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  • Why should I not wrap every block in "try"-"catch"?

    - by Konrad
    I have always been of the belief that if a method can throw an exception then it is reckless not to protect this call with a meaningful try block. I just posted 'You should ALWAYS wrap calls that can throw in try, catch blocks.' to this question and was told that it was 'remarkably bad advice' - I'd like to understand why. Thanks!

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  • Handling Java stdout and stderr in Perl

    - by syker
    I am trying to run a Java program from my Perl script. I would like to avoid using System.exit(1) and System.exit(-1) commands in Java. I am however printing to STDOUT and STDERR from Java. In my Perl script, I am reading from Java's stdout and using that line by line output. How do I print stderr and fail if I ever see stderr? This is what I have so far: my $java_command = ...; open(DATA, ">$java_command"); while (<DATA>) { chomp($_); .... .... }

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  • ELMAH - Using custom error pages to collecting user feedback

    - by vdh_ant
    Hey guys I'm looking at using ELMAH for the first time but have a requirement that needs to be met that I'm not sure how to go about achieving... Basically, I am going to configure ELMAH to work under asp.net MVC and get it to log errors to the database when they occur. On top of this I be using customErrors to direct the user to a friendly message page when an error occurs. Fairly standard stuff... The requirement is that on this custom error page I have a form which enables to user to provide extra information if they wish. Now the problem arises due to the fact that at this point the error is already logged and I need to associate the loged error with the users feedback. Normally, if I was using my own custom implementation, after I log the error I would pass through the ID of the error to the custom error page so that an association can be made. But because of the way that ELMAH works, I don't think the same is quite possible. Hence I was wondering how people thought that one might go about doing this.... Cheers UPDATE: My solution to the problem is as follows: public class UserCurrentConextUsingWebContext : IUserCurrentConext { private const string _StoredExceptionName = "System.StoredException."; private const string _StoredExceptionIdName = "System.StoredExceptionId."; public virtual string UniqueAddress { get { return HttpContext.Current.Request.UserHostAddress; } } public Exception StoredException { get { return HttpContext.Current.Application[_StoredExceptionName + this.UniqueAddress] as Exception; } set { HttpContext.Current.Application[_StoredExceptionName + this.UniqueAddress] = value; } } public string StoredExceptionId { get { return HttpContext.Current.Application[_StoredExceptionIdName + this.UniqueAddress] as string; } set { HttpContext.Current.Application[_StoredExceptionIdName + this.UniqueAddress] = value; } } } Then when the error occurs, I have something like this in my Global.asax: public void ErrorLog_Logged(object sender, ErrorLoggedEventArgs args) { var item = new UserCurrentConextUsingWebContext(); item.StoredException = args.Entry.Error.Exception; item.StoredExceptionId = args.Entry.Id; } Then where ever you are later you can pull out the details by var item = new UserCurrentConextUsingWebContext(); var error = item.StoredException; var errorId = item.StoredExceptionId; item.StoredException = null; item.StoredExceptionId = null; Note this isn't 100% perfect as its possible for the same IP to have multiple requests to have errors at the same time. But the likely hood of that happening is remote. And this solution is independent of the session, which in our case is important, also some errors can cause sessions to be terminated, etc. Hence why this approach has worked nicely for us.

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  • need to get the context value in top of page, where the context value will be set only at the bottom

