android - SendMail 执行中的应用程序崩溃

Question

我正在开发一个使用 fragment 内的 JavaMail API 发送电子邮件的应用程序。整个应用程序运行良好，但是当我单击按钮发送电子邮件时，应用程序崩溃了。我试图更改 SendMail 代码中的上下文，但它并没有解决我的问题。我正在发布我遇到的调试错误和我的 Java 代码，如果您需要其他任何东西，请问我。非常欢迎任何帮助。

SendMail.Java

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

    //Declaring Variables

    private Context context;
    private Session session;

    //Information to send email
    private String email;
    private String subject;
    private String message;

    //Progressdialog to show while sending email
    private ProgressDialog progressDialog;

    //Class Constructor
    public SendMail(OneFragment oneFragment, String email, String subject, String message) {
        //Initializing variables
        this.context = context;
        this.email = email;
        this.subject = subject;
        this.message = message;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        //Showing progress dialog while sending email
        progressDialog = ProgressDialog.show(context,"Enviando mensagem","Aguarde um momento...",false,false);
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        //Dismissing the progress dialog
        progressDialog.dismiss();
        //Showing a success message
        Toast.makeText(context,"Mensagem enviada",Toast.LENGTH_LONG).show();
    }

    @Override
    protected Void doInBackground(Void... params) {
        //Creating properties
        Properties props = new Properties();

        //Configuring properties for gmail
        //If you are not using gmail you may need to change the values
        props.put("mail.smtp.host", "smtp.gmail.com");
        props.put("mail.smtp.socketFactory.port", "465");
        props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.port", "465");

        //Creating a new session
        session = Session.getDefaultInstance(props,
                new javax.mail.Authenticator() {
                    //Authenticating the password
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication(Config.EMAIL,Config.PASSWORD);
                    }
                });

        try {
            //Creating MimeMessage object
            MimeMessage mm = new MimeMessage(session);

            //Setting sender address
            mm.setFrom(new InternetAddress(Config.EMAIL));
            //Adding receiver
            mm.addRecipient(Message.RecipientType.TO, new InternetAddress(email));
            //Adding subject
            mm.setSubject(subject);
            //Adding message
            mm.setText(message);

            //Sending email
            Transport.send(mm);

        } catch (MessagingException e) {
            e.printStackTrace();
        }
        return null;

    }
}

错误调试

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: info.androidhive.materialtabs, PID: 6870
                  java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources$Theme android.content.Context.getTheme()' on a null object reference
                      at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:154)
                      at android.app.AlertDialog.<init>(AlertDialog.java:109)
                      at android.app.ProgressDialog.<init>(ProgressDialog.java:77)
                      at android.app.ProgressDialog.show(ProgressDialog.java:110)
                      at android.app.ProgressDialog.show(ProgressDialog.java:104)
                      at info.androidhive.materialtabs.SendMail.onPreExecute(SendMail.java:50)
                      at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
                      at android.os.AsyncTask.execute(AsyncTask.java:535)
                      at info.androidhive.materialtabs.fragments.OneFragment.sendEmail(OneFragment.java:45)
                      at info.androidhive.materialtabs.fragments.OneFragment.onClick(OneFragment.java:50)
                      at android.view.View.performClick(View.java:5156)
                      at android.view.View$PerformClick.run(View.java:20755)
                      at android.os.Handler.handleCallback(Handler.java:739)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:145)
                      at android.app.ActivityThread.main(ActivityThread.java:5832)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:372)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

一个 fragment

//More Code

@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);}


    private void sendEmail() {
        //Getting content for email
        String email = "myemail";
        String subject = "subject";
        String message = editTextMessage.getText().toString().trim();

        //Creating SendMail object
        SendMail sm = new SendMail(this, email, subject, message);

        //Executing sendmail to send email
        sm.execute();
    }

    @Override
    public void onClick(View v) {
        sendEmail();
    }

//More Code

Answer 1

检查 SendMail 任务的构造函数

  //Class Constructor
    public SendMail(OneFragment oneFragment, String email, String subject, String message) {
        //Initializing variables
        this.context = context;
        this.email = email;
        this.subject = subject;
        this.message = message;
    }

您没有收到 context 值，因此 context 为 null :)

那么你这里有问题了:

progressDialog = ProgressDialog.show(context,"Enviando mensagem","Aguarde um momento...",false,false);

更新:修复您的代码

 //Class Constructor
    public SendMail(OneFragment oneFragment, String email, String subject, String message) {
        //Initializing variables
        this.context = oneFragment.getActivity();
        this.email = email;
        this.subject = subject;
        this.message = message;
    }