Question

此代码用于从Android客户端发送电子邮件，并且不断崩溃。当我检查错误日志时，它显示：我已经尝试过故障排除，看看这个错误来自哪里，我无法看到。请帮助。

  10-02 16:15:14.536    7493-7493/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.ken4ward.emailsender, PID: 7493
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ken4ward.emailsender/com.example.ken4ward.emailsender.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5021)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.ken4ward.emailsender.MainActivity.onCreate(MainActivity.java:46)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1090)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5021)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643)
            at dalvik.system.NativeStart.main(Native Method)

这是代码。

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.util.Properties;

import javax.mail.Authenticator;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

//import android.support.v7.app.AppCompatActivity;

public class MainActivity extends Activity implements View.OnClickListener{

    EditText fieldEmail, emailSubject, emailBody;
    String strFieldEmail, strEmailSubject, strEmailBody;
    Button buttonLogin;
    Context context = null ;
    Session session = null;
    ProgressDialog progressDialog;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        progressDialog = new ProgressDialog(MainActivity.this);
        context = this;

        fieldEmail = (EditText)this.findViewById(R.id.editEmail);
        emailSubject = (EditText)this.findViewById(R.id.editSubject);
        emailBody = (EditText)this.findViewById(R.id.editBody);

        buttonLogin.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        strFieldEmail = fieldEmail.getText().toString();
        strEmailSubject = emailSubject.getText().toString();
        strEmailBody = emailBody.getText().toString();

        Properties properties = new Properties();
        properties.put("mail.smtp.host", "smtp.gmail.com");
        properties.put("mail.smtp.socketFactory.port", "465");
        properties.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.port", "465");

        session = Session.getDefaultInstance(properties, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("kehindeadeoya@gmail.com", "321g201115@...Ademnew");
            }
        });
        progressDialog = ProgressDialog.show(context, "", "Sending email", true);
        ReceivedFeedTask receivedFeedTask = new ReceivedFeedTask();
        receivedFeedTask.execute();
    }

    class ReceivedFeedTask extends AsyncTask<String, Void, String>
    {
        @Override
        protected String doInBackground(String... params) {
            try
            {
                Message message = new MimeMessage(session);
                message.setFrom(new InternetAddress("kehindeadeoya@gmail.com"));
                message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(strFieldEmail));
                message.setSubject(strEmailSubject);
                message.setContent(strEmailBody, "text/html; charset=utf-8");
                Transport.send(message);

            }catch (MessagingException messagingException)
            {
                messagingException.printStackTrace();
            }catch (Exception exception)
            {
                exception.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(String result)
        {
            progressDialog.dismiss();
            fieldEmail.setText("");
            emailSubject.setText("");
            emailBody.setText("");
            Toast.makeText(getApplicationContext(), "Message sent", Toast.LENGTH_LONG).show();
        }

    }
}

Answer 1

需要在 oncreate（） 中正确初始化ProgressDialog progressDialog ;并致电progressDialog。

实际上您的Locat会抛出

引起：java.lang.NullPointerException 在android.content.ContextWrapper.getApplicationInfo（ContextWrapper.java:152）在android.view.ContextThemeWrapper.getTheme（ContextThemeWrapper.java:103）在android.app.AlertDialog.resolveDialogTheme（AlertDialog.java:143）在android.app.AlertDialog。（AlertDialog.java:98）在android.app.ProgressDialog。（ProgressDialog.java：77）

试试这种方式，我希望它会对你有帮助。

public class MainActivity extends Activity implements View.OnClickListener{

EditText fieldEmail, emailSubject, emailBody;
String strFieldEmail, strEmailSubject, strEmailBody;
Button buttonLogin;
Context context = null ;
Session session = null;
ProgressDialog progressDialog ; 

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    progressDialog = new ProgressDialog(MainActivity.this);
    fieldEmail = (EditText)findViewById(R.id.editEmail);
    emailSubject = (EditText)findViewById(R.id.editSubject);
    emailBody = (EditText)findViewById(R.id.editBody);

    buttonLogin.setOnClickListener(this);
}

Answer 2

您必须在清单文件中添加活动。这可能是个问题。

Answer 3

你犯了一个愚蠢的错误。

最初你宣布了

ProgressDialog progressDialog = new ProgressDialog(this);

你又在这里初步化了

progressDialog = ProgressDialog.show(context, "", "Sending email", true);

所以只需从

中删除它

ProgressDialog progressDialog = new ProgressDialog(this);

到

ProgressDialog progressDialog;

抛出nullPointerException和app崩溃

3 个答案: