feat: 서재UI/UX 개편 (11) - 탭 변경 시에도 스크롤 유지되도록 기능 구현

app/src/main/java/com/into/websoso/ui/main/MainActivity.kt

@@ -1,16 +1,14 @@
 package com.into.websoso.ui.main
 
+import android.annotation.SuppressLint
 import android.content.Context
 import android.content.Intent
 import android.os.Bundle
-import android.view.MenuItem
 import android.view.View
 import androidx.activity.OnBackPressedCallback
 import androidx.activity.viewModels
 import androidx.annotation.IntegerRes
 import androidx.fragment.app.Fragment
-import androidx.fragment.app.commit
-import androidx.fragment.app.replace
 import com.into.websoso.R.id.fcv_main
 import com.into.websoso.R.id.menu_explore
 import com.into.websoso.R.id.menu_feed
@@ -40,12 +38,22 @@ import dagger.hilt.android.AndroidEntryPoint
 class MainActivity : BaseActivity<ActivityMainBinding>(activity_main) {
     private val mainViewModel: MainViewModel by viewModels()
     private var backPressedTime: Long = 0L
+    private var currentFragment: Fragment? = null
+    private var currentSelectedItemId: Int = menu_home
+
+    private val fragmentTags = mapOf(
+        menu_home to HomeFragment::class.java.name,
+        menu_explore to ExploreFragment::class.java.name,
+        menu_feed to FeedFragment::class.java.name,
+        menu_library to LibraryFragment::class.java.name,
+        menu_my_page to MyPageFragment::class.java.name,
+    )
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 
         setupBackButtonListener()
-        setBottomNavigationView()
+        setupBottomNavigationView()
         setupObserver()
         onViewGuestClick()
         handleNavigation(intent.getSerializableExtra(DESTINATION_KEY) as? FragmentType)
@@ -75,13 +83,74 @@ class MainActivity : BaseActivity<ActivityMainBinding>(activity_main) {
         }
     }
 
-    private fun setBottomNavigationView() {
+    @SuppressLint("CommitTransaction")
+    private fun setupBottomNavigationView() {
+        setupInitialFragment()
+        setupBottomNavListener()
         binding.bnvMain.selectedItemId = menu_home
-        replaceFragment<HomeFragment>()
+    }
+
+    private fun setupInitialFragment() {
+        val initialItemId = menu_home
+        val initialTag = fragmentTags[initialItemId]!!
+        val initialFragment = findOrCreateFragment(initialTag)
+
+        if (!initialFragment.isAdded) {
+            supportFragmentManager
+                .beginTransaction()
+                .add(fcv_main, initialFragment, initialTag)
+                .commit()
+        }
+
+        currentFragment = initialFragment
+    }
+
+    private fun setupBottomNavListener() {
+        binding.bnvMain.setOnItemSelectedListener { item ->
+            if (item.itemId == currentSelectedItemId && item.itemId == menu_library) {
+                val libraryFragment = supportFragmentManager.findFragmentByTag(
+                    LibraryFragment::class.java.name,
+                ) as? LibraryFragment
+
+                libraryFragment?.resetScrollPosition()
+            } else {
+                replaceCurrentFragment(item.itemId)
+                currentSelectedItemId = item.itemId
+            }
 
-        binding.bnvMain.setOnItemSelectedListener(::replaceFragment)
+            true
+        }
     }
 
