Sample code to create BaseActivity for Android

activity_base

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <android.support.v7.widget.Toolbar
            app:contentInsetEnd="0dp"
            app:contentInsetLeft="0dp"
            app:contentInsetRight="0dp"
            app:contentInsetStart="0dp"
            android:layout_width="match_parent"
            android:layout_height="56dp"
            android:background="@color/color_primary_vtu"
            android:contentInsetEnd="0dp"
            android:contentInsetLeft="0dp"
            android:contentInsetRight="0dp"
            android:contentInsetStart="0dp">

            <include layout="@layout/layout_toolbar_back" />
        </android.support.v7.widget.Toolbar>

        <FrameLayout
            android:id="@+id/layout_container"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </LinearLayout>

</android.support.design.widget.CoordinatorLayout>

BaseActivity.java

package com.vtuforum.android.views

import android.app.ProgressDialog
import android.os.Bundle
import android.support.design.widget.CoordinatorLayout
import android.support.v7.app.AppCompatActivity
import android.widget.FrameLayout
import android.widget.ImageButton
import android.widget.TextView
import com.vtuforum.vtustudies.R

abstract class BaseActivity : AppCompatActivity() {

    lateinit var mTextViewScreenTitle: TextView
    lateinit var mImageButtonBack: ImageButton
    lateinit var mProgressDialog: ProgressDialog

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        mProgressDialog = ProgressDialog(this)
        mProgressDialog.setMessage("Loading")
        mProgressDialog.setCancelable(false)
        mProgressDialog.isIndeterminate = true
    }

    override fun setContentView(layoutResID: Int) {
        var coordinatorLayout: CoordinatorLayout = layoutInflater.inflate(R.layout.activity_back_base, null) as CoordinatorLayout
        var activityContainer: FrameLayout = coordinatorLayout.findViewById(R.id.layout_container)
        mTextViewScreenTitle = coordinatorLayout.findViewById(R.id.text_screen_title) as TextView
        mImageButtonBack = coordinatorLayout.findViewById(R.id.image_back_button)

        layoutInflater.inflate(layoutResID, activityContainer, true)

        super.setContentView(coordinatorLayout)
    }

    fun setScreenTitle(resId: Int) {
        mTextViewScreenTitle.text = getString(resId)
    }

    fun setScreenTitle(title: String) {
        mTextViewScreenTitle.text = title
    }

    fun getBackButton(): ImageButton {
        return mImageButtonBack;
    }

    fun showProgressDialog() {
        if(!mProgressDialog.isShowing) {
            mProgressDialog.show()
        }
    }

    fun dismissProgressDialog() {
        if (mProgressDialog.isShowing) {
            mProgressDialog.dismiss()
        }
    }
}

layout_toolbar_back

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/color_primary_vtu">

    <ImageButton
        android:id="@+id/image_back_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:layout_marginStart="16dp"
        android:background="@android:color/transparent"
        android:src="@drawable/baseline_arrow_back_white_24" />

    <TextView
        android:id="@+id/text_screen_title"
        style="@style/TextStyle16Sp"
        fontPath="fonts/Roboto-Light.ttf"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:layout_marginStart="24dp"
        android:layout_toEndOf="@id/image_back_button"
        android:fontFamily="@font/roboto_light"
        android:textSize="20sp"
        tools:text="Screen Title" />
</RelativeLayout>

MainActivity.java

package com.vtuforum.android

import android.os.Bundle
import android.support.v4.content.ContextCompat
import com.vtuforum.android.R
import com.vtuforum.android.views.BackActivity

public class MainActivity: BackBaseActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        initlizeViews()
    }

    private fun initlizeViews() {
        setScreenTitle(R.string.home_labmanuals)
    }
}