Reputation: 933
I experience some difficulties in adding or removing widgets in kivy. This is the case:
The main form should contain two of three widgets, Widget1, Widget2, and Widget3. Pressing the button of Widget1, Widget2 should be removed and Widget3 should appear.
This is the main.py file:
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.factory import Factory
class TableApp(App):
def on_pause(self): return True
def on_resume(self): pass
class Form(BoxLayout):
def click(self, instance, arg):
print 'this is the Form class'
print 'this is my arg ... ', arg
print 'this is the button pressed ... ', instance
print 'these are the children of the Form class:', self.children
Form().remove_widget(Widget2)
Form().add_widget(Widget3)
class Widget1(BoxLayout):
def click(self, instance, arg):
print 'this is the Widget 1'
print 'this is my arg ... ', arg
print 'this is my instance', instance, '\n'
Factory.Form().click(instance,arg)
class Widget2(BoxLayout):
pass
class Widget3(BoxLayout):
pass
if __name__ in ('__android__', '__main__'):
TableApp().run()
and this is the .kv file:
#:import Factory kivy.factory.Factory
Form:
<Form>:
orientation: 'vertical'
Widget1:
Widget2:
<Widget1>:
Button:
text: "Widget 1 Button"
on_press: root.click(self, 'arg')
<Widget2>:
Button:
text: 'Widget 2 Button'
<Widget3>:
Button:
text: 'Widget 3 Button'
In the class Form I check that Widgets1 and 2 are children of the class:
print 'these are the children of the Form class:', self.children
and I get:
these are the children of the Form class: [<__main__.Widget2 object at 0x7fe5833317c0>, <__main__.Widget1 object at 0x7fe5833316e0>]
So when I try to remove an existing child and add a new one I get:
TypeError: descriptor 'unbind' of 'kivy._event.EventDispatcher' object needs an argument
Could somebody help? Thank you.
Upvotes: 1
Views: 4912
Reputation: 12199
The only reason you see children in that print
log is because they are used in kv
lang. This doesn't work at all:
Form().remove_widget(Widget2)
Form().add_widget(Widget3)
Let's do a little bit of drawing:
App | "Form()" called: # this is how Form (A) gets created
| | |
|- Form (A) | new Form instance created # this is the click event beginning
| | |
|- Widget1 | |- remove_widget of -> Form()
| | | |
| |- Button | new Form instance created -|
| | | |
|- Widget2 | |- remove_widget(class) |
| | ^ |
|- Button | |- crash |
| |
| new Form instance created -|
The left part is what kv
file does, the right part is you/python code. Let's call the already available (via kv
) Form
a form A
:
click
methodA
instance's graphical representation i.e. in the BoxLayout
's areaprint
s, so it'll pass just OK, instance
will be probably Button
instance (and you should really use *args
, read about (un)packing arguments)A
the Form()
lines get noticed and that's the right side of my drawing
Form()
will create a new instance (not related to form A
) of class Form
(those brackets)remove_widget
with parameter Widget2
unbind
"Form
instance. The children are in form A
Upvotes: 1
Reputation: 8041
Most of the problems ocurr because you created new widgets instead of using the existing ones.
Here is a working example (look at the comments):
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.factory import Factory #no need for this
class Form(BoxLayout):
def click(self, instance, arg):
print ('this is the Form class')
print ('this is my arg ... ', arg)
print ('this is the button pressed ... ', instance)
print ('these are the children of the Form class:', self.children)
#notice! here we use self, not Form() which will make a new Form instance
self.remove_widget(self.children[0]) #should be Widget2
self.add_widget(Widget3()) #Here we really want a new widget
class Widget1(BoxLayout):
def click(self, instance, arg):
print ('this is the Widget 1')
print ('this is my arg ... ', arg)
print ('this is my instance', instance, '\n')
self.parent.click(instance,arg) #changed to use the existing From instance instead of tring to create a new one
class Widget2(BoxLayout):
pass
class Widget3(BoxLayout):
pass
class TableApp(App):
def on_pause(self): return True
def on_resume(self): pass
if __name__ in ('__android__', '__main__'):
TableApp().run()
Upvotes: 3