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  • Array of pointers in objective-c

    - by Justin
    I'm getting confused by pointers in objective-c. Basically I have a bunch of static data in my code. static int dataSet0[2][2] = {{0, 1}, {2, 3}}; static int dataSet1[2][2] = {{4, 5}, {6, 7}}; And I want to have an array to index it all. dataSets[0]; //Would give me dataSet0... What should the type of dataSets be, and how would I initialize it?

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  • Pass Data to Data Template Selector

    - by Michael Sync
    How do you guys pass the data (parameter) to DataTemplate Selector? The only one that I can think of is to use an attached property in DataTemplate Selector? Example: public class DisableWeekendsSelection : DataTemplateSelector { [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2211:NonConstantFieldsShouldNotBeVisible", Justification = "DependencyProperty")] public static readonly DependencyProperty Parameter = DependencyProperty.RegisterAttached("Parameter", typeof(ObservableCollection<Date>), typeof(DisableWeekendsSelection), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault)); public static ObservableCollection<Date> GetParameter(DependencyObject dp) { return dp.GetValue(Parameter) as ObservableCollection<Date>; } public static void SetParameter(DependencyObject dp, ObservableCollection<Date> value) { dp.SetValue(Parameter, value); } public override DataTemplate SelectTemplate(object item, DependencyObject container) { The problem with this approach is that I'm not able to get the value of Parameter in SelectTemplate method. Any suggestion would be appreciated. Thanks in advance.

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  • algorithm diagram

    - by tunl
    This is the max searching algorithm diagram: So, I wonder how can draw diagram for Recursion in HaNoi Tower program: package tunl; public class TowersApp { static int n = 3; public static void main(String[] args) { TowersApp.doTowers(3, 'A', 'B', 'C'); } public static void doTowers(int n, char from, char inter, char to) { if (n == 1) { System.out.println("disk 1 from "+ from + " to " + to); } else { doTowers(n-1, from, to, inter); System.out.println("disk " + n + " from " + from + " to " + to); doTowers(n-1, inter, from, to); } } } I can't draw it. Anyone can help me !!!

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  • Grails: Problem with nested associations in criteria builder

    - by Mr.B
    I have a frustrating problem with the criteria builder. I have an application in which one user has one calendar, and a calendar has many entries. Seems straightforward enough, but when I try to get the calendar entries for a given user, I can't access the user property (MissingMethodException). Here's the code: def getEntries(User user) { def entries = Entries.createCriteria().list() { calendar { user { eq("user.id", user.id) } } } } I have even tried the following variation: def getEntries(User user) { def entries = Entries.createCriteria().list() { calendar { eq("user", user) } } } That did not raise an exception, but didn't work either. Here's the relevant parts of the domain classes: class Calendar { static belongsTo = [user: User] static hasMany = [entries: Entries] ... } class User { Calendar calendar ... } class Entry { static belongsTo = [calendar: Calendar] ... } When Googling I came across a similar problem noted in early 2008: http://jira.codehaus.org/browse/GRAILS-1412 But according to that link this issue should have been solved long ago. What am I doing wrong?

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  • NHibernate mapping error SQL Server 2008 Express

    - by developer
    Hi All, I tried an example from NHibernate in Action book and when I try to run the app, it throws an exception saying "Could not compile the mapping document: HelloNHibernate.Employee.hbm.xml" Below is my code, Employee.hbm.xml <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" auto-import="true"> <class name="HelloNHibernate.Employee, HelloNHibernate" lazy="false" table="Employee"> <id name="id" access="field"> <generator class="native"/> </id> <property name="name" access="field" column="name"/> <many-to-one access="field" name="manager" column="manager" cascade="all"/> </class> Program.cs using System; using System.Collections.Generic; using System.Linq; using System.Text; using NHibernate; using System.Reflection; using NHibernate.Cfg; namespace HelloNHibernate { class Program { static void Main(string[] args) { CreateEmployeeAndSaveToDatabase(); UpdateTobinAndAssignPierreHenriAsManager(); LoadEmployeesFromDatabase(); Console.WriteLine("Press any key to exit..."); Console.ReadKey(); } static void CreateEmployeeAndSaveToDatabase() { Employee tobin = new Employee(); tobin.name = "Tobin Harris"; using (ISession session = OpenSession()) { using (ITransaction transaction = session.BeginTransaction()) { session.Save(tobin); transaction.Commit(); } Console.WriteLine("Saved Tobin to the database"); } } static ISession OpenSession() { if (factory == null) { Configuration c = new Configuration(); c.AddAssembly(Assembly.GetCallingAssembly()); factory = c.BuildSessionFactory(); } return factory.OpenSession(); } static void LoadEmployeesFromDatabase() { using (ISession session = OpenSession()) { IQuery query = session.CreateQuery("from Employee as emp order by emp.name asc"); IList<Employee> foundEmployees = query.List<Employee>(); Console.WriteLine("\n{0} employees found:", foundEmployees.Count); foreach (Employee employee in foundEmployees) Console.WriteLine(employee.SayHello()); } } static void UpdateTobinAndAssignPierreHenriAsManager() { using (ISession session = OpenSession()) { using (ITransaction transaction = session.BeginTransaction()) { IQuery q = session.CreateQuery("from Employee where name='Tobin Harris'"); Employee tobin = q.List<Employee>()[0]; tobin.name = "Tobin David Harris"; Employee pierreHenri = new Employee(); pierreHenri.name = "Pierre Henri Kuate"; tobin.manager = pierreHenri; transaction.Commit(); Console.WriteLine("Updated Tobin and added Pierre Henri"); } } } static ISessionFactory factory; } } Employee.cs using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace HelloNHibernate { class Employee { public int id; public string name; public Employee manager; public string SayHello() { return string.Format("'Hello World!', said {0}.", name); } } } App.config <?xml version="1.0" encoding="utf-8" ?> <configuration> <configSections> <section name="hibernate-configuration" type="NHibernate.Cfg.ConfigurationSectionHandler,NHibernate"/> </configSections> <hibernate-configuration xmlns="urn:nhibernate-configuration-2.2"> <session-factory> <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property> <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property> <property name="connection.connection_string"> Data Source=SQLEXPRESS2008;Integrated Security=True; User ID=SQL2008;Password=;initial catalog=HelloNHibernate </property> <property name="dialect">NHibernate.Dialect.MsSql2008Dialect</property> <property name="show_sql">false</property> </session-factory> </hibernate-configuration> </configuration>

