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  • Using singleton instead of a global static instance

    - by Farstucker
    I ran into a problem today and a friend recommended I use a global static instance or more elegantly a singleton pattern. I spent a few hours reading about singletons but a few things still escape me. Background: What Im trying to accomplish is creating an instance of an API and use this one instance in all my classes (as opposed to making a new connection, etc). There seems to be about 100 ways of creating a singleton but with some help from yoda I found some thread safe examples. ..so given the following code: public sealed class Singleton { public static Singleton Instance { get; private set; } private Singleton() { APIClass api = new APIClass(); //Can this be done? } static Singleton() { Instance = new Singleton(); } } How/Where would you instantiate the this new class and how should it be called from a separate class? EDIT: I realize the Singleton class can be called with something like Singleton obj1 = Singleton.Instance(); but would I be able to access the methods within the APIs Class (ie. obj1.Start)? (not that I need to, just asking) EDIT #2: I might have been a bit premature in checking the answer but I do have one small thing that is still causing me problems. The API is launching just fine, unfortunately Im able to launch two instances? New Code public sealed class SingletonAPI { public static SingletonAPI Instance { get; private set; } private SingletonAPI() {} static SingletonAPI() { Instance = new SingletonAPI(); } // API method: public void Start() { API myAPI = new API();} } but if I try to do something like this... SingletonAPI api = SingletonAPI.Instance; api.Start(); SingletonAPI api2 = SingletonAPI.Instance; // This was just for testing. api2.Start(); I get an error saying that I cannot start more than one instance.

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  • Retrieve COM ProgID from exe without registering it

    - by mangelo
    Background: I would like to extract the COM data from a VB6 application so I can register it correctly (according to Microsoft best practice) the application. I am using WiX 3.0 and heat.exe will not extract the data (known issue with heat) and I do not have ready access to the associated TLB file. The VB6 application does not have compatibility turned on so it regenerates the COM GUIDs every build (They want to have the application be able to run side by side with an older version.) I created a C# application that will collect the TypeLib, interface and CoClass information from the VB6 application without registering it and create a wxs file for candle to use. My company has several other older applications like this and I would like to make it a more generic solution. The Issues: 1.Is there a way to collect the 'true' ProgID (programmer intended one) from the application with out the project or TLB file and without registering it? 2.Is there a way to find out the intended Threading Model from a DLL without registering it? (I intend that it can handle all COM active items, might as well be complete) Thank you.

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  • Set the caret/cursor position to the end of the string value WPF textbox

    - by Zamboni
    I am try to set the caret/cursor position to the end of the string value in my WPF textbox when I open my window for the first time. I use the FocusManager to set the focus on my textbox when my window opens. Nothing seems to work. Any ideas? Note, I am using the MVVM pattern, and I included only a portion of the XAML from my code. <Window FocusManager.FocusedElement="{Binding ElementName=NumberOfDigits}" Height="400" Width="800"> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition/> <RowDefinition/> </Grid.RowDefinitions> <TextBox Grid.Column="0" Grid.Row="0" x:Name="NumberOfDigits" IsReadOnly="{Binding Path=IsRunning, Mode=TwoWay}" VerticalContentAlignment="Center" Text="{Binding Path=Digits, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/> <Button Grid.Column="0" Grid.Row="1" Margin="10,0,10,0" IsDefault="True" Content="Start" Command="{Binding StartCommand}"/> </Grid> </Window>

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  • In Seam what's the difference between injected EntityManager and getEntityManager from EntityHome

