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• What is the equivalent of .NET events in Ruby?

  - by Gishu

  The problem is very simple. An object needs to notify some events that might be of interest to observers. When I sat to validate a design that I cooked up now in Ruby just to validate it.. I find myself stumped as to how to implement the object events. In .Net this would be a one-liner.. .Net also does handler method signature verification,etc. e.g. // Object with events public delegate void HandlerSignature(int a); public event HandlerSignature MyEvent; public event HandlerSignature AnotherCriticalEvent; // Client MyObject.MyEvent += new HandlerSignature(MyHandlerMethod); // MyHandlerMethod has same signature as delegate Is there an EventDispatcher module or something that I am missing that I can strap on to a Ruby class ? Hoping for an answer that plays along with Ruby's principle of least surprise. An event would be the name of the event plus a queue of [observer, methodName] objects that need to be invoked when the event takes place.

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• Java Concurrency : Synchronized(this) => and this.wait() and this.notify()

  - by jens

  Hello Experts, I would appreciate your help in understand a "Concurrency Example" from: http://forums.sun.com/thread.jspa?threadID=735386 Qute Start: public synchronized void enqueue(T obj) { // do addition to internal list and then... this.notify(); } public synchronized T dequeue() { while (this.size()==0) { this.wait(); } return // something from the queue } Quote End: My Question is: Why is this code valid? = When I synchronize a method like "public synchronized" = then I synchronize on the "Instance of the Object == this". However in the example above: Calling "dequeue" I will get the "lock/monitor" on this Now I am in the dequeue method. As the list is zero, the calling thread will be "waited" From my understanding I have now a deadlock situation, as I will have no chance of ever enquing an object (from an nother thread), as the "dequeue" method is not yet finised and the dequeue "method" holds the lock on this: So I will never ever get the possibility to call "enequeue" as I will not get the "this" lock. Backround: I have exactly the same problem: I have some kind of connection pool (List of Connections) and need to block if all connections are checked. What is the correct way to synchronize the List to block, if size exceeds a limit or is zero? Thank you very much Jens

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• Setting up DrJava to work through Friedman / Felleisen "A Little Java"

  - by JDelage

  All, I'm going through the Friedman & Felleisen book "A Little Java, A Few Patterns". I'm trying to type the examples in DrJava, but I'm getting some errors. I'm a beginner, so I might be making rookie mistakes. Here is what I have set-up: public class ALittleJava { //ABSTRACT CLASS POINT abstract class Point { abstract int distanceToO(); } class CartesianPt extends Point { int x; int y; int distanceToO(){ return((int)Math.sqrt(x*x+y*y)); } CartesianPt(int _x, int _y) { x=_x; y=_y; } } class ManhattanPt extends Point { int x; int y; int distanceToO(){ return(x+y); } ManhattanPt(int _x, int _y){ x=_x; y=_y; } } } And on the main's side: public class Main{ public static void main (String [] args){ Point y = new ManhattanPt(2,8); System.out.println(y.distanceToO()); } } The compiler cannot find the symbols Point and ManhattanPt in the program. If I precede each by ALittleJava., I get another error in the main, i.e., an enclosing instance that contains ALittleJava.ManhattanPt is required I've tried to find ressources on the 'net, but the book must have a pretty confidential following and I couldn't find much. Thank you all. JDelage

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• Declaring functors for comparison ??

  - by Mr.Gando

  Hello, I have seen other people questions but found none that applied to what I'm trying to achieve here. I'm trying to sort Entities via my EntityManager class using std::sort and a std::vector<Entity *> /*Entity.h*/ class Entity { public: float x,y; }; struct compareByX{ bool operator()(const GameEntity &a, const GameEntity &b) { return (a.x < b.x); } }; /*Class EntityManager that uses Entitiy*/ typedef std::vector<Entity *> ENTITY_VECTOR; //Entity reference vector class EntityManager: public Entity { private: ENTITY_VECTOR managedEntities; public: void sortEntitiesX(); }; void EntityManager::sortEntitiesX() { /*perform sorting of the entitiesList by their X value*/ compareByX comparer; std::sort(entityList.begin(), entityList.end(), comparer); } I'm getting a dozen of errors like : error: no match for call to '(compareByX) (GameEntity* const&, GameEntity* const&)' : note: candidates are: bool compareByX::operator()(const GameEntity&, const GameEntity&) I'm not sure but ENTITY_VECTOR is std::vector<Entity *> , and I don't know if that could be the problem when using the compareByX functor ? I'm pretty new to C++, so any kind of help is welcome.

