Доделал

app/build.gradle

@@ -3,12 +3,8 @@ plugins {
     id 'org.jetbrains.kotlin.android'
 }
 
-kotlin {
-    jvmToolchain(17)
-}
-
 android {
-    compileSdk 34
+    compileSdk 35
     namespace "otus.gpb.homework.fragments"
 
     defaultConfig {
@@ -42,6 +38,8 @@ dependencies {
     implementation 'androidx.appcompat:appcompat:1.5.1'
     implementation 'com.google.android.material:material:1.6.1'
     implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
+    implementation 'androidx.activity:activity:1.10.1'
+    implementation 'androidx.fragment:fragment-ktx:1.8.6'
     testImplementation 'junit:junit:4.13.2'
     androidTestImplementation 'androidx.test.ext:junit:1.1.3'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'

app/src/main/AndroidManifest.xml

@@ -12,6 +12,12 @@
         android:supportsRtl="true"
         android:theme="@style/Theme.Fragments"
         tools:targetApi="31">
+        <activity
+            android:name=".ui.ActivityB"
+            android:exported="false" />
+        <activity
+            android:name=".ui.ActivityA"
+            android:exported="false" />
         <activity
             android:name=".MainActivity"
             android:exported="true">

app/src/main/java/otus/gpb/homework/fragments/ColorGenerator.kt

@@ -1,13 +1,13 @@
 package otus.gpb.homework.fragments
 
-import android.graphics.Color
 import java.util.Random
+import androidx.core.graphics.toColorInt
 
 object ColorGenerator {
 
     fun generateColor(): Int {
         val nextInt = Random().nextInt(0xffffff + 1)
         val colorCode = String.format("#%06x", nextInt)
-        return Color.parseColor(colorCode)
+        return colorCode.toColorInt()
     }
 }

app/src/main/java/otus/gpb/homework/fragments/MainActivity.kt

@@ -1,12 +1,25 @@
 package otus.gpb.homework.fragments
 
 import android.os.Bundle
+import android.widget.Button
 import androidx.appcompat.app.AppCompatActivity
+import otus.gpb.homework.fragments.ui.ActivityA
+import otus.gpb.homework.fragments.ui.ActivityB
+import android.content.Intent
 
 class MainActivity : AppCompatActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
+
+        findViewById<Button>(R.id.buttonOpenActivityA).setOnClickListener{
+            startActivity(Intent(this@MainActivity, ActivityA::class.java))
+        }
+
+        findViewById<Button>(R.id.buttonOpenActivityB).setOnClickListener{
+            startActivity(Intent(this@MainActivity, ActivityB::class.java))
+        }
     }
+
 }

app/src/main/java/otus/gpb/homework/fragments/ui/ActivityA.kt

@@ -0,0 +1,24 @@
+package otus.gpb.homework.fragments.ui
+
+import android.os.Bundle
+import androidx.activity.enableEdgeToEdge
+import androidx.appcompat.app.AppCompatActivity
+import androidx.core.view.ViewCompat
+import androidx.core.view.WindowInsetsCompat
+import otus.gpb.homework.fragments.R
+
+class ActivityA : AppCompatActivity() {
+    private lateinit var fragmentA: FragmentA
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_a)
+
+        if (savedInstanceState == null) {
+            fragmentA = FragmentA()
+            supportFragmentManager.beginTransaction()
+                .replace(R.id.fragment_container, fragmentA, "fragmentA")
+                .commit()
+        }
+    }
+}

