如何解决替换 AsyncTask 以连接套接字的问题？

Question

我正在尝试使用This approach(Marked Answer) 将我的代码替换为AsyncTask 以在android 中的用户和服务器之间建立连接，这就是我所做的：

注意：我没有使用任何特定的模式，只是试图在基本结构上实现这一目标。

主要活动：

public class MainActivity extends AppCompatActivity {
    private ClientConnection connection;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        connection = new ClientConnection(inputServerIp.getText().toString(), inputUserName.getText().toString(), Integer.parseInt(inputPort.getText().toString()));
    }
}

客户端连接：

public class ClientConnection {
    private Socket serverSocket;
    private ConnectionTask taskRunner;

    public ClientConnection(String ipAddress, String userName, int dstPort) {
        this.ipAddress = ipAddress;
        this.userName = userName;
        this.dstPort = dstPort;
    }

    public void connect() {
        taskRunner.executeAsync(new ConnectionRunningTask(ipAddress, dstPort), (data) -> {
            serverSocket = data;
        });
    }

连接任务：

public class ConnectionTask {

    private final Executor executor = Executors.newSingleThreadExecutor();
    private final Handler handler = new Handler(Looper.getMainLooper());

    public interface Callback<R> {
        void onComplete(R result);
    }

    public void executeAsync(Callable<R> callable, Callback<R> callback) {
        executor.execute(() -> {
            try {
                final R result = callable.call();
                handler.post(() -> {
                    callback.onComplete(result);
                });
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
    }
}

ConnectionRunningTask：

public class ConnectionRunningTask implements Callable<Socket> {
    private final String ipAddress;
    private final Integer dstPort;

    public ConnectionRunningTask(String ipAddress, Integer dstPort) {
        this.ipAddress = ipAddress;
        this.dstPort = dstPort;
    }

    @Override
    public Socket call() throws IOException {
        return new Socket(ipAddress, dstPort);
    }
}

所以基于上面的代码，我将尝试解释我尝试过的内容以及当前的问题：

问题： 基于上面的代码，我在 connect() 中收到以下错误，它告诉我数据是 R，您不能将其设置为 serverSocket，因此错误我无法构建应用程序。

然后我尝试将 ConnectionTask 类（回调和可调用中的 R）中的所有 R 替换为 Socket，在这种情况下，应用程序能够构建和运行。

public interface Callback<Socket> {
    void onComplete(Socket result);
}

public void executeAsync(Callable<Socket> callable, Callback<Socket> callback) {
    executor.execute(() -> {
        try {
            final Socket result = callable.call();
            handler.post(() -> {
                callback.onComplete(result);
            });
        } catch (Exception e) {
            e.printStackTrace();
        }
    });
}

但是基于上述方法，当我点击连接按钮时会出现错误，这就是我所得到的：

2021-12-06 04:02:26.942 16417-16417/ir.atlaspio.atlasclientchat E/AndroidRuntime: FATAL EXCEPTION: main
    Process: ir.atlaspio.atlasclientchat, PID: 16417
    java.lang.NullPointerException: Attempt to invoke virtual method 'void ir.atlaspio.atlasclientchat.networking.ConnectionTask.executeAsync(java.util.concurrent.Callable, ir.atlaspio.atlasclientchat.networking.ConnectionTask$Callback)' on a null object reference
        at ir.atlaspio.atlasclientchat.networking.ClientConnection.connect(ClientConnection.java:38)
        at ir.atlaspio.atlasclientchat.MainActivity$1.onClick(MainActivity.java:61)
        at android.view.View.performClick(View.java:4780)
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
        at android.view.View$PerformClick.run(View.java:19866)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
2021-12-06 04:07:27.221 16417-16417/ir.atlaspio.atlasclientchat I/Process: Sending signal. PID: 16417 SIG: 9

在服务器端，我也检查了传入的连接，但那里什么也没发生...

Answer 1

您没有在ClientConnection 中实例化taskRunner。将此行添加到构造函数中：

public ClientConnection(String ipAddress, String userName, int dstPort) {
    this.ipAddress = ipAddress;
    this.userName = userName;
    this.dstPort = dstPort;
    this.taskRunner = new ConnectionTask(); // <-- this line here
}