    - by Navi
    I am testing a Seam application using the needle test API. In my code I am using the getEntityManager() method from EntityHome. When I run the unit tests against an in memory database I get the following exception: java.lang.IllegalStateException: No application context active at org.jboss.seam.Component.forName(Component.java:1945) at org.jboss.seam.Component.getInstance(Component.java:2005) at org.jboss.seam.Component.getInstance(Component.java:1983) at org.jboss.seam.Component.getInstance(Component.java:1977) at org.jboss.seam.Component.getInstance(Component.java:1972) at org.jboss.seam.framework.Controller.getComponentInstance(Controller.java:272) at org.jboss.seam.framework.PersistenceController.getPersistenceContext(PersistenceController.java:20) at org.jboss.seam.framework.EntityHome.getEntityManager(EntityHome.java:177) etc .. I can resolve some of these errors by injecting the EntityManager with @In EntityManager entityManager; Unfortunately the persist method of EntityHome also calls the getEntityManager. This means a lot of mocks or rewriting the code somehow. Is there any workaround and why is this exception thrown anyway? I am using Seam 2.2.0 GA by the way. There is nothing special about the components. They are generated by seam-gen. The test is performed with in memory database - I followed the examples in http://jbosscc-needle.sourceforge.net/jbosscc-needle/1.0/db-util.html.

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  • Core Data NSPredicate to filter results

    - by Bryan
    I have a NSManagedObject that contains a bID and a pID. Within the set of NSManagedObjects, I only want a subset returned and I'm struggling to find the correct NSPredicate or way to get what I need out of Core Data. Here's my full list: bid pid 41 0 42 41 43 0 44 0 47 41 48 0 49 0 50 43 There is a parent-child relationship above. Rules: If a record's PID = 0, it means that that record IS a parent record. If a record's PID != 0, then that record's PID refers to it's parent record's BID. Example: 1) BID = 41 is a parent record. Why? Because records BID=42 and record BID=47 have PID's of 41, meaning those are children of its PID record. 2) BID = 42 has a parent record with a BID = 41. 3) BID = 43 is a parent record. 4) BID = 44 is a parent record. 5) BID = 47 has a parent record with a BID = 41 because its PID = 41. See #1 above. 6) BID = 48 is a parent record. 7) BID = 49 is a parent record. 8) BID = 50 is a child record, and its parent record has a BID = 43. See the pattern? Now, basically from that, I want only the following rows fetched: bid pid 44 0 47 41 48 0 49 0 50 43 BID = 41, BID = 48, BID = 49 should all be returned because there are no records with a PID equal to their BID. BID = 47 should be returned because it is the most recent child of PID = 41. BID = 50 should be returned because it is the most recent child of PID = 43. Hope this helps explain it more.

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  • Spelling correction for data normalization in Java

    - by dareios
    I am looking for a Java library to do some initial spell checking / data normalization on user generated text content, imagine the interests entered in a Facebook profile. This text will be tokenized at some point (before or after spell correction, whatever works better) and some of it used as keys to search for (exact match). It would be nice to cut down misspellings and the like to produce more matches. It would be even better if the correction would perform well on tokens longer than just one word, e.g. "trinking coffee" would become "drinking coffee" and not "thinking coffee". I found the following Java libraries for doing spelling correction: JAZZY does not seem to be under active development. Also, the dictionary-distance based approach seems inadequate because of the use of non-standard language in social network profiles and multi-word tokens. APACHE LUCENE seems to have a statistical spell checker that should be much more suited. Question here would how to create a good dictionary? (We are not using Lucene otherwise, so there is no existing index.) Any suggestions are welcome!

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  • Mode specific key bindings

    - by rejeep
    Hey, I have a minor mode that also comes with a global mode. The mode have some key bindings and I want the user to have the posibility to specify what bindings should work for each mode. (my-minor-mode-bindings-for-mode 'some-mode '(key1 key2 ...)) (my-minor-mode-bindings-for-mode 'some-other-mode '(key3 key4 ...)) So I need some kind of mode/buffer-local key map. Buffer local is a bit problematic since the user can change the major mode. I have tried some solutions of which neither works any good. Bind all possible keys always and when the user types the key, check if the key should be active in that mode. Execute action if true, otherwise fall back. Like the previous case only that no keys are bound. Instead I use a pre command hook and check if the key pressed should do anything. For each buffer update (whatever that means), run a function that first clears the key map and then updates it with the bindings for that particular mode. I have tried these approaches and I found problems with all of them. Do you know of any good way to solve this? Thanks!