app/src/main/java/otus/gpb/homework/fragments/ui/ActivityB.kt

@@ -0,0 +1,27 @@
+package otus.gpb.homework.fragments.ui
+
+import android.os.Bundle
+import androidx.activity.enableEdgeToEdge
+import androidx.appcompat.app.AppCompatActivity
+import androidx.core.view.ViewCompat
+import androidx.core.view.WindowInsetsCompat
+import otus.gpb.homework.fragments.R
+
+class ActivityB : AppCompatActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        enableEdgeToEdge()
+        setContentView(R.layout.activity_b)
+        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main)) { v, insets ->
+            val systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars())
+            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom)
+            insets
+        }
+        if (savedInstanceState == null) {
+            val fragmentB = FragmentB()
+            supportFragmentManager.beginTransaction()
+                .replace(R.id.fragment_container, fragmentB, "fragmentB")
+                .commit()
+        }
+    }
+}

app/src/main/java/otus/gpb/homework/fragments/ui/FragmentA.kt

@@ -0,0 +1,80 @@
+package otus.gpb.homework.fragments.ui
+
+import android.content.Context
+import android.os.Bundle
+import androidx.fragment.app.Fragment
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import android.widget.Button
+import androidx.activity.OnBackPressedCallback
+import otus.gpb.homework.fragments.ColorGenerator
+import otus.gpb.homework.fragments.R
+import androidx.fragment.app.setFragmentResultListener
+
+class FragmentA : Fragment() {
+
+    private lateinit var openButton: Button
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        arguments?.let {
+
+        }
+    }
+
+    override fun onCreateView(
+        inflater: LayoutInflater, container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View? {
+        // Inflate the layout for this fragment
+        val rootView = inflater.inflate(R.layout.fragment_a, container, false)
+        openButton = rootView.findViewById(R.id.buttonOpenAA)
+        rootView.findViewById<Button>(R.id.buttonOpenAA).setOnClickListener {
+            val color = ColorGenerator.generateColor()
+            val fragmentAA = FragmentAA.newInstance(color)
+            childFragmentManager.beginTransaction()
+                .replace(R.id.container, fragmentAA, "fragmentAA")
+                .addToBackStack("fragmentAA")
+                .commit()
+            openButton.visibility = View.GONE
+        }
+        return rootView
+    }
+
+    override fun onAttach(context: Context) {
+        super.onAttach(context)
+
+        val callback = object : OnBackPressedCallback(true) {
+            override fun handleOnBackPressed() {
+                if (childFragmentManager.backStackEntryCount > 0) {
+                    childFragmentManager.popBackStack()
+                    if (childFragmentManager.backStackEntryCount == 1)
+                        openButton.visibility = View.VISIBLE
+                } else {
+                    requireActivity().finish()
+                }
+            }
+        }
+        requireActivity().onBackPressedDispatcher.addCallback(callback)
+    }
+
+    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+        super.onViewCreated(view, savedInstanceState)
+
+        childFragmentManager.setFragmentResultListener(SHOW_FRAGMENT_AB, this) { _, _ ->
+            val color = ColorGenerator.generateColor()
+            val fragmentAB = FragmentAB.newInstance(color)
+            childFragmentManager.beginTransaction()
+                .replace(R.id.container, fragmentAB, "fragmentAB")
+                .addToBackStack("fragmentAB")
+                .commit()
+            openButton.visibility = View.GONE
+        }
+    }
+
+
+    companion object{
+        const val SHOW_FRAGMENT_AB = "show fragmentAB"
+    }
+}

