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  • C# - Why can't I enforce derived classes to have parameterless constructors?

    - by FrisbeeBen
    I am trying to do the following: public class foo<T> where T : bar, new { _t = new T(); private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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  • Retreiving data from grid view cell to a text box

    - by Bader
    Hello , i am trying to retrieve a cell data to a textbox , that will happen when i select any row in the grid view , the textbox will take the new value i already enabled auto post back to the textbox here is my code protected void GridView2_SelectedIndexChanged(object sender, EventArgs e) { TextBox3.Text = GridView2.Rows[GridView2.SelectedIndex].Cells[2].Text; } however , there is not error in the syntax , it doesn't retrieve any thing in the textbox , any suggestions ? i am using using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Data.SqlClient; using System.Data.Sql; i work in C# , Visual studio 2010 express web developer

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  • Remove items from one list in another

    - by coffeeaddict
    I'm trying to figure out how to traverse a generic list of items that I want to remove from another list of items. So lest say I have this as a hypothetical example List<car> list1 = GetTheList(); List<car> list2 = GetSomeOtherList(); I want to traverse list1 with a foreach and remove each item in List1 in List2. I'm not quite sure how to go about that as foreach is not index based.

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  • How to use #ifdef entities as part of functions in header files

    - by Crazyjavahacking
    I would like to ask if it is possible to use the entities defined in #ifdef block in header files. To be clear, I have following code: #ifdef #include <winsock2.h> #define SOCKET_HANDLE SOCKET #define CONNECTION_HANDLE SOCKET #endif SOCKET_HANDLE createServerSocket(const char* hostAddress, short port); I am Java developer and this seems completely fine for me. However compiler has a problem with this. Can you explain why is that code a problem? Also how can I force to compile it. (The idea is to have generic interface and conditional compilation to determine real types according to running platform at compile time.) Thanks

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  • Express XPath as an expression tree

    - by 47d_
    If I have an XPath query like NodeA/NodeB[@WIDTH and not(@WIDTH="20")] | NodeC[@WIDTH and not(@WIDTH="20")]/NodeD Is there any API available to visualize this XPath query as a stack of atomic expressions, something like (following is generic) Get results of NodeA, call it "first set" Get results of NodeB from "first set" Filter where [@WIDTH and not(@WIDTH="20")] Filter NodeD, call this "node d for B" Get results of NodeC from "first set" Filter where [@WIDTH and not(@WIDTH="20")] Filter NodeD, call this "node d for C" Combine "node d for B" and "node d for C" I am trying to see if we can convert the XPath expression into custom expression which is close to english and vice versa. If no API is available, what would be the best approach? Thanks in advance.

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  • Can't update rows in my database using Entity Framework...?

    - by Dissonant
    Okay, this is really weird. I made a simple database with a single table, Customer, which has a single column, Name. From the database I auto-generated an ADO.NET Entity Data Model, and I'm trying to add a new Customer to it like so: using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Test { class Program { static void Main() { Database1Entities db = new Database1Entities(); Customer c = new Customer(); c.Name = "Harry"; db.AddToCustomer(c); db.SaveChanges(); } } } But it doesn't persist Customer "Harry" to the database! I've been scratching my head for a while now wondering why such a simple operation doesn't work. What on earth could be the problem!?

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  • Can using non primitive Integer/ Long datatypes too frequently in the application, hurt the performance??

    - by Marcos
    I am using Long/Integer data types very frequently in my application, to build Generic datatypes. I fear that using these wrapper objects instead of primitive data types may be harmful for performance since each time it needs to create objects which is an expensive operation. but also it seems that I have no other choice(when I have to use primtives with generics) rather than just using them. However, still it would be great if you can suggest if there is anything I could do to make it better. or any way if I could just avoid it ?? Also What may be the downsides of this ? Suggestions welcomed!

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  • How do you set a cookie to be accessible across the entire domain in Javascript

    - by Tzarkov
    I suppose there should be a way to set a cookie to be accessible from the entire domain nevermind from which directory you are setting the cookie. Say in mypage.com/blue/index.php y set the cookie "colour=blue;" this way: document.cookie = "colour" + "=" + "blue" + "; expires=" + expireDate.toGMTString() + "; path=/"; Using this code, the cookie retrieval function in mypage.com/home.php can't access the content of the cookie. If it was just from first level directories that the cookie needs to be set, we would be ok by doing path=../ instead of path=/ But how do you go about writing generic code that sets a cookie that is accessible from any page in that domain not minding how deep in the file structure is the page the cookie is being set from?

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  • How to solve this Java type safety warning? (Struts2)

    - by Nicolas Raoul
    Map session = ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: The method put(Object, Object) belongs to the raw type Map. References to generic type Map should be parameterized. Map<String, Serializable> session = (Map<String, Serializable>)ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: Unchecked cast from Map to Map. The getSession method belongs to Struts2 so I can't modify it. I would like to avoid using @SuppressWarnings because other warnings can be useful. I guess all Struts2 users in the world faced the same problem... is there an elegant solution?

