Widgets inside Tabbed Panel in Kivy

I'm new to designing in kivy and I'm trying to display a listview, inputbox and label inside a Tab panel but it's showing empty panel. I'm not sure where is my mistake. I want to do a simple search of users by just typing the username in the inputbox then the listview will automatically update the records inside the listview.

I'm using kivy 1.10.0 and python 3.6

Here is my code in kivy file:

<AdminMainScreen@Screen>:#===================MAIN SCREEN=========================
txt_search: txt_search
view_user_list: view_user_list

BoxLayout:
    size_hint_y: 1
    size_hint_x: 1

    canvas:
        Color:
            rgb: .132, .232, .249
        Rectangle:
            size: self.size

    TabbedPanel:
        do_default_tab: False

        TabbedPanelItem:
            text:"1st Tab"
            Label:
                text: "Content of Admin Panel"

        TabbedPanelItem:
            text:"2nd Tab"
            Label:
                text: "Content of Second Panel"

        TabbedPanelItem:
            text:"Manage Users"
            BoxLayout:
                size_hint_y: .2
                size_hint_x: 1
                orientation: 'horizontal'

                Label:
                    text: "Search User"
                    size_hint_x: .25
                    spacing: .2, .2

                TextInput:
                    id: txt_search
                    text: ""
                    size_hint_x: .3
                    spacing: .2, .2
            Label:
                id: lbl_search
                size_hint_y:None
                height: 10
                text: ""

            ListView:
                color: [0,0,0]
                id: view_user_list
                size_hint_x: 1
                size_hint_y: .8
                item_strings: []
                adapters:
                    ListAdapter(data=[], cls = ListItemButton)