vb.net interview questions
Top vb.net frequently asked interview questions
Should you set all the objects to null (Nothing in VB.NET) once you have finished with them?
I understand that in .NET it is essential to dispose of any instances of objects that implement the IDisposable interface to release some resources although the object can still be something after it is disposed (hence the isDisposed property in forms), so I assume it can still reside in memory or at least in part?
I also know that when an object goes out of scope it is then marked for collection ready for the next pass of the garbage collector (although this may take time).
So with this in mind will setting it to null speed up the system releasing the memory as it does not have to work out that it is no longer in scope and are they any bad side effects?
MSDN articles never do this in examples and currently I do this as I cannot
see the harm. However I have come across a mixture of opinions so any comments are useful.
Source: (StackOverflow)
If I am given a MemoryStream that I know has been populated with a String, how do I get a String back out?
Source: (StackOverflow)
How do I get a human-readable file size in bytes abbreviation using .NET?
Example:
Take input 7,326,629 and display 6.98 MB
Source: (StackOverflow)
How to calculate the difference in months between two dates in C#?
Is there is equivalent of VB's DateDiff() method in C#. I need to find difference in months between two dates that are years apart. The documentation says that I can use TimeSpan like:
TimeSpan ts = date1 - date2;
but this gives me data in Days. I don't want to divide this number by 30 because not every month is 30 days and since the two operand values are quite apart from each other, I am afraid dividing by 30 might give me a wrong value.
Any suggestions?
Source: (StackOverflow)
In most of programming languages, dictionaries are preferred over hashtables.
What are the reasons behind that?
Source: (StackOverflow)
I have a .NET application which has different configuration files for Debug and Release builds. E.g. the debug app.config file points to a development SQL Server which has debugging enabled and the release target points to the live SQL Server. There are also other settings, some of which are different in debug/release.
I currently use two separate configuration files (debug.app.config and release.app.config). I have a build event on the project which says if this is a release build then copy release.app.config to app.config, else copy debug.app.config to app.config.
The problem is that the application seems to get its settings from the settings.settings file, so I have to open settings.settings in Visual Studio which then prompts me that the settings have changed so I accept the changes, save settings.settings and have to rebuild to make it use the correct settings.
Is there a better/recommended/preferred method for achieving a similar effect? Or equally, have I approached this completely wrong and is there a better approach?
Source: (StackOverflow)
So I am learning MSIL right now to learn to debug my C# .NET applications.
I've always wondered: what is the purpose of the stack?
Just to put my question in context:
Why is there a transfer from memory to stack or "loading?"
On the other hand, why is there a transfer from stack to memory or "storing"?
Why not just have them all placed in the memory?
- Is it because it's faster?
- Is it because it's RAM based?
- For efficiency?
I'm trying to grasp this to help me understand CIL codes much more deeply.
Source: (StackOverflow)
I like instantiating my WCF service clients within a using block as it's pretty much the standard way to use resources that implement IDisposable:
using (var client = new SomeWCFServiceClient())
{
//Do something with the client
}
But, as noted in this MSDN article, wrapping a WCF client in a using block could mask any errors that result in the client being left in a faulted state (like a timeout or communication problem). Long story short, when Dispose() is called, the client's Close() method fires, but throws an error because it's in a faulted state. The original exception is then masked by the second exception. Not good.
The suggested workaround in the MSDN article is to completely avoid using a using block, and to instead instantiate your clients and use them something like this:
try
{
...
client.Close();
}
catch (CommunicationException e)
{
...
client.Abort();
}
catch (TimeoutException e)
{
...
client.Abort();
}
catch (Exception e)
{
...
client.Abort();
throw;
}
Compared to the using block, I think that's ugly. And a lot of code to write each time you need a client.
Luckily, I found a few other workarounds, such as this one on IServiceOriented. You start with:
public delegate void UseServiceDelegate<T>(T proxy);
public static class Service<T>
{
public static ChannelFactory<T> _channelFactory = new ChannelFactory<T>("");
public static void Use(UseServiceDelegate<T> codeBlock)
{
IClientChannel proxy = (IClientChannel)_channelFactory.CreateChannel();
bool success = false;
try
{
codeBlock((T)proxy);
proxy.Close();
success = true;
}
finally
{
if (!success)
{
proxy.Abort();
}
}
}
}
Which then allows:
Service<IOrderService>.Use(orderService =>
{
orderService.PlaceOrder(request);
});
That's not bad, but I don't think it's as expressive and easily understandable as the using block.
The workaround I'm currently trying to use I first read about on blog.davidbarret.net. Basically you override the client's Dispose() method wherever you use it. Something like:
public partial class SomeWCFServiceClient : IDisposable
{
void IDisposable.Dispose()
{
if (this.State == CommunicationState.Faulted)
{
this.Abort();
}
else
{
this.Close();
}
}
}
This appears to be able to allow the using block again without the danger of masking a faulted state exception.
So, are there any other gotchas I have to look out for using these workarounds? Has anybody come up with anything better?
Source: (StackOverflow)
I have found several open-source/freeware programs that allow you to convert .doc files to .pdf files, but they're all of the application/printer driver variety, with no SDK attached.
I have found several programs that do have an SDK allowing you to convert .doc files to .pdf files, but they're all of the proprietary type, $2,000 a license or thereabouts.
Does anyone know of any clean, inexpensive (preferably free) programmatic solution to my problem, using C# or VB.NET?
Thanks!
Source: (StackOverflow)
I have some code and when it executes, it throws a NullReferenceException, saying:
Object reference not set to an instance of an object.
What does this mean, and what can I do about it?
Source: (StackOverflow)
Question: I want to define a global exception handler for unhandled exceptions in my console application. In asp.net, one can define one in global.asax, and in windows applications /services, one can define as below
AppDomain currentDomain = AppDomain.CurrentDomain;
currentDomain.UnhandledException += new UnhandledExceptionEventHandler(MyExceptionHandler);
But how can I define a global exception handler for a console application ?
currentDomain seems not to work (.NET 2.0) ?
Edit:
Argh, stupid mistake.
In VB.NET, one needs to add the "AddHandler" keyword in front of currentDomain, or else one doesn't see the UnhandledException event in IntelliSense...
That's because the VB.NET and C# compilers treat event handling differently.
Source: (StackOverflow)
I have two objects in C# and don't know if it's Boolean or any other type.
However when I try to compare those C# fails to give the right answer.
I have tried the same code with VB.NET and that did it !
Can anyone tell me how to fix this if there is a solution ?
C#:
object a = true;
object b = true;
object c = false;
if (a == b) c = true;
MessageBox.Show(c.ToString()); //Outputs False !!
VB.NET:
Dim a As Object = True
Dim b As Object = True
Dim c As Object = False
If (a = b) Then c = True
MessageBox.Show(c.ToString()) '// Outputs True
Source: (StackOverflow)