+    private fun replaceCurrentFragment(itemId: Int) {
+        val tag = fragmentTags[itemId]!!
+        val targetFragment = findOrCreateFragment(tag)
+
+        val transaction = supportFragmentManager.beginTransaction()
+
+        currentFragment?.let { transaction.hide(it) }
+
+        if (!targetFragment.isAdded) {
+            transaction.add(fcv_main, targetFragment, tag)
+        } else {
+            transaction.show(targetFragment)
+        }
+
+        transaction.commit()
+        currentFragment = targetFragment
+    }
+
+    private fun findOrCreateFragment(tag: String): Fragment =
+        supportFragmentManager.findFragmentByTag(tag)
+            ?: when (tag) {
+                HomeFragment::class.java.name -> HomeFragment()
+                ExploreFragment::class.java.name -> ExploreFragment()
+                FeedFragment::class.java.name -> FeedFragment()
+                LibraryFragment::class.java.name -> LibraryFragment()
+                MyPageFragment::class.java.name -> MyPageFragment()
+                else -> throw IllegalArgumentException("Unknown fragment tag: $tag")
+            }
+
     private fun setupObserver() {
         mainViewModel.isLogin.observe(this) { isLogin ->
             when (isLogin) {
@@ -101,87 +170,22 @@ class MainActivity : BaseActivity<ActivityMainBinding>(activity_main) {
         }
     }
 
-    private fun replaceFragment(item: MenuItem): Boolean {
-        when (FragmentType.valueOf(item.itemId)) {
-            HOME -> replaceFragment<HomeFragment>()
-            EXPLORE -> replaceFragment<ExploreFragment>()
-            FEED -> replaceFragment<FeedFragment>()
-            LIBRARY -> replaceFragment<LibraryFragment>()
-            MY_PAGE -> replaceFragment<MyPageFragment>()
-        }
-        return true
-    }
-
-    private inline fun <reified T : Fragment> replaceFragment() {
-        supportFragmentManager.commit {
-            replace<T>(fcv_main)
-            setReorderingAllowed(true)
-        }
-    }
-
-    enum class FragmentType(
-        @IntegerRes private val resId: Int,
-    ) {
-        LIBRARY(menu_library),
-        HOME(menu_home),
-        EXPLORE(menu_explore),
-        FEED(menu_feed),
-        MY_PAGE(menu_my_page),
-        ;
-
-        companion object {
-            fun valueOf(id: Int): FragmentType =
-                entries.find { fragmentType -> fragmentType.resId == id }
-                    ?: throw IllegalArgumentException()
-
-            fun valueOf(fragmentName: String): FragmentType =
-                entries.find { fragmentType -> fragmentType.name == fragmentName }
-                    ?: throw IllegalArgumentException()
-        }
-    }
-
     private fun showLoginRequestDialog() {
         val dialog = LoginRequestDialogFragment.newInstance()
         dialog.show(supportFragmentManager, LoginRequestDialogFragment.TAG)
     }
 
     private fun handleNavigation(destination: FragmentType?) {
-        when (destination) {
-            EXPLORE -> selectFragment(EXPLORE)
-            MY_PAGE -> selectFragment(MY_PAGE)
-            FEED -> selectFragment(FEED)
-            LIBRARY -> selectFragment(LIBRARY)
-            HOME, null -> selectFragment(HOME)
+        val menuId = when (destination) {
+            EXPLORE -> menu_explore
+            MY_PAGE -> menu_my_page
+            FEED -> menu_feed
+            LIBRARY -> menu_library
+            HOME, null -> menu_home
         }
-    }
-
-    private fun selectFragment(fragmentType: FragmentType) {
-        when (fragmentType) {
-            HOME -> {
-                binding.bnvMain.selectedItemId = menu_home
-                replaceFragment<HomeFragment>()
-            }
-
-            EXPLORE -> {
-                binding.bnvMain.selectedItemId = menu_explore
-                replaceFragment<ExploreFragment>()
-            }
-
-            FEED -> {
-                binding.bnvMain.selectedItemId = menu_feed
-                replaceFragment<FeedFragment>()
-            }
 