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  • WebClient DownloadStringCompleted Never Fired in Console Application

    - by azamsharp
    I am not sure why the callback methods are not fired AT ALL. I am using VS 2010. static void Main(string[] args) { try { var url = "some link to RSS FEED"; var client = new WebClient(); client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(client_DownloadStringCompleted); client.DownloadDataCompleted += new DownloadDataCompletedEventHandler(client_DownloadDataCompleted); client.DownloadStringAsync(new Uri(url)); } catch (Exception ex) { Console.WriteLine(ex.Message); } } // THIS IS NEVER FIRED static void client_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e) { Console.WriteLine("something"); } // THIS IS NEVER FIRED static void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e) { Console.WriteLine("do something"); var rss = XElement.Parse(e.Result); var pictures = from item in rss.Descendants("channel") select new Picture { Name = item.Element("title").Value }; foreach (var picture in pictures) { Console.WriteLine(picture.Name); Console.WriteLine(picture.Url); } }

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  • Confused about this factory, as it doesn't look like an Abstract Factory nor Factory Method

    - by Pin
    I'm looking into Guice and I've been reading its documentation recently. Reading the motivation section I don't understand the factories part, why they name it that way. To me that factory is just a wrapper for the implementing class they want it to return after calling getInstance(). public class CreditCardProcessorFactory { private static CreditCardProcessor instance; public static void setInstance(CreditCardProcessor creditCardProcessor) { instance = creditCardProcessor; } public static CreditCardProcessor getInstance() { if (instance == null) { throw new IllegalStateException("CreditCardProcessorFactory not initialized. " + "Did you forget to call CreditCardProcessor.setInstance() ?"); } return instance; } } Why do they call it factory as well if it is neither an abstract factory nor a factory method? Or am I missing something? Thanks.

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  • Anatomy of a .NET Assembly - Custom attribute encoding

    - by Simon Cooper
    In my previous post, I covered how field, method, and other types of signatures are encoded in a .NET assembly. Custom attribute signatures differ quite a bit from these, which consequently affects attribute specifications in C#. Custom attribute specifications In C#, you can apply a custom attribute to a type or type member, specifying a constructor as well as the values of fields or properties on the attribute type: public class ExampleAttribute : Attribute { public ExampleAttribute(int ctorArg1, string ctorArg2) { ... } public Type ExampleType { get; set; } } [Example(5, "6", ExampleType = typeof(string))] public class C { ... } How does this specification actually get encoded and stored in an assembly? Specification blob values Custom attribute specification signatures use the same building blocks as other types of signatures; the ELEMENT_TYPE structure. However, they significantly differ from other types of signatures, in that the actual parameter values need to be stored along with type information. There are two types of specification arguments in a signature blob; fixed args and named args. Fixed args are the arguments to the attribute type constructor, named arguments are specified after the constructor arguments to provide a value to a field or property on the constructed attribute type (PropertyName = propValue) Values in an attribute blob are limited to one of the basic types (one of the number types, character, or boolean), a reference to a type, an enum (which, in .NET, has to use one of the integer types as a base representation), or arrays of any of those. Enums and the basic types are easy to store in a blob - you simply store the binary representation. Strings are stored starting with a compressed integer indicating the length of the string, followed by the UTF8 characters. Array values start with an integer indicating the number of elements in the array, then the item values concatentated together. Rather than using a coded token, Type values are stored using a string representing the type name and fully qualified assembly name (for example, MyNs.MyType, MyAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=0123456789abcdef). If the type is in the current assembly or mscorlib then just the type name can be used. This is probably done to prevent direct references between assemblies solely because of attribute specification arguments; assemblies can be loaded in the reflection-only context and attribute arguments still processed, without loading the entire assembly. Fixed and named arguments Each entry in the CustomAttribute metadata table contains a reference to the object the attribute is applied to, the attribute constructor, and the specification blob. The number and type of arguments to the constructor (the fixed args) can be worked out by the method signature referenced by the attribute constructor, and so the fixed args can simply be concatenated together in the blob without any extra type information. Named args are different. These specify the value to assign to a field or property once the attribute type has been constructed. In the CLR, fields and properties can be overloaded just on their type; different fields and properties can have the same name. Therefore, to uniquely identify a field or property you need: Whether it's a field or property (indicated using byte values 0x53 and 0x54, respectively) The field or property type The field or property name After the fixed arg values is a 2-byte number specifying the number of named args in the blob. Each named argument has the above information concatenated together, mostly using the basic ELEMENT_TYPE values, in the same way as a method or field signature. A Type argument is represented using the byte 0x50, and an enum argument is represented using the byte 0x55 followed by a string specifying the name and assembly of the enum type. The named argument property information is followed by the argument value, using the same encoding as fixed args. Boxed objects This would be all very well, were it not for object and object[]. Arguments and properties of type object allow a value of any allowed argument type to be specified. As a result, more information needs to be specified in the blob to interpret the argument bytes as the correct type. So, the argument value is simple prepended with the type of the value by specifying the ELEMENT_TYPE or name of the enum the value represents. For named arguments, a field or property of type object is represented using the byte 0x51, with the actual type specified in the argument value. Some examples... All property signatures start with the 2-byte value 0x0001. Similar to my previous post in the series, names in capitals correspond to a particular byte value in the ELEMENT_TYPE structure. For strings, I'll simply give the string value, rather than the length and UTF8 encoding in the actual blob. I'll be using the following enum and attribute types to demonstrate specification encodings: class AttrAttribute : Attribute { public AttrAttribute() {} public AttrAttribute(Type[] tArray) {} public AttrAttribute(object o) {} public AttrAttribute(MyEnum e) {} public AttrAttribute(ushort x, int y) {} public AttrAttribute(string str, Type type1, Type type2) {} public int Prop1 { get; set; } public object Prop2 { get; set; } public object[] ObjectArray; } enum MyEnum : int { Val1 = 1, Val2 = 2 } Now, some examples: Here, the the specification binds to the (ushort, int) attribute constructor, with fixed args only. The specification blob starts off with a prolog, followed by the two constructor arguments, then the number of named arguments (zero): [Attr(42, 84)] 0x0001 0x002a 0x00000054 0x0000 An example of string and type encoding: [Attr("MyString", typeof(Array), typeof(System.Windows.Forms.Form))] 0x0001 "MyString" "System.Array" "System.Windows.Forms.Form, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" 0x0000 As you can see, the full assembly specification of a type is only needed if the type isn't in the current assembly or mscorlib. Note, however, that the C# compiler currently chooses to fully-qualify mscorlib types anyway. An object argument (this binds to the object attribute constructor), and two named arguments (a null string is represented by 0xff and the empty string by 0x00) [Attr((ushort)40, Prop1 = 12, Prop2 = "")] 0x0001 U2 0x0028 0x0002 0x54 I4 "Prop1" 0x0000000c 0x54 0x51 "Prop2" STRING 0x00 Right, more complicated now. A type array as a fixed argument: [Attr(new[] { typeof(string), typeof(object) })] 0x0001 0x00000002 // the number of elements "System.String" "System.Object" 0x0000 An enum value, which is simply represented using the underlying value. The CLR works out that it's an enum using information in the attribute constructor signature: [Attr(MyEnum.Val1)] 0x0001 0x00000001 0x0000 And finally, a null array, and an object array as a named argument: [Attr((Type[])null, ObjectArray = new object[] { (byte)2, typeof(decimal), null, MyEnum.Val2 })] 0x0001 0xffffffff 0x0001 0x53 SZARRAY 0x51 "ObjectArray" 0x00000004 U1 0x02 0x50 "System.Decimal" STRING 0xff 0x55 "MyEnum" 0x00000002 As you'll notice, a null object is encoded as a null string value, and a null array is represented using a length of -1 (0xffffffff). How does this affect C#? So, we can now explain why the limits on attribute arguments are so strict in C#. Attribute specification blobs are limited to basic numbers, enums, types, and arrays. As you can see, this is because the raw CLR encoding can only accommodate those types. Special byte patterns have to be used to indicate object, string, Type, or enum values in named arguments; you can't specify an arbitary object type, as there isn't a generalised way of encoding the resulting value in the specification blob. In particular, decimal values can't be encoded, as it isn't a 'built-in' CLR type that has a native representation (you'll notice that decimal constants in C# programs are compiled as several integer arguments to DecimalConstantAttribute). Jagged arrays also aren't natively supported, although you can get around it by using an array as a value to an object argument: [Attr(new object[] { new object[] { new Type[] { typeof(string) } }, 42 })] Finally... Phew! That was a bit longer than I thought it would be. Custom attribute encodings are complicated! Hopefully this series has been an informative look at what exactly goes on inside a .NET assembly. In the next blog posts, I'll be carrying on with the 'Inside Red Gate' series.

