在ASP.NET 2.0中操作数据之三十八：处理BLL和DAL的异常

<asp:DataList ID="Products" runat="server" DataKeyField="ProductID"
 DataSourceID="ProductsDataSource" RepeatColumns="2">
 <ItemTemplate>
  <h5>
   <asp:Label runat="server" ID="ProductNameLabel"
    Text='<%# Eval("ProductName") %>' />
  </h5>
  Price:
   <asp:Label runat="server" ID="Label1"
    Text='<%# Eval("UnitPrice", "{0:C}") %>' />
  <br />
   <asp:Button runat="server" id="EditProduct" CommandName="Edit"
    Text="Edit" />
  <br />
  <br />
 </ItemTemplate>
 <EditItemTemplate>
  Product name:
   <asp:TextBox ID="ProductName" runat="server"
    Text='<%# Eval("ProductName") %>' />
  <br />
  Price:
   <asp:TextBox ID="UnitPrice" runat="server"
    Text='<%# Eval("UnitPrice", "{0:C}") %>' />
  <br />
  <br />
   <asp:Button ID="UpdateProduct" runat="server" CommandName="Update"
    Text="Update" /> 
   <asp:Button ID="CancelUpdate" runat="server" CommandName="Cancel"
    Text="Cancel" />
 </EditItemTemplate>
</asp:DataList>
<asp:ObjectDataSource ID="ProductsDataSource" runat="server"
 SelectMethod="GetProducts" TypeName="ProductsBLL"
 OldValuesParameterFormatString="original_{0}">
</asp:ObjectDataSource> 

protected void Products_EditCommand(object source, DataListCommandEventArgs e)
{
 // Set the DataList's EditItemIndex property to the
 // index of the DataListItem that was clicked
 Products.EditItemIndex = e.Item.ItemIndex;
 // Rebind the data to the DataList
 Products.DataBind();
}
protected void Products_CancelCommand(object source, DataListCommandEventArgs e)
{
 // Set the DataList's EditItemIndex property to -1
 Products.EditItemIndex = -1;
 // Rebind the data to the DataList
 Products.DataBind();
}

protected void Products_UpdateCommand(object source, DataListCommandEventArgs e)
{
 // Read in the ProductID from the DataKeys collection
 int productID = Convert.ToInt32(Products.DataKeys[e.Item.ItemIndex]);
 // Read in the product name and price values
 TextBox productName = (TextBox)e.Item.FindControl("ProductName");
 TextBox unitPrice = (TextBox)e.Item.FindControl("UnitPrice");
 string productNameValue = null;
 if (productName.Text.Trim().Length > 0)
  productNameValue = productName.Text.Trim();
 decimal? unitPriceValue = null;
 if (unitPrice.Text.Trim().Length > 0)
  unitPriceValue = Decimal.Parse(unitPrice.Text.Trim(),
   System.Globalization.NumberStyles.Currency);
 // Call the ProductsBLL's UpdateProduct method...
 ProductsBLL productsAPI = new ProductsBLL();
 productsAPI.UpdateProduct(productNameValue, unitPriceValue, productID);
 // Revert the DataList back to its pre-editing state
 Products.EditItemIndex = -1;
 Products.DataBind();
}

<asp:Label ID="ExceptionDetails" EnableViewState="False" CssClass="Warning"
 runat="server" />

protected void Products_UpdateCommand(object source, DataListCommandEventArgs e)
{
 // Handle any exceptions raised during the editing process
 try
 {
  // Read in the ProductID from the DataKeys collection
  int productID = Convert.ToInt32(Products.DataKeys[e.Item.ItemIndex]);
  ... Some code omitted for brevity ...
 }
 catch (Exception ex)
 {
  // TODO: Display information about the exception in ExceptionDetails
 }
}

private void DisplayExceptionDetails(Exception ex)
{
 // Display a user-friendly message
 ExceptionDetails.Text = "There was a problem updating the product. ";
 if (ex is System.Data.Common.DbException)
  ExceptionDetails.Text += "Our database is currently experiencing problems.
   Please try again later.";
 else if (ex is NoNullAllowedException)
  ExceptionDetails.Text += "There are one or more required fields that are
   missing.";
 else if (ex is ArgumentException)
 {
  string paramName = ((ArgumentException)ex).ParamName;
  ExceptionDetails.Text +=
   string.Concat("The ", paramName, " value is illegal.");
 }
 else if (ex is ApplicationException)
  ExceptionDetails.Text += ex.Message;
}