Qt – How to make a QVector of widgets

qtqt4qvectorqwidget

How do I make a QVector (or some other container class) of a dynamic number of widgets, such as QPushButton or QComboBox in Qt 4?

I've used the following in my window class's constructor:

QVector<QComboBox*> foo; // Vector of pointers to QComboBox's

And now I want to fill it with some number of controls which can change dynamically:

for(int count = 0; count < getNumControls(); ++count) {
    foo[count] = new QComboBox();
}

I've searched for hours trying to find the answer to this. The Qt forums mention making a QPtrList, but that class no longer exists in Qt4.
I'd later try to get the text value from each using array-style indexing or the .at() function.

I would really appreciate an example of declaring, initializing, and populating any data structure of any QWidgets (QComboBox, QPushButton, etc.)

Best Answer

here you go :)

#include <QWidget>
#include <QList>
#include <QLabel>
...
QList< QLabel* > list;
...

list << new QLabel( parent, "label 1" );
..
..

foreach( QLabel* label, list )  {
label->text();
label->setText( "my text" );
}

If you are trying just to get a simple example to work, its important that your widgets have a parent (for context / clean up) purposes.

Hope this helps.

1. Modern C++20 solution

auto cmp = [](int a, int b) { return ... };
std::set<int, decltype(cmp)> s;

We use lambda function as comparator. As usual, comparator should return boolean value, indicating whether the element passed as first argument is considered to go before the second in the specific strict weak ordering it defines.

Online demo

2. Modern C++11 solution

auto cmp = [](int a, int b) { return ... };
std::set<int, decltype(cmp)> s(cmp);

Before C++20 we need to pass lambda as argument to set constructor

Online demo

3. Similar to first solution, but with function instead of lambda

Make comparator as usual boolean function

bool cmp(int a, int b) {
    return ...;
}

Then use it, either this way:

std::set<int, decltype(cmp)*> s(cmp);

Online demo

or this way:

std::set<int, decltype(&cmp)> s(&cmp);

Online demo

4. Old solution using struct with `()` operator

struct cmp {
    bool operator() (int a, int b) const {
        return ...
    }
};

// ...
// later
std::set<int, cmp> s;

Online demo

5. Alternative solution: create struct from boolean function

Take boolean function

bool cmp(int a, int b) {
    return ...;
}

And make struct from it using std::integral_constant

#include <type_traits>
using Cmp = std::integral_constant<decltype(&cmp), &cmp>;

Finally, use the struct as comparator

std::set<X, Cmp> set;

Online demo

Best Answer

Related Solutions

Qt – How to Clear all the Widgets in Parent Widgets

C++ – Using custom std::set comparator

1. Modern C++20 solution

2. Modern C++11 solution

3. Similar to first solution, but with function instead of lambda

4. Old solution using struct with () operator

5. Alternative solution: create struct from boolean function

Related Topic

4. Old solution using struct with `()` operator