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  • Is it better to return NULL or empty values from functions/methods where the return value is not present?

    - by P B
    I am looking for a recommendation here. I am struggling with whether it is better to return NULL or an empty value from a method when the return value is not present or cannot be determined. Take the following two methods as an examples: string ReverseString(string stringToReverse) // takes a string and reverses it. Person FindPerson(int personID) // finds a Person with a matching personID. In ReverseString(), I would say return an empty string because the return type is string, so the caller is expecting that. Also, this way, the caller would not have to check to see if a NULL was returned. In FindPerson(), returning NULL seems like a better fit. Regardless of whether or not NULL or an empty Person Object (new Person()) is returned the caller is going to have to check to see if the Person Object is NULL or empty before doing anything to it (like calling UpdateName()). So why not just return NULL here and then the caller only has to check for NULL. Does anyone else struggle with this? Any help or insight is appreciated.

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  • Does C++ support subtyping?

    - by the_naive
    I know it might be a silly question to ask, but I didn't quite get an a absolute clear answer on this matter, so I thought I'd put it here. Does c++ support the subtyping in the sense that it fulfills Liskov's principle fully? I understand how parametric polymorphism, inclusion polymorphism(subclassing and overriding) work in c++ but I'm not entirely sure or understand if subtyping exists in the context of C++. Could you please explain?

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  • is it valid that a state machine can have more than one possible state for some transition?

    - by shankbond
    I have a requirement for a workflow which I am trying to model as a state machine, I see that there is more than one outcome of a given transition(or activity). Is it valid for a state machine to have more than one possible states, but only one state will be true at a given time? Note: This is my first attempt to model a state machine. Eg. might be: s1-t1-s2 s1-t1-s3 s1-t1-s4 where s1, s2, s3, s4 are states and t1 is transition/activity. A fictitious real world example might be: For a human, there can be two states: hungry, not hungry A basket can have only one item from: apple, orange. So, to model it we will have: hungry-pick from basket-apple found hungry-pick from basket-orange found apple found-eat-not hungry orange found-take juice out of it and then drink- not hungry

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  • Good Domain Driven Design samples

    - by jlembke
    I'm learning about DDD and enjoying every minute of it. However, there are some practical issues that are confusing to me that I think seeing some good samples might clear up. So being at peace with those issues, does anyone know of some good working code samples that do a good job of modeling basic DDD concepts? Particularly interested in An illustrative Domain Model Repositories Use of Domain/Application Services Value Objects Aggregate Roots I know I'm probably asking for too much, but anything close will help.

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  • Event handler of Dropdownlist inside Gridview

    - by hotcoder
    I've added Dropdownlist in Gridview at RowDataBound event. The code is: if (e.Row.RowType == DataControlRowType.DataRow) { DropDownList ddlSeason = new DropDownList(); ddlSeason.DataSourceID = "odsRoomSeason"; ddlSeason.DataTextField = "SeasonTittle"; ddlSeason.DataValueField = "SeasonID"; ddlSeason.AutoPostBack = true; ddlSeason.SelectedIndexChanged += new EventHandler(ddlSeason_SelectedIndexChanged); TableCell tcSeason= new TableCell(); tcSeason.Controls.Add(ddlSeason); e.Row.Cells.AddAt(e.Row.Cells.Count, tcSeason); } The event handler I've added is: protected void ddlSeason_SelectedIndexChanged(object sender, EventArgs e) { // } But the problem is that the event handler function doesn't catch the event. Please tell me how to write the correct event handler, also I need to get the row from which the Dropdownlist's event has fired.

