Crash when open activity contains fragment
• So, I create 2 fragments by testing the "Inter-fragment communication" pattern:
• FragmentA contains ListView, FragmentB contains TextView.
In portrait mode: MainActivity contains a FragmentA (listview) if the user clicks on an element and then navigate to AnotherActivity which contains a FragmentB (textview) with some text.
• In lanescape mode: MainActivity contains both FragmentA and B ..
• My lanescape mode worked fine, in portrait mode, if I click on an element, it crashed.
FragmentA.java:
public class FragmentA extends Fragment implements OnItemClickListener {
ListView list;
Communicator comm;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
return inflater.inflate(R.layout.fragment_layout_a, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
list = (ListView) getActivity().findViewById(R.id.listView1);
ArrayAdapter adapter = ArrayAdapter.createFromResource(getActivity(),
R.array.titles, android.R.layout.simple_list_item_1);
list.setAdapter(adapter);
list.setOnItemClickListener(this);
Log.d("this", "Done setting listview");
}
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
// TODO Auto-generated method stub
comm.respone(arg2);
}
void setCommunicator(Communicator c) {
comm = c;
}
public interface Communicator {
public void respone(int index);
}
}
FragmentB.java:
public class FragmentB extends Fragment {
TextView display;
String[] data;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
return inflater.inflate(R.layout.fragment_layout_b, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
display = (TextView) getActivity().findViewById(R.id.textView1);
Resources res = getResources();
data = res.getStringArray(R.array.detail);
Log.d("this", "Fragment B created ");
super.onActivityCreated(savedInstanceState);
}
void changeText(int index) {
display.setText(data[index]);
Log.d("this", "changing text");
}
}
MainActivity.java:
public class MainActivity extends Activity implements FragmentA.Communicator {
FragmentA f1;
FragmentB f2;
FragmentManager manager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
manager = getFragmentManager();
f1 = (FragmentA) manager.findFragmentById(R.id.fragment1);
f1.setCommunicator(this);
Log.d("this", "setCommunicator");
}
@Override
public void respone(int index) {
// TODO Auto-generated method stub
f2 = (FragmentB) manager.findFragmentById(R.id.fragment2);
Log.d("this", "f2 referenced from Main");
if (f2 != null && f2.isVisible())// landscape
{
f2.changeText(index);
} else // portrait
{
Intent i = new Intent(this, AnotherActivity.class);
i.putExtra("index", index);
startActivity(i);
}
}
}
AnotherActivity.java:
public class AnotherActivity extends Activity {
FragmentB f2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_another);
Log.d("this", "Another Activity");
f2 = (FragmentB) getFragmentManager().findFragmentById(R.id.fragment2);
Log.d("this","fragment2 in Another Activity");
Intent i = getIntent();
int index = i.getIntExtra("index", 0);
Log.d("this", "Get intent extras");
if (f2 != null)
{
f2.changeText(index);
Log.d("this", "changing text in Another Activity");
}
}
}
activity_main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.fragmentdemo_2.MainActivity" >
<fragment
android:id="@+id/fragment1"
android:name="com.example.fragmentdemo_2.FragmentA"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
activity_another.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.fragmentdemo_2.AnotherActivity" >
<fragment
android:id="@+id/fragment2"
android:name="com.example.fragmentdemo_2.FragmentB"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true" />
</RelativeLayout>
fragment_layout_a.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ListView
android:id="@+id/listView1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentLeft="true"
android:background="#addbb3"
android:layout_alignParentTop="true" >
</ListView>
</RelativeLayout>
fragment_layout_b.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:id="@+id/textView1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:text="..."