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  • C++ Types Impossible to Name

    - by Kirakun
    While reading Wikipedia's page on decltype, I was curious about the statement, Its [decltype's] primary intended use is in generic programming, where it is often difficult, or even impossible, to name types that depend on template parameters. While I can understand the difficulty part of that statement, what is an example where there is a need to name a type that cannot be named under C++03? EDIT: My point is that since everything in C++ has a declaration of types. Why would there ever be a case where it is impossible to name a type? Furthermore, aren't trait classes designed to yield type informations? Could trait classes be an alternative to decltype?

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  • Linq to SQL - How to compare against a collection in the where clause?

    - by Sgraffite
    I'd like to compare against an IEnumerable collection in my where clause. Do I need to manually loop through the collection to pull out the column I want to compare against, or is there a generic way to handle this? I want something like this: public IEnumerable<Cookie> GetCookiesForUsers(IEnumerable<User> Users) { var cookies = from c in db.Cookies join uc in db.UserCookies on c.CookieID equals uc.CookieID join u in db.Users on uc.UserID equals u.UserID where u.UserID.Equals(Users.UserID) select c; return cookies.ToList(); } I'm used to using the lambda Linq to SQL syntax, but I decided to try the SQLesque syntax since I was using joins this time. What is a good way to do this?

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  • updated validation example for web api

    - by MonkeyBonkey
    I tried the validation example code for web api on the latest mvc 4 download and I'm getting some errors. Does anyone have an updated example of the ValidationActionFilter class. Here's the original code public class ValidationActionFilter : ActionFilterAttribute { public override void OnActionExecuting(HttpActionContext context) { var modelState = context.ModelState; if (!modelState.IsValid) { dynamic errors = new JsonObject(); foreach (var key in modelState.Keys) { var state = modelState[key]; if (state.Errors.Any()) { errors[key] = state.Errors.First().ErrorMessage; } } context.Response = new HttpResponseMessage<JsonValue>(errors, HttpStatusCode.BadRequest); } } } I'm getting an error on HttpResponseMessage The non-generic type 'System.Net.Http.HttpResponseMessage' cannot be used with type arguments Also it looks like I need to add a Json reference, but should I be using JSON.net instead? An example of this using Json.net?

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  • Create a WebPart which displays people who have rights on lists

    - by cocoggu
    I want to develop a WebPart in C# to display peoples who have a certain right on the list of the SharePoint page. So I began by creating a "Visual Web Part" in VS2010, and in the View Designer I add a DataList because I think it is the most relevant. But now, I don't know how to link my data with this DataList. It ask me for an XML file but which one choose ? And where can I take it ? After all, how to make this WebPart generic with all my SharePoint pages which implements one list ?

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  • haskell sorting

    - by snorlaks
    Hello, How can it be done in most simply way to write (or maybe there is something embedded in haskell) function which takse as arguments list of tuples (String, Int) and Int x and return top x tuples as list according to x value. I wonder if its possible to write a function which also takes 3 argument which is the name of (or index) of filed in tuple according to which sorting has to be done. What are best solutions to make it quite generic, Im new to haskell I would do somethink like that in imperative languages without any problems but I want to know how to write it in quite good way in haskell, thanks for help

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  • How to prevent CAST errors on SSIS ?

    - by manitra
    Hello, The question Is it possible to ask SSIS to cast a value and return NULL in case the cast is not allowed instead of throwing an error ? My environment I'm using Visual Studio 2005 and Sql Server 2005 on Windows Server 2003. The general context Just in case you're curious, here is my use case. I have to store data coming from somewhere in a generic table (key/value structure with history) witch contains some sort of value that can be strings, numbers or dates. The structure is something like this : table Values { Id int, Date datetime, -- for history Key nvarchar(50) not null, Value nvarchar(50), DateValue datetime, NumberValue numeric(19,9) } I want to put the raw value in the Value column and try to put the same value in the DateValue column when i'm able to cast it to Datetime in the NumberValue column when i'm able to cast it to a number Those two typed columns would make all sort of aggregation and manipulation much easier and faster later. That's it, now you know why i'm asking this strange question. ============ Thanks in advance for your help.

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  • Array::ConvertAll in managed C++

    - by danny.lesnik
    This is a continuation from this post. I'm trying to parse this string in managed C++: String ^ rgba = "[0.09019608,0.5176471,0.9058824,1]"; cli::array<System::Double> ^ RGB = System::Array::ConvertAll<String,cli::array<System::Double> >((rgba->Substring(1,rgba->Length-2)->Split(',')),double::Parse); Compiler throws me the following error: Error 15 error C2770: invalid explicit generic argument(s) for 'cli::array<Type,dimension> ^System::Array::ConvertAll(cli::array<TInput,1> ^,System::Converter<TInput,TOutput> ^)' What am I doing wrong?

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  • Regular expressions in java

    - by rookie
    String s= "(See <a href=\"/wiki/Grass_fed_beef\" title=\"Grass fed beef\" " + "class=\"mw-redirect\">grass fed beef.) They have been used for " + "<a href=\"/wiki/Paper\" title=\"Paper\">paper-making since " + "2400 BC or before."; In the string above I have inter-mixed html with text. Well the requirement is that the output looks like:- They have been used for paper-making since 2400 BC or before. Could some one help me with a generic regular expression that would produce the desired output from the given input? Thanks in advance!

