vb.net学习

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Public Class Form_main

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim sqlcon As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\VB.mdb;Persist Security Info=False"
Dim con As New System.Data.OleDb.OleDbConnection(sqlcon)
con.Open()

Try
Dim sql_select As String = "select * from table1 order by id asc"
Dim cmd_id As New System.Data.OleDb.OleDbCommand(sql_select, con)
Dim drs As System.Data.OleDb.OleDbDataReader
drs = cmd_id.ExecuteReader()
drs.Read()
Dim id As String
id = drs.GetInt32(0)
MessageBox.Show(id)
Catch ex As Exception
MessageBox.Show(ex.Message())
End Try

Try
Dim sql1 As String = "insert into table1 values(1,'XC')"
Dim cmd As New System.Data.OleDb.OleDbCommand(sql1, con)
cmd.ExecuteReader()
Catch ex As Exception
MessageBox.Show("插入数据失败，ID号不能重复")
End Try


Dim sql As String = "select * from table1"
Dim cmd2 As New System.Data.OleDb.OleDbCommand(sql, con)
Dim dr As System.Data.OleDb.OleDbDataReader
dr = cmd2.ExecuteReader()
Dim str As String
While dr.Read()
str += dr.GetInt32(0).ToString()
str += " "
str += dr.GetString(1)
str += "\\n"
End While
MessageBox.Show(str)

dr.Close()
con.Close()
End Sub

Private Sub TreeView1_MouseDoubleClick(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs)
MessageBox.Show("OK")
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
PictureBox1.Refresh()
Dim size As Drawing.Size
size = PictureBox1.Size()
PictureBox1.CreateGraphics().DrawLine(Pens.Blue, New Point(0, 0), New Point(size.Width / 3 * 2, size.Height / 3 * 2))
End Sub

Private Sub PictureBox1_SizeChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PictureBox1.SizeChanged
PictureBox1.Refresh()
Dim size As Drawing.Size
size = PictureBox1.Size()
Dim pen As New System.Drawing.Pen(System.Drawing.Color.Blue, 1)
pen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dash
PictureBox1.CreateGraphics().DrawLine(pen, New Point(0, 0), New Point(size.Width / 3 * 2, size.Height / 3 * 2))
PictureBox1.CreateGraphics.DrawLine(pen, New Point(0, 10), New Point(100, 10))
End Sub

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
Dim str As String
str = TextBox1.Text()
TextBox1.Text() = "aec"
MessageBox.Show(str)
End Sub

Private Sub Form_main_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
TreeView1.Nodes.Add("PA")
TreeView1.Nodes(0).Nodes.Add("P")
TreeView1.Nodes(0).Nodes.Add("A")
End Sub
End Class