Catch NullReferenceException Or Test For Nothing First?
Nov 12, 2010
We have a property whose job is to look up a description. If the lookup fails it should show an empty string.
So we can code the property like this:
If foo.bar Is Not Nothing Then
Return foo.bar.Description
Else
[Code]....
But are there any problems (performance, purity, other?) with just catching and ignoring the error?
You sometimes read it's expensive to throw an exception but I am not sure whether the author means it's expensive to build in exceptions using the Throw keyword (which I am not doing) or whether he means it's expensive to allow exceptions to occur (as I would be doing).
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Oct 19, 2009
Tell me if this is efficient code. or if there would be a more efficient way of doing this:
CODE:
I'm wondering if error catching will take more. time than a few more lines of code to accomplish the same.
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Feb 19, 2012
MVC3, VB.NET, using EF. I am working on coding up a simple function to handle checking for a valid MySQL connection. If the connection fails the test it will use the secondary server connection. This is required because our hosting provider does not provide failover or redundant MySQL servers. The problem is I tried to use a simple try catch method in the HomeController. This fails early because the Entity Framework is looking the connection that was set up when I set it up... Is there anyway to control that connection dynamically?
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Mar 25, 2011
I have a program in VB.Net that receives mails from Outlook, extracts attachments and inserts the attachments into a table through a query. I would like to put the query/queries in a Try/Catch block, but cannot do so as Outlook exceptions cannot be caught, and it gives me an error, and unless I put a very specific exception, I cannot catch it. Is there a workaround?
Edit:
Try
Catch ex As Exception
End Try
Exception is underlined and when I hover on it, it says: "Catch cannot catch type 'Microsoft.Office.Interop.Outlook.Exception' because it is not in 'System.Exception' or a class that inherits from 'System.Exception'". This is affecting all my other code which I'd like to put into a Try/Catch block.
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Jun 19, 2012
The following code causes a "Warning" that Variable is used before value assigned.How do I restructure this Try/catch to eliminate error on the myreader.close command in the Catch part? Code appears to work fine but I dont like Warnings. [code]
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Apr 1, 2011
i have problem when i click a ADD button, there is one null value in the textbox .. so the try catch statemnt is to catch that null value error but after that the catch is success but the button click never stop excute the statemnt till the end of the button event.
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Mar 4, 2009
I have this scenario: in a Sub I have a Try...Catch statement.Within that Try..Catch I call another sub.In that 2nd sub is also a Try...Catch.(see below for example).Now if an exception occurs in the 2nd sub's Try...Catch, which Catch gets excecuted? The 2nd one, the 1st one or both?
Private Sub sub1()
Try
..do stuff[code].....
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Jun 2, 2009
If I throw an exception from within a catch, does the finally (from the catch) still execute? i.e.
Try
..some code with an exception in it...
catch ex as Exception
throw new SpecialException("blah blah" & ex.Message, ex)
[code]....
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Jan 23, 2012
I need to catch log4net exceptions (its own exceptions not app exceptions logged by it). I wish there's a way of doing it this way: [code] I have this code implemented and there's no errors in compilation but i force log4net to have an error (pointing to a non existing database in the config file) and nothing is threw.I've tried the listener aproach: [code] and it's writing the errors to log4net.txt, the forced ones i mean.This last aproach has a couple of drawbacks: it won't append every error to the file, if the error is the same it doesn't write it, i can't get the listener to write every error to that file, only one (I don't know how to fully configure the trace listener, it might be that). Thus it won't append the date and hour to every line wich is a necesity for me. Finally i can't give structure to it (xml). Even if the listener work i need to use the try/catch aproach, since i'm using ExceptionHandling from Enterprise library to log the errors in my app.
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Sep 25, 2010
I don't understand the error, Argument not specified for parameter 'test' of 'Public Shared Function TestThis(test As String)'.
Partial Public Class Form1
Shared Sub ReceiveCallback(ByVal ar As IAsyncResult)
Form1.Invoke(TestThis, New Object(){"test"}) 'error
[code].....
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Feb 12, 2010
I am using VB.NET 2005 to create a Windows forms application. I have a procedure named SendMail that creates an instance of Outlook.Application, to send an email from my application. I found the code on this forum, I think.The procedure works fine, but I can't use error handling with it.I call the procedure from a button click event. I put the procedure call in a try/catch block, and the application won't build, with the following error.
