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VB.NET 与 XML 的实例操作


  ' 再建立项目的文件夹的bin文件夹下
  
  '创建两个文件
  
  '一个是"myxml.xml"
  
  '一个是"myxml.mdb"
  
  '这里面有一个表"users"三个字段名"nameid","age","faverity"
  
  
  '再转到图形界面
  
  '单击"工具箱"的"数据"把"OleDbConnection"," OleDbComman","DataSet","OleDbDataAdapter"
  
  '拉入窗体界面
  
  '依次对这几个控件进行操作
  
  '我的文件夹是D:\vbproject\WindowsApplication1
  
  'D:\vbproject\WindowsApplication1/bin/myxml.xml
  
  'D:\vbproject\WindowsApplication1/bin/myxml.mdb
  
  //======================准备结束==============
  
  (1)首先在机子上要有.Net FrameWork
  
  打开VS.NET依次展开:文件-新建-项目;
  
  再选择VISUAL-BASIC-项目-Windows应用程序
  
  这就是所需要一个小界面
  
  现在一步步的来写代码,完成它的功能
  
  首先来完成添加功能:
  
  我们目标是:通过这三个文本框(姓名,年龄,爱好)来添加到数据库中。然后再把这个数据库的表保存成XML格式
  
  双击"添加"按钮
  
  在里面写下以下这些代:(VB写的语言,不是C#)
  
  If TextBox1.Text <> "" And TextBox2.Text <> "" And TextBox3.Text <> "" Then
  
  '在三个文本框都不为空时,执行以下操作,
  
  '否则出错
  Dim strsel As String
  strsel = "select * from users where nameid='" & TextBox1.Text & "'"
  
  '建立一个查询字符串,看要要添加的姓名,是否已在数据中存在,如果不存在就可以添加
  OleDbCommand1 = New OleDbCommand
  Me.OleDbCommand1.CommandText = strsel
  Me.OleDbCommand1.Connection = OleDbConnection1
  OleDbConnection1.Open()
  Try
  
  '进行异常处理
  
  Dim reader As OleDbDataReader = OleDbCommand1.ExecuteReader()
  If reader.Read() Then
  
  '通过DataReader来读取,如果读得到,表明数据在有这个姓名存在,不添加;
  ListBox1.Items.Add("已经有该记录!")
  Else
  reader.Close()
  
  '要对数据库进行操作,首先把DataReader关掉;
  Dim insert As String
  insert = "insert into users(nameid,age,faverity) values('" & TextBox1.Text & "','" & TextBox2.Text & "','" & TextBox3.Text & "')"
  
  '建立一个插入字符串
  OleDbCommand1 = New OleDbCommand
  Me.OleDbCommand1.CommandText = insert
  Me.OleDbCommand1.Connection = Me.OleDbConnection1
  Me.OleDbCommand1.ExecuteNonQuery()
  ListBox1.Items.Add("添加成功!!")
  
  '以下是把数据库的数据保存为XML格式
  DataSet1 = New DataSet
  OleDbDataAdapter1 = New OleDbDataAdapter("select * from users", OleDbConnection1)
  OleDbDataAdapter1.Fill(DataSet1, "users")
  DataSet1.WriteXml("myxml.xml")
  End If
  Catch ex As Exception
  ListBox1.Items.Add("Errors!")
  End Try
  
  OleDbConnection1.Close()
  Else
  MessageBox.Show("请输入完整!!")
  End If
  
  //==================接下来是对数据库进行查询===================
  
  '双击"查找"按钮
  
  '写入以下代码
  
  If TextBox4.Text <> "" Then
  
  '还是和上面一样如果文本框为空,就不执行,如果不为空,就执行下面的操作
  ListBox1.Items.Clear()
  
  '首先把listBox清空
  Dim searchtext As String
  searchtext = TextBox4.Text
  OleDbConnection1.Open()
  Dim selstring As String
  selstring = "select * from users where nameid like '%" & searchtext & "%'"
  
  ' 建立查询字符串,可以支持模糊查询
  OleDbCommand1 = New OleDbCommand
  Me.OleDbCommand1.CommandText = selstring
  Me.OleDbCommand1.Connection = OleDbConnection1
  
  '以下几句是显示匹配的条数
  DataSet1 = New DataSet
  OleDbDataAdapter1 = New OleDbDataAdapter(selstring, OleDbConnection1)
  OleDbDataAdapter1.Fill(DataSet1, "users")
  ListBox1.Items.Add("共有" & DataSet1.Tables("users").Rows.Count & "条匹配的记录")
  ListBox1.Items.Add("-------------------------------------------------------------")
  Try
  