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  • A Django form for entering a 0 to n email addresses

    - by Erik
    I have a Django application with some fairly common models in it: UserProfile and Organization. A UserProfile or an Organization can both have 0 to n emails, so I have an Email model that has a GenericForeignKey. UserProfile and Organization Models both have a GenericRelation called emails that points back to the Email model (summary code provided below). The question: what is the best way to provide an Organization form that allows a user to enter organization details including 0 to n email addresses? My Organization create view is a Django class-based view. I'm leading towards creating a dynamic form and an enabling it with Javascript to allow the user to add as many email addresses as necessary. I will render the form with django-crispy-forms. I've thought about doing this with a formset embedded within the form, but this seems like overkill for email addresses. Embedding a formset in a form delivered by a class-based view is cumbersome too. Note that the same issue occurs with the Organization fields phone_numbers and locations. emails.py: from django.db import models from parent_mixins import Parent_Mixin class Email(Parent_Mixin,models.Model): email_type = models.CharField(blank=True,max_length=100,null=True,default=None,verbose_name='Email Type') email = models.EmailField() class Meta: app_label = 'core' organizations.py: from emails import Email from locations import Location from phone_numbers import Phone_Number from django.contrib.contenttypes import generic from django.db import models class Organization(models.Model): active = models.BooleanField() duns_number = models.CharField(blank=True,default=None,null=True,max_length=9) # need to validate this emails = generic.GenericRelation(Email,content_type_field='parent_type',object_id_field='parent_id') legal_name = models.CharField(blank=True,default=None,null=True,max_length=200) locations = generic.GenericRelation(Location,content_type_field='parent_type',object_id_field='parent_id') name = models.CharField(blank=True,default=None,null=True,max_length=200) organization_group = models.CharField(blank=True,default=None,null=True,max_length=200) organization_type = models.CharField(blank=True,default=None,null=True,max_length=200) phone_numbers = generic.GenericRelation(Phone_Number,content_type_field='parent_type',object_id_field='parent_id') taxpayer_id_number = models.CharField(blank=True,default=None,null=True,max_length=9) # need to validate this class Meta: app_label = 'core' parent_mixins.py from django.contrib.contenttypes.models import ContentType from django.contrib.contenttypes import generic from django.db import models class Parent_Mixin(models.Model): parent_type = models.ForeignKey(ContentType,blank=True,null=True) parent_id = models.PositiveIntegerField(blank=True,null=True) parent = generic.GenericForeignKey('parent_type', 'parent_id') class Meta: abstract = True app_label = 'core'

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  • Strange activity stack behavior when using MapActivity

    - by AndroidDev
    I have the following activity structure in my application A simple "splash screen" activity is started when the application is fired up (let's call it "Splash"). This activity starts the main activity when the user presses a button (I will call it "Main"). Main can in turn start two activities from the menu. The first activity presents a simple form (let's call this one "Form"), the second is a MapActivity that presents a map (it is called "Map"). Main, Form, and Map are declared exactly the same in the manifest: <activity android:name="fully qualified activity class" android:screenOrientation="landscape" android:configChanges="keyboard|keyboardHidden|orientation" > <intent-filter> <action android:name="android.intent.action.DEFAULT" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter> </activity> When Main is active and I start Form and press "back", Main comes up again. Pressing "back" again brings up "Splash". Nothing strange here. Now comes the strange part: when I am in Main, start Map, and press "back", Main comes up as expected. But pressing "back" again just restarts Main. A second press on "back" is needed to bring me back to Splash! So it seems that starting the Map activity somehow results in Main ending up on the activity stack twice while starting the Form activity does not! Both Form and Map are started like this: startActivity(new Intent(this, MyActivity.class)); I don not catch the back key in any activity. Any clues on what is going on or how to debug this?

