android 异步任务 NetworkOnMainThreadException

Question

我正在尝试使用套接字在 android 中编写一个服务器/客户端应用程序，并且我在 AsyncTask 中处理客户端套接字(服务器不是 android，只是普通的 java)。当我得到异常时我正在尝试从服务器读取。我发现当我从 android list 中删除 android:targetSdkVersion="16" 时，异常消失了，我可以从服务器读取。

我不明白这是为什么？谁能帮我澄清一下？我在理解 asynctask 方法 doInBackground 和我自己的方法之间的关系时也遇到了问题。 conhandler.execute() 是否运行 doInBackground() 然后一直等到我调用其他方法？感谢您的帮助。

public class ConnectionHandler extends AsyncTask<Void, Void, Void>{

public static String serverip = "10.0.2.2";
public static int serverport = 5000;
Socket s;
PrintWriter out;
BufferedReader in;

protected Void doInBackground(Void... params) {
    try {
        s = new Socket(serverip, serverport);
        Log.i("AsyncTank", "doInBackgoung: Created Socket");
    }...
    if (s.isConnected()) {
    try {
        in = new BufferedReader(new InputStreamReader(s.getInputStream()));
        out = new PrintWriter(s.getOutputStream(), true);
        Log.i("AsyncTank", "doInBackgoung: Socket created, Streams assigned");

    } ....
 }

public void writeToStream(String message) {
 try {
     if (s.isConnected()){
        out.println(message);
    } else {
        Log.i("AsynkTask", "writeToStream : Cannot write to stream, Socket is closed");
    }
    } catch (Exception e) {
    Log.i("AsynkTask", "writeToStream : Writing failed");
   }  
 }

 public String readFromStream() {
try {
    if (s.isConnected()) {
        Log.i("AsynkTask", "readFromStream : Reading message");
        String ret=in.readLine();
        Log.i("AsynkTask", "readFromStream : read "+ret);
        return ret;
    } else {
        Log.i("AsynkTask", "readFromStream : Cannot Read, Socket is closed");
    }
} catch (Exception e) {
    Log.i("AsynkTask", "readFromStream : Reading failed"+e.getClass());
}
return null;
}
}

这是我的主要 Activity

  public class MainActivity extends Activity {
private EditText view_email;
private EditText view_password;
TextView result;
ConnectionHandler conhandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    conhandler = new ConnectionHandler();
    conhandler.execute();       
    }


public void register(View view) {
     view_email= (EditText) findViewById(R.id.email);
    view_password = (EditText) findViewById(R.id.password);
    String email=view_email.getText().toString();
    String password=view_password.getText().toString();
    conhandler.writeToStream("register");
    conhandler.writeToStream(email);
    conhandler.writeToStream(password);
    String res=conhandler.readFromStream(); //here's the exception
    result=(TextView) findViewById(R.id.result);
    result.setText(res);
 }
 }

Answer 1

这个问题有两个解决方案。

1) 不要在 Main UIThread 中编写网络调用，为此使用 Async Task。

2) 在 setContentView(R.layout.activity_main) 之后将下面的代码写入您的 MainActivity 文件；

if (android.os.Build.VERSION.SDK_INT > 9) {
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);
}

然后将下面的 import 语句导入到您的 java 文件中。

import android.os.StrictMode;