  '进行异常处理
  Dim cmdreader As OleDbDataReader = OleDbCommand1.ExecuteReader()
  
  While cmdreader.Read
  
  '注意这里要用while
  
  '不然就无法进行循环,就只能进行一次查询
  ListBox1.Items.Add(cmdreader("nameid").ToString())
  ListBox1.Items.Add(cmdreader("age").ToString())
  ListBox1.Items.Add(cmdreader("faverity").ToString())
  ListBox1.Items.Add("----------------------------------")
  End While
  
  cmdreader.Close()
  
  OleDbConnection1.Close()
  Catch ex As Exception
  ListBox1.Items.Add("Errors")
  End Try
  Else
  End If
  
  //================再把来XML文档,以XML形式显示在ListBox里面
  
  双击"XML文档" 写进下面这些代码:
  
  ListBox1.Items.Clear()
  
  ' 清空listBox
  Dim xtr As XmlTextReader = New XmlTextReader("myxml.xml")
  
  '创建成一个XmlTextReader读取"myxml.xml"文档
  While xtr.Read
  Select Case (xtr.NodeType)
  
  ' 咱们用select case 形式来选择xml节点类型
  Case XmlNodeType.XmlDeclaration
  
  '先从ListBox里写进xml声明=====xmldeclaration
  ListBox1.Items.Add("<?xml version='1.0' encoding='gb2312'?>")
  
  '再依次显示节点的名称,值
  
  '包括根节点
  Case XmlNodeType.Element
  ListBox1.Items.Add("<" & xtr.Name & ">")
  Case XmlNodeType.Text
  ListBox1.Items.Add(xtr.Value)
  Case XmlNodeType.EndElement
  ListBox1.Items.Add("</" & xtr.Name & ">")
  
  End Select
  End While
  xtr.Close()
  
  '关闭xmlTextReader
  
  //========再把数据库中所有数据显示在ListBox中========
  
  '双击"查看全部"按钮
  
  '写入下面的一些代码:
  
  ListBox1.Items.Clear()
  
  '这些代码大家应该可以看得懂了
  OleDbConnection1.Open()
  Dim selall As String
  selall = "select * from users"
  OleDbCommand1 = New OleDbCommand
  Me.OleDbCommand1.CommandText = selall
  Me.OleDbCommand1.Connection = OleDbConnection1
  Try
  Dim creader As OleDbDataReader = OleDbCommand1.ExecuteReader()
  While creader.Read
  ListBox1.Items.Add("name: " & creader("nameid").ToString() & "; age :" & creader("age").ToString() & "; faverity :" & creader("faverity").ToString())
  End While
  creader.Close()
  Catch ex As Exception
  ListBox1.Items.Add("Errors")
  End Try
  OleDbConnection1.Close()
  
  //==========================再来进完成删除按钮=================
  
  '双击"删除"按钮
  
  '写入以下的代码
  
  If TextBox4.Text <> "" Then
  
  '如果不为空,进行以下操作
  ListBox1.Items.Clear()
  
  '先清空ListBox
  OleDbConnection1.Open()
  
  ' 建立连接
  Dim delstring As String
  delstring = TextBox4.Text
  Dim delsel As String
  delsel = "select * from users where nameid='" & delstring & "'"
  
  '创建查询字符串
  OleDbCommand1 = New OleDbCommand
  Me.OleDbCommand1.CommandText = delsel
  Me.OleDbCommand1.Connection = OleDbConnection1
  Try
  Dim selreader As OleDbDataReader = OleDbCommand1.ExecuteReader()
  If Not selreader.Read Then
  
  '假如读不到,就表明数据库无此数据,无法进行删除操作
  MessageBox.Show("数据库中无该记录!")
  Else
  selreader.Close()
  
  '要对数据进行操作,必须首把DataReader关掉
  Dim delrecord As String
  delrecord = "delete * from users where nameid='" & delstring & "'"
  
  '建立删除字符串sql语句,以上都是
  OleDbCommand1 = New OleDbCommand
  Me.OleDbCommand1.CommandText = delrecord
  Me.OleDbCommand1.Connection = OleDbConnection1
  Me.OleDbCommand1.ExecuteNonQuery()
  Me
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