In ASP. NET, DropDownList and ListBox implement two-level linkage functions,

In ASP. NET, DropDownList and ListBox implement two-level linkage functions,

DropDownList and ListBox implement two-level linkage functions. They can bind the information searched from the background database. The function to be implemented here is to select "save" in DropDownList ", then let ListBox automatically display the "city" in its province. This is the so-called two-level linkage function, which we can see on many registered webpages, today, we will solve ASP for everyone. NET secret.
1. Set the foreground interface and add the DropDownList and ListBox controls to the Web form.

The following figure shows the interface.

2. compile background code
The background code is written in the Page_Load event of the form.

<Span style = "font-family: KaiTi_GB2312; font-size: 18px;"> protected void Page_Load (object sender, EventArgs e) {if (! Page. isPostBack) // determine whether the page is loaded for the first time {SqlConnection con = DB. createConnection (); // This method has been introduced in the previous article, calling a method that has been compiled to create a database connection. SqlCommand cmd = new SqlCommand ("select * from province", con); SqlDataReader sdr = cmd. executeReader (); this. dropDownList1.DataTextField = "proName"; this. dropDownList1.DataValueField = "proID"; // primary key field this. dropDownList1.DataSource = sdr; this. dropDownList1.DataBind (); sdr. close () ;}</span>

Compile the DropDownList1_SelectedIndexChanged Event code, and click "Province". ListBox automatically adds the "city" of the "Province"

<span style="font-family:KaiTi_GB2312;font-size:18px;"> protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)  {   this.ListBox1.Items.Clear();   SqlConnection con2 = DB.createConnection();   SqlCommand cmd1 = new SqlCommand("select * from city where proID=" + this.DropDownList1.SelectedValue, con2);   SqlDataReader sdr1 = cmd1.ExecuteReader();   while (sdr1.Read())   {   this.ListBox1.Items.Add(new ListItem(sdr1.GetString(2),sdr1.GetInt32(0).ToString()));   }  }</span> 

Run the file as follows:

I have not added a complete list of cities in Hebei Province, just to implement the two-level linkage function. Compared with the use of Web controls GridView and Repeater in the previous two articles, although the functions of the GridView and Repeater are quite powerful, different controls have different purposes. How can they be used here?

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