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  • How can I stop an auto-generated Linq to SQL class from loading ALL data?

    - by Gary McGill
    I have an ASP.NET MVC project, much like the NerdDinner tutorial example. (I'm using MVC 2, but followed the NerdDinner tutorial in order to create it). As per the instructions in part 3 of the tutorial, I've created a Linq-to-SQL model of my database by creating a "Linq to SQL Classes" (.dbml) surface, and dropping my database tables onto it. The designer has automatically added relationships between the generated classes based on my database tables. Let's say that my classes are as per the NerdDinner example, so I have Dinner and RSVP tables, where each Dinner record is associated with many RSVP records - hence in the generated classes, the Dinner object has a RSVPs property which is a list of RSVP objects. My problem is this: it appears (and I'd be gladly proved wrong on this) that as soon as I access a Dinner object, it's loading all of the corresponding RSVP objects, even if I don't use the RSVPs member. First question: is this really the default behavior for the generated classes? In my particular situation, the object graph contains many more tables (which have an order of magnitude more records), and so this is disastrous behaviour - I'd be loading tons of data when all I want to do is show the details of a single parent record. Second question: are there any properties exposed through the designer UI that would let me modify this behavior? (I can't find any). Third question: I've seen a description of how to control the loading of related records in a DataContext by using a DataShape object associated with the DataContext. Is that what I'm meant to do, and if so are there any tutorials like the NerdDinner one that would show not only how to do it, but also suggest a 'pattern' for normal use?

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  • How can I stop an auto-generated Linq to SQL class from loading ALL data?

    - by Gary McGill
    DUPLICATE of http://stackoverflow.com/questions/2433422/how-can-i-stop-an-auto-generated-linq-to-sql-class-from-loading-all-data post answers there! I have an ASP.NET MVC project, much like the NerdDinner tutorial example. (I'm using MVC 2, but followed the NerdDinner tutorial in order to create it). As per the instructions in part 3 of the tutorial, I've created a Linq-to-SQL model of my database by creating a "Linq to SQL Classes" (.dbml) surface, and dropping my database tables onto it. The designer has automatically added relationships between the generated classes based on my database tables. Let's say that my classes are as per the NerdDinner example, so I have Dinner and RSVP tables, where each Dinner record is associated with many RSVP records - hence in the generated classes, the Dinner object has a RSVPs property which is a list of RSVP objects. My problem is this: it appears (and I'd be gladly proved wrong on this) that as soon as I access a Dinner object, it's loading all of the corresponding RSVP objects, even if I don't use the RSVPs member. First question: is this really the default behavior for the generated classes? In my particular situation, the object graph contains many more tables (which have an order of magnitude more records), and so this is disastrous behaviour - I'd be loading tons of data when all I want to do is show the details of a single parent record. Second question: are there any properties exposed through the designer UI that would let me modify this behavior? (I can't find any). Third question: I've seen a description of how to control the loading of related records in a DataContext by using a DataShape object associated with the DataContext. Is that what I'm meant to do, and if so are there any tutorials like the NerdDinner one that would show not only how to do it, but also suggest a 'pattern' for normal use?

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  • Put message after long idle time does not work

