java - Android AsyncTask 卡住了

Question

上下文:Android 应用程序的以下 AsyncTask 从服务器发送和接收所谓的 Request 对象。如果用户在应用程序中更改了他的内容，则会生成新的请求对象并将其添加到同步队列中。如果他随后点击同步按钮，AsyncTask 将被创建并以他的请求作为参数执行。

处理程序最终获取所有答案并在数据库中设置必要的结果。然后，他最终通过在 UI 线程 (onPostExecute) 上调用一个方法来更新 UI。

public class RequestSender extends AsyncTask<Request, Void, Boolean>{

// Server data
private String host;
private int port = 1337;

private Socket socket;
private AnswerHandler handler;

public RequestSender(AnswerHandler handler) {
    this.host = "hostNameHere";
    this.handler = handler;
}

/**
 * This method gets started as asynchronous task when you call .run()
 * @return 
 */
@Override
protected Boolean doInBackground(Request... requests) {
    return sendAndReceive(requests);
}

private boolean sendAndReceive(Request... requests) {
    boolean isConnected = this.initSocket();
    if(isConnected) {
        this.send(requests);
        this.waitForAnswer();
    } else {
        handler.setRequests(requests);
    }
    return isConnected;
}

/**
 * Tries to open a socket on the android device to a specified Host
 */
private boolean initSocket() {
    try {
        SocketAddress sockaddr = new InetSocketAddress(host, port);
        socket = new Socket();
        socket.connect(sockaddr, 5000);
        return true;
    } catch (UnknownHostException e) {
        System.err.println("Unknown Host in initSocket()");
    } catch (IOException e) {
        System.err.println("Connection timed out");
    }
    return false;
}

/**
 * Tries to send a request to the server
 * @param request
 */

public void send(Request... request) {
    if(socket != null) {
        try {
            ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
            out.writeObject(request);
            out.flush();
        } catch (IOException e) {
            System.err.println("Couldn't write to socket in RequestSender");
        }
    }
}

/**
 * Waits for the answer from the server and reports the result in the handler
 */
private void waitForAnswer() {
    try {
        socket.setSoTimeout(5000);
        ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
        Request[] answers = (Request[]) in.readObject();
        socket.close();
        handler.setRequests(answers);
    } catch (StreamCorruptedException e) {
        System.err.println("Failed to open stream from server");
    } catch (IOException e) {
        System.err.println("Failed to read answers from server");
    } catch (ClassNotFoundException e) {
        System.err.println("Failed to read class from server");
    }
}

@Override
protected void onPostExecute(Boolean a) {
    handler.updateUI();
}

}

现在我的问题:整个过程几次都没有任何问题(这取决于我手机的善意多少次)，但似乎任务卡在某个地方而没有给我任何关于 System.err 的错误消息。重新启动应用程序解决了问题，它再次运行没有任何问题。

我已经读到 AsyncTasks 从 Honeycomb 开始在一个线程上执行。我在打开的套接字上设置了超时并读入，因此卡住的任务应该在该超时后终止。

我的代码有什么问题吗？您能想出解决方案吗？

Answer 1

最近我遇到了这个问题，经过大量调试和头脑 Storm 一周后，我终于找到了这个错误。

好的，让我们做一些功课。

发送/接收数据的过程

1. 建立联系。假设 connectToServer() 是一个将设备物理连接到服务器的函数。
2. 套接字/TCP 部分。在您的情况下，您有 doInbackground()，您在其中调用 initSocket() 来启动套接字连接。

In real world scenario when you request a connection to a server it takes some time, may be a one or two seconds. So you should wait for that time before initiating a socket connection request. If a socket request send before a connection then it goes to lock state and releases after the default time out is finished which make it stuck.

编程场景

connectToServer();

// wait for 1 or 2 second.

initSocket();   

示例代码

    /* Function to check whether we are physically connected to the server or not */
private boolean isConnEstablished(){
    WifiInfo connInfo = mManager.getConnectionInfo();
    return mManager.isWifiEnabled() && connInfo.getNetworkId() != -1 && connInfo.getIpAddress() != 0;
}

private void initSocket() {
    boolean scanning = true;
    int tryCount = 5; // we trying for 5 times

    try {
        while (scanning && tryCount > 0) {
            try {
                if (isConnEstablished()) {
                    try{
                        Thread.sleep(500);
                    }catch (InterruptedException e){
                        Log.e("Yo", "sleep-error");
                    }
                    tConnection = new Socket(host, port);
                    scanning = false;
                    Log.e(getClass().getName(), "Socket connection established");
                }else {
                    throw new ConnectException();
                }
            } catch (ConnectException e) {
                Log.e(getClass().getName(), "connecting again...");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException ex) {
                    Log.e(getClass().getName(), "System sleep-error: " + ex.getMessage());
                }
            }
           tryCount--;
        }

}