如何使用 ViewModel 通过 EditText 的输入更新 TextView？

Question

我有 3 个问题，每个问题都显示在一个片段中。在每个问题之后，都有一个带有 TextView 的片段，其中包含在上一个问题片段的 EditText 中输入的答案。我按照教程的说明进行操作，但这并没有更新 TextViews。如何使用此处显示的代码，以便每个问题的输入仅显示在下一个片段的 TextView 中？ （片段：问题 1 --> 答案 1 --> 问题 2 --> 答案 2 --> 问题 3 --> 答案 3）

这是前两个片段和 ViewModel 的代码：

第一个问题片段：

public class FragmentQuestion1 extends Fragment {

private Button btnNavFrag1;
private EditText mEditTextQuestion1;
private SharedViewModel viewModel;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_question_1, container, false);

    btnNavFrag1 = view.findViewById(R.id.btn_question1);

    mEditTextQuestion1 = view.findViewById(R.id.edit_text_question_1);

    btnNavFrag1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            viewModel.getAnswer(1);

            ((GameActivity)getActivity()).setViewPager(2);

        }
    });

    return view;
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    viewModel = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
    viewModel.getAnswer(1).observe(this, new Observer<String>() {
        @Override
        public void onChanged(@Nullable String answer) {
            viewModel.setAnswer(1, answer);
            mEditTextQuestion1.setText(answer);
        }
    });
}

第一个答案概述片段：

public class FragmentAnswer1 extends Fragment {

private View btnNavFragAns1;
private TextView tv_answer1;
private SharedViewModel viewModel;

@Nullable
@Override
public View onCreateView( LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_question_answer_1, container, false);

    btnNavFragAns1 = view.findViewById(R.id.next_question_1);

    tv_answer1 = view.findViewById(R.id.answer_player_1_text_view);

    btnNavFragAns1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            ((GameActivity)getActivity()).setViewPager(3);

        }
    });

    return view;
}

@Override
public void onActivityCreated(Bundle bundle) {
    super.onActivityCreated(bundle);

    viewModel = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
    viewModel.getAnswer(1).observe(this, new Observer<String>() {
        @Override
        public void onChanged(@Nullable String answer) {
            viewModel.setAnswer(1, answer);
            tv_answer1.setText(answer);
        }
    });
}

共享视图模型：

public class SharedViewModel extends ViewModel {


public HashMap<Integer, MutableLiveData<String>> answers = new HashMap<Integer, MutableLiveData<String>>(){{
    put(1, new MutableLiveData<String>());
    put(2, new MutableLiveData<String>());
    put(3, new MutableLiveData<String>());
}};



public MutableLiveData<String> getAnswer(int questionId) {
    return answers.get(questionId);
}

public void setAnswer(int questionId, String answer) {
    if (answers.get(questionId) != null) {
        answers.get(questionId).setValue(answer);
    }
}
}

Answer 1

这不起作用，因为您正在更改 onChange 回调中的答案，因此永远不会调用此回调。

viewModel.getAnswer(1).observe(this, new Observer<String>() {
        @Override
        public void onChanged(@Nullable String answer) {
            viewModel.setAnswer(1, answer);
            tv_answer1.setText(answer);
        }
    });

我真正推荐你的是在这种情况下使用 2-way 数据绑定。

不管你不想，你可以在编辑文本时实现一个TextWatcher：

tv_answer1.addTextChangedListener(mTextWatcher)

这样实现：

private TextWatcher mTextWatcher = new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
        }

        @Override
        public void onTextChanged(CharSequence answer, int i, int i1, int i2) {
             viewModel.setAnswer(1, answer);
        }

        @Override
        public void afterTextChanged(Editable editable) {
        }
    };