Controlling Horizontal Widget Resizing with QSizePolicy::horizontalStretch() in Qt

• Multiple Widgets with Stretch
  When multiple widgets have set horizontal stretch factors, the available space will be distributed proportionally based on their assigned factors. For example, if one widget has a stretch factor of 2 and another has 1, the first widget will occupy roughly twice the horizontal space as the second.
• Value 0 = No Stretch
  A value of 0 means the widget won't stretch horizontally and will prefer its minimum size.
• Higher Value = More Stretch
  A value greater than 0 indicates the widget's willingness to expand horizontally. The higher the value, the more the widget will try to take up available space compared to other widgets with lower stretch factors.
• Controls Horizontal Resizing
  It sets a factor that determines how much a widget will try to grow horizontally compared to other widgets in the same layout.

Here are some common use cases for horizontalStretch()

• Balancing Space
  Setting appropriate stretch factors helps distribute available space proportionally between widgets in a layout.
• Creating Resizable Areas
  Using stretch factors on multiple widgets helps create resizable interfaces where elements can adapt to different window sizes.
• Filling Empty Space
  Assigning a high stretch factor to a widget allows it to fill any remaining horizontal space in the layout.

1. Get the Size Policy
   Retrieve the current size policy of the widget using widget->sizePolicy().
2. Set the Stretch Factor
   Call policy.setHorizontalStretch(factor) on the retrieved size policy object, where factor is the desired horizontal stretch value.
3. Apply the Policy
   Set the modified size policy back to the widget using widget->setSizePolicy(policy).

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Example 1: Filling Empty Space

This example creates two widgets: a label and a button. The label will have a fixed size, and the button will stretch to fill the remaining horizontal space.

#include <QtWidgets>

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);

  // Create a label with fixed size
  QLabel *label = new QLabel("This is a fixed label");
  label->setFixedSize(100, 30);

  // Create a button that stretches
  QPushButton *button = new QPushButton("Stretch Button");
  QSizePolicy policy = button->sizePolicy();
  policy.setHorizontalStretch(2); // Higher value for more stretch
  button->setSizePolicy(policy);

  // Add widgets to a layout
  QHBoxLayout *layout = new QHBoxLayout;
  layout->addWidget(label);
  layout->addWidget(button);

  // Create a window and set the layout
  QWidget *window = new QWidget;
  window->setLayout(layout);
  window->show();

  return app.exec();
}

Example 2: Balancing Space between Widgets

This example creates two text edit widgets with equal stretch factors. They will resize proportionally within the available horizontal space.

#include <QtWidgets>

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);

  // Create two text edit widgets
  QTextEdit *edit1 = new QTextEdit;
  QTextEdit *edit2 = new QTextEdit;

  // Set equal stretch factors
  QSizePolicy policy;
  policy.setHorizontalStretch(1); // Same value for both edits
  edit1->setSizePolicy(policy);
  edit2->setSizePolicy(policy);

  // Add widgets to a layout
  QHBoxLayout *layout = new QHBoxLayout;
  layout->addWidget(edit1);
  layout->addWidget(edit2);

  // Create a window and set the layout
  QWidget *window = new QWidget;
  window->setLayout(layout);
  window->show();

  return app.exec();
}

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QSizePolicy::Expanding

This setting in the QSizePolicy class allows the widget to expand horizontally to fill available space as much as possible. It achieves a similar effect to a high stretch factor but is simpler to set.

QSizePolicy policy;
policy.setHorizontalPolicy(QSizePolicy::Expanding);
widget->setSizePolicy(policy);

Minimum and Maximum Sizes

By setting the minimum and maximum sizes for a widget using widget->setFixedMinimumSize(QSize) and widget->setFixedMaximumSize(QSize), you can restrict its horizontal growth. This approach provides more control over the exact size range but might be less flexible for dynamic layouts.

Layout Spacers

Qt provides layout spacer widgets like QSpacerItem that can be inserted into layouts to consume extra space. This allows you to control how remaining space is distributed between other widgets without directly setting stretch factors.

Custom Layout Management

For complex layouts, you can implement custom layout classes that handle resizing behavior manually. This gives you the most control but requires more code and might be overkill for simpler scenarios.

• Custom layout classes are suitable for highly customized resizing behavior but require more effort.
• Layout spacers offer flexibility in distributing space without stretch factors.
• For precise size control, consider using minimum and maximum sizes.
• If you simply want a widget to fill available space, QSizePolicy::Expanding is a good choice.