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• Advice for Architecture Design Logic for software application

  - by Prasad

  Hi, I have a framework of basic to complex set of objects/classes (C++) running into around 500. With some rules and regulations - all these objects can communicate with each other and hence can cover most of the common queries in the domain. My Dream: I want to provide these objects as icons/glyphs (as I learnt recently) on a workspace. All these objects can be dragged/dropped into the workspace. They have to communicate only through their methods(interface) and in addition to few iterative and conditional statements. All these objects are arranged finally to execute a protocol/workflow/dataflow/process. After drawing the flow, the user clicks the Execute/run button. All the user interaction should be multi-touch enabled. The best way to show my dream is : Jeff Han's Multitouch Video. consider Jeff is playing with my objects instead of the google maps. :-) it should be like playing a jigsaw puzzle. Objective: how can I achieve the following while working on this final product: a) the development should be flexible to enable provision for web services b) the development should enable easy web application development c) The development should enable client-server architecture - d) further it should also enable mouse based drag/drop desktop application like Adobe programs etc. I mean to say: I want to economize on investments. Now I list my efforts till now in design : a) Created an Editor (VB) where the user writes (manually) the object / class code b) On Run/Execute, the code is copied into a main() function and passed to interpreter. c) Catch the output and show it in the console. The interpreter can be separated to become a server and the Editor can become the client. This needs lot of standard client-server architecture work. But some how I am not comfortable in the tightness of this system. Without interpreter is there much faster and better embeddable solution to this? - other than writing a special compiler for these objects. Recently learned about AXIS-C++ can help me - looks like - a friend suggested. Is that the way to go ? Here are my questions: (pl. consider me a self taught programmer and NOT my domain) a) From the stage of C++ objects to multi-touch product, how can I make sure I will develop the parallel product/service models as well.? What should be architecture aspects I should consider ? b) What technologies are best suited for this? c) If I am thinking of moving to Cloud Computing, how difficult/ how redundant / how unnecessary my efforts will be ? d) How much time in months would it take to get the first beta ? I take the liberty to ask if any of the experts here are interested in this project, please email me: [email protected] Thank you for any help. Looking forward.

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• Not able to show video with html5

  - by shin

  I am testing html 5 video tag. I am using http://www.kaltura.org/project/HTML5_Video_Media_JavaScript_Library and http://camendesign.co.uk/. I downloaded the creative common video. When I use an external link, it plays the video. So I uploaded the video to my server but it does not play. It asks if I want to save it or asking an application to play. When I go to the external link, http://cdn.kaltura.org/apis/html5lib/kplayer-examples/media/bbb400p.ogv, it plays it on the browser automatically. I also tested locally, but it does not play either. I am hoping someone gives me why and how to solve the problem. This code works. <figure> <video id="vid1" width="500" height="300" style="position:absolute" poster="http://cdn.kaltura.org/apis/html5lib/kplayer-examples/media/bbb480.jpg" durationHint="33" controls = "true"> <source src="http://cdn.kaltura.org/apis/html5lib/kplayer-examples/media/bbb400p.ogv" /> <source src="http://cdn.kaltura.org/apis/html5lib/kplayer-examples/media/bbb_trailer_iphone.m4v"/> </video> </figure> This does not. <figure> <video id="vid1" width="500" height="300" style="position:absolute" poster="http://cdn.kaltura.org/apis/html5lib/kplayer-examples/media/bbb480.jpg" durationHint="33" controls = "true"> <source src="http://www.mywebsite.com/media/bbb400p.ogv" /> <source src="http://www.mywebsite.com/media/bbb_trailer_iphone.m4v"/> </video> </figure> This does not work either. <figure> <video id="vid1" width="500" height="300" style="position:absolute" poster="http://cdn.kaltura.org/apis/html5lib/kplayer-examples/media/bbb480.jpg" durationHint="33" controls = "true"> <source src="http://127.0.0.1/html5videotest/media/bbb400p.ogv" /> <source src="http://127.0.0.1/html5videotest/media/bbb_trailer_iphone.m4v"/> </video> </figure>

