for loop application

[cooper]

Hi everyone,

I have a question about the for() loop function in Qt.
in my program, i have 10 labels, which indicate 10 led lights.
I can change the color for each label by using:

ui->label_led_1->setPixmap(picLedRed);
ui->label_led_2->setPixmap(picLedRed);
...

ui->label_led_1->setPixmap(picLedRed);
ui->label_led_2->setPixmap(picLedRed);
...

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I wonder how can i use the For() loop to simplify the code.
ex:

for (int i = 1; i <=10; i ++)
   ui->label_led_i->setPixmap(picLedRed);

for (int i = 1; i <=10; i ++)
   ui->label_led_i->setPixmap(picLedRed);

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Can any one tell me how i can increment the label number i, please?

Thanks in advance.

[helloworld]

Try this:

for (int i = 1; i <= 10; i++)
{
    QLabel *label = qFindChild<QLabel *>(this, "label_led_" + QString::number(i));
    if (label) { label->setPixmap(picLedRed); }
}

for (int i = 1; i <= 10; i++)
{
    QLabel *label = qFindChild<QLabel *>(this, "label_led_" + QString::number(i));
    if (label) { label->setPixmap(picLedRed); }
}

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Edit: (or replace 'this' with a pointer to the MainWindow if the loop is in another class)

[tbscope]

Or put your labels in a list.

example:

QList<QLabel*> myLedLabels;
myLedLabel->append(ui->label_led_1);
// do append for all your led labels
 
for (int i = 0; i < 10; ++i)
{
    myLedLabels.at(i).setPixmap(picLedRed);
}

QList<QLabel*> myLedLabels;
myLedLabel->append(ui->label_led_1);
// do append for all your led labels

for (int i = 0; i < 10; ++i)
{
    myLedLabels.at(i).setPixmap(picLedRed);
}

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[Lykurg]

I would probably also take the way with qFindChild. But to avoid to call qFindChild ten times, one could use

QList<QLabel*> labels = qFindChildren<QLabel*>(this, QRegExp("^label_led_[0-9]+$"));

QList<QLabel*> labels = qFindChildren<QLabel*>(this, QRegExp("^label_led_[0-9]+$"));

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[wysota]

If I have 10 labels added with designer then I would construct a function or a macro and copy&paste the code ten times instead of creating artificial lists. Unless of course you intend to reuse the list multiple times for other purposes.

[stampede]

Another way (if you have numbered your labels starting from 0):

#include <boost/preprocessor.hpp>
 
#define TO_REPEAT(z,count,action) _ui->label_led_ ## count -> action ;
 
// and use it like:
 
QPixmap pixmap(":/pic.jpg");
BOOST_PP_REPEAT(10, TO_REPEAT, setPixmap(pixmap) );
 
// expands to :
_ui->label_led_0->setPixmap(pixmap);
_ui->label_led_1->setPixmap(pixmap);
// ...
_ui->label_led_9->setPixmap(pixmap);

#include <boost/preprocessor.hpp>

#define TO_REPEAT(z,count,action) _ui->label_led_ ## count -> action ;

// and use it like:

QPixmap pixmap(":/pic.jpg");
BOOST_PP_REPEAT(10, TO_REPEAT, setPixmap(pixmap) );

// expands to :
_ui->label_led_0->setPixmap(pixmap);
_ui->label_led_1->setPixmap(pixmap);
// ...
_ui->label_led_9->setPixmap(pixmap);

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[cooper]

Thanks for you all. I really appreciate you guys' help. I will give it a try