示例:使用AsyncTask的Android雙向網絡套接字


Answers

SendDataToNetwork任務在主ui線程中運行,這意味著由於NetworkOnMainThreadException致命異常,它將使Honeycomb或更高版本的應用程序崩潰。 以下是我的SendDataToNetwork以避免此問題的方式:

public boolean sendDataToNetwork(final byte[] cmd)
{ 
    if (_nsocket.isConnected())
    {
        Log.i(TAG, "SendDataToNetwork: Writing received message to socket");
        new Thread(new Runnable()
        {
            public void run() 
            {
                try
                {
                    _nos.write(cmd);
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                    Log.i(TAG, "SendDataToNetwork: Message send failed. Caught an exception");
                }
            }
        }).start();

        return true;
    }

    Log.i(TAG, "SendDataToNetwork: Cannot send message. Socket is closed");
    return false;
}
Question

我在Android上找到的大多數網絡套接字示例都是單向的。 我需要一個雙向數據流的解決方案。 我最終了解到了AsyncTask。 此示例顯示如何從套接字獲取數據並將數據發送回它。 由於正在接收數據的套接字的阻塞性質,阻塞需要在UI線程以外的線程中運行。

為了示例,此代碼連接到Web服務器。 按“Start AsyncTask”按鈕將打開套接字。 套接字打開後,Web服務器將等待請求。 按“發送消息”按鈕將向服務器發送請求。 服務器的任何響應都將顯示在TextView中。 對於http,一旦發送了所有數據,Web服務器將斷開與客戶端的連接。 對於其他TCP數據流,連接將一直保持到一側斷開連接。

截圖:

AndroidManifest.xml中:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.exampleasynctask"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="8" />
    <uses-permission android:name="android.permission.INTERNET" />
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MainActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

水庫\佈局\ main.xml中:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<Button android:id="@+id/btnStart" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Start AsyncTask"></Button>
<Button android:id="@+id/btnSend" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Send Message"></Button>
<TextView android:id="@+id/textStatus" android:textSize="24sp" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Status Goes Here" />
</LinearLayout>

SRC \ com.exampleasynctask \ MainActivity.java:

package com.exampleasynctask;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {
    Button btnStart, btnSend;
    TextView textStatus;
    NetworkTask networktask;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        btnStart = (Button)findViewById(R.id.btnStart);
        btnSend = (Button)findViewById(R.id.btnSend);
        textStatus = (TextView)findViewById(R.id.textStatus);
        btnStart.setOnClickListener(btnStartListener);
        btnSend.setOnClickListener(btnSendListener);
        networktask = new NetworkTask(); //Create initial instance so SendDataToNetwork doesn't throw an error.
    }

    private OnClickListener btnStartListener = new OnClickListener() {
        public void onClick(View v){
            btnStart.setVisibility(View.INVISIBLE);
            networktask = new NetworkTask(); //New instance of NetworkTask
            networktask.execute();
        }
    };
    private OnClickListener btnSendListener = new OnClickListener() {
        public void onClick(View v){
            textStatus.setText("Sending Message to AsyncTask.");
            networktask.SendDataToNetwork("GET / HTTP/1.1\r\n\r\n");
        }
    };

    public class NetworkTask extends AsyncTask<Void, byte[], Boolean> {
        Socket nsocket; //Network Socket
        InputStream nis; //Network Input Stream
        OutputStream nos; //Network Output Stream

        @Override
        protected void onPreExecute() {
            Log.i("AsyncTask", "onPreExecute");
        }

        @Override
        protected Boolean doInBackground(Void... params) { //This runs on a different thread
            boolean result = false;
            try {
                Log.i("AsyncTask", "doInBackground: Creating socket");
                SocketAddress sockaddr = new InetSocketAddress("192.168.1.1", 80);
                nsocket = new Socket();
                nsocket.connect(sockaddr, 5000); //10 second connection timeout
                if (nsocket.isConnected()) { 
                    nis = nsocket.getInputStream();
                    nos = nsocket.getOutputStream();
                    Log.i("AsyncTask", "doInBackground: Socket created, streams assigned");
                    Log.i("AsyncTask", "doInBackground: Waiting for inital data...");
                    byte[] buffer = new byte[4096];
                    int read = nis.read(buffer, 0, 4096); //This is blocking
                    while(read != -1){
                        byte[] tempdata = new byte[read];
                        System.arraycopy(buffer, 0, tempdata, 0, read);
                        publishProgress(tempdata);
                        Log.i("AsyncTask", "doInBackground: Got some data");
                        read = nis.read(buffer, 0, 4096); //This is blocking
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
                Log.i("AsyncTask", "doInBackground: IOException");
                result = true;
            } catch (Exception e) {
                e.printStackTrace();
                Log.i("AsyncTask", "doInBackground: Exception");
                result = true;
            } finally {
                try {
                    nis.close();
                    nos.close();
                    nsocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                Log.i("AsyncTask", "doInBackground: Finished");
            }
            return result;
        }

        public void SendDataToNetwork(String cmd) { //You run this from the main thread.
            try {
                if (nsocket.isConnected()) {
                    Log.i("AsyncTask", "SendDataToNetwork: Writing received message to socket");
                    nos.write(cmd.getBytes());
                } else {
                    Log.i("AsyncTask", "SendDataToNetwork: Cannot send message. Socket is closed");
                }
            } catch (Exception e) {
                Log.i("AsyncTask", "SendDataToNetwork: Message send failed. Caught an exception");
            }
        }

        @Override
        protected void onProgressUpdate(byte[]... values) {
            if (values.length > 0) {
                Log.i("AsyncTask", "onProgressUpdate: " + values[0].length + " bytes received.");
                textStatus.setText(new String(values[0]));
            }
        }
        @Override
        protected void onCancelled() {
            Log.i("AsyncTask", "Cancelled.");
            btnStart.setVisibility(View.VISIBLE);
        }
        @Override
        protected void onPostExecute(Boolean result) {
            if (result) {
                Log.i("AsyncTask", "onPostExecute: Completed with an Error.");
                textStatus.setText("There was a connection error.");
            } else {
                Log.i("AsyncTask", "onPostExecute: Completed.");
            }
            btnStart.setVisibility(View.VISIBLE);
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        networktask.cancel(true); //In case the task is currently running
    }
}



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