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  • help on ejb stateless datagram and message driven beans

    - by Kemmal
    i have a client thats sending a message to the ejbserver using UDP, i want the server(stateless bean) to echo back this message to the client but i cant seem to do this. or can i implement the same logic by using JMS? please help and enlighten. this is just a test, in the end i want a midp to be sending the message to the ejb using datagrams. here is my code. @Stateless public class SessionFacadeBean implements SessionFacadeRemote { public SessionFacadeBean() { } public static void main(String[] args) { DatagramSocket aSocket = null; byte[] buffer = null; try { while(true) { DatagramPacket request = new DatagramPacket(buffer, buffer.length); aSocket.receive(request); DatagramPacket reply = new DatagramPacket(request.getData(), request.getLength(), request.getAddress(), request.getPort()); aSocket.send(reply); } } catch (SocketException e) { System.out.println("Socket: " + e.getMessage()); } catch (IOException e) { System.out.println("IO: " + e.getMessage()); } finally { if(aSocket != null) aSocket.close(); } } } and the client: public static void main(String[] args) { DatagramSocket aSocket = null; try { aSocket = new DatagramSocket(); byte [] m = "Test message!".getBytes(); InetAddress aHost = InetAddress.getByName("localhost"); int serverPort = 6789; DatagramPacket request = new DatagramPacket(m, m.length, aHost, serverPort); aSocket.send(request); byte[] buffer = new byte[1000]; DatagramPacket reply = new DatagramPacket(buffer, buffer.length); aSocket.receive(reply); System.out.println("Reply: " + new String(reply.getData())); } catch (SocketException e) { System.out.println("Socket: " + e.getMessage()); } catch (IOException e) { System.out.println("IO: " + e.getMessage()); } finally { if(aSocket != null) aSocket.close(); } } please help.

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  • Understanding Domain Driven Design

    - by Nihilist
    Hi I have been trying to understand DDD for few weeks now. Its very confusing. I dont understand how I organise my projects. I have lot of questions on UnitOfWork, Repository, Associations and the list goes on... Lets take a simple example. Album and Tracks. Album: AlbumId, Name, ListOf Tracks Tracks: TrackId, Name Question1: Should i expose Tracks as a IList/IEnumerabe property on Album ? If that how do i add an album ? OR should i expose a ReadOnlyCollection of Tracks and expose a AddTrack method? Question2: How do i load Tracks for Album [assuming lazy loading]? should the getter check for null and then use a repository to load the tracks if need be? Question3: How do we organise the assemblies. Like what does each assembly have? Model.dll - does it only have the domain entities? Where do the repositories go? Interfaces and implementations both. Can i define IAlbumRepository in Model.dll? Infrastructure.dll : what shold this have? Question4: Where is unit of work defined? How do repository and unit of work communicate? [ or should they ] for example. if i need to add multiple tracks to album, again should this be defined as AddTrack on Album OR should there a method in the repository? Regardless of where the method is, how do I implement unit of work here? Question5: Should the UI use Infrastructure..dll or should there be ServiceLayer? Do my quesitons make sense? Regards

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  • User Control as container at design time

