只读组合框提供程序

 

• 下载source code - 20 KB

介绍 我已经见过许多

  

 

使组合框只读的创造性方法。我发现最好的方法是为组合框创建一个ExtenderProvider，将其中的dropdownstyle更改为simple，然后捕捉所有的击键。 我发现将一个combobox设置为readonly很有用，就像我喜欢在文本框上使用readonly一样。 即为了: 让我的用户从组合框中复制文本(禁用不允许复制)让关联的工具提示启用(禁用组合框也将禁用关联的工具提示) 背景 此代码基于IExtenderProvider接口。你可能会想要谷歌!本文还假设您已经了解捕获击键和哈希表的使用。 的兴趣点 IExtenderProvider可以在各种情况下使用，比如在文本框控件中捕获击键。在以后的文章中，我将展示这种技术的示例。 使用的代码 在添加ReadOnlyComboProvider类之后，需要重新构建项目。然后，只需将其中一个从工具箱拖到窗体上，并通过属性窗口或代码设置属性。 要通过代码设置readonly属性，你可以这样做: 隐藏,复制Code

Me.ReadOnlyComboProvider1.SetReadOnly(myComboBox, True)

下面是ExtenderProvider的代码: 隐藏,收缩,复制Code

Option Explicit On 
Option Strict On 
Option Compare Text 
 
Imports System.ComponentModel 
Imports System.Windows.Forms 
 
<Drawing.ToolboxBitmap(GetType(System.Windows.Forms.TextBox)), _ 
System.ComponentModel.DesignerCategoryAttribute("Code"), _ 
ProvideProperty("ReadOnly", GetType(Control)), _ 
ProvideProperty("OrigDropDownStyle", GetType(Control))> _ 
Public Class ReadOnlyComboProvider 

Inherits System.ComponentModel.Component 

Implements IExtenderProvider 
 
''This hash table stores all the controls extended by this extender provider 
Friend htProvidedProperties As New Hashtable 
 
Public Function CanExtend(ByVal extendee As Object) As Boolean _
       Implements System.ComponentModel.IExtenderProvider.CanExtend 
    If TypeOf extendee Is ComboBox Then 
        Return True 
    Else 
        Return False 
    End If 
End Function 
 
Private Class ComboBoxProperties 
    Public IsReadOnly As Boolean = False 
    Public OrigComboBoxStyle As ComboBoxStyle = ComboBoxStyle.DropDown 
End Class 
 
<Category("Read Only Combobox Provider")> _ 
Sub SetReadOnly(ByVal ctrl As Control, ByVal value As Boolean) 
    Dim cbo As ComboBox = CType(ctrl, ComboBox) 
    If value = True Then 
        cbo.DropDownStyle = ComboBoxStyle.Simple 
    Else 
        cbo.DropDownStyle = GetControlFromHashtable(ctrl).OrigComboBoxStyle 
    End If 
    GetControlFromHashtable(ctrl).IsReadOnly = value 
End Sub 
 
<Category("Read Only Combobox Provider")> _ 
Function GetReadOnly(ByVal ctrl As Control) As Boolean 
    Return GetControlFromHashtable(ctrl).IsReadOnly 
End Function 
 
<Category("Read Only Combobox Provider")> _ 
Sub SetOrigDropDownStyle(ByVal ctrl As Control, ByVal value As ComboBoxStyle) 
    GetControlFromHashtable(ctrl).OrigComboBoxStyle = value 
End Sub 
 
<Category("Read Only Combobox Provider")> _ 
Function GetOrigDropDownStyle(ByVal ctrl As Control) As ComboBoxStyle 
    Return GetControlFromHashtable(ctrl).OrigComboBoxStyle 
End Function 
 
Private Function GetControlFromHashtable(ByVal ctrl As Control) As ComboBoxProperties 
    If htProvidedProperties.Contains(ctrl) Then 
        Return DirectCast(htProvidedProperties(ctrl), ComboBoxProperties) 
    Else 
        Dim ProvidedProperties As New ComboBoxProperties

        ''Add A KeyPress Event Handler as the control is added to hash table 
        AddHandler ctrl.KeyPress, AddressOf KeyPressHandler 
        htProvidedProperties.Add(ctrl, ProvidedProperties) 
        Return ProvidedProperties 
    End If 
End Function 
 
Private Sub KeyPressHandler(ByVal sender As Object, ByVal e As KeyPressEventArgs) 
    Dim cboSender As ComboBox = CType(sender, ComboBox) 
    If GetControlFromHashtable(cboSender).IsReadOnly = True Then 
        e.Handled = True 
    Else 
        e.Handled = False 
    End If 
End Sub 
 
End Class

历史 5/22/08 -第一版发布。 本文转载于：http://www.diyabc.com/frontweb/news234.html