    - by Sydney
    I wrote a simple Java client using MQ v7 libraries (No JMS). I try to put a message in a queue using the following pattern: Put a message Wait for x minutes Put a message again It works but if the idle time is too long (between 5-7 minutes), I get the following error: MQJE001: An MQException occurred: Completion Code 2, Reason 2195 MQJE007: IO error reading message data Error occured during API call - reason code0 MQJE001: Completion Code 2, Reason 2009 MQJE001: An MQException occurred: Completion Code 2, Reason 2009 MQJE003: IO error transmitting message buffer MQJE001: Completion Code 2, Reason 2009 MQJE001: An MQException occurred: Completion Code 2, Reason 2009 MQJE003: IO error transmitting message buffer MQJE001: Completion Code 2, Reason 2009 MQJE001: An MQException occurred: Completion Code 2, Reason 2009 MQJE003: IO error transmitting message buffer MQJE001: Completion Code 2, Reason 2009 MQJE001: An MQException occurred: Completion Code 2, Reason 2009 MQJE003: IO error transmitting message buffer MQJE001: An MQException occurred: Completion Code 2, Reason 2009 MQJE003: IO error transmitting message buffer MQJE001: Completion Code 2, Reason 2009 An MQSeries error occurred : Completion code 2 Reason code 2009 com.ibm.mq.MQException: MQJE001: Completion Code 2, Reason 2009 at com.ibm.mq.MQQueue.put(MQQueue.java:1511) After reading several threads on the subject, this error is usually creating FDC dumps but I have nothing in the system and queue manager logs. The channel is a SVRCONN channel.

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  • ActionMailer sent with body unavailable in view

    - by yelvert
    So ive got a ActionMailer mailer class ReportMailer < ActionMailer::Base def notify_doctor_of_updated_document(document) recipients document.user.email_id from "(removed for privacy)" subject "Document #{document.document_number} has been updated and saved as #{document.status}" sent_on Time.now body :document => document end end and the view is Document <%= @document.class %> but when running >> d = Document.last => #<Document id: "fff52d70-7ba2-11de-9b70-001ec9e252ed", document_number: "ABCD1234", procedures_count: 0, user_id: "630", created_at: "2009-07-28 18:18:07", updated_at: "2009-08-30 20:59:41", active: false, facility_id: 94157, status: "incomplete", staff_id: nil, transcriptionist_id: nil, job_length: nil, work_type: nil, transcription_date: nil, non_trans_edit_date: nil, pervasync_flag: true, old_id: nil> >> ReportMailer.deliver_notify_doctor_of_updated_document(d) => #<TMail::Mail port=#<TMail::StringPort:id=0x8185326c> bodyport=#<TMail::StringPort:id=0x8184d6b4>> from the console this is printed in the log Sent mail to (removed for privacy) Date: Tue, 11 May 2010 20:45:14 -0500 From: (removed for privacy) To: (removed for privacy) Subject: Document ABCD1234 has been updated and saved as incomplete Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=mimepart_4bea082ab4ae8_aa4800b81ac13f5 --mimepart_4bea082ab4ae8_aa4800b81ac13f5 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: Quoted-printable Content-Disposition: inline Document NilClass= --mimepart_4bea082ab4ae8_aa4800b81ac13f5--

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  • Django's self.client.login(...) does not work in unit tests

    - by thebossman
    I have created users for my unit tests in two ways: 1) Create a fixture for "auth.user" that looks roughly like this: { "pk": 1, "model": "auth.user", "fields": { "username": "homer", "is_active": 1, "password": "sha1$72cd3$4935449e2cd7efb8b3723fb9958fe3bb100a30f2", ... } } I've left out the seemingly unimportant parts. 2) Use 'create_user' in the setUp function (although I'd rather keep everything in my fixtures class): def setUp(self): User.objects.create_user('homer', '[email protected]', 'simpson') Note that the password is simpson in both cases. I've verified that this info is correctly being loaded into the test database time and time again. I can grab the User object using User.objects.get. I can verify the password is correct using 'check_password.' The user is active. Yet, invariably, self.client.login(username='homer', password='simpson') FAILS. I'm baffled as to why. I think I've read every single Internet discussion pertaining to this. Can anybody help? The login code in my unit test looks like this: login = self.client.login(username='homer', password='simpson') self.assertTrue(login) Thanks.

