弹出消息框

 $name1 = $ent1 -> get();
 $name2 = $ent2 -> get();
 $name3 = $ent3 -> get();

if  ($name1 == ""){
  $answer => $mw->messageBox(-title => 'Please Reply', -message => '请输入主机名?', -type => 'YesNo', -icon => 'question', -default => 'yes');
  undef $name1;

}

弹出框 如果输入的为空,就弹出消息框提示