Question

当我们从一个activity转到另一个activity并从堆栈中移除当前activity时，我得到NullPointer exception。假设我有class A和class B。我将从A转到B，然后从B转到A并使用finish()方法或使用Flag_clear_Top从堆栈中删除B活动。

“A”类作为MainClass

public class MainClass extends Activity{

    Button callBTN;
    Button messageBTN;
    Button emailBTN;
    Button referBTN;
    TextView nameTXT;

    String name ;
    String email;
    String mobile;

    @Override
    protected void onCreate(Bundle savedInstanceState) {



        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_class_layout);
         Intent myIntent = getIntent();
        Bundle b = myIntent.getExtras();
        name = b.getString("name");
        email = b.getString("email");
        mobile = b.getString("mobile");

         Log.e("Name String", name);
            Log.e("email String", email);
            Log.e("mobile String", mobile);

          nameTXT=(TextView)findViewById(R.id.name_TXT); 

            callBTN=(Button)findViewById(R.id.call_BTN);
            messageBTN=(Button)findViewById(R.id.message_BTN);
            emailBTN=(Button)findViewById(R.id.email_BTN);
            referBTN=(Button)findViewById(R.id.refer_BTN);

           nameTXT.setText(name);
           callBTN.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) 

            {
                // TODO Auto-generated method stub
                Intent callIntent = new Intent(Intent.ACTION_CALL);
                callIntent.setData(Uri.parse("tel:"+ mobile));
                startActivity(callIntent);

            }

        });

           messageBTN.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
            Log.e("MainClass","to find mobile number"+mobile);
                Intent intentSendMessage=new Intent(MainClass.this,SmsSender.class);
                intentSendMessage.putExtra("mobile_number",mobile);
                startActivity(intentSendMessage);

            }
        });
           emailBTN.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                Intent intentEmail =new Intent(MainClass.this,EmailSender.class);
                intentEmail.putExtra("mail_Str",email);
                startActivity(intentEmail);

            }
        });

           referBTN.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                Intent intentRefer=new Intent(MainClass.this,References.class);
                intentRefer.putExtra("emailAgent",email);

                startActivity(intentRefer);

            }
        });







    }

}

“B”类作为参考文献：

package com.cql.ins;

import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.ViewDebug.FlagToString;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.cqlsys.help.UserFunctions;

public class References  extends Activity
{

    EditText nameEDt,emailEDt,phoneEDt,commentEDT;
    TextView errorTXT;
    Button referenceSendBTN;

    String emailReferAgent;


    // JSON Response node names
        private static String KEY_SUCCESS = "status";
        private static String KEY_Message ="message";
        private static String KEY_ERROR = "error";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.references_layout);

        Intent emailIntent = getIntent();
        Bundle d = emailIntent.getExtras();
        emailReferAgent = d.getString("emailAgent");

        nameEDt=(EditText)findViewById(R.id.name_Refer_EDt);
        emailEDt=(EditText)findViewById(R.id.email_Refer_EDT);
        phoneEDt=(EditText)findViewById(R.id.phone_refer_EDT);
        commentEDT=(EditText)findViewById(R.id.comment_Refer_EDT);
        errorTXT=(TextView)findViewById(R.id.errorTXT);
        referenceSendBTN=(Button)findViewById(R.id.refer_send_BTN);



        referenceSendBTN.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                String nameReferStr = nameEDt.getText().toString();
                String emailReferStr = emailEDt.getText().toString();
                String phoneReferStr =phoneEDt.getText().toString();
                String commentReferStr =commentEDT.getText().toString();    

            UserFunctions userFunction = new UserFunctions();

                JSONObject json =userFunction.referUser(nameReferStr, emailReferStr, phoneReferStr,commentReferStr,emailReferAgent);

                // check for  response
                try {
                    if (json.getString(KEY_SUCCESS) != null) {
                        errorTXT.setText("hello");
                        String res = json.getString(KEY_SUCCESS); 
                        Log.e("REferences Status Tag", res);

                        if(Boolean.parseBoolean(res) == true){
                            // user successfully submit
                            //Toast.makeText(getApplicationContext(), "msg msg", Toast.LENGTH_SHORT).show();
                            Intent intentbackMainClass=new Intent(References.this,MainClass.class);
                            //intentbackMainClass.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
                            startActivity(intentbackMainClass);
                            finish();
                        }else{
                            // Error in submit the data
                            errorTXT.setText("Error occured in registration");
                        }


                    }
            }
                 catch (JSONException e) {
                        e.printStackTrace();
                    }
            }
        });

    }

}

但我得到以下例外：

** threadid = 1：线程退出，未捕获异常（group = 0x4001d800） 01-19 02：43：27.507：E / AndroidRuntime（13801）：致命异常：主要 01-19 02：43：27.507：E / AndroidRuntime（13801）：java.lang.RuntimeException：无法启动活动ComponentInfo {com.cqlsys.insagent / com.cql.ins.MainClass}：java.lang.NullPointerException **

01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.os.Looper.loop(Looper.java:123)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.app.ActivityThread.main(ActivityThread.java:4627)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at java.lang.reflect.Method.invokeNative(Native Method)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at java.lang.reflect.Method.invoke(Method.java:521)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at dalvik.system.NativeStart.main(Native Method)
01-19 02:43:27.507: E/AndroidRuntime(13801): Caused by: java.lang.NullPointerException
01-19 02:43:27.507: E/AndroidRuntime(13801):    at com.cqlsys.insagent.MainClass.onCreate(MainClass.java:39)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-19 02:43:27.507: E/AndroidRuntime(13801):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
01-19 02:43:27.507: E/AndroidRuntime(13801):    ... 11 more

我该如何解决这个问题？

Answer 1

我猜是因为这些值为null，

   name = b.getString("name");
    email = b.getString("email");
    mobile = b.getString("mobile");

但是你试图在这里的日志中打印它们，

            Log.e("Name String", name);
            Log.e("email String", email);
            Log.e("mobile String", mobile);

问题是，我没有看到你从你调用startActivity（）的地方传递额外内容，因此它们在这里为null并且你得到了异常。

如果您不希望日志崩溃您的应用，请按照这样编辑您的日志

                Log.e("Name String", name+"");
                Log.e("email String", email+"");
                Log.e("mobile String", mobile+"");

如果值为null，则打印“null”，否则打印值本身。

Answer 2

我不确定但是如果你没有从活动B传递任何东西并且将“b”作为Null，则会发生这种情况。

而不是代码。在通过Intent获得所需的所有值后，首先应检查 b == null或不。

所以相反

   Bundle b = myIntent.getExtras();
        name = b.getString("name");
        email = b.getString("email");
        mobile = b.getString("mobile");

尝试使用以下代码。

  Bundle b = myIntent.getExtras();
  if(b!=null){

            name = b.getString("name");
            email = b.getString("email");
            mobile = b.getString("mobile");
  }

Answer 3

尝试使用上面setContentView()

以上的getExtras

  Intent emailIntent = getIntent();
  Bundle d = emailIntent.getExtras();
  emailReferAgent = d.getString("emailAgent");

Answer 4

nameTXT.setText(name);

这似乎是问题，因为您正在尝试设置名称文本，如果名称没有返回任何值，那么它将生成nullpointerexception。

请检查从B级到A级是否有价值。

当我从一个活动转到另一个活动时，我得到空指针异常

4 个答案: