Question

我的页面加载中的代码背后有代码，用于设置下拉列表文本和值。我选择一个值，它重新加载页面，因为我有自动回发。即使在回发后我也需要保持选择的价值。我该怎么做呢？以下是我的代码：

protected void Page_Load(object sender, EventArgs e)
{
    List<string> list = new List<string>
      { "Month", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12"};

    DropDownListMonth.DataSource = list;
    DropDownListMonth.DataBind();
    DropDownListMonth.SelectedIndex = 0;

    foreach (ListItem item in DropDownListMonth.Items)
    {
        int i = 0;
        string month = Convert.ToString(i);
        item.Value = month;
        i = Convert.ToInt32(month);
        i++;
    }   
}

Answer 1

有一个名为Page.IsPostBack的Page属性，用于指示页面是第一次呈现还是正在加载以响应回发。

因此，您可以将此属性与if条件块一起使用，以避免重新绑定ddl。

protected void Page_Load(object sender, EventArgs e)
{
    if(!IsPostBack)
    {
      List<string> list = new List<string>
      { "Month", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12"};

    DropDownListMonth.DataSource = list;
    DropDownListMonth.DataBind();
    DropDownListMonth.SelectedIndex = 0;

    foreach (ListItem item in DropDownListMonth.Items)
    {
        int i = 0;
        string month = Convert.ToString(i);
        item.Value = month;
        i = Convert.ToInt32(month);
        i++;
    } 
  }  
}

Answer 2

您需要使用IsPostBack()验证：

protected void Page_Load(object sender, EventArgs e)
{
    if(!Page.IsPostBack())
    {
        List<string> list = new List<string>
      { "Month", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12"};

        DropDownListMonth.DataSource = list;
        DropDownListMonth.DataBind();
        DropDownListMonth.SelectedIndex = 0;

        foreach (ListItem item in DropDownListMonth.Items)
        {
            int i = 0;
            string month = Convert.ToString(i);
            item.Value = month;
            i = Convert.ToInt32(month);
            i++;
        }
    }   
}

Answer 3

DropDownListMonth.DataSource = list;
DropDownListMonth.DataBind();
DropDownListMonth.SelectedIndex = 0;
string selectedValue=DropDownListMonth.SelectedItem.Tostring();
foreach (ListItem item in DropDownListMonth.Items)
{
       int i = 0;
       string month = Convert.ToString(i);
       item.Value = month;
       i = Convert.ToInt32(month);
       i++;
       if(item.Value.Tostring()==selectedValue)
       {
         item.Selected=true;
       }
}

在回发下拉列表后获得保持选择的价值

3 个答案: