Android中的ViewModel LiveData无法正常工作

如何解决Android中的ViewModel LiveData无法正常工作

我刚刚了解了liveata视图模型。我有一个对象，main_activity由2个片段组成，其中当我更改ControlFragment的值时，DetailFragment上的值将更改。但是它不起作用，虽然我更改了片段控制中的值，但片段2中的值没有改变。

请帮我解决问题

ViewModelMedal

public class ViewModelMedal extends ViewModel {
public MutableLiveData<Integer> numberGold = new MutableLiveData<>();
public MutableLiveData<Integer> numberSilver = new MutableLiveData<>();
public MutableLiveData<Integer> numberBronze = new MutableLiveData<>();

public ViewModelMedal() {
    numberGold.setValue(0);
    numberSilver.setValue(0);
    numberBronze.setValue(0);
}

}

ControlFragment.java

public class ControlFragmentJava extends Fragment implements View.OnClickListener {
private Button btnGold,btnGoldPlus,btnSilver,btnSilverPlus,btnCu,btnCuPlus;
private TextView tvGold,tvSilver,tvBronze;
private ViewModelMedal mViewModelMedal;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_control,container,false);
    mViewModelMedal = ViewModelProviders.of(this).get(ViewModelMedal.class);

    .
    .
    .

    return view;
}

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.btnBronzePlus:
            mViewModelMedal.numberCBronze.setValue(mViewModelMedal.numberCu.getValue()+1);
            initSetData();
            break;
        case R.id.btnBronzeMinus:
            mViewModelMedal.numberBronze.setValue(mViewModelMedal.numberCu.getValue()-1);
            initSetData();
            break;
        case R.id.btnGoldMinus:
            mViewModelMedal.numberGold.setValue(mViewModelMedal.numberGold.getValue()-1);
            initSetData();
            break;
        case R.id.btnGoldPlus:
            mViewModelMedal.numberGold.setValue(mViewModelMedal.numberGold.getValue()+1);
            initSetData();
            break;
        case R.id.btnSilverMinus:
            mViewModelMedal.numberSilver.setValue(mViewModelMedal.numberSilver.getValue()-1);
            initSetData();
            break;
        case R.id.btnSilverPlus:
            mViewModelMedal.numberSilver.setValue(mViewModelMedal.numberSilver.getValue()+1);
            initSetData();
            break;

    }

}

}

DetailFragment

public class DetailFragment extends Fragment {
public ViewModelMedal mViewModelMedal;
private TextView tvGold,tvBronze;


@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,@Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_detail,false);
    tvBronze = view.findViewById(R.id.tvDetailBronzeNumber);
    tvGold = view.findViewById(R.id.tvDetailGoldNumber);
    tvSilver = view.findViewById(R.id.tvDetailSilverNumber);
    mViewModelMedal = ViewModelProviders.of(this).get(ViewModelMedal.class);
    mViewModelMedal.numberBronze.observe(this,new Observer<Integer>() {
        @Override
        public void onChanged(Integer integer) {
            tvCu.setText(String.valueOf(mViewModelMedal.numberCu.getValue()));
        }
    });
    mViewModelMedal.numberGold.observe(this,new Observer<Integer>() {
        @Override
        public void onChanged(Integer integer) {
            tvGold.setText(String.valueOf(mViewModelMedal.numberGold.getValue()));
        }
    });
    mViewModelMedal.numberSilver.observe(this,new Observer<Integer>() {
        @Override
        public void onChanged(Integer integer) {
            tvSilver.setText(String.valueOf(mViewModelMedal.numberSilver.getValue()));
        }
    });
    return view;
}

解决方法

问题在这里非常简单：您有ViewModelMedal类的两个实例，因为您在ViewModelStoreOwner调用中将两个片段用作ViewModelProviders.of(this)。可能会帮助您使用父级Activity通过调用ViewModelProviders.of(requireActivity())来管理视图模型。

请注意，ViewModelProviders类已被弃用，如其页面上的消息所述：

不推荐使用此类。

直接使用ViewModelProvider的构造函数。