ControlDesigner.ViewControl 属性

定义

命名空间:

System.Web.UI.Design

程序集:

System.Design.dll

获取或设置可用于预览设计时 HTML 标记的 Web 服务器控件。

public:
 property System::Web::UI::Control ^ ViewControl { System::Web::UI::Control ^ get(); void set(System::Web::UI::Control ^ value); };

public System.Web.UI.Control ViewControl { get; set; }

member this.ViewControl : System.Web.UI.Control with get, set

Public Property ViewControl As Control

属性值

Control

基类用于生成设计时 HTML 标记的 Control 对象。

示例

下面的代码示例演示如何使用 SupportsPreviewControlAttribute 属性标记控件设计器。 代码示例从 Label 类派生 Web 服务器控件，并将该控件与自定义控件设计器实现相关联。 控件设计器类声明标记为属性 SupportsPreviewControl 设置为 true. 控件设计器重写 GetDesignTimeHtml 该方法，然后在设计时以斜体显示 Text 控件的属性。

using System;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Web.UI;
using System.Web.UI.Design;
using System.Web.UI.Design.WebControls;
using System.Web.UI.WebControls;
using System.Reflection;

namespace ControlDesignerSamples.CS
{
    // Define a simple designer associated with a 
    // simple text web control.
    
    // Mark the designer with the SupportsPreviewControlAttribute set
    // to true.  This means the base.UsePreviewControl returns true,
    // and base.ViewControl returns a temporary preview copy of the control.
    [SupportsPreviewControl(true)]
    public class SimpleTextControlDesigner : TextControlDesigner
    {		
        // Override the base GetDesignTimeHtml method to display 
        // the design time text in italics.
        public override string GetDesignTimeHtml()
        {
            string html = String.Empty;
 
            try
            {
                // Initialize the return string to the default
                // design time html of the base TextControlDesigner.
                html = base.GetDesignTimeHtml();

                // Get the ViewControl for the associated control.
                Label ctrl = (Label)ViewControl;

                ctrl.Style.Add(HtmlTextWriterStyle.FontStyle, "Italic");
                html = base.GetDesignTimeHtml();
            }
            catch (System.Exception e)
            {
               if (String.IsNullOrEmpty(html))
               {
                   html = GetErrorDesignTimeHtml(e);
               }
            }
            
            return html;
        }
    }

    // Derive a simple Web control from Label to render a text string.
    // Associate this control with the SimpleTextControlDesigner.
    [DesignerAttribute("ControlDesignerSamples.CS.SimpleTextControlDesigner"),
    ToolboxData("<{0}:MyLabelControl Runat=\"Server\"><{0}:MyLabelControl>")]
    public class MyLabelControl : Label
    {
        // Use the Label control implementation, but associate
        // the derived class with the custom control designer.
    }
}

Imports System.ComponentModel
Imports System.ComponentModel.Design
Imports System.Web.UI
Imports System.Web.UI.Design
Imports System.Web.UI.Design.WebControls
Imports System.Web.UI.WebControls
Imports System.Reflection

Namespace ControlDesignerSamples.VB

    ' Derive a simple Web control from Label to render a text string.
    ' Associate this control with the SimpleTextControlDesigner.
    <DesignerAttribute("ControlDesignerSamples.CS.SimpleTextControlDesigner"), _
    ToolboxData("<{0}:MyLabelControl Runat=""Server""><{0}:MyLabelControl>")> _
    Public Class MyLabelControl
        Inherits Label

        ' Use the Label control implementation, but associate
        ' the derived class with the custom control designer.
    End Class


    ' Mark the designer with the SupportsPreviewControlAttribute set
    ' to true.  This means the base.UsePreviewControl returns true,
    ' and base.ViewControl returns a temporary preview copy of the control.
    <SupportsPreviewControl(True)> _
    Public Class SimpleTextControlDesigner
        Inherits TextControlDesigner

        ' Override the base GetDesignTimeHtml method to display 
        ' the design time text in italics.
        Public Overrides Function GetDesignTimeHtml() As String
            Dim html As String = String.Empty

            Try
                ' Get the ViewControl for the associated control.
                Dim ctrl As Label = CType(ViewControl, Label)

                ' Set the default text, if necessary
                If ctrl.Text.Length = 0 Then
                    ctrl.Text = "Sample Text"
                End If

                ' Set the style to italic
                ctrl.Style.Add(HtmlTextWriterStyle.FontStyle, "italic")

                ' Let the base class create the HTML markup
                html = MyBase.GetDesignTimeHtml()
            Catch ex As Exception
                If String.IsNullOrEmpty(html) Then
                    ' Display the exception message
                    html = GetErrorDesignTimeHtml(ex)
                End If
            End Try

            Return html
        End Function

    End Class
End Namespace

注解

该 ViewControl 属性使用该 UsePreviewControl 属性来确定其返回值。

UsePreviewControl如果该属性是true，该ViewControl属性将返回控件的临时副本。 临时控件的更改不会持久保存。

UsePreviewControl如果该属性为 false，则ViewControl属性返回控件的属性的实例Component。 对控件实例的更改将保留。

对象 SupportsPreviewControl 中的 SupportsPreviewControlAttribute 设置用于设置属性的值 UsePreviewControl 。 因此，该SupportsPreviewControl设置确定基ControlDesigner类中的属性返回ViewControl的控件的类型。 SupportsPreviewControlAttribute如果未在控件设计器声明中指定对象行为，则ControlDesigner对象行为等效于将SupportsPreviewControl属性指定为 false。

另请参阅

• SupportsPreviewControlAttribute
• UsePreviewControl
• GetViewRendering
• PreviewControlDesigner
• ASP.NET 控件设计器概述