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  • Java Windows Service with Procrun, StopMethod problem

    - by mcdon
    My Java class contains the following methods: public static void main(String[] argv) //start the service public static void stop() //stop the service I'm using Procrun from Apache Commons Daemon to setup the Java class as a Windows Service. I get an error when I try to stop the service "[618 javajni.c] [error] Static method 'void main(String[])' in Class com/caphyon/service/JavaService not found". The problem is I am trying to call the stop method when the service is shutting down, but it appears to override the StopMethod with 'void main(String[])'. Here are the stop and start parameters I am using when setting up the service: prunsrv.exe //US//JavaService --StartClass=com.caphyon.service.JavaService --StartMode=jvm --StartPath="C:\JavaService" prunsrv.exe //US//JavaService --StopClass=com.caphyon.service.JavaService --StopMode=jvm --StopPath="C:\JavaService" --StopMethod="void stop()" How do I set the StopMethod prunsrv will call when shutting down the service?

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  • EJB3 lookup on websphere

    - by dcp
    I'm just starting to try to learn Websphere, and I have my ejb deployed, but I cannot look it up. Here's is what I have: public class RemoteEJBCount { public static Context ctx; private static String jndiNameStateless = "EJB3CounterSample/EJB3Beans.jar/StatelessCounterBean/com/ibm/websphere/ejb3sample/counter/RemoteCounter"; public static void main(String[] args) throws NamingException { RemoteCounter statelessCounter; Hashtable<String, Object> env = new Hashtable<String, Object>(); env.put(Context.PROVIDER_URL, "corbaloc:iiop:localhost:2809"); env.put(Context.INITIAL_CONTEXT_FACTORY, "com.ibm.websphere.naming.WsnInitialContextFactory"); ctx = new InitialContext(env); statelessCounter = (RemoteCounter)ctx.lookup(jndiNameStateless); } } Is there something I need to be doing differently to look up the EJB?

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  • tile_static, tile_barrier, and tiled matrix multiplication with C++ AMP

