当我尝试运行我的应用程序时,它会因为这个logcat错误而崩溃。这个问题非常类似于这篇文章,但所有提到的解决方案都不适合我。
当我搜索这个错误时,我发现这通常是因为viewmodelproviders过时了,人们建议在factory类中使用新的viewmodelprovider,但即使这样也不适合我。 java.lang.RuntimeException: Cannot create an instance of class com.emirhalici.notetakingappnvvmexample.NoteViewModel
我不知道哪里会有问题,如果我有一个小的语法错误或其他东西。这让我发疯了,因为我是一个初学者,正在努力学习android架构组件。我在关注一个链接到这里的youtube播放列表,当他运行它时,他的代码运行得完美无瑕。请先看一下,然后再标记为复制品。我在这里真是太不懂了。提前谢谢。
logcat错误
Process: com.emirhalici.notetakingappnvvmexample, PID: 17577
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.emirhalici.notetakingappnvvmexample/com.emirhalici.notetakingappnvvmexample.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.emirhalici.notetakingappnvvmexample.NoteViewModel
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.RuntimeException: Cannot create an instance of class com.emirhalici.notetakingappnvvmexample.NoteViewModel
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:275)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.emirhalici.notetakingappnvvmexample.MainActivity.onCreate(MainActivity.java:26)
at android.app.Activity.performCreate(Activity.java:8000)
at android.app.Activity.performCreate(Activity.java:7984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
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)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.emirhalici.notetakingappnvvmexample.MainActivity.onCreate(MainActivity.java:26)
at android.app.Activity.performCreate(Activity.java:8000)
at android.app.Activity.performCreate(Activity.java:7984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.RuntimeException: cannot find implementation for com.emirhalici.notetakingappnvvmexample.NoteDatabase. NoteDatabase_Impl does not exist
at androidx.room.Room.getGeneratedImplementation(Room.java:97)
at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:1358)
at com.emirhalici.notetakingappnvvmexample.NoteDatabase.getInstance(NoteDatabase.java:25)
at com.emirhalici.notetakingappnvvmexample.NoteRepository.<init>(NoteRepository.java:15)
at com.emirhalici.notetakingappnvvmexample.NoteViewModel.<init>(NoteViewModel.java:19)
at java.lang.reflect.Constructor.newInstance0(Native Method)
at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.emirhalici.notetakingappnvvmexample.MainActivity.onCreate(MainActivity.java:26)
at android.app.Activity.performCreate(Activity.java:8000)
at android.app.Activity.performCreate(Activity.java:7984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
主活动.java
public class MainActivity extends AppCompatActivity {
private NoteViewModel noteViewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// these didn't work
//noteViewModel = new ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication())).get(NoteViewModel.class);
//noteViewModel = new ViewModelProvider(this).get(NoteViewModel.class);
//noteViewModel = ViewModelProviders.of(this).get(NoteViewModel.class);
// i tried this but this don't work either
noteViewModel = new ViewModelProvider(this,
ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication())).get(NoteViewModel.class);
noteViewModel.getAllNotes().observe(this, new Observer<List<Note>>() {
@Override
public void onChanged(List<Note> notes) {
// update RecyclerView
Toast.makeText(MainActivity.this, "onChanged", Toast.LENGTH_SHORT).show();
}
});
} }
note.java(实体类)
@Entity(tableName = "note_table")
public class Note {
@PrimaryKey(autoGenerate = true)
private int id;
private String title;
private String description;
private int priority;
// getters
public int getId() {
return id;
}
public String getTitle() {
return title;
}
public String getDescription() {
return description;
}
public int getPriority() {
return priority;
}
// id setter
public void setId(int id) {
this.id = id;
}
// constructor
public Note(String title, String description, int priority) {
this.title = title;
this.description = description;
this.priority = priority;
}
}
注解.java
@Dao
public interface NoteDao {
