问题描述
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
If ComboBox1.SelectedValue.ToString() <> " " Then
Dim Country_id As Integer = Convert.ToString(ComboBox1.SelectedValue.ToString())
fillstate(Country_id)
ComboBox3.SelectedIndex = 0
End If
End Sub
Private Sub fillstate(ByVal Country_id As Integer)
Dim adpt As New SqlDataAdapter
Dim ds As New DataSet
Dim con As New SqlConnection
con.ConnectionString = str
cmd = New SqlCommand("SELECT S_id,S_name from state where C_id=@C_id", con)
cmd.Parameters.AddWithValue("@C_id", Country_id)
adpt.SelectCommand = cmd
adpt.Fill(ds)
If ds.Tables(0).Rows.Count > 0 Then
ComboBox2.ValueMember = "S_id"
ComboBox2.DisplayMember = "S_name"
ComboBox2.DataSource = ds.Tables(0)
End If
以上代码使用参数作为整数ie，country_id作为整数
如果我使用country_id作为字符串我应该更正使其作为参数传递
the above code is used arguments as integer ie,country_id as integer
if i use country_id as string where should i correct to make it pass as arguments
推荐答案
Dim Country_id As Integer = Convert.ToString(ComboBox1.SelectedValue.ToString())
fillstate(Country_id)有点......嗯......很奇怪。
Is a little...um...odd.
ComboBox1.SelectedValue可能已经是一个整数，特别是如果你直接从数据库中读取它。所以...
May be an integer already, particularly if you have read it directly form the DB. So...
ComboBox1.SelectedValue.ToString()使它成为一个字符串。所以...
Makes it a string. So...
Convert.ToString(ComboBox1.SelectedValue.ToString())将字符串转换为...一个字符串.. 。
Converts the string to...a string...
Dim Country_id As Integer = Convert.ToString(ComboBox1.SelectedValue.ToString())然后使用隐式转换将其更改为整数以传递给您的方法，这需要一个整数...
那么，为什么不首先将Value作为整数传递，或者在其上调用CInt以确保它是一个整数？
播放带有可变类型的音乐椅只是让你的代码更混乱，更不可靠的好方法......
Then uses an implicit conversion to change it to an integer to pass to your method, which takes an integer...
So, why not just pass the Value as an integer in the first place, or call CInt on it to ensure it is an integer?
Playing "musical chairs" with variable types is just a good way to make your code more confusing and less reliable...
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