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• Why is XmlSerializer so hard to use?

  - by mafutrct

  I imagine to use XML serialization like this: class Foo { public Foo (string name) { Name1 = name; Name2 = name; } [XmlInclude] public string Name1 { get; private set; } [XmlInclude] private string Name2; } StreamWriter wr = new StreamWriter("path.xml"); new XmlSerializer<Foo>().Serialize (wr, new Foo ("me")); But this does not work at all: XmlSerializer is not generic. I have to cast from and to object on (de)serialization. Every property has to be fully public. Why aren't we just using Reflection to access private setters? Private fields cannot be serialized. I'd like to decorate private fields with an attribute to have XmlSerializer include them. Did I miss something and XmlSerializer is actually offering the described possibilities? Are there alternate serializers to XML that handle these cases more sophisticatedly? If not: We're in 2010 after all, and .NET has been around for many years. XML serialization is often used, totally standard and should be really easy to perform. Or is my understanding possibly wrong and XML serialization ought not to expose the described features for a good reason? (Feel free to adjust caption or tags. If this should be CW, please just drop a note.)

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• Partial template specialization on a class

  - by Jonathan Swinney

  I'm looking for a better way to this. I have a chunk of code that needs to handle several different objects that contain different types. The structure that I have looks like this: class Base { // some generic methods } template <typename T> class TypedBase : public Base { // common code with template specialization private: std::map<int,T> mapContainingSomeDataOfTypeT; } template <> class TypedBase<std::string> : public Base { // common code with template specialization public: void set( std::string ); // functions not needed for other types std::string get(); private: std::map<int,std::string> mapContainingSomeDataOfTypeT; // some data not needed for other types } Now I need to add some additional functionality that only applies to one of the derivative classes. Specifically the std::string derivation, but the type doesn't actually matter. The class is big enough that I would prefer not copy the whole thing simply to specialize a small part of it. I need to add a couple of functions (and accessor and modifier) and modify the body of several of the other functions. Is there a better way to accomplish this?

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• I'm getting an error in my Java code but I can't see whats wrong with it. Help?

  - by Fraz

  The error i'm getting is in the fillPayroll() method in the while loop where it says payroll.add(employee). The error says I can't invoke add() on an array type Person but the Employee class inherits from Person so I thought this would be possible. Can anyone clarify this for me? import java.io.*; import java.util.*; public class Payroll { private int monthlyPay, tax; private Person [] payroll = new Person [1]; //Method adds person to payroll array public void add(Person person) { if(payroll[0] == null) //If array is empty, fill first element with person { payroll[payroll.length-1] = person; } else //Creates copy of payroll with new person added { Person [] newPayroll = new Person [payroll.length+1]; for(int i = 0;i<payroll.length;i++) { newPayroll[i] = payroll[i]; } newPayroll[newPayroll.length] = person; payroll = newPayroll; } } public void fillPayroll() { try { FileReader fromEmployee = new FileReader ("EmployeeData.txt"); Scanner data = new Scanner(fromEmployee); Employee employee = new Employee(); while (data.hasNextLine()) { employee.readData(data.nextLine()); payroll.add(employee); } } catch (FileNotFoundException e) { System.out.println("Error: File Not Found"); } } }

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• Android Loading listview items from service results in hang

  - by Isaac Waller

  Hello, In my Android application, I have a ListActivity. This ListActivity uses a SimpleAdapter that I fill with items from my service. So, in my code, I do: MySuperCoolService.Binder serviceBinder = null; private ServiceConnection serviceConnection = new ServiceConnection() { public void onServiceConnected(ComponentName className, IBinder service) { Log.d(TAG, "Service connection: connected!"); serviceBinder = (MySuperCoolService.Binder)service; } public void onServiceDisconnected(ComponentName className) { Log.d(TAG, "Service connection: disconnected"); serviceBinder = null; } }; bindService(new Intent(this, MySuperCoolService.class), serviceConnection, BIND_AUTO_CREATE); while(serviceBinder==null) { Thread.Sleep(1000); } // now retrieve from service using binder and set list adapter This whole operation takes hardly any time (less than a second), so I want it to run in the UI thread. See my onCreate: public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); fillDataUsingCodeAbove(); } The reason I want this to run in the UI thread is that if you have a list item selected, or you have scrolled to a certain position in the ListView, and you rotate the device or take out the keyboard or something (to trigger a configuration change) when my activity is restarted, Android will try to restore the state right after onCreate. But, if I run it in a separate thread, it will not. Also there is a cool fadein animation too :) The problem I am having with running it in the UI thread is that when I try to bind to the service, that service bind request gets put onto the message queue. But then when I go into my loop, I stop the message queue from looping. So my program hangs, because it's waiting for the service to get bound, and the service won't get bound until the loop ends. I have thought of putting Looper.loop() inside my loop, but that just hangs it at Looper.loop() (I don't know why.) Sorry for such a long question, Isaac Waller

