MDBottomAppBar（Kivymd）异常：仅显底色无控件问题求助

问题原因 #

1. right_action_items格式错误：底部导航栏内的MDTopAppBar的right_action_items未使用正确的嵌套列表格式，导致Kivy无法解析动作项，控件无法正常渲染。
2. Window模块未导入：ScrollView高度计算依赖Window，但Python代码未显式导入，可能引发潜在运行问题。

修改方案 #

1. 修正KV文件中的right_action_items格式 #

将底部导航栏的right_action_items修改为正确的嵌套列表结构（所有动作项包裹在一个外层列表中）：

<MDBottomAppBar:
    MDTopAppBar:
        id:bottom_app_bar
        elevation:20
        title:"My Bottom Bar!"
        icon:"plus-circle"
        type:"bottom"
        icon_color: 1, 0, .4, .1
        md_bg_bottom_color: "orange"
        left_action_items:["menu",lambda x:app.chanje_mounyo()]
        right_action_items: [["gmail", lambda x:app.chanje_mounyo()], ["bookmark", lambda x:None], ["instagram", lambda x:None]]

2. 在Python代码中导入Window模块 #

在Python文件开头添加Window导入语句，确保高度计算逻辑正常运行：

from kivy.core.window import Window

修改后的完整代码 #

KV文件（mybanner.kv） #

<EkzampBanner@Screen>
    MDBanner:
        id:banner
        text:["Yon sel liyn teks san aksyon."]
        over_widget:scroll
        vertical_pad:toolbar.height

    MDTopAppBar:
        id:toolbar
        title:"My banner for me!"
        md_bg_color:.3,.3,.4,.1
        elevation:20
        left_action_items:["menu",lambda x:app.change_items()]
        right_action_items:["dots-vertical",lambda x:app.change_items()]
        pos_hint: {'top':1}    
    MDBottomAppBar:
        MDTopAppBar:
            id:bottom_app_bar
            elevation:20
            title:"My Bottom Bar!"
            icon:"plus-circle"
            type:"bottom"
            icon_color: 1, 0, .4, .1
            md_bg_bottom_color: "orange"
            left_action_items:["menu",lambda x:app.chanje_mounyo()]
            right_action_items: [["gmail", lambda x:app.chanje_mounyo()], ["bookmark", lambda x:None], ["instagram", lambda x:None]]
    ScrollView:
        id:scroll
        size_hint_y:None
        height:Window.height - toolbar.height

        MDGridLayout:
            id:box
            adaptive_height:True
            cols:1
            padding:"10dp"
            spacing:"10dp"

            OneLineListItem:
                text: "ThreeLineBanner"
                on_release:
                    banner.type = "three-line"
                    banner.text = \
                    [\
                    "Three line string text example with two actions.", \
                    "This is the second line of the banner message.", \
                    "and this is the third line of the banner message.",
                    ]
                    banner.left_action = ["CANCEL", lambda x: None]
                    banner.right_action = ["CLOSE", lambda x: banner.hide()]
                    banner.show()
            
            OneLineListItem:
                text: "TwoLineIconBanner"
                on_release:
                    banner.type = "two-line-icon"
                    banner.text = \
                    [\
                    "One line string text example with two actions.", \
                    "This is the second line of the banner message.", \
                    ]
                    banner.left_action = ["CANCEL", lambda x: None]
                    banner.right_action = ["CLOSE", lambda x: banner.hide()]
                    banner.show()

            OneLineListItem:
                text: "OneLineIconBanner"
                on_release:
                    banner.type = "one-line-icon"
                    banner.text = ["One line string text example with two actions."]
                    banner.left_action = ["CANCEL", lambda x: None]
                    banner.right_action = ["CLOSE", lambda x: banner.hide()]
                    banner.show()

            OneLineListItem:
                text: "Banner without actions"
                on_release:
                    banner.type = "one-line-icon"
                    banner.text = ["One line string text example without actions."]
                    banner.left_action = []
                    banner.right_action = []
                    banner.show()

            OneLineListItem:
                text: "Banner with one actions"
                on_release:
                    banner.type = "one-line-icon"
                    banner.text = ["One line string text example without actions."]
                    banner.left_action = []
                    banner.right_action = ["CLOSE", lambda x: banner.hide()]
                    banner.show()

Python文件 #

from kivy.lang import Builder
from kivy.factory import Factory
from kivy.core.window import Window
from kivymd.app import MDApp
from kivymd.uix.screen import MDScreen

class EkzampBanner(MDScreen):
    pass

class MyBanner(MDApp):
    def change_items(self):
        self.root.ids.bottom_app_bar.right_action_items=[["whatsapp"],["facebook"],["twitter"]]
        self.root.ids.bottom_app_bar.md_bg_bottom_color="lightgray"
        self.root.ids.bottom_app_bar.icon="account-circle"
        self.root.ids.toolbar.md_bg_color = "#FFA500"
        self.root.ids.bottom_app_bar.icon_color=[0, 0, 1, 1]

    def chanje_mounyo(self):
        self.root.ids.bottom_app_bar.md_bg_bottom_color="orange"
        self.root.ids.bottom_app_bar.icon="account-circle"
        self.root.ids.toolbar.md_bg_color= [.3,.3,.4,.1]
        self.root.ids.bottom_app_bar.icon_color=[1, 0, .4, .1]
        
    
    def build(self):
        Builder.load_file('mybanner.kv')
        return EkzampBanner()

if __name__=='__main__':
    MyBanner().run()

内容的提问来源于stack exchange，提问作者Piets