What is the difference between adding cleanup code in finally block and cleanup code after the catch block ?
try
{
//some code
}
catch
{
}
finally
{
//cleanup
}
and
try
{
//some code
}
catch
{
}
//cleanup
If you throw a throwable from the try .. catch block that is not caught by this catch, the cleanup code inside the finally clause will execute and the code immediately after the catch block will not.
In your second case if the code rethrows an exception or return from the catch block then your cleanup code will not be called. In case of finally block it will be executed even if you have an exception or a return statement from the catch block.
The MSDN says:
By using a finally block, you can clean up any resources that are
allocated in a try block, and you can run code even if an exception
occurs in the try block. Typically, the statements of a finally block
run when control leaves a try statement. The transfer of control can
occur as a result of normal execution, of execution of a break,
continue, goto, or return statement, or of propagation of an exception
out of the try statement.
Related
In my application I am getting System.NullReferenceException for my REST call.
This Error is caused by code inside Catch block.
Is it a good idea to put another try catch block inside Catch block?
In the below code following line of code in Catch block is throwing error.
resultObject.ErrorResponse = _client.GetErrorResponse(Of List(Of ErrorResponseObject))(ex, "{""errors"":")
How do I fix this issue, so that user doesn't see any error.
Here is my code.
Public Shared Function POSTCall()
_client = New BaseClient()
Try
strJsonResponse = _client.ExecuteURI(serviceUrl, requestHeader, "POST", resultObject, False, False)
Catch ex As WebException
resultObject.ErrorResponse = _client.GetErrorResponse(Of List(Of ErrorResponseObject))(ex, "{""errors"":") 'This line causing error
If Not IsNothing(resultObject.ErrorResponse) Then
' do some work
End If
Catch Exp As Exception
'Supress the error. Let user goto next step.
Finally
_client = Nothing
End Try
Return resultObject
End Function
You have to catch the error Inside the catch block. This is especially appropriate since what the code is trying to do is to get more info about an error that has already occurrred. Of course, it might be a good idea to log any error occurring, even if the application can continue.
I prefer doing things that are not asynchronous inside the catch. In a case where I need to perform an asynchronous function say rolling back a database transaction, I'll just throw the error and have another asynchronous function handle it in it's catch block in a synchronous way
I am working on a Windows Store (C++) app. This is a method that reads from the database using the web service.
task<std::wstring> Ternet::GetFromDB(cancellation_token cancellationToken)
{
uriString = ref new String(L"http://myHost:1234/RestServiceImpl.svc/attempt");
auto uri = ref new Windows::Foundation::Uri(Helpers::Trim(uriString));
cancellationTokenSource = cancellation_token_source();
return httpRequest.GetAsync(uri, cancellationTokenSource.get_token()).then([this](task<std::wstring> response)->std::wstring
{
try
{
Windows::UI::Popups::MessageDialog wMsg(ref new String(response.get().c_str()), "success");
wMsg.ShowAsync();
return response.get();
}
catch (const task_canceled&)
{
Windows::UI::Popups::MessageDialog wMsg("Couldn't load content. Check internet connectivity.", "Error");
wMsg.ShowAsync();
std::wstring abc;
return abc;
}
catch (Exception^ ex)
{
Windows::UI::Popups::MessageDialog wMsg("Couldn't load content. Check internet connectivity.", "Error");
wMsg.ShowAsync();
std::wstring abc;
return abc;
}
} , task_continuation_context::use_current());
}
I'm confused how to return the received data to the calling function. Now, I am calling this function in the constructor of my data class like this:
ternet.GetFromDB(cancellationTokenSource.get_token()).then([this](task<std::wstring> response)
{
data = ref new String(response.get().c_str());
});
I am getting a COM exception whenever I try to receive the returned data from GetFromDB(). But this one runs fine:
ternet.GetFromDB(cancellationTokenSource.get_token());
Please suggest a better way of chaining the completion of GetFromDB to other code. And how to get the returned value from inside the try{} block of GetFromDB() 's then. Please keep in mind I am a very new student of async programming.
If the continuation of the call to GetFromDB is happening on the UI thread (which I believe it will by default, assuming the call site you pasted is occurring in the UI thread), then calling get() on the returned task will throw an exception. It won't let you block the UI thread waiting for a task to finish.
Two suggestions, either of which should fix that problem. The first should work regardless, while the second is only a good option if you're not trying to get the response string to the UI thread (to be displayed, for example).
1) Write your continuations (lambdas that you pass to then) so that they take the actual result of the previous task, rather than the previous task itself. In other words, instead of writing this:
ternet.GetFromDB(...).then([this](task<std::wstring> response) { ... });
write this:
ternet.GetFromDB(...).then([this](std::wstring response) { ... });
The difference with the latter is that the continuation machinery will call get() for you (on a background thread) and then give the result to your continuation function, which is a lot easier all around. You only need to have your continuation take the actual task as an argument if you want to catch exceptions that might have been thrown by the task as it executed.