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• How to return a recordset from a function

  - by Scott

  I'm building a data access layer in Excel VBA and having trouble returning a recordset. The Execute() function in my class is definitely retrieving a row from the database, but doesn't seem to be returning anything. The following function is contained in a class called DataAccessLayer. The class contains functions Connect and Disconnect which handle opening and closing the connection. Public Function Execute(ByVal sqlQuery as String) As ADODB.recordset Set recordset = New ADODB.recordset Dim recordsAffected As Long ' Make sure we are connected to the database. If Connect Then Set command = New ADODB.command With command .ActiveConnection = connection .CommandText = sqlQuery .CommandType = adCmdText End With ' These seem to be equivalent. 'Set recordset = command.Execute(recordsAffected) recordset.Open command.Execute(recordsAffected) Set Execute = recordset recordset.ActiveConnection = Nothing recordset.Close Set command = Nothing Call Disconnect End If Set recordset = Nothing End Function Here's a public function that I'm using in cell A1 of my spreadsheet for testing. Public Function Scott_Test() Dim Database As New DataAccessLayer 'Dim rs As ADODB.recordset 'Set rs = CreateObject("ADODB.Recordset") Set rs = New ADODB.recordset Set rs = Database.Execute("SELECT item_desc_1 FROM imitmidx_sql WHERE item_no = '11001'") 'rs.Open Database.Execute("SELECT item_desc_1 FROM imitmidx_sql WHERE item_no = '11001'") 'rs.Open ' This never displays. MsgBox rs.EOF If Not rs.EOF Then ' This is displaying #VALUE! in cell A1. Scott_Test = rs!item_desc_1 End If rs.ActiveConnection = Nothing Set rs = Nothing End Function What am I doing wrong?

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• Incremental Timer

  - by Donal Rafferty

  I'm currently using a Timer and TimerTask to perform some work every 30 seconds. My problem is that after each time I do this work I want to increment the interval time of the Timer. So for example it starts off with 30 seconds between the timer firing but I want to add 10 seconds to the interval then so that the next time the Timer takes 40 seconds before it fires. Here is my current code: public void StartScanning() { scanTask = new TimerTask() { public void run() { handler.post(new Runnable() { public void run() { wifiManager.startScan(); scanCount++; if(SCAN_INTERVAL_TIME <= SCAN_MAX_INTERVAL){ SCAN_INTERVAL_TIME = SCAN_INTERVAL_TIME + SCAN_INCREASE_INTERVAL; t.schedule(scanTask, 0, SCAN_INTERVAL_TIME); } } }); }}; Log.d("SCAN_INTERVAL_TIME ** ", "SCAN_INTERVAL_TIME ** = " + SCAN_INTERVAL_TIME); t.schedule(scanTask, 0, SCAN_INTERVAL_TIME); } But the above gives the following error: 05-26 11:48:02.472: ERROR/AndroidRuntime(4210): java.lang.IllegalStateException: TimerTask is scheduled already Calling cancel or purge doesn't help. So I was wondering if anyone can help me find a solution? Is a timer even the right way to approach this?

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• Problem with Unit testing of ASP.NET project (NullReferenceException when running the test)

