.NET C＃DropDownList将参数传递给函数

Question

I don't really know how to word this...I have a drop down list that queries a database and displays a list of descriptions based on ids. I want the user to be able to select a description, push a button and call my getQueryResults() function with the id being passed and not the description. getQueryResults(DropDownList1.SelectedValue) doesn't work because of conflicting types. What else can I use?

    protected void Page_Load(object sender, EventArgs e)
    {
        DataConnector dc = new DataConnector();
        DropDownList1.DataSource = dc.getCodeTypes();
        DropDownList1.DataValueField = "id";
        DropDownList1.DataTextField = "description";
        DropDownList1.DataBind();
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        DataConnector dc = new DataConnector();
        GridView2.DataSource = dc.getQueryResults(DropDownList1.SelectedValue); //error: cannot convert from string to int
        GridView2.DataBind();

    }

    public List<CodeDesc> getQueryResults(int searchTerm)
    {
        try
        {
            string query = "select id, code, descr from code_desc where code_type_id = :searchTerm";
           //more stuff

My manager does not want me to change the query string. (previously I had used "select id, code, descr from code_desc where code_type_id = (select id from code_desc where descr = :searchTerm);" where searchTerm was the string description thus eliminating the need for the id)

Answer 1

Start by wrapping your DropDownList DataBinding inside an IsPostBack check.

if (!Page.IsPostBack)
{
    DropDownList1.DataSource = dc.getCodeTypes();
    DropDownList1.DataValueField = "id";
    DropDownList1.DataTextField = "description";
    DropDownList1.DataBind();
}

I you do not, every time you load the page the data is bound again and the DropDownList goes back to it's first value.

Then you can call the getQueryResults with the SelectedValue by converting the value to an int .

GridView2.DataSource = dc.getQueryResults(Convert.ToInt32(DropDownList1.SelectedValue));

Finally, google parameratized queries .

Answer 2

The SelectedValue property from the DropDownList class is a string

https://msdn.microsoft.com/fr-fr/library/system.web.ui.webcontrols.listcontrol.selectedvalue(v=vs.110).aspx

[BindableAttribute(true, BindingDirection.TwoWay)]
[BrowsableAttribute(false)]
[ThemeableAttribute(false)]
public virtual string SelectedValue { get; set; }

An that is why you get this convertion error, you need to parse the string into an int or even better just pass the string value.

Answer 3

您可以使用它来传递一个int值。

int parameter = Convert.ToInt32(DropDownList1.SelectedValue);

Answer 4

   public class ComboboxItem
    {
        public string Text { get; set; }
        public object Value { get; set; }

        public override string ToString()
        {
            return Text;
        }
    }

 protected void Page_Load(object sender, EventArgs e)
{
    DataConnector dc = new DataConnector();
    DropDownList1.DataSource = dc.getCodeTypes();
    ComboboxItem item = new ComboboxItem();
            item.Text = "id"
            item.Value = "description";

            DropDownList1.Items.Add(item);
}