如何解决android中的NetworkOnMainThreadException错误？

Question

我以前javamail用安卓发送电子邮件。但它抛出异常NetworkOnMainThreadException。如何解决这个异常呢？

主要活动

package com.aaa;
import android.os.Bundle;
import android.os.NetworkOnMainThreadException;
import android.app.Activity;
import android.util.Log; 
import android.view.Menu;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends Activity  {
private Mail m;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    m = new Mail("mail@gmail.com", "pwd");
}
 public void sendEmail(View view){
        String[] toArr = {"samp@gmail.com"};
        m.setTo(toArr);
        m.setFrom("mail613@gmail.com");
        m.setSubject("subject"); 
        m.setBody("your message goes here"); 

        try { 
            //m.addAttachment("/sdcard/myPicture.jpg");
            if(m.send()) { 
                // success
                Toast.makeText(MainActivity.this, "Email was sent successfully.", Toast.LENGTH_LONG).show(); 
            } else { 
                // failure
                Toast.makeText(MainActivity.this, "Email was not sent.", Toast.LENGTH_LONG).show(); 
            } 
        } catch(Exception e) { 
            // some other problem
            //Toast.makeText(MainActivity.this, "Email was not sent.", Toast.LENGTH_LONG).show(e);
            Toast.makeText(MainActivity.this, ""+e+"", Toast.LENGTH_LONG).show(); 
            Log.e("SendMail",e.getMessage(),e);
        } 

    }

 }

邮件.java

package com.aaa;

import java.util.Date; 
import java.util.Properties; 
import javax.activation.CommandMap; 
import javax.activation.DataHandler; 
import javax.activation.DataSource; 
import javax.activation.FileDataSource; 
import javax.activation.MailcapCommandMap; 
import javax.mail.BodyPart; 
import javax.mail.Multipart; 
import javax.mail.PasswordAuthentication; 
import javax.mail.Session; 
import javax.mail.Transport; 
import javax.mail.internet.InternetAddress; 
import javax.mail.internet.MimeBodyPart; 
import javax.mail.internet.MimeMessage; 
import javax.mail.internet.MimeMultipart;

public class Mail extends javax.mail.Authenticator { 
private String _user; 
private String _pass; 

private String[] _to; 
private String _from; 

private String _port; 
private String _sport; 

private String _host; 

private String _subject; 
private String _body; 

private boolean _auth; 

private boolean _debuggable; 

private Multipart _multipart; 


public Mail() { 
    _host = "smtp.gmail.com"; // default smtp server 
    _port = "465"; // default smtp port 
    _sport = "465"; // default socketfactory port 

    _user = ""; // username 
    _pass = ""; // password 
    _from = ""; // email sent from 
    _subject = ""; // email subject 
    _body = ""; // email body 

    _debuggable = false; // debug mode on or off - default off 
    _auth = true; // smtp authentication - default on 

    _multipart = new MimeMultipart(); 

    // There is something wrong with MailCap, javamail can not find a handler for the multipart/mixed part, so this bit needs to be added. 
    MailcapCommandMap mc = (MailcapCommandMap) CommandMap.getDefaultCommandMap(); 
    mc.addMailcap("text/html;; x-java-content-handler=com.sun.mail.handlers.text_html"); 
    mc.addMailcap("text/xml;; x-java-content-handler=com.sun.mail.handlers.text_xml"); 
    mc.addMailcap("text/plain;; x-java-content-handler=com.sun.mail.handlers.text_plain"); 
    mc.addMailcap("multipart/*;; x-java-content-handler=com.sun.mail.handlers.multipart_mixed"); 
    mc.addMailcap("message/rfc822;; x-java-content-handler=com.sun.mail.handlers.message_rfc822"); 
    CommandMap.setDefaultCommandMap(mc); 
} 

public Mail(String user, String pass) { 
    this(); 

    _user = user; 
    _pass = pass; 
} 

public boolean send() throws Exception { 
    Properties props = _setProperties(); 

    if(!_user.equals("") && !_pass.equals("") && _to.length > 0 && !_from.equals("") && !_subject.equals("") && !_body.equals("")) { 
        Session session = Session.getInstance(props, this); 

        MimeMessage msg = new MimeMessage(session); 

        msg.setFrom(new InternetAddress(_from)); 

        InternetAddress[] addressTo = new InternetAddress[_to.length]; 
        for (int i = 0; i < _to.length; i++) { 
            addressTo[i] = new InternetAddress(_to[i]); 
        } 
        msg.setRecipients(MimeMessage.RecipientType.TO, addressTo); 

        msg.setSubject(_subject); 
        msg.setSentDate(new Date()); 

        // setup message body 
        BodyPart messageBodyPart = new MimeBodyPart(); 
        messageBodyPart.setText(_body); 
        _multipart.addBodyPart(messageBodyPart); 

        // Put parts in message 
        msg.setContent(_multipart); 

        // send email 
        Transport.send(msg); 

        return true; 
    } else { 
        return false; 
    } 
} 

public void addAttachment(String filename) throws Exception { 
    BodyPart messageBodyPart = new MimeBodyPart(); 
    DataSource source = new FileDataSource(filename); 
    messageBodyPart.setDataHandler(new DataHandler(source)); 
    messageBodyPart.setFileName(filename); 

    _multipart.addBodyPart(messageBodyPart); 
} 

@Override 
public PasswordAuthentication getPasswordAuthentication() { 
    return new PasswordAuthentication(_user, _pass); 
} 

private Properties _setProperties() { 
    Properties props = new Properties(); 

    props.put("mail.smtp.host", _host); 

    if(_debuggable) { 
        props.put("mail.debug", "true"); 
    } 

    if(_auth) { 
        props.put("mail.smtp.auth", "true"); 
    } 

    props.put("mail.smtp.port", _port); 
    props.put("mail.smtp.socketFactory.port", _sport); 
    props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory"); 
    props.put("mail.smtp.socketFactory.fallback", "false"); 

    return props; 
} 

// the getters and setters 
public String getBody() { 
    return _body; 
} 

public void setBody(String _body) { 
    this._body = _body; 
} 

public void setTo(String[] toArr) {
    this._to = toArr;
}

public void setFrom(String string) {
    this._from = string;
}

public void setSubject(String string) {
    this._subject = string;
}

// more of the getters and setters ….. 
    } `

Answer 1

您需要使用AsyncTask来执行所有网络操作。

您的网络操作可能会花费大量时间，并且如果在主 UI 线程上完成，UI 将变得无响应。如果你的用户界面长时间冻结，应用程序可能会被操作系统杀死。

因此，Android 4+ 强制要求使用后台线程来执行网络操作。

将执行网络活动的代码doInBacground()以及所有使用execute().

您的 AsyncTask 如下所示：

private class SendMail extends AsyncTask<String, Integer, Void> {
     protected void doInBackground() {
        sendEmail();
 }

 protected void onProgressUpdate() {
    //called when the background task makes any progress
 }

  protected void onPreExecute() {
     //called before doInBackground() is started
 }
 protected void onPostExecute() {
     //called after doInBackground() has finished 
 }
  }

您可以使用以下命令在任何地方调用它new SendMail().execute("");