  - by Alex

  Hi, I'm trying to create a bunch of MS visual studio unit tests for my n-tiered web app but for some reason I can't run those tests and I get the following error - "Object reference not set to an instance of an object" What I'm trying to do is testing of my data access layer where I use LINQ data context class to execute a certain function and return a result,however during the debugging process I found out that all the tests fail as soon as they get to the LINQ data context class and it has something to do with the connection string but I cant figure out what is the problem. The debugging of tests fails here(the second line): public EICDataClassesDataContext() : base(global::System.Configuration.ConfigurationManager.ConnectionStrings["EICDatabaseConnectionString"].ConnectionString, mappingSource) { OnCreated(); } And my test is as follows: TestMethod()] public void OnGetCustomerIDTest() { FrontLineStaffDataAccess target = new FrontLineStaffDataAccess(); // TODO: Initialize to an appropriate value string regNo = "jonh"; // TODO: Initialize to an appropriate value int expected = 10; // TODO: Initialize to an appropriate value int actual; actual = target.OnGetCustomerID(regNo); Assert.AreEqual(expected, actual); } The method which I call from DAL is: public int OnGetCustomerID(string regNo) { using (LINQDataAccess.EICDataClassesDataContext dataContext = new LINQDataAccess.EICDataClassesDataContext()) { IEnumerable<LINQDataAccess.GetCustomerIDResult> sProcCustomerIDResult = dataContext.GetCustomerID(regNo); int customerID = sProcCustomerIDResult.First().CustomerID; return customerID; } } So basically everything fails after it reaches the 1st line of DA layer method and when it tries to instantiate the LINQ data access class... I've spent around 10 hours trying to troubleshoot the problem but no result...I would really appreciate any help! UPDATE: Finally I've fixed this!!!!:) I dont know why but for some reasons in the app.config file the connection to my database was as follows: AttachDbFilename=|DataDirectory|\EICDatabase.MDF So what I did is I just changed the path and instead of |DataDirectory| I put the actual path where my MDF file sits,i.e C:\Users\1\Documents\Visual Studio 2008\Projects\EICWebSystem\EICWebSystem\App_Data\EICDatabase.mdf After I had done that it worked out!But still it's a bit not clear what was the problem...probably incorrect path to the database?My web.config of ASP.NET project contains the |DataDirectory|\EICDatabase.MDF path though..

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• Class; Struct; Enum confusion, what is better?

  - by Angel Brighteyes

  I have 46 rows of information, 2 columns each row ("Code Number", "Description"). These codes are returned to the client dependent upon the success or failure of their initial submission request. I do not want to use a database file (csv, sqlite, etc) for the storage/access. The closest type that I can think of for how I want these codes to be shown to the client is the exception class. Correct me if I'm wrong, but from what I can tell enums do not allow strings, though this sort of structure seemed the better option initially based on how it works (e.g. 100 = "missing name in request"). Thinking about it, creating a class might be the best modus operandi. However I would appreciate more experienced advice or direction and input from those who might have been in a similar situation. Currently this is what I have: class ReturnCode { private int _code; private string _message; public ReturnCode(int code) { Code = code; } public int Code { get { return _code; } set { _code = value; _message = RetrieveMessage(value); } } public string Message { get { return _message; } } private string RetrieveMessage(int value) { string message; switch (value) { case 100: message = "Request completed successfuly"; break; case 201: message = "Missing name in request."; break; default: message = "Unexpected failure, please email for support"; break; } return message; } }

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• Configure WebLogic MDB to listen to Foreing AMQ Server

  - by eliel.lobo

  I'm trying to create an MDB(EJB 3.0) on WebLogic 10.3.5. to listen to a Queue in an external AMQ server. but after much work and combination of tutorials i get the followin error when deployin on WwebLogic. [EJB:015027]The Message-Driven EJB is transactional but JMS connection factory referenced by the JNDI name: ActiveMQXAConnectionFactory is not a JMS XA connection factory. Here is a brief of the work i have done: I have added the corresponding libraries to my WLS classpath (following thos tuturial http://amadei.com.br/blog/index.php/connecting-weblogic-and-activemq) and I have created the corresponding JMS Modules as indicated in the tutorial. As connection factory I have used ActiveMQConnectionFactory initially and ActiveMQXAConnectionFactory later, I also ignome the jms. notation an just put plain names as testQueue. Then create a simple MDB whit the following structure. I explicitly defined "connectionFactoryJndiName" property because otherwise it assumes a WebLogic connection factory which is not found an then raises an error. @MessageDriven( activationConfig = { @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue"), @ActivationConfigProperty(propertyName = "destination", propertyValue = "testQueue"), @ActivationConfigProperty(propertyName = "connectionFactoryJndiName", propertyValue = "ActiveMQXAConnectionFactory") }, mappedName = "testQueue") public class ROMELReceiver implements MessageListener { /** * Default constructor. */ public ROMELReceiver() { // TODO Auto-generated constructor stub } /** * @see MessageListener#onMessage(Message) */ public void onMessage(Message message) { System.out.println("Message received"); } } At this point I'm stuck with the error mentioned above. Even though I use ActiveMQXAConnectionFactory instead of simply ActiveMQConnectionFactory, JNDI resources tree in web logic server shows org.apache.activemq.ActiveMQConnectionFactory as class for my configured connection factory. am i missing something? or is this just a completely wrong way to connect WebLogic whith AMQ? Thanks in advance.