    - by Mahadevan Alagar
    <script runat="server"> protected void Page_Load(object sender, EventArgs e) { Response.Write("Page Load:"); } public string setContext(string sName, string sVal) { HttpContext.Current.Items[sName] = sVal; return sVal; } public string getContext(string sName) { string sVal = "default"; if (HttpContext.Current.Items[sName] != null) sVal = HttpContext.Current.Items[sName].ToString(); else sVal = "empty"; return sVal; } </script> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Get Context in TOP ???</title> </head> <body> <div> <div id="divDest" name="divDest"> Top Content: Get1 :<%= getContext("topcontent") %> // returns "empty", BUT I Need "value to set" </div> <br /> Set1 : <%= setContext("topcontent", "value to set")%> <br /> // set the value <br /> Get2 : <%= getContext("topcontent") %><br /> // returns "value to set" <br /> <script language="javascript"> var elval = getElementVal("divTest"); document.getElementById("divDest").innerHTML = elval; //alert(elval); function getElementVal(elemid) { var elemval = document.getElementById(elemid); return elemval.innerHTML; } </script> </body> </html> I need to get the context value in top of page, where the context value will be set at the bottom of the page. Get context value == "empty", BUT need "something" Set context value to "something" Get context value == "something" I may use JS/AJAX, where the page source the value won't be present. BUT I need the TEXT in the View Source of the page too. Is there a way to wait for the context to set and then get, I have tried with User Control, prerender and render methods too. But I can't able to get it right. Any idea?

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  • Writing catch block with cleanup operations in Java ...

    - by kedarmhaswade
    I was not able to find any advise on catch blocks in Java that involve some cleanup operations which themselves could throw exceptions. The classic example is that of stream.close() which we usually call in the finally clause and if that throws an exception, we either ignore it by calling it in a try-catch block or declare it to be rethrown. But in general, how do I handle cases like: public void doIt() throws ApiException { //ApiException is my "higher level" exception try { doLower(); } catch(Exception le) { doCleanup(); //this throws exception too which I can't communicate to caller throw new ApiException(le); } } I could do: catch(Exception le) { try { doCleanup(); } catch(Exception e) { //ignore? //log? } throw new ApiException(le); //I must throw le } But that means I will have to do some log analysis to understand why cleanup failed. If I did: catch(Exception le) { try { doCleanup(); } catch(Exception e) { throw new ApiException(e); } It results in losing the le that got me here in the catch block in the fist place. What are some of the idioms people use here? Declare the lower level exceptions in throws clause? Ignore the exceptions during cleanup operation?

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  • Handling MVC2 variables with hyphens in their name

    - by Jaxidian
    I'm working with some third-party software that creates querystring parameters with hyphens in their names. I was taking a look at this SO question and it seems like their solution is very close to what I need but I'm too ignorant to the underlying MVC stuff to figure out how to adapt this to do what I need. Ideally, I'd like to simply replace hyphens with underscores and that would be a good enough solution. If there's a better one, then I'm interested in hearing it. An example of a URL I want to handle is this: http://localhost/app/Person/List?First-Name=Bob with this Controller: public ActionResult List(string First_Name) { {...} } To repeat, I cannot change the querystring being generated so I need to support it with my controller somehow. But how? For reference, below is the custom RouteHandler that is being used to handle underscores in controller names and action names from the SO question I referenced above that we might be able to modify to accomplish what I want: public class HyphenatedRouteHandler : MvcRouteHandler { protected override IHttpHandler GetHttpHandler(RequestContext requestContext) { requestContext.RouteData.Values["controller"] = requestContext.RouteData.Values["controller"].ToString().Replace("-", "_"); requestContext.RouteData.Values["action"] = requestContext.RouteData.Values["action"].ToString().Replace("-", "_"); return base.GetHttpHandler(requestContext); } }

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  • Extending Throwable in Java

    - by polygenelubricants
    Java lets you create an entirely new subtype of Throwable, e.g: public class FlyingPig extends Throwable { ... } Now, very rarely, I may do something like this: throw new FlyingPig("Oink!"); and of course elsewhere: try { ... } catch (FlyingPig porky) { ... } My questions are: Is this a bad idea? And if so, why? What could've been done to prevent this subtyping if it is a bad idea? Since it's not preventable (as far as I know), what catastrophies could result? If this isn't such a bad idea, why not? How can you make something useful out of the fact that you can extends Throwable?