-            LIBRARY -> {
-                binding.bnvMain.selectedItemId = menu_library
-                replaceFragment<LibraryFragment>()
-            }
-
-            MY_PAGE -> {
-                binding.bnvMain.selectedItemId = menu_my_page
-                replaceFragment<MyPageFragment>()
-            }
-        }
+        binding.bnvMain.selectedItemId = menuId
+        replaceCurrentFragment(menuId)
     }
 
     companion object {
@@ -210,4 +214,25 @@ class MainActivity : BaseActivity<ActivityMainBinding>(activity_main) {
                 flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK
             }
     }
+
+    enum class FragmentType(
+        @IntegerRes val resId: Int,
+    ) {
+        LIBRARY(menu_library),
+        HOME(menu_home),
+        EXPLORE(menu_explore),
+        FEED(menu_feed),
+        MY_PAGE(menu_my_page),
+        ;
+
+        companion object {
+            fun valueOf(id: Int): FragmentType =
+                entries.find { it.resId == id }
+                    ?: throw IllegalArgumentException()
+
+            fun valueOf(fragmentName: String): FragmentType =
+                entries.find { it.name == fragmentName }
+                    ?: throw IllegalArgumentException()
+        }
+    }
 }

app/src/main/java/com/into/websoso/ui/main/library/LibraryFragment.kt

@@ -7,10 +7,12 @@ import android.view.ViewGroup
 import androidx.compose.ui.platform.ComposeView
 import androidx.compose.ui.platform.ViewCompositionStrategy
 import androidx.fragment.app.Fragment
+import androidx.fragment.app.viewModels
 import com.into.websoso.R
 import com.into.websoso.core.common.navigator.NavigatorProvider
 import com.into.websoso.core.designsystem.theme.WebsosoTheme
 import com.into.websoso.feature.library.LibraryScreen
+import com.into.websoso.feature.library.LibraryViewModel
 import dagger.hilt.android.AndroidEntryPoint
 import javax.inject.Inject
 
@@ -43,4 +45,9 @@ class LibraryFragment : Fragment() {
         }
         return view
     }
+
+    fun resetScrollPosition() {
+        val viewModel: LibraryViewModel by viewModels()
+        viewModel.resetScrollPosition()
+    }
 }

feature/library/src/main/java/com/into/websoso/feature/library/LibraryScreen.kt

@@ -6,8 +6,6 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.lazy.LazyListState
 import androidx.compose.foundation.lazy.grid.LazyGridState
-import androidx.compose.foundation.lazy.grid.rememberLazyGridState
-import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.SheetState
 import androidx.compose.material3.rememberModalBottomSheetState
@@ -56,8 +54,8 @@ fun LibraryScreen(
         .map { it.map { novel -> novel.toUiModel() } }
         .collectAsLazyPagingItems()
     var isShowBottomSheet by remember { mutableStateOf(false) }
-    val listState = rememberLazyListState()
-    val gridState = rememberLazyGridState()
+    val listState = libraryViewModel.listState
+    val gridState = libraryViewModel.gridState
     val bottomSheetState = rememberModalBottomSheetState(
         skipPartiallyExpanded = true,
         confirmValueChange = { false },

feature/library/src/main/java/com/into/websoso/feature/library/LibraryViewModel.kt

@@ -1,5 +1,10 @@
 package com.into.websoso.feature.library
 
+import androidx.compose.foundation.lazy.LazyListState
+import androidx.compose.foundation.lazy.grid.LazyGridState
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import androidx.paging.PagingData
@@ -35,6 +40,12 @@ class LibraryViewModel
         private val _uiState = MutableStateFlow(LibraryUiState())
         val uiState: StateFlow<LibraryUiState> = _uiState.asStateFlow()
 
+        var listState by mutableStateOf(LazyListState())
+            private set
+
+        var gridState by mutableStateOf(LazyGridState())
+            private set
+
         init {
             updateMyLibraryFilter()
         }
@@ -88,4 +99,14 @@ class LibraryViewModel
                 it.copy(isInterested = !it.isInterested)
             }
         }
+
+        fun resetScrollPosition() {
+            viewModelScope.launch {
+                if (uiState.value.isGrid) {
+                    gridState.scrollToItem(0)
+                } else {
+                    listState.scrollToItem(0)
+                }
+            }
+        }
     }