A textfield and a button in a horizontal box layout the textfield taking most of the screen space button getting little

I don't know if I resolve all problems but I describe what I found.

It seems MDButton works different than other widgets.

Here is original MDButton.init

    def init(self, args, kwargs):
        super().__init__(args, kwargs)
        Clock.scheduleonce(self.adjustwidth, 0.2)
        Clock.scheduleonce(self.adjustpos, 0.2)

It uses Clock to run self.adjustwidth after 0.2 seconds to create button with minimal width - so it doesn't allow to use self.width at once in own init because it will be replaced by width calculated in self.adjustwidth

(by the way: as I remember init can't calculate it directly because Kivy creates real objects later, sets values from files .kv, and after that code can change sizes - and this is why it has to use Clock to run code later)

I see two methods for this:

1. use also Clock to run own function which will change width little later

from kivy.clock import Clock
class mkbtn(MDButton):
    def init(...):
        # ... code ...
        Clock.scheduleonce(self.updatelater, 0.2)
    def updatelater(self, args):
        self.width = dp(120)

2. replace adjustwidth with own function - empty code - and it will not calculate own width

class mkbtn(MDButton):
    def init(...):
        # ... code ...
        self.width = dp(120)
    def adjustwidth(self, args):
        pass

#from kivy.clock import Clock
if you put this before class mkbtn then you can use func=dummyfunc
def dummyfunc(x="", y=""):
    pass
class mkbtn(MDButton):
    def init(
        self,
        text,
        style="elevated",  #
        radius=[20, 20, 20, 20],
        icon=None,
        # func=lambda x: dummyfunc(x),
        func=dummyfunc,
        kwargs
    ):
        super().init(kwargs)
        self.style = style
        self.radius = radius
        self.sizehintx = None
        # self.adaptivewidth=True
        # self.sizehintminx = 0.3
        # self.wide = dp(120)
        self.width = dp(120)
        if icon:
            self.addwidget(MDButtonIcon(icon))
        self.addwidget(MDButtonText(text=text))
        self.bind(onrelease=func)
        # center text on button - has to be after addwidget(MDButtonText(..>))
        self.buttontext.poshint = {"centerx": 0.5, "centery": 0.5}
        # center button 
        # self.poshint = {"centerx": 0.5, "centery": 0.5}  # center Y
        # Clock.scheduleonce(self.updatelater, 0.2)
    # def updatelater(self, args):
    #    self.width = dp(120)
    def adjustwidth(self, args):
        pass

If in Button and TextField you use poshint = {"centey": 0.5} then both widgets will looks like in one line.

#from kivy.clock import Clock
class TxtField(MDTextField):
    def init(self, ilen=7, htxt="", shintx=0.7, kwargs):
        super().init(kwargs)
        self.mode = "outlined"  # "filled"
        self.sizehintx = 0.5
        # center textfield in layout (Box)
        self.poshint = {"centerx": 0.5, "centery": 0.5}  # center Y
        self.inputfilter = lambda s, u: (
            s if (len(self.text) < ilen and s.isdigit()) else ""
        )
        if not htxt:
            htxt = "input:"
        self.addwidget(MDTextFieldHintText(text=htxt))
if you put this before class mkbtn then you can use func=dummyfunc

def dummyfunc(x="", y=""):
    pass
class mkbtn(MDButton):
    def init(
        self,
        text,
        style="elevated",  #
        radius=[20, 20, 20, 20],
        icon=None,
        # func=lambda x: dummyfunc(x),
        func=dummyfunc,
        kwargs
    ):
        super().init(kwargs)
        self.style = style
        self.radius = radius
        self.sizehintx = None
        # self.adaptivewidth=True
        # self.sizehintminx = 0.3
        # self.wide = dp(120)
        self.width = dp(120)
        if icon:
            self.addwidget(MDButtonIcon(icon))
        self.addwidget(MDButtonText(text=text))
        self.bind(onrelease=func)
        # center text on button - has to be after addwidget(MDButtonText(..>))
        self.buttontext.poshint = {"centerx": 0.5, "centery": 0.5}
        # center button in layout (Box)
        self.poshint = {"centerx": 0.5, "centery": 0.5}  # center Y
        # Clock.scheduleonce(self.updatelater, 0.2)
    # def updatelater(self, args):
    #    self.width = dp(120)
    def adjustwidth(self, args):
        pass

If you add background color in MDBoxLayout then you see how it is centered

        self.hlay5 = MDBoxLayout(
            orientation="horizontal",
            padding=[5, 5, 5, 5],
            spacing=dp(10),
            mdbgcolor=[1, 0, 0, 1],
        )