    - by Luca
    I'm designing a simple expander control. I've derived from UserControl, drawn inner controls, built, run; all ok. Since an inner Control is a Panel, I'd like to use it as container at design time. Indeed I've used the attributes: [Designer(typeof(ExpanderControlDesigner))] [Designer("System.Windows.Forms.Design.ParentControlDesigner, System.Design", typeof(IDesigner))] Great I say. But it isn't... The result is that I can use it as container at design time but: The added controls go back the inner controls already embedded in the user control Even if I push to top a control added at design time, at runtime it is back again on controls embedded to the user control I cannot restrict the container area at design time into a Panel area What am I missing? Here is the code for completeness... why this snippet of code is not working? [Designer(typeof(ExpanderControlDesigner))] [Designer("System.Windows.Forms.Design.ParentControlDesigner, System.Design", typeof(IDesigner))] public partial class ExpanderControl : UserControl { public ExpanderControl() { InitializeComponent(); .... [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")] internal class ExpanderControlDesigner : ControlDesigner { private ExpanderControl MyControl; public override void Initialize(IComponent component) { base.Initialize(component); MyControl = (ExpanderControl)component; // Hook up events ISelectionService s = (ISelectionService)GetService(typeof(ISelectionService)); IComponentChangeService c = (IComponentChangeService)GetService(typeof(IComponentChangeService)); s.SelectionChanged += new EventHandler(OnSelectionChanged); c.ComponentRemoving += new ComponentEventHandler(OnComponentRemoving); } private void OnSelectionChanged(object sender, System.EventArgs e) { } private void OnComponentRemoving(object sender, ComponentEventArgs e) { } protected override void Dispose(bool disposing) { ISelectionService s = (ISelectionService)GetService(typeof(ISelectionService)); IComponentChangeService c = (IComponentChangeService)GetService(typeof(IComponentChangeService)); // Unhook events s.SelectionChanged -= new EventHandler(OnSelectionChanged); c.ComponentRemoving -= new ComponentEventHandler(OnComponentRemoving); base.Dispose(disposing); } public override System.ComponentModel.Design.DesignerVerbCollection Verbs { get { DesignerVerbCollection v = new DesignerVerbCollection(); v.Add(new DesignerVerb("&asd", new EventHandler(null))); return v; } } } I've found many resources (Interaction, designed, limited area), but nothing was usefull for being operative... Actually there is a trick, since System.Windows.Forms classes can be designed (as usual) and have a correct behavior at runtime (TabControl, for example).

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  • Design and Implementation with Prototyping Methodology

    - by Shahin
    I'm developing a game for my dissertation, and I'm using the spiral method approach. I'm having a bit of difficulty structuring my dissertation, specifically the design and implementation section. My solution was designed as much as possible initially, and then after each prototype implementation, the design was refined and extended and prototyped again (this was repeated a few times). My problem is how to structure this in my dissertation, my current idea is: Design Chapter Prototype 1 (Initial) Design Prototype 2 Design Prototype 3 Design Implementation Chapter Prototype 1 (Initial) Implementation Prototype 2 Implementation Prototype 3 Implementation Any suggestions?

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  • Delphi: How to assign dynamically an event handler without overwriting the existing event handler?

    - by user193655
    I need to loop through Components and assign an event handler (for example Dynamically assigning OnClick event for all TButton to ShowMessage('You clicked on ' + (Sender as TButton).Name); The problem is that in some cases I alreasy assigned the TButton OnClick event. Is there a way to solve the problem? Let's imagine I have Button1 for which the harcoded onclick event handler is: ShowMessage('This is Button1'); After my "parsing" I would like that the full event handler for Button1 becomes: ShowMessage('This is Button1'); // design time event handler code ShowMessage('You clicked on ' + (Sender as TButton).Name); // runtime added Note: I am looking for a soliution that allows me to use TButton as it is without inheriting from it.

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  • New set up DHCP Server on Server 2008 R2 won't work, Event-ID 1046

    - by Ian
    I just set up a 2008 R2 as DC, and DNS. Both worked fine, DNS works fine forward and reverse lookup. Now I wanted to install DHCP. As soon as the installation of the role is finished, I get this Event-ID Error 1046: Link When I first set it up there was also a Event-ID 1059 Error: Link The dhcp server is authorized. I don't know what else I should do. Getting crazy here, hope you guys can help me.

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  • Syslog - capturing event logs from Win2k boxes

    - by molecule
    Hi all, I asked this question in SuperUser without much luck and so I am posting it here to see if anyone can assist. We have a central syslog server and we want it to capture event log events from Windows hosts. We are specifically interested in logging service start/stop events. We installed "Eventlog to Syslog" on these windows hosts and all works well with XP hosts (Events come from Service Control Manager). However, we are having issues with Win2k hosts. For some reason, service start/stop events do not get logged in the Event Log for Win2k hosts. I got another friend from another company to test on a Win2k host and he does get start/stop events on them. I have searched around for local audit policies i need to enable but with not much luck. Anyone have any ideas? Thanks in advance.

