使用 Livedata 并在显示 MutableLiveData<Float> 结果时遇到问题

Question

我正在测试 Android 架构组件的 ViewModel 和 LiveData。我有这个基本的 Activity 和一个 EditText 来从用户那里接收一个数字，当单击 Convert 按钮时，Textview 应该给出乘以 0.87 的结果。例如，当我在 EditText 中输入 100 并单击 Convert 按钮时，它应该给出 87 的结果。但是当我单击 Convert 按钮时，Textview 给出 "android.arch.lifecycle.MutableLiveData@eb84a7b" 的值。当我旋转屏幕时，结果变成了 87。请你看看我的代码，告诉我应该在哪里修改代码，以便在我单击“转换”按钮时结果给出数字？

ViewModelLiveDataActivity.java:

public class ViewModelLiveDataActivity extends AppCompatActivity {

private ViewModel2 mViewModel;

private EditText mEditText;
private TextView mTextView;
private Button mButton;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.viewmodellivedata_activity_layout);

    mViewModel = ViewModelProviders.of(this).get(ViewModel2.class);

    mEditText = (EditText) findViewById(R.id.livedata_editText);
    mTextView = (TextView) findViewById(R.id.livedata_textView);
    mButton = (Button) findViewById(R.id.livedata_button);

    final Observer<Float> resultObserver = new Observer<Float>() {
        @Override
        public void onChanged(@Nullable final Float result) {
            mTextView.setText(result.toString());

        }
    };

    mViewModel.getResult().observe(this, resultObserver);

    mButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //Doing the calculations using ViewModel class
            String dollarText = mEditText.getText().toString();
            mViewModel.setAmount(dollarText);
            mTextView.setText(mViewModel.getResult().toString());
        }
    });



}
}

ViewModel2.java:

public class ViewModel2 extends ViewModel {

private static final float EURO_DOLLAR_EXCHANGE_RATE = 0.87f;
private String dollarString = ""; //the value of UI EditText
private MutableLiveData<Float> result = new MutableLiveData<>();

public void setAmount(String value) {
    this.dollarString = value;
    result.setValue(Float.valueOf(dollarString) * EURO_DOLLAR_EXCHANGE_RATE);
}

public MutableLiveData<Float> getResult() {
    return result;
}
}

Answer 1

使用 getValue() 而不是 toString()

mTextView.setText(mViewModel.getResult().getValue());

使用 Livedata 并在显示 MutableLiveData<Float> 结果时遇到问题

Using Livedata and having a problem with displaying MutableLiveData<Float> result

java

android

android-livedata

mutablelivedata