DataBinding在第一次远程调用时显示null值

Question

在我的应用程序中，我有一个片段，它调用远程服务来获取用户配置文件信息并显示它，我使用DataBinding来显示数据。

这是我的布局：

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<variable
name="viewModel"
type="com.myapp.ProfileViewModel" />
</data>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="@+id/name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@{viewModel.profile.firstName+ ' '+ viewModel.profile.lastName}" />
<!-- Other textviews -->
</LinearLayout>
</layout>

这是ProfileViewModel类

class ProfileViewModel : ViewModel() {
@Inject
lateinit var profileRepository: ProfileRepository
private var _profile = MutableLiveData<Profile>()
val profile: LiveData<Profile>
get() = _profile
fun getProfile(token: String) {
profileRepository.profile(
token,
{
// success
_profile.value = it.value
},
{
//error
}
)
}
}
data class Profile(
firstName : String,
lastName : String,
// other fields
)

这是应该显示配置文件的片段：

class ProfileFragment : Fragment() {
private lateinit var binding: FragmentProfileBinding
private lateinit var viewModel: ProfileViewModel
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding = DataBindingUtil.inflate(
inflater,
R.layout.fragment_profile,
container,
false
)
viewModel = activity?.run {
ViewModelProviders.of(this)[ProfileViewModel::class.java]
} ?: throw Exception("Invalid Activity")
binding.viewModel = viewModel
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel.getProfile(
"aToken"
)
}
}

现在，当我第一次打开片段时，存储库调用服务并正确获取数据，但"null"显示在文本视图中。如果我关闭片段并重新打开它，那么edittext就会正确填充。我的代码出了什么问题？

Answer 1

在片段类中设置binding.lifecycleOwner，以便LiveData对象中的更新反映在相应的视图中。你的碎片类应该是这样的：

class ProfileFragment : Fragment() {
private lateinit var binding: FragmentProfileBinding
private lateinit var viewModel: ProfileViewModel
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding = DataBindingUtil.inflate(
inflater,
R.layout.fragment_profile,
container,
false
)
viewModel = activity?.run {
ViewModelProviders.of(this)[ProfileViewModel::class.java]
} ?: throw Exception("Invalid Activity")
binding.viewModel = viewModel 
//add lifecycleOwner
binding.lifecycleOwner = this
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel.getProfile(
"aToken"
)
}
}