Before centering:

After centering:

To reduce height in rows I have to use sizehinty=None in every hlay and bind function which will calculates minimal height for every hlay

self.hlay4.bind(minimumheight=self.hlay4.setter("height"))

class MainScreen(MDScreen):
    def init(self, kwargs):
        super().init(kwargs)
        self.mdbgcolor = [1, 1, 1, 1]
        # mdbgcolor: self.themecls.secondaryContainerColor
        self.mainlayout = MDBoxLayout(orientation="vertical")
        self.appbar = MDTopAppBar(type="small")
        self.abtitle = MDTopAppBarTitle(
            text="WOS Squad Ratio (Bear/CJ)", halign="center"
        )
        self.appbar.addwidget(self.abtitle)
        self.contentlayout = MDBoxLayout(
            orientation="vertical",
            padding=[5, 5, 5, 5],
            spacing=dp(10),
        )
        self.hlay1 = MDBoxLayout(
            orientation="horizontal",
            padding=[5, 5, 5, 5],
            spacing=dp(10),
            sizehinty=None,
        )
        self.bdctf = TxtField(htxt="Bear DC", ilen=6)
        self.profbtn = mkbtn("Profiles", icon="triangle-small-down")
        self.hlay1.addwidget(self.bdctf)
        self.hlay1.addwidget(self.profbtn)
        self.hlay1.bind(minimumheight=self.hlay1.setter("height"))
        ###
        self.hlay2 = MDBoxLayout(
            orientation="horizontal",
            padding=[5, 5, 5, 5],
            spacing=dp(10),
            sizehinty=None,
        )
        self.cdctf = TxtField(htxt="CJ DC", ilen=6)
        self.aprofbtn = mkbtn("Add Profiles")
        self.hlay2.addwidget(self.cdctf)
        self.hlay2.addwidget(self.aprofbtn)
        self.hlay2.bind(minimumheight=self.hlay2.setter("height"))
        ###
        self.hlay3 = MDBoxLayout(
            orientation="horizontal",
            padding=[5, 5, 5, 5],
            spacing=dp(10),
            sizehinty=None,
        )
        self.titf = TxtField(htxt="Total Infantry", ilen=7)
        self.cbbtn = mkbtn("Calc Bear")
        self.hlay3.addwidget(self.titf)
        self.hlay3.addwidget(self.cbbtn)
        self.hlay3.bind(minimumheight=self.hlay3.setter("height"))
        ###
        self.hlay4 = MDBoxLayout(
            orientation="horizontal",
            padding=[5, 5, 5, 5],
            spacing=dp(10),
            sizehinty=None,
        )
        self.tltf = TxtField(htxt="Total Lancer", ilen=7)
        self.ccbtn = mkbtn("Calc CJ")
        self.hlay4.addwidget(self.tltf)
        self.hlay4.addwidget(self.ccbtn)
        self.hlay4.bind(minimumheight=self.hlay4.setter("height"))
        ###
        self.hlay5 = MDBoxLayout(
            orientation="horizontal",
            padding=[5, 5, 5, 5],
            spacing=dp(10),
            mdbgcolor=[1, 0, 0, 1],
            sizehinty=None,
        )
        self.tmtf = TxtField(htxt="Total Lancer", ilen=7)
        self.sdbtn = mkbtn("Save Data")
        self.hlay5.addwidget(self.tmtf)
        self.hlay5.addwidget(self.sdbtn)
        self.hlay5.bind(minimumheight=self.hlay5.setter("height"))
        ###
        self.tlbl = MDLabel(
            halign="left",
            role="large",
            padding=[5, 0, 0, 500],
            text="",
        )
        def cnglbl(txt):
            self.tlbl.text = txt
        ###
        self.contentlayout.addwidget(self.hlay1)
        self.contentlayout.addwidget(self.hlay2)
        self.contentlayout.addwidget(self.hlay3)
        self.contentlayout.addwidget(self.hlay4)
        self.contentlayout.addwidget(self.hlay5)
        self.contentlayout.addwidget(
            MDWidget(
                # sizehinty=1,  # doesn't need this
                mdbgcolor=[0, 1, 0, 1],
            )
        )
        ###
        self.mainlayout.addwidget(self.appbar)
        self.mainlayout.addwidget(self.contentlayout)
        ###
        self.addwidget(self.main_layout)

It keeps sizes after resizing window.

but problem is when window is too small to keep all elements