Android button onclick if dialog open close it else open it

In my app i open dialog using a button onclick, Dialog open nicely if i press again same button i want close dialog.

 final ImageButton topmenu = (ImageButton) findViewById(R.id.menu);
    topmenu.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            final Dialog dialog = new Dialog(Search.this);
            dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
            dialog.setContentView(R.layout.actionmenu);

            TextView text1 = (TextView) dialog.findViewById(R.id.textDialog1);
            text1.setText("Search");
            dialog.show();

        }
    });

I need button onclick, "If dialog open 'close' it else 'open' it."