如何在GUI初始化后更新Swing组件以避免Java Swing中的NPE?

在开发Swing应用程序时,我遇到了一个自己无法处理的问题。我正在努力坚持 Model-Viewer-Presenter 图案请记住,我可能误解了如何利用这种模式。在 Presenter 层我正在读取文件内容(I/O操作,相当长)。阅读完成后,我想设置的内容 JLabel 到从文件中读取的内容。看起来很容易。然而,读取文件内容的代码非常快,它试图在构建GUI和初始化类中的JLabel字段之前设置JLabel域的内容。

import javax.swing.SwingUtilities;

public class Presenter {

   private final View view;
   private final Model model;

   @Inject
   public Presenter(final View view, final Model model) {
      this.view = view;
      this.model = model;
      /**
       * In reality, I have here reading a file and invoking
       * view.updateStatusLabel() with its content.
       * The following code will produces NPE as view has not been initialized.
       * */
      SwingUtilities.invokeLater(() -> view.updateStatusLabel("test"));
   }

}

这是 View GUI初始化的部分:

public class View {

   private final Presenter presenter;

   private JLabel statusLabel;
   private JTextField inputField;

   public View() {
      this.presenter = new Presenter(this, new Model());
   }


   public void createUI() {
      this.statusLabel = new JLabel();
      // other GUI initilization
      // ...
   }
   //called by the presenter to update the status label
   public void updateStatusLabel(final String text) {
        statusLabel.setText(text);
   }
}

应用 main 方法:

import com.google.inject.Guice;
import com.google.inject.Inject;
import lombok.RequiredArgsConstructor;

import javax.swing.SwingUtilities;

@RequiredArgsConstructor(onConstructor = @__(@Inject))
public class Main {

   private final View view;

   public static void main(final String[] args) {

      final Main main = Guice.createInjector().getInstance(Main.class);

      SwingUtilities.invokeLater(main.view::createUI);
   }
}

如果这是重要的事情,我使用 Guice 以覆盖依赖项注入。即使没有 Guice 就会出现这个问题。以下是我的依赖项:

<guice.version>7.0.0</guice.version>
<dependency>
      <groupId>com.google.inject</groupId>
      <artifactId>guice</artifactId>
      <version>${guice.version}</version>
    </dependency>

    <dependency>
      <groupId>com.google.inject.extensions</groupId>
      <artifactId>guice-assistedinject</artifactId>
      <version>${guice.version}</version>
    </dependency>

    <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
      <version>1.18.28</version>
      <scope>provided</scope>
    </dependency>

编辑

感谢@Gilbert勒布朗克的评论,我设法重写了代码以避免NPE。请参阅下面的更新代码。我通过删除了依赖项注入 Guice 这样代码现在读起来(我希望如此)就更容易了。代码按预期工作。然而,由于我是Swing的新手,我可能犯了一些错误,希望有人能指出这些错误,以便纠正。

应用程序起点:

import javax.swing.SwingUtilities;

public class Main {

   public static void main(final String[] args) {

      SwingUtilities.invokeLater(new View()::createUI);
   }
}

型号:

    public class Model {
    
       private String password;
       private boolean initiliaized;

       // getters and setters here

       
    }

所需的接口 Observer 设计模式:

interface Observer {
   void guiInitialized();
}

interface Subject {

   void registerObserver(Observer observer);

   void notifyObservers();
}

节目主持人

public class Presenter implements Observer {

   private final View view;
   private final Model model;

   public Presenter(final View view, final Model model) {
      this.view = view;
      this.model = model;
      new Thread(() -> {
         try {
            Thread.sleep(5_000);
            model.setPassword("password");
            model.setInitiliaized(true);
         } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
         }
      }).start();
   }

   @Override
   public void guiInitialized() {
      // wait until gui is initialized
      new Thread(() -> {
         while ( !model.isInitiliaized() ) {
            try {
               Thread.sleep(500);
            } catch (InterruptedException e) {
               Thread.currentThread().interrupt();
            }
         }
         // GUI is initliazed by now
         view.updateStatusLabel("init");
      }).start();
   }

}

看法

public class View {

   private final Presenter presenter;

   private final List<Observer> observers = new ArrayList<>();
   

   private JLabel statusLabel;
   private JTextField inputField;

   public View() {
      this.presenter = new Presenter(this, new Model());
   }

   @Override
   public void registerObserver(final Observer observer) {
      this.observers.add(observer);
   }

   @Override
   public void notifyObservers() {
      observers.forEach(Observer::guiInitialized);
   }


   public void createUI() {
      this.statusLabel = new JLabel();
      // other GUI initilization
      // ...

      registerObserver(presenter);

      notifyObservers();
   }

   //called by the presenter to update the status label
   public void updateStatusLabel(final String text) {
      statusLabel.setText(text);
   }
}