ImageField コンストラクタとは何？わかりやすく解説 Weblio辞書

メモ
フィールドはデータバインドコントロールに動的に追加することもできますが、フィールドを静的に宣言しておき、適宜、表示または非表示にすることをお勧めします。フィールドをすべて静的に宣言すると、親データバインドコントロールのビューステートのサイズを削減できます。

使用例

このコンストラクタを使用して、ImageField オブジェクトを GridView コントロールの Columns コレクションに動的に追加する方法を次の例に示します。

Visual Basic

<%@ Page language="VB" %>

<script runat="server">

  Sub Page_Load(ByVal sender As
 Object, ByVal e As EventArgs)

    If Not IsPostBack Then
      
      ' Dynamically create a GridView control.
      Dim employeesView As GridView = New
 GridView()
      employeesView.ID = "EmployeesGrid"
      employeesView.AutoGenerateColumns = False
      employeesView.DataSourceID = "EmployeeSource"

      ' Dynamically create field columns to display the desired
      ' fields from the data source.

      ' Create an ImageField object to display an employee's photo.
      Dim photoImageField As ImageField = New
 ImageField()
      photoImageField.DataImageUrlField = "PhotoPath"
      photoImageField.AlternateText = "Employee Photo"
      photoImageField.NullDisplayText = "No image on file."
      photoImageField.HeaderText = "Photo"
      photoImageField.ReadOnly = True

      ' Create a BoundField object to display an employee's last name.
      Dim lastNameBoundField As BoundField
 = New BoundField()
      lastNameBoundField.DataField = "LastName"
      lastNameBoundField.HeaderText = "Last Name"

      ' Create a BoundField object to display an employee's first name.
      Dim firstNameBoundField As BoundField
 = New BoundField()
      firstNameBoundField.DataField = "FirstName"
      firstNameBoundField.HeaderText = "First Name"

      ' Add the field columns to the Fields collection of the
      ' GridView control.
      employeesView.Columns.Add(photoImageField)
      employeesView.Columns.Add(lastNameBoundField)
      employeesView.Columns.Add(firstNameBoundField)
      
      ' Add the GridView control to the Controls collection
      ' of the PlaceHolder control. 
      GridViewPlaceHolder.Controls.Add(employeesView)

    End If

  End Sub

</script>

<html>
  <body>
    <form runat="server">
        
      <h3>ImageField Constructor Example</h3>
                  
      <asp:placeholder id="GridViewPlaceHolder"
        runat="server"/>            
           
      <!-- 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="C#" %>

<script runat="server">

  void Page_Load(Object sender, EventArgs e)
  {

    if (!IsPostBack)
    {
      
      // Dynamically create a GridView control.
      GridView employeesView = new GridView();
      employeesView.ID = "EmployeesGrid";
      employeesView.AutoGenerateColumns = false;
      employeesView.DataSourceID = "EmployeeSource";

      // Dynamically create field columns to display the desired
      // fields from the data source.

      // Create an ImageField object to display an employee's photo.
      ImageField photoImageField = new ImageField();
      photoImageField.DataImageUrlField = "PhotoPath";
      photoImageField.AlternateText = "Employee Photo";
      photoImageField.NullDisplayText = "No image on file.";
      photoImageField.HeaderText = "Photo";
      photoImageField.ReadOnly = true;

      // Create a BoundField object to display an employee's last name.
      BoundField lastNameBoundField = new BoundField();
      lastNameBoundField.DataField = "LastName";
      lastNameBoundField.HeaderText = "Last Name";

      // Create a BoundField object to display an employee's first name.
      BoundField firstNameBoundField = new BoundField();
      firstNameBoundField.DataField = "FirstName";
      firstNameBoundField.HeaderText = "First Name";

      // Add the field columns to the Fields collection of the
      // GridView control.
      employeesView.Columns.Add(photoImageField);
      employeesView.Columns.Add(lastNameBoundField);
      employeesView.Columns.Add(firstNameBoundField);
      
      // Add the GridView control to the Controls collection
      // of the PlaceHolder control. 
      GridViewPlaceHolder.Controls.Add(employeesView);

    }

  }

</script>

<html>
  <body>
    <form runat="server">
        
      <h3>ImageField Constructor Example</h3>
                  
      <asp:placeholder id="GridViewPlaceHolder"
        runat="server"/>            
           
      <!-- 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>