The base of all widgets here is a vertical box, which itself is a child of the
window. The child widgets are not displayed homogeneously and there is no
additional spacing (other than the standard spacing). There are six horizontal
boxes in the vertical box, as defined by the function
which has the type as shown. Furthermore, there are two labels in the vertical
box as well as two horizontal separators. The last widget is the Quit
onClicked signal is attached to the
The separators are created with
hSeparatorNew and they are spaced
boxPackStart with a padding of ten pixels. The labels are
labelNew which takes a
Maybe String and
their positioning is set by
miscSetAlignment to be left and top
makeBox :: Bool -> Int -> Packing -> Int -> IO
HBox demonstrates how Gtk2Hs widgets fit into the Haskell type system.
Packing is just a type like
IO HBox is just like
IO String in the usual
IO. The function creates five buttons, labels them with the
appropriate text and packs them into a horizontal box. The function is then
used in the main program to create the desired ways of packing.
import Graphics.UI.Gtk main :: IO () main = do initGUI window <- windowNew vbox <- vBoxNew False 0 set window [containerBorderWidth := 10, windowTitle := "Packing Demonstration", containerChild := vbox] label1 <- labelNew (Just "hBoxNew False 0") miscSetAlignment label1 0 0 boxPackStart vbox label1 PackNatural 0 box1 <- makeBox False 0 PackNatural 0 boxPackStart vbox box1 PackNatural 0 box2 <- makeBox False 0 PackRepel 0 boxPackStart vbox box2 PackNatural 0 box3 <- makeBox False 0 PackGrow 0 boxPackStart vbox box3 PackNatural 0 sep1 <- hSeparatorNew boxPackStart vbox sep1 PackNatural 10 label2 <- labelNew (Just "hBoxNew True 0") miscSetAlignment label2 0 0 boxPackStart vbox label2 PackNatural 0 box4 <- makeBox True 0 PackNatural 0 boxPackStart vbox box4 PackNatural 0 box5 <- makeBox True 0 PackRepel 0 boxPackStart vbox box5 PackNatural 0 box6 <- makeBox False 0 PackGrow 0 boxPackStart vbox box6 PackNatural 0 sep <- hSeparatorNew boxPackStart vbox sep PackNatural 10 quitbox <- hBoxNew False 0 boxPackStart vbox quitbox PackNatural 0 quitbutton <- buttonNewWithLabel "Quit" boxPackStart quitbox quitbutton PackRepel 0 onClicked quitbutton mainQuit onDestroy window mainQuit widgetShowAll window mainGUI makeBox :: Bool -> Int -> Packing -> Int -> IO HBox makeBox homogeneous spacing packing padding = do box <- hBoxNew homogeneous spacing button1 <- buttonNewWithLabel "boxPackStart" boxPackStart box button1 packing padding button2 <- buttonNewWithLabel "box" boxPackStart box button2 packing padding button3 <- buttonNewWithLabel "button" boxPackStart box button3 packing padding button4 <- case packing of PackNatural -> buttonNewWithLabel "PackNatural" PackRepel -> buttonNewWithLabel "PackRepel" PackGrow -> buttonNewWithLabel "PackGrow" boxPackStart box button4 packing padding button5 <- buttonNewWithLabel (show padding) boxPackStart box button5 packing padding return box
The image below shows the effects of resizing the window horizontally. In the first group, with homogeneous set to False horizontal resizing leaves the first row of buttons as it is, spaces the second row evenly, and enlarges the buttons in the third row. In the second group the buttons are set to be packed homogeneously, and the first two rows will look the same. Resizing the window vertically just adds extra space at the end, because the vertical box was initialized with False.