从另一个下拉列表中选择一个值后填充下拉列表

Question

I want to be able to populate a dropdown list(ddlExercise) after selecting a value from another dropdown list(ddlType) At the moment I am getting the values for the ddlType dropdown from a sql query which is populating the dropdown list but when I select something, the 2nd dropdown list remains empty. I have 3 values in the ddlType dropdown(Gym,Core,Cardio) and once I select one of these, I am using the dropdownlist.selectedvalue to retrieve its corresponding results. Here is my code:

    protected void Page_Load(object sender, EventArgs e)
    {
       SqlConnection con = new SqlConnection(@"Con String");


        if (!IsPostBack)

        { BindExerciseType(); }
    }

     public void BindExerciseType()
    {
        con.Open();
        SqlCommand cmd = new SqlCommand("select ExerciseType from ExerciseType", con);
        SqlDataReader dr = cmd.ExecuteReader();
        ddlType.DataSource = dr;
        ddlType.Items.Clear();
        ddlType.Items.Add("--Please Select country--");
        ddlType.DataTextField = "ExerciseType";
        ddlType.DataValueField = "ExerciseType";
        ddlType.DataBind();
        con.Close();



    }

    public void BindExercise()
    {
        con.Open();
        SqlCommand cmd = new SqlCommand("select ExerciseName from ExerciseDisplay   Where TypeName='" + ddlType.SelectedValue + "'", con);
        SqlDataReader dr = cmd.ExecuteReader();
        ddlExercise.DataSource = dr;
        ddlExercise.Items.Clear();
        ddlExercise.Items.Add("--Please Select country--");
        ddlExercise.DataTextField = "ExerciseName";
        ddlExercise.DataValueField = "ExerciseName";
        ddlExercise.DataBind();
        con.Close();

    }

        protected void ddlExercise_SelectedIndexChanged(object sender, EventArgs e)
    {
        BindExercise();
    }

Any ideas why this may be wrong? I have the autopostback propert set to true on both drop down lists. Any help would be greatly appreciated!

Answer 1

Your second SQL query is wrong. There should be a space between WHERE and TypeName. Like This :

SqlCommand cmd = new SqlCommand("select ExerciseName from ExerciseDisplay   Where TypeName='" + ddlType.SelectedValue + "'", con);

Answer 2

The problem is your event, you event is for the other drop down, your event should be:

protected void ddlType_SelectedIndexChanged(object sender, EventArgs e)
{
    BindExercise();
}

A contribution to your code, if you populate your dropdown with datasource, the items that you add will not appear if they are before the bind (). You must add the following, to stay but the latest:

ddlType.Items.Insert(0, "--Please Select country--");

I hope I have been helpful, and good luck with your question. (Sorry form my english)

Answer 3

问题出现在selectedIndexChanged函数中，当ddltype下拉列表的索引改变而不是dllExericese时，可能会触发该问题，在使用autopost方法后，你应该确保dlltype selectedindex没有改变，方法是在函数dlltype_selectedindexchanged中设置dlltype.SelectedIndex = dlltyp.selectedindex与dlltype下拉列表关联。