The final variable from the resource file

Question

I have activity with some final variables . I extracted their values ​​(suppose they are all strings) into a resource file.

Problem:

If I directly assign them to an instance (as follows):

private final String PREFERENCE_NAME = getResources().getString(R.string.preference_name);

I get the following error:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference

I understand the problem; the onCreate () method has not yet been called, which means that I cannot access the context related methods ( getResources()).

If I want to assign a value in the onCreate () method of an activity, I get an error Cannot assign value to final variable 'PREFERENCE_NAME'

Question . How can I get my final variables from a resource file? And if this is not possible, what is the best practice to solve?

Thanks in advance.

Answer 1

, , . , getResources() .

Answer 2

: .

final (.. ).

getResources().getString(R.string.preference_name); .

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:

public class FinalMessage {

    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        FinalMessage f = new FinalMessage("Hello World!");
        System.out.println(f.getMessage());
        f.changeFinalMessage("Hello Mars!");
        System.out.println(f.getMessage());
    }

    private final String message;

    public FinalMessage(String message) {
        this.message = message;
    }

    void changeFinalMessage(String newMessage) throws IllegalAccessException, NoSuchFieldException {
        final Field field = FinalMessage.class.getDeclaredField("message");
        field.setAccessible(true);

        Field modifiersField = Field.class.getDeclaredField("modifiers");
        modifiersField.setAccessible(true);
        modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);

        field.set(this, newMessage);
    }

    String getMessage() {
        return message;
    }
}

:

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, :

public class FinalMessage {

    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        FinalMessage f = new FinalMessage();
        System.out.println(f.getMessage());
        f.changeFinalMessage("Hello Mars!");
        System.out.println(f.getMessage());
    }

    private final String message = "Hello World!";

    void changeFinalMessage(String newMessage) throws IllegalAccessException, NoSuchFieldException {
        final Field field = FinalMessage.class.getDeclaredField("message");
        field.setAccessible(true);

        Field modifiersField = Field.class.getDeclaredField("modifiers");
        modifiersField.setAccessible(true);
        modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);

        field.set(this, newMessage);
    }

    String getMessage() {
        return message;
    }
}

:

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, , message "Hello World!", "Hello World!" f.getMessage(). , , "Hello Mars!", , .

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Answer 3

factory, .

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, , factory, final .

-

class MyFactory {
   private Resource getResources() { ... }
   public MyObject build() { 
       String perference_name = getResources().getString(R.string.preference_name);
       /...
       return new MyObject(perfence_name ,....);
   }
}

Answer 4

:

• :

  public class MyApplication extends Application {
  
      private static Context mContext;
  
      @Override
      public void onCreate() {
          super.onCreate();
          mContext = getApplicationContext();
      }
  
      public static String getStr(int resId) {
          return mContext.getString(resId);
      }
  
  }
  

• :

  <application
      android:name=".MyApplication"
      ...
  

• :

  static final String NAME = MyApplication.getStr(R.string.app_name);
  

Answer 5

:

private final String PREFERENCE_NAME() {
    return getResources().getString(R.string.preference_name);}