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  • Prevent Ninject from calling Initialize multiple times when binding to several interfaces

    - by Ahe
    Hi We have a concrete singleton service which implements Ninject.IInitializable and 2 interfaces. Problem is that services Initialize-methdod is called 2 times, when only one is desired. We are using .NET 3.5 and Ninject 2.0.0.0. Is there a pattern in Ninject prevent this from happening. Neither of the interfaces implement Ninject.IInitializable. the service class is: public class ConcreteService : IService1, IService2, Ninject.IInitializable { public void Initialize() { // This is called twice! } } And module looks like this: public class ServiceModule : NinjectModule { public override void Load() { this.Singleton<Iservice1, Iservice2, ConcreteService>(); } } where Singleton is an extension method defined like this: public static void Singleton<K, T>(this NinjectModule module) where T : K { module.Bind<K>().To<T>().InSingletonScope(); } public static void Singleton<K, L, T>(this NinjectModule module) where T : K, L { Singleton<K, T>(module); module.Bind<L>().ToMethod(n => n.Kernel.Get<T>()); } Of course we could add bool initialized-member to ConcreteService and initialize only when it is false, but it seems quite a bit of a hack. And it would require repeating the same logic in every service that implements two or more interfaces. Thanks for all the answers! I learned something from all of them! (I am having a hard time to decide which one mark correct). We ended up creating IActivable interface and extending ninject kernel (it also removed nicely code level dependencies to ninject, allthough attributes still remain).

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  • SECURITY Flaws in this design for User authentication.

    - by Shao
    SECURITY Flaws in this design for User authentication. From: http://wiki.pylonshq.com/display/pylonscookbook/Simple+Homegrown+Authentication Note: a. Project follows the MVC pattern. b. Only a user with a valid username and password is allowed submit something. Design: a. Have a base controller from which all controllers are derived from. b. Before any of the actions in the derived controllers are called the system calls a before action in the base controller. c. In each controller user hardcodes the actions that need to be verified in an array. d. The before action first looks in the array that has the actions that are protected and sees if a user is logged in or not by peaking into the session. If a user is present then user is allowed to submit otherwise user is redirected to login page. What do you think?

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  • What type of webapp is the sweet spot for Scala's Lift framework?

    - by ajay
    What kind of applications are the sweet spot for Scala's lift web framework. My requirements: Ease of development and maintainability Ready for production purposes. i.e. good active online community, regular patches and updates for security and performance fixes etc. Framework should survive a few years. I don't want to write a app in a framework for which no updates/patches are available after 1 year. Has good UI templating engines Interoperation with Java (Scala satisfies this arleady. Just mentioning here for completeness sake) Good component oriented development. Time required to develop should be proportion to the complexity of web application. Should not be totally configuration based. I hate it when code gets automatically generated for me and does all sorts of magic under the hood. That is a debugging nightmare. Amount of Lift knowledge required to develop a webapp should be proportional to the complexity of the web application. i.e I should't have to spend 10+ hours learning Lift just to develop a simple TODO application. (I have knowledge of Databases, Scala) Does Lift satisfy these requirements?

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  • How to protect/monitor your site from crawling by malicious user

    - by deathy
    Situation: Site with content protected by username/password (not all controlled since they can be trial/test users) a normal search engine can't get at it because of username/password restrictions a malicious user can still login and pass the session cookie to a "wget -r" or something else. The question would be what is the best solution to monitor such activity and respond to it (considering the site policy is no-crawling/scraping allowed) I can think of some options: Set up some traffic monitoring solution to limit the number of requests for a given user/IP. Related to the first point: Automatically block some user-agents (Evil :)) Set up a hidden link that when accessed logs out the user and disables his account. (Presumably this would not be accessed by a normal user since he wouldn't see it to click it, but a bot will crawl all links.) For point 1. do you know of a good already-implemented solution? Any experiences with it? One problem would be that some false positives might show up for very active but human users. For point 3: do you think this is really evil? Or do you see any possible problems with it? Also accepting other suggestions.

