# arrange Label in parent widget

Transcription

1 Much of today s software uses a point-and-click graphical user interface (GUI). The standard library modules Tkinter and Tix allow for portable, event-driven, GUI development in Python. A Python/Tkinter program is entirely event-driven, i.e., the program construct tailored GUI widgets via inheritence to suit the program s needs, register associated event-handles (call-back functions) with the Python virtual machine, then wait for the user to generate events (e.g., clicking the mouse on, entering some text into a field, typing some key at the keyboard, etc.) that the event-handles react to A very simple example would be to display a Label that s tailored as: from Tkinter import Label # load Label class widget = Label(None, text= Hellow World ) widget.pack() widget.mainloop() # make a customized Label object # arrange Label in parent widget # start event loop of Tkinter This would look slightly different under MAC or Linux operating system, but it would have the same functionality. Conceptually, the mainloop of Tkinter performs the following algorithm: def mainloop(): while the main window has not been closed: if an event has occurred: run the associated event handler function 1. A Button can have an event-handler associated with it (the command argument) that gets called when it is pressed. def myevent(): print "Button Pressed" # load Tkinter root = Tk() # Tk is the main window of program # make a customized Button object mybutton = Button(root, text= press, command=myevent) mybutton.pack(side=bottom, expand=no) # arrange Button in parent root.mainloop() # start event loop of root After running and pressing the button several times, the window containing the button and IDLE window is: Button Pressed Button Pressed Button Pressed Lecture 22 Page 1

2 2. Below is a simple example that constructs a frame and packs two buttons and a label into a frame # Hello_frameB.py class Hello(Frame): # Extend Frame class def init (self, parent=none): Frame. init (self, parent) # call superclass init self.pack() self.data = 0 self.showdatastring = StringVar() # create a String control variable self.showdatastring.set('data = %d' % (self.data)) self.make_widgets() # attach widgets to self def make_widgets(self): Button(self, text='count Clicks', command=self.message).pack(side=left) quitbutton = Button(self, text='quit', command=self.quit) quitbutton.pack(side=bottom) countlabel = Label(self, textvariable=self.showdatastring, width=50, justify=center) countlabel.pack(side=right) def message(self): self.data += 1 self.showdatastring.set('data = %d' % (self.data)) # end class Hello(Frame) Hello().mainloop() Every time the Count Clicks button is pressed, the Data = # label is updated using the control variable, showdatastring. A control variable is a special object that can be shared by several different widgets and updated automatically on the screen by using the.set( value ) method. Control variables also have a.get() method to return its current value. Control variables of type integer and float can be gotten using using the constructors IntVar() and DoubleVar(), respectively. Some examples where you might want to use control variables are: The Entry widget allows you to enter a line of text, which is normally linked to a control variable. A group of radiobuttons normally share a single control variable that allows them to tell which one gets selected and allows it to be cleared. Checkbuttons use a control variable to hold its current state: on or off. Lecture 22 Page 2

3 3. An example using the Entry widget to allow a line of text to be entered is: # EntryTest.py """Test the Entry widget""" self.name = StringVar() self.name.set("enter name here") self.age = IntVar() self.age.set("enter age here") self.textentry = Entry(self, takefocus=1, textvariable = self.name, width = 40) self.textentry.grid(row=0, sticky=e+w) self.ageentry = Entry(self, takefocus=1, textvariable = self.age, width = 20) self.ageentry.grid(row=1, sticky=w) The corresponding window is: The takefocus=1 allows you to <tab> between these items. The.grid() method is a layout manager for your GUI widgets that allows you to treat every window/frame as a two-dimensional grid of rows and columns. The width of a column is the width of its widest cell, similarly for rows. Widgets too small for their cells can expand (or not) by using the sticky option in the.grid() method, and specifying directions (N+S+E+W) for expansion. Widgets can also span multiple cells by specifying rowspan and columnspan options in the.grid() method. Lecture 22 Page 3

4 4. The following code illustrates a Listbox widget that allows election of several lines of text. # ListboxTest.py """Test the Listbox widget with event handling""" self.prompt = Label(self, text="select your favorite animals (select all \ that apply):") self.prompt.grid(row=0, sticky=w+e) self.yscroll = Scrollbar(self, orient=vertical) self.yscroll.grid(row=1, column=1,sticky=n+s) self.xscroll = Scrollbar(self, orient=horizontal) self.xscroll.grid(row=2, column=0,sticky=e+w) self.mylistbox = Listbox(self, xscrollcommand=self.xscroll.set, yscrollcommand=self.yscroll.set, selectmode=multiple) self.mylistbox.grid(row=1, column=0, sticky=n+s+e+w) self.mylistbox.insert(end, 'cat') self.mylistbox.insert(end, 'dog') self.mylistbox.insert(end, 'mouseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee') self.mylistbox.insert(end, 'rat') self.mylistbox.insert(end, 'fish') self.xscroll["command"] = self.mylistbox.xview self.yscroll["command"] = self.mylistbox.yview self.donebutton = Button(self, text='click when \n done', command=self.readselections) self.donebutton.grid(row=3) def readselections(self): selectionstuple = self.mylistbox.curselection() print selectionstuple print "Favorite Animals:" for i in selectionstuple: print i, self.mylistbox.get(i) For the selections shown in the window, the Click when done button causes the following output to IDLE: ('0', '1', '4') Favorite Animals: 0 cat 1 dog 4 fish Lecture 22 Page 4

