increase speed of back navigation between screens

core/src/main/java/com/example/util/simpletimetracker/core/base/BaseFragment.kt

@@ -14,30 +14,46 @@ import kotlinx.coroutines.Job
 abstract class BaseFragment<T : ViewBinding> : Fragment(), Throttler {
 
     abstract val inflater: (LayoutInflater, ViewGroup?, Boolean) -> T
-    protected val binding: T get() = _binding!!
+    override var throttleJob: Job? = null
+    protected open val binding: T get() = _binding!!
     private var _binding: T? = null
     private var preDrawListeners: MutableList<OnPreDrawListener> = mutableListOf()
-    override var throttleJob: Job? = null
+    private var initialized: Boolean = false
 
     override fun onCreateView(
         inflater: LayoutInflater,
         container: ViewGroup?,
         savedInstanceState: Bundle?,
     ): View? {
-        _binding = inflater(inflater, container, false)
-        return binding.root
+        // Use previously saved view to avoid whole screen reinflating on back navigation,
+        // because of android nav component using fragment.replace internally.
+        // This also somehow fixes memory leaks occurring on navigation
+        // from main to some edit screen and back.
+        // If this ever changes - need to also fix these memory leaks.
+        return _binding?.root?.also {
+            initialized = true
+        } ?: run {
+            initialized = false
+            _binding = inflater(inflater, container, false)
+            binding.root
+        }
     }
 
     override fun onActivityCreated(savedInstanceState: Bundle?) {
         super.onActivityCreated(savedInstanceState)
-        initUi()
-        initUx()
+        if (!initialized) {
+            initUi()
+            initUx()
+        }
+        // Need to observe ViewModel again because LiveData.observe() uses fragment lifecycle,
+        // meaning that the subscriptions are removed on view destroy event.
         initViewModel()
     }
 
     override fun onDestroy() {
         super.onDestroy()
         preDrawListeners.forEach { view?.viewTreeObserver?.removeOnPreDrawListener(it) }
+        preDrawListeners.clear()
         _binding = null
     }
 

core/src/main/java/com/example/util/simpletimetracker/core/extension/FragmentExtensions.kt

@@ -35,13 +35,16 @@ inline fun Fragment.setSharedTransitions(
     ViewCompat.setTransitionName(sharedView, transitionName)
 }
 
-fun Fragment.addOnBackPressedListener(isEnabled: Boolean = true, action: () -> Unit) {
-    activity?.onBackPressedDispatcher?.addCallback(
-        this,
-        object : OnBackPressedCallback(isEnabled) {
-            override fun handleOnBackPressed() = action()
-        },
-    )
+fun Fragment.addOnBackPressedListener(
+    isEnabled: Boolean = true,
+    action: () -> Unit,
+): OnBackPressedCallback {
+    val callback = object : OnBackPressedCallback(isEnabled) {
+        override fun handleOnBackPressed() = action()
+    }
+    // Using fragment lifecycle to avoid listener removed on view destroy event.
+    activity?.onBackPressedDispatcher?.addCallback(this, callback)
+    return callback
 }
 
 fun Fragment.getDrawable(@DrawableRes resId: Int): Drawable? {

features/feature_change_activity_filter/src/main/java/com/example/util/simpletimetracker/feature_change_activity_filter/view/ChangeActivityFilterFragment.kt

@@ -104,7 +104,7 @@ class ChangeActivityFilterFragment :
         }
     }
 
-    override fun initUx() = with(binding) {
+    override fun initUx(): Unit = with(binding) {
         etChangeActivityFilterName.doAfterTextChanged { viewModel.onNameChange(it.toString()) }
         fieldChangeActivityFilterColor.setOnClick(viewModel::onColorChooserClick)
         fieldChangeActivityFilterType.setOnClick(viewModel::onTypeChooserClick)

features/feature_change_category/src/main/java/com/example/util/simpletimetracker/feature_change_category/view/ChangeCategoryFragment.kt

@@ -119,7 +119,7 @@ class ChangeCategoryFragment :
         )
     }
 
-    override fun initUx() = with(binding) {
+    override fun initUx(): Unit = with(binding) {
         etChangeCategoryName.doAfterTextChanged { viewModel.onNameChange(it.toString()) }
         fieldChangeCategoryColor.setOnClick(viewModel::onColorChooserClick)
         fieldChangeCategoryType.setOnClick(viewModel::onTypeChooserClick)

features/feature_change_record_tag/src/main/java/com/example/util/simpletimetracker/feature_change_record_tag/view/ChangeRecordTagFragment.kt

