Attempt to invoke virtual method 'void android.widget.GridView.setAdapter(android.widget.ListAdapter)' on a null object reference - Android Activity - android-adapter

Question

I have been trying to develop an app, whereby clicking on the Image button, it draws the whole screen using bitmap and saves it in a directory, and will show the complete list of all images in that directory by passing the intent....The above two steps will be done with a single click, where I am able to save the bitmap in the specified directory, but not able to retrieve the images in a custom grid view gallery...posting the code which I wrote
public class Share extends SecureActivity {
private int count;
Context context;
private Bitmap[] thumbnails;
private boolean[] thumbnailsselection;
private String[] arrPath;
private ImageAdapter imageAdapter = null;
ArrayList<String> f = new ArrayList<String>();// list of file paths
File[] listFile;
GridView imageGrid;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
getFromSdcard();
imageGrid = (GridView) findViewById(R.id.imageGrid);
imageAdapter = new ImageAdapter();
imageGrid.setAdapter(imageAdapter);
}
public void getFromSdcard()
{
File file= new File(android.os.Environment.getExternalStorageDirectory(),"ScreenShots");
if (file.isDirectory())
{
listFile = file.listFiles();
for (int i = 0; i < listFile.length; i++)
{
f.add(listFile[i].getAbsolutePath());
}
}
String size = String.valueOf(f.size());
String name = f.get(f.size()-1);
/*// ImageView imagegrid = (ImageView) findViewById(R.id.PhoneImageGrid);
try{
Bitmap bm = BitmapFactory.decodeFile(name);
bm.prepareToDraw();
imagegrid.setImageBitmap(bm);
}
catch(Exception e)
{
e.printStackTrace();
}
Log.d(size,"number of files");
Log.d(name,"image file");
*/
}
public class ImageAdapter extends BaseAdapter {
private LayoutInflater mInflater;
public ImageAdapter() {
mInflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
public int getCount() {
return f.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
holder = new ViewHolder();
convertView = mInflater.inflate(
R.layout.gallery_item, null);
holder.imageview = (ImageView) convertView.findViewById(R.id.thumbImage);
convertView.setTag(holder);
}
else {
holder = (ViewHolder) convertView.getTag();
}
Bitmap myBitmap = BitmapFactory.decodeFile(f.get(position));
holder.imageview.setImageBitmap(myBitmap);
return convertView;
}
}
class ViewHolder {
ImageView imageview;
}
with this, I am getting below error
FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.edutor.ignitor/com.edutor.ignitor.EdutorShare}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.GridView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2491)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2556)
at android.app.ActivityThread.access$800(ActivityThread.java:170)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1441)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5568)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:955)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:750)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.GridView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.edutor.ignitor.EdutorShare.onCreate(EdutorShare.java:43)
at android.app.Activity.performCreate(Activity.java:6041)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1111)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2437)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2556)
at android.app.ActivityThread.access$800(ActivityThread.java:170)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1441)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5568)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:955)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:750)
can someone please help...where I went wrong