如何在 vb.net 中使用 try catch 和 finally 块？
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How do I use try catch and finally block in vb.net?
提问by Shaikh Nadeem
Below is the code in which I wanted to use try catch and finally block But I am unable to do the same , I am new in programming, Please help me to introduce try catch and finally block in the below code in vb.net, Also help to code for finally block where I will be checking whether connection is open or not , I Connection is open then it should be closed in finally block but after checking . If
下面是我想在其中使用 try catch 和 finally 块的代码但我无法这样做，我是编程新手，请帮助我在 vb.net 中的以下代码中介绍 try catch 和 finally 块，另外帮助为 finally 块编写代码，我将在其中检查连接是否打开，我连接已打开，然后它应该在 finally 块中关闭，但在检查之后。如果
conditions..
状况..
else
'Try
con.Open()
adp = New OleDbDataAdapter("select * from Login ", con)
adp.Fill(dt, "Login")
Dim i As Integer
For i = 0 To dt.Tables(0).Rows.Count - 1
If (cbType.Text = dt.Tables(0).Rows(i).Item(1) And txtUname.Text = dt.Tables(0).Rows(i).Item(2) And txtPass.Text = dt.Tables(0).Rows(i).Item(3)) Then
MDIParent1.Show()
Exit Sub
End If
' Catch ex As Exception
Next
MsgBox("You Are Not A Valid User!!", MsgBoxStyle.Information)
End If
回答by Vishal
It is very simple.
这很简单。
Just see the code below.
请看下面的代码。
Try
'In this block your program will try to execute your code.
'If it catches any runtime error it will go to the Catch Block straight away without executing the next code in your Try Block.
'If there are no errors then Finally Block will be executed after Try Block. Catch Block will be skipped.
Catch
'It will display the errors here.
'So you can use Catch ex as exception.
'If you want to see the errors in Messagebox you can write the below line.
'MessageBox.Show(ex.Message)
Finally
'If your program finds errors or not this block will be executed always.
End Try
So you can use Try...Catch in your code as follows :
所以你可以在你的代码中使用 Try...Catch 如下：
Dim ValidUser as Boolean = False
Try
con.Open()
adp = New OleDbDataAdapter("select * from Login ", con)
adp.Fill(dt, "Login")
Dim i As Integer
For i = 0 To dt.Tables(0).Rows.Count - 1
If (cbType.Text = dt.Tables(0).Rows(i).Item(1) And txtUname.Text = dt.Tables(0).Rows(i).Item(2) And txtPass.Text = dt.Tables(0).Rows(i).Item(3)) Then
ValidUser = true
Exit For
End If
Next
If ValidUser = True
MDIParent1.Show()
Else
MsgBox("You Are Not A Valid User!!", MsgBoxStyle.Information)
End If
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
if con.State = ConnectionState.Open then
con.close()
End If
ValidUser = False
End Try