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  • Handling Character Encoding in URI on Tomcat

    - by ZZ Coder
    On the web site I am trying to help with, user can type in an URL in the browser, like following Chinese characters, http://localhost:8080?a=?? On server, we get GET /a=%E6%B5%8B%E8%AF%95 HTTP/1.1 As you can see, it's UTF-8 encoded, then URL encoded. We can handle this correctly by setting encoding to UTF-8 in Tomcat. However, sometimes we get Latin1 encoding on certain browsers, http://localhost:8080?a=ß turns into GET /a=%DF HTTP/1.1 Is there anyway to handle this correctly in Tomcat? Looks like the server has to do some intelligent guessing. We don't expect to handle the Latin1 correctly 100% but anything is better than what we are doing now by assuming everything is UTF-8. The server is Tomcat 5.5. The supported browsers are IE 6+, Firefox 2+ and Safari on iPhone.

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  • Handling over-long UTF-8 sequences

    - by Grant McLean
    I've just been reworking my Encoding::FixLatin Perl module to handle over-long utf8 byte sequences and convert them to the shortest normal form. My question is quite simply "is this a bad idea"? A number of sources (including this RFC) suggest that any over-long utf8 should be treated as an error and rejected. They caution against "naive implementations" and leave me with the impression that these things are inherently unsafe. Since the whole purpose of my module is to clean up messy data files with mixed encodings and convert them to nice clean utf8, this seems like just one more thing I can clean up so the application layer doesn't have to deal with it. My code does not concern itself with any semantic meaning the resulting characters might have, it simply converts them into a normalised form. Am I missing something. Is there a hidden danger I haven't considered?

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  • How to implement an EventHandler to update controls