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  • Several "SideBySide" errors in the event viewer (Windows XP SP3)

    - by Wesley
    Hi all, For some reason, my netbook continuously comes up with SideBySide errors in the event viewer under Computer Management. Is there some way to get rid of these errors? My netbook occasionally BSODs and looking back into the event viewer after, at least 8 SideBySide errors were logged prior to BSOD. Please help! Thanks in advance. Netbook is a Samsung N120 with upgraded RAM to 2 GB. EDIT: So, SideBySide errors have been resolved and apparently the BSOD isn't related. But I remember specifically, that last time I had a BSOD, it was due to an "unknown hard error." What causes that?

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  • Get the "source network address" in Event ID 529 audit entries on Windows XP

    - by Make it useful Keep it simple
    In windows server 2003 when an Event 529 (logon failure) occures with a logon type of 10 (remote logon), the source network IP address is recorded in the event log. On a windows XP machine, this (and some other details) are omitted. If a bot is trying a brute force over RDP (some of my XP machines are (and need to be) exposed with a public IP address), i cannot see the originating IP address so i don't know what to block (with a script i run every few minutes). The DC does not log this detail either when the logon attempt is to the client xp machine and the DC is only asked to authenticate the credentials. Any help getting this detail in the log would be appreciated.

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  • Windows 7 just restarts, no BSOD, shows "Event ID 14 volsnap"

    - by Mdc007
    My Windows 7 just restarts without giving me a BSOD. When it reboots, it will hang sometimes and you have to let it rest. Sometimes it will print a message saying that Hal.dll is missing or corrupt. When it does restart I can't run a backup or a clone drive – it comes up with constant errors. I tried to run chkdsk – it says everything's clean. What is really puzzling is SyncToy on a different drive hangs half way through and won't run either. Machine: OCZ SSD Agility 2 for C drive SATA HDD for programs, documents on D drive MSI AMD 880 chipset Event viewer says something about critical power failure I/O operations and "Event ID 14 volsnap" – but that is just telling me the computer powered off which I already know.

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  • Get the "source network address" in Event ID 529 audit entries on Windows XP

    - by Make it useful Keep it simple
    In windows server 2003 when an Event 529 (logon failure) occures with a logon type of 10 (remote logon), the source network IP address is recorded in the event log. On a windows XP machine, this (and some other details) are omitted. If a bot is trying a brute force over RDP (some of my XP machines are (and need to be) exposed with a public IP address), i cannot see the originating IP address so i don't know what to block (with a script i run every few minutes). The DC does not log this detail either when the logon attempt is to the client xp machine and the DC is only asked to authenticate the credentials. Any help getting this detail in the log would be appreciated.

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  • Message Driven Bean JMS integration

    - by Anthony Shorten
    In Oracle Utilities Application Framework V4.1 and above the product introduced the concept of real time JMS integration within the Framework for interfacing. Customer familiar with older versions of the Framework will recall that we used a component called the Multi-purpose Listener (MPL) which was a very light service bus for calling interface channels (including JMS). The MPL is not supplied with all products and customers prefer to use Oracle SOA Suite and native methods rather then MPL. In Oracle Utilities Application Framework V4.1 (and for Oracle Utilities Application Framework V2.2 via Patches 9454971, 9256359, 9672027 and 9838219) we introduced real time JMS integration natively for outbound JMS integration and using Message Driven Beans (MDB) for incoming integration. The outbound integration has not changed a lot between releases where you create an Outbound Message Type to indicate the record types to send out, create a JMS sender (though now you use the Real Time Sender) and then create an External System definition to complete the configuration. When an outbound message appears in the table of the type and external system configured (via a business event such as an algorithm or plug-in script) the Oracle Utilities Application Framework will place the message on the configured Queue linked to the JMS Sender. The inbound integration has changed. In the past you created XAI Receivers and specified configuration about what types of transactions to process. This is now all configuration file driven. The configuration files for the Business Application Server (ejb-jar.xml and weblogic-ejb-jar.xml) define Message Driven Beans and the queues to monitor. When a message appears on the queue, the MDB processes it through our web services interface. Configuration of the MDB can be native (via editing the configuration files) or through the new user exit capabilities (which is aimed at maintaining custom configuration across upgrades). The latter is better as you build fragments of configuration to make it easier to maintain. In the next few weeks a number of new whitepaper will be released to illustrate the features of the Oracle WebLogic JMS and Oracle SOA Suite integration capabilities.

