it in QTime ?.


    See my implentation:
    Qt Code:
    1. countdownDialog::countdownDialog(QWidget *parent)
    2. :QDialog(parent)
    3.  
    4. {
    5.  
    6. setupUi(this);
    7.  
    8.  
    9. QTimer *timer = new QTimer(this);
    10. connect(timer, SIGNAL(timeout()), this, SLOT(displayTime()));
    11. timer->start(1000);
    12.  
    13. }
    14. void countdownDialog::displayTime()
    15. {
    16. QTime *time = new QTime();
    17. time->setHMS(5,0,0,0);
    18. lcdNumber->display(time->toString());
    19.  
    20. }
    21.  
    22. Thanks in advance.
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  2. #2
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    Default Re: QTime

    Let's start with fixing an obvious memory leak. Here "time" is allocated on the heap but never deleted:
    Quote Originally Posted by dragon View Post
    Qt Code:
    1. void countdownDialog::displayTime()
    2. {
    3. QTime *time = new QTime();
    4. time->setHMS(5,0,0,0);
    5. lcdNumber->display(time->toString());
    6. }
    To copy to clipboard, switch view to plain text mode 
    Just for the learning purposes, you should start with rewriting it as:
    Qt Code:
    1. void countdownDialog::displayTime()
    2. {
    3. QTime time;
    4. time.setHMS(5,0,0,0);
    5. lcdNumber->display(time.toString());
    6. }
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    Now, "time" get automatically destructed while going out of scope.

    The next thing is to actually implement some counter functionality. All the above code does is converting the same time (05:00:00) over and over again to a string and setting it to the lcd number widget. You could make the time object a member variable instead and reduce a second every iteration:
    Qt Code:
    1. class countdownDialog
    2. {
    3. ...
    4. private:
    5. QTime time; // declare a member variable
    6. }
    7.  
    8. countdownDialog::countdownDialog(QWidget *parent)
    9. :QDialog(parent)
    10. {
    11. ...
    12. // initialize it to anything you want,
    13. // for example 5 hours as you did before in displayTime()
    14. time = QTime(5, 0, 0, 0);
    15. }
    16.  
    17. void countdownDialog::displayTime()
    18. {
    19. time = time.addSecs(-1); // reduce a second
    20. lcdNumber->display(time.toString());
    21. }
    To copy to clipboard, switch view to plain text mode 
    J-P Nurmi

  3. #3
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    Default Re: QTime

    Thanks J-P Nurmi for advise its works fine now.

  4. #4
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    Default Re: QTime

    A bit more precise solution is to substract the elapsed time from 5 hours every time. It may happen that a timer event gets stalled, so substracting a second every time it is triggered might get your timer out of sync. But if you don't expect a heavy load, it should work fine too.

  5. #5
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    Default Re: QTime

    I have a question i only see the hours, minutes, seconds in the lcdNumber.
    I.don't see the milliseconds.
    Is this depending on the system where the program is running on.
    How can i change the code to see the milliseconds and counting down in lcdNumber.

    thanks in advance.

  6. #6
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    Default Re: QTime

    instead of time.toString() you can build your own representation by using QTime::hour(), minute(), second() and msec().
    Just convert them to QString and concatenate them.

    Regards

  7. #7
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    Default Re: QTime


    That, or:
    Qt Code:
    1. time.toString("hh:mm:ss.zzz");
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    There are other formatters from which you can choose.

    Regards

  8. #8
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    Default Re: QTime

    I see in my lcdNumber the milliseconds but is not counting down only the seconds is counting down.
    Must i time.addMSecs to the code?

  9. #9
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    Default Re: QTime

    You are only reducing the number of seconds so how do you expect anything else to change?

  10. #10
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    Default Re: QTime

    Yes, addMsecs(-x), where x is smaller than 1000, in order to see a difference.

    Regards

  11. #11
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    Default Re: QTime

    Thanks Marcel and Wysota for your advise.

  12. #12
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    Default Re: QTime

    Or try my approach

  13. #13
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    Default Re: QTime

    hello.

    is it possible to add a start, reset and pause button

    but already thank you for what i see here :-)

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