Fragment Problems

app/src/main/java/com/example/androidconcepts/MainActivity.kt

@@ -2,13 +2,61 @@ package com.example.androidconcepts
 
 import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity
+import com.example.androidconcepts.fragments.problems.problem1.FragProbOneFragment
+import com.example.androidconcepts.fragments.problems.problem2.FragProbTwoFragment
 
 class MainActivity : AppCompatActivity() {
 
+    enum class CURRENT_BUILD {
+        FRAG_PROBLEM_1, FRAG_PROBLEM_2
+    }
+
+    // change this to modify app's state.
+    private val currentBuild = CURRENT_BUILD.FRAG_PROBLEM_2
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
 
         // AndroidThreadSpammer().execute()
+
+        if (currentBuild == CURRENT_BUILD.FRAG_PROBLEM_1) {
+            if (savedInstanceState == null) {
+                supportFragmentManager.beginTransaction()
+                    .replace(R.id.root_fragment_container, FragProbOneFragment())
+                    .commit()
+            }
+        } else if (currentBuild == CURRENT_BUILD.FRAG_PROBLEM_2) {
+            if (savedInstanceState == null) {
+                supportFragmentManager.beginTransaction()
+                    .replace(R.id.root_fragment_container, FragProbTwoFragment())
+                    .commit()
+            }
+        }
+    }
+
+    override fun onBackPressed() {
+
+// ------------------------------
+// ----------  for FRAG PROBLEM 1
+
+//        if (currentBuild == CURRENT_BUILD.FRAG_PROBLEM_1) {
+
+//            SOLUTION : manually remove the unintended fragments attached.
+
+//            val currentFragment = supportFragmentManager.findFragmentById(R.id.root_fragment_container)
+//                ?: return
+
+//            Log.d("frag problem", "current frag : " + (currentFragment as FragProbOneFragment).number)
+
+//            this does the main fix, i.e remove currently unintended shown fragment from the fm.
+
+//            supportFragmentManager.beginTransaction().remove(currentFragment).commit()
+//        }
+
+// ----------  for FRAG PROBLEM 1
+// ------------------------------
+
+        super.onBackPressed() // internally does popBackStackImmediate or finish activity.
     }
 }

app/src/main/java/com/example/androidconcepts/fragments/problems/problem1/FragProbOneFragment.kt

@@ -0,0 +1,83 @@
+package com.example.androidconcepts.fragments.problems.problem1
+
+import android.graphics.Color
+import android.os.Bundle
+import android.util.Log
+import android.view.Gravity
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import android.widget.FrameLayout
+import android.widget.FrameLayout.LayoutParams
+import android.widget.Toast
+import androidx.fragment.app.Fragment
+import com.example.androidconcepts.R
+import com.google.android.material.button.MaterialButton
+
+class FragProbOneFragment : Fragment() {
+
+    private lateinit var button: MaterialButton
+
+    var number = 0
+
+    private fun getInstance(number: Int): FragProbOneFragment {
+        return FragProbOneFragment().apply {
+            val bundle = Bundle()
+            bundle.putInt("number", number)
+            this.arguments = bundle
+        }
+    }
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        number = arguments?.getInt("number", 0) ?: 0
+    }
+
+    override fun onCreateView(
+        inflater: LayoutInflater,
+        container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View {
+        val rootView = FrameLayout(requireContext())
+
+        rootView.layoutParams = ViewGroup.LayoutParams(
+            ViewGroup.LayoutParams.MATCH_PARENT,
+            ViewGroup.LayoutParams.MATCH_PARENT
+        )
+
+        rootView.setBackgroundColor(Color.WHITE) // hides the other fragments, due to this I never found this issue.
+        rootView.isClickable = true // prevents clicking through the current fragment.
+
+        button = MaterialButton(requireContext())
+        button.text = "Fragment Problem : $number"
+        val lp = LayoutParams(
+            LayoutParams.WRAP_CONTENT,
+            LayoutParams.WRAP_CONTENT
+        )
+        lp.gravity = Gravity.TOP
+        lp.topMargin = number * 50
+        button.layoutParams = lp
+
+        rootView.addView(button)
+
+        return rootView
+    }
+
+    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+        super.onViewCreated(view, savedInstanceState)
+
+        Log.d("frag problem", "frags size : " + requireActivity().supportFragmentManager.fragments.size
+                + " backstack count : " + requireActivity().supportFragmentManager.backStackEntryCount)
+
+        button.setOnClickListener {
+            val ft = requireActivity().supportFragmentManager.beginTransaction()
+            ft.replace(R.id.root_fragment_container, getInstance(number + 1))
+
+            if (number % 2 == 1) // only add if current fragment number is odd. eg: frag 3 to 4 is added but 4 to 5 isn't.
+                ft.addToBackStack(null)
+
+            ft.commit()
+        }
+    }
+
+}

app/src/main/java/com/example/androidconcepts/fragments/problems/problem2/FragProbTwoFragment.kt