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  • Failure Driven Development

    - by DevSolo
    At our shop, we strive to be agile. And I'd say we are making great strides. That said, a few of us have spotted a pattern we have started calling "Failure Driven Development". Failure Driven Development can basically be desribed as an agile release/iteration cycle where the bugs/features are guided not by tasks and stories with acceptance criteria, but with defects entered in the defect tracking software. Our team has a great Project Manager who strives to get the acceptance criteria from the customer(s), but it's not always possible. From my development chair, this is due to the customer either not knowing exactly what they want or (and this is the kicker) two different "camps" at the customer's main office conflict with how a story should be implemented. Camp A will losely dictate that Feature X works like this, then Camp B will fail it due not functioning like that. Hence, the term "FDD". The process is driven by "failures". This leads to my question: Has anyone else encountered this and if so, any tips/suggestions for dealing with it? We have, of course, tried to get Camp A and B to agree prior, but everyone knows this isn't always the case. Thanks

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  • ASP.Net ListView and event handling.

    - by Neil
    I have an .ascx which contains a listview. Let's call it the parent. Within its ItemTemplate I reference a second .ascx which is basically another listview, let's call it the child. On the parent, the child control is wrapped in a placeholder tag. I use this place holder tag to show and hide the child. Psuedo code: The child listview has a 'close' button in its Layout Template. Let's call it "btnClose" with an onClick event of "btnClose_Click". I want to use this button to set the visibility of the containing placeholder. I'm trying to avoid doing something like using PlaceHolder plhChild = (PlaceHolder)childListCtl.NamingContainer since I can't guarantee every instance of the child .ascx will be contained within a placeholder. I tried creating an event in the child that could be subscribed to. Psuedo code: public delegate CloseButtonHandler(); public event CloseButtonHandler CloseButtonEvent; And in the actual btnClose_Click(Object sender, EventArgs e) event I have: if (CloseButtonEvent != null) CloseButtonEvent(); My problem is that the delegate CloseButtonEvent is always null. I've tried assigning the delegate in the listview's OnDatabound event of the parent and on the click event, to set the plhChild.visible = true, and I've stepped through the code and know the delegate instantiation works in both place, but again, when it gets to the btnClose_Click event on the child, the delegate is null. Any help would be appreciated. Neil

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  • Color blindness: Are you aware of it? Do you design for it?

    - by User
    I'm curious whether many of us who do design or take design decisions have ever heard of this problem. I'm aware there are dangerous color combinations, like green + red. This is probably one of the most popular cases of color blindness. If you have green text on a red background and vice versa some people won't see anything. I've also seen in practice that green text on a blue background was not seen by one guy. What other color compositions should be avoided, and how often these cases are to be expected? Let us make some ranging by encounter probability who has the numbers. Addition: I've just remembered one very bad example that causes problems to just about everyone - blue text on a black background. It's unreadable for all intents and purposes. Never could understand what could possibly compel a web master to use this color combination...

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  • What is the most underused or underappreciated design pattern?

    - by Rob Packwood
    I have been reading a lot on design patterns lately and some of them can make our lives much easier and some of them seem to just complicate things (at least to me they do). I am curious to know what design patterns everyone sees as underunsed or underappreciated. Some patterns are simple and many people do not even realize they are using a pattern (decorator probably being the most used, without realized). My goal from this is to give us pattern-newbies some appreciation for some of the more complex or unknown patterns and why we should use them.

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