无法创建我的 AndroidViewModel 的实例
Cannot create an instance of my AndroidViewModel
这是我第一次使用 android 和 mvvm。
我收到这个错误：
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ClementF.logged, PID: 11719
java.lang.RuntimeException: Cannot create an instance of class com.ClementF.logged.ActivityViewModel
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:275)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.ClementF.logged.ActivitySelectorFragment.onCreate(ActivitySelectorFragment.java:34)
at androidx.fragment.app.Fragment.performCreate(Fragment.java:2684)
at androidx.fragment.app.FragmentStateManager.create(FragmentStateManager.java:270)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1173)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:442)
at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2167)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1990)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1945)
at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1816)
at androidx.fragment.app.BackStackRecord.commitNow(BackStackRecord.java:297)
at androidx.viewpager2.adapter.FragmentStateAdapter.placeFragmentInViewHolder(FragmentStateAdapter.java:341)
at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:276)
at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:67)
at androidx.recyclerview.widget.RecyclerView.dispatchChildAttached(RecyclerView.java:7556)
at androidx.recyclerview.widget.RecyclerView.addView(RecyclerView.java:860)
at androidx.recyclerview.widget.ChildHelper.addView(ChildHelper.java:107)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addViewInt(RecyclerView.java:8601)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8559)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8547)
at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1641)
at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.viewpager2.widget.ViewPager2.onLayout(ViewPager2.java:527)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:148)
at com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:43)
at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onLayoutChild(AppBarLayout.java:1996)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:918)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
E/AndroidRuntime: at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:784)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3470)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2938)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1952)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8171)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:972)
at android.view.Choreographer.doCallbacks(Choreographer.java:796)
at android.view.Choreographer.doFrame(Choreographer.java:731)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:957)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Constructor.newInstance0(Native Method)
at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267)
... 79 more
Caused by: java.lang.RuntimeException: cannot find implementation for com.ClementF.logged.ActivityDatabase. ActivityDatabase_Impl does not exist
at androidx.room.Room.getGeneratedImplementation(Room.java:94)
at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:952)
at com.ClementF.logged.ActivityDatabase.getInstance(ActivityDatabase.java:24)
at com.ClementF.logged.ActivityRepository.<init>(ActivityRepository.java:19)
at com.ClementF.logged.ActivityViewModel.<init>(ActivityViewModel.java:18)
... 82 more
这是我的 AndroidViewModel：
package com.ClementF.logged;
import android.app.Application;
import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import java.util.List;
public class ActivityViewModel extends AndroidViewModel {
private ActivityRepository activityRepository;
private LiveData<List<ActivityEntity>> activities;
public ActivityViewModel(@NonNull Application application) {
super(application);
activityRepository = new ActivityRepository(application);
activities = activityRepository.getAllActivities();
}
public void insert(ActivityEntity activity) {
activityRepository.insert(activity);
}
public void update(ActivityEntity activity) {
activityRepository.update(activity);
}
public void delete(ActivityEntity activity) {
activityRepository.delete(activity);
}
public LiveData<List<ActivityEntity>> getAllActivities() {
return activityRepository.getAllActivities();
}
}
这是试图访问 ViewModel 的片段
package com.ClementF.logged;
import android.app.Application;
import android.os.Bundle;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModel;
import androidx.lifecycle.ViewModelProvider;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import java.util.List;
public class ActivitySelectorFragment extends Fragment {
private ActivityViewModel activityViewModel;
public ActivitySelectorFragment() {
// Required empty public constructor
}
public static ActivitySelectorFragment newInstance() {
return new ActivitySelectorFragment();
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// setup view model
activityViewModel = new ViewModelProvider(this).get(ActivityViewModel.class);
activityViewModel.getAllActivities().observe(this, new Observer<List<ActivityEntity>>() {
@Override
public void onChanged(List<ActivityEntity> activityEntities) {
// TODO: update recycler view
}
});
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_activity_selector, container, false);
}
}
我尝试在 ViewModelProvider 构造函数中传递一个 ViewModelProvider.AndroidViewModelFactory，但是我得到了同样的错误。
关于我做错了什么有什么想法吗？非常感谢！
如果您需要知道这是来自我的 main_activity 的 ViewPager2 中的片段，我使用的是选项卡布局。
发现ViewModel居然没有错误
将这两行添加到您的 gradle 以便 Room 库可以编译 SQL 代码，处理注释和编译。
annotationProcessor "androidx.room:room-compiler:$room_version"
androidTestImplementation "androidx.room:room-testing:$room_version"
room_version 是 Google
提供的最新版本
然后同步 Gradle
将 ColumnInfo 添加到 ActivityEntity 中的 table 以便它可以将您的数据存储在列下并根据您的喜好命名，我只是将其命名为 activity
@ColumnInfo(name="activity")
