Android: Call Method from another Class which starts a new Intent

Question

as the title already said, I’m trying to call a method LoginSuccess() from the Class JSON_Factroy_Return_Handler.java which then should start an Intent. I always get a java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference.

To make it more clear what I want to do, I’m going to post the important code snippet.

Login_Activity.java

public void Login(View view) { //Button Login pressed calls Login-Method ... new JSON_Factory_Test().execute(result); //Calls AsyncTask-Class ... } public void LoginSuccess() { Intent mainIntent = new Intent(getApplicationContext(), Main_Activity.class); startActivity(mainIntent); finish(); }

JSON_Factory_Test.java

public class JSON_Factory_Test extends AsyncTask<String, String, JSONObject> { @Override protected JSONObject doInBackground(String... args) { ... return jsonobject; } @Override protected void onPostExecute(JSONObject jsonobject) { new JSON_Factory_Return_Handler().JSON_Factory_Retrun(jsonobject); } }

JSON_Factroy_Return_Handler.java

public class JSON_Factory_Return_Handler { ... public void JSON_Factory_Retrun(JSONObject jsonresult) { ... if(jsonParams.get("result").toString().equals("TRUE")) { new Login_Activity().LoginSuccess(); } else { ... } ... } }

When I then run this Project I alway get a NullPointerException!

FATAL EXCEPTION: main Process: com.example.project, PID: 2855 java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:105) at com.example.project.main.Login_Activity.LoginSuccess(Login_Activity.java:138) at com.example.project.json.JSON_Factory_Return_Handler.JSON_Factory_Retrun(JSON_Factory_Return_Handler.java:27) at com.example.project.json.JSON_Factory_Test.onPostExecute(JSON_Factory_Test.java:49) at com.example.project.json.JSON_Factory_Test.onPostExecute(JSON_Factory_Test.java:1) at android.os.AsyncTask.finish(AsyncTask.java:632) at android.os.AsyncTask.access$600(AsyncTask.java:177) at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5070) 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:836) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:631)

I also tried this for the Login_Activity.java but this also won't work either

public void LoginSuccess() { Intent mainIntent = new Intent(Login_Activity.this, Main_Activity.class); Login_Activity.this.startActivity(mainIntent); finish(); }

When I then run this Project I also get a NullPointerException!

 FATAL EXCEPTION: main Process: com.example.project, PID: 3187 java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference at android.content.ContextWrapper.getPackageName(ContextWrapper.java:131) at android.content.ComponentName.<init>(ComponentName.java:77) at android.content.Intent.<init>(Intent.java:4011) at com.example.project.main.Login_Activity.LoginSuccess(Login_Activity.java:138) at com.example.project.json.JSON_Factory_Return_Handler.JSON_Factory_Retrun(JSON_Factory_Return_Handler.java:27) at com.example.project.json.JSON_Factory_Test.onPostExecute(JSON_Factory_Test.java:49) at com.example.project.json.JSON_Factory_Test.onPostExecute(JSON_Factory_Test.java:1) at android.os.AsyncTask.finish(AsyncTask.java:632) at android.os.AsyncTask.access$600(AsyncTask.java:177) at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5070) 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:836) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:631)

I know that I could do everything in one Class but I need the AsyncTask more than once. And I also need the JSON_Factory_Return_Handler.java because this Class checks the returned values and then it should call new methods.

If you guys need more information I would be happy if I could give them to you :)

Thanks for your help in advance, Cheers 3dDi

SHASHIDHAR MANCHUKONDA · Accepted Answer · 2014-09-21 14:09:15Z

6

((Login_Activity())mContext).LoginSuccess();

where mContext is your Login_Activity reference

you need pass activity reference

answered Sep 21, 2014 at 14:09

SHASHIDHAR MANCHUKONDA

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1 Comment

3dDi92 Over a year ago

Thank you so much :) I just need to pass the reference and I didn't saw that...new Login_Activity().LoginSuccess(mContext);

Андрей Иванов · Accepted Answer · 2022-11-11 12:57:29Z

0

for example, I'm calling a method from another class MenuF:

new MenuF(this, fabMain).onClick_myCard();

answered Nov 11, 2022 at 12:57

Андрей Иванов

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1 Comment

DigCamara Over a year ago

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