Exploring QHeaderView::length() in Qt for Header Sizing

Purpose

• Returns the total length of the header along its orientation (horizontal or vertical). In simpler terms, it provides the width if the header is horizontal and the height if it's vertical.

Context: QHeaderView Class

• QHeaderView is a class in Qt Widgets that represents a generic header for views like tables or trees. It offers functionalities like managing sections, sorting indicators, and resizing behavior.

How it Works

• When you call length() on a QHeaderView object, it calculates the total size based on the individual sections and their sizes.

Things to Consider

• This function works in conjunction with other QHeaderView properties like setSectionResizeMode(), which determines how sections respond to resizing, and offset(), which provides the visible offset of the header.

Example

Imagine you have a horizontal header (QHeaderView::Horizontal) in a table with three sections of widths 100px, 150px, and 200px respectively. Calling length() on the header would return the total width, which is 450px (100px + 150px + 200px).

• If you're working with Python bindings like PySide2, you'll find similar usage patterns for QHeaderView and length().

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Example 1: Getting the Total Width of a Horizontal Header

#include <QApplication>
#include <QHeaderView>

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

  // Create a horizontal header
  QHeaderView header(Qt::Horizontal);

  // Set section sizes
  header.resizeSection(0, 100);
  header.resizeSection(1, 150);
  header.resizeSection(2, 200);

  // Get the total length (width)
  int totalWidth = header.length();

  qDebug() << "Total width of the header:" << totalWidth;

  return app.exec();
}

This code creates a horizontal header, assigns specific widths to three sections, and then uses length() to retrieve the total width of the header, which will be 450 (100 + 150 + 200).

Example 2: Checking if the Header Fits Available Space

#include <QApplication>
#include <QHeaderView>

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

  // Create a horizontal header
  QHeaderView header(Qt::Horizontal);

  // Set section sizes
  header.resizeSection(0, 100);
  header.resizeSection(1, 150);
  header.resizeSection(2, 200);

  // Get the total length (width)
  int totalWidth = header.length();

  // Simulate available space
  int availableSpace = 300;

  if (totalWidth <= availableSpace) {
    qDebug() << "Header fits the available space";
  } else {
    qDebug() << "Header needs more space: " << totalWidth << " vs " << availableSpace;
  }

  return app.exec();
}

This code builds upon the previous example but adds a check to see if the total header width (totalWidth) fits within a simulated available space (availableSpace). It demonstrates how length() can be used to manage header sizing in your application.

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Iterating Through Sections

• Accumulate the section sizes in a variable to get the total length.
• For each section, use sectionSize() to get the individual width (horizontal) or height (vertical).
• Loop through all sections in the QHeaderView using a for loop and count().

This approach offers more granular control if you need to process section sizes individually.

Using visualRect()

• Access the width() or height() of the rectangle depending on the header orientation to get the total length.
• This function returns a QRect representing the visible rectangle of the header.
• Call visualRect() on the header object.

This method is useful if you only care about the visible portion of the header, considering scrollbars or hidden sections.

int totalLength = 0;
for (int i = 0; i < header.count(); ++i) {
  totalLength += header.sectionSize(i);
}