    - by Daniel Moth
    We ended the previous post with a mechanical transformation of the C++ AMP matrix multiplication example to the tiled model and in the process introduced tiled_index and tiled_grid. This is part 2. tile_static memory You all know that in regular CPU code, static variables have the same value regardless of which thread accesses the static variable. This is in contrast with non-static local variables, where each thread has its own copy. Back to C++ AMP, the same rules apply and each thread has its own value for local variables in your lambda, whereas all threads see the same global memory, which is the data they have access to via the array and array_view. In addition, on an accelerator like the GPU, there is a programmable cache, a third kind of memory type if you'd like to think of it that way (some call it shared memory, others call it scratchpad memory). Variables stored in that memory share the same value for every thread in the same tile. So, when you use the tiled model, you can have variables where each thread in the same tile sees the same value for that variable, that threads from other tiles do not. The new storage class for local variables introduced for this purpose is called tile_static. You can only use tile_static in restrict(direct3d) functions, and only when explicitly using the tiled model. What this looks like in code should be no surprise, but here is a snippet to confirm your mental image, using a good old regular C array // each tile of threads has its own copy of locA, // shared among the threads of the tile tile_static float locA[16][16]; Note that tile_static variables are scoped and have the lifetime of the tile, and they cannot have constructors or destructors. tile_barrier In amp.h one of the types introduced is tile_barrier. You cannot construct this object yourself (although if you had one, you could use a copy constructor to create another one). So how do you get one of these? You get it, from a tiled_index object. Beyond the 4 properties returning index objects, tiled_index has another property, barrier, that returns a tile_barrier object. The tile_barrier class exposes a single member, the method wait. 15: // Given a tiled_index object named t_idx 16: t_idx.barrier.wait(); 17: // more code …in the code above, all threads in the tile will reach line 16 before a single one progresses to line 17. Note that all threads must be able to reach the barrier, i.e. if you had branchy code in such a way which meant that there is a chance that not all threads could reach line 16, then the code above would be illegal. Tiled Matrix Multiplication Example – part 2 So now that we added to our understanding the concepts of tile_static and tile_barrier, let me obfuscate rewrite the matrix multiplication code so that it takes advantage of tiling. Before you start reading this, I suggest you get a cup of your favorite non-alcoholic beverage to enjoy while you try to fully understand the code. 01: void MatrixMultiplyTiled(vector<float>& vC, const vector<float>& vA, const vector<float>& vB, int M, int N, int W) 02: { 03: static const int TS = 16; 04: array_view<const float,2> a(M, W, vA); 05: array_view<const float,2> b(W, N, vB); 06: array_view<writeonly<float>,2> c(M,N,vC); 07: parallel_for_each(c.grid.tile< TS, TS >(), 08: [=] (tiled_index< TS, TS> t_idx) restrict(direct3d) 09: { 10: int row = t_idx.local[0]; int col = t_idx.local[1]; 11: float sum = 0.0f; 12: for (int i = 0; i < W; i += TS) { 13: tile_static float locA[TS][TS], locB[TS][TS]; 14: locA[row][col] = a(t_idx.global[0], col + i); 15: locB[row][col] = b(row + i, t_idx.global[1]); 16: t_idx.barrier.wait(); 17: for (int k = 0; k < TS; k++) 18: sum += locA[row][k] * locB[k][col]; 19: t_idx.barrier.wait(); 20: } 21: c[t_idx.global] = sum; 22: }); 23: } Notice that all the code up to line 9 is the same as per the changes we made in part 1 of tiling introduction. If you squint, the body of the lambda itself preserves the original algorithm on lines 10, 11, and 17, 18, and 21. The difference being that those lines use new indexing and the tile_static arrays; the tile_static arrays are declared and initialized on the brand new lines 13-15. On those lines we copy from the global memory represented by the array_view objects (a and b), to the tile_static vanilla arrays (locA and locB) – we are copying enough to fit a tile. Because in the code that follows on line 18 we expect the data for this tile to be in the tile_static storage, we need to synchronize the threads within each tile with a barrier, which we do on line 16 (to avoid accessing uninitialized memory on line 18). We also need to synchronize the threads within a tile on line 19, again to avoid the race between lines 14, 15 (retrieving the next set of data for each tile and overwriting the previous set) and line 18 (not being done processing the previous set of data). Luckily, as part of the awesome C++ AMP debugger in Visual Studio there is an option that helps you find such races, but that is a story for another blog post another time. May I suggest reading the next section, and then coming back to re-read and walk through this code with pen and paper to really grok what is going on, if you haven't already? Cool. Why would I introduce this tiling complexity into my code? Funny you should ask that, I was just about to tell you. There is only one reason we tiled our extent, had to deal with finding a good tile size, ensure the number of threads we schedule are correctly divisible with the tile size, had to use a tiled_index instead of a normal index, and had to understand tile_barrier and to figure out where we need to use it, and double the size of our lambda in terms of lines of code: the reason is to be able to use tile_static memory. Why do we want to use tile_static memory? Because accessing tile_static memory is around 10 times faster than accessing the global memory on an accelerator like the GPU, e.g. in the code above, if you can get 150GB/second accessing data from the array_view a, you can get 1500GB/second accessing the tile_static array locA. And since by definition you are dealing with really large data sets, the savings really pay off. We have seen tiled implementations being twice as fast as their non-tiled counterparts. Now, some algorithms will not have performance benefits from tiling (and in fact may deteriorate), e.g. algorithms that require you to go only once to global memory will not benefit from tiling, since with tiling you already have to fetch the data once from global memory! Other algorithms may benefit, but you may decide that you are happy with your code being 150 times faster than the serial-version you had, and you do not need to invest to make it 250 times faster. Also algorithms with more than 3 dimensions, which C++ AMP supports in the non-tiled model, cannot be tiled. Also note that in future releases, we may invest in making the non-tiled model, which already uses tiling under the covers, go the extra step and use tile_static memory on your behalf, but it is obviously way to early to commit to anything like that, and we certainly don't do any of that today. Comments about this post by Daniel Moth welcome at the original blog.

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  • PreApplicationStartMethod Attribute causes exception

    - by Joop
    Strange thing happening to me with the PreApplicationStartMethod Attribute. I did implement it in my latest project. In the AssemblyInfo.cs I have the following line: [assembly: PreApplicationStartMethod(typeof(MyAssembly.Initializer), "Initialize")] The Type and method look like this: namespace MyAssembly { public static class Initializer { public static void Initialize() { TranslationKeys.Initialize(); } } } When I rebuild my application and load it in the browser I get the following error: The method specified by the PreApplicationStartMethodAttribute on assembly 'MyWebApp, Version=0.0.1.0, Culture=neutral, PublicKeyToken=null' cannot be resolved. Type: 'MyAssembly.Initializer', MethodName: 'Initialize'. Verify that the type is public and the method is public and static (Shared in Visual Basic). I really have no idea what the problem is.

