null pointer exception when starting new activity

Question

Okay, I'm getting a null pointer exception when I start my third activity. Here is the LogCat message:

12-28 04:38:00.350: ERROR/AndroidRuntime(776): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.acithium.main/com.acithium.rss.ShowDescription}: java.lang.NullPointerException
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2417)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.access$2100(ActivityThread.java:116)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.os.Looper.loop(Looper.java:123)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.main(ActivityThread.java:4203)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at java.lang.reflect.Method.invokeNative(Native Method)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at java.lang.reflect.Method.invoke(Method.java:521)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at dalvik.system.NativeStart.main(Native Method)
12-28 04:38:00.350: ERROR/AndroidRuntime(776): Caused by: java.lang.NullPointerException
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at com.acithium.rss.ShowDescription.onCreate(ShowDescription.java:48)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     ... 11 more

Here is the section of code where I call the activity:

public void onItemClick(AdapterView parent, View v, int position, long id)
 {
     Log.i(tag,"item clicked! [" + feed.getItem(position).getTitle() + "]");

     Intent itemintent = new Intent(this,com.acithium.rss.ShowDescription.class);
     //Intent itemintent = new Intent();
     //itemintent.setClassName("com.acithium.main", "com.acithium.rss.ShowDescription");
     Bundle b = new Bundle();
     b.putString("title", feed.getItem(position).getTitle());
     b.putString("description", feed.getItem(position).getDescription());
     b.putString("link", feed.getItem(position).getLink());
     itemintent.putExtra("android.intent.extra.INTENT", b);

     startActivityForResult(itemintent,0);
 }

And here is new activity class that is called:

public class ShowDescription extends Activity 
{

    public void onCreate(Bundle icicle) 
    {
        super.onCreate(icicle);
        setContentView(R.layout.showdescription);

        String theStory = null;


        Intent startingIntent = getIntent();


        if (startingIntent != null)
        {
            Bundle b = startingIntent.getBundleExtra("android.intent.extra.INTENT");
            if (b == null)
            {
                theStory = "bad bundle?";
            }
            else
            {
                theStory =  b.getString("title") + "\n\n" + b.getString("description") + "\n\nMore information:\n" + b.getString("link");
            }
        }
        else
        {
            theStory = "Information Not Found.";

        }
        TextView db= (TextView) findViewById(R.id.storybox);
        db.setText(theStory);

        Button backbutton = (Button) findViewById(R.id.back);

        backbutton.setOnClickListener(new Button.OnClickListener() 
        {
            public void onClick(View v) 
            {
                finish();
            }
        });        
    }
}

here is the showdescription.xml file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <ScrollView android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
            <LinearLayout 
                android:orientation="vertical"
                android:layout_width="fill_parent" 
                android:layout_height="fill_parent">
        <TextView  
             android:layout_width="fill_parent" 
                 android:layout_height="wrap_content" 
                 android:autoLink="all"
                 android:text="story goes here ...."
             android:id="@+id/storybox" />
        <Button
                android:layout_height="wrap_content" 
                android:text="Back"
            android:id="@+id/back" 
            android:layout_width="100px" 
            android:layout_marginLeft="100px"/>   
        </LinearLayout>
    </ScrollView>
</LinearLayout>

Solution 1

This is your clue, from the stack trace:

12-28 03:47:21.670: ERROR/AndroidRuntime(862): Caused by: java.lang.NullPointerException
12-28 03:47:21.670: ERROR/AndroidRuntime(862): at com.acithium.rss.ShowDescription.onCreate(ShowDescription.java:47)

What's line 47 in ShowDescription.java?

Solution 2

If I understood the code right, you should invoke the findViewById() of the showdescription view that you set for the activity and not of the activity, because both, button and textview, seem to be part of that view:

super.onCreate(icicle);
View showdescription = this.findViewById(R.id.showdescription);
setContentView(showdescription);

// ..

TextView db = (TextView)showdescription.findViewById(R.id.storybox);
db.setText(theStory);

Button backbutton = (Button)showdescription.findViewById(R.id.back);
backbutton.setOnClickListener(new Button.OnClickListener() 
{
    public void onClick(View v) 
    {
        finish();
    }
});

Comments

[acithium]

Well, I found a workaround. Initially I had these classes in a separate package, but I moved all of them to the same package and deleted the unused R file associated with that package. Once I did that everything started working. I wouldn't call that "solved" as much as I would call that a workaround.

[Vinay Pai]

Ah! That explains it! If it's in a different package, the "R" you refer to ends up being not the R you need! Hmm on second thoughts that may not be exactly right... that would have failed to compile.

[acithium]

Yeah, I don't get it either. When they were in 2 second packages, I added the import statement for the R file, but I was still getting the null pointer. I guess I'll just leave it this way for now. Thanks

[acithium]

//line 47 is the blank line between these 2 lines. db.setText(theStory); //blank line Button backbutton = (Button) findViewById(R.id.back);

[Vinay Pai]

acithium: That doesn't make any sense. You must have edited the source after you got that error. Try rebuilding and running it again so we can accurately tell what line it was on.

[acithium]

okay, now it says db.setText(theStory); is the line that is causing the problems.

[acithium]

i posted the new logcat, which shows it to be on line 48 now. That line of code is: db.setText(theStory);

[Vinay Pai]

I agree with atk. From looking at the code it doesn't seem like there is any path that can lead to theStory being null at that point, so it must be db. Can you double-check that the TextView has the correct ID (or post your layout/showdescription.xml file)

[acithium]

posted, hopefully this will shed some light of the issue.