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• Segmenting a double array of labels

  - by Ami

  The Problem: I have a large double array populated with various labels. Each element (cell) in the double array contains a set of labels and some elements in the double array may be empty. I need an algorithm to cluster elements in the double array into discrete segments. A segment is defined as a set of pixels that are adjacent within the double array and one label that all those pixels in the segment have in common. (Diagonal adjacency doesn't count and I'm not clustering empty cells). |-------|-------|------| | Jane | Joe | | | Jack | Jane | | |-------|-------|------| | Jane | Jane | | | | Joe | | |-------|-------|------| | | Jack | Jane | | | Joe | | |-------|-------|------| In the above arrangement of labels distributed over nine elements, the largest cluster is the “Jane” cluster occupying the four upper left cells. What I've Considered: I've considered iterating through every label of every cell in the double array and testing to see if the cell-label combination under inspection can be associated with a preexisting segment. If the element under inspection cannot be associated with a preexisting segment it becomes the first member of a new segment. If the label/cell combination can be associated with a preexisting segment it associates. Of course, to make this method reasonable I'd have to implement an elaborate hashing system. I'd have to keep track of all the cell-label combinations that stand adjacent to preexisting segments and are in the path of the incrementing indices that are iterating through the double array. This hash method would avoid having to iterate through every pixel in every preexisting segment to find an adjacency. Why I Don't Like it: As is, the above algorithm doesn't take into consideration the case where an element in the double array can be associated with two unique segments, one in the horizontal direction and one in the vertical direction. To handle these cases properly, I would need to implement a test for this specific case and then implement a method that will both associate the element under inspection with a segment and then concatenate the two adjacent identical segments. On the whole, this method and the intricate hashing system that it would require feels very inelegant. Additionally, I really only care about finding the large segments in the double array and I'm much more concerned with the speed of this algorithm than with the accuracy of the segmentation, so I'm looking for a better way. I assume there is some stochastic method for doing this that I haven't thought of. Any suggestions?

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• Recursive N-way merge/diff algorithm for directory trees?

  - by BobMcGee

  What algorithms or Java libraries are available to do N-way, recursive diff/merge of directories? I need to be able to generate a list of folder trees that have many identical files, and have subdirectories with many similar files. I want to be able to use 2-way merge operations to quickly remove as much redundancy as possible. Goals: Find pairs of directories that have many similar files between them. Generate short list of directory pairs that can be synchronized with 2-way merge to eliminate duplicates Should operate recursively (there may be nested duplicates of higher-level directories) Run time and storage should be O(n log n) in numbers of directories and files Should be able to use an embedded DB or page to disk for processing more files than fit in memory (100,000+). Optional: generate an ancestry and change-set between folders Optional: sort the merge operations by how many duplicates they can elliminate I know how to use hashes to find duplicate files in roughly O(n) space, but I'm at a loss for how to go from this to finding partially overlapping sets between folders and their children. EDIT: some clarification The tricky part is the difference between "exact same" contents (otherwise hashing file hashes would work) and "similar" (which will not). Basically, I want to feed this algorithm at a set of directories and have it return a set of 2-way merge operations I can perform in order to reduce duplicates as much as possible with as few conflicts possible. It's effectively constructing an ancestry tree showing which folders are derived from each other. The end goal is to let me incorporate a bunch of different folders into one common tree. For example, I may have a folder holding programming projects, and then copy some of its contents to another computer to work on it. Then I might back up and intermediate version to flash drive. Except I may have 8 or 10 different versions, with slightly different organizational structures or folder names. I need to be able to merge them one step at a time, so I can chose how to incorporate changes at each step of the way. This is actually more or less what I intend to do with my utility (bring together a bunch of scattered backups from different points in time). I figure if I can do it right I may as well release it as a small open source util. I think the same tricks might be useful for comparing XML trees though.

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• Is this scenario in compliance with GPLv3?

