好奇怪的webservice异步调用的问题，望高手指教一下

quicklight 2004-12-19 01:14:03

我是做一个dot net 精简版的客户端程序，当中调用webservice来读取数据库中的内容来绑定到一个datagrid，但是出现了一个奇怪的问题，程序如下：

private void BindData(string strJobID, byte byStatus, bool bType)
{
InfoForm Info = new InfoForm();
Info.Parent = this;
Info.Location = new Point(10,40);
Info.Size = new Size(200,100);
Info.FormBorderStyle = FormBorderStyle.FixedToolWindow;
Info.Infomation = "正在获取备件列表，请稍候……";
Info.BringToFront();
if(byStatus == 0)//创建询问请求
{
MainArea.Visible = true;
BackFillArea.Visible = false;
PartNo.Visible = true;
SearchPartInfo.Visible = true;
SearchPart.Visible = true;
PartList.Top = 40;
PartList.Height = 160;
Submit.Visible = true;
PartList.ContextMenu = PartOperation;
if(IsNewJob)
CurJobInfo = new RequestInfo(strJobID);//logical problem here

Info.Show();
resultBindData= server.BeginGetPartsByJobID(strJobID, bType,cbAfterBindData,Info);

}
else if (byStatus == 4)// 报关单回填
{

InitBackFillArea(strJobID);
return;
}
else
{
Submit.Visible = false;
MainArea.Visible = true;
BackFillArea.Visible = false;
PartNo.Visible = false;
SearchPartInfo.Visible = false;
SearchPart.Visible = false;
PartList.Top = 15;
PartList.Height = 210;
PartList.ContextMenu = null;

Info.Show();
resultBindData = server.BeginGetPartsByRequest(strJobID, bType,cbAfterBindData,Info);
}

}
private void AfterBindData(System.IAsyncResult result)
{
InfoForm info = (InfoForm)result.AsyncState;
if(info != null)
info.Close();
DataSet ds;
if(CurNodeData.Status == 0)
ds = server.EndGetPartsByJobID(resultBindData);
else
ds = server.EndGetPartsByRequest(resultBindData);

JobIDShow.Text = "工作单号: " + CurNodeData.JobID;
JobIDShow.Visible = true;
CurPartTable = ds.Tables["PartInfo"];
CurPartIndex = -1;
DataTable table = new DataTable("PartInfo");
table.Columns.Add("备件号",Type.GetType("System.String"));
table.Columns.Add("品名", Type.GetType("System.String"));
table.Columns.Add("HSCODE", Type.GetType("System.String"));
table.Columns.Add("状态", Type.GetType("System.String"));

string strStatus;
foreach(DataRow row in CurPartTable.Rows)
{
DataRow newRow = table.NewRow();
newRow["备件号"] = row["PartNo"];
newRow["品名"] = row["ChineseName"];
newRow["HSCODE"] = row["HSCODE"];

strStatus = StatusArray[(byte)row["Status"]];
if((byte)row["Status"] == 2)
{
if((bool)row["SubStatus"])
{
strStatus += "(A)";
}
else
{
strStatus += "(Q)";
}
}
else if((byte)row["Status"] == 0)//需处理的备件，编辑问题列表
{
string strPartNo = (string) row["PartNo"];
PartInfo part = CurJobInfo.GetPart(strPartNo);
if(part != null)
{
strStatus = "已编辑";
}

}
newRow["状态"] = strStatus;
table.Rows.Add(newRow);
}

PartList.DataSource = table;
PartList.Visible = true;
}

在异步调用中我把前面显示的对话框（InfoForm，主要用于给出一个提示，表明正在读取服务器的信息，让用户等待操作完成）的引用作为AsyncState参数传递给调用，然后在回调函数（AfterBindData）中显示强制转化成InfoForm的变量，然后关闭这个对话框，程序错误就出现在这里，根本就不能继续执行下去，我调试跟踪发现，在港开始进去回调函数时候，result是一个对象，但是执行了强制转换操作之后，result就成了null，太奇怪了，什么地方是的这个IAsyncResult型的变量被释放了呢，实在是不明白

...全文