检查数据库设置 - >变量''在分配值之前使用

I'm writing a simple function that returns me true if my sqlDB connection is ok. I read my DB settings from an XML file and i'm sure this part works because my values (server, database, user, password) get a value assigned after my xml read. When i want to use these variables in my connectionstring is says i'm using them without any value?I'm writing a simple function that returns me t