Android: Call Method from another Class which starts a new Intent
((Login_Activity())mContext).LoginSuccess();
where mContext is your Login_Activity reference
you need pass activity reference
3dDi92
Updated on June 05, 2022Comments
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3dDi92 almost 2 years
as the title already said, I’m trying to call a method
LoginSuccess()
from the ClassJSON_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
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3dDi92 over 9 yearsThank you so much :) I just need to pass the reference and I didn't saw that...
new Login_Activity().LoginSuccess(mContext);