将上下文传递到非活动类以使用AssetManager.getAssets（）

Question

I am working on an android app and I am trying to open an xml file in assets folder containing references to images located also in assets folder. I am using AssetManager in a non-activity Class and tried to pass context to its constructor with no success.There are no errors in Eclipse but when I run the app it crushes. The code I use for the 2 classes and the XML is below.

XML File:

<scene>

   <sprite>
     <img src="100789.jpg" positionx="100" positiony="200" name="100789.jpg"/>
   </sprite>

   <sprite>
     <img src="100788.jpg" positionx="2" positiony="20" name="100788" />
   </sprite>

</scene> 

Main Class (Activity)

import android.content.Context;
....

public class Test extends AndroidGame {

     Context context=getApplicationContext();

     @Override
     public Screen getStartScreen() {
         return new LoadingScreen(this, context); 
   }
}

Load Class (Screen)

import java.io.InputStream;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import android.content.Context;
import android.content.res.AssetManager;
....

public class LoadingScreen extends Screen {
    private Context context;
    public Document doc;

  public LoadingScreen(Game game, Context context) {
    super(game);
    this.context=context;
}

AssetManager gi = con.getAssets();

@Override
public void update(float deltaTime) {


try {

    InputStream inStream = gi.open("assets.xml");
    DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
    Document doc = builder.parse(inStream);
    doc.getDocumentElement().normalize();


}catch (Exception e) {
  e.printStackTrace();
  }


    Graphics g = game.getGraphics();
    Assets.background = g.newPixmap(doc.getDocumentElement().getElementsByTagName("sprite").item(0).getChildNodes().item(1).getAttributes().getNamedItem("name").getNodeValue(), PixmapFormat.RGB565);
    ....
    ....
    game.setScreen(new MainMenuScreen(game));




}

So am I doing something wrong ?

I have also tried to put the following code in the constructor with no success:

public LoadingScreen(Game game, Context context) {
    super(game);
    this.context=context;

AssetManager gi = con.getAssets();
try {
    InputStream inStream = gi.open("assets.xml");
    DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
    Document doc = builder.parse(inStream);
    doc.getDocumentElement().normalize();


}catch (Exception e) {
  e.printStackTrace();
  }
}

Answer 1

You are trying to access context (the Context member) before you initialise it, causing a NullPointerException . move AssetManager gi = con.getAssets(); inside the method

@Override
public void update(float deltaTime) {
  AssetManager gi = context.getAssets();
   ...

}

Answer 2

Since AndroidGame class inherits from an Activity you have to keep in mind the activity life cycle. An activity doesn't have a Context until just before onCreate() is called and calling getApplicationContext() before then will return null. So you need to set the context field inside of onCreate.

Basically

public class Test extends AndroidGame {

    private Context context;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        this.context = getApplicationContext();
    }

    ...

}