Question

I am new to Android, know a little JAVA, but i want to learn and i keep doing tutorials. The idea of what i want to do is the following:
I have a rendered menu, for example:
1. BIRDS
2. ROCKS
3. PLANTS
and when I press BIRDS I want to show pictures and a small description. The id’s of the images and the description I keep in a xml. Like this:

<signs>
    <sign id="1_1" category="1">
        <name>desc1</name>
    </sign>
    <sign id="1_2" category="1">
        <name>desc2</name>
    </sign>
    <sign id="1_3_1" category="1">
        <name>desc3</name>
    </sign>
    <sign id="1_3_2" category="1">
        <name>desc4</name>
    </sign>
</signs>

the picture goes like sign_1_1.png, sign_1_2.png in drawables.

I made the gallery, it is showing, the description and images also are visible. I made that on image gallery Selected image to show the corresponding description in a TextView.
But when I tap i get a FATAL EXCEPTION:

E/AndroidRuntime(22141): FATAL EXCEPTION: main
E/AndroidRuntime(22141): java.lang.NullPointerException
E/AndroidRuntime(22141): at apcmag.examples.singleSignListItem$ImageAdapter.getView(singleSignListItem.java:117)
E/AndroidRuntime(22141):    at android.widget.Gallery.makeAndAddView(Gallery.java:849)
E/AndroidRuntime(22141): at android.widget.Gallery.fillToGalleryRightLtr(Gallery.java:803)
E/AndroidRuntime(22141):    at android.widget.Gallery.fillToGalleryRight(Gallery.java:747)
E/AndroidRuntime(22141):    at android.widget.Gallery.layout(Gallery.java:656)
E/AndroidRuntime(22141):    at android.widget.Gallery.onLayout(Gallery.java:351)
E/AndroidRuntime(22141):    at android.view.View.layout(View.java:13754)
E/AndroidRuntime(22141):    at android.view.ViewGroup.layout(ViewGroup.java:4362)

The code is:

package apcmag.examples;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;

import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;


public class singleSignListItem extends Activity
{

    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);

        this.setContentView(R.layout.single_sign_gallery);

        Gallery g = (Gallery) findViewById(R.id.gallery);

        final Intent i = getIntent();
        final String REGEX = "/%%/";

        String product = i.getStringExtra("product");

        setTitle(product);

        g.setAdapter(new ImageAdapter(this));

        g.setOnItemSelectedListener(new OnItemSelectedListener() {
          public void onItemSelected(AdapterView<?> parent, View view, int position, long id)
            {
                String [] products = i.getStringExtra("product_text").split(REGEX);
                Toast.makeText(singleSignListItem.this, ""+position, Toast.LENGTH_SHORT).show();
                TextView show_intro = (TextView) findViewById(R.id.show_intro);
                show_intro.setText(""+products[position]);
            }

            public void onNothingSelected(AdapterView<?> parent)
            {
                // TODO Auto-generated method stub

            }
        });
    }

    public class ImageAdapter extends BaseAdapter {
        int mGalleryItemBackground;
        private Context mContext;


//        private Integer[] mImageIds = {
//                R.drawable.sign_1_1,
//                R.drawable.sign_1_1,
//                R.drawable.sign_1_1,
//                R.drawable.sign_1_1
//        };

        private Integer[] mImages = takePhotos();

        public Integer[] takePhotos (){
            Intent g = getIntent();
            String Reg = "/%%/";
            String Reg2 = "_%_";

            String dataList = g.getStringExtra("product_text");
            String [] datastring = dataList.split(Reg);

            Integer[] imageResource = new Integer[20];

            String[] dd = null;

            for(int k = 0; k<datastring.length;k++){
                dd = datastring[k].split(Reg2);

            String imagename = "sign_"+dd[0];

            imageResource[k] = getResources().getIdentifier(imagename, "drawable", getPackageName());

            }

            return imageResource;

        }

        public ImageAdapter(Context c) {
            mContext = c;
            TypedArray a = obtainStyledAttributes(R.styleable.HelloGallery);
            mGalleryItemBackground = a.getResourceId(
                    R.styleable.HelloGallery_android_galleryItemBackground, 0);
            a.recycle();
        }

        public int getCount() {
            return mImages.length;
        }

        public Object getItem(int position) {
            return position;
        }

        public long getItemId(int position) {
            return position;
        }

        public View getView(int position, View convertView, ViewGroup parent) {
            ImageView i = new ImageView(mContext);

            i.setImageResource(mImages[position]);
            i.setLayoutParams(new Gallery.LayoutParams(115, 200));
            i.setScaleType(ImageView.ScaleType.FIT_XY);
            i.setBackgroundResource(mGalleryItemBackground);

            return i;
        }
    }

}

I can’t get what the problem is for hours, and i have some ideas that it might be here:

 i.setLayoutParams(new Gallery.LayoutParams(115, 200));

but i am not so sure what to do

UPDATE

Actually i found the problem:

On Line 77 I was Initializing ImageResource with size 20

Integer[] imageResource = new Integer[20];

but the splited datastring had just 4 elements

String [] datastring = dataList.split(Reg);

so mImages variable

 private Integer[] mImages = takePhotos();

would have 20 elements from which 16 would be null
and in the end

i.setImageResource(mImages[position]);

it could not render the null elements and it crashed.

So there i have another question:

If i don’t know the size of the posible Integer[] how do I initiliaze and push in it elements ? With List ?

Answer 1

Actually i found the problem:

On Line 77 I was Initializing ImageResource with size 20

Integer[] imageResource = new Integer[20];

but the splited datastring had just 4 elements

String [] datastring = dataList.split(Reg);

so mImages variable

 private Integer[] mImages = takePhotos();

would have 20 elements from which 16 would be null and in the end

i.setImageResource(mImages[position]);

it could not render the null elements and it crashed.