simpleKivy.kv

# File name: app.py
#:kivy 1.8.0

Root:
    text_input: text_input

    BoxLayout:
        orientation: 'vertical'
        BoxLayout:
            size_hint_y: None
            height: 30
            Button:
                text: 'Load'
                on_release: root.show_load()
            Button:
                text: 'Save'
                on_release: root.show_save()

        BoxLayout:
            TextInput:
                id: text_input
                text: ''

            RstDocument:
                text: text_input.text
                show_errors: True

<LoadDialog>:
    BoxLayout:
        size: root.size
        pos: root.pos
        orientation: "vertical"
        FileChooserListView:
            id: filechooser

        BoxLayout:
            size_hint_y: None
            height: 30
            Button:
                text: "Cancel"
                on_release: root.cancel()

            Button:
                text: "Load"
                on_release: root.load(filechooser.path, filechooser.selection)

<SaveDialog>:
    text_input: text_input
    BoxLayout:
        size: root.size
        pos: root.pos
        orientation: "vertical"
        FileChooserListView:
            id: filechooser
            on_selection: text_input.text = self.selection and self.selection[0] or ''

        TextInput:
            id: text_input
            size_hint_y: None
            height: 30
            multiline: False

        BoxLayout:
            size_hint_y: None
            height: 30
            Button:
                text: "Cancel"
                on_release: root.cancel()

            Button:
                text: "Save"
                on_release: root.save(filechooser.path, text_input.text)