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  • In C#, what thread will Events be handled in?

    - by Ben
    Hi, I have attempted to implement a producer/consumer pattern in c#. I have a consumer thread that monitors a shared queue, and a producer thread that places items onto the shared queue. The producer thread is subscribed to receive data...that is, it has an event handler, and just sits around and waits for an OnData event to fire (the data is being sent from a 3rd party api). When it gets the data, it sticks it on the queue so the consumer can handle it. When the OnData event does fire in the producer, I had expected it to be handled by my producer thread. But that doesn't seem to be what is happening. The OnData event seems as if it's being handled on a new thread instead! Is this how .net always works...events are handled on their own thread? Can I control what thread will handle events when they're raised? What if hundreds of events are raised near-simultaneously...would each have its own thread? Thank in advance! Ben

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  • How to know if a graphics card provides hardware rendering for wpf

    - by happyclicker
    I have to run a wpf-app in an environment that has all the same dell-pc's with an intel gma 3000 graphics chip (onbard, Q963/Q965). The app renders only with software rendering (Stated so by the RenderCapability.Tier-property (it says the rendering tier is 0!) and I also see this with Perforator). On all of this machines, DirectX 9c is installed and DXDiag states on many but not on all of this machines, that Direct-3d and Direct-Draw-acceleration is activated. I checked also the registry if the setup of these machines disabled wpf-hw rendering but that's also not the case. On one machine I also updated the video-driver and dx with no success. I found a lot of ressources that say, that directX must be installed and active, so that wpf does not use its own software renderer but uses the DirectX HW-Rendering. But on the above machines, DX9c is installed but there is no hw rendering. May it be that wpf uses dx-graphicscards but does the communication with the graphics card direct and not over dx? How can I find out if a specific graphics-chip has to support hardware rendering for wpf or not. The statement that the graphics card must support dx 9c seems not to be the only condition. The second question is, if wpf renders through dx, is this done through direct-3d or is direct-draw used. Is there any good documentation on this topic?

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  • IUsable: controlling resources in a better way than IDisposable

    - by Ilya Ryzhenkov
    I wish we have "Usable" pattern in C#, when code block of using construct would be passed to a function as delegate: class Usable : IUsable { public void Use(Action action) // implements IUsable { // acquire resources action(); // release resources } } and in user code: using (new Usable()) { // this code block is converted to delegate and passed to Use method above } Pros: Controlled execution, exceptions The fact of using "Usable" is visible in call stack Cons: Cost of delegate Do you think it is feasible and useful, and if it doesn't have any problems from the language point of view? Are there any pitfalls you can see? EDIT: David Schmitt proposed the following using(new Usable(delegate() { // actions here }) {} It can work in the sample scenario like that, but usually you have resource already allocated and want it to look like this: using (Repository.GlobalResource) { // actions here } Where GlobalResource (yes, I know global resources are bad) implements IUsable. You can rewrite is as short as Repository.GlobalResource.Use(() => { // actions here }); But it looks a little bit weird (and more weird if you implement interface explicitly), and this is so often case in various flavours, that I thought it deserve to be new syntactic sugar in a language.

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  • Should DAL always return business objects in MVP

    - by Chathuranga
    In Model View Presenter (MVP) pattern, it is said that our DAL always should returns business models. But let's say if I want to get just a number from database like the last ClientID (the latest clients ID) which is a string, should my DAL method returns a ClientInfo object which has about 10 other fields as well like ClientName, Address etc.? If I want to get a list of business objects from my DAL, is it acceptable to do it as follows or better to get a DataTable from DAL and then in the applications BLL, converts it a List? public List<Employee> GetNewEmployees() { string selectStatement = "SELECT Employee.Emp_ID, Employee.Initials + ' ' + Employee.Surname AS Name,..."; using (SqlConnection sqlConnection = new SqlConnection(db.GetConnectionString)) { using (SqlCommand sqlCommand = new SqlCommand(selectStatement, sqlConnection)) { sqlConnection.Open(); using (SqlDataReader dataReader = sqlCommand.ExecuteReader()) { List<Employee> list = new List<Employee>(); while (dataReader.Read()) { list.Add ( new EpfEtfMaster { EmployeeID = (int) dataReader ["emp_id"], EmployeeName = (string) dataReader ["Name"], AppointmentDate = (DateTime) dataReader["appointment_date"], }); } return list; } } } }

