Guards and null checks against unsaved fragment transactions on configuration change

Fixes #1555

Author: TranceLove

app/src/androidTest/java/com/amaze/filemanager/ui/fragments/TabFragmentTest.kt

@@ -0,0 +1,93 @@
+package com.amaze.filemanager.ui.fragments
+
+import android.content.pm.ActivityInfo
+import androidx.test.espresso.Espresso.onView
+import androidx.test.espresso.action.ViewActions.swipeLeft
+import androidx.test.espresso.action.ViewActions.swipeRight
+import androidx.test.espresso.matcher.ViewMatchers.withId
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.platform.app.InstrumentationRegistry
+import androidx.test.rule.ActivityTestRule
+import androidx.test.rule.GrantPermissionRule
+import com.amaze.filemanager.R
+import com.amaze.filemanager.ui.activities.MainActivity
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/**
+ * Tests for [TabFragment] functionality, mainly for
+ * https://github.com/TeamAmaze/AmazeFileManager/issues/1555.
+ *
+ * Note: deprecated methods and classes are used here for best reproducing the issues.
+ */
+@Suppress("DEPRECATION")
+@RunWith(AndroidJUnit4::class)
+class TabFragmentTest {
+    @get:Rule
+    val activityRule = ActivityTestRule(MainActivity::class.java)
+
+    @Rule
+    @JvmField
+    val storagePermissionRule: GrantPermissionRule =
+        GrantPermissionRule
+            .grant(android.Manifest.permission.WRITE_EXTERNAL_STORAGE)
+
+    /**
+     * Check if the fragment state is saved correctly during a configuration change
+     * by rotate the screen while swiping between the tabs.
+     */
+    @Test
+    fun testFragmentStateSavingDuringConfigChange() {
+        // First perform the swipe action
+        onView(withId(R.id.pager)).perform(swipeLeft())
+
+        // Force a configuration change by rotating the screen
+        activityRule.activity.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE
+        Thread.sleep(1000) // Give time for the rotation to complete
+        activityRule.activity.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_PORTRAIT
+    }
+
+    /**
+     * Check if the fragment state is saved correctly during rapid tab swiping.
+     */
+    @Test
+    fun testRapidTabSwitchingAndStateSaving() {
+        // Perform rapid tab switches
+        repeat(10) {
+            onView(withId(R.id.pager)).perform(swipeLeft())
+            Thread.sleep(100) // Small delay to ensure swipe completes
+            onView(withId(R.id.pager)).perform(swipeRight())
+            Thread.sleep(100) // Small delay to ensure swipe completes
+        }
+
+        // Force a save state by rotating
+        activityRule.activity.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE
+    }
+
+    /**
+     * Check if the fragment state is saved correctly when the fragment is detached.
+     */
+    @Test
+    fun testFragmentDetachmentAndStateSaving() {
+        // First switch to a different tab
+        onView(withId(R.id.pager)).perform(swipeLeft())
+
+        // Get the TabFragment
+        InstrumentationRegistry.getInstrumentation().runOnMainSync {
+            val activity = activityRule.activity
+            val tabFragment =
+                activity.supportFragmentManager
+                    .findFragmentById(R.id.content_frame) as TabFragment
+
+            // Detach fragment through FragmentManager
+            activity.supportFragmentManager.beginTransaction().apply {
+                tabFragment.fragments.firstOrNull()?.let { detach(it) }
+                commit()
+            }
+        }
+
+        // Force state save through configuration change
+        activityRule.activity.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE
+    }
+} 

app/src/main/java/com/amaze/filemanager/adapters/RecyclerAdapter.java

@@ -683,7 +683,7 @@ public void createHeaders(boolean invalidate, List<IconDataParcelable> uris) {
 
   @Override
   public int getItemCount() {
-    return getItemsDigested().size();
+    return getItemsDigested() != null ? getItemsDigested().size() : 0;
   }
 
   @Override