Android视图模型类没有零参数构造函数，在片段中引发实例化异常。

huangapple
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英文:

Android view model class has no zero argument constructor,Instantiation Exception in fragment

问题

我有一个视图模型类，需要在片段中实例化它。但是我遇到了以下问题：

  1. java.lang.RuntimeException: 无法创建 com.example.project.favourites.FavViewModel 类的实例

以及

  1. Caused by: java.lang.InstantiationException: java.lang.Class<com.example.project.favourites.FavViewModel> 没有零参数构造函数

导致崩溃的代码行是：

  1. favViewModel = new ViewModelProvider(this).get(FavViewModel.class);
  2. （此行位于片段的 onViewCreated 方法中）

请帮忙！！！

以下是 FavViewModel 类的内容：

  1. public class FavViewModel extends AndroidViewModel {
  2.     private FavRepository repository;
  3.     private LiveData<List<FavItem>> allFav;
  5.     public FavViewModel(@NonNull Application application) {
  6.         super(application);
  7.         repository = new FavRepository(application);
  8.         allFav = repository.getAllFav();
  9.     }
  11.     public void insert(FavItem favItem) {
  12.         repository.insert(favItem);
  13.     }
  15.     public void delete(FavItem favItem) {
  16.         repository.delete(favItem);
  17.     }
  19.     public void deleteAll() {
  20.         repository.deleteAll();
  21.     }
  23.     public LiveData<List<FavItem>> getAllFav() {
  24.         return allFav;
  25.     }
  26. }
英文:

i have a view model class and i need to instantiate it in a fragment.
But I am getting :

  1. java.lang.RuntimeException: Cannot create an instance of class com.example.project.favourites.FavViewModel

and

  1. Caused by: java.lang.InstantiationException: java.lang.Class<com.example.project.favourites.FavViewModel> has no zero argument constructor

This is the line causing crash:

  1. favViewModel= new ViewModelProvider(this).get(FavViewModel.class); 
  2. (This line is within onViewCreated in fragment)

pls help!!!!!

Below is FavViewModel Class

  1. public class FavViewModel extends AndroidViewModel {
  2.     private FavRepository repository;
  3.     private LiveData<List<FavItem>> allFav;
  5.     public FavViewModel(@NonNull Application application) {
  6.         super(application);
  7.         repository=new FavRepository(application);
  8.         allFav=repository.getAllFav();
  9.     }
  12.     public void insert(FavItem favItem){
  13.         repository.insert(favItem);
  14.     }
  16.     public void delete(FavItem favItem){
  17.         repository.delete(favItem);
  18.     }
  20.     public void deleteAll(){
  21.         repository.deleteAll();
  22.     }
  23.     public LiveData<List<FavItem>> getAllFav(){
  24.         return allFav;
  25.     }
  26. }
  29. </details>
  32. # 答案1
  33. **得分**: 1
  35. 你可以使用以下注解为你的模型类进行注解：
  37. **`@NoArgsConstructor`**
  39. 你可以通过此链接[**`lombok`**][1]深入了解lombok、NoArgsConstructor和其他许多注解。
  41.   [1]: https://projectlombok.org/features/constructor
  43. <details>
  44. <summary>英文:</summary>
  46. You can annotate your model class with below annotation
  48. **`@NoArgsConstructor`**
  50. You will get more idea about lombok , NoArgsConstructor and many more annotations using this link[**`lombok`**][1]
  53.   [1]: https://projectlombok.org/features/constructor
  55. </details>
  59. # 答案2
  60. **得分**: 0
  62. 尝试使用这个...
  64. 像这样初始化 `ViewModel`。你还需要在 `ViewModelProvider` 构造函数中传递 `ViewModelFactory`。
  66. ```java
  67. favViewModel = new ViewModelProvider(this,
  68.                 new ViewModelProvider.AndroidViewModelFactory(getApplication())).get(FavViewModel.class);
  69. ```
  71. 希望对你有帮助。如有疑问，请随意提问...
  73. <details>
  74. <summary>英文:</summary>
  76. Try using this...
  78. Initialise `ViewModel` like this. You need to also pass `ViewModelFactory` with `ViewModelProvider` constructor.
  80. ```
  81. favViewModel = new ViewModelProvider(this,
  82.                 new ViewModelProvider.AndroidViewModelFactory(getApplication())).get(FavViewModel.class);
  83. ```
  85. Hope this helps. Feel free to ask for clarifications...
  87. </details>

huangapple
  • 本文由 发表于 2020年8月23日 22:12:09
  • 转载请务必保留本文链接：https://go.coder-hub.com/63547942.html
  • android
  • android-room
  • java
  • mvvm
  • viewmodel
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