问题描述
我希望在我的片段页面中更改工具栏标题,该标题在我的主要活动中。我的项目基于具有数据绑定的MVVM体系结构。
这是我的main_activity.xml
<?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"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="viewModel"
type="com.lalsoft.toolbar_mvvm_databinding.viewmodel.MainViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".view.MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<com.google.android.material.appbar.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:elevation="0dp"
android:theme="@style/AppTheme.AppBarOverlay">
<androidx.appcompat.widget.Toolbar
android:id="@+id/toolbar"
android:minHeight="?attr/actionBarSize"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:titleTextColor="@android:color/white"
app:navigationIcon="@drawable/ic_arrow_back"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay"
app:navigationOnClickListener="@{()->viewModel.navBackClicked()}"
app:title="@{viewModel.toolbarTitle}"/>
</com.google.android.material.appbar.AppBarLayout>
<FrameLayout
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
这是我的mainActivity.kt
private const val TAG = "MainActivity"
class MainActivity : AppCompatActivity() {
private lateinit var viewModel: MainViewModel
private lateinit var dataBinding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
dataBinding = DataBindingUtil.setContentView(this,R.layout.activity_main)
viewModel = ViewModelProvider(this).get(MainViewModel::class.java)
//setSupportActionBar(dataBinding.toolbar)
//dataBinding.toolbar.setNavigationIcon(R.drawable.ic_arrow_back)
viewModel.navClicked.observe(this,navClickObserver)
viewModel.toolbarTitle.observe(this,toolbarTitleObserver)
dataBinding.viewModel = viewModel
if (savedInstanceState == null) {
supportFragmentManager.beginTransaction().replace(
R.id.fragment_container,FirstFragment()
).commit()
}
}
private val navClickObserver = Observer<Boolean> {
supportFragmentManager.popBackStack()
Log.e(TAG,"Nav Back clicked")
}
private val toolbarTitleObserver = Observer<String> {
Log.e(TAG,"Title set : $it")
}
}
这是我的MainViewModel
private const val TAG = "MainViewModel"
open class MainViewModel : ViewModel() {
val toolbarTitle: MutableLiveData<String> = MutableLiveData()
private val _navClicked: MutableLiveData<Boolean> = MutableLiveData()
val navClicked: LiveData<Boolean> = _navClicked
init {
Log.e(TAG,"Inside Init")
//toolbarTitle.value ="Main Activity"
}
fun navBackClicked() {
_navClicked.value = true
}
}
现在,我试图通过更改mainActivityViewModel的可变toolbarTitle来更改FragmentViewModel中的工具栏标题。
private const val TAG = "FirstViewModel"
class FirstViewModel : MainViewModel() {
private val _navigateToDetails = MutableLiveData<Event<String>>()
val navigateToFragment: LiveData<Event<String>>
get() = _navigateToDetails
init {
Log.e(TAG,"Inside Init")
toolbarTitle.value="First Fragment"
}
fun onBtnClick() {
_navigateToDetails.value = Event("Second Fragment")
}
}
这是我的片段类
private const val TAG = "FirstFragment"
class FirstFragment : Fragment() {
private lateinit var viewModel: FirstViewModel
private lateinit var dataBinding: FirstFragmentBinding
override fun onCreateView(
inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?
): View? {
dataBinding = DataBindingUtil.inflate(inflater,R.layout.first_fragment,container,false)
return dataBinding.root
}
override fun onViewCreated(view: View,savedInstanceState: Bundle?) {
super.onViewCreated(view,savedInstanceState)
viewModel = ViewModelProvider(this).get(FirstViewModel::class.java)
viewModel.toolbarTitle.observe(viewLifecycleOwner,toolbarTitleObserver)
viewModel.navigateToFragment.observe(viewLifecycleOwner,navigateToFragmentObserver)
//(activity as MainActivity?)!!.toolbar.title = "Check"
dataBinding.viewModel = viewModel
}
private val toolbarTitleObserver = Observer<String> {
Log.e(TAG,"Title set : $it")
//(activity as MainActivity?)!!.toolbar.title = "Check"
//Log.e(TAG,"Title set : Check")
}
private val navigateToFragmentObserver = Observer<Event<String>> { it ->
it.getContentIfNotHandled()?.let { // Only proceed if the event has never been handled
Log.i(TAG,"checkIt string $it")
parentFragmentManager.beginTransaction().replace(
R.id.fragment_container,SecondFragment()
).addToBackStack(null).commit()
}
}
}
尽管正确观察了工具栏标题,但程序中的标题未更改。 希望能得到一些帮助,以解决这个问题。
这是我的示例git项目,我正在尝试执行以下操作:github
解决方法
我同样努力! 我认为问题是生命周期所有者。但是找不到答案。 目前,我从ViewModel观察值,并在观察者内部分配值。 但是我认为有更好的方法!
,如果您的 Fragment 正在使用 ViewModel,则应将其范围限定为宿主 Activity,由 activityViewModels() 委托使用:
@AndroidEntryPoint
class HomeFragment : Fragment() {
private val viewModel: SharedViewModel by activityViewModels()
}
我认为这个答案也会有所帮助。
https://stackoverflow.com/a/62560605
当您使用 viewModels 时,您正在创建一个作用域为该单独 Fragment 的 ViewModel - 这意味着每个 Fragment 将拥有该 ViewModel 类的自己的单独实例。如果您希望单个 ViewModel 实例作用于整个 Activity,则需要通过 activityViewModels 使用