QGridLayout issue with inserting widgets

(Using Qt 4.6.3, x64, linux)

I'm testing how to properly insert widgets into a existing a QGridLayout filled with various widgets. A broken down contrived case is the following:

QApplication app(argc,argv);
QWidget      w;
QGridLayout* gl     = new QGridLayout(&w);
QLabel*      label  = new QLabel("Image Size:");
QLineEdit*   wedit  = new QLineEdit("100");
QLabel*      xlabel = new QLabel("x");

wedit->setAlignment(Qt::AlignRight);
gl->addWidget(label);
gl->addWidget(xlabel, 0, 1, 1, 1);
gl->addWidget(wedit,  0, gl->columnCount());

Which creates the following widget:

.

Assuming that have an existing QGridLayout as above, but without the "x" label, and I wished to insert this into the layout, switching the latter two addWidget lines might seem valid, i.e.:

\\ same as above
gl->addWidget(label);
gl->addWidget(wedit,  0, gl->columnCount());
gl->addWidget(xlabel, 0, 1, 1, 1);

This however, creates the following:

The gl->columnCount() after this is still 2, as both the x-label and the QLineEdit are filling the same cell. Based on this knowledge, the following code produces the initial desired result:

gl->addWidget(label);
gl->addWidget(wedit,  0, 2); // note: specified column 2, columnCount() is now 3
gl->addWidget(xlabel, 0, 1, 1, 1);

Though this is not particularly useful, as the original layout in question isn't built with later layouts in mind.

Since addWidget allows for specifying cell position, as well as row/column span, it seems odd that Qt wouldn't automatically replace the existing widgets in the layout. Does anyone have a suggestion as to how I might overcome this? I assume it would be possible to recreate a QGridLayout and copy into it the chi开发者_Python百科ldren of the original, taking care to insert the additional widget in the right location. This however is ugly, and susceptible to Qt version issues (as I want to modify a built in widget).

Edit:

I realize that I'm making the assumption of thinking in a QHBoxLayout way, where inserting a widget is uniquely understood, whereas in a QGridLayout this isn't the case (?).

I can clarify that I ultimately would like to modify QFileDialog::getSaveFileName, by inserting a widget (similar to the widget shown above) right above the two lower rows (i.e. above "File &Name:").

Thanks

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Switching the latter two addWidget lines is not valid. For the following code:

gl->addWidget(label);
gl->addWidget(wedit,  0, gl->columnCount());
gl->addWidget(xlabel, 0, 1, 1, 1);

The arguments for the addWidget() calls are evaluated prior to adding the widget. Therefore, gl->columnCount() evaluates to one instead of two for the second call, since the column still has to be created. You are effectively adding two widgets to column one.

---

A possible solution is to re-add the widgets that should be relocated. I.e.

QLayoutItem* x01 = gl->itemAtPosition(0,1);
gl->addWidget(x01->widget(), 0, 2);
gl->addWidget(xlabel, 0, 1, 1, 1);

Now, this isn't particularly pretty, or easy to maintain, as a new version of Qt might change the original widget, and blindly handpicking and relocating children isn't that clever. The following real example (the one I actually wanted to solve) was to alter the Qt's "Save As" dialog window, that shows up using QFileDialog::getSaveFileName.

class ImageFileDialog : public QFileDialog {
public:
  ImageFileDialog(QWidget* parent);
  ~ImageFileDialog();
  QString getFileName() const;
  QSize getImageSize() const;
  QDialog::DialogCode exec(); // Overriden

protected:
  void showEvent(QShowEvent* event); // Overriden

private:
  QString    fileName_;
  QSize      imageSize_;
  QLineEdit* widthLineEdit_;
  QLineEdit* heightLineEdit_;
};

And in the source (showing just constructor, focus handling and exec):

