对话类：

public class SomeDialog extends DialogFragment{

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    LayoutInflater inflater = getActivity().getLayoutInflater();

    builder.setView(inflater.inflate(R.layout.somelayout,null));

    return super.onCreateDialog(savedInstanceState);
}
}

在活动中,创建对象并调用show方法：

SomeDialog obj = new SomeDialog();
obj.show(getFragmentManager(),"randomtag");