从另一个表单调用主窗体上的方法 [英] calling method on main form from another form

问题描述

我创建了一个名为UserId的类

I have created a class called UserId

class UserId
    {
        public string username;
        public string userlevel;
        public string firstname;
        public string lastname;
        
    }

和我的应用程序的主要表格在加载事件我有这个代码（昨天解决了这里在codeproject :)）

and on Main form of my app on load event I have this code ( yesterday solved here in codeproject:) )

SqlCommand commanduser = new SqlCommand("SELECT * from Users  WHERE Username = @Username", cs);
            commanduser.Parameters.Add("@Username", SqlDbType.NVarChar);
            commanduser.Parameters["@Username"].Value = username.Text;

            SqlDataAdapter dataAdapteruser = new SqlDataAdapter(commanduser);

            DataTable dataTableuser = new DataTable();

            dataAdapteruser.Fill(dataTableuser);

            userid.username = (String)dataTableuser.Rows[0]["Username"];
            userid.userlevel = (String)dataTableuser.Rows[0]["UserLevel"];
            userid.firstname = (String)dataTableuser.Rows[0]["FirstName"];
            userid.lastname = (String)dataTableuser.Rows[0]["LastName"];

，这在我工作时效果很好我在以后的表单上使用这些字符串，但问题是当我在这个应用程序上打开另一个表单时我必须使用字符串中的那些值，但它们是空的



我想我必须以某种方式从Main表单调用这个方法，但不知道怎么做



或者我想到用这个来创建另一个类我将在任何表格上放置的方法



我接受的任何建议

谢谢

and this works great when I am using those strings later on on this form, but the problem is when I open another form on this app I have to use those values from strings but they are empty

I am thinking I have to somehow call this method from Main form but don't know how to do it

or it came to my mind to create another class with this method which I will place on any form

any advice I accept
thank you

推荐答案

这是关于表单协作的流行问题。最强大的解决方案是在表单类中实现适当的接口，并传递接口引用而不是引用Form的整个实例。有关更多详细信息，请参阅我以前的解决方案：如何以两种形式复制列表框之间的所有项目 [ ^ ]。



另请参阅此处的其他解决方案讨论。如果应用程序足够简单，解决方案就像在一个表单中声明一些 internal 属性并将对一个表单的实例的引用传递给另一个表单的实例一样简单形成。对于更复杂的项目，这种违反严格封装的样式和松散耦合可能会增加代码的意外复杂性并引发错误，因此封装良好的解决方案将是优惠。



另请参阅：

http://en.wikipedia.org/wiki/Accidental_complexity [ ^ ]，

http://en.wikipedia.org/wiki/Loose_coupling [ ^ ]。

-SA

This is the popular question about form collaboration. The most robust solution is implementation of an appropriate interface in form class and passing the interface reference instead of reference to a "whole instance" of a Form. Please see my past solution for more detail: How to copy all the items between listboxes in two forms[^].

Please also see other solutions in this discussion. If the application is simple enough, the solution could be as simple as declaring of some internal property in one form and passing a reference to the instance of one form to the instance of another form. For more complex projects, such violation of strictly encapsulated style and loose coupling could add up the the accidental complexity of the code and invite mistakes, so the well-encapsulated solution would be preferable.

Please see also:
http://en.wikipedia.org/wiki/Accidental_complexity[^],
http://en.wikipedia.org/wiki/Loose_coupling[^].

—SA

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