  - by Sean Kinsey

  For arguments sake, say that we create a web application , that depends on a GPLv3 licensed component, lets say Ext JS. Based on Section 0 of the license, the common notion is that the entire web application (the client side javascript) falls under the definition of a covered work: A “covered work” means either the unmodified Program or a work based on the Program. and that it will therefor have to be distributed under the same license Ok, so here comes the fun part: This is a short 'program' that is based on Ext JS var myPanel = new Ext.Panel(); The question that arises is: Have I now violated the GPL by not including the source of Ext JS and its license? Ok, so lets take another example <!doctype html> <html> <head> <title>my title</title> <script type="text/javascript" src="http://extjs.cachefly.net/ext-3.2.1/ext-all.js"> </script> <link rel="stylesheet" type="text/css" href="http://extjs.cachefly.net/ext-3.2.1/resources/css/ext-all.css" /> <script type="text/javascript"> var myPanel = new Ext.Panel(); </script> </head> <body> </body> </html> Have I now violated the terms of the GPL? The code conveyed by me to you is in a non-functional state - it will have to be combined with the actual source of Ext JS, which you(your browser) will have to retrieve, from a source made public by someone else to be usable. Now, if the answer to the above is no, how does me conveying this code in visible form differ from the 'invisible' form conveyed by my web server? As a side note, a very similar thing is done in Linux with many projects that depends on less permissive licenses - the user has to retrieve these on its own and make these available for the primary lib/executable. How is this not the same if the user is informed on beforehand that he (the browser) will have to retrieve the needed resources from a different source? Just to make it clear, I'm pro FLOSS, and I have also published a number of projects licensed under more permissive licenses. The reason I'm asking this is that I still haven't found anyone offering a definitive answer to this.

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• Sanity check on this idea for an Image Viewer in a web app

  - by Charlie Flowers

  I have an approach in mind for an image viewer in a web app, and want to get a sanity check and any thoughts you stackoverflowers might have. Here's the whirlwind nutshell summary: I'm working on an ASP.NET MVC application that will run in my company's retail stores. Even though it is a web application, we own the store machines and have control over them. We have a "windows agent" running on the store machine which we can talk to via http post (it is a WCF service, and our web app has permission to talk to it from the browser). One of the web pages needs to be an "image viewer" page with some common things like Rotate & Zoom. Now, there are some WebForms controls that offer Rotate and Zoom. However, they take up server resources and generate a good bit of traffic between the server and the browser. For example, the Rotate function would cause an ajax call to the server, which would then generate a new image written to a .NET Canvas object, which would then be written to a file on the server, which would then be returned from the ajax call and refreshed inside the browser. Normally, that's a pretty good way of doing things. But in our case, we have code running on the store machine that we can communicate with. This leads me to consider the following approach: When the user asks to view an image, we tell our "windows agent" to download it from our image server to the store machine. We then redirect our browser to our image viewer page, which will pull the image from the local file we just wrote to the store machine. When the user clicks "Rotate", we cause JavaScript code in the browser to call our "windows agent" software, asking it to perform the "Rotate" function. The "windows agent" does the rotation using the same kind of imaging control that would formerly have been used on the server, but it does so now on the store machine. Javascript in the browser then refreshes the image on the page to show the newly rotated image. Zoom and similar features would be implemented the same way. This seems to be much more efficient, scalable, and responsive for the end-users. However, I've never heard of anything like it being done, mostly because it's rare to have this combination of a web app plus a "windows agent" on the client machine. What do you think? Feasible? Reasonable? Any pitfalls I overlooked or improvements / suggestions you can see? Has anyone done anything like this who would like to offer the wisdom of experience? Thanks!