:)
这是我第一次使用 android 和 mvvm。
我收到这个错误：
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ClementF.logged, PID: 11719
java.lang.RuntimeException: Cannot create an instance of class com.ClementF.logged.ActivityViewModel
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:275)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.ClementF.logged.ActivitySelectorFragment.onCreate(ActivitySelectorFragment.java:34)
at androidx.fragment.app.Fragment.performCreate(Fragment.java:2684)
at androidx.fragment.app.FragmentStateManager.create(FragmentStateManager.java:270)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1173)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:442)
at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2167)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1990)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1945)
at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1816)
at androidx.fragment.app.BackStackRecord.commitNow(BackStackRecord.java:297)
at androidx.viewpager2.adapter.FragmentStateAdapter.placeFragmentInViewHolder(FragmentStateAdapter.java:341)
at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:276)
at androidx.viewpager2.adapter.FragmentStateAdapter.onViewAttachedToWindow(FragmentStateAdapter.java:67)
at androidx.recyclerview.widget.RecyclerView.dispatchChildAttached(RecyclerView.java:7556)
at androidx.recyclerview.widget.RecyclerView.addView(RecyclerView.java:860)
at androidx.recyclerview.widget.ChildHelper.addView(ChildHelper.java:107)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addViewInt(RecyclerView.java:8601)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8559)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:8547)
at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1641)
at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.viewpager2.widget.ViewPager2.onLayout(ViewPager2.java:527)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:148)
at com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:43)
at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onLayoutChild(AppBarLayout.java:1996)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:918)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
E/AndroidRuntime: at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:784)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3470)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2938)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1952)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8171)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:972)
at android.view.Choreographer.doCallbacks(Choreographer.java:796)
at android.view.Choreographer.doFrame(Choreographer.java:731)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:957)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Constructor.newInstance0(Native Method)
at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267)
... 79 more
Caused by: java.lang.RuntimeException: cannot find implementation for com.ClementF.logged.ActivityDatabase. ActivityDatabase_Impl does not exist
at androidx.room.Room.getGeneratedImplementation(Room.java:94)
at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:952)
at com.ClementF.logged.ActivityDatabase.getInstance(ActivityDatabase.java:24)
at com.ClementF.logged.ActivityRepository.<init>(ActivityRepository.java:19)
at com.ClementF.logged.ActivityViewModel.<init>(ActivityViewModel.java:18)
... 82 more
这是我的 AndroidViewModel：
package com.ClementF.logged;
import android.app.Application;
import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import java.util.List;
public class ActivityViewModel extends AndroidViewModel {
private ActivityRepository activityRepository;
private LiveData<List<ActivityEntity>> activities;
public ActivityViewModel(@NonNull Application application) {
super(application);
activityRepository = new ActivityRepository(application);
activities = activityRepository.getAllActivities();
}
public void insert(ActivityEntity activity) {
activityRepository.insert(activity);
}
public void update(ActivityEntity activity) {
activityRepository.update(activity);
}
public void delete(ActivityEntity activity) {
activityRepository.delete(activity);
}
public LiveData<List<ActivityEntity>> getAllActivities() {
return activityRepository.getAllActivities();
}
}
这是试图访问 ViewModel 的片段
package com.ClementF.logged;
import android.app.Application;
import android.os.Bundle;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModel;
import androidx.lifecycle.ViewModelProvider;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import java.util.List;
public class ActivitySelectorFragment extends Fragment {
private ActivityViewModel activityViewModel;
public ActivitySelectorFragment() {
// Required empty public constructor
}
public static ActivitySelectorFragment newInstance() {
return new ActivitySelectorFragment();
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// setup view model
activityViewModel = new ViewModelProvider(this).get(ActivityViewModel.class);
activityViewModel.getAllActivities().observe(this, new Observer<List<ActivityEntity>>() {
@Override
public void onChanged(List<ActivityEntity> activityEntities) {
// TODO: update recycler view
}
});
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_activity_selector, container, false);
}
}
我尝试在 ViewModelProvider 构造函数中传递一个 ViewModelProvider.AndroidViewModelFactory，但是我得到了同样的错误。
关于我做错了什么有什么想法吗？非常感谢！
如果您需要知道这是来自我的 main_activity 的 ViewPager2 中的片段，我使用的是选项卡布局。
发现ViewModel居然没有错误
将这两行添加到您的 gradle 以便 Room 库可以编译 SQL 代码，处理注释和编译。
annotationProcessor "androidx.room:room-compiler:$room_version"
androidTestImplementation "androidx.room:room-testing:$room_version"
room_version 是 Google
提供的最新版本然后同步 Gradle
将 ColumnInfo 添加到 ActivityEntity 中的 table 以便它可以将您的数据存储在列下并根据您的喜好命名，我只是将其命名为 activity
@ColumnInfo(name="activity")
:)