@@ -0,0 +1,113 @@
+package com.example.androidconcepts.fragments.problems.problem2
+
+import android.graphics.Color
+import android.os.Bundle
+import android.util.Log
+import android.view.Gravity
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import android.widget.FrameLayout
+import androidx.fragment.app.Fragment
+import com.example.androidconcepts.R
+import com.google.android.material.button.MaterialButton
+
+class FragProbTwoFragment : Fragment() {
+
+    private lateinit var button: MaterialButton
+
+    var number = 0
+
+    private fun getInstance(number: Int): FragProbTwoFragment {
+        return FragProbTwoFragment().apply {
+            val bundle = Bundle()
+            bundle.putInt("number", number)
+            this.arguments = bundle
+        }
+    }
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        number = arguments?.getInt("number", 0) ?: 0
+    }
+
+    override fun onCreateView(
+        inflater: LayoutInflater,
+        container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View {
+        val rootView = FrameLayout(requireContext())
+
+        rootView.layoutParams = ViewGroup.LayoutParams(
+            ViewGroup.LayoutParams.MATCH_PARENT,
+            ViewGroup.LayoutParams.MATCH_PARENT
+        )
+
+        rootView.setBackgroundColor(Color.WHITE) // hides the other fragments, due to this I never found this issue.
+        rootView.isClickable = true // prevents clicking through the current fragment.
+
+        button = MaterialButton(requireContext())
+        button.text = "Fragment Problem : $number"
+        val lp = FrameLayout.LayoutParams(
+            FrameLayout.LayoutParams.WRAP_CONTENT,
+            FrameLayout.LayoutParams.WRAP_CONTENT
+        )
+        lp.gravity = Gravity.TOP
+        lp.topMargin = number * 50
+        button.layoutParams = lp
+
+        rootView.addView(button)
+
+        return rootView
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        Log.d("frag problem", "$number onSaveInstanceState")
+        super.onSaveInstanceState(outState)
+    }
+
+    override fun onStart() {
+        // state is set to false here. eg : minimize app, state = true, reopen, state = false.
+        Log.d("frag problem", "$number onStart, isStateSaved : $isStateSaved")
+        super.onStart()
+    }
+
+    override fun onResume() {
+        Log.d("frag problem", "$number onResume, isStateSaved : $isStateSaved")
+        super.onResume()
+    }
+
+    override fun onPause() {
+
+        // as far as experimented, isStateSaved is false in onPause.
+        Log.d("frag problem", "$number onPause, isStateSaved : $isStateSaved")
+
+        super.onPause()
+
+        // very common case in which we do a fragment transaction on a network call result.
+        // user initiates the network call and minimises the app and before opening again the result is fetched
+        // and hence a frag transaction is committed.
+        // then perhaps, the app would crash throwing "java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState".
+
+        button.postDelayed({
+            val fm = requireActivity().supportFragmentManager
+            fm.beginTransaction()
+                .replace(R.id.root_fragment_container, this.getInstance(number + 1))
+                .addToBackStack(null)
+                .commit()
+        }, 1500L)
+    }
+
+    override fun onStop() {
+        // weirdly, isStateSaved is true here even when onSaveInstanceState is called yet.
+        // also if I commit frag transactions in onStop then isStateSaved is false.
+        Log.d("frag problem", "$number onStop, isStateSaved : $isStateSaved")
+        super.onStop()
+    }
+
+    override fun onDestroyView() {
+        Log.d("frag problem", "$number onDestroyView, isStateSaved : $isStateSaved")
+        super.onDestroyView()
+    }
+
+}

app/src/main/res/layout/activity_main.xml

@@ -7,43 +7,9 @@
     android:background="@color/white"
     tools:context=".MainActivity">
 
-<!--    <com.example.androidconcepts.ui.retroDesign.RetroLayout-->
-<!--        android:id="@+id/neopop"-->
-<!--        android:layout_width="match_parent"-->
-<!--        android:layout_height="wrap_content"-->
-<!--        android:layout_margin="20dp"-->
-<!--        app:layout_constraintBottom_toBottomOf="parent"-->
-<!--        app:layout_constraintEnd_toEndOf="parent"-->
-<!--        app:layout_constraintStart_toStartOf="parent">-->
-
-<!--        <LinearLayout-->
-<!--            android:layout_width="wrap_content"-->
-<!--            android:layout_height="wrap_content"-->
-<!--            android:layout_gravity="center"-->
-<!--            android:orientation="horizontal">-->
-
-<!--            <TextView-->
-<!--                android:id="@+id/tv"-->
-<!--                android:layout_width="wrap_content"-->
-<!--                android:layout_height="wrap_content"-->
-<!--                android:layout_gravity="center"-->
-<!--                android:padding="20dp"-->
-<!--                android:paddingEnd="0dp"-->
-<!--                android:text="OKAY"-->
-<!--                android:textColor="@color/black"-->
-<!--                android:textSize="20dp"-->
-<!--                app:layout_constraintStart_toStartOf="parent"-->
-<!--                app:layout_constraintTop_toTopOf="parent" />-->
-
-<!--            <ImageView-->
-<!--                android:layout_width="32dp"-->
-<!--                android:layout_height="32dp"-->
-<!--                android:layout_gravity="center"-->
-<!--                android:layout_margin="12dp"-->
-<!--                android:src="@drawable/ic_baseline_arrow_circle_right_24" />-->
-
-<!--        </LinearLayout>-->
-
-<!--    </com.example.androidconcepts.ui.retroDesign.RetroLayout>-->
+    <FrameLayout
+        android:id="@+id/root_fragment_container"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"/>
 
 </androidx.constraintlayout.widget.ConstraintLayout>

app/src/test/java/com/example/androidconcepts/common/Benchmark.kt

@@ -5,6 +5,6 @@ fun measureTime(action: () -> Unit): Long {
     action.invoke()
     val endTime = System.currentTimeMillis()
     val measuredTime = endTime - startTime
-    println("measure time = " + measuredTime + "ms")
+    println("measured time = " + measuredTime + "ms")
     return measuredTime
 }