DataTable.Merge 抛出错误：未将对象引用设置到实例
我想合并 DropDownList selectedindex 更改事件中的数据表。所以我在 DropDownList_SelectedIndexChanged 事件中编写了以下代码。
DataTable dt = (DataTable)POBLL.GetPOAdhocDetail();
DataView dv = new DataView(dt);
dv.RowFilter = "IndentTypeID = " + ddlIndentType.SelectedValue + "AND IndentID = " + ddlIndentNumber.SelectedValue;
DataTable dtView = dv.ToTable();
gvPODetails.DataSource = dtView;
gvPODetails.DataBind();
DTMerge.Merge(dtView);
其中 DTMerge 是 DataTable，我将其声明如下：
public DataTable DTMerge
{
get
{
if (ViewState["Merge"] != null)
{
return (DataTable)ViewState["Merge"];
}
else
return null;
}
set
{
ViewState["Merge"] = value;
}
}
但它会抛出错误“对象引用未设置到实例”。怎么解决这个问题呢？
I want to merge datatables in the DropDownList selectedindex changed event. So I have written the below code in the DropDownList_SelectedIndexChanged Event.
DataTable dt = (DataTable)POBLL.GetPOAdhocDetail();
DataView dv = new DataView(dt);
dv.RowFilter = "IndentTypeID = " + ddlIndentType.SelectedValue + "AND IndentID = " + ddlIndentNumber.SelectedValue;
DataTable dtView = dv.ToTable();
gvPODetails.DataSource = dtView;
gvPODetails.DataBind();
DTMerge.Merge(dtView);
where DTMerge is the DataTable and I declared it like below:
public DataTable DTMerge
{
get
{
if (ViewState["Merge"] != null)
{
return (DataTable)ViewState["Merge"];
}
else
return null;
}
set
{
ViewState["Merge"] = value;
}
}
But it throws the Error "Object reference not set to an instance". How to solve this?
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您请求了 DTMerge 属性，该属性需要存在相应的 ViewState 才能有效。在访问 DTMerge 属性时，您还没有 ViewState。
这很可能就是问题所在。
You requested DTMerge property, which for being valid need of presence of corresponding ViewState. You don't have a ViewState yet, at the moment you access DTMerge property.
This is most likely the problem.