如何设置等于在RowUpdating为空字段值（...） [英] How to set field values equal to null in RowUpdating(...)

问题描述

这是我的code：

    protected void ConfigurationGridView_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        // row's Update button is clicked, but before the GridView control 
        // updates the row
        DropDownList ddlst = 
           ((DropDownList)ConfigurationGridView.Rows[e.RowIndex].FindControl("SubUnitDropDownList"));

        if (ddlst != null)
        {
            ListItem li = ddlst.SelectedItem;

            if (li != null)
            {
                if (Convert.ToInt32(li.Value) == -1)
                {
                    // next line is where the problem is
                    // null doesn't change the old value
                    // it does nothing, how to I change this value to null??
                    e.NewValues["SubUnitId"] = null;
                }
                else
                {
                    // we set the actual value
                    // this works nicely
                    e.NewValues["SubUnitId"] = li.Value;
                }
            }
        }
    }

基本上，我有一个字段，它通过组合框获取其值，在组合的第一个值重新presents未分配的/不适用/不设置值，或者该记录的空值，它的工作原理时，我指定其他值，例如1，2或3，当组合得-1我要清除该值，即把空值，但线之上似乎并没有做任何事情，我已经试过可空＆LT; INT32＆gt;中的Int32？值= NULL，Convert.ToInt32（空）其实是把0，而不是空。
当我尝试System.DBNull.Value我得到一个错误：
    System.DBNull'类型的对象''不能转换为类型'System.Nullable`1 [System.Int32]'。

Basically, I have one field that gets its value via a combo box, the first value in the combos represents the unassigned/not applicable/not set value, or the null value for that record, it works when I assign other values, say 1, 2, or 3, when the combo gets -1 I want to clear this value i.e. put the null value, but the line above doesn't seem to do anything, I've tried Nullable<int32>, Int32? value = null, Convert.ToInt32(null) actually puts 0 instead of null. When I try System.DBNull.Value I get an error: 'Object of type 'System.DBNull' cannot be converted to type 'System.Nullable`1[System.Int32]'.'.

我是什么做错了吗？在此先感谢您的输入。

What am I doing wrong? thanks in advance for your input.

推荐答案

也许你可以试试这个：

e.NewValues["SubUnitId"]=System.DBNull.Value

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