    - by Bill
    May I ask for help with the following? I am attempting to connect and control three pieces of household electronic equipment by computer through a GlobalCache GC-100 and iTach. As you will see in the following code, I created a class-instance of GlobalCacheAdapter that communicates with each piece of equipment. Although the code seems to work well in controlling the equipment, I am having trouble updating controls with the feedback from the equipment. The procedure "ReaderThreadProc" captures the feedback; however I don't know how to update the associated TextBox with the feedback. I believe that I need to create an EventHandler to notify the TextBox of the available update; however I am uncertain as to how an EventHandler like this would be implemented. Any help wold be greatly appreciated. using System; using System.IO; using System.Net; using System.Net.Sockets; using System.Threading; using System.Windows.Forms; namespace WindowsFormsApplication1 { public partial class Form1 : Form { // Create three new instances of GlobalCacheAdaptor and connect. // GC-100 (Elan) 192.168.1.70 4998 // GC-100 (TuneSuite) 192.168.1.70 5000 // GC iTach (Lighting) 192.168.1.71 4999 private GlobalCacheAdaptor elanGlobalCacheAdaptor; private GlobalCacheAdaptor tuneSuiteGlobalCacheAdaptor; private GlobalCacheAdaptor lutronGlobalCacheAdaptor; public Form1() { InitializeComponent(); elanGlobalCacheAdaptor = new GlobalCacheAdaptor(); elanGlobalCacheAdaptor.ConnectToDevice(IPAddress.Parse("192.168.1.70"), 4998); tuneSuiteGlobalCacheAdaptor = new GlobalCacheAdaptor(); tuneSuiteGlobalCacheAdaptor.ConnectToDevice(IPAddress.Parse("192.168.1.70"), 5000); lutronGlobalCacheAdaptor = new GlobalCacheAdaptor(); lutronGlobalCacheAdaptor.ConnectToDevice(IPAddress.Parse("192.168.1.71"), 4999); elanTextBox.Text = elanGlobalCacheAdaptor._line; tuneSuiteTextBox.Text = tuneSuiteGlobalCacheAdaptor._line; lutronTextBox.Text = lutronGlobalCacheAdaptor._line; } private void btnZoneOnOff_Click(object sender, EventArgs e) { elanGlobalCacheAdaptor.SendMessage("sendir,4:3,1,40000,4,1,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,800" + Environment.NewLine); } private void btnSourceInput1_Click(object sender, EventArgs e) { elanGlobalCacheAdaptor.SendMessage("sendir,4:3,1,40000,1,1,20,179,20,179,20,179,20,179,20,179,20,179,20,179,20,278,20,179,20,179,20,179,20,780" + Environment.NewLine); } private void btnSystemOff_Click(object sender, EventArgs e) { elanGlobalCacheAdaptor.SendMessage("sendir,4:3,1,40000,1,1,20,184,20,184,20,184,20,184,20,184,20,286,20,286,20,286,20,184,20,184,20,184,20,820" + Environment.NewLine); } private void btnLightOff_Click(object sender, EventArgs e) { lutronGlobalCacheAdaptor.SendMessage("sdl,14,0,0,S2\x0d"); } private void btnLightOn_Click(object sender, EventArgs e) { lutronGlobalCacheAdaptor.SendMessage("sdl,14,100,0,S2\x0d"); } private void btnChannel31_Click(object sender, EventArgs e) { tuneSuiteGlobalCacheAdaptor.SendMessage("\xB8\x4D\xB5\x33\x31\x00\x30\x21\xB8\x0D"); } private void btnChannel30_Click(object sender, EventArgs e) { tuneSuiteGlobalCacheAdaptor.SendMessage("\xB8\x4D\xB5\x33\x30\x00\x30\x21\xB8\x0D"); } } } public class GlobalCacheAdaptor { public Socket _multicastListener; public string _preferredDeviceID; public IPAddress _deviceAddress; public Socket _deviceSocket; public StreamWriter _deviceWriter; public bool _isConnected; public int _port; public IPAddress _address; public string _line; public GlobalCacheAdaptor() { } public static readonly GlobalCacheAdaptor Instance = new GlobalCacheAdaptor(); public bool IsListening { get { return _multicastListener != null; } } public GlobalCacheAdaptor ConnectToDevice(IPAddress address, int port) { if (_deviceSocket != null) _deviceSocket.Close(); try { _port = port; _address = address; _deviceSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); _deviceSocket.Connect(new IPEndPoint(address, port)); ; _deviceAddress = address; var stream = new NetworkStream(_deviceSocket); var reader = new StreamReader(stream); var writer = new StreamWriter(stream) { NewLine = "\r", AutoFlush = true }; _deviceWriter = writer; writer.WriteLine("getdevices"); var readerThread = new Thread(ReaderThreadProc) { IsBackground = true }; readerThread.Start(reader); _isConnected = true; return Instance; } catch { DisconnectFromDevice(); MessageBox.Show("ConnectToDevice Error."); throw; } } public void SendMessage(string message) { try { var stream = new NetworkStream(_deviceSocket); var reader = new StreamReader(stream); var writer = new StreamWriter(stream) { NewLine = "\r", AutoFlush = true }; _deviceWriter = writer; writer.WriteLine(message); var readerThread = new Thread(ReaderThreadProc) { IsBackground = true }; readerThread.Start(reader); } catch { MessageBox.Show("SendMessage() Error."); } } public void DisconnectFromDevice() { if (_deviceSocket != null) { try { _deviceSocket.Close(); _isConnected = false; } catch { MessageBox.Show("DisconnectFromDevice Error."); } _deviceSocket = null; } _deviceWriter = null; _deviceAddress = null; } private void ReaderThreadProc(object state) { var reader = (StreamReader)state; try { while (true) { var line = reader.ReadLine(); if (line == null) break; _line = _line + line + Environment.NewLine; } // Need to create EventHandler to notify the TextBoxes to update with _line } catch { MessageBox.Show("ReaderThreadProc Error."); } } }

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  • Ruby: Continue a loop after catching an exception

    - by Santa
    Basically, I want to do something like this (in Python, or similar imperative languages): for i in xrange(1, 5): try: do_something_that_might_raise_exceptions(i) except: continue # continue the loop at i = i + 1 How do I do this in Ruby? I know there are the redo and retry keywords, but they seem to re-execute the "try" block, instead of continuing the loop: for i in 1..5 begin do_something_that_might_raise_exceptions(i) rescue retry # do_something_* again, with same i end end

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  • Rails - handling global site settings

