java - Model-View-Presenter被动 View : bootstraping - who displays the view initially?

Question

在“被动 View 模型 View 呈现器”模式中，谁负责显示 View ？我已经找到了其他MVP版本的相关答案，但是它们似乎不适用于被动 View 版本。

我有一个使用Java Swing的具体示例。这很简单，但是基本上我们有一个SwingCustomersView，它在内部构建一个带有表(客户列表)和显示当前所选客户年龄的标签的JPanel。当在表中选择一个客户时，演示者将从模型中检索所选的客户年龄。我认为该示例是MVP Passive View的正确实现，但是如果我错了，请更正我。

问题是我们如何引导这些类？例如，如果我们想在JFrame中显示SwingCustomersView。一个人会怎么做？我想像的东西如下:

void launcher() {
    CustomersModel model = new CustomersModel();
    SwingCustomersView view = new SwingCustomersView();
    CustomersPresenter presenter = new CustomersPresenter(view, model);
}

这是初始接线，但什么也没显示。我们如何实际显示 View ？显示 View 是(1)launcher()，(2)SwingCustomersView或(3)CustomersPresenter的责任吗？不幸的是，我不认为这些都是很好的，从下面我的想法中可以看出。也许还有另一种方式？

(1.a):启动器

使SwingCustomersView扩展JFrame并将其内部JPanel添加到其自身的内容 Pane 中。然后我们可以这样做:

void launcher() {
    CustomersModel model = new CustomersModel();
    SwingCustomersView view = new SwingCustomersView();
    CustomersPresenter presenter = new CustomersPresenter(view, model);
    view.setVisible(true); // Displays the view
}

但是，在这种情况下，我们不使用presenter实例进行任何操作。那不是很奇怪吗？它就在这里进行接线，我们也可以删除变量并执行new CustomersPresenter(view, model)。

(2):SwingCustomersView

使SwingCustomersView在应该向其添加内部JPanel的构造函数中采用Container:

void launcher() {
    CustomersModel model = new CustomersModel();
    JFrame frame = new JFrame("Some title");
    SwingCustomersView view = new SwingCustomersView(frame.getContentPane());
    CustomersPresenter presenter = new CustomersPresenter(view, model);
    frame.pack(); 
    frame.setVisible(true) // Displays the view
}

但是，与(1)相同的问题是:presenter实例不执行任何操作。好像很奇怪此外，使用(1)和(2)都可以在演示者挂机之前显示 View ，我想这在某些情况下可能会导致奇怪的结果。

(3):客户演示者

使CustomersPresenter负责显示 View 。然后我们可以这样做:

void launcher() {
    CustomersModel model = new CustomersModel();
    SwingCustomersView view = new SwingCustomersView();
    CustomersPresenter presenter = new CustomersPresenter(view, model);
    presenter.show() // Displays the view
}

这样可以解决构造后不将其用于任何东西的问题。但是我不更改CustomersView接口(interface)或使CustomersPresenter过于依赖底层GUI实现，就看不到该怎么做。此外，显示 View 听起来不像演示逻辑，因此似乎不属于演示者。

例子

public class CustomersModel {
    private List<Customer> customers;

    public CustomersModel() {
        customers = new ArrayList<Customer>();
        customers.add(new Customer("SomeCustomer", "31"));
        customers.add(new Customer("SomeCustomer", "32"));
    }

    public List<Customer> getCustomers() {
        return customers;
    }
}

public class Customer {
    public String name;
    public String age;

    public Customer(String name, String age) {
        this.name = name;
        this.age = age;
    }
}

public interface CustomersView {
    void addCustomerSelectionChangeListener(ItemListener listener);
    void onNewActiveCustomer(String age);
    void onNewCustomers(List<String> newCustomers);
}

public class SwingCustomersView implements CustomersView {
    // Swing components here all put into a main JPanel

    public void addCustomerSelectionChangeListener(ItemListener listener) {
       // Add event listener to table
    }

    public void onNewActiveCustomer(String age) {
        // Display age in label beneath table
    }

    public void onNewCustomers(List<String> newCustomers) {
        // Display customers in table
    }
}

public class CustomersPresenter {
    private final CustomersView view;
    private final CustomersModel model;

    public CustomersPresenter(CustomersView view, CustomersModel model) {
        this.view = view;
        this.model = model;
        initPresentationLogic();
        populateView();
    }

    private void initPresentationLogic() {
        view.addCustomerSelectionChangeListener(new ItemListener() {
            @Override
            public void itemStateChanged(ItemEvent e) {
                String selectedName = (String)e.getItem();
                List<Customer> customers = model.getCustomers();
                for (Customer c : customers)
                    if (c.name.equals(selectedName))
                        view.onNewActiveCustomer(c.age);
            }
        });
    }

    private void populateView() {
        List<Customer> customers = model.getCustomers();
        List<String> names = new ArrayList<String>();
        for (Customer c : customers)
            names.add(c.name);

        // View will now populate its table, which in turn will call customerSelectionChangeListener
        // so the view 'automagically' updates the selected contact age too
        view.onNewCustomers(names);
    }
}

Answer 1

选项(3)一直。演示者的工作是“控制” View ，包括使其可见。是的，您需要添加到 View 的界面以允许这种情况发生，但这没什么大不了的。请记住，您可以使 View 尽可能被动。没有逻辑!

