我不确定我是否正确理解了Android中的ViewModel架构。我认为ViewModel的生命周期与Activity相关,因此我们期望获得相同的实例,无论是将Activity或Fragment上下文传递给ViewModelProvider都没有关系。
无论如何,这是我的ViewModel:
class MainViewModel : ViewModel() {
var teamName: String = "Warriors";
}
这是我的活动:
class MainActivity : AppCompatActivity() {
private lateinit var viewModel: MainViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.main_activity)
viewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)
viewModel.teamName = "Cavaliers";
Log.d("YouQi", "activity viewModel.teamName: ${viewModel.teamName}");
if (savedInstanceState == null) {
supportFragmentManager.beginTransaction()
.replace(R.id.container, MainFragment.newInstance())
.commitNow()
}
}
}
最后,这是我的Fragment:
class MainFragment : androidx.fragment.app.Fragment() {
companion object {
fun newInstance() = MainFragment()
}
private lateinit var viewModel: MainViewModel
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
return inflater.inflate(R.layout.main_fragment, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
viewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)
Log.d("YouQi", "fragment viewModel.teamName: ${viewModel.teamName}");
}
}
我在Logcat中得到以下输出:
2018-06-03 16:06:24.591 31124-31124/com.axzae.zapkotlin D/YouQi: activity viewModel.teamName: Cavaliers
2018-06-03 16:06:24.652 31124-31124/com.axzae.zapkotlin D/YouQi: fragment viewModel.teamName: Warriors
显示值并没有更新到骑士队。我是否错误地使用了ViewModel?应该使用Dagger来实现单例模式吗?