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• How do I avoid repetition in Java ResourceBundle strings?

  - by Trejkaz

  We had a lot of strings which contained the same sub-string, from sentences about checking the log or how to contact support, to branding-like strings containing the company or product name. The repetition was causing a few issues for ourselves (primarily typos or copy/paste errors) but it also causes issues in that it increases the amount of text our translator has to translate. The solution I came up with went something like this: public class ExpandingResourceBundleControl extends ResourceBundle.Control { public static final ResourceBundle.Control EXPANDING = new ExpandingResourceBundleControl(); private ExpandingResourceBundleControl() { } @Override public ResourceBundle newBundle(String baseName, Locale locale, String format, ClassLoader loader, boolean reload) throws IllegalAccessException, InstantiationException, IOException { ResourceBundle inner = super.newBundle(baseName, locale, format, loader, reload); return inner == null ? null : new ExpandingResourceBundle(inner, loader); } } ExpandingResourceBundle delegates to the real resource bundle but performs conversion of {{this.kind.of.thing}} to look up the key in the resources. Every time you want to get one of these, you have to go: ResourceBundle.getBundle("com/acme/app/Bundle", EXPANDING); And this works fine -- for a while. What eventually happens is that some new code (in our case autogenerated code which was spat out of Matisse) looks up the same resource bundle without specifying the custom control. This appears to be non-reproducible if you write a simple unit test which calls it with and then without, but it occurs when the application is run for real. Somehow the cache inside ResourceBundle ejects the good value and replaces it with the broken one. I am yet to figure out why and Sun's jar files were compiled without debug info so debugging it is a chore. My questions: Is there some way of globally setting the default ResourceBundle.Control that I might not be aware of? That would solve everything rather elegantly. Is there some other way of handling this kind of thing elegantly, perhaps without tampering with the ResourceBundle classes at all?

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• Windows Media Encoder object not created in ASP.NET on MS Server 2003 64 bit

  - by Ron

  Hello, I created (and used) a Windows Media Encoder object in Microsoft Visual C# 2008 Express Edition on MS Server 2003 64 bit. This worked fine. However, when I attempted to create the equivalent Windows Media Encoder object using Microsoft Visual Web Developer 2008 on MS Server 2003 64 bit, the following exception was thrown: "Retrieving the COM class factory for component with CLSID {632B606A-BBC6-11D2-A329-006097C4E476} failed due to the following error: 80040154." It cannot be that the component isn’t registered, because both have a reference to the same WMEncEng.dll file. The Microsoft Visual Web Developer 2008 code also worked fine on XP 32 bit. Could it be a problem with permissions? Regardless, anyone have any ideas why this problem is occurring and, more importantly, how to resolve it? Thank you. Here are the two code snippets from MS Server 2003 64 bit: Microsoft Visual Web Developer 2008 (did not work): using System; using WMEncoderLib; namespace TestWMEnc { public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { try { WMEncoder encoder = new WMEncoder(); //exception thrown // ... } catch (Exception err) { string exception = err.Message; } } } } Microsoft Visual C# 2008 Express Edition (worked fine): using System; using System.Windows.Forms; using WMEncoderLib; namespace testWMEncoder { public partial class Form1 : Form { public Form1() { InitializeComponent(); } private void button1_Click(object sender, EventArgs e) { try { WMEncoder encoder = new WMEncoder(); // ... } catch (Exception err) { string exception = err.Message; } } } }

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• Create Generic method constraining T to an Enum

  - by johnc

  I'm building a function to extend the Enum.Parse concept that allows a default value to be parsed in case that an Enum value is not found Is case insensitive So I wrote the following public static T GetEnumFromString<T>(string value, T defaultValue) where T : Enum { if (string.IsNullOrEmpty(value)) return defaultValue; foreach (T item in Enum.GetValues(typeof(T))) { if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item; } return defaultValue; } I am getting a Error Constraint cannot be special class 'System.Enum' Fair enough, but is there a workaround to allow a Generic Enum, or am I going to have to mimic the Parse function and pass a type as an attribute, which forces the ugly boxing requirement to your code. EDIT All suggestions below have been greatly appreciated, thanks Have settled on (I've left the loop to maintain case insensitivity - I am usng this when parsing XML) public static class EnumUtils { public static T ParseEnum<T>(string value, T defaultValue) where T : struct, IConvertible { if (!typeof(T).IsEnum) throw new ArgumentException("T must be an enumerated type"); if (string.IsNullOrEmpty(value)) return defaultValue; foreach (T item in Enum.GetValues(typeof(T))) { if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item; } return defaultValue; } }

