使用 Android 服务处理网络连接

发布于 2024-11-02 14:32:33 字数 139 浏览 1 评论 0原文

我正在开发一个 Android 应用程序，需要保持与聊天服务器的网络连接。我知道我可以创建一个服务来启动与服务器的连接，但是该服务如何通知 Android 活动新传入的消息？活动需要更新视图以显示新消息。我对 Android 还很陌生，所以非常感谢您的帮助。谢谢！

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就像说晚安 2024-11-09 14:32:33

您可以将处理程序传递给您的服务吗？

首先，将您的处理程序定义为接口。这是一个示例，因此您的示例可能更复杂。

public interface ServerResponseHandler {

    public void success(Message[] msgs); // msgs may be null if no new messages
    public void error();

}

在您的活动中定义处理程序的实例。由于它是一个接口，您将在活动中提供实现，因此您可以从处理程序中引用封闭活动的字段和方法。

public class YourActivity extends Activity {

// ... class implementation here ...

    updateUI() { 
        // TODO: UI update work here
    }

    ServerResponseHandler callback = new ServerResponseHandler() {

        @Override
        public void success(Message[] msgs) {
            // TODO: update UI with messages from msgs[]

            YourActivity.this.updateUI();
        }

        @Override
        public void error() { 
            // TODO: show error dialog here? (or handle error differently)
        }

    }

    void onCheckForMessages() { 
        networkService.checkForMessages(callback);
    }

NetworkService 将包含类似以下内容：

void checkForMessages(ServerResponseHandler callback) { 

    // TODO: contact server, check for new messages here

    // call back to UI
    if (successful) { 
        callback.success(msgs);
    } else {
        callback.error();
    }
}

另外，正如 Aleadam 所说，您还应该避免服务默认在同一线程上运行。对于网络等事物来说，这通常不是首选行为。 Android 服务基础页面明确警告不要在没有单独线程的情况下进行网络连接：

警告：服务在其托管进程的主线程中运行 - 该服务不
创建自己的线程并且不会在单独的进程中运行（除非您指定
否则）。这意味着，如果您的服务要执行任何 CPU 密集型工作或
阻塞操作（例如 MP3 播放或联网），您应该创建一个新线程
在服务范围内完成这项工作。通过使用单独的线程，您将减少
应用程序无响应 (ANR) 错误的风险，并且应用程序的主线程可以继续专用于用户与您的活动的交互。

有关在服务中使用线程的更多信息，请查看 SO 文章应用程序线程与服务线程和如何在 android 中的新线程中启动服务

Can you pass a handler to your service?

First, define your handler as an interface. This is an example, so yours may be more complex.

public interface ServerResponseHandler {

    public void success(Message[] msgs); // msgs may be null if no new messages
    public void error();

}

Define an instance of your handler in your activity. Since it's an interface you'll provide the implementation here in the activity, so you can reference the enclosing activity's fields and methods from within the handler.

public class YourActivity extends Activity {

// ... class implementation here ...

    updateUI() { 
        // TODO: UI update work here
    }

    ServerResponseHandler callback = new ServerResponseHandler() {

        @Override
        public void success(Message[] msgs) {
            // TODO: update UI with messages from msgs[]

            YourActivity.this.updateUI();
        }

        @Override
        public void error() { 
            // TODO: show error dialog here? (or handle error differently)
        }

    }

    void onCheckForMessages() { 
        networkService.checkForMessages(callback);
    }

and NetworkService would contain something like:

void checkForMessages(ServerResponseHandler callback) { 

    // TODO: contact server, check for new messages here

    // call back to UI
    if (successful) { 
        callback.success(msgs);
    } else {
        callback.error();
    }
}

Also, as Aleadam says, you should also be away that a service runs on the same thread by default. This is often not preferred behavior for something like networking. The Android Fundamentals Page on Services explicitly warns against networking without separate threads:

Caution: A service runs in the main thread of its hosting process—the service does not
create its own thread and does not run in a separate process (unless you specify
otherwise). This means that, if your service is going to do any CPU intensive work or
blocking operations (such as MP3 playback or networking), you should create a new thread
within the service to do that work. By using a separate thread, you will reduce the
risk of Application Not Responding (ANR) errors and the application's main thread can remain dedicated to user interaction with your activities.

For more information on using threads in your service, check out the SO articles Application threads vs Service threads and How to start service in new thread in android

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