Android：數據綁定文本未更新

Question

我希望用戶在EditText中輸入其名稱並在TextView內顯示Hello {name}。當我將TextView的文本設置爲可觀察屬性（user.firstName）時，文本會更新。即使我將文本設置爲模型的toString()方法，它仍然可以正常工作。但是，如果我改用viewModel.hello，則文本不會更新。我錯過了什麼？

型號：

public class User extends BaseObservable { 
    public String firstName; 
    public String lastName; 

    public User(String firstName, String lastName) { 
     this.firstName = firstName; 
     this.lastName = lastName; 
    } 

    @Bindable 
    public String getFirstName() { 
     return firstName; 
    } 

    public void setFirstName(String firstName) { 
     this.firstName = firstName; 
     notifyPropertyChanged(BR.firstName); 
    } 

    @Bindable 
    public String getLastName() { 
     return lastName; 
    } 

    public void setLastName(String lastName) { 
     this.lastName = lastName; 
     notifyPropertyChanged(BR.lastName); 
    } 

    @Override 
    public String toString() { 
     return getFirstName() + " " + getLastName(); 
    } 
} 

視圖模型：

public class ViewModel { 
    public User user; 

    public ViewModel() { 
     user = new User("", ""); 
    } 

    public String hello() { 
     return "Hello " + user.toString(); 
    } 

    public TextWatcher userNameTextWatcher() { 
     return new TextWatcher() { 
      @Override 
      public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) { 

      } 

      @Override 
      public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) { 

      } 

      @Override 
      public void afterTextChanged(Editable editable) { 
       if (editable.toString().length() == 0) { 
        user.setFirstName(""); 
        user.setLastName(""); 
        user.notifyChange(); 
        return; 
       } 
       String[] name = editable.toString().split(" "); 
       if (name.length == 1) { 
        user.setFirstName(name[0]); 
        user.setLastName(""); 
        user.notifyChange(); 
        return; 
       } 
       String firstName = name[0] + " "; 
       for (int i = 0; i < name.length - 2; i++) { 
        firstName = firstName + " " + name[i] + " "; 
       } 
       user.setFirstName(firstName); 
       user.setLastName(name[name.length - 1]); 
       user.notifyChange(); 
      } 
     }; 
    } 
} 

佈局：

<data> 
    <variable 
     name="viewModel" 
     type=".ViewModel"/> 
</data> 

<TextView 
     android:id="@+id/textView" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     tools:text="@{viewModel.hello}"/> 

    <EditText 
     android:id="@+id/editText" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/textView" 
     android:layout_marginTop="8dp" 
     app:addEditTextWatcher="@{viewModel.userNameTextWatcher}"/> 

Answer 1

的一個問題是，您的視圖模型是觀察不到的，所以改變你好（）不會體現在模型中。由於它是一個可觀察的單個字段，因此您也可以使用ObservableField作爲hello字符串，但我會用Observable ViewModel來演示它。

public class ViewModel extends BaseObservable { 
    public final User user; 

    public ViewModel() { 
     user = new User("", ""); 
     user.addOnPropertyChangedCallback(new OnPropertyChangedCallback { 
      @Override 
      public void onPropertyChanged(Observable sender, int property) { 
       if (property == BR.firstName || property == BR.lastName) { 
        notifyPropertyChanged(ViewModel.this, BR.hello); 
       } 
      } 
     }); 
    } 

    @Bindable 
    public String hello() { 
     return "Hello " + user.toString(); 
    } 

    public TextWatcher userNameTextWatcher() { 
     return new TextWatcher() { ... } 
    }; 
} 

}

但我認爲這將是很容易聽直接在XML用戶以及不需要擔心視圖模型可觀察到：

<data> 
    <variable 
     name="viewModel" 
     type=".ViewModel"/> 
</data> 

<TextView 
    android:id="@+id/textView" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    tools:text="@{@string/hello(viewModel.user.firstName, viewModel.user.lastName)}"/> 

<EditText 
    android:id="@+id/editText" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_below="@+id/textView" 
    android:layout_marginTop="8dp" 
    app:addEditTextWatcher="@{viewModel.userNameTextWatcher}"/> 

而且你必須一個字符串資源：

<string name="hello">Hello %1$s %2$s</string>