Labels are used a lot in Gtk2Hs, and are relatively simple. Labels emit no
signals as they do not have an associated X window. If you need to catch
signals, or do clipping, place it inside an
which allows you to catch signals for widgets which do not have their own
window, or a button.
To create a new label, use:
labelNew :: Maybe String -> IO Label labelNewWithMnemonic :: String -> IO Label
With the second function, if characters in the string are preceded by an
underscore, they are underlined. If you need a literal underscore character in
a label, use "__" (two underscores). The first underlined character represents
a keyboard accelerator called a mnemonic. When that key is pressed the
activable widget which contains the label (e.g. a button) will be activated.
The widget which is to be affected can also be set by
To change the label's text after creation, or to get the label's text, use the functions:
labelSetText :: LabelClass self => self -> String -> IO () labelGetLabel :: LabelClass self => self -> IO String
or, of course, the generic
get functions. The
space needed for the new string will be automatically adjusted if needed. You
can produce multi-line labels by putting line breaks in the label string. If
you have multi-line labels the lines can be justified relatively to each other
labelSetJustify :: LabelClass self => self -> Justification -> IO ()
where the type
Justification has one of four constructors:
The label widget is also capable of line wrapping the text automatically. This can be activated using:
labelSetLineWrap :: LabelClass self => self -> Bool -> IO ()
If you want your label underlined, then you can set a pattern on the label:
labelSetPattern :: LabelClass self => self -> [Int] -> IO ()
The list of
Ints marks the underlined parts of the label text
alternated by the non-interlined parts. For example, [3, 1, 3] means
first three characters underlined, the next not, and the next three underlined.
You can also make text in a label selectable, so the user can copy and paste it, and use some formatting options.
Below is a short example to illustrate a few of these functions. It makes use
Frame widget to better demonstrate the label styles. A
Frame is just an ornament like a
HSeparator and a
VSeparator but it surrounds the widget and is an instance of
Container. Therefore the widget it frames must be added to it with
containerAdd. A frame itself can have a label to convey
information about its contents.
Because all the labels are framed, a function
is defined, which returns a tuple. Gtk2Hs is truly Haskell, so you can use all
the Haskell data types and features. The justifications are pretty obvious, but
they only refer to the lines inside the label. So, to right justify
label2 itself, you need
miscSetAlignment as shown
below. The last two widgets in the left horizontal box are packed with
boxPackEnd instead of the usual
button label demonstrates the use of a mnemonic as an accellerator key.
Pressing Alt-C on the keyboard has the same effect as clicking
Note: When tested on Fedora 6, pressing Enter or the space bar also had this effect. Also note the effect of the character "y" on the placement of the underline.
import Graphics.UI.Gtk main:: IO () main = do initGUI window <- windowNew set window [windowTitle := "Labels", containerBorderWidth := 10] mainbox <- vBoxNew False 10 containerAdd window mainbox hbox <- hBoxNew True 5 boxPackStart mainbox hbox PackNatural 0 vbox1 <- vBoxNew False 10 vbox2 <- vBoxNew False 0 boxPackStart hbox vbox1 PackNatural 0 boxPackStart hbox vbox2 PackNatural 0 (label1,frame1) <- myLabelWithFrameNew boxPackStart vbox1 frame1 PackNatural 0 labelSetText label1 "Penny Harter" (label2,frame2) <- myLabelWithFrameNew boxPackStart vbox1 frame2 PackNatural 0 labelSetText label2 "broken bowl\nthe pieces\nstill rocking" miscSetAlignment label2 0.0 0.0 hsep1 <- hSeparatorNew boxPackStart vbox1 hsep1 PackNatural 10 (label3,frame3) <- myLabelWithFrameNew boxPackStart vbox1 frame3 PackNatural 0 labelSetText label3 "Gary Snyder" (label4,frame4) <- myLabelWithFrameNew boxPackStart vbox1 frame4 PackNatural 0 labelSetText label4 "After weeks of watching the roof leak\nI fixed it tonight\nby moving a single board" labelSetJustify label4 JustifyCenter (label5,frame5) <- myLabelWithFrameNew boxPackStart vbox2 frame5 PackNatural 0 labelSetText label5 "Kobayashi Issa" (label7,frame7) <- myLabelWithFrameNew boxPackEnd vbox2 frame7 PackNatural 0 labelSetText label7 "only one guy and\nonly one fly trying to\nmake the guest room do" labelSetJustify label7 JustifyRight (label6,frame6) <- myLabelWithFrameNew boxPackEnd vbox2 frame6 PackNatural 10 labelSetText label6 "One Guy" frameSetLabel frame6 "Title:" labelSetPattern label6 [3, 1, 3] button <- buttonNew boxPackEnd mainbox button PackNatural 20 buttonlabel <- labelNewWithMnemonic "Haiku _Clicked" containerAdd button buttonlabel widgetShowAll window onClicked button (putStrLn "button clicked...") onDestroy window mainQuit mainGUI myLabelWithFrameNew :: IO (Label,Frame) myLabelWithFrameNew = do label <- labelNew Nothing frame <- frameNew containerAdd frame label frameSetShadowType frame ShadowOut return (label, frame) -- Haikus quoted from X.J. Kennedy, Dana Gioia, Introduction to Poetry, Longman, 1997