Changing fragments via bottom navigation view works well now! Also started work on SettingsFragment.kt

app/src/main/java/com/denizk0461/studip/activity/MainActivity.kt

@@ -1,6 +1,7 @@
 package com.denizk0461.studip.activity
 
 import android.os.Bundle
+import android.util.Log
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.view.WindowCompat
 import androidx.navigation.findNavController
@@ -8,15 +9,23 @@ import androidx.navigation.ui.AppBarConfiguration
 import androidx.navigation.ui.navigateUp
 import android.view.Menu
 import android.view.MenuItem
+import androidx.fragment.app.Fragment
+import androidx.fragment.app.FragmentTransaction
+import androidx.lifecycle.Lifecycle
 import com.denizk0461.studip.R
 import com.denizk0461.studip.data.Dependencies
 import com.denizk0461.studip.databinding.ActivityMainBinding
 import com.denizk0461.studip.db.EventRepository
+import com.denizk0461.studip.fragment.EventFragment
+import com.denizk0461.studip.fragment.FoodFragment
+import com.denizk0461.studip.fragment.SettingsFragment
 
 class MainActivity : AppCompatActivity() {
 
     private lateinit var appBarConfiguration: AppBarConfiguration
     private lateinit var binding: ActivityMainBinding
+    private var currentFragment = FragmentType.SCHEDULE
+    private val fragments = listOf(EventFragment(), FoodFragment(), SettingsFragment())
 
     override fun onCreate(savedInstanceState: Bundle?) {
         WindowCompat.setDecorFitsSystemWindows(window, false)
@@ -27,6 +36,12 @@ class MainActivity : AppCompatActivity() {
         binding = ActivityMainBinding.inflate(layoutInflater)
         setContentView(binding.root)
 
+        binding.contentMain.navView.setOnItemSelectedListener { item ->
+            loadFragment(bottomIdToType(item.itemId))
+        }
+
+        loadFragment(currentFragment)
+
 //        setSupportActionBar(binding.toolbar)
 
 //        val navController = findNavController(R.id.nav_host_fragment_content_main)
@@ -41,6 +56,36 @@ class MainActivity : AppCompatActivity() {
 //        }
     }
 
+    private fun loadFragment(type: FragmentType): Boolean {
+//        val fragment = supportFragmentManager.findFragmentByTag(type.type) ?: getFragmentByType(type)
+        val fragment = getFragment(type)
+
+        if (fragment.lifecycle.currentState != Lifecycle.State.INITIALIZED) {
+            return false
+        }
+
+//        if (supportFragmentManager.fragments.size > 1) {
+//
+//            val currentFragment = supportFragmentManager.findFragmentByTag(currentFragment.type)
+//            if (currentFragment != null) {
+//                supportFragmentManager.beginTransaction().remove(currentFragment).commit()
+//                supportFragmentManager.popBackStack()
+//            }
+//        }
+
+//        supportFragmentManager.popBackStack()
+        supportFragmentManager.beginTransaction()
+            .replace(R.id.nav_host_fragment_content_main, fragment, type.type)
+            .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
+            .commit()
+
+        binding.contentMain.appTitleBar.text = getTitleString(type)
+
+        currentFragment = type
+
+        return true
+    }
+
     override fun onCreateOptionsMenu(menu: Menu): Boolean {
         // Inflate the menu; this adds items to the action bar if it is present.
         menuInflater.inflate(R.menu.menu_main, menu)
@@ -62,4 +107,37 @@ class MainActivity : AppCompatActivity() {
         return navController.navigateUp(appBarConfiguration)
                 || super.onSupportNavigateUp()
     }
+
+    private fun getFragmentByType(type: FragmentType): Fragment {
+//        Log.d("AAA!", "help")
+        return when (type) {
+            FragmentType.SCHEDULE -> EventFragment()
+            FragmentType.FOOD -> FoodFragment() // TODO once this fragment has been implemented
+            FragmentType.SETTINGS -> SettingsFragment()
+        }
+    }
+
+    private fun bottomIdToType(id: Int): FragmentType = when (id) {
+        R.id.food -> FragmentType.FOOD
+        R.id.settings -> FragmentType.SETTINGS
+        else -> FragmentType.SCHEDULE
+    }
+
+    private fun getFragment(type: FragmentType) = when (type) {
+        FragmentType.SCHEDULE -> fragments[0]
+        FragmentType.FOOD -> fragments[1]
+        FragmentType.SETTINGS -> fragments[2]
+    }
+
+    private fun getTitleString(type: FragmentType) = when (type) {
+        FragmentType.SCHEDULE -> getString(R.string.title_schedule)
+        FragmentType.FOOD -> getString(R.string.title_food)
+        FragmentType.SETTINGS -> getString(R.string.title_settings)
+    }
+
+    enum class FragmentType(val type: String) {
+        SCHEDULE("schedule"),
+        FOOD("food"),
+        SETTINGS("settings"),
+    }
 }