架构导航组件：每次都会调用 onCreateView答案

【问题标题】：Architecture Navigation Component : onCreateView gets called every time架构导航组件：每次都会调用 onCreateView
【发布时间】：2019-02-26 06:27:55
【问题描述】：

每次创建片段实例并在您按下返回时重新加载。

如何解决这个问题？

无法在导航控制器中拥有适当的后台堆栈是一个巨大的生产力问题。希望这是一个缺失的功能或故意制作的解决方法...... IMO 这是一个必须具备的，并且必须尽早引入（但是：https://issuetracker.google.com/issues/109856764 说 我们不会允许自定义可预见的未来的交易类型（例如隐藏/显示等）。）：（

Nav-Framework is nice, however, it create fragment's view every time

有人有解决办法吗？

我的代码是使用 Navigation 进行导航

object NavigationHelper : Navigational {


override fun moveDownWithPop(view: View,id: Int,popStackId: Int) {
    Navigation.findNavController(view).navigate(id,
            null,
            NavOptions.Builder()
                    .setPopUpTo(popStackId,
                            true).build()
    )
}

override fun moveDownWithDataPop(view: View,id: Int,popStackId: Int,bundle : Bundle) {
    Navigation.findNavController(view).navigate(id,
            bundle,
            NavOptions.Builder()
                    .setPopUpTo(popStackId,
                            true).build()
    )
}

override fun moveUp(view: View) {
    Navigation.findNavController(view).navigateUp()
}

override fun moveDown(view: View,id: Int) {
    Navigation.findNavController(view).navigate(id)
}

override fun moveDown(view: View,id: Int,args : Bundle) {
    Navigation.findNavController(view).navigate(id,args)
}

fun navigateGraph(graphId : Int,context : Context){
    var finalHost: NavHostFragment?  = NavHostFragment.create(graphId)
    (context as MainActivity).supportFragmentManager.beginTransaction()
            .replace(com.admision.R.id.content,finalHost!!)
            .setPrimaryNavigationFragment(finalHost) // this is the equivalent to app:defaultNavHost="true"
            .commit()
}
}

我找到了一些博客Why I Will Not Use Architecture Navigation Component

【问题讨论】：

标签： android androidx fragment-backstack android-architecture-navigation

【解决方案1】：

我确实喜欢这个，但我仍在等待谷歌的解决方案。

我们做到了，但仍在等待更好的方法

if (manageEventViewModel == null) {
    manageEventViewModel = ViewModelProviders.of(activity!!).get(ManageEventViewModel::class.java)
    manageEventViewModel!!.setBinder(binding!!,context!!,listingType)
    loadAdvertisement(binding!!.advertise.imgAdvertisement,binding!!.advertise.tvAdvertisement,binding!!.advertise.llAdvertisement)
}

完整代码

class ManageEventsFragment : BaseFragment() {

private var binding: FragmentFindEventsBinding? = null
private var manageEventViewModel: ManageEventViewModel? = null
override fun onCreateView(inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?): View? {
    if (binding == null)
        binding = DataBindingUtil.inflate(inflater,R.layout.fragment_find_events,container,false)


    var listingType: String? = null
    if (arguments != null) {
        listingType = arguments!!.getString(Constant.LISTINGTYPE)
        /*if (listingType != null && listingType.equals(Constant.SEARCHLIST)) {
            val data = arguments!!.getString(Constant.SEARCHEVENTMODEL)
            val managetEventDataModel = com.admision.manageevents.utils.Utils.getManageEventDataModel(data)
            manageEventViewModel!!.setSearchDataModel(managetEventDataModel!!)
        }*/
    }

    val sharedViewModel = ViewModelProviders.of(activity!!).get(SharedViewModel::class.java)
    sharedViewModel!!.dataToShare.observe(this,Observer<ManageEventsDataModel> { managetEventDataModel ->
        listingType = Constant.SEARCHLIST
        manageEventViewModel!!.setSearchDataModel(managetEventDataModel!!)
    })

    if (manageEventViewModel == null) {
        manageEventViewModel = ViewModelProviders.of(activity!!).get(ManageEventViewModel::class.java)
        manageEventViewModel!!.setBinder(binding!!,context!!,listingType)
        loadAdvertisement(binding!!.advertise.imgAdvertisement,binding!!.advertise.tvAdvertisement,binding!!.advertise.llAdvertisement)
    }
    return binding!!.root
}
}

【讨论】：

谢谢，它有效，但正如你所说，如果谷歌修复它，我们将不胜感激

【解决方案2】：

就像 Bhavesh 所做的那样，在我的例子中，我只有一个列表，在 onCreateView 中这行对我来说就足够了：

if (adapter.isEmpty()) {
            viewModel.getShopCats()
}

适配器只需要有这个：

fun isEmpty(): Boolean {
        return modelList.isNullOrEmpty()
}

【讨论】：