Android : Using Dialog to an activity - Android

I have an activity that is working already!

And I have created a new class where I can call that activity through "Dialog". The problem is when I'm on the dialog, the functions I assign to the widgets doesn't work anymore. I am new to Android and Java so please bear with me. Btw, this is the code of the dialog activity.

public class FilterDialog extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_filter_dialog);

    Button btnFilterDialog = (Button) findViewById(R.id.btnFilterDialog);
    btnFilterDialog.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            final Dialog dialog = new Dialog(FilterDialog.this);
            dialog.setContentView(R.layout.activity_filter);
            dialog.setTitle("Set your tags");
            dialog.setCancelable(true);

            Button btnDone = (Button) dialog.findViewById(R.id.btnBack);
            btnDone.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    dialog.dismiss();
                }
            });
            dialog.show();
        }
    });
}

}

UPDATE: What I want to happen is when after I click the button "Next", a dialog will appear containing my first activity, which is working already as a regular activity. But when I put it inside the Dialog. All widgets seems to be disabled and not working.