Q:

How do you equally space out elements in a Row?

Row{
    width: parent.width
    spacing: ????
    Checkbox{}
    Checkbox{}
    Checkbox{}
    Checkbox{}
}

So just to be clear, the checkboxes should be spaced in such a manner that however wide the row is, it will expand or compress the spacing in accordance to this.

A:

The simplest solution would be to set width: parent.width/4 for each of the checkboxes.  If you want to keep the checkbox width set at some known value, you could instead set spacing: (parent.width - 4 * checkboxwidth)/3 on the Row.  Note that this will cause the elements to overlap when the parent is narrow.
If you're targeting Qt 5.1 or higher, you may want a RowLayout.  I'm still on 5.0, though, so I can't help you there.
Yet another way to do this would to be to put each CheckBox in an Item.  Each Item would have width: parent.width/4, and each CheckBox would have anchors.centerIn: parent.  This would give a half-width margin on the far left and far right, which may or may not be desired.