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• Rails: constraint violation on create but not on update

  - by justinbach

  Note: This is a "railsier" (and more succinct) version of this question, which was getting a little long. I'm getting Rails behavior on a production server that I can't replicate on the development server. The codebases are identical save for credentials and caching settings, and both are powered by Oracle 10g databases with identical schema (but different data). My Rails application contains a user model, which has_one registration; registration in turn has_and_belongs_to_many company_ownerships through a registration_ownerships table. Upon registering, users fill out data pertinent to all three models, including a series of checkboxes indicating what registration_ownerships might apply to their account. On the dev server, the registration process is seamless, no matter what data is entered. On production, however, if users check off any of the company ownership fields before submitting their registration, Oracle complains about a constraint violation on the primary key of the company_ownerships table (which is a two-field key based on company_ownership_id and registration_id) and users get the standard Rails 500 error screen. In every case, I've verified that no conflicting record on these two fields exists in the production database, so I don't know why the constraint is getting violated. To further confuse things, if a user registers without listing any ownerships and later goes back and modifies their account to reflect ownership data (which is done through the same interface), the application happily complies with their request and Oracle is well-behaved (this is both on production and dev). I've spent the past couple days trying to figure out what might be causing this problem and am reaching the end of my wits. Any advice would be greatly appreciated!

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• How can I read a DBF file with incorrectly defined column data types using ADO.NET?

  - by Jason

  I have a several DBF files generated by a third party that I need to be able to query. I am having trouble because all of the column types have been defined as characters, but the data within some of these fields actually contain binary data. If I try to read these fields using an OleDbDataReader as anything other than a string or character array, I get an InvalidCastException thrown, but I need to be able to read them as a binary value or at least cast/convert them after they are read. The columns that actually DO contain text are being returned as expected. For example, the very first column is defined as a character field with a length of 2 bytes, but the field contains a 16-bit integer. I have written the following test code to read the first column and convert it to the appropriate data type, but the value is not coming out right. The first row of the database has a value of 17365 (0x43D5) in the first column. Running the following code, what I end up getting is 17215 (0x433F). I'm pretty sure it has to do with using the ASCII encoding to get the bytes from the string returned by the data reader, but I'm not sure of another way to get the value into the format that I need, other that to write my own DBF reader and bypass ADO.NET altogether which I don't want to do unless I absolutely have to. Any help would be greatly appreciated. byte[] c0; int i0; string con = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\ASTM;Extended Properties=dBASE III;User ID=Admin;Password=;"; using (OleDbConnection c = new OleDbConnection(con)) { c.Open(); OleDbCommand cmd = c.CreateCommand(); cmd.CommandText = "SELECT * FROM astm2007"; OleDbDataReader dr = cmd.ExecuteReader(); while (dr.Read()) { c0 = Encoding.ASCII.GetBytes(dr.GetValue(0).ToString()); i0 = BitConverter.ToInt16(c0, 0); } dr.Dispose(); }

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• CharField values disappearing after save (readonly field)

  - by jamida

  I'm implementing simple "grade book" application where the teacher would be able to update the grades w/o being allowed to change the students' names (at least not on the update grade page). To do this I'm using one of the read-only tricks, the simplest one. The problem is that after the SUBMIT the view is re-displayed with 'blank' values for the students. I'd like the students' names to re-appear. Below is the simplest example that exhibits this problem. (This is poor DB design, I know, I've extracted just the relevant parts of the code to showcase the problem. In the real example, student is in its own table but the problem still exists there.) models.py class Grade1(models.Model): student = models.CharField(max_length=50, unique=True) finalGrade = models.CharField(max_length=3) class Grade1OForm(ModelForm): student = forms.CharField(max_length=50, required=False) def __init__(self, *args, **kwargs): super(Grade1OForm,self).__init__(*args, **kwargs) instance = getattr(self, 'instance', None) if instance and instance.id: self.fields['student'].widget.attrs['readonly'] = True self.fields['student'].widget.attrs['disabled'] = 'disabled' def clean_student(self): instance = getattr(self,'instance',None) if instance: return instance.student else: return self.cleaned_data.get('student',None) class Meta: model=Grade1 views.py from django.forms.models import modelformset_factory def modifyAllGrades1(request): gradeFormSetFactory = modelformset_factory(Grade1, form=Grade1OForm, extra=0) studentQueryset = Grade1.objects.all() if request.method=='POST': myGradeFormSet = gradeFormSetFactory(request.POST, queryset=studentQueryset) if myGradeFormSet.is_valid(): myGradeFormSet.save() info = "successfully modified" else: myGradeFormSet = gradeFormSetFactory(queryset=studentQueryset) return render_to_response('grades/modifyAllGrades.html',locals()) template <p>{{ info }}</p> <form method="POST" action=""> <table> {{ myGradeFormSet.management_form }} {% for myform in myGradeFormSet.forms %} {# myform.as_table #} <tr> {% for field in myform %} <td> {{ field }} {{ field.errors }} </td> {% endfor %} </tr> {% endfor %} </table> <input type="submit" value="Submit"> </form>

