无法创建我的AndroidViewModel的实例

如何解决无法创建我的AndroidViewModel的实例

这是我第一次使用android和mvvm。

我收到此错误：

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$5.addView(RecyclerView.java:860)
        at androidx.recyclerview.widget.ChildHelper.addView(ChildHelper.java:107)
        at androidx.recyclerview.widget.RecyclerView$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构造函数内部传递ViewModelProvider.AndroidViewModelFactory，但是遇到相同的错误。

关于我在做什么错的任何想法吗？非常感谢！

如果您要从main_activity中知道这是ViewPager2内部的一个片段，则我使用的是选项卡布局。

Git回购：https://github.com/Teariest/Logged

解决方法

发现ViewModel实际上没有错误。

将这两行添加到gradle中，以便Room库可以编译SQL代码，处理注释以及进行编译。

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

然后同步抓斗

将ColumnInfo添加到 ActivityEntity 中的表中，以便它可以将您的数据存储在列下，并按您喜欢的名称命名，我将其命名为 activity em>

@ColumnInfo(name="activity")

：）