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  • Array Multiplication and Division

    - by Narfanator
    I came across a question that (eventually) landed me wondering about array arithmetic. I'm thinking specifically in Ruby, but I think the concepts are language independent. So, addition and subtraction are defined, in Ruby, as such: [1,6,8,3,6] + [5,6,7] == [1,6,8,3,6,5,6,7] # All the elements of the first, then all the elements of the second [1,6,8,3,6] - [5,6,7] == [1,8,3] # From the first, remove anything found in the second and array * scalar is defined: [1,2,3] * 2 == [1,2,3,1,2,3] But What, conceptually, should the following be? None of these are (as far as I can find) defined: Array x Array: [1,2,3] * [1,2,3] #=> ? Array / Scalar: [1,2,3,4,5] / 2 #=> ? Array / Scalar: [1,2,3,4,5] % 2 #=> ? Array / Array: [1,2,3,4,5] / [1,2] #=> ? Array / Array: [1,2,3,4,5] % [1,2] #=> ? I've found some mathematical descriptions of these operations for set theory, but I couldn't really follow them, and sets don't have duplicates (arrays do). Edit: Note, I do not mean vector (matrix) arithmetic, which is completely defined. Edit2: If this is the wrong stack exchange, tell me which is the right one and I'll move it. Edit 3: Add mod operators to the list. Edit 4: I figure array / scalar is derivable from array * scalar: a * b = c => a = b / c [1,2,3] * 3 = [1,2,3]+[1,2,3]+[1,2,3] = [1,2,3,1,2,3,1,2,3] => [1,2,3] = [1,2,3,1,2,3,1,2,3] / 3 Which, given that programmer's division ignore the remained and has modulus: [1,2,3,4,5] / 2 = [[1,2], [3,4]] [1,2,3,4,5] % 2 = [5] Except that these are pretty clearly non-reversible operations (not that modulus ever is), which is non-ideal. Edit: I asked a question over on Math that led me to Multisets. I think maybe extensible arrays are "multisets", but I'm not sure yet.

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  • I need help with Widget and PendingIntents

    - by YaW
    Hi, I've asked here a question about Task Killers and widgets stop working (SO Question) but now, I have reports of user that they don't use any Task Killer and the widgets didn't work after a while. I have a Nexus One and I don't have this problem. I don't know if this is a problem of memory or something. Based on the API: A PendingIntent itself is simply a reference to a token maintained by the system describing the original data used to retrieve it. This means that, even if its owning application's process is killed, the PendingIntent itself will remain usable from other processes that have been given it. So, I don't know why widget stop working, if Android doesn't kill the PendingIntent by itself, what's the problem? This is my manifest code: <receiver android:name=".widget.InstantWidget" android:label="@string/app_name"> <intent-filter> <action android:name="android.appwidget.action.APPWIDGET_UPDATE" /> </intent-filter> <meta-data android:name="android.appwidget.provider" android:resource="@xml/widget_provider" /> </receiver> And the widget code: public class InstantWidget extends AppWidgetProvider { public static ArrayList<Integer> alWidgetsId = new ArrayList<Integer>(); private static final String PREFS_NAME = "com.cremagames.instant.InstantWidget"; private static final String PREF_PREFIX_NOM = "nom_"; private static final String PREF_PREFIX_RAW = "raw_"; /** * Esto se llama cuando se crea el widget. Metemos en las preferencias los valores de nombre y raw para tenerlos en proximos reboot. * @param context * @param appWidgetManager * @param appWidgetId * @param nombreSound * @param rawSound */ static void updateAppWidget(Context context, AppWidgetManager appWidgetManager, int appWidgetId, String nombreSound, int rawSound){ //Guardamos en las prefs los valores SharedPreferences.Editor prefs = context.getSharedPreferences(PREFS_NAME, 0).edit(); prefs.putString(PREF_PREFIX_NOM + appWidgetId, nombreSound); prefs.putInt(PREF_PREFIX_RAW + appWidgetId, rawSound); prefs.commit(); //Actualizamos la interfaz updateWidgetGrafico(context, appWidgetManager, appWidgetId, nombreSound, rawSound); } /** * Actualiza la interfaz gráfica del widget (pone el nombre y crea el intent con el raw) * @param context * @param appWidgetManager * @param appWidgetId * @param nombreSound * @param rawSound */ private static void updateWidgetGrafico(Context context, AppWidgetManager appWidgetManager, int appWidgetId, String nombreSound, int rawSound){ RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.widget); //Nombre del Button remoteViews.setTextViewText(R.id.tvWidget, nombreSound); //Creamos el PendingIntent para el onclik del boton Intent active = new Intent(context, InstantWidget.class); active.setAction(String.valueOf(appWidgetId)); active.putExtra("sonido", rawSound); PendingIntent actionPendingIntent = PendingIntent.getBroadcast(context, 0, active, 0); actionPendingIntent.cancel(); actionPendingIntent = PendingIntent.getBroadcast(context, 0, active, 0); remoteViews.setOnClickPendingIntent(R.id.btWidget, actionPendingIntent); appWidgetManager.updateAppWidget(appWidgetId, remoteViews); } public void onReceive(Context context, Intent intent) { final String action = intent.getAction(); //Esto se usa en la 1.5 para que se borre bien el widget if (AppWidgetManager.ACTION_APPWIDGET_DELETED.equals(action)) { final int appWidgetId = intent.getExtras().getInt( AppWidgetManager.EXTRA_APPWIDGET_ID, AppWidgetManager.INVALID_APPWIDGET_ID); if (appWidgetId != AppWidgetManager.INVALID_APPWIDGET_ID) { this.onDeleted(context, new int[] { appWidgetId }); } } else { //Listener de los botones for(int i=0; i<alWidgetsId.size(); i++){ if (intent.getAction().equals(String.valueOf(alWidgetsId.get(i)))) { int sonidoRaw = 0; try { sonidoRaw = intent.getIntExtra("sonido", 0); } catch (NullPointerException e) { } MediaPlayer mp = MediaPlayer.create(context, sonidoRaw); mp.start(); mp.setOnCompletionListener(completionListener); } } super.onReceive(context, intent); } } /** Al borrar el widget, borramos también las preferencias **/ public void onDeleted(Context context, int[] appWidgetIds) { for(int i=0; i<appWidgetIds.length; i++){ //Recogemos las preferencias SharedPreferences.Editor prefs = context.getSharedPreferences(PREFS_NAME, 0).edit(); prefs.remove(PREF_PREFIX_NOM + appWidgetIds[i]); prefs.remove(PREF_PREFIX_RAW + appWidgetIds[i]); prefs.commit(); } super.onDeleted(context, appWidgetIds); } /**Este método se llama cada vez que se refresca un widget. En nuestro caso, al crearse y al reboot del telefono. Al crearse lo único que hace es guardar el id en el arrayList Al reboot, vienen varios ID así que los recorremos y guardamos todos y también recuperamos de las preferencias el nombre y el sonido*/ public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) { for(int i=0; i<appWidgetIds.length; i++){ //Metemos en el array los IDs de los widgets alWidgetsId.add(appWidgetIds[i]); //Recogemos las preferencias SharedPreferences prefs = context.getSharedPreferences(PREFS_NAME, 0); String nomSound = prefs.getString(PREF_PREFIX_NOM + appWidgetIds[i], null); int rawSound = prefs.getInt(PREF_PREFIX_RAW + appWidgetIds[i], 0); //Si están creadas, actualizamos la interfaz if(nomSound != null){ updateWidgetGrafico(context, appWidgetManager, appWidgetIds[i], nomSound, rawSound); } } } MediaPlayer.OnCompletionListener completionListener = new MediaPlayer.OnCompletionListener(){ public void onCompletion(MediaPlayer mp) { if(mp != null){ mp.stop(); mp.release(); mp = null; } } }; } Sorry for the comments in Spanish. I have the possibility to put differents widgets on the desktop, that's why I use the widgetId as the "unique id" for the PendingIntent. Any ideas please? The 70% of the functionality of my app is the widgets, and it isn't working for some users :( Thanks in advance and sorry for my English.

