Beyond QFileSystemModel::headerData(): Alternative Approaches for File System View Headers in Qt

• Return Value
  A QVariant containing the data based on the requested role.

• Parameters
  

  • section: The index of the header section (usually a column number).
  • orientation: Specifies horizontal (Qt::Horizontal) or vertical (Qt::Vertical) header.
  • role (optional): Defines the type of data requested (default: Qt::DisplayRole - for displaying text). Common roles include:
    • Qt::DisplayRole: Text displayed in the header.
    • Qt::TextAlignmentRole: Alignment of the text (e.g., Qt::AlignLeft).
    • Qt::DecorationRole: (For QFileSystemModel, currently not well-supported)

• Purpose
  Provides data for the headers in a file system view (e.g., column names in a table view).

Key Points

• You can't directly change the header labels using headerData().
• By default, QFileSystemModel provides text labels like "Name", "Size", etc., for horizontal headers and doesn't offer customization for decoration (icons).

Customizing Headers

If you want to modify the header labels or add icons:

1. Subclass QFileSystemModel
   Create a new class inheriting from QFileSystemModel.
2. Override headerData()
   Implement your own logic in the overridden function to return the desired data (text or icon) based on the role.

---

Subclassing QFileSystemModel

#include <QFileSystemModel>

class MyFileSystemModel : public QFileSystemModel {
  Q_OBJECT

public:
  explicit MyFileSystemModel(QObject* parent = nullptr) : QFileSystemModel(parent) {}

  QVariant headerData(int section, Qt::Orientation orientation, int role) const override {
    if (role == Qt::DisplayRole && orientation == Qt::Horizontal) {
      switch (section) {
        case 0:
          return tr("Custom Name");  // Change "Name" to "Custom Name"
        case 1:
          return tr("File Size");    // Change default "Size" to "File Size"
        default:
          return QFileSystemModel::headerData(section, orientation, role);
      }
    }
    return QFileSystemModel::headerData(section, orientation, role);
  }
};

• For other roles or sections, we call the base class implementation using QFileSystemModel::headerData().
• Based on the section (column number), we return custom text for the first two columns.
• We check for Qt::DisplayRole and Qt::Horizontal orientation (for horizontal headers).
• The headerData() function is overridden.
• We create a new class MyFileSystemModel inheriting from QFileSystemModel.

Using the Custom Model

#include <QApplication>
#include <QTreeView>

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

  // Create the custom model
  MyFileSystemModel model;
  model.setRootPath(QDir::currentPath());  // Set the starting directory

  // Create a tree view
  QTreeView treeView;
  treeView.setModel(&model);
  treeView.show();

  return app.exec();
}

• This will display the file system with custom labels for the first two columns.
• We create a QTreeView and set the custom model using setModel().
• We set the root path for the model using setRootPath().
• We create an instance of MyFileSystemModel.

1. Save the code in separate files (e.g., myfilesystemmodel.cpp and main.cpp).
2. Include necessary Qt libraries while compiling (-lQtGui etc.).
3. Run the compiled application.

---

1. Subclassing QAbstractItemModel
   

• This approach gives you complete control over both item and header data.
• Within data(), you can check for specific roles (like Qt::DisplayRole) and sections to return custom data for headers.
• Implement all abstract methods like data(), rowCount(), columnCount(), etc., to handle retrieving data for both items and headers.
• You create a new class inheriting from QAbstractItemModel.
• This is a more flexible approach but requires more work.

1. Using a Custom Delegate
   

• However, it might be less efficient for large datasets compared to a custom model.
• This offers more control over the visual appearance of the headers.
• You can override the paint() function of the delegate to draw custom headers with desired text and icons.
• A delegate controls how data is displayed in the view.
• This approach involves creating a custom delegate class for your tree view.

1. Third-Party Models
   

• However, it introduces additional dependencies and might have limitations compared to the Qt framework's models.
• This can be a quicker solution if it meets your specific needs.
• Some third-party libraries might offer file system models with built-in header customization options.

• Evaluate third-party models only if they offer specific functionalities not available in Qt's built-in models.
• If the visual style is a priority, consider using a custom delegate.
• For more complex customization or complete control over data, subclassing QAbstractItemModel is a better option.
• If you need simple header label changes, overriding headerData() in a subclass might suffice.