5 5. The Menubutton and Menu widgets allow you to build pull-down menus, for example: # MenuTest.py """Test the Menu widget with event handling""" self.breadmenubutton = Menubutton(self, text="bread", relief=raised) self.breadmenubutton.grid(row=0, column=0, sticky=n+w+e) self.rowconfigure(0, pad=100) self.breadmenubutton.menu = Menu(self.breadMenubutton, tearoff=0) self.breadmenubutton["menu"] = self.breadmenubutton.menu self.breadvar = StringVar() self.breadmenubutton.menu.add_radiobutton(label="white", variable=self.breadvar) self.breadmenubutton.menu.add_radiobutton(label="wheat", variable=self.breadvar) self.breadmenubutton.menu.add_radiobutton(label="rye", variable=self.breadvar) self.condimentsmenubutton = Menubutton(self, text="condiments", relief=raised) self.condimentsmenubutton.grid(row=0, column=1, sticky=n+w+e) self.condimentsmenubutton.menu = Menu(self.condimentsMenubutton, tearoff=0) self.condimentsmenubutton["menu"] = self.condimentsmenubutton.menu self.mayovar = IntVar() self.ketchupvar = IntVar() self.condimentsmenubutton.menu.add_checkbutton( label="mayo", variable=self.mayovar) self.condimentsmenubutton.menu.add_checkbutton( label="ketchup", variable=self.ketchupvar) self.donebutton = Button(self, text='click when done', command=self.readselections) self.donebutton.grid(row=3, column=0, columnspan=2,sticky=w+e) def readselections(self): print "Bread: ", self.breadvar.get() print "Condiments: ", if self.mayovar.get() == 1: print "mayo", if self.ketchupvar.get() == 1: print "ketchup", print The output of selecting rye and both mayo and ketchup would be: Bread: rye Condiments: mayo ketchup How would you add a Meat Menubutton with selections of beef, ham, turkey, and salami? Lecture 22 Page 5

6 6. A canvas can be used to draw objects and text as in: # CanvasTest.py """Test the Canvas widget and mouse events""" import sys self.dragging = False self.currentshapeid = None # end init self.shapemenubutton = Menubutton(self, text="shape", relief=raised) self.shapemenubutton.grid(row=0, column=0, sticky=n) self.shapemenubutton.menu = Menu(self.shapeMenubutton, tearoff=0) self.shapemenubutton["menu"] = self.shapemenubutton.menu self.shapevar = StringVar() self.shapemenubutton.menu.add_radiobutton( label="oval", command=self.shapeselection, value = "circle", variable=self.shapevar) self.shapemenubutton.menu.add_radiobutton( label="rectangle", command=self.shapeselection, value = "top_left_corner", variable=self.shapevar) self.shapevar.set("circle") self.mycanvas = Canvas(self, cursor=self.shapevar.get(),borderwidth=4, height='5i', width='7i') self.mycanvas.grid(row=1, column=0, columnspan=2) self.mycanvas.bind("<button-1>", self.startshape) self.mycanvas.bind("<motion>", self.sizeshape) self.mycanvas.bind("<buttonrelease-1>", self.endshape) self.donebutton = Button(self, text='click when done', command=self.doneselections) self.donebutton.grid(row=3, column=0, columnspan=2,sticky=w+e) # end createwidgets def shapeselection(self): print "Shape selected:", self.shapevar.get() self.mycanvas["cursor"] = self.shapevar.get() # end shapeselection def startshape(self, event): print "startshape: shape =", self.shapevar.get(),"x =", event.x, "y =", event.y self.dragging = True if self.shapevar.get() == "circle": self.currentshapeid = self.mycanvas.create_oval(event.x, event.y, event.x, event.y) elif self.shapevar.get() == "top_left_corner": self.currentshapeid = self.mycanvas.create_rectangle(event.x, event.y, event.x, event.y) # end startshape (Continued on Next Page) Lecture 22 Page 6

7 def sizeshape(self, event): if self.dragging: oldcoords = self.mycanvas.coords(self.currentshapeid) self.mycanvas.delete(self.currentshapeid) if self.shapevar.get() == "circle": self.currentshapeid = self.mycanvas.create_oval(oldcoords[0], oldcoords[1], event.x, event.y) elif self.shapevar.get() == "top_left_corner": self.currentshapeid = self.mycanvas.create_rectangle(oldcoords[0], oldcoords[1], event.x, event.y) # end if # end if # end sizeshape def endshape(self, event): self.dragging = False # end endshape def doneselections(self): print "Done" self.mycanvas.postscript(file="simpledrawout.eps") sys.exit # end doneselections Has a menu to select the Shape of either an oval or rectangle. The cursor changes accordingly, and a postscript file is written when the done button is clicked. Add a line shape to the drawing program. startshape: shape = circle x = 125 y = 60 Shape selected: top_left_corner startshape: shape = top_left_corner x = 225 y = 149 Done Lecture 22 Page 7