Communicating with fragment NullPointerException

Question

I'm very new to Android UI, I've been looking for a place I can learn the basic structure of UI and how communication and layouts should work. But regardless. My problem comes from me trying to change the value of a TextView within a fragment. I keep getting a nullPointerException when i try to change the value. I am using a fragment manager to refer to the fragment.

Here's the fragment code:

package com.archronix.infotainment;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;


public class Fragment1 extends android.support.v4.app.Fragment {
public TextView status;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.fragment_fragment1, container, 
    false);
    return v;
}

public static Fragment1 newInstance() {
    Fragment1 f = new Fragment1();
    return f;
}

public void postText(String str){
    status.setText(status.getText()+"\n"+str);
}
}

And this is how i declare my fragment manager:

fragment1 = (Fragment1) 
getSupportFragmentManager().findFragmentById(R.id.fragment1);

And, how I use it:

fragment1.postText("testtext");

My logcat:

05-15 10:56:42.406 4109-4109/com.archronix.infotainment E/AndroidRuntime: FATAL EXCEPTION: main Process: com.archronix.infotainment, PID: 4109 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.archronix.infotainment/com.archronix.infotainment.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.archronix.infotainment.Fragment1.postText(java.lang.String)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) 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:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.archronix.infotainment.Fragment1.postText(java.lang.String)' on a null object reference at com.archronix.infotainment.MainActivity.onCreate(MainActivity.java:102) at android.app.Activity.performCreate(Activity.java:5933) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) 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:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Apologies for my newbieness. I've read 20 stack overflow posts regarding similar topics but all seem to be either outdated or not consistent. What is the best way to accomplish my task? Thank you.

I have read the post. And i understand how NullPointerExceptions work, my problem is i cant seem to identify where and with what variable the problem occurs in my code. — Arin Yaldizciyan, May 15 '17 at 15:20
As you can see, the debugger tells me that it is on the call to the method from. I do not know why that calls a NullPointerException. I wish I understood android methods well enough to be able to trace my problem but sadly I do not. I'm sorry if there is a solution available, I'm not sure what else to search for. — Arin Yaldizciyan, May 15 '17 at 15:27
That's not the debugger. have a look here https://developer.android.com/studio/debug/index.html — Daniele, May 15 '17 at 15:29

score 1 · Answer 1 · answered May 15 '17 at 15:24

1

status variable is not assigned to any textview. Add the following code in onCreateView before return statement

status=v.findViewById(R.id.<nameoftextview>);

answered May 15 '17 at 15:24

kunwar97

655
6
13

score 0 · Accepted Answer · edited May 23 '17 at 12:18

0

In onCreateView you should initialize your TextView like so:

status = (TextView) v.findViewById(R.id.tv_status);

If you know the text that you want to set before the FragmentTransaction you can use a Bundle (How to transfer some data to another Fragment?)

edited May 23 '17 at 12:18

Community

1
1

answered May 15 '17 at 15:22

Rene Ferrari

3,446
3
19
26

Thank you very much! Although can I use bundles multiple times on runtime during the application and not just in onCreate? – Arin Yaldizciyan May 15 '17 at 15:26
Well the Bundle is also used when the screen orientation changes and you want to save some values (since the activity is destroyed and recreated). – Rene Ferrari May 15 '17 at 15:37
Generally a Bundle is used for transferring Data from Activity A to Activity B or between Fragments. – Rene Ferrari May 15 '17 at 15:41
I appreciate all your help! – Arin Yaldizciyan May 15 '17 at 15:45

Communicating with fragment NullPointerException

2 Answers2