[英]Cannot create an instance of class ViewModel in Android MVVM
I am learning android MVVM pattern android development.我正在学习android MVVM模式android开发。 I wanted to create a recycclerview activity to show data from server.
我想创建一个 recyclerview 活动来显示来自服务器的数据。 But it's not accepting my viewmodel class.
但它不接受我的视图模型 class。 Bellow is my logcat errors.
Bellow 是我的 logcat 错误。
2020-04-12 21:03:18.026 2008-2008/com.shovon.mvvm E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.shovon.mvvm, PID: 2008
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.shovon.mvvm/com.shovon.mvvm.activity.RecyclerActivity}: java.lang.RuntimeException: Cannot create an instance of class com.shovon.mvvm.viewmodel.RecyclerActivityViewModel
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
Caused by: java.lang.RuntimeException: Cannot create an instance of class com.shovon.mvvm.viewmodel.RecyclerActivityViewModel
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:221)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.shovon.mvvm.activity.RecyclerActivity.onCreate(RecyclerActivity.kt:23)
at android.app.Activity.performCreate(Activity.java:7802)
at android.app.Activity.performCreate(Activity.java:7791)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
**Caused by: java.lang.InstantiationException: java.lang.Class<com.shovon.mvvm.viewmodel.RecyclerActivityViewModel> has no zero argument constructor**
at java.lang.Class.newInstance(Native Method)
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:219)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.shovon.mvvm.activity.RecyclerActivity.onCreate(RecyclerActivity.kt:23)
at android.app.Activity.performCreate(Activity.java:7802)
at android.app.Activity.performCreate(Activity.java:7791)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
Here is my viewmodel class.这是我的视图模型 class。 I am passing some data to activity from this viewmodel.
我正在将此视图模型中的一些数据传递给活动。 But problem is activity does not accept this viewmodel.
但问题是活动不接受这个视图模型。 Maybe viewmodel has any issue.
也许viewmodel有任何问题。
class RecyclerActivityViewModel(application: Application) : AndroidViewModel(application) {
val repository = RecyclerActivityRepository(application)
fun userData(): LiveData<ArrayList<UserResponse>>{
return repository.getUserData()
}
}
class RecyclerActivityRepository(application: Application) {
var liveData = MutableLiveData<ArrayList<UserResponse>>()
private val userList = ArrayList<UserResponse>()
private var adapter: UserAdapter? = null
fun getUserData(): MutableLiveData<ArrayList<UserResponse>>{
if (liveData == null){
liveData = MutableLiveData<ArrayList<UserResponse>>()
}
RetrofitClient.instance.getUsers()
.enqueue(object : Callback<List<UserResponse>> {
override fun onFailure(call: Call<List<UserResponse>>, t: Throwable) {
Log.v("Retrofit", t.message.toString())
}
override fun onResponse(
call: Call<List<UserResponse>>,
response: Response<List<UserResponse>>
) {
Log.v("Retrofit", "Success")
Log.v("response_code", response.code().toString())
try {
userList.addAll(response.body()!!)
adapter?.notifyDataSetChanged()
}catch (e: Exception){
Log.v("error", e.message.toString())}
}
})
return liveData
}
}
Here is my logic code这是我的逻辑代码
class RecyclerActivity : AppCompatActivity() {
private lateinit var viewModel: RecyclerActivityViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_recycler)
viewModel = ViewModelProvider(this).get(RecyclerActivityViewModel::class.java)
}
}
this might help这可能会有所帮助
viewModel= ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication())).get(RecyclerActivityViewModel::class.java)
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