あなたの回答に基づいて質問を更新した後、これが私の .Class です。
public class ShareScreen extends Activity{
         private ShareScreenAdapter adapter;
         private ViewPager viewPager;
         private String[] mThumbIds = Constants.IMAGES;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
             super.onCreate(savedInstanceState);
             setContentView(R.layout.share_screen);
             viewPager = (ViewPager) findViewById(R.id.pager);
             ImageButton sharingButton = new ImageButton(this);   
             sharingButton.setLayoutParams(new ViewGroup.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
             sharingButton.setImageResource(R.drawable.share);
             Intent i = getIntent();
             int position = i.getIntExtra("position", 0);
             adapter = new ShareScreenAdapter(ShareScreen.this, mThumbIds);
             viewPager.setAdapter(adapter);
             // displaying selected image first
             viewPager.setCurrentItem(position);   
     }
        @Override
        public boolean onCreateOptionsMenu(Menu menu) { 
            MenuInflater inflater = getMenuInflater();
            inflater.inflate(R.menu.main_share, menu);
            return true;
        }
        @Override
        public boolean onOptionsItemSelected(MenuItem item) {
             switch (item.getItemId()) {
                case R.id.menu_item_share:
                    shareIt();
                    break;
                default:
                    break;
            }
             return true;
        }
        private void shareIt()
        {
            //sharing implementation here
            String shareBody = "Here is the share content body";
            Intent sharingIntent = new Intent(android.content.Intent.ACTION_SEND);
            sharingIntent.setType("text/plain");
            sharingIntent.putExtra(android.content.Intent.EXTRA_SUBJECT, "Subject Here");
            sharingIntent.putExtra(android.content.Intent.EXTRA_TEXT, shareBody);
            startActivity(Intent.createChooser(sharingIntent, "Share via"));
        }
}
menu/main_share.xml には共有ボタンがあります:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android" >
     <item
            android:id="@+id/menu_item_share"
            android:title="Share"
            android:showAsAction="always"
            android:actionProviderClass=
                "android.widget.ShareActionProvider" />
</menu>
まだ動作していません !問題は、アクションバーの shareButton が機能しないことです。クリックしても何も起こりません!