Question

I’m having some difficulty debugging a null pointer exception.

E/AndroidRuntime( 1760): java.lang.RuntimeException: Unable to instantiate application edu.lafayette.cs.geology.GeoDatabase: java.lang.NullPointerException

...

E/AndroidRuntime( 1760): Caused by: java.lang.NullPointerException
E/AndroidRuntime( 1760):    at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:101)
E/AndroidRuntime( 1760):    at android.content.Loader.<init>(Loader.java:85)
E/AndroidRuntime( 1760):    at android.content.AsyncTaskLoader.<init>(AsyncTaskLoader.java:90)
E/AndroidRuntime( 1760):    at android.content.CursorLoader.<init>(CursorLoader.java:113)
E/AndroidRuntime( 1760):    at edu.lafayette.cs.geology.GeoDatabase.createLoader(GeoDatabase.java:123)

Here is the relevant method createLoader in my code.

private CursorLoader createLoader(int id) {
    Uri tableUri;
    String[] projection;

    // Set the URI to query depending on the id of this loader.
    switch (id) {
    case LOCAL_FOLDER_LOADER:
        tableUri = LocalProvider.CONTENT_URI_FOLDER;
        projection = Folder.COLUMNS;
        break;
    case LOCAL_BEDDING_LOADER:
        tableUri = LocalProvider.CONTENT_URI_BEDDING;
        projection = Bedding.COLUMNS;
        break;
    case LOCAL_CONTACT_LOADER:
        tableUri = LocalProvider.CONTENT_URI_CONTACT;
        projection = Contact.COLUMNS;
        break;
    case LOCAL_FAULT_LOADER:
        tableUri = LocalProvider.CONTENT_URI_FAULT;
        projection = Fault.COLUMNS;
        break;
    case LOCAL_JOINT_SET_LOADER:
        tableUri = LocalProvider.CONTENT_URI_JOINT_SET;
        projection = JointSet.COLUMNS;
        break;
    default:
        throw new IllegalArgumentException("Unknown cursor loader id");
    }

    // Load up that cursor loader. Next, onLoadComplete is called.
    Log.d("createLoader", ""+tableUri);
    Log.d("createLoader", ""+projection);
    Log.d("createLoader", ""+this);
    CursorLoader cursorLoader = new CursorLoader(this, tableUri,
            projection, null, null, null);
    Log.d("createLoader", "statement reached");
    cursorLoader.registerListener(id, this);
    return cursorLoader;
}

Line 125 is the one calling the CursorLoader constructor, in between the log statements. The log shows that tableUri, projection, and of course this are not null. The “statement reached” call is never reached. The rest of the nulls in the constructor call are supposed to be there, and they are specified in the API. I can change the constructor call to use string literals and arrays instead of those three nulls, and the same exception is thrown. Anyone know what’s up?

I’d love to check out the CursorLoader source for clues, but Google has not released the source for the classes in API level 12 of this “open source” project.

Answer 1

The problem had nothing to do with CursorLoader, it was that I passed the CursorLoader a reference to this before the constructor finished. The method createLoader was called by a method which was called by a method which was called by the constructor.

This code is inside a subclass of Application, which as far as I’m aware is bad practice because all I’m using that for is sharing data between activities, where that should be done with Intents and Bundles. So I actually just changed the method header for the constructor to override the onCreate method instead, which was more appropriate, and fixed my issue.