android:background="#22c936"
android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>
manifesto
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.fragmentdemo_2"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".AnotherActivity"
android:label="@string/title_activity_another" >
<intent-filter>
<action android:name="android.intent.action.ANOTHERACTIVITY" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
• Logcat:
09-30 11:38:40.406: E/AndroidRuntime(14991): FATAL EXCEPTION: main
09-30 11:38:40.406: E/AndroidRuntime(14991): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fragmentdemo_2/com.example.fragmentdemo_2.AnotherActivity}: java.lang.NullPointerException
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2245)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2295)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.app.ActivityThread.access$700(ActivityThread.java:150)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.os.Handler.dispatchMessage(Handler.java:99)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.os.Looper.loop(Looper.java:137)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.app.ActivityThread.main(ActivityThread.java:5279)
09-30 11:38:40.406: E/AndroidRuntime(14991): at java.lang.reflect.Method.invokeNative(Native Method)
09-30 11:38:40.406: E/AndroidRuntime(14991): at java.lang.reflect.Method.invoke(Method.java:511)
09-30 11:38:40.406: E/AndroidRuntime(14991): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
09-30 11:38:40.406: E/AndroidRuntime(14991): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
09-30 11:38:40.406: E/AndroidRuntime(14991): at dalvik.system.NativeStart.main(Native Method)
09-30 11:38:40.406: E/AndroidRuntime(14991): Caused by: java.lang.NullPointerException
09-30 11:38:40.406: E/AndroidRuntime(14991): at com.example.fragmentdemo_2.FragmentB.changeText(FragmentB.java:38)
09-30 11:38:40.406: E/AndroidRuntime(14991): at com.example.fragmentdemo_2.AnotherActivity.onCreate(AnotherActivity.java:27)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.app.Activity.performCreate(Activity.java:5267)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)
09-30 11:38:40.406: E/AndroidRuntime(14991): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
09-30 11:38:40.406: E/AndroidRuntime(14991): ... 11 more
• Logcat with filter "this":
09-29 22:02:16.098: D/this(7795): setCommunicator
09-29 22:02:16.098: D/this(7795): Done setting listview
09-29 22:02:36.848: D/this(7795): f2 referenced from Main
09-29 22:02:36.948: D/this(7795): Another Activity
09-29 22:02:36.948: D/this(7795): fragment2 in Another Activity
09-29 22:02:36.948: D/this(7795): Get intent extras
Please help, thanks in advance! (I'm new to Java-Android)
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1 answer
The problem was that you weren't following the correct fragment and activity hierarchy. You can always access the views and methods of the fragments after loading the fragment.
In your case, you indirectly passed a value from MainActivity
to FragmentA
, and from FragmentA
you opened AnotherActivity
, which contains your FragmentB
. In your case, you were trying to pass a value through intent from one fragment to another using Intent
which is not valid. You can always pass values between fragments via Bundle
and receive it from Bundle
. Check out my changes below, it works now. and make the appropriate changes according to your needs.
Just make the following changes in all classes.
MainActivity.java
public class MainActivity extends Activity {
FragmentA f1;
FragmentB f2;
FragmentManager manager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
manager = getFragmentManager();
f1 = (FragmentA) manager.findFragmentById(R.id.fragment1);
Log.d("this", "setCommunicator");
}
/* @Override
public void respone(int index) {
// TODO Auto-generated method stub
f2 = (FragmentB) manager.findFragmentById(R.id.fragment2);
Log.d("this", "f2 referenced from Main");
if (f2 != null && f2.isVisible())// landscape
{
f2.changeText(index);
} else // portrait
{
Intent i = new Intent(this, AnotherActivity.class);
i.putExtra("index", index);
startActivity(i);
}
}*/
}
FragmentA.java
public class FragmentA extends Fragment implements OnItemClickListener {
ListView list;
Communicator comm;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
return inflater.inflate(R.layout.fragment_layout_a, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
list = (ListView) getActivity().findViewById(R.id.listView1);
ArrayAdapter adapter = ArrayAdapter.createFromResource(getActivity(),
R.array.titles, android.R.layout.simple_list_item_1);
list.setAdapter(adapter);
list.setOnItemClickListener(this);
Log.d("this", "Done setting listview");
}
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
// TODO Auto-generated method stub
Intent i = new Intent(FragmentA.this.getActivity(), AnotherActivity.class);
i.putExtra("index", arg2);
startActivity(i);
}
void setCommunicator(Communicator c) {
comm = c;
}
public interface Communicator {
public void respone(int index);
}
}
AnotherActivity.java
public class AnotherActivity extends Activity {
FragmentB f2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_another);
FragmentManager mang = getFragmentManager();
Log.d("this", "Another Activity");
Log.d("this", "fragment2 in Another Activity");
Intent i = getIntent();
int index = i.getIntExtra("index", 0);
Bundle bund = new Bundle();
bund.putInt("val", index);
f2 = (FragmentB) mang.findFragmentById(R.id.fragment2);
f2.changeText(index);
Log.d("this", "Get intent extras");
}
}
FragmentB.java
public class FragmentB extends Fragment {
TextView display;
String[] data;
int val;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
View m_view;
m_view = inflater.inflate(R.layout.fragment_layout_b, container, false);
display = (TextView) m_view.findViewById(R.id.textView1);
Resources res = getActivity().getResources();
data = res.getStringArray(R.array.titles);
Log.d("this", "Fragment B created ");
return m_view;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
}
public void changeText(int index) {
val=getActivity().getIntent().getIntExtra("index",0);
display.setText(data[val]);
Log.d("this", "changing text");
}
}
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