为什么当我尝试发送到服务器时，我的getters返回null？

Question

我知道这个问题在这里已经被问了无数次了，我已经搜索了SO和其他来源来寻找解决方法，但我就是无法解决这个错误。我的ClientPlayer类属性有一个getter和setter，当某个按钮被调用时setter在GUI中被调用，我希望在客户端连接对象并将对象发送到服务器后使用getter。调用方法“This.client.SendTCP（ClientPlayer.GetPlayerName（））；”返回NullPointerException。

错误：“JavaFX Application Thread”java.lang.IllegalArgumentException：对象不能为空。

public class ClientPlayer implements Serializable {

public ClientPlayer() {

}

private String playerName;

public void setPlayerName(String playerName) {
    this.playerName = playerName;
   }

public String getPlayerName() {
    return this.playerName;
   }
}  

    ClientPlayer clientPlayer = new ClientPlayer();  

    clientToGame.setOnAction((ActionEvent w) -> {
         clientPlayer.setPlayerName(clientNameText.getText());
         clientController.connect();
         window.setScene(lobbyScene);
    });

    public class ClientController() {
     ClientPlayer clientPlayer = new ClientPlayer();

    public void connect() {
    if (client.isConnected()) {
        Logger.getLogger(getClass().getName()).log(Level.INFO, "You are      already connected to :{0}", config.getHost());
        return;
    }
    this.client.start();
    try {
        this.client.connect(5000, config.getHost(), config.getTCPPort());
        System.out.println("Successfully connected to " + config.getHost());
        this.client.sendTCP(clientPlayer.getPlayerName());

    } catch (IOException ex) {
        Logger.getLogger(getClass().getName()).log(Level.SEVERE, "Server connection failed: {0}", ex.getMessage());
        throw new RuntimeException(ex);
    }

    MessageRegistry.registerMessages(client.getKryo());
    this.client.addListener(listener);
  }
 }

Answer 1

在GUI中，创建一个ClientPlayer实例，并对其调用setPlayerName()。然后在ClientController中，创建一个新的ClientPlayer实例（您从不对其调用SetPlayerName())，并对其调用GetPlayerName()。由于您从未为该实例设置播放器名称，getPlayerName()当然返回null。

您需要决定“拥有”ClientPlayer实例是谁的责任。如果这是ClientController的责任，则向ClientController添加getClientPlayer()方法，然后执行

clientToGame.setOnAction((ActionEvent w) -> {
     clientController.getClientPlayer().setPlayerName(clientNameText.getText());
     clientController.connect();
     window.setScene(lobbyScene);
});

并从GUI类中完全删除ClientPlayer。如果GUI类负责拥有它，则将对它的引用传递给connect()方法，并从控制器中删除ClientPlayer字段：

public class ClientController() {
     // ClientPlayer clientPlayer = new ClientPlayer();

    public void connect(ClientPlayer clientPlayer) {
    if (client.isConnected()) {
        Logger.getLogger(getClass().getName()).log(Level.INFO, "You are      already connected to :{0}", config.getHost());
        return;
    }
    this.client.start();
    try {
        this.client.connect(5000, config.getHost(), config.getTCPPort());
        System.out.println("Successfully connected to " + config.getHost());
        this.client.sendTCP(clientPlayer.getPlayerName());

    } catch (IOException ex) {
        Logger.getLogger(getClass().getName()).log(Level.SEVERE, "Server connection failed: {0}", ex.getMessage());
        throw new RuntimeException(ex);
    }

    MessageRegistry.registerMessages(client.getKryo());
    this.client.addListener(listener);
  }
 }

当然还有

clientToGame.setOnAction((ActionEvent w) -> {
     clientPlayer.setPlayerName(clientNameText.getText());
     clientController.connect(clientPlayer);
     window.setScene(lobbyScene);
});