组合框中的静态插入的项目在单击按钮时会翻倍不止一次

Question

我有一个已插入以下项目的组合框

public void SetOperationDropDown()
    {
    //ByDefault the selected text in the cmbOperations will be -SELECT OPERATIONS-.
    cmbOperations.SelectedItem = "-SELECT OPERATIONS-";

    //This is for adding four operations with value in operation dropdown
    cmbOperations.Items.Insert(0, "PrimaryKeyTables");
    cmbOperations.Items.Insert(1, "NonPrimaryKeyTables");
    cmbOperations.Items.Insert(2, "ForeignKeyTables");
    cmbOperations.Items.Insert(3, "NonForeignKeyTables");
    cmbOperations.Items.Insert(4, "UPPERCASEDTables");
    cmbOperations.Items.Insert(5, "lowercasedtables");
    }

但是，当用户单击按钮不止一次时，该值就会翻倍，或者该值发生任何不必要的变化。

点击按钮是

private void btnConnect_Click(object sender, EventArgs e)
    {
    //Function call for validating the textboxes entry
    ValidateForm();

    //Variable to store server address
    string localHost = "192.168.10.3";

    //Variable to store userId and password of the database
    string logInDetails = "gp";

    try
        {
        //Checking for the Valid entries in textboxes if all entries are correct then call functions accordingly
        if((txtPassword.Text == logInDetails) && (txtUsername.Text == logInDetails) && (txtHost.Text == localHost))
            {

            //If connected then give this message to user
            lblMessage.Visible = true;
            lblMessage.Text = "You are connected to the SQL Server....";

            if(lblMessage.Text != string.Empty)
                {
                //Function call for binding the dropdown with all DB names 
                BindDBDropDown();

                //Function call for binding the operation names in dropdown 
                SetOperationDropDown();

                }
            }
        else
            {
            //Else give the error message to user
            lblMessage.Text = "Invalid Credentials";
            }
        }
    catch(Exception ex)
        {
        //All the exceptions are handled and written in the EventLog.
        EventLog log = new EventLog("Application");
        log.Source = "MFDBAnalyser";
        log.WriteEntry(ex.Message);
        }
    }

谁能帮我吗？

Answer 1

public void SetOperationDropDown()
{
if(CmbOperations.Items.Count == 0)
{
//ByDefault the selected text in the cmbOperations will be -SELECT OPERATIONS-. 
cmbOperations.SelectedItem = "-SELECT OPERATIONS-"; 
//This is for adding four operations with value in operation dropdown 
cmbOperations.Items.Insert(0, "PrimaryKeyTables"); 
cmbOperations.Items.Insert(1, "NonPrimaryKeyTables"); 
cmbOperations.Items.Insert(2, "ForeignKeyTables"); 
cmbOperations.Items.Insert(3, "NonForeignKeyTables"); 
cmbOperations.Items.Insert(4, "UPPERCASEDTables"); 
cmbOperations.Items.Insert(5, "lowercasedtables"); 


}
else
{
int? cbSelectedValue = null;
if(!string.IsNullOrEmpty(cmbOperations.SelectedValue))
cbSelectedValue = convert.toInt32(cmbOperations.SelectedValue);
}
//load your combo again
if(cbSelectedValue != null)
cmbOperations.SelectedValue = cbSelectedValue.ToString();
}

由于我没有使用VS，所以可能会有一些小的语法错误。

Answer 2

仅当页面的加载不是postback时才调用SetOperationDropDown()

 if (!IsPostBack) {
    SetOperationDropDown();
 }

Answer 3

用户单击时禁用该按钮，将cmbOperations SelectItem重置为“不执行任何操作”值，并在完成请求处理后重新启用该按钮。

Answer 4

这是在WinForms下标记的，因此我认为回发不适用于此处。 在您的btnStartAnalysis_Click方法中，我看不到它调用SetOperationDropDown 。 尝试进入DEBUG模式并在SetOperationDropDown放置一个断点。 然后单击您的按钮，查看是否达到了断点。 如果是这样，则请参考您的堆栈跟踪以查看从何处SetOperationDropDown 。

如果WinForms标记不正确，而您实际上正在使用WebForms / ASP.NET，请执行Stefanvds和Marcel的建议。 但是我认为弄清楚SetOperationDropDown从哪里被错误地调用很重要。