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• WPF Application Slow Unresponsive when demonstrating using remote sharing software

  - by Kev

  After spending 14 hours on this I think its time to share my woes and see if anyone has experienced this issue before. Ill describe the issue and tests I have done to rule out certain things. Ok so I have a WPF application which loads in data from an SQL database. I am using DevExpress Components for datagrids, ribbons etc.. and FluentNhibernate to provide a session for database operations. I am also using log4net to log events to a textfile. Using the application on my laptop with SQL Express 2008 works fine.. the application starts up, retrieves 1000 records and I can tab through the controls on the ribbon. Now, I decided to demo the application to a third party and used remote login/sharing software online to share my desktop with the other person so as I could load the application on my laptop and they could view me using the application. Now, the application takes approx 45 seconds to load... 30 seconds with a blank database where as, when im not sharing out my screen using the online software the application loads in about 7-10 seconds. As well as that, even using the controls in the application during the demo were very sticky, slow and unresponsive. During the sharing session though however I was able to use other applications without any problems.. everything else worked fine. But I cannot understand how my application works ok under normal conditions , even browsing the net at the same time etc... BUT totally fails to perform correctly when I am sharing a session with another user... the CPU usage shot up to 100% too at times when the application was trying to start up... Please see below a list of 3rd party dlls I am using as references in my project. DevExpress dlls FluidKit PixelLab.WPF PixelLab.Common Galasoft WPF Kit FluentNHibernate NHibernate Nhibernate.ByteCode.Castle Skype4ComLib TXTEXTControl log4net LinqKit All of these DLLs are in the output folder with the application dlls created from the class assemblys in the project. So when installed via an installer on a machine the dlls will be in the same application folder as the application file itself. Many thanks

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• log4j performance

  - by Bob

  Hi, I'm developing a web app, and I'd like to log some information to help me improve and observe the app. (I'm using Tomcat6) First I thought I would use StringBuilders, append the logs to them and a task would persist them into the database like every 2 minutes. Because I was worried about the out-of-the-box logging system's performance. Then I made some test. Especially with log4j. Here is my code: Main.java public static void main(String[] args) { Thread[] threads = new Thread[LoggerThread.threadsNumber]; for(int i = 0; i < LoggerThread.threadsNumber; ++i){ threads[i] = new Thread(new LoggerThread("name - " + i)); } LoggerThread.startTimestamp = System.currentTimeMillis(); for(int i = 0; i < LoggerThread.threadsNumber; ++i){ threads[i].start(); } LoggerThread.java public class LoggerThread implements Runnable{ public static int threadsNumber = 10; public static long startTimestamp; private static int counter = 0; private String name; public LoggerThread(String name) { this.name = name; } private Logger log = Logger.getLogger(this.getClass()); @Override public void run() { for(int i=0; i<10000; ++i){ log.info(name + ": " + i); if(i == 9999){ int c = increaseCounter(); if(c == threadsNumber){ System.out.println("Elapsed time: " + (System.currentTimeMillis() - startTimestamp)); } } } } private synchronized int increaseCounter(){ return ++counter; } } } log4j.properties log4j.logger.main.LoggerThread=debug, f log4j.appender.f=org.apache.log4j.RollingFileAppender log4j.appender.f.layout=org.apache.log4j.PatternLayout log4j.appender.f.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n log4j.appender.f.File=c:/logs/logging.log log4j.appender.f.MaxFileSize=15000KB log4j.appender.f.MaxBackupIndex=50 I think this is a very common configuration for log4j. First I used log4j 1.2.14 then I realized there was a newer version, so I switched to 1.2.16 Here are the figures (all in millisec) LoggerThread.threadsNumber = 10 1.2.14: 4235, 4267, 4328, 4282 1.2.16: 2780, 2781, 2797, 2781 LoggerThread.threadsNumber = 100 1.2.14: 41312, 41014, 42251 1.2.16: 25606, 25729, 25922 I think this is very fast. Don't forget that: in every cycle the run method not just log into the file, it has to concatenate strings (name + ": " + i), and check an if test (i == 9999). When threadsNumber is 10, there are 100.000 loggings and if tests and concatenations. When it is 100, there are 1.000.000 loggings and if tests and concatenations. (I've read somewhere JVM uses StringBuilder's append for concatenation, not simple concatenation). Did I missed something? Am I doing something wrong? Did I forget any factor that could decrease the performance? If these figures are correct I think, I don't have to worry about log4j's performance even if I heavily log, do I?