Error 68 'Catch' cannot catch type 'Microsoft.Office.Interop.Outlook.Exception' because it is not 'System.Exception' or a class that inherits from 'System.Exception'. C:datadevdmtiQTSQTSv7_1_20100212wQTSQTSReportsCriteria
pt_frmReportViewer.vb 43 21 QTS
Here is the code:
Sub SendMail(ByVal sFile As String)
' Create an Outlook application.
Dim oApp As Outlook._Application
[code]....
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May 25, 2009
[code]...
and from VB6 project I reference to Test.dll but an error messege was appear A reference to Test.dll file could not be added (If I create VB NET project and reference to file Test.dll it OK )
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Aug 10, 2010
I'm getting 'Catch' cannot catch type 'Object' because it is not 'System.Exception' or a class that inherits from 'System.Exception'. and 'Expression detected' Code underlined in blue: Catch obj1 As Object When (?)
Private Sub OpenJAMem()
Dim num3 As Integer
Try
[code]....
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Sep 20, 2011
Probably a dumb question, but can you write a unit test project in one language to test against another project in a different language?I'd like to translate one of our VB assemblies into C#, but want to build unit tests to verify the results. I've tried to set a unit test project up to do this, but I can't seem to access the VB code within a unit test... I can't figure out if I'm just missing/doing something stupid, or it really isn't allowed.
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Apr 16, 2012
I have a project converted from Visual Studio 2005 to Visual Studio 2010. It compiles and runs.
When I prune "unused references's from this project as listed by Visual Studio, the project fails to compile with the subject error message.
In particular one of the "unused refererences" is to "Microsoft.VisualBasic.dll". The IDE does not allow me to add back this particular reference.
What do I need to add back as a referenceto get this items?
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Apr 20, 2010
A few weeks back in reply to a thread, I said then that it's sometimes worse to use a Try/Catch when there's nothing in the Catch!There are exceptions to that I'm sure, but too often the Try/Catch is used with a blank Catch that makes even the developer scratch their heads when the program crashes because they have nothing to go on (by their own doing).DevExpress (and I'm a big fan of their stuff) has a little three minute video that encapsulates that concept well and I thought that you all might enjoy watching it:[URL]
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Feb 17, 2010
I understand how try-catch works and how try-finally works, but I find myself using those (usually) in two completely different scenarios:
try-finally (or using in C# and VB) is mostly used around some medium-sized code block that uses some resource that needs to be disposed properly.
try-catch is mostly used either
around a single statement that can fail in a very specific way or (as a catch-all) at a very high level of the application, usually directly below some user interface action.
In my experience, cases where a try-catch-finally would be appropriate, i.e., where the block in which I want to catch some particular exception is exactly the same block in which I use some disposable resource, are extremely rare. Yet, the language designers of C#, VB and Java seem to consider this to be a highly common scenario; the VB designers even think about adding catch to using.
Or am I just overly pedantic with my restrictive use of try-catch?
EDIT: To clarify: My code usually looks like this (functions unrolled for clarity):
Try
do something
Aquire Resource (e.g. get DB connection)
Try
[Code]....
which just seems to make much more sense than putting any of the two catches on the same level as finally just to avoid indentation.
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Oct 21, 2010
I am getting a NullReferenceException was unhandled error when i run my debugging in this part of my code:Dim x As Integer = Val(index.Chars(0))
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Sep 19, 2011
This never happened to me, and the less data one has (usually) the less you can say what happened.I am trying to write a simple query analyser. I randomly receive these kind of crashes:
[Code]...
The file specified above does not exist. The place where it crashes is wrapped with Try-End Try. Moreover, yes, I have the painting event set up but it should not concern it (or maybe it does?). I have to add that I use visual basic express edition. The error occurs ocasionally - sometimes when I'm lucky nothing happens, and when I'm not then I get this crash.
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Apr 5, 2011
When I debug a program my IDE simply does not catch System.NullReferenceException - execution continues as if there were nothing wrong.Moreover, when I go to the menu Debug/Exceptions System.NullReferenceException is not even in the list(Common Language Runtime Exceptions).
