vb.net基类 VBNet
vb.net或者c#.net中,派生类如何删除基类成员?
在.NET中,彻底的删除应该是不可能的
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如果你反编译一下就可以知道
这个问题就好像两个人生个孩子,你说盲肠没什么用,还容易发生危险(需要手术),那生下来就没有多好,这个要求似乎优点不合理
vb.net派生类重写基类函数的问题?
vb.net的MyBase(mybase)与java的super能基本对应。
下图是一个例子:
VB.NET实例化类
可以,但是变量不能用ClassA或B来定义,可以用Object,或ClassA,ClassB的基类,,使用类的成员时,再把变量类型转换成相应的类
VB.NET窗体继承问题
在继承类中添加了空的事件过程,估计也会调用基类事件过程的,也就是两个事件过程都会被调用。可以试试在继承类构造函数中用 RemoveHandler 语句能不能撤销基类的事件过程的绑定。
另外一般的过程可以用override关键字隐藏基类的同名方法,比如基类调用的方法被继承类override重写后,就会调用继承类的方法了。所以可以把事件处理代码放在一普通过程中,由事件过程调用,这样继承类可以用空的同名方法覆盖基类方法了。
vb.net有没有类似vb6.0控件数组的功能
可以实现
首先创建一个Button类型控件数组:
1、创建“Windows应用程序”类型的工程,添加名为ButtonArray的类,并使该类继承 System.Collection.CollectionBase 类。System.Collections.CollectionBase类是.NET框架类库中为集合操作提供抽象的基类,通过对它的继承可以为我们的ButtonArray类具备集合增加、删除、索引的功能。
2、为ButtonArray类添加ParentForm属性,即控件组所在窗体,创建初始化函数(构造函数);
3、为控件数组类增加AddItem方法,该方法在控件数组类中添加成员;
4、为控件数组类增加RemoveItem方法,该方法在控件数组中删除一个成员。
示例代码:
Public Class ButtonArray
Inherits System.Collections.CollectionBase
Private ReadOnly ParentForm As System.Windows.Forms.Form
Public Sub New(ByVal pForm As System.Windows.Forms.Form)
ParentForm = pForm
End Sub
Default Public ReadOnly Property Item(ByVal index As Integer) As System.Windows.Forms.Button
Get
Return Me.List.Item(index) ' ButtonArray的List 属性从CollectionBase 继承
End Get
End Property
Public Sub AddItem()
Dim btnItem As New System.Windows.Forms.Button
Me.List.Add(btnItem)
ParentForm.Controls.Add(btnItem) '向窗体中增加控件
btnItem.Tag = Me.Count 'Count属性从CollectionBase 继承
btnItem.Top = Me.Count * 30
btnItem.Left = 200
btnItem.Text = "Button" Me.Count.ToString
AddHandler btnItem.Click, AddressOf btnItem_Click '绑定事件处理程序
End Sub
Public Sub AddItem(ByVal btnItem As System.Windows.Forms.Button)
Me.List.Add(btnItem)
AddHandler btnItem.Click, AddressOf btnItem_Click '绑定事件处理程序
End Sub
Public Sub RemoveItem()
If Me.Count 0 Then
ParentForm.Controls.Remove(Me(Me.Count - 1))
Me.List.RemoveAt(Me.Count - 1)
End If
End Sub
Public Sub btnItem_Click(ByVal sender As Object, ByVal e As System.EventArgs)
'在这里编写控件数组对点击事件的响应
'例如:
MsgBox("点击:" sender.GetType().ToString CType(CType(sender, Button).Tag, String))
End Sub
End Class
使用创建的控件数组
在Form1中放置两个按钮Button1、Button2,分别测试控件数组的增添、删除。
双击Form添加代码:
Public Class Form1
Inherits System.Windows.Forms.Form
……Windows窗体设计器生成的代码……
Dim Buttons As New ButtonArray(Me)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Buttons.AddItem()
End Sub
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Buttons.RemoveItem()
End Sub
End Class
其他的控件数组也可以用类似的方式来实现
例如 Label控件数组
LabelArray.vb代码如下:
Public Class LabelArray
Inherits System.Collections.CollectionBase
Private ReadOnly ParentForm As System.Windows.Forms.Form
Public Sub New(ByVal pForm As System.Windows.Forms.Form)
ParentForm = pForm
End Sub
Default Public ReadOnly Property Item(ByVal index As Integer) As System.Windows.Forms.Label
Get
Return Me.List.Item(index) ' ButtonArray的List 属性从CollectionBase 继承
End Get
End Property
Public Sub AddItem(ByVal btnItem As System.Windows.Forms.Label)
Me.List.Add(btnItem)
AddHandler btnItem.Click, AddressOf btnItem_Click '绑定事件处理程序
End Sub
Public Sub btnItem_Click(ByVal sender As Object, ByVal e As System.EventArgs)
'在这里编写控件数组对点击事件的响应
'例如:
MsgBox("点击:" sender.GetType().ToString CType(CType(sender, Label).Tag, String))
End Sub
End Class
使用创建的Label控件
在Form1中放置两个按钮Label1、Label2
双击Form添加代码:
Public Class Form1
Inherits System.Windows.Forms.Form
#Region " Windows 窗体设计器生成的代码 "
Public Sub New()
MyBase.New()
'该调用是 Windows 窗体设计器所必需的。
InitializeComponent()
'在 InitializeComponent() 调用之后添加任何初始化
'用来绑定label
BindArray()
End Sub
……Windows窗体设计器生成的其他代码……
#End Region
Dim Labels As New LabelArray(Me)
Public Sub BindArray()
Me.Label1.Tag = "1111"
