我创建了一个包含4个片段的底部导航项目，并将setHasOptionsMenu(true)放在qponFragment的onCreate()中，以便在切换Fragments之后保持qponFragment的相同内容。但是，它不起作用，从其他片段切回后，qponFragment仍会刷新。请帮助修复它，并找出我的代码有什么问题。
这里是MainActivity.kt的代码
class MainActivity : AppCompatActivity() {
private var mFirebaseAnalytics: FirebaseAnalytics? = null
private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.navigation_qpon -> {
//message.setText(R.string.title_qpon)
actionBarIcon(R.drawable.ic_title_black)
createQponFragment()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_me-> {
//message.setText(R.string.title_me)
actionBarIcon(R.drawable.logged)
createMeFragment()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_tool -> {
//message.setText(R.string.title_tool)
actionBarIcon(R.drawable.logged)
createToolFragment()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_tutorial -> {
//message.setText(R.string.title_tutorial)
actionBarIcon(R.drawable.tutorial)
createTutorialFragment()
return@OnNavigationItemSelectedListener true
}
}
false
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// Obtain the FirebaseAnalytics instance.
mFirebaseAnalytics = FirebaseAnalytics.getInstance(this)
actionBarIcon(R.drawable.ic_title_black)
createQponFragment()
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)
}
fun actionBarIcon(imageName:Int) {
setSupportActionBar(findViewById(R.id.my_toolbar))
my_toolbar.setLogo(imageName)
if (imageName == R.drawable.ic_title_black) {
my_toolbar.setTitle("")
}
if (imageName == R.drawable.logged) {
my_toolbar.setTitle("login name")
}
if (imageName == R.drawable.tutorial) {
my_toolbar.setTitle("Tutorial")
}
}
val manager = supportFragmentManager
fun createQponFragment() {
val transaction = manager.beginTransaction()
val fragment = qponFragment()
transaction.replace(R.id.fragmentholder,fragment)
transaction.addToBackStack(null)
transaction.commit()
}
fun createMeFragment() {
val transaction = manager.beginTransaction()
val fragment = meFragment()
transaction.replace(R.id.fragmentholder,fragment)
transaction.addToBackStack(null)
transaction.commit()
}
fun createToolFragment() {
val transaction = manager.beginTransaction()
val fragment = toolFragment()
transaction.replace(R.id.fragmentholder,fragment)
transaction.addToBackStack(null)
transaction.commit()
}
fun createTutorialFragment() {
val transaction = manager.beginTransaction()
val fragment = tutorialFragment()
transaction.replace(R.id.fragmentholder,fragment)
transaction.addToBackStack(null)
transaction.commit()
}
}
这里带有qponFragment.kt的代码
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setRetainInstance(true)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
setHasOptionsMenu(true)
return inflater.inflate(R.layout.fragment_qpon, container, false)
}
最佳答案
如果您尝试保留片段实例而不是每次都创建新实例，则它应该起作用。请找到代码bel
class MainActivity : AppCompatActivity() {
private var mFirebaseAnalytics: FirebaseAnalytics? = null
private var meFragment:Fragment? = null
var toolFragment :Fragment? =null
var qponFragment:Fragment? =null
var tutorialFragment:Fragment? = null
private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.navigation_qpon -> {
//message.setText(R.string.title_qpon)
actionBarIcon(R.drawable.ic_title_black)
createQponFragment()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_me-> {
//message.setText(R.string.title_me)
actionBarIcon(R.drawable.logged)
createMeFragment()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_tool -> {
//message.setText(R.string.title_tool)
actionBarIcon(R.drawable.logged)
createToolFragment()
return@OnNavigationItemSelectedListener true
}
R.id.navigation_tutorial -> {
//message.setText(R.string.title_tutorial)
actionBarIcon(R.drawable.tutorial)
createTutorialFragment()
return@OnNavigationItemSelectedListener true
}
}
false
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// Obtain the FirebaseAnalytics instance.
mFirebaseAnalytics = FirebaseAnalytics.getInstance(this)
actionBarIcon(R.drawable.ic_title_black)
createQponFragment()
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)
}
fun actionBarIcon(imageName:Int) {
setSupportActionBar(findViewById(R.id.my_toolbar))
my_toolbar.setLogo(imageName)
if (imageName == R.drawable.ic_title_black) {
my_toolbar.setTitle("")
}
if (imageName == R.drawable.logged) {
my_toolbar.setTitle("login name")
}
if (imageName == R.drawable.tutorial) {
my_toolbar.setTitle("Tutorial")
}
}
val manager = supportFragmentManager
fun createQponFragment() {
val transaction = manager.beginTransaction()
if(qponFragment == null) qponFragment = qponFragment() // *****code changed here***********
transaction.replace(R.id.fragmentholder,qponFragment)
transaction.addToBackStack(null)
transaction.commit()
}
fun createMeFragment() {
val transaction = manager.beginTransaction()
if(meFragment == null) meFragment = meFragment()
transaction.replace(R.id.fragmentholder,meFragment)
transaction.addToBackStack(null)
transaction.commit()
}
fun createToolFragment() {
val transaction = manager.beginTransaction()
if(toolFragment == null) toolFragment = toolFragment()
transaction.replace(R.id.fragmentholder,toolFragment)
transaction.addToBackStack(null)
transaction.commit()
}
fun createTutorialFragment() {
val transaction = manager.beginTransaction()
val fragment = tutorialFragment()
if(tutorialFragment == null) toolFragment = tutorialFragment() // *****code changed here***********
transaction.replace(R.id.fragmentholder,tutorialFragment)
transaction.replace(R.id.fragmentholder,fragment)
transaction.addToBackStack(null)
transaction.commit()
}
}
它显示错误:
关于android - Kotlin Android底部导航 fragment setRetainInstance(true)，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/50551850/