Επεξεργασία

Κοινή χρήση μέσω

ImageField.NullImageUrl Property

  • Reference

Definition

Namespace:
System.Web.UI.WebControls
Assembly:
System.Web.dll

Gets or sets the URL to an alternate image displayed in an ImageField object when the value of the field specified by the DataImageUrlField property is null.

public:
 virtual property System::String ^ NullImageUrl { System::String ^ get(); void set(System::String ^ value); };
public virtual string NullImageUrl { get; set; }
member this.NullImageUrl : string with get, set
Public Overridable Property NullImageUrl As String

Property Value

String

The URL to an alternate image displayed when the value of a field is null. The default is an empty string (""), which indicates that this property is not set.

Examples

The following example demonstrates how to use the NullImageUrl property to specify the URL to an alternate image to display when the value of the field specified by the DataImageUrlField property is 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>ImageField Example</title>
</head>
<body>
    <form id="form1" runat="server">
        
      <h3>ImageField Example</h3>
                       
      <asp:gridview id="EmployeesGrid"
        autogeneratecolumns="false"
        datasourceid="EmployeeSource"  
        runat="server">
      
        <columns>

          <asp:imagefield dataimageurlfield="PhotoPath"
            alternatetext="Employee Photo"
            nullimageurl="~\Images\NoPhoto.jpg"
            headertext="Photo"  
            readonly="true"/>
          <asp:boundfield datafield="FirstName"
            headertext="First Name"/>
          <asp:boundfield datafield="LastName"
            headertext="Last Name"/>
        
        </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="EmployeeSource"
        selectcommand="Select [EmployeeID], [LastName], [FirstName], [PhotoPath] From [Employees]"
        connectionstring="<%$ ConnectionStrings:NorthWindConnectionString%>" 
        runat="server"/>
            
    </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>ImageField Example</title>
</head>
<body>
    <form id="form1" runat="server">
        
      <h3>ImageField Example</h3>
                       
      <asp:gridview id="EmployeesGrid"
        autogeneratecolumns="false"
        datasourceid="EmployeeSource"  
        runat="server">
      
        <columns>

          <asp:imagefield dataimageurlfield="PhotoPath"
            alternatetext="Employee Photo"
            nullimageurl="~\Images\NoPhoto.jpg"
            headertext="Photo"  
            readonly="true"/>
          <asp:boundfield datafield="FirstName"
            headertext="First Name"/>
          <asp:boundfield datafield="LastName"
            headertext="Last Name"/>
        
        </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="EmployeeSource"
        selectcommand="Select [EmployeeID], [LastName], [FirstName], [PhotoPath] From [Employees]"
        connectionstring="<%$ ConnectionStrings:NorthWindConnectionString%>" 
        runat="server"/>
            
    </form>
  </body>
</html>

Remarks

When the value of the field specified by the DataImageUrlField property is null, an image cannot be displayed in an ImageField object. Use the NullImageUrl property to specify the URL to an alternate image to display. The alternate image is usually an image that indicates that the normal image is not available or cannot be found.

Note

As an alternative, you can simply display text when the field value is null by setting the NullDisplayText property instead of this property. If the NullImageUrl and NullDisplayText properties are both set, the NullImageUrl property has precedence.

Applies to

See also