ImageFileDialog::ImageFileDialog(QWidget* parent)
  : fileName_(""),
    imageSize_(0,0),
    widthLineEdit_(0),
    heightLineEdit_(0)
{
  setAcceptMode(QFileDialog::AcceptSave);
  setFileMode(QFileDialog::AnyFile);
  setConfirmOverwrite(true);

  QGridLayout* mainLayout = dynamic_cast<QGridLayout*>(layout());
  assert(mainLayout->columnCount() == 3);
  assert(mainLayout->rowCount()    == 4);

  QWidget*     container      = new QWidget();
  QGridLayout* glayout        = new QGridLayout();
  QLabel*      imageSizeLabel = new QLabel("Image Size:");
  widthLineEdit_              = new QLineEdit("400");
  heightLineEdit_             = new QLineEdit("300");
  widthLineEdit_->setAlignment(Qt::AlignRight);
  heightLineEdit_->setAlignment(Qt::AlignRight);

  container->setLayout(glayout);
  glayout->setAlignment(Qt::AlignLeft);
  glayout->addWidget(widthLineEdit_);
  glayout->addWidget(new QLabel("x"), 0, 1);
  glayout->addWidget(heightLineEdit_, 0, 2);
  glayout->addWidget(new QLabel("[pixels]"), 0, 3);
  glayout->addItem(new QSpacerItem(250, 0), 0, 4);
  glayout->setContentsMargins(0,0,0,0); // Removes unwanted spacing

  // Shifting relevant child widgets one row down.
  int rowCount = mainLayout->rowCount();
  QLayoutItem* x00 = mainLayout->itemAtPosition(mainLayout->rowCount()-2,0);
  QLayoutItem* x10 = mainLayout->itemAtPosition(mainLayout->rowCount()-1,0);
  QLayoutItem* x01 = mainLayout->itemAtPosition(mainLayout->rowCount()-2,1);
  QLayoutItem* x11 = mainLayout->itemAtPosition(mainLayout->rowCount()-1,1);
  QLayoutItem* x02 = mainLayout->itemAtPosition(mainLayout->rowCount()-1,2);
  assert(x00);   assert(x01);   assert(x10);   assert(x11);   assert(x02);

  mainLayout->addWidget(x00->widget(), rowCount-1, 0, 1, 1);
  mainLayout->addWidget(x10->widget(), rowCount,   0, 1, 1);
  mainLayout->addWidget(x01->widget(), rowCount-1, 1, 1, 1);
  mainLayout->addWidget(x11->widget(), rowCount,   1, 1, 1);
  mainLayout->addWidget(x02->widget(), rowCount-1, 2, 2, 1);

  // Adding the widgets in the now empty row.
  rowCount        = mainLayout->rowCount();
  mainLayout->addWidget(imageSizeLabel, rowCount-3, 0, 1, 1 );
  mainLayout->addWidget(container,      rowCount-3, 1, 1, 1);

  // Setting the proper tab-order
  QLayoutItem* tmp  = mainLayout->itemAtPosition(mainLayout->rowCount()-2,1);
  QLayoutItem* tmp2 = mainLayout->itemAtPosition(mainLayout->rowCount()-1,1);
  assert(tmp); assert(tmp2);
  QWidget::setTabOrder(heightLineEdit_      , tmp->widget());
  QWidget::setTabOrder(tmp->widget(), tmp2->widget());
}

// Makes sure the right widget is in focus
void ImageFileDialog::showEvent(QShowEvent* event)
{
  widthLineEdit_->setFocus(Qt::OtherFocusReason);
}

// Called to create the widget
QDialog::DialogCode ImageFileDialog::exec()
{
  if (QFileDialog::exec() == QDialog::Rejected)
    return QDialog::Rejected;
  // The code that processes the widget form and stores results for later calls to
  // getImageSize()
  return QDialog:Accepted;
}

Which, using for instance

ImageFileDialog* dialog = new ImageFileDialog(&w);
dialog->exec();

Creates the following widget:

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Comments and ways to do this better, or why this is just plain wrong are most welcome :)