c# - 重置下拉值

Question

我的页面中有 3 个级联下拉菜单。默认情况下，在我所有下拉菜单的页面加载时，我有一个默认选项，如下所示

--Select--

因此，当用户尝试在下拉列表中选择此 -- Select-- 选项时，它会抛出错误。

错误信息:

Validation of viewstate MAC failed

我的页面中有一个 gridview，当我选择第一个下拉值时，gridview 会填充数据。当我选择第二个下拉值时，前两个下拉值的组合将填充到网格中。现在，当我在第二个下拉列表中选择此 --Select-- 选项时，gridview 显示找到 0 条记录，而不是显示第一个下拉值。此外，当我为第一个下拉菜单选择选项 --Select-- 时，它必须返回页面加载时发生的所有网格数据值。

ddlGroup.Items.Insert(0, "--Select--");

代码隐藏:

第一个下拉列表:

 protected void ddlDate_SelectedIndexChanged(object sender, EventArgs e)
{
        SqlConnection conn = new SqlConnection(strcon);
        conn.Open();
        string strQuery = "select distinct(Group) from Application where Date = '" + ddlDate.Text + "'";
        SqlCommand cmd = new SqlCommand(strQuery, conn);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        ddlGroup.DataSource = dt;
        ddlGroup.DataTextField = "Group";
        ddlGroup.DataBind();
        ddlGroup.Items.Insert(0, new ListItem("--Select--", "0"));
        conn.Close();
        ddlCode.Items.Clear();
        ddlCode.Items.Insert(0, new ListItem("--Select--", "0"));
        DataTable dtDate = DataRepository.GetDate(ddlDate.Text);
        gvDetails.DataSource = dtDate;
        gvDetails.DataBind();           
}

第二个下拉菜单

 protected void ddlGroup_SelectedIndexChanged(object sender, EventArgs e)
{
        SqlConnection conn = new SqlConnection(strcon);
        conn.Open();
        string strQuery = "select distinct(Code) from Application where Date = '" + ddlDate.Text + "' and Group='" + ddlGroup.Text + "'";
        SqlCommand cmd = new SqlCommand(strQuery, conn);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        ddlCode.DataSource = dt;
        ddlCode.DataTextField = "Code";
        ddlCode.DataBind();
        ddlCode.Items.Insert(0, new ListItem("--Select--", "0"));
        conn.Close();
        DataTable dtGroup = DataRepository.GetGroup(ddlDate.Text, ddlGroup.Text);
        gvDetails.DataSource = dtGroup;
        gvDetails.DataBind();                                  
}

第三个下拉列表:

protected void ddlCode_SelectedIndexChanged(object sender, EventArgs e)
{
    DataTable dtCode = DataRepository.GetCode(ddlDate.Text, ddlGroup.Text, ddlCode.Text);
    gvDetails.DataSource = dtCode;
    gvDetails.DataBind();        
}

Answer 1

绑定(bind)gridview前需要检查下拉值

每当您将所选值更改为 --SELECT-- 时，它都会调用 ddlGroup_SelectedIndexChanged 函数。

尝试:

     protected void ddlGroup_SelectedIndexChanged(object sender, EventArgs e)
    {
if(ddlGroup.Text!="--Select--")
{
            SqlConnection conn = new SqlConnection(strcon);
            conn.Open();
            string strQuery = "select distinct(Code) from Application where Date = '" + ddlDate.Text + "' and Group='" + ddlGroup.Text + "'";
            SqlCommand cmd = new SqlCommand(strQuery, conn);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            da.Fill(dt);
            ddlCode.DataSource = dt;
            ddlCode.DataTextField = "Code";
            ddlCode.DataBind();
            ddlCode.Items.Insert(0, new ListItem("--Select--", "0"));
            conn.Close();
            DataTable dtGroup = DataRepository.GetGroup(ddlDate.Text, ddlGroup.Text);
            gvDetails.DataSource = dtGroup;
            gvDetails.DataBind();
}

else
{
// call ddlDate_SelectedIndexChanged 
}                                  
    }