Me.Label2.Tag = "222"
Labels.AddItem(Me.Label1)
Labels.AddItem(Me.Label2)
End Sub
End Class
然后可以测试点击两个label可以显示相应的Tag的信息。
VB.NET没有操作XML的基类吗?高手救命啊
使用System.XML
Imports Microsoft.VisualBasic
Imports System
Imports System.IO
Imports System.Xml
namespace HowTo.Samples.XML
public class WriteXmlFileSample
private const document as string = "newbooks.xml"
shared sub Main()
Dim myWriteXmlFileSample as WriteXmlFileSample
myWriteXmlFileSample = new WriteXmlFileSample()
myWriteXmlFileSample.Run(document)
end sub
public sub Run(args As String)
Dim myXmlTextReader as XmlTextReader = nothing
Dim myXmlTextWriter as XmlTextWriter = nothing
try
myXmlTextWriter = new XmlTextWriter (args, nothing)
myXmlTextWriter.Formatting = System.Xml.Formatting.Indented
myXmlTextWriter.WriteStartDocument(false)
myXmlTextWriter.WriteDocType("bookstore", nothing, "books.dtd", nothing)
myXmlTextWriter.WriteComment("此文件表示书店库存数据库的另一个片断")
myXmlTextWriter.WriteStartElement("bookstore")
myXmlTextWriter.WriteStartElement("book", nothing)
myXmlTextWriter.WriteAttributeString("genre","autobiography")
myXmlTextWriter.WriteAttributeString("publicationdate","1979")
myXmlTextWriter.WriteAttributeString("ISBN","0-7356-0562-9")
myXmlTextWriter.WriteElementString("title", nothing, "The Autobiography of Mark Twain")
myXmlTextWriter.WriteStartElement("Author", nothing)
myXmlTextWriter.WriteElementString("first-name", "Mark")
myXmlTextWriter.WriteElementString("last-name", "Twain")
myXmlTextWriter.WriteEndElement()
myXmlTextWriter.WriteElementString("price", "7.99")
myXmlTextWriter.WriteEndElement()
myXmlTextWriter.WriteEndElement()
'向文件写 XML 并关闭编写器
myXmlTextWriter.Flush()
myXmlTextWriter.Close()
' 读取返回的文件并进行分析以确保正确生成 XML
myXmlTextReader = new XmlTextReader (args)
FormatXml (myXmlTextReader, args)
catch e as Exception
Console.WriteLine ("异常:{0}", e.ToString())
finally
Console.WriteLine()
Console.WriteLine("对文件 {0} 的处理已完成。", args)
If Not myXmlTextReader Is Nothing
myXmlTextReader.Close()
end if
'关闭编写器
If Not myXmlTextWriter Is Nothing
myXmlTextWriter.Close()
end if
End try
End Sub
private shared Sub FormatXml (reader as XmlTextReader, filename as String)
Dim piCount, docCount, commentCount, elementCount as Integer
Dim attributeCount, textCount, whitespaceCount as Integer
While reader.Read()
Select (reader.NodeType)
case XmlNodeType.ProcessingInstruction:
Format (reader, "ProcessingInstruction")
piCount += 1
case XmlNodeType.DocumentType:
Format (reader, "DocumentType")
docCount += 1
case XmlNodeType.Comment:
Format (reader, "Comment")
commentCount += 1
case XmlNodeType.Element:
Format (reader, "Element")
elementCount += 1
While reader.MoveToNextAttribute()
Format (reader, "Attribute")
end While
if (reader.HasAttributes)
attributeCount += reader.AttributeCount
end if
case XmlNodeType.Text:
Format (reader, "Text")
textCount += 1
case XmlNodeType.Whitespace:
whitespaceCount += 1
End Select
End While
' 显示该文件的统计信息
Console.WriteLine ()
Console.WriteLine("{0} 文件的统计信息", filename)
Console.WriteLine ()
Console.WriteLine("处理指令:" piCount)
Console.WriteLine("文档类型:" docCount)
Console.WriteLine("注释:" commentCount)
Console.WriteLine("元素:" elementCount)
Console.WriteLine("属性:" attributeCount)
Console.WriteLine("文本:" textCount)
Console.WriteLine("空白:" whitespaceCount)
End Sub
private shared Sub Format(byref reader as XmlTextReader , NodeType as String)
' 格式化输出
Console.Write(reader.Depth " ")
Console.Write(reader.AttributeCount " ")
Dim i as Integer
for i = 0 to reader.Depth - 1
Console.Write(Strings.chr(9))
Next
Console.Write(reader.Prefix NodeType "" reader.Name "" reader.Value)
Console.WriteLine()
End Sub
End Class
End Namespace
参考:
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