c#如何存储在全局变量中

Question

How do I store the voterid into a global variable so I can use it on another form? I will use this voterid in order to check if the voter has already voted.

MessageBox.Show("Welcome!");
OleDbCommand comd1 = new OleDbCommand();
comd1.Connection = connection;
comd1.CommandText = "SELECT VoterID FROM tbl_voter where Uname='" +
                    txt_user.Text + "' and Pword='" + txt_pass.Text + "'";
voterid = Convert.ToString(comd1.ExecuteScalar());
MessageBox.Show(voterid);

connection.Close();
connection.Dispose();

this.Hide();
vote form3 = new vote();
form3.ShowDialog();

Answer 1

If we are talking about a Windows Forms application, and by "global" you mean "common across the process," then you can use astatic variable .

In this example i create a special class just to hold static variables, and declare one field and one property that will be available to your program and will hold one and only one value across the entire process.

static class GlobalVariables
{
    static public string SomeVariable { get; set ; }  //As a property
    static public string SomeOtherVariable;           //As a field
}

Note that if your program is multi-threaded, it may be a good idea to put a critical section around static variables, like this:

static class GlobalVariables
{
    static private string LockObject = new Object();
    static private string _someVariable;

    static public string SomeVariable 
    { 
        get
        {
            lock(LockObject) { return _someVariable; }
        }
        set
        {
            lock(LockObject) { _someVariable = value; }
        }
    }
}

Answer 2

Application state belongs in the application state object. WinForms apps don't have one of these but you could create an AppState class and put an instance in a static property on the Program class. You can then define whatever global state you like as strongly type properties of AppState and reference them from anywhere in your program as Program.AppState.MyGlobalStronglyTypedValue

You can then put the (de)serialisation logic in the AppState class if you need to persist app state.