@@ -176,7 +176,7 @@ class ChangeRecordTagFragment :
         }
     }
 
-    override fun initUx() = with(binding) {
+    override fun initUx(): Unit = with(binding) {
         etChangeRecordTagName.doAfterTextChanged { viewModel.onNameChange(it.toString()) }
         fieldChangeRecordTagColor.setOnClick(viewModel::onColorChooserClick)
         fieldChangeRecordTagIcon.setOnClick(viewModel::onIconChooserClick)

features/feature_change_record_type/src/main/java/com/example/util/simpletimetracker/feature_change_record_type/view/ChangeRecordTypeFragment.kt

@@ -182,7 +182,7 @@ class ChangeRecordTypeFragment :
         }
     }
 
-    override fun initUx() = with(binding) {
+    override fun initUx(): Unit = with(binding) {
         etChangeRecordTypeName.doAfterTextChanged { viewModel.onNameChange(it.toString()) }
         fieldChangeRecordTypeColor.setOnClick(viewModel::onColorChooserClick)
         fieldChangeRecordTypeIcon.setOnClick(viewModel::onIconChooserClick)

features/feature_main/src/main/java/com/example/util/simpletimetracker/feature_main/view/MainFragment.kt

@@ -13,6 +13,7 @@ import androidx.fragment.app.viewModels
 import androidx.viewpager2.widget.ViewPager2
 import com.example.util.simpletimetracker.core.base.BaseFragment
 import com.example.util.simpletimetracker.core.di.BaseViewModelFactory
+import com.example.util.simpletimetracker.core.extension.addOnBackPressedListener
 import com.example.util.simpletimetracker.core.extension.addOnPageChangeCallback
 import com.example.util.simpletimetracker.core.sharedViewModel.MainTabsViewModel
 import com.example.util.simpletimetracker.core.utils.SHORTCUT_NAVIGATION_KEY
@@ -48,7 +49,7 @@ class MainFragment : BaseFragment<Binding>() {
 
     private val selectedColorFilter by lazy { getColorFilter(R.attr.appTabSelectedColor) }
     private val unselectedColorFilter by lazy { getColorFilter(R.attr.appTabUnselectedColor) }
-    private val backPressedCallback: OnBackPressedCallback = getOnBackPressedCallback()
+    private var backPressedCallback: OnBackPressedCallback? = null
     private var shortcutNavigationHandled = false
     private val mainPagePosition by lazy {
         mainTabsProvider.mainTab.let(mainTabsProvider::mapTabToPosition)
@@ -57,7 +58,10 @@ class MainFragment : BaseFragment<Binding>() {
     override fun initUi() {
         setupPager()
         checkForShortcutNavigation()
-        activity?.onBackPressedDispatcher?.addCallback(viewLifecycleOwner, backPressedCallback)
+    }
+
+    override fun initUx() {
+        backPressedCallback = addOnBackPressedListener(false, ::onBackPressed)
     }
 
     override fun initViewModel() {
@@ -102,7 +106,7 @@ class MainFragment : BaseFragment<Binding>() {
 
                 override fun onTabSelected(tab: TabLayout.Tab?) {
                     tab?.icon?.colorFilter = selectedColorFilter
-                    backPressedCallback.isEnabled = tab?.position.orZero() != mainPagePosition
+                    backPressedCallback?.isEnabled = tab?.position.orZero() != mainPagePosition
                 }
             },
         )
@@ -132,12 +136,8 @@ class MainFragment : BaseFragment<Binding>() {
         }.let(mainTabs::setSelectedTabIndicatorGravity)
     }
 
-    private fun getOnBackPressedCallback(): OnBackPressedCallback {
-        return object : OnBackPressedCallback(false) {
-            override fun handleOnBackPressed() {
-                binding.mainPager.setCurrentItem(mainPagePosition, true)
-            }
-        }
+    private fun onBackPressed() {
+        binding.mainPager.setCurrentItem(mainPagePosition, true)
     }
 
     private fun checkForShortcutNavigation() = with(binding) {