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  • Strip parity bits in C from 8 bits of data followed by 1 parity bit

    - by dubnde
    I have a buffer of bits with 8 bits of data followed by 1 parity bit. This pattern repeats itself. The buffer is currently stored as an array of octets. Example (p are parity bits): 0001 0001 p000 0100 0p00 0001 00p01 1100 ... should become 0001 0001 0000 1000 0000 0100 0111 00 ... Basically, I need to strip of every ninth bit to just obtain the data bits. How can I achieve this? This is related to another question asked here sometime back. This is on a 32 bit machine so the solution to the related question may not be applicable. The maximum possible number of bits is 45 i.e. 5 data octets This is what I have tried so far. I have created a "boolean" array and added the bits into the array based on the the bitset of the octet. I then look at every ninth index of the array and through it away. Then move the remaining array down one index. Then I've got only the data bits left. I was thinking there may be better ways of doing this.

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  • Thread implemented as a Singleton

    - by rocknroll
    Hi all, I have a commercial application made with C,C++/Qt on Linux platform. The app collects data from different sensors and displays them on GUI. Each of the protocol for interfacing with sensors is implemented using singleton pattern and threads from Qt QThreads class. All the protocols except one work fine. Each protocol's run function for thread has following structure: void <ProtocolClassName>::run() { while(!mStop) //check whether screen is closed or not { mutex.lock() while(!waitcondition.wait(&mutex,5)) { if(mStop) return; } //Code for receiving and processing incoming data mutex.unlock(); } //end while } Hierarchy of GUI. 1.Login screen. 2. Screen of action. When a user logs in from login screen, we enter the action screen where all data is displayed and all the thread's for different sensors start. They wait on mStop variable in idle time and when data arrives they jump to receiving and processing data. Incoming data for the problem protocol is 117 bytes. In the main GUI threads there are timers which when timeout, grab the running instance of protocol using <ProtocolName>::instance() function Check the update variable of singleton class if its true and display the data. When the data display is done they reset the update variable in singleton class to false. The problematic protocol has the update time of 1 sec, which is also the frame rate of protocol. When I comment out the display function it runs fine. But when display is activated the application hangs consistently after 6-7 hours. I have asked this question on many forums but haven't received any worthwhile suggestions. I Hope that here I will get some help. Also, I have read a lot of literature on Singleton, multithreading, and found that people always discourage the use of singletons especially in C++. But in my application I can think of no other design for implementation. Thanks in advance A Hapless programmer

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  • Empty data problem - data layer or DAL?

    - by luckyluke
    I designing the new App now and giving the following question a lot of thought. I consume a lot of data from the warehouse, and the entities have a lot of dictionary based values (currency, country, tax-whatever data) - dimensions. I cannot be assured though that there won't be nulls. So I am thinking: create an empty value in each of teh dictionaries with special keyID - ie. -1 do the ETL (ssis) do the correct stuff and insert -1 where it needs to let the DAL know that -1 is special (Static const whatever thing) don't care in the code to check for nullness of dictionary entries because THEY will always have a value But maybe I should be thinking: import data AS IS let the DAL do the thinking using empty record Pattern still don't care in the code because business layer will have what it needs from DAL. I think is more of a approach thing but maybe i am missing something important here... What do You think? Am i clear? Please don't confuse it with empty record problem. I do use emptyCustomer think all the time and other defaults too.

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