Android : Android get leaked window error when re-open application

in my application i'm create simple dialog class to use it every where in application. after re-open application and show this dialog i get error, but i'm wondering after waiting some second i dont get problem

Error:

E/WindowManager﹕ Activity ir.jaziire.app.porseman.ActivityHome has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{411d8b20 V.E..... R......D 0,0-640,236} that was originally added here
    android.view.WindowLeaked: Activity ir.jaziire.app.porseman.ActivityHome has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{411d8b20 V.E..... R......D 0,0-640,236} that was originally added here
            at android.view.ViewRootImpl.<init>(ViewRootImpl.java:424)
            at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:218)
            at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
            at android.app.Dialog.show(Dialog.java:281)
            at ir.jaziire.Classes.ProgressDialog.showDialog(ProgressDialog.java:33)

my simple dialog class:

public class ProgressDialog {

    private Context mContext;
    private Dialog  dialog;
    private String  dialogMessage   = "";
    private boolean setCancelable = false;
    private boolean setCanceledOnTouchOutside = false;

    public ProgressDialog() {
    }

    public ProgressDialog(Context context) {
        mContext = context;
        dialog = new Dialog(mContext, R.style.theme_sms_receive_dialog);
        dialog.setContentView(R.layout.progress_dialog);
        dialog.setCancelable(setCancelable);
        dialog.setCanceledOnTouchOutside(setCanceledOnTouchOutside);
    }

    public void showDialog(){
        TextView tv_progress_title = (TextView) dialog.findViewById(R.id.tv_progress_title);
        tv_progress_title.setText(dialogMessage);
        dialog.show();
    }

    public void dismissDialog(){
        dialog.dismiss();
    }

    public ProgressDialog setMessage(String message){
        dialogMessage = message;
        return this;
    }

    public ProgressDialog setCancelable(boolean state){
        setCancelable = state;
        return this;
    }

    public ProgressDialog setCanceledOnTouch(boolean state){
        setCanceledOnTouchOutside = state;
        return this;
    }
}

i'm using this class with way:

public class FragmentViewAllSubjects extends Fragment {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        ............

    G.currentActivity = FragmentViewAllSubjects.this.getActivity();
ProgressDialog mProgressDialog = new ProgressDialog(G.currentActivity)
                .setCancelable(false).setCanceledOnTouch(false);
mProgressDialog.setMessage(UC.getResourcesText(R.string.connection_to_server));
        mProgressDialog.showDialog();