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• How to serialize object containing NSData?

  - by AO

  I'm trying to serialize an object containing a number of data fields...where one of the fields is of datatype NSData which won't serialize. I've followed instructions at http://www.isolated.se but my code (see below) results in the error "[NSConcreteData data]: unrecognized selector sent to instance...". How do I serialize my object? Header file: @interface Donkey : NSObject<NSCoding> { NSString* s; NSData* d; } @property (nonatomic, retain) NSString* s; @property (nonatomic, retain) NSData* d; - (NSData*) serialize; @end Implementation file: @implementation Donkey @synthesize s, d; static NSString* const KEY_S = @"string"; static NSString* const KEY_D = @"data"; - (void) encodeWithCoder:(NSCoder*)coder { [coder encodeObject:self.s forKey:KEY_S]; [coder encodeObject:self.d forKey:KEY_D]; } - (id) initWithCoder:(NSCoder*)coder; { if(self = [super init]) { self.s = [coder decodeObjectForKey:KEY_STRING]; self.d [coder decodeObjectForKey:KEY_DATA]; } return self; } - (NSData*) serialize { return [NSKeyedArchiver archivedDataWithRootObject:self]; } @end

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• Convert Lambda from C# to VB.NET

  - by Iosu

  How would I translate this C# lambda expression into VB.NET ? query.ExecuteAsync(op => op.Results.ForEach(Employees.Add)); using System; using System.Net; using System.Windows; using System.Windows.Controls; using System.Windows.Documents; using System.Windows.Ink; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Animation; using System.Windows.Shapes; using System.Collections.ObjectModel; using IdeaBlade.Core; using IdeaBlade.EntityModel; namespace SimpleSteps { public class MainPageViewModel { public MainPageViewModel() { Employees = new ObservableCollection(); var mgr = new NorthwindIBEntities(); var query = mgr.Employees; query.ExecuteAsync(op = op.Results.ForEach(Employees.Add)); } public ObservableCollection<Employee> Employees { get; private set; } } }

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• Adivce on Method overloads.

  - by Muhammad Kashif Nadeem

  Please see following methods. public static ProductsCollection GetDummyData(int? customerId, int? supplierId) { try { if (customerId != null && customerId > 0) { Filter.Add(Customres.CustomerId == customerId); } if (supplierId != null && supplierId > 0) { Filter.Add(Suppliers.SupplierId == supplierId); } ProductsCollection products = new ProductsCollection(); products.FetchData(Filter); return products; } catch { throw; } } public static ProductsCollection GetDummyData(int? customerId) { return ProductsCollection GetDummyData(customerId, (int?)null); } public static ProductsCollection GetDummyData() { return ProductsCollection GetDummyData((int?)null); } 1- Please advice how can I make overloads for both CustomerId and SupplierId because only one overload can be created with GetDummyData(int? ). Should I add another argument to mention that first argument is CustomerId or SupplierId for example GetDummyData(int?, string). OR should I use enum as 2nd argument and mention that first argument is CustoemId or SupplierId. 2- Is this condition is correct or just checking 0 is sufficient - if (customerId != null && customerId 0) 3- Using Try/catch like this is correct? 4- Passing (int?)null is correct or any other better approach. Edit: I have found some other posts like this and because I have no knowledge of Generics that is why I am facing this problem. Am I right? Following is the post. http://stackoverflow.com/questions/422625/overloaded-method-calling-overloaded-method

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• How to construct LambdaExpression with conversion