I manually add it (there is the Add button) and I put a checkmark in the 'Thrown' and 'User unhandled' column - now IDE catches it, but after I re-load the project the situation re-appears - and NullReferenceException is not on the list again. What may be wrong?
Update:No, when I step through the code the execution does not continue but exits the current block of code (sub or function). There were no Try...Catch blocks and there is a message: A System.NullReferenceException occured in MSCorlib.dll... But why doesn't the debugger stop at this line?
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Jun 8, 2010
How can I get a NullReferenceException in the following scenario?
Dim langs As IEnumerable(Of SomeCustomObject) = //some LINQ query
If langs Is Nothing Then Return Nothing
If langs.Count = 1 Then //NullReferenceException here
What am I missing here? Debug shows that langs is really just a LINQ queryresult without any results...
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Nov 21, 2009
Okay after searching two listbox's on a form I am trying to put a number as a string in a label setup for that but keep exgetting a NullReferenceexception error on the label. Label being "shippingDataLabel.text".e is my code;
Public Class MainForm
Dim fifteenShipping As Integer = 15
Dim twentyShipping As Integer = 20
[code].....
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Jul 25, 2011
I have a VB.NET solution that I just upgraded. It was originally in .NET 1.1, I upgraded to .NET 2.0 and verified that it would build and run correctly. Then I upgraded from 2.0 to 4.0. It is still building with no errors, but when I try to run I am getting a NullReferenceException in Global.asax.vb. The really weird thing is, the line that is throwing the exception is this:
Dim dt As System.Data.DataTable I am not trying to use the variable, just declare it. Further down a Function is called that returns a DataTable and sets the variable, but I don't even get to that line. It is throwing the NullReferenceException on the Dim line. Has anyone run across this before? Is this some issue with upgrading?
[Code]...
I did a Rebuild Solution before posting. This is a web application and the only files I see in the bin folder are the dll files I am referencing. I'm not sure what else I should clean up.
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Mar 16, 2009
I've seen so many posts on this but I just don't understand how to fix it.
HTML
Me.txtDeletedItem.Text = objDeleteLog.Name
[b]Me.txtDeleteReason.Text = objDeleteLog.Code.Description[/b]
[code]....
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Jan 25, 2012
vb
Imports System.Windows.Forms.HtmlDocument
Public Class test_vbdotnet
Private Sub runtime()
[Code].....
I want VB.NET to get access to the innerText and make a if statement out of it. But it always returns error. (see the comments for details.)
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Nov 30, 2010
This is driving me slighty madder than i usually am. The thing thats bugging me is the EXACT same code works in a test project i did with an sdf database.See my comments in the code
vb Private Sub tbScan_KeyUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles tbScan.KeyUp
[Code]...
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May 7, 2011
VB
Dimserial As New Processserial.StartInfo.FileName = "adb"serial.StartInfo.Arguments = "get-serialno"serial.StartInfo.UseShellExecute = Falseserial.StartInfo.RedirectStandardOutput =
[code].....
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Feb 24, 2010
I've got a little problem here:
Code:
Dim DirInfo As IO.DirectoryInfo = Nothing
... some code ...
Me.Tag = DirInfo.FullName
In this code, DirInfo.FullName is sometimes null. So I put this code inside a Try Catch. Although it works fine but I see a System.NullReferenceException in Immediate Windows. I just want to prevent it.
So tried:
If DirInfo.FullName IsNot Nothing Then Me.Tag = DirInfo.FullName
If DirInfo.FullName <> Nothing Then Me.Tag = DirInfo.FullName
If DirInfo.FullName <> "" Then Me.Tag = DirInfo.FullName
But I still get this System.NullReferenceException! How should I check DirInfo.FullName so I prevent this exception?
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May 12, 2009
I keep getting a NullReferenceException error on this UNZIP code:
Dim Sh As New Shell
Dim SF As Folder = Sh.NameSpace("C:\test.zip")
Dim DF As Folder = Sh.NameSpace("C:\test")
[Code]....
i checked to see if i had a test.zip file in my root dir...its there... i have shell32 referenced
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Jul 21, 2011
I am trying to flatten a multi-dimensional array with ConvertAll but I can't get it to work:
Private Function Flatten(ByRef a As Object) As Object
Dim elements As Integer = 0
Dim size As Integer[code]...
Why does it throw NullReferenceException?
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