An event is just calling a function - you want an event to be generated every time the user does something, such as clicking a button, dragging a scale, or pressing a key...

The Button has an event automatically linked to it - whenever you press it, a function gets called. The other widgets don't.

Types of Event

appJar currently has four basic types of event you can register:

Change & Submit Functions

These do similar things, so probably shouldn't both exist, but have evolved from a single .set XXX Function() which is now deprecated.

WARNING - it's possible to generate a RuntimeError. If you've got two widgets changing the same variable, say a Scale and a SpinBox, and you want a change in one widget to cause an update in the other, you might inadvertently end up stuck in a recursive loop, until the stack overflows.

In this case, make sure you set the optional parameter callFunction = False when you call the set XXX Function() of a widget.

from appJar import gui

def songChanged(rb):

def reset(btn):
    # set back to the default, but don't call the change function
    app.setRadioButton("song", "Killer Queen", callFunction=False)

app.addRadioButton("song", "Killer Queen")
app.addRadioButton("song", "Paradise City")
app.setRadioButtonChangeFunction("song", songChanged)
app.addButton("Reset", reset)

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Over Functions

Set functions to call whenever the mouse enters (goes over) or leaves the specified widget.

    from appJar import gui

    def enter(wdgt): 
        print("IN", wdgt)
    def leave(wdgt):
        print("OUT", wdgt)

    app.addLabel("l1", "Testing...")
    app.setLabelOverFunction("l1", [enter, leave])

Drag Functions

Set functions to call when the mouse button is clicked and dragged on a Label, then released.

Registering Other Event Types

It's possible to register any of the standard event types with appJar widgets

app.getEntryWidget("widget_name").bind("<FocusOut>", function_name, add="+")

Binding Keys

As well as changing widgets, we sometimes want keys to trigger events.
The classic example is the <Enter> key, we often want to be able to hit the <Enter> key to submit a form...

You may also want to bind other keys to events.
See here for a detailed list of the Event Formats.

from appJar import gui
def keyPress(key):
    if key == "<Up>":
    elif key == "<Down>":
    elif key == "<F1>":

app = gui("Button Demo")
app.addLabel("title", "Press the arrow keys to change the font")
app.bindKey("<Up>", keyPress)
app.bindKey("<Down>", keyPress)
app.bindKey("<F1>", keyPress)

Stopping the GUI

Usually the user just presses the close icon to stop the GUI.
However, you might want to let them do it in other ways - maybe by pressing a button...

To stop the GUI, simply call app.stop()

If you want to add a feature to confirm the user really wants to exit, or to save some data, then you'll need a stop function.

def checkStop():
    return app.yesNoBox("Confirm Exit", "Are you sure you want to exit the application?")