simerpeet jassal simerpeet jassal - 1 year ago 95
Android Question

activity unable to start Fragment and unable to show layout related to this. ending with null pointer

I am very new to android. i am following book but following code unable to start

CrimeFragment()
fragment. nothing appear on screen.
Activity
code is following. file name is CrimeActivity

package com.example.simerpreetjassal.criminalintent;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;

public class CrimeActivity extends FragmentActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_crime);
FragmentManager fm = getSupportFragmentManager();
Fragment fragment = fm.findFragmentById(R.id.framgment_container);
if(fragment==null) {
fragment = new CrimeFragment();
(fm.beginTransaction().add(R.id.framgment_container, fragment)).commit();
}

}
}


layout for upper activity. file name is content_crime

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/framgment_container"
android:layout_height="match_parent"
android:layout_width="match_parent"
/>


Fragment code is following. it is unable to show layout related to this and getting null pointer exception on edit text(mTittleField).Can't find valid reason.how can i initialized mTittleField to get rid from null pointer? file name is CrimeFragment

package com.example.simerpreetjassal.criminalintent;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;

public class CrimeFragment extends Fragment {
private Crime mCrime;
private EditText mTittleField;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mCrime = new Crime();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_crime, container, false);
mTittleField = (EditText) v.findViewById((R.id.crime_title));
mTittleField.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {

}

@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {

}

@Override
public void afterTextChanged(Editable s) {

}
});
return v;

}
}


Layout related to this:file name is crime_fragment

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="@string/crime_title_hint"
android:id="@+id/crime_title"
/>
</LinearLayout>


Logcat

07-28 11:27:09.056 3083-3083/com.example.simerpreetjassal.criminalintent W/System: ClassLoader referenced unknown path: /data/app/com.example.simerpreetjassal.criminalintent-1/lib/x86
07-28 11:27:09.187 3083-3083/com.example.simerpreetjassal.criminalintent W/System: ClassLoader referenced unknown path: /data/app/com.example.simerpreetjassal.criminalintent-1/lib/x86
07-28 11:27:09.309 3083-3083/com.example.simerpreetjassal.criminalintent D/AndroidRuntime: Shutting down VM
07-28 11:27:09.310 3083-3083/com.example.simerpreetjassal.criminalintent E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.simerpreetjassal.criminalintent, PID: 3083
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.simerpreetjassal.criminalintent/com.example.simerpreetjassal.criminalintent.CrimeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.addTextChangedListener(android.text.TextWatcher)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.addTextChangedListener(android.text.TextWatcher)' on a null object reference
at com.example.simerpreetjassal.criminalintent.CrimeFragment.onCreateView(CrimeFragment.java:26)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:330)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:547)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1237)
at android.app.Activity.performStart(Activity.java:6253)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
07-28 11:27:10.147 3083-3089/com.example.simerpreetjassal.criminalintent W/art: Suspending all threads took: 7.535ms

Answer Source

The name of the xml layout file is not the same you are referring to in the onCreateView() of your fragment.

Your fragment layout xml file is crime_fragment.xml and the layout you are referring to from your Java code is fragment_crime.xml (through the R class).