app/src/main/java/otus/gpb/homework/fragments/ui/FragmentAA.kt

@@ -0,0 +1,50 @@
+package otus.gpb.homework.fragments.ui
+
+import android.os.Bundle
+import androidx.fragment.app.Fragment
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import android.widget.Button
+import otus.gpb.homework.fragments.R
+import androidx.core.graphics.drawable.toDrawable
+import androidx.core.os.bundleOf
+import androidx.fragment.app.setFragmentResult
+import otus.gpb.homework.fragments.ColorGenerator
+
+private const val COLOR = "color"
+
+class FragmentAA : Fragment() {
+    private var color: Int? = null
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        arguments?.let {
+            color = it.getInt(COLOR)
+        }
+    }
+
+    override fun onCreateView(
+        inflater: LayoutInflater, container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View? {
+        // Inflate the layout for this fragment
+        val rootView =  inflater.inflate(R.layout.fragment_aa, container, false)
+        rootView.background = color?.toDrawable()
+        rootView.findViewById<Button>(R.id.buttonOpenAB).setOnClickListener{
+            rootView.findViewById<Button>(R.id.buttonOpenAB).visibility = View.GONE
+            setFragmentResult(FragmentA.SHOW_FRAGMENT_AB, bundleOf())
+        }
+        return rootView
+    }
+
+    companion object {
+        @JvmStatic
+        fun newInstance(color: Int) =
+            FragmentAA().apply {
+                arguments = Bundle().apply {
+                    putInt(COLOR, color)
+                }
+            }
+    }
+}

app/src/main/java/otus/gpb/homework/fragments/ui/FragmentAB.kt

@@ -0,0 +1,42 @@
+package otus.gpb.homework.fragments.ui
+
+import android.os.Bundle
+import androidx.fragment.app.Fragment
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import androidx.core.graphics.drawable.toDrawable
+import otus.gpb.homework.fragments.R
+
+
+private const val COLOR = "color"
+
+class FragmentAB : Fragment() {
+    private var color: Int? = null
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        arguments?.let {
+            color = it.getInt(COLOR)
+        }
+    }
+
+    override fun onCreateView(
+        inflater: LayoutInflater, container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View? {
+        val rootView =  inflater.inflate(R.layout.fragment_aa, container, false)
+        rootView.background = color?.toDrawable()
+        return rootView
+    }
+
+    companion object {
+        @JvmStatic
+        fun newInstance(color: Int) =
+            FragmentAA().apply {
+                arguments = Bundle().apply {
+                    putInt(COLOR, color)
+                }
+            }
+    }
+}

app/src/main/java/otus/gpb/homework/fragments/ui/FragmentB.kt

@@ -0,0 +1,62 @@
+package otus.gpb.homework.fragments.ui
+
+import android.content.Context
+import android.os.Bundle
+import androidx.fragment.app.Fragment
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import androidx.activity.OnBackPressedCallback
+import otus.gpb.homework.fragments.ColorGenerator
+import otus.gpb.homework.fragments.R
+
+class FragmentB : Fragment() {
+
+    override fun onCreateView(
+        inflater: LayoutInflater, container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View? {
+        // Inflate the layout for this fragment
+        val rootView = inflater.inflate(R.layout.fragment_b, container, false)
+        rootView.findViewById<View>(R.id.container)?.let {
+            createFragmentBA(it.id)
+        }
+        rootView.findViewById<View>(R.id.containerLeft)?.let {
+            createFragmentBA(it.id)
+        }
+        rootView.findViewById<View>(R.id.containerRight)?.let {
+            createFragmentBB(it.id)
+        }
+        return rootView
+    }
+
+    override fun onAttach(context: Context) {
+        super.onAttach(context)
+
+        val callback = object : OnBackPressedCallback(true) {
+            override fun handleOnBackPressed() {
+                if (childFragmentManager.backStackEntryCount > 1) {
+                    childFragmentManager.popBackStack()
+                } else {
+                    requireActivity().finish()
+                }
+            }
+        }
+        requireActivity().onBackPressedDispatcher.addCallback(callback)
+    }
+
+    private fun createFragmentBA(containerId: Int){
+        val fragmentBA = FragmentBA()
+        childFragmentManager.beginTransaction()
+            .replace(containerId, fragmentBA, "fragmentBA")
+            .addToBackStack("fragmentBA")
+            .commit()
+    }
+
+    private fun createFragmentBB(containerId: Int){
+        val fragmentBB = FragmentBB()
+        childFragmentManager.beginTransaction()
+            .replace(containerId, fragmentBB, "fragmentBB")
+            .commit()
+    }
+}