QGridLayout, 3 panes, not expanding properly

Question

I'm trying to layout a window (all in code) with a QGridLayout. I can add widgets to the layout and they display in my window, but I can't figure out how to resize them properly. Here's what I'd like

[Leftmost][--------Center---------][Rightmost]

Those are the 3 "panes" of my window (all three of them lists). The left and right ones should be of a static width and hug their respective sides, and the center should expand to fill the width as the window grows (or shrinks).

Some code:

// Create the subviews, add them to a grid layout, and set the layout to the window.
QTableView *list = new QTableView(0);
list->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
QTableView *flashList = new QTableView(0);
flashList->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

QPushButton *infoButton = new QPushButton("Info!");
QPushButton *flashFeedsButton = new QPushButton("Flashfeeds");

QGridLayout *gridLayout = new QGridLayout;



// Set the minimum widths for all three columns of the grid
gridLayout->setColumnMinimumWidth(GridColumnFirst, 300);
gridLayout->setColumnMinimumWidth(GridColumnSecond, 300);
gridLayout->setColumnMinimumWidth(GridColumnThird, 300);

// Set the minimum heights for all rows of the grid
int headerFooterHeight = 44;
gridLayout->setRowMinimumHeight(GridRowFirst, headerFooterHeight);
gridLayout->setRowMinimumHeight(GridRowSecond, 200);
gridLayout->setRowMinimumHeight(GridRowThird, headerFooterHeight);


// Set the stretch factors
gridLayout->setColumnStretch(GridColumnFirst, 1);
gridLayout->setColumnStretch(GridColumnFirst, 2);
gridLayout->setColumnStretch(GridColumnThird, 1);

gridLayout->addWidget(list, 1, 0, Qt::AlignLeft);
gridLayout->addWidget(flashList, 1, 1, Qt::AlignCenter);
gridLayout->addWidget(infoButton, 0, 3, Qt::AlignRight);
gridLayout->addWidget(flashFeedsButton, 0, 1, Qt::AlignLeft);

_mainWindow->setLayout(gridLayout);

(As you might be able to tell, this is going to eventually be a 9x9 grid, but the point remains, I'm trying to get my middle row (GridRowSecond) to have the stretchy columns).

The rows themselves expand just fine. The problem seems to be getting the widgets at each cell to expand to take up their containing space. How do I do this? (also, vertically, my list is expanding properly, but not horizontally).

Answer 1

Look at the docs on QGridLayout::AddWidget:

The default alignment is 0, which means that the widget fills the entire cell.

But you have the following:

gridLayout->addWidget(list, 1, 0, Qt::AlignLeft);
gridLayout->addWidget(flashList, 1, 1, Qt::AlignCenter);
gridLayout->addWidget(infoButton, 0, 3, Qt::AlignRight);
gridLayout->addWidget(flashFeedsButton, 0, 1, Qt::AlignLeft);

Thus, you've specifically told the grid layout that you want your widget aligned to the left, center, right, and left of their cells, respectively. In your case you probably want to use the default alignment allowing the widgets to fill the cells and follow their own respective size policies.

Answer 2

It should just be a matter of setting the proper size policy on your widgets. So the buttons on the left and right:

button->setSizePolicy( QSizePolicy::Fixed, QSizePolicy::Fixed );

and for the middle button

button->setSizePolicy( QSizePolicy::Expanding, QSizePolicy::Fixed );

where the first argument defines the horizontal size policy and the second one defines the vertical size policy.

See the size policy documentation as well

Answer 3

You have a lot of variables going here (different widgets, different size policies on widgets, and size policies working on the layout itself, so it's a bit difficult to know where things are going wrong. A couple of suggestions:

1) First try to accomplish what you want with just one type of widget. For example, all QLabels with all Expanding size policies. 2) Only adjust the size policies of the widgets, I found that adding stuff in the grid layout starts making things confusing. The stretch factor for the widget's size policy should work fine. 3) Don't be afraid to try different ratios for stretch factors.

I've found that this is one of the things where Qt Designer (Creator) is helpful for puzzling these things out. It's much faster to adjust things in Designer and resize then the run compile cycle. After you have solved the issue there, you can take the properties you have found and put it in your code instead of a edit, compile, run.