    - by egarcia
    I'm developing a new rails application which is supposed to be installed several times in order to implement several sites. There are some things, like the "Site Title" or the "Default Number of Items per Page" that clearly belong to a "global settings" table / config file. I've made a list of the things I think I'll need: ActiveRecord model that is capable of: Storing different kinds of data. I suppose this would be accomplished encoding the values on a string on the db, probably with a "type" field. Indexing settings by name Validations based on a "type" attribute (i.e. don't accept invalid dates on "date" settings) Validations based on a allows_nil property. A controller that allows me to change settings via views. I'm pretty sure I could implement this myself, but I'm not willing to reinvent the wheel. I've done some searching, but I could only find rails-settings, which doesn't really serve me: I need a proper model & controller so I can use declarative-authorization, and it does not provide any controller or view facilities. Is there a gem or plugin out there that implements what I want, or any library I should look at? Thanks a lot.

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  • Trap error or 'Resume Next'

    - by Craig Johnston
    I realise this is an older programming environment, but I have to clean up some VB6 code and I am finding that most of it uses: Resume Next What is the general consensus about the use of Resume Next? Surely, if there is an error, you would want the app to stop what it was doing, rollback any data changes, and inform the user of the error, rather than just resuming. When is it good idea to use Resume?

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  • dynamically created controls and responding to control events

    - by Dirk
    I'm working on an ASP.NET project in which the vast majority of the forms are generated dynamically at run time (form definitions are stored in a DB for customizability). Therefore, I have to dynamically create and add my controls to the Page every time OnLoad fires, regardless of IsPostBack. This has been working just fine and .NET takes care of managing ViewState for these controls. protected override void OnLoad(EventArgs e) { base.OnLoad(e); RenderDynamicControls() } private void RenderDynamicControls(){ //1. call service layer to retrieve form definition //2. create and add controls to page container } I have a new requirement in which if a user clicks on a given button (this button is created at design time) the page should be re-rendered in a slightly different way. So in addition to the code that executes in OnLoad (i.e. RenderDynamicControls()), I have this code: protected void MyButton_Click(object sender, EventArgs e) { RenderDynamicControlsALittleDifferently() } private void RenderDynamicControlsALittleDifferently() (){ //1. clear all controls from the page container added in RenderDynamicControls() //2. call service layer to retrieve form definition //3. create and add controls to page container } My question is, is this really the only way to accomplish what I'm after? It seems beyond hacky to effectively render the form twice simply to respond to a button click. I gather from my research that this is simply how the page-lifecycle works in ASP.NET: Namely, that OnLoad must fire on every Postback before child events are invoked. Still, it's worthwhile to check with the SO community before having to drink the kool-aid. On a related note, once I get this feature completed, I'm planning on throwing an UpdatePanel on the page to perform the page updates via Ajax. Any code/advice that make that transition easier would be much appreciated. Thanks

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  • ASP.NET: disabling authentication for a single aspx page (custom error page)?

    - by Richard Collette
    I am using a custom error page: <customErrors redirectMode="ResponseRedirect" mode="On" defaultRedirect="Error2.aspx"/> I want to disable authentication for the custom error page because the error being raised is related to an authentication module and I don't want to get into an infinite loop and I want to display a clean error page to the user. I have been trying the following configuration to do that. <location path="Error2.aspx"> <system.web> <authentication mode="None"/> <authorization> <allow users="?"/> <allow users="*"/> </authorization> </system.web> </location> I am getting a System.Configuration.ConfigurationErrorsException for the line that sets the authentication mode. It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS. I have verified that there are no other web.config files in subdirectories under the application's folder. The applications folder is configured as an application in IIS and the error page is at the application's root. File permissions set for the error page in IIS include anonymous and windows authentication (I have tried just anonymous as well).

