getting the activity for my app

Question

I've been having some issues reading an XML file in my 'res' folder and I think I've narrowed it down to an issue with my apps 'activity'.

I keep getting a NullPointerException on line # 2 below.

Here is my code to get the activity. Is there a better or a right way to do this?

1. Activity activity = this;

2. Resources res = activity.getResources();

3. XmlResourceParser xpp = res.getXml(R.xml.encounters);

Here is the class:

public class XmlParser extends Activity  {


public XmlParser()
    throws XmlPullParserException, IOException
{
    try {
        XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
        factory.setValidating(false);

        Activity activity = this;
        Resources res = activity.getResources();
        XmlResourceParser xpp = res.getXml(R.xml.encounters);

    } catch (Exception e) {
        String stackTrace = Log.getStackTraceString(e);
        Log.e("error", stackTrace);
    }
   }
}

And I'm getting the error on the "Resources res = activity.getResources();" line... Thanks!

I thought this just refers to the app? I'm thinking I'm wrong? — SkyeBoniwell, Jan 03 '12 at 17:53
@999cm999 Unfortunately `this` refers to the instance of the class that the code is currently executing in. You really need to post more code for us to figure out what's going on. — Chris Thompson, Jan 03 '12 at 17:56

score 3 · Accepted Answer · edited May 23 '17 at 12:03

Something tells me that there's a problem with this or activity and there's some code missing here. The code that you've put there shouldn't ever generate a NPE because this is never null and if 2 followed 1 immediately, activity shouldn't be null. It's possible that this isn't an instance of Activity but that would generate a compile error, not an NPE.

Edit Ah, I think I see your problem. You need to override onCreate() and this Activity will be instantiated by the Android framework. You then need to move all of the code from the constructor and put it in the onCreate() method. However, I think this is indicative of a fundamental understanding of how applications work in Android. Instead, what I would do is create a standard Android application in Eclipse. That will create a base activity for you. From there, remove the subclassing Activity from your XmlParser class and change the constructor to take a Context argument. From there, instantiate the XmlParser in your other Activity, the one that was created by Eclipse.

All of that said, I think you should spend some time reading over the application fundamentals in the developer docs to understand how you're supposed to access resources, etc.

Edit 2 For more information about Activities check out this link. Also, check out this SO post for how to do what you're trying to do.

wow, that flew way over my head. I've been reading through the documentation at 'http://developer.android.com'. Is there anything there that would help explain what you wrote above? -- thanks — SkyeBoniwell, Jan 03 '12 at 18:11

score 1 · Answer 2 · answered Jan 03 '12 at 17:58

1

If you run that code inside of a Activity class then you could simply do:

Resources res = this.getResources();

XmlResourceParser xpp = res.getXml(R.xml.encounters);

answered Jan 03 '12 at 17:58

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getting the activity for my app

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