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  • Boiler plate code replacement - is there anything bad about this code?

    - by Benjol
    I've recently created these two (unrelated) methods to replace lots of boiler-plate code in my winforms application. As far as I can tell, they work ok, but I need some reassurance/advice on whether there are some problems I might be missing. (from memory) static class SafeInvoker { //Utility to avoid boiler-plate InvokeRequired code //Usage: SafeInvoker.Invoke(myCtrl, () => myCtrl.Enabled = false); public static void Invoke(Control ctrl, Action cmd) { if (ctrl.InvokeRequired) ctrl.BeginInvoke(new MethodInvoker(cmd)); else cmd(); } //Replaces OnMyEventRaised boiler-plate code //Usage: SafeInvoker.RaiseEvent(this, MyEventRaised) public static void RaiseEvent(object sender, EventHandler evnt) { var handler = evnt; if (handler != null) handler(sender, EventArgs.Empty); } } EDIT: See related question here UPDATE Following on from deadlock problems (related in this question), I have switched from Invoke to BeginInvoke (see an explanation here). Another Update Regarding the second snippet, I am increasingly inclined to use the 'empty delegate' pattern, which fixes this problem 'at source' by declaring the event directly with an empty handler, like so: event EventHandler MyEventRaised = delegate {};

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  • JBoss Seam: components injected into POJOs, but not Session Beans

    - by purecharger
    I have a Seam component that handles login, with the name "authenticator": @Name("authenticator") public class AuthenticatorAction implements Authenticator { @PersistenceContext private EntityManager em; @In(required=false) @Out(required=false, scope = SESSION) private User user; public boolean authenticate(){ ... } } This works just fine, Seam injects the EntityManager instance. However, as soon as I add the @Stateless annotation, none of the injection happens! In this case, the EntityManager instance is null upon entry to the authenticate() method. Another interesting note is that with a separate stateful session bean I have, the Logger instance in that class is only injected if I make it static. If i have it non-static, it is not injected. Thats fine for the logger, but for stateless session beans like that, I obviously can't have static member variables for these components. I'm confused because this authenticator is exactly how it is in the Seam booking example: a stateless session bean with a private member variable being injected. Any ideas?

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  • Using polygons instead of quads on Cocos2d

    - by rraallvv
    I've been looking under the hood of Cocos2d, and I think (please correct me if I'm wrong) that although working with quads is a key feature of the engine, it should't be dificult to make it work with arrays of vertices (aka polygons) instead of quads, being the quads a special case of an array of four vertices by the way, does anyone have any code that makes cocos2d render a texture filled polygon inside a batch node? the code posted here (http://www.cocos2d-iphone.org/forum/topic/8142/page/2#post-89393) does a nice job rendering a texture filled polygon but the class doesn't work with batch nodes

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  • Overly accessible and incredibly resource hungry relationships between business objects. How can I f

    - by Mike
    Hi, Firstly, This might seem like a long question. I don't think it is... The code is just an overview of what im currently doing. It doesn't feel right, so I am looking for constructive criticism and warnings for pitfalls and suggestions of what I can do. I have a database with business objects. I need to access properties of parent objects. I need to maintain some sort of state through business objects. If you look at the classes, I don't think that the access modifiers are right. I don't think its structured very well. Most of the relationships are modelled with public properties. SubAccount.Account.User.ID <-- all of those are public.. Is there a better way to model a relationship between classes than this so its not so "public"? The other part of this question is about resources: If I was to make a User.GetUserList() function that returns a List, and I had 9000 users, when I call the GetUsers method, it will make 9000 User objects and inside that it will make 9000 new AccountCollection objects. What can I do to make this project not so resource hungry? Please find the code below and rip it to shreds. public class User { public string ID {get;set;} public string FirstName {get; set;} public string LastName {get; set;} public string PhoneNo {get; set;} public AccountCollection accounts {get; set;} public User { accounts = new AccountCollection(this); } public static List<Users> GetUsers() { return Data.GetUsers(); } } public AccountCollection : IEnumerable<Account> { private User user; public AccountCollection(User user) { this.user = user; } public IEnumerable<Account> GetEnumerator() { return Data.GetAccounts(user); } } public class Account { public User User {get; set;} //This is public so that the subaccount can access its Account's User's ID public int ID; public string Name; public Account(User user) { this.user = user; } } public SubAccountCollection : IEnumerable<SubAccount> { public Account account {get; set;} public SubAccountCollection(Account account) { this.account = account; } public IEnumerable<SubAccount> GetEnumerator() { return Data.GetSubAccounts(account); } } public class SubAccount { public Account account {get; set;} //this is public so that my Data class can access the account, to get the account's user's ID. public SubAccount(Account account) { this.account = account; } public Report GenerateReport() { Data.GetReport(this); } } public static class Data { public static List<Account> GetSubAccounts(Account account) { using (var dc = new databaseDataContext()) { List<SubAccount> query = (from a in dc.Accounts where a.UserID == account.User.ID //this is getting the account's user's ID select new SubAccount(account) { ID = a.ID, Name = a.Name, }).ToList(); } } public static List<Account> GetAccounts(User user) { using (var dc = new databaseDataContext()) { List<Account> query = (from a in dc.Accounts where a.UserID == User.ID //this is getting the user's ID select new Account(user) { ID = a.ID, Name = a.Name, }).ToList(); } } public static Report GetReport(SubAccount subAccount) { Report report = new Report(); //database access code here //need to get the user id of the subaccount's account for data querying. //i've got the subaccount, but how should i get the user id. //i would imagine something like this: int accountID = subAccount.Account.User.ID; //but this would require the subaccount's Account property to be public. //i do not want this to be accessible from my other project (UI). //reading up on internal seems to do the trick, but within my code it still feels //public. I could restrict the property to read, and only private set. return report; } public static List<User> GetUsers() { using (var dc = new databaseDataContext()) { var query = (from u in dc.Users select new User { ID = u.ID, FirstName = u.FirstName, LastName = u.LastName, PhoneNo = u.PhoneNo }).ToList(); return query; } } }