工作示例:

我偶然发现了使用MVC架构的简单Swing游戏的this example。由于我是使用MVP而不是MVC编写Swing应用程序的，因此如果这个例子是MVC的真实和纯粹的例子，我不能授权。在我看来，这还可以，并且作者trashgod在使用Swing的SO方面已经证明了自己，所以我会认为它是合理的。

作为练习，我决定使用MVP架构重写它。

驱动程序:

正如您在下面的代码中看到的那样，这非常简单。您应该跳出来的是关注点分离(通过检查构造函数):

模型类是独立的，不了解 View 或演示者。

View 接口(interface)是由独立的GUI类实现的，它们都不了解模型或演示者。

Presenter 类同时了解模型和 View 。

代码:

import java.awt.*;

/**
 * MVP version of https://stackoverflow.com/q/3066590/230513
 */
public class MVPGame implements Runnable
{
  public static void main(String[] args)
  {
    EventQueue.invokeLater(new MVPGame());
  }

  @Override
  public void run()
  {
    Model model = new Model();
    View view = new Gui();
    Presenter presenter = new Presenter(model, view);
    presenter.start();
  }
}

以及我们将用于游戏的GamePiece:

import java.awt.*;

public enum GamePiece
{
  Red(Color.red), Green(Color.green), Blue(Color.blue);
  public Color color;

  private GamePiece(Color color)
  {
    this.color = color;
  }
}

模型:首先，模型的工作是:

为UI提供数据(应要求提供)

数据验证(应要求)

数据的长期存储(应要求)

代码:

import java.util.*;

public class Model
{
  private static final Random rnd = new Random();
  private static final GamePiece[] pieces = GamePiece.values();

  private GamePiece selection;

  public Model()
  {
    reset();
  }

  public void reset()
  {
    selection = pieces[randomInt(0, pieces.length)];
  }

  public boolean check(GamePiece guess)
  {
    return selection.equals(guess);
  }

  public List<GamePiece> getAllPieces()
  {
    return Arrays.asList(GamePiece.values());
  }

  private static int randomInt(int min, int max)
  {
    return rnd.nextInt((max - min) + 1) + min;
  }
}

View :此处的想法是通过尽可能多地剥离应用程序逻辑来使它尽可能“笨拙”(目标是不使用任何逻辑)。好处:

该应用程序现在可以100％进行JUnit的测试，因为Swing代码

中未混入任何应用程序逻辑

您可以在不启动整个应用程序的情况下启动GUI，这使得原型(prototype)制作的速度更快

代码:

import java.awt.*;
import java.awt.event.*;
import java.util.List;

public interface View
{
  public void addPieceActionListener(GamePiece piece, ActionListener listener);
  public void addResetActionListener(ActionListener listener);
  public void setGamePieces(List<GamePiece> pieces);
  public void setResult(Color color, String message);
}

和GUI:

import java.awt.*;
import java.awt.event.*;
import java.util.List;
import javax.swing.*;

/**
 * View is "dumb". It has no reference to Model or Presenter.
 * No application code - Swing code only!
 */
public class Gui implements View
{
  private JFrame frame;
  private ColorIcon icon;
  private JLabel resultLabel;
  private JButton resetButton;
  private JButton[] pieceButtons;
  private List<GamePiece> pieceChoices;

  public Gui()
  {
    frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    icon = new ColorIcon(80, Color.WHITE);
  }

  public void setGamePieces(List<GamePiece> pieces)
  {
    this.pieceChoices = pieces;

    frame.add(getMainPanel());
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }

  public void setResult(Color color, String message)
  {
    icon.color = color;
    resultLabel.setText(message);
    resultLabel.repaint();
  }

  private JPanel getMainPanel()
  {
    JPanel panel = new JPanel(new BorderLayout());
    panel.add(getInstructionPanel(), BorderLayout.NORTH);
    panel.add(getGamePanel(), BorderLayout.CENTER);
    panel.add(getResetPanel(), BorderLayout.SOUTH);
    return panel;
  }

  private JPanel getInstructionPanel()
  {
    JPanel panel = new JPanel();
    panel.add(new JLabel("Guess what color!", JLabel.CENTER));
    return panel;
  }

  private JPanel getGamePanel()
  {
    resultLabel = new JLabel("No selection made", icon, JLabel.CENTER);
    resultLabel.setVerticalTextPosition(JLabel.BOTTOM);
    resultLabel.setHorizontalTextPosition(JLabel.CENTER);

