通过

BoundField.ConvertEmptyStringToNull 属性

  • 参考

定义

命名空间:
System.Web.UI.WebControls
程序集:
System.Web.dll

获取或设置一个值，该值指示在数据源中更新数据字段时是否将空字符串值 ("") 自动转换为 null 值。

public:
 virtual property bool ConvertEmptyStringToNull { bool get(); void set(bool value); };
public virtual bool ConvertEmptyStringToNull { get; set; }
member this.ConvertEmptyStringToNull : bool with get, set
Public Overridable Property ConvertEmptyStringToNull As Boolean

属性值

Boolean

若要将空字符串值自动转换为 null 值，则为 true；否则为 false。 默认值为 true。

示例

下面的代码示例演示如何使用 ConvertEmptyStringToNull 属性指定应自动将空字符串 (“”) 字段值转换为 null。


<%@ Page language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
  <head runat="server">
    <title>BoundField Example</title>
</head>
<body>
    <form id="form1" runat="server">
        
      <h3>BoundField Example</h3>

      <!-- The GridView control automatically sets the columns     -->
      <!-- specified in the datakeynames property as read-only.    -->
      <!-- No input controls are rendered for these columns in     -->
      <!-- edit mode.                                              -->
      <asp:gridview id="CustomersGridView" 
        datasourceid="CustomersSqlDataSource" 
        autogeneratecolumns="false"
        autogenerateeditbutton="true"
        datakeynames="CustomerID"  
        allowpaging="true" 
        runat="server">
        
        <columns>
          <asp:boundfield datafield="CustomerID"
            readonly="true"      
            headertext="Customer ID"/>
          <asp:boundfield datafield="CompanyName"
            convertemptystringtonull="true"
            headertext="Customer Name"/>
          <asp:boundfield datafield="Address"
            convertemptystringtonull="true"
            headertext="Address"/>
          <asp:boundfield datafield="City"
            convertemptystringtonull="true"
            headertext="City"/>
          <asp:boundfield datafield="PostalCode"
            convertemptystringtonull="true"
            headertext="ZIP Code"/>
          <asp:boundfield datafield="Country"
            convertemptystringtonull="true"
            headertext="Country"/>
        </columns>
        
      </asp:gridview>
            
      <!-- This example uses Microsoft SQL Server and connects  -->
      <!-- to the Northwind sample database. Use an ASP.NET     -->
      <!-- expression to retrieve the connection string value   -->
      <!-- from the Web.config file.                            -->
      <asp:sqldatasource id="CustomersSqlDataSource"  
        selectcommand="Select [CustomerID], [CompanyName], [Address], [City], [PostalCode], [Country] From [Customers]"
        updatecommand="Update Customers Set CompanyName=@CompanyName, Address=@Address, City=@City, PostalCode=@PostalCode, Country=@Country Where (CustomerID = @CustomerID)"
        connectionstring="<%$ ConnectionStrings:NorthWindConnectionString%>"
        runat="server">
      </asp:sqldatasource>
            
    </form>
  </body>
</html>


<%@ Page language="VB" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
  <head runat="server">
    <title>BoundField Example</title>
</head>
<body>
    <form id="form1" runat="server">
        
      <h3>BoundField Example</h3>

      <!-- The GridView control automatically sets the columns     -->
      <!-- specified in the datakeynames property as read-only.    -->
      <!-- No input controls are rendered for these columns in     -->
      <!-- edit mode.                                              -->
      <asp:gridview id="CustomersGridView" 
        datasourceid="CustomersSqlDataSource" 
        autogeneratecolumns="false"
        autogenerateeditbutton="true"
        datakeynames="CustomerID" 
        allowpaging="true" 
        runat="server">
        
        <columns>
          <asp:boundfield datafield="CustomerID"
            readonly="true"      
            headertext="Customer ID"/>
          <asp:boundfield datafield="CompanyName"
            convertemptystringtonull="true"
            headertext="Customer Name"/>
          <asp:boundfield datafield="Address"
            convertemptystringtonull="true"
            headertext="Address"/>
          <asp:boundfield datafield="City"
            convertemptystringtonull="true"
            headertext="City"/>
          <asp:boundfield datafield="PostalCode"
            convertemptystringtonull="true"
            headertext="ZIP Code"/>
          <asp:boundfield datafield="Country"
            convertemptystringtonull="true"
            headertext="Country"/>
        </columns>
        
      </asp:gridview>
            
      <!-- This example uses Microsoft SQL Server and connects  -->
      <!-- to the Northwind sample database. Use an ASP.NET     -->
      <!-- expression to retrieve the connection string value   -->
      <!-- from the Web.config file.                            -->
      <asp:sqldatasource id="CustomersSqlDataSource"  
        selectcommand="Select [CustomerID], [CompanyName], [Address], [City], [PostalCode], [Country] From [Customers]"
        updatecommand="Update Customers Set CompanyName=@CompanyName, Address=@Address, City=@City, PostalCode=@PostalCode, Country=@Country Where (CustomerID = @CustomerID)"
        connectionstring="<%$ ConnectionStrings:NorthWindConnectionString%>"
        runat="server">
      </asp:sqldatasource>
            
    </form>
  </body>
</html>

注解

有时，在更新或插入记录时，用户可能会为字段值输入空字符串。 ConvertEmptyStringToNull使用该属性指定在数据源中更新数据字段时，空字符串值是否自动转换为 null。

备注

默认情况下，对象 BoundField 将 null 值显示为空字符串。 若要显示其他值，请设置 NullDisplayText 属性。

适用于

另请参阅