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  • asp.net - csharp - jquery - looking for a better and usage solution

    - by LostLord
    hi my dear friends i have a little problem about using jquery...(i reeally do not know jquery but i forced to use it) i am using vs 2008 - asp.net web app with c# also i am using telerik controls in my pages also i am using sqldatasources (Connecting to storedprocedures) in my pages my pages base on master and content pages and in content pages i have mutiviews ================================================================================= in one of the views(inside one of those multiviews)i had made two radcombo boxes for country and city requirement like cascading dropdowns as parent and child combo boxes. i used old way for doing that , i mean i used update panel and in the SelectedIndexChange Event of Parent RadComboBox(Country) i Wrote this code : protected void RadcomboboxCountry_SelectedIndexChanged(object o, RadComboBoxSelectedIndexChangedEventArgs e) { hfSelectedCo_ID.Value = RadcomboboxCountry.SelectedValue; RadcomboboxCity.Items.Clear(); RadcomboboxCity.Items.Add(new RadComboBoxItem(" ...", "5")); RadcomboboxCity.DataBind(); RadcomboboxCity.SelectedIndex = 0; } my child radcombo box can fill by upper code , let me tell you how : the child sqldatasource have a sp that has a parameter and i fill that parameter by this line - hfSelectedCo_ID.Value = RadcbCoNameInInsert.SelectedValue; RadcbCoNameInInsert.SelectedValue means country ID. after doing that SelectedIndexChange Event of Parent RadComboBox(Country) could not be fire therefore i forced to set the autopostback property to true. afetr doing that every thing was ok until some one told me can u control focus and keydown of your radcombo boxes (when u press enter key on the parent combobox[country] , so child combobox gets focus -- and when u press upperkey on child radcombobox [city], so parent combobox[country] gets focus) (For Users That Do Not Want To Use Mouse for Input Info And Choose items) i told him this is web app , not win form and we can not do that. i googled it and i found jquery the only way for doing that ... so i started using jquery . i wrote this code with jquery for both of them : <script src="../JQuery/jquery-1.4.1.js" language="javascript" type="text/javascript"></script> <script type="text/javascript"> $(function() { $('input[id$=RadcomboboxCountry_Input]').focus(); $('input[id$=RadcomboboxCountry_Input]').select(); $('input[id$=RadcomboboxCountry_Input]').bind('keyup', function(e) { var code = (e.keyCode ? e.keyCode : e.which); if (code == 13) { -----------> Enter Key $('input[id$=RadcomboboxCity_Input]').focus(); $('input[id$=RadcomboboxCity_Input]').select(); } }); $('input[id$=RadcomboboxCity_Input]').bind('keyup', function(e) { var code = (e.keyCode ? e.keyCode : e.which); if (code == 38) { -----------> Upper Key $('input[id$=RadcomboboxCountry_Input]').focus(); $('input[id$=RadcomboboxCountry_Input]').select(); } }); }); </script> this jquery code worked BBBBBBUUUUUUUTTTTTT autopostback=true of the Parent RadComboBox Became A Problem , Because when SelectedIndex Change Of ParentRadComboBox is fired after that Telerik Skins runs and after that i lost parent ComboBox Focus and we should use mouse but we don't want it.... for fix this problem i decided to set autopostback of perentCB to false and convert protected void RadcomboboxCountry_SelectedIndexChanged(object o, RadComboBoxSelectedIndexChangedEventArgs e) { hfSelectedCo_ID.Value = RadcomboboxCountry.SelectedValue; RadcomboboxCity.Items.Clear(); RadcomboboxCity.Items.Add(new RadComboBoxItem(" ...", "5")); RadcomboboxCity.DataBind(); RadcomboboxCity.SelectedIndex = 0; } to a public non static method without parameters and call it with jquey like this : (i used onclientchanged property of parentcombo box like onclientchanged = "MyMethodForParentCB_InJquery();" insread of selectedindexchange event) public void MyMethodForParentCB_InCodeBehind() { hfSelectedCo_ID.Value = RadcomboboxCountry.SelectedValue; RadcomboboxCity.Items.Clear(); RadcomboboxCity.Items.Add(new RadComboBoxItem(" ...", "5")); RadcomboboxCity.DataBind(); RadcomboboxCity.SelectedIndex = 0; } for doing that i read the blow manual and do that step by step : ======================================================================= http://www.ajaxprojects.com/ajax/tutorialdetails.php?itemid=732 ======================================================================= but this manual is about static methods and this is my new problem ... when i am using static method like : public static void MyMethodForParentCB_InCodeBehind() { hfSelectedCo_ID.Value = RadcomboboxCountry.SelectedValue; RadcomboboxCity.Items.Clear(); RadcomboboxCity.Items.Add(new RadComboBoxItem(" ...", "5")); RadcomboboxCity.DataBind(); RadcomboboxCity.SelectedIndex = 0; } so i recieved some errors and this method could not recognize my controls and hidden field... one of those errors like this : Error 2 An object reference is required for the non-static field, method, or property 'Darman.SuperAdmin.Users.hfSelectedCo_ID' C:\Javad\Copy of Darman 6\Darman\SuperAdmin\Users.aspx.cs 231 13 Darman any idea or is there any way to call non static methods with jquery (i know we can not do that but is there another way to solve my problem)???????????????