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  • Using variables within Attributes in C#

    - by tehp
    We have some Well-Attributed DB code, like so: [Display(Name = "Phone Number")] public string Phone { get; set; } Since it is quite generic we'd like to use it again, but with a different string in the Name part of the attribute. Since it's an attribute it seems to want things to be const, so we tried: const string AddressType = "Student "; [Display(Name = AddressType + "Phone Number")] public string Phone { get; set; } This seems to work alright, except that having a const string means we can't overwrite it in any base classes, thereby removing the functionality that we originally were intending to add, and exposing my question: Is there a way to use some sort of variable inside of an attribute so that we can inherit and keep the attribute decorations?

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  • How to generilize view?

    - by MexicanHacker
    Hey guys, I'm in the process of designing a set of views that use the same model in my app, the difference is that some views will differ in Read Only and Modifiable fields. So for example for view A I want to be able to modify A.One but no A.Two properties and for view B I want to have B.One and B.Two as modifiable fields. I was thinking in having a map that will hold this information and iterate both the modifiable and non-modifiable lists in a generic view, but I was thinking that maybe I can get feedback from you guys. What do you think?

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  • Java generics conversion

    - by LittleGreenMan
    I have build a generic datacontainer and now I want to manipulate data depending on their type. However, I get an incompatable types warning. What am I doing wrong? Type _Value; public void set(Type t) throws Exception { if (_Value instanceof Integer && t instanceof Integer) { _Value = (((Integer) t - _MinValue + getRange()) % getRange()) + _MinValue; } else if (_Value instanceof Boolean && t instanceof Boolean) { _Value = t; } else throw new Exception("Invalid type"); }

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  • When should one let an application crash because of an exception in Java (design issue)?

    - by JVerstry
    In most cases, it is possible to catch exceptions in Java, even unchecked ones. But, it is not necessarily possible to do something about it (for example out of memory). For other cases, the issue I am trying to solve is a design principle one. I am trying to set-up a design principle or a set of rules indicating when one should give up on an exceptional situation, even if it is detected in time. The objective is trying to not crash the application as much as possible. Has someone already brainstormed and communicated about this? I am looking for specific generic cases and possible solutions, or thumb-rules. UPDATE Suggestions so far: Stop running if data coherency can be compromised Stop running if data can be deleted Stop running if you can't do anything about it (Out of memory...) Stop running if key service is not available or becomes unavailable and cannot be restarted If application must be stopped, degrade as gracefully as possible Use rollbacks in db transactions Log as much relevant information as you can Notify the developers

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  • How to create unique user key

    - by Grayson Mitchell
    Scenario: I have a fairly generic table (Data), that has an identity column. The data in this table is grouped (lets say by city). The users need an identifier in order for printing on paper forms, etc. The users can only access their cites data, so if they use the identity column for this purpose they will see odd numbers (e.g. a 'New York' user might see 1,37,2028... as the listed keys. Idealy they would see 1,2,3... (or something similar) The problem of course is concurrency, this being a web application you can't just have something like: UserId = Select Count(*)+1 from Data Where City='New York' Has anyone come up with any cunning ways around this problem?

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  • Rails has_one vs belongs_to semantics

    - by Anurag
    I have a model representing a Content item that contains some images. The number of images are fixed as these image references are very specific to the content. For example, the Content model refers to the Image model twice (profile image, and background image). I am trying to avoid a generic has_many, and sticking to multiple has_one's. The current database structure looks like: contents - id:integer - integer:profile_image_id - integer:background_image_id images - integer:id - string:filename - integer:content_id I just can't figure out how to setup the associations correctly here. The Content model could contain two belongs_to references to an Image, but that doesn't seem semantically right cause ideally an image belongs to the content, or in other words, the content has two images. This is the best I could think of (by breaking the semantics): class Content belongs_to :profile_image, :class_name => 'Image', :foreign_key => 'profile_image_id' belongs_to :background_image, :class_name => 'Image', :foreign_key => 'background_image_id' end Am I way off, and there a better way to achieve this association?

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  • Is there a way to inspect all controller variables at once in Rails?

    - by m.u.sheikh
    I am exploring an big controller method, with about 10 or so instance variables. Some of them are set in before_filter methods, and some others inside the method itself. I want to inspect them with puts, but dont want to write all of them out example: puts "var1: #{@var1.inspect}....var15: #{@var15.inspect}" Is there a generic method that will display all the instance variables with an @ sign set so far in the current method? If not, what is the next best way to inspect all of them at once without having to write all of them in a puts statement?

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  • Are there any pitfalls to having two different Models from two different assemblies? (EF)

    - by Jonn
    I have two projects, both of them data access layers, and both using EF. I have another project calling services related to the two different assemblies. Are there any pitfalls on using two different models on two different databases linked to the same database? I'm asking this because I've been getting this generic "EntitySqlException" could not be resolved in the current scope or context. Make sure that all referenced variables are in scope, that required schemas are loaded, and that namespaces are referenced correctly., near escaped identifier. that does not appear when are run separately but appear when under the same project.

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