@Insert
void insert(Note note);
@Update
void update(Note note);
@Delete
void delete(Note note);
@Query("DELETE FROM note_table")
void deleteAll();
@Query("SELECT * FROM note_table ORDER BY priority DESC")
LiveData<List<Note>> getAllNotes();
}
注解数据库.java
@Database(entities = Note.class, version = 1)
public abstract class NoteDatabase extends RoomDatabase {
private static NoteDatabase instance;
public abstract NoteDao noteDao();
public static synchronized NoteDatabase getInstance(Context context) {
if (instance == null) {
instance = Room.databaseBuilder(context.getApplicationContext(),
NoteDatabase.class, "note_database")
.fallbackToDestructiveMigration()
.addCallback(roomCallback)
.build();
}
return instance;
}
private static RoomDatabase.Callback roomCallback = new RoomDatabase.Callback() {
@Override
public void onCreate(@NonNull SupportSQLiteDatabase db) {
super.onCreate(db);
new PopulateDbAsyncTask(instance).execute();
}
};
private static class PopulateDbAsyncTask extends AsyncTask<Void, Void, Void> {
private NoteDao noteDao;
private PopulateDbAsyncTask(NoteDatabase db) {
noteDao = db.noteDao();
}
@Override
protected Void doInBackground(Void... voids) {
noteDao.insert(new Note("Title 1","Description 1", 1));
noteDao.insert(new Note("Title 2","Description 2", 2));
noteDao.insert(new Note("Title 3","Description 3", 3));
noteDao.insert(new Note("Title 4","Description 4", 1));
noteDao.insert(new Note("Title 5","Description 5", 2));
noteDao.insert(new Note("Title 6","Description 6", 4));
return null;
}
}
}
noterepository.java文件
public class NoteRepository {
private NoteDao noteDao;
private LiveData<List<Note>> allNotes;
public NoteRepository(Application application) {
NoteDatabase database = NoteDatabase.getInstance(application);
noteDao = database.noteDao();
allNotes = noteDao.getAllNotes();
}
public void insert(Note note) {
new InsertNoteAsyncTask(noteDao).execute(note);
}
public void update(Note note) {
new UpdateNoteAsyncTask(noteDao).execute(note);
}
public void delete(Note note) {
new DeleteNoteAsyncTask(noteDao).execute(note);
}
public void deleteAll() {
new DeleteAllNotesAsyncTask(noteDao).execute();
}
public LiveData<List<Note>> getAllNotes() {
return allNotes;
}
private static class InsertNoteAsyncTask extends AsyncTask<Note, Void, Void> {
private NoteDao noteDao;
private InsertNoteAsyncTask(NoteDao noteDao) {
this.noteDao = noteDao;
}
@Override
protected Void doInBackground(Note... notes) {
noteDao.insert(notes[0]);
return null;
}
}
private static class UpdateNoteAsyncTask extends AsyncTask<Note, Void, Void> {
private NoteDao noteDao;
private UpdateNoteAsyncTask(NoteDao noteDao) {
this.noteDao = noteDao;
}
@Override
protected Void doInBackground(Note... notes) {
noteDao.update(notes[0]);
return null;
}
}
private static class DeleteNoteAsyncTask extends AsyncTask<Note, Void, Void> {
private NoteDao noteDao;
private DeleteNoteAsyncTask(NoteDao noteDao) {
this.noteDao = noteDao;
}
@Override
protected Void doInBackground(Note... notes) {
noteDao.delete(notes[0]);
return null;
}
}
private static class DeleteAllNotesAsyncTask extends AsyncTask<Note, Void, Void> {
private NoteDao noteDao;
private DeleteAllNotesAsyncTask(NoteDao noteDao) {
this.noteDao = noteDao;
}
@Override
protected Void doInBackground(Note... voids) {
noteDao.deleteAll();
return null;
}
}
}
noteviewmodel.java文件
public class NoteViewModel extends AndroidViewModel {
private NoteRepository repository;
private LiveData<List<Note>> allNotes;
public NoteViewModel(@NonNull Application application) {
super(application);
repository = new NoteRepository(application);
allNotes = repository.getAllNotes();
}
public void insert(Note note) {
repository.insert(note);
}
public void update(Note note) {
repository.update(note);
}
public void delete(Note note) {
repository.delete(note);
}
public void deleteAllNotes() {
repository.deleteAll();
}
public LiveData<List<Note>> getAllNotes() {
return allNotes;
}
}
暂无答案!
目前还没有任何答案,快来回答吧!