2) Tell it to run your continuation on a background/arbitrary thread:
ternet.GetFromDB(...).then([this](task<std::wstring> response) { ... }, task_continuation_context::use_arbitrary());
It won't care if you block a background thread, it only cares if you call get() on the UI thread.
I want to redirect to another page using Server.Transfer and I have this simple code:
if (Page.IsPostBack)
{
try
{
Server.Transfer("AnotherPage.aspx");
}
catch (Exception)
{
throw ;
}
}
But I'm getting an error: "Error executing child request for AnotherPage.aspx.". Could not find the solution on the net.
Just to mention, Response.Redirect works flawlessly.
The error is likely caused by something in AnotherPage.aspx. You may want to insert a try... catch handler in AnotherPage.aspx's Load event.
I am getting an error:
"Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack."
when I am redirecting my page from one to another.
I am using this code:
try
{
Session["objtwitter"] = obj_UserDetSumit;
Response.Redirect("TwitterLogin.aspx");
}
catch (Exception ex)
{
lblStatus.Text = "Account Creation Failed, Please Try Again";
}
And I got a solution and I tried also this Response.Redirect("home.aspx",false);
It's not throwing an error but it's also not redirecting page.
Try - catch creates a thread around code within it in order to catch exceptions. When you Redirect you are effectively terminating execution of the thread thus causing an error since execution ended unnaturely (though this is by design). You should not Redirect from within try-catch and if you do you should use Response.Redirect( "some url", false ); and also specifically catch ThreadAbortException.
Reference here: http://msdn.microsoft.com/en-us/library/t9dwyts4.aspx
Response.Redirect calls the Response.End, which throws a ThreadAbortException, so you'd want to change your code to:
try
{
Response.Redirect("home.aspx");
}
catch(System.Threading.ThreadAbortException)
{
// do nothing
}
catch(Exception ex)
{
// do whatever
}
First, make sure that you are working with a debug build and not a release build of your project. And second, make sure that you are debugging in mixed mode (both managed and native) so that you can see all of the current call stack.
I'd try moving your Response.Redirect outside of the try catch block like this:
try
{
Session["objtwitter"] = obj_UserDetSumit;
}
catch (Exception ex)
{
lblStatus.Text = "Account Creation Failed, Please Try Again";
return;
}
Response.Redirect("TwitterLogin.aspx");
Most people having this issue here resolved it with calling Response.Redirect("TwitterLogin.aspx", false); which doesn't explicitly kill the thread immediately. I'm not sure why this didn't work for you.
I think the issue is having your Response.Redirect inside of a try catch block. Calling Response.Redirect(url); calls Response.End();, which will throw a ThreadAbortException.
Make sure you're not trying to do any more processing after you do your redirect.
Using Reflector, you can see that Response.Redirect(url); calls Response.Redirect(url, true);
Passing true then calls Response.End(); which looks like this:
public void End()
{
if (this._context.IsInCancellablePeriod)
{
InternalSecurityPermissions.ControlThread.Assert();
Thread.CurrentThread.Abort(new HttpApplication.CancelModuleException(false));
}
....
}
Even though you don't have a finally in your code snippet, it may be trying to execute the "empty" finally, but can't because the thread is being aborted. Just a thought.
If you replace your code these line you won't get an exception in the first place
try
{
Response.Redirect("home.aspx", False);
//Directs the thread to finish, bypassing additional processing
Context.ApplicationInstance.CompleteRequest();
}
catch(Exception ex)
{
// exception logging
}
Hope it helps
I seem to be missing some information from my stack trace, here is what i'm getting:
at Foo.Bar(DataTable table) in D:\Foo\Bar\authoring\App_Code\FooBar.vb:line 87
Where is the rest of the stack trace infomation?
EDIT:
Custom errors in the Web.Config is set to off, i'm handling the error where it's caught like this:
Catch ex As Exception
Respose.Write(ex.StackTrace)
End Try
The Stack Trace is still getting truncated.
Make sure customErrors is set to "RemoteOnly" or "Off" in your web.config to disable friendly errors.
Or possibly stack trace getting reset? (Although if this was the case you still should see something)
Will reset your stack trace.
catch(Exception ex)
{
throw ex;
}
Will NOT reset your stack trace.
catch(Exception ex)
{
throw;
}
EDIT:
ex.StackTrace gets the current stack. The stacktrace starts
where the exception was thrown(error happens) and ends at the current stack frame where the exception is caught. So it is reversing the call stack. Since you are writing out stacktrace as soon as it happens it doesn't get a chance to go any further up the callstack.
Depending on what you are doing you can try a few things.
//To just see the stackTrace
Catch ex As Exception
Throw
End Try
Environment.StackTrace - Gets current stack trace information
//If you are trying to log the stacktrace
Catch ex As Exception
Respose.Write(Environment.StackTrace)
Respose.Write(ex.StackTrace)
End Try
//If is hiding then try - hiding as in throw ex vs just throw
Catch ex As Exception
//careful innerException can be null
//so need to check before using it
Respose.Write(ex.InnerException)
End Try
One of those methods should work for you.