FontNamesConverter.CanConvertFrom(ITypeDescriptorContext, Type) 方法

  • 参考

定义

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

确定此转换器是否可以将指定数据类型的对象转换为包含个别字体名称的字符串数组。

public:
 override bool CanConvertFrom(System::ComponentModel::ITypeDescriptorContext ^ context, Type ^ sourceType);
public override bool CanConvertFrom (System.ComponentModel.ITypeDescriptorContext context, Type sourceType);
override this.CanConvertFrom : System.ComponentModel.ITypeDescriptorContext * Type -> bool
Public Overrides Function CanConvertFrom (context As ITypeDescriptorContext, sourceType As Type) As Boolean

参数

context
ITypeDescriptorContext

提供类型转换器上下文信息的 ITypeDescriptorContext 对象。 可以选择为该参数传入 null。

sourceType
Type

表示要从中转换的数据类型的 Type。

返回

Boolean

如果可以转换类型，则为 true；否则为 false。

示例

下面的代码示例演示如何使用 CanConvertFrom 方法。 该示例确定在执行转换之前，是否可以将指定的数据类型转换为包含单个字体名称的字符串数组。

<%@ Page Language="C#" AutoEventWireup="True" %>

<!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>
    <title>FontNamesConverter Example</title>
<script language="C#" runat="server">

      void Page_Load(Object sender, EventArgs e) 
      {

         // Declare local variables.
         System.Globalization.CultureInfo culture = new System.Globalization.CultureInfo("en");
         System.ComponentModel.ITypeDescriptorContext context = null;
         Object names; 
         Object name_string;

         // Create FontNamesConverter object.
         FontNamesConverter fontconverter = new FontNamesConverter();

         // Create original list of fonts.
         string font_list = "arial, times new roman, verdana";

         // Check for type compatibility.
         if (fontconverter.CanConvertFrom(context, typeof(string)))
         {

            // Display original string.
            Label1.Text = "Original String :" + "<br /><br />" + font_list;

            // Convert string to array to strings and display results.
            names = fontconverter.ConvertFrom(context, culture, font_list);
            Label2.Text = "Converted to Array of Strings : " + "<br /><br />";
            foreach (string name_element in (string[])names)
            {
               Label2.Text += name_element + "<br />";
            }

            // Convert array of strings back to a string and display results.
            name_string = fontconverter.ConvertTo(context, culture, names, typeof(string)); 
            Label3.Text = "Converted back to String :" + "<br /><br />" + (string)name_string;

         }
          
      }

   </script>

</head>
<body>

   <h3>FontNamesConverter Example</h3>
   <br />

   <form id="form1" runat="server">
        
      <asp:Label id="Label1" runat="server"/>
      <br /><hr />
      <asp:Label id="Label2" runat="server"/>
      <br /><hr />
      <asp:Label id="Label3" runat="server"/>
        
   </form>

</body>
</html>

<%@ Page Language="VB" AutoEventWireup="True" %>

<!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>
    <title>FontNamesConverter Example</title>
<script language="VB" runat="server">
    Sub Page_Load(sender As Object, e As EventArgs)
        
        ' Declare local variables.
        Dim culture As New System.Globalization.CultureInfo("en")
        Dim context As System.ComponentModel.ITypeDescriptorContext = Nothing
        Dim names As Object
        Dim name_string As Object
        
        ' Create FontNamesConverter object.
        Dim fontconverter As New FontNamesConverter()
        
        ' Create original list of fonts.
        Dim font_list As String = "arial, times new roman, verdana"
        
        ' Check for type compatibility.
        If fontconverter.CanConvertFrom(context, GetType(String)) Then
            
            ' Display original string.
            Label1.Text = "Original String :" & "<br /><br />" & font_list
            
            ' Convert string to array to strings and display results.
            names = fontconverter.ConvertFrom(context, culture, font_list)
            Label2.Text = "Converted to Array of Strings : " & "<br /><br />"
            Dim name_element As String
            For Each name_element In CType(names, String())
                Label2.Text &= name_element & "<br />"
            Next name_element
            
            ' Convert array of strings back to a string and display results.
            name_string = fontconverter.ConvertTo(context, culture, names, _
                GetType(String))
            Label3.Text = "Converted back to String :" & "<br /><br />" & _
                CType(name_string, String)
        End If 
    End Sub 'Page_Load
  </script>

</head>
<body>

   <h3>FontNamesConverter Example</h3>
   <br />

   <form id="form1" runat="server">
        
      <asp:Label id="Label1" runat="server"/>
      <br /><hr />
      <asp:Label id="Label2" runat="server"/>
      <br /><hr />
      <asp:Label id="Label3" runat="server"/>
        
   </form>

</body>
</html>

注解

CanConvertFrom使用 方法确定是否可以将指定的数据类型转换为包含单个字体名称的字符串数组。

注意

此转换器只能从 string 数据类型进行转换。 参数 sourceType 的类型必须为 String。 否则，此方法返回 false 以指示无法转换指定的数据类型。

可以选择为 参数传入 nullcontext 。

适用于

另请参阅