没有构造函数参数的ViewModelFactory和ViewModel

Question

我得到了MyViewModel，它的构造函数是空的

public class MyViewModel extends ViewModel {
    private MutableLiveData<RxBleClient> rxBleClient = new MutableLiveData<RxBleClient>();


    public MyViewModel() {

    }
    
    public MutableLiveData<RxBleClient> getRxBleClient() {
        return rxBleClient;
    }

    public void setRxBleClient(MutableLiveData<RxBleClient> rxBleClient) {
        this.rxBleClient = rxBleClient;
    }
}

我想提供这样的新模型，但有一个问题：

MyViewModel model = new ViewModelProvider(this).get(MyViewModel.class);

error: no suitable constructor found for ViewModelProvider(MainActivity)
        MyViewModel model = new ViewModelProvider(this).get(MyViewModel.class);
                            ^
    constructor ViewModelProvider.ViewModelProvider(ViewModelStoreOwner,Factory) is not applicable
      (actual and formal argument lists differ in length)
    constructor ViewModelProvider.ViewModelProvider(ViewModelStore,Factory) is not applicable
      (actual and formal argument lists differ in length)

我确实实现了ViewModelProvider.Factory

public class ViewModelFactory implements ViewModelProvider.Factory {

    ViewModelFactory() {
    }

    @NonNull
    @Override
    public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
        try {
//            what do I need to do here?
            return modelClass.newInstance();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }
}

但我不知道该怎么办，把没有指标的工厂退回去。如何实现？
谢谢

Answer 1

MainActivity可能不是从AppCompatActivity继承的，这就是它不是有效的ViewModelStoreOwner的原因。或者您没有使用ViewModelProvider的AndroidX版本。

关于工厂，如果viewmodel有一个默认构造函数，则不需要工厂。