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  • .delegate equivalent of an existing .live method in jQuery 1.4.2

    - by kim3er
    I have an event handler bound to the hover event using the .live method, which is below: $(".nav li").hover(function () { $(this).addClass("hover"); }, function () { $(this).removeClass("hover"); }); It is important to note, that I require both functions within the handler to ensure synchronisation. Is it possible to rewrite the function using .delegate, as the following does not work? $(".nav").delegate("li", "hover", function () { $(this).addClass("hover"); }, function () { $(this).removeClass("hover"); }); Rich

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  • "Unable to open file", when the program tries to open file in /proc

    - by tristartom
    Hi, I try to read file /proc/'pid'/status, using c program. The code is as follows, and even I use sudo to run it, the prompt still keeps throwing "Unable to open file". Please let me know if you have any ideas on how to fix this. thanks Richard ... int main (int argc, char* argv[]) { string line; char* fileLoc; if(argc != 2) { cout << "a.out file_path" << endl; fileLoc = "/proc/net/dev"; } else { sprintf(fileLoc, "/proc/%d/status", atoi(argv[1])); } cout<< fileLoc << endl; ifstream myfile (fileLoc); if (myfile.is_open()) { while (! myfile.eof() ) { getline (myfile,line); cout << line << endl; } myfile.close(); } else cout << "Unable to open file"; return 0; }

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  • Java: how to access assignments in try-catch -loop?

    - by HH
    $ javac TestInit2.java TestInit2.java:13: variable unknown might not have been initialized System.out.println(unknown); ^ 1 error Code import java.util.*; import java.io.*; public class TestInit2 { public static void main(String[] args){ String unknown; try{ unknown="cannot see me, why?"; }catch(Exception e){ e.printStackTrace(); } System.out.println(unknown); } }

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  • How to get the current eventNumber for creating an event with NSEvent

    - by Chris
    Hello I'm creating an os x application for which I try to add a remote interface. For this I need to be able to send mouse down and mouse up commands to the window of my application. I found code with which I can successfully do this, it looks as follows: int mask = 0x100; NSEvent* eventMouseDown = [NSEvent mouseEventWithType:NSLeftMouseDown location:p modifierFlags:mask timestamp:[NSDate timeIntervalSinceSystemStartup] windowNumber:[w windowNumber] context:[NSGraphicsContext graphicsContextWithWindow:w] eventNumber:++eventCounter +42599 clickCount:1 pressure:0]; NSLog(@"Mouse down event: %@", eventMouseDown); [[NSApplication sharedApplication] sendEvent:eventMouseDown]; I have only one problem with this code thought and this is the eventNumer parameter. As far as I found out it is a number which get increased with each event. But I cannot find a way to find the current number from where on I need to increase. The number I use there currently is just try and error and also does not seam to work always.

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  • Need to determine if ELMAH is logging an unhandled exception or one raised by ErrorSignal.Raise()

    - by Ronnie Overby
    I am using the Elmah Logged event in my Global.asax file to transfer users to a feedback form when an unhandled exception occurs. Sometimes I log other handled exceptions. For example: ErrorSignal.FromCurrentContext().Raise(new System.ApplicationException("Program code not found: " + Student.MostRecentApplication.ProgramCode)); // more code that should execute after logging this exception The problem I am having is that the Logged event gets fired for both unhandled and these handled, raised exceptions. Is there a way to determine, in the Logged event handler, whether the exception was raised via ErrorSignal class or was simply unhandled? Are there other Elmah events that I can take advantage of?

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  • LINQ method chaining and granular error handling

    - by Clafou
    I have a method which can be written pretty neatly through method chaining: return viewer.ServerReport.GetParameters() .Single(p => p.Name == Convention.Ssrs.RegionParamName) .ValidValues .Select(v => v.Value); However I'd like to be able to do some checks at each point as I wish to provide helpful diagnostics information if any of the chained methods returns unexpected results. To achieve this, I need to break up all my chaining and follow each call with an if block. It makes the code a lot less readable. Ideally I'd like to be able to weave in some chained method calls which would allow me to handle unexpected outcomes at each point (e.g. throw a meaningful exception such as new ConventionException("The report contains no parameter") if the first method returns an empty collection). Can anyone suggest a simple way to achieve such a thing?

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