  - by nerijus

  I need to sort in ajax response grid by column name. Column value is number stored as a string. Let's say some trivial class (in real-life situation there is no possibility to modify this class): class TestObject { public TestObject(string v) { this.Value = v; } public string Value { get; set; } } then simple test: [Test] public void LambdaConstructionTest() { var queryable = new List<TestObject> { new TestObject("5"), new TestObject("55"), new TestObject("90"), new TestObject("9"), new TestObject("09"), new TestObject("900"), }.AsQueryable(); var sortingColumn = "Value"; ParameterExpression parameter = Expression.Parameter(queryable.ElementType); MemberExpression property = Expression.Property(parameter, sortingColumn); //// tried this one: var c = Expression.Convert(property, typeof(double)); LambdaExpression lambda = Expression.Lambda(property, parameter); //// constructs: o=>o.Value var callExpression = Expression.Call(typeof (Double), "Parse", null, property); var methodCallExpression = Expression.Call( typeof(Queryable), "OrderBy", new[] { queryable.ElementType, property.Type }, queryable.Expression, Expression.Quote(lambda)); // works, but sorts by string values. //Expression.Quote(callExpression)); // getting: System.ArgumentException {"Quoted expression must be a lambda"} var querable = queryable.Provider.CreateQuery<TestObject>(methodCallExpression); // return querable; // <- this is the return of what I need. } Sorry for not being clear in my first post as @SLaks answer was correct but I do not know how to construct correct lambda expression in this case.

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• Show WPF tooltip on disabled item only

  - by DT

  Just wondering if it is possible to show a WPF on a disabled item ONLY (and not when the item is enabled). I would like to give the user a tooltip explaining why an item is currently disabled. I have an IValueConverter to invert the boolean IsEnabled property binding. But it doesn't seem to work in this situation. The tooltip is show both when the item is enabled and disabled. So is is possible to bind a tooltip.IsEnabled property exclusively to an item's own !IsEnabled? Pretty straightforward question I guess, but code example here anyway: public class BoolToOppositeBoolConverter : IValueConverter { #region IValueConverter Members public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { if (targetType != typeof(bool)) throw new InvalidOperationException("The target must be a boolean"); return !(bool)value; } public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { if (targetType != typeof(bool)) throw new InvalidOperationException("The target must be a boolean"); return !(bool)value; } #endregion } And the binding: <TabItem Header="Tab 2" Name="tabItem2" ToolTip="Not enabled in this situation." ToolTipService.ShowOnDisabled="True" ToolTipService.IsEnabled="{Binding Path=IsEnabled, ElementName=tabItem2, Converter={StaticResource oppositeConverter}}"> <Label Content="Item content goes here" /> </TabItem> Thanks folks.

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• Django's post_save signal behaves weirdly with models using multi-table inheritance

  - by hekevintran

  Django's post_save signal behaves weirdly with models using multi-table inheritance I am noticing an odd behavior in the way Django's post_save signal works when using a model that has multi-table inheritance. I have these two models: class Animal(models.Model): category = models.CharField(max_length=20) class Dog(Animal): color = models.CharField(max_length=10) I have a post save callback called echo_category: def echo_category(sender, **kwargs): print "category: '%s'" % kwargs['instance'].category post_save.connect(echo_category, sender=Dog) I have this fixture: [ { "pk": 1, "model": "animal.animal", "fields": { "category": "omnivore" } }, { "pk": 1, "model": "animal.dog", "fields": { "color": "brown" } } ] In every part of the program except for in the post_save callback the following is true: from animal.models import Dog Dog.objects.get(pk=1).category == u'omnivore' # True When I run syncdb and the fixture is installed, the echo_category function is run. The output from syncdb is: $ python manage.py syncdb --noinput Installing json fixture 'initial_data' from '~/my_proj/animal/fixtures'. category: '' Installed 2 object(s) from 1 fixture(s) The weird thing here is that the dog object's category attribute is an empty string. Why is it not 'omnivore' like it is everywhere else? As a temporary (hopefully) workaround I reload the object from the database in the post_save callback: def echo_category(sender, **kwargs): instance = kwargs['instance'] instance = sender.objects.get(pk=instance.pk) print "category: '%s'" % instance.category post_save.connect(echo_category, sender=Dog) This works but it is not something I like because I must remember to do it when the model inherits from another model and it must hit the database again. The other weird thing is that I must do instance.pk to get the primary key. The normal 'id' attribute does not work (I cannot use instance.id). I do not know why this is. Maybe this is related to the reason why the category attribute is not doing the right thing?

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