Android : Dialog not Showing and OnCreate Deprecated

I want to show dialog file chooser but it is showing deprecated onCreateDialog in FileDialog Class and not called. As newbie, i want to know how to solve it.

Inside MainActivity OnCreate

ImageView imageFileView = (ImageView) findViewById(R.id.imageFileView);
        imageFileView.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                openFile();
            }
        });
private void openFile() {
        FileDialog fileDialog = new FileDialog();
        fileDialog.loadFileList();
        //fileDialog.onCreateDialog(10);

    }

FileDialog Class

public class FileDialog extends Activity {
    private String[] mFileList;
    private File mPath = new File(Environment.getExternalStorageDirectory() + "//test//");
    private String mChosenFile;
    private static final String FTYPE = ".txt";
    private static final int DIALOG_LOAD_FILE = 1000;

    public void loadFileList() {
        try {
            mPath.mkdirs();
        } catch (SecurityException e) {
            Log.e("123", "unable to write on the sd card " + e.toString());
        }
        if (mPath.exists()) {
            FilenameFilter filter = new FilenameFilter() {

                @Override
                public boolean accept(File dir, String filename) {
                    File sel = new File(dir, filename);
                    return filename.contains(FTYPE) || sel.isDirectory();
                }

            };
            //mFileList = new String[]{"a.txt","b.txt"};
            mFileList = mPath.list(filter);
        } else {
            //mFileList = new String[]{"a.txt","b.txt"};
            mFileList = new String[0];
        }

        Log.d("abc", "" + mFileList.length);
        //showDialog(DIALOG_LOAD_FILE);
    }

    @Override
    protected Dialog onCreateDialog(int id) {
        Dialog dialog = null;
        AlertDialog.Builder builder= new AlertDialog.Builder(this);
        Log.d("abc", "58695896");
        switch (id) {
            case DIALOG_LOAD_FILE:
                builder.setTitle("Choose your file");
                if (mFileList == null) {
                    Log.e("abc", "Showing file picker before loading the file list");
                    dialog = builder.create();
                    return dialog;
                }
                builder.setItems(mFileList, new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        mChosenFile = mFileList[which];
                        //you can do stuff with the file here too
                    }
                });
                break;
        }
        dialog = builder.show();
        return dialog;
    }
}