Custom view default style overload example

CustomButton.kt

package <yourpackage>

import android.content.Context
import android.util.AttributeSet
import androidx.annotation.AttrRes
import com.google.android.material.button.MaterialButton

class CustomButton @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    // redefine the attribute so that the default style can be controlled from the theme, and also overridden in the xml layout via style="@style/..."
    @AttrRes defStyleAttr: Int = R.attr.customButtonStyle
) : MaterialButton(
    context.apply { 
        // in case R.attr.customButtonStyle wont be defined in the main theme
        theme.applyStyle(R.style.CustomButtonThemeDefault, false)
    },
    attrs,
    defStyleAttr
)

values_custom_button.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <attr name="customButtonStyle" format="reference"/>

    <style name="CustomButtonThemeDefault">
        <item name="customButtonStyle">@style/CustomButtonStyle</item>
    </style>

    <style name="CustomButtonStyle" parent="Widget.MaterialComponents.Button">
        <!-- Styling by default -->
    </style>
</resources>