    JPanel piecePanel = new JPanel();
    int pieceCount = pieceChoices.size();
    pieceButtons = new JButton[pieceCount];

    for (int i = 0; i < pieceCount; i++)
    {
      pieceButtons[i] = createPiece(pieceChoices.get(i));
      piecePanel.add(pieceButtons[i]);
    }

    JPanel panel = new JPanel(new BorderLayout());
    panel.add(resultLabel, BorderLayout.CENTER);
    panel.add(piecePanel, BorderLayout.SOUTH);

    return panel;
  }

  private JPanel getResetPanel()
  {
    resetButton = new JButton("Reset");

    JPanel panel = new JPanel();
    panel.add(resetButton);
    return panel;
  }

  private JButton createPiece(GamePiece piece)
  {
    JButton btn = new JButton();
    btn.setIcon(new ColorIcon(16, piece.color));
    btn.setActionCommand(piece.name());
    return btn;
  }

  public void addPieceActionListener(GamePiece piece, ActionListener listener)
  {
    for (JButton button : pieceButtons)
    {
      if (button.getActionCommand().equals(piece.name()))
      {
        button.addActionListener(listener);
        break;
      }
    }
  }

  public void addResetActionListener(ActionListener listener)
  {
    resetButton.addActionListener(listener);
  }

  private class ColorIcon implements Icon
  {
    private int size;
    private Color color;

    public ColorIcon(int size, Color color)
    {
      this.size = size;
      this.color = color;
    }

    @Override
    public void paintIcon(Component c, Graphics g, int x, int y)
    {
      Graphics2D g2d = (Graphics2D) g;
      g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
          RenderingHints.VALUE_ANTIALIAS_ON);
      g2d.setColor(color);
      g2d.fillOval(x, y, size, size);
    }

    @Override
    public int getIconWidth()
    {
      return size;
    }

    @Override
    public int getIconHeight()
    {
      return size;
    }
  }
}

立即可能看不到的是View界面有多大。对于GUI上的每个Swing组件，您可能需要:

添加/删除组件的监听器，该监听器的类型很多(ActionListener，FocusListener，MouseListener等)。

获取/设置组件

上的数据

设置组件的“可用性”状态(启用，可见，可编辑，可聚焦等)。

这会很快变得笨拙。作为解决方案(此示例中未显示)，将为每个字段创建一个 key ，并且GUI用其 key 注册每个组件(使用HashMap)。然后，代替View定义方法，例如:

public void addResetActionListener(ActionListener listener);
// and then repeat for every field that needs an ActionListener

您将有一个方法:

public void addActionListener(SomeEnum someField, ActionListener listener);

其中“SomeEnum”是一个enum，它定义了给定UI上的所有字段。然后，当GUI收到该调用时，它会查找适当的组件以对该方法进行调用。所有这些繁重的工作都将在实现View的抽象父类(super class)中完成。

演示者:的职责是:

使用其初始值初始化 View

通过附加适当的监听器

来响应View上的所有用户交互

必要时更新View的状态

从 View 中获取所有数据，然后传递给模型进行保存(如有必要)

代码(请注意，这里没有Swing):

import java.awt.*;
import java.awt.event.*;

public class Presenter
{
  private Model model;
  private View view;

  public Presenter()
  {
    System.out.println("ctor");
  }

  public Presenter(Model model, View view)
  {
    this.model = model;
    this.view = view;
  }

  public void start()
  {
    view.setGamePieces(model.getAllPieces());
    reset();

    view.addResetActionListener(new ActionListener()
    {
      public void actionPerformed(ActionEvent e)
      {
        reset();
      }
    });

    for (int i = 0; i < GamePiece.values().length; i++)
    {
      final GamePiece aPiece = GamePiece.values()[i];
      view.addPieceActionListener(aPiece, new ActionListener()
      {
        public void actionPerformed(ActionEvent e)
        {
          pieceSelected(aPiece);
        }
      });
    }
  }

  private void reset()
  {
    model.reset();
    view.setResult(Color.GRAY, "Click a button.");
  }

  private void pieceSelected(GamePiece piece)
  {
    boolean valid = model.check(piece);
    view.setResult(piece.color, valid ? "Win!" : "Keep trying.");
  }
}

请记住，MVP体系结构的每个部分都可以/将委派给其他类(对其他2个部分隐藏)来执行其许多任务。 Model，View和Presenter类只是代码库层次结构中的高级部分。