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  • Making GWT application crawlable by a search engine.

    - by Philippe Beaudoin
    I want to use the #! token to make my GWT application crawlable, as described here: http://code.google.com/web/ajaxcrawling/ There is a GWT sample app available online that uses this, for example: http://gwt.google.com/samples/Showcase/Showcase.html#!CwRadioButton Will serve the following static webpage to the googlebot: http://gwt.google.com/samples/Showcase/Showcase.html?_escaped_fragment_=CwRadioButton I want my GWT app to do something similar. In short, I'd like to serve a different flavor of the page whenever the _escaped_fragment_ parameter is found in the URL. What should I modify in order for the server to serve something else (a static page, or a page dynamically generated through a headless browser like HTML Unit)? I'm guessing it could be the web.xml file, but I'm not sure. (Note: I thought of checking the Showcase app provided with the GWT SDK, but unfortunately it doesn't seem to support serving static files on _escaped_fragment_ and it doesn't use the #! token..)

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  • Is there an appropriate coding style for implementing an algorithm during an interview?

    - by GlenPeterson
    I failed an interview question in C years ago about converting hex to decimal by not exploiting the ASCII table if (inputDigitByte > 9) hex = inputDigitByte - 'a'. The rise of Unicode has made this question pretty silly, but the point was that the interviewer valued raw execution speed above readability and error handling. They tell you to review algorithms textbooks to prepare for these interviews, yet these same textbooks tend to favor the implementation with the fewest lines of code, even if it has to rely on magic numbers (like "infinity") and a slower, more memory-intensive implementation (like a linked list instead of an array) to do that. I don't know what is right. Coding an algorithm within the space of an interview has at least 3 constraints: time to code, elegance/readability, and efficiency of execution. What trade-offs are appropriate for interview code? How much do you follow the textbook definition of an algorithm? Is it better to eliminate recursion, unroll loops, and use arrays for efficiency? Or is it better to use recursion and special values like "infinity" or Integer.MAX_VALUE to reduce the number of lines of code needed to write the algorithm? Interface: Make a very self-contained, bullet-proof interface, or sloppy and fast? On the one extreme, the array to be sorted might be a public static variable. On the other extreme, it might need to be passed to each method, allowing methods to be called individually from different threads for different purposes. Is it appropriate to use a linked-list data structure for items that are traversed in one direction vs. using arrays and doubling the size when the array is full? Implementing a singly-linked list during the interview is often much faster to code and easier remember for recursive algorithms like MergeSort. Thread safety - just document that it's unsafe, or say so verbally? How much should the interviewee be looking for opportunities for parallel processing? Is bit shifting appropriate? x / 2 or x >> 1 Polymorphism, type safety, and generics? Comments? Variable and method names: qs(a, p, q, r) vs: quickSort(theArray, minIdx, partIdx, maxIdx) How much should you use existing APIs? Obviously you can't use a java.util.HashMap to implement a hash-table, but what about using a java.util.List to accumulate your sorted results? Are there any guiding principals that would answer these and other questions, or is the guiding principal to ask the interviewer? Or maybe this should be the basis of a discussion while writing the code? If an interviewer can't or won't answer one of these questions, are there any tips for coaxing the information out of them?

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  • Throwing exception vs returning null value with switch statement

    - by Greg
    So I have function that formats a date to coerce to given enum DateType{CURRENT, START, END} what would be the best way to handling return value with cases that use switch statement public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... default:throw new ("Something strange happend"); } } OR throw excpetion at the end public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... } //It will never reach here, just to make compiler happy throw new IllegalArgumentException("Something strange happend"); } OR return null public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... } return null; } What would be the best practice here ? Also all the enum values will be handled in the case statement

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  • Return/consume dynamic anonymous type across assembly boundaries

    - by friism
    The code below works great. If the Get and Use methods are in different assemblies, the code fails with a RuntimeBinderException. This is because the .Net runtime system only guarantees commonality of anonymous types (<string, int> in this case) within assemblies. Is there any way to fool the runtime system to overcome this? I can expect the object in the debugger on the Use side, and the debugger can see the relevant properties. class Program { static void Main(string[] args) { UsePerson(); Console.ReadLine(); } public static void UsePerson() { var person = GetPerson(); Console.WriteLine(person.Name); } public static dynamic GetPerson() { return new { Name = "Foo", Age = 30 }; } }

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  • Attribute class not calling constructor

    - by Coppermill
    I have created an Attribute, call MyAttribute, which is performing some security and for some reason the Constructor is not being fired, any reason why? public class Driver { // Entry point of the program public static void Main(string[] Args) { Console.WriteLine(SayHello1("Hello to Me 1")); Console.WriteLine(SayHello2("Hello to Me 2")); Console.ReadLine(); } [MyAttribute("hello")] public static string SayHello1(string str) { return str; } [MyAttribute("Wrong Key, should fail")] public static string SayHello2(string str) { return str; } } [AttributeUsage(AttributeTargets.Method)] public class MyAttribute : Attribute { public MyAttribute(string VRegKey) { if (VRegKey == "hello") { Console.WriteLine("Aha! You're Registered"); } else { throw new Exception("Oho! You're not Registered"); }; } }

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  • How to show that the double-checked-lock pattern with Dictionary's TryGetValue is not threadsafe in

    - by Amir
    Recently I've seen some C# projects that use a double-checked-lock pattern on a Dictionary. Something like this: private static readonly object _lock = new object(); private static volatile IDictionary<string, object> _cache = new Dictionary<string, object>(); public static object Create(string key) { object val; if (!_cache.TryGetValue(key, out val)) { lock (_lock) { if (!_cache.TryGetValue(key, out val)) { val = new object(); // factory construction based on key here. _cache.Add(key, val); } } } return val; } This code is incorrect, since the Dictionary can be "growing" the collection in _cache.Add() while _cache.TryGetValue (outside the lock) is iterating over the collection. It might be extremely unlikely in many situations, but is still wrong. Is there a simple program to demonstrate that this code fails? Does it make sense to incorporate this into a unit test? And if so, how?

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