Keyboard and Mouse Events

We've got something that works, more or less -- but its interface is still a bit unwieldy. It would be nice if we could use the mouse and keyboard to make things a bit more intuitive. When you're running the Tk main loop, hitting a key on the keyboard or moving the mouse around generates events, which you can bind to callback functions in a similar way to when a button is pressed. Let's take a look at how we could make the text box respond to pressing Return rather than clicking the button. Now we've already got a function to handle that, the Button3 callback -- unfortunately we can't just use that since callbacks from events are different from buttons. We'll have to wrap it in another function:

def ReturnInsert(event):
	Button3()

Then we register this callback with the event we're looking for using the bind function:

text.bind("<Return>", ReturnInsert)

It's important here that we use the <Return> event code rather than the <Enter> event code, since the second triggers when the mouse enters the listbox. Now say we want to let the user use right click to remove items from the listbox, it's pretty much the same process. First we write a callback that accepts the event as input:

def DeleteCurrent(event):
	listbox.delete(ANCHOR)	

Then we bind the event to this callback:

listbox.bind("<Double-Button-3>", DeleteCurrent)

The right mouse button is called Button-3 in Tk (not to be confused with the name of our third form button callback), since the second mouse button refers to middle click. Finally, let's allow the user to copy a note back to the text box, in case they want to modify it. We don't have a function that allows this yet, so we'll have to write some new code in the callback:

def CopyToText(event):
	text.delete(0,END)
	current_note = listbox.get(ANCHOR)
	text.insert(0, current_note)

Then bind the event to the callback like before:

listbox.bind("<Double-Button-1>", CopyToText)

That's all there is to it. You're not just limited to these events though, for a guide to which events you can bind, check out the Tkinter library introduction.

Now seems like a good time to clean up our program. Button1 is a poor name for a function -- we've already been tripped up by similar names once, let's not do it again. We'll also take this opportunity to change some of the button effects, as it makes more sense for the Enter button to be closest to the text box for example, and Button1 isn't particularly useful, so let's get rid of it. No real changes to functionality, but the program now looks like this:

#!/usr/bin/python

from Tkinter import *

root = Tk()
root.geometry("600x400")
root.title("Note Taker")

def Enter():
	text_contents = text.get()
	listbox.insert(END, text_contents)
	text.delete(0,END)

def Remove():
	listbox.delete(ANCHOR)	

def Save():
	pass

def ReturnInsert(event):
	Enter()

def DeleteCurrent(event):
	Remove()

def CopyToText(event):
	text.delete(0, END)
	current_note = listbox.get(ANCHOR)
	text.insert(0, current_note)

textframe = Frame(root)
listframe = Frame(root)

enter_button = Button(textframe, text="Enter", command = Enter)
remove_button = Button(textframe, text="Remove", command = Remove)
save_button = Button(textframe, text="Save", command = Save)

text = Entry(textframe)

scrollbar = Scrollbar(listframe, orient=VERTICAL)
listbox = Listbox(listframe, yscrollcommand=scrollbar.set, selectmode=EXTENDED)
scrollbar.configure(command=listbox.yview)

text.bind("<Return>", ReturnInsert)
listbox.bind("<Double-Button-3>", DeleteCurrent)
listbox.bind("<Double-Button-1>", CopyToText)

text.pack(side=LEFT, fill=X, expand=1)
enter_button.pack(side=LEFT)
remove_button.pack(side=LEFT)
save_button.pack(side=LEFT)
listbox.pack(side=LEFT,fill=BOTH, expand=1)
scrollbar.pack(side=RIGHT, fill=Y)

textframe.pack(fill=X)
listframe.pack(fill=BOTH, expand=1)

root.mainloop()