Screen Manager, Screen events. on_pre_enter etc

[Sam Berry]

Hey,

Iv got a Screenmanager app already up and running. However within one of my screens i want to update the information from a file every time i enter that screen. Iv seen in the documentation for Screenmanager that you can use commands such as on_pre_enter, on_enter etc. However i have no idea how to implement these commands.

Has anybody used these? or can give me a quick example of how to call a function on_pre_enter to a screen?

Thanks, Sam

[Gabriel Pettier]

Hi

as can be seen in the doc
(http://kivy.org/docs/api-kivy.uix.screenmanager.html#kivy.uix.screenmanager.Screen)
these are events dispatched by the screen instance, so you can bind to
them, either from python:

```
sm = Screenmanager()
s = Screen(name='test')
s.bind(on_enter=some_callback)
sm.add_widget(s)
```

or in kv:

```
ScreenManager:
Screen:
name: 'test'
on_enter: some_callback()
```

hope this helps

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[Sam Berry]

Hey,

Thanks for the quick reply. That helps me to an extent, however i tried implementing it and failed. I have been building my App using the examples and pot luck really. Within my python file for the screenmanager i have....

sm = ScreenManager(transition=SwapTransition())
sm.add_widget(Home(name='Menu'))
sm.add_widget(Camera1(name='Camera 1'))
sm.add_widget(Camera2(name='Camera 2'))
sm.add_widget(Record(name='Record Page'))
sm.add_widget(Settings1(name='Settings Page'))
sm.add_widget(Team_Select(name='Team_Select'))

And a snippet of the kv file which i would like the function to be run when entering

<Team_Select>:
    canvas:
        Color:
            rgb: 0,0,.1
        Rectangle:
            size: self.size
 
    BoxLayout:
        orientation: 'vertical'
        GridLayout:
            rows: 6
            columns: 2
            CheckBox:
                group: 'Team1'
                on_active: root.set_active(self)
            Label:
                font_size: 15
                text: 'Team1'
            CheckBox:
                group: 'Team2'
                on_active: root.set_active(self) 
            Label:
                font_size: 15
                text: 'Team2'

I have tried adding on_pre_enter: root.Myfunction() within the kv file with many errors, which from looking at your Kv example i haven't set up my ScreenManager in a conventional way?

I then tried adding

ts = Screen(name='Team_Select')
ts.bind(on_enter=Test())

And adding the Test() function into     class Team_Select(Screen):  with no success.

Sorry for the essay! Just trying to give as much info as possible as iv been stuck on this for hours!

Thanks, Sam

[Gabriel Pettier]

Hi,

your bindind must pass the function/method object, like any regular
python callback passing.

assuming i do

```
def test(*args):
print args
```

I can do

```
my_object.bind(on_something=test)
```

because "test" is a known function name here.

But if i do

```
class MyClass(SomeWidgetClass):
def test(self, *args):
print args

my_object = MyClass()
```

i have to do:

```
my_object.bind(on_something=my_object.test)
```

because "test" is nothing here, we only have "my_object" which has a
"test" method, that's this one we want to pass.

cheers