AndroidViewModel 没有零参数构造函数
2022-09-04 23:43:17
我正在尝试在 MainActivity 中创建我的 AndroidViewModel 的实例。当我这样做时,我得到以下错误没有零参数构造函数
这是我的食谱ViewModel
package com.example.kookrecepten;
import android.app.Application;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import java.util.List;
public class RecipeViewModel extends AndroidViewModel {
private RecipeRepository recipeRepository;
private LiveData<List<Recipe>> allRecipes;
public RecipeViewModel(Application application) {
super(application);
recipeRepository = new RecipeRepository(application);
allRecipes = recipeRepository.getAllRecipes();
}
public void insert(Recipe recipe) {
recipeRepository.insert(recipe);
}
public void update(Recipe recipe) {
recipeRepository.update(recipe);
}
public void delete(Recipe recipe) {
recipeRepository.delete(recipe);
}
public void deleteAll() {
recipeRepository.deleteAllRecipes();
}
public LiveData<List<Recipe>> getAllRecipes() {
return allRecipes;
}
}
如果我错了,现在请纠正我,但AndroidViewModel需要在构造函数中提供应用程序上下文,而ViewModel不需要。所以我不知道为什么android要求零参数构造函数。
这是我的主要活动,我要求一个实例。
package com.example.kookrecepten;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;
import com.example.kookrecepten.databinding.ActivityMainBinding;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private ActivityMainBinding binding;
private RecipeViewModel recipeViewModel;
protected void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
binding = ActivityMainBinding.inflate(getLayoutInflater());
View view = binding.getRoot();
setContentView(view);
//Get an instance of the RecipeViewModel.
recipeViewModel = new ViewModelProvider(this).get(RecipeViewModel.class);
recipeViewModel.getAllRecipes().observe(this, new Observer<List<Recipe>>() {
@Override
public void onChanged(List<Recipe> recipes) {
//Update recycle view
Toast.makeText(MainActivity.this, "triggered", Toast.LENGTH_SHORT).show();
}
});
}
}
这是我的实现。
def lifecycle_version = "2.2.0"
def room_version = "2.2.5"
//LifeCycle Components
// ViewModel
implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version"
// LiveData
implementation "androidx.lifecycle:lifecycle-livedata:$lifecycle_version"
// Annotation processor
implementation "androidx.lifecycle:lifecycle-common-java8:$lifecycle_version"
//Room Components
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"