NullPointerException while starting an activity in android

Question

I am getting NullPointerException while starting a helloworld activity. I am starting this class from FileEvent.java class, which code I have put down here.

public class FileEvent extends Activity implements ObserverActivity{
public static String path2;
public String filename;
public String path; 
public adapter info ;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
           this.info  = new adapter(this); 

}

    public void insert(String path) {
        // TODO Auto-generated method stub
//      try{

    this.info = new adapter(this);
    this.filename = path; 

            System.out.println("Starting intent in fileevent");
            try{
        startActivity(new Intent(FileEvent.this,hello.class)); // In this line I am getting nullpointerexception was caught.
            }
            catch(Exception e)
            {
                Log.v("Caught in insert() of FileEvent : ",e.toString());
            }

    }

hello.class consists of a simple textview.

AndroidManifest.xml :-

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.sample_fileobserver"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.sample_fileobserver.hello"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.hello" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity> 
        <activity
            android:name="com.example.sample_fileobserver.FileEvent"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.FIleEvent" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity> 
    </application>

</manifest>

The logcat shows the following message -

09-28 05:51:55.307: I/System.out(13542): Starting intent in fileevent
09-28 05:51:55.307: A/FileObserver(13542): Unhandled exception in FileObserver com.example.sample_fileobserver.MyFileObserver@b11bec18
09-28 05:51:55.307: A/FileObserver(13542): java.lang.NullPointerException
09-28 05:51:55.307: A/FileObserver(13542):  at android.content.ContextWrapper.getPackageName(ContextWrapper.java:135)
09-28 05:51:55.307: A/FileObserver(13542):  at android.content.ComponentName.<init>(ComponentName.java:75)
09-28 05:51:55.307: A/FileObserver(13542):  at android.content.Intent.<init>(Intent.java:3662)
09-28 05:51:55.307: A/FileObserver(13542):  at com.example.sample_fileobserver.FileEvent.insert(FileEvent.java:42)
09-28 05:51:55.307: A/FileObserver(13542):  at com.example.sample_fileobserver.MyFileObserver.onEvent(MyFileObserver.java:70)
09-28 05:51:55.307: A/FileObserver(13542):  at android.os.FileObserver$ObserverThread.onEvent(FileObserver.java:125)
09-28 05:51:55.307: A/FileObserver(13542):  at android.os.FileObserver$ObserverThread.observe(Native Method)
09-28 05:51:55.307: A/FileObserver(13542):  at android.os.FileObserver$ObserverThread.run(FileObserver.java:88)

Note :-

1) I have not declared setContentView() in FileEvent class, since it does not going to use UI.

2) Here onCreate() is not running, as I am calling insert() from another class of my application.

It might seem that, this question might be duplicate of many other questions, but I did not find the right solution from those questions.

Thanks in advance.

Why are you using an Activity if you don't want to have/set a UI? — fasteque, Sep 28 '13 at 09:48
@fasteque, If I did not use it, I cannot write Intent code right? — nki, Sep 28 '13 at 09:54
i have tried it already @DanielBo. I have tried other ways also, like using action name in Intent,getapplicationcontext(),getbasecontext(), like that. But none gave me right outout. — nki, Sep 28 '13 at 10:01
is that your complete Activity code? Are you including the package name? I mean is the correct one? Then, you are developing using Java, you are not forced to use and Activity. Which is the goal of FileEvent? If you don't need to have a UI do not use an Activity, it's not a proper design decision. — fasteque, Sep 28 '13 at 10:02
yes @fasteque, I don't need to use a UI, but I have to start an intent. so definitely I need to extend an activity. with out extending an Activity, I cannot start an Intent. If I did, I will get `The method startActivity(Intent) is undefined for the type FileEvent` error. — nki, Sep 28 '13 at 10:09
Thanks for showing up an error in manifest @Simon, I have corrected in my code. But there is no change in the error. — nki, Sep 28 '13 at 10:27
@nki. You can start an Activity from a Service, a Fragment, a BroadcastReceiver or any other part of your code if have passed a valid context. — fasteque, Sep 28 '13 at 10:33
@fasteque, if you dont mind, can you please provide some source code regarding your suggestion, or if possible, can you please modify my question and provide it as answer? — nki, Sep 28 '13 at 11:07

score 1 · Answer 1 · edited Sep 29 '13 at 07:58

1

Change your manifest:

<activity
  android:name="com.example.sample_fileobserver.FileEvent"
  android:label="@string/app_name" > 
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

edited Sep 29 '13 at 07:58

J. Steen

15,470
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answered Sep 28 '13 at 09:52

gbl

178
2
12

actually I have another activity as `LAUNCHER`. from that activity, I am calling this `insert()` method. – nki Sep 28 '13 at 09:56

score 1 · Accepted Answer · answered Sep 28 '13 at 11:00

You are getting error because you are trying to call another activity with FileEvent class context. I think it is not possible.

If you are calling insert() method from another class, have to pass context of that class.

Try to pass Context of that class.

Your Method should be

public void insert(String path, Context context)
{
     info = new adapter(context);
     filename = path; 

     try
     {
         startActivity(new Intent(context,hello.class));
     }
     catch(Exception e)
     {
         Log.v("Caught in insert() of FileEvent : ",e.toString());
     } 
}

Hope it will help you.

Thanks for the answer @Andrain, but I previously tried printing some log messages in insert() method. They worked. So, I don't think that there might be problem in calling insert() from another class. My app is suspended at startActivity() in FileEvent method. — nki, Sep 28 '13 at 11:06

NullPointerException while starting an activity in android

2 Answers2