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• What's the standard algorithm for syncing two lists of objects?

  - by Oliver Giesen

  I'm pretty sure this must be in some kind of text book (or more likely in all of them) but I seem to be using the wrong keywords to search for it... :( A common task I'm facing while programming is that I am dealing with lists of objects from different sources which I need to keep in sync somehow. Typically there's some sort of "master list" e.g. returned by some external API and then a list of objects I create myself each of which corresponds to an object in the master list. Sometimes the nature of the external API will not allow me to do a live sync: For instance the external list might not implement notifications about items being added or removed or it might notify me but not give me a reference to the actual item that was added or removed. Furthermore, refreshing the external list might return a completely new set of instances even though they still represent the same information so simply storing references to the external objects might also not always be feasible. Another characteristic of the problem is that both lists cannot be sorted in any meaningful way. You should also assume that initializing new objects in the "slave list" is expensive, i.e. simply clearing and rebuilding it from scratch is not an option. So how would I typically tackle this? What's the name of the algorithm I should google for? In the past I have implemented this in various ways (see below for an example) but it always felt like there should be a cleaner and more efficient way. Here's an example approach: Iterate over the master list Look up each item in the "slave list" Add items that do not yet exist Somehow keep track of items that already exist in both lists (e.g. by tagging them or keeping yet another list) When done iterate once more over the slave list Remove all objects that have not been tagged (see 4.) Update Thanks for all your responses so far! I will need some time to look at the links. Maybe one more thing worthy of note: In many of the situations where I needed this the implementation of the "master list" is completely hidden from me. In the most extreme cases the only access I might have to the master list might be a COM-interface that exposes nothing but GetFirst-, GetNext-style methods. I'm mentioning this because of the suggestions to either sort the list or to subclass it both of which is unfortunately not practical in these cases unless I copy the elements into a list of my own and I don't think that would be very efficient. I also might not have made it clear enough that the elements in the two lists are of different types, i.e. not assignment-compatible: Especially, the elements in the master list might be available as interface references only.

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• Function Point Analysis -- a seriously over-estimating technique?

  - by kizzx2

  I know questions about FPA has been asked numerous times before, but this time I'm taking a more analytical angle at it, backed up with data. 1. First, some data This question is based on a tutorial. He had a "Sample Count" section where he demonstrated it step by step. You can see some screenshots of his sample application here. In the end, he calculated the unadjusted FP to be 99. There is another article on InformIT with industry data on typical hour/FP. It ranges from 2 hours/FP to 27.4 hours/FP. Let's try to stick with 2 for the moment (since SO readers are probably the more efficient crowd :p). 2. Reality check!? Now just check out the screenshots again. Do a little math here 99 * 2 = 198 hours 198 hours / 40 hours per week = 5 weeks Seriously? That sample application is going to take 5 weeks to implement? Is it just my feeling that it wouldn't take any decent programmer longer than one week to have it completed? Now let's try estimating the cost of the project. We'll use New York's minimum wage at the moment (Wikipedia), which is $7.25 198 * 7.25 = $1435.5 From what I could see from the screenshots, this application is a small excel-improvement app. I could have bought MS Office Pro for 200 bucks which gives me greater interoperability (.xls files) and flexibility (spreadsheets). (For the record, that same Web site has another article discussing productivity. It seems like they typically use 4.2 hours/FP, which gives us even more shocking stats: 99 * 4.2 = 415 hours = 10 weeks = almost 3 whopping months! 415 hours * $7.25 = $3000 zomg (That's even assuming that all our poor coders get the minimum wage!) 3. Am I missing something here? Right now, I could come up with several possible explanation: FPA is really only suited for bigger projects (1000+ FPs) so it becomes extremely inaccurate at smaller scale. The hours/FP metric fluctuates abruptly from team to team, project to project. For a small project like this, we could have used something like 0.5 hour/FP or something. (Now this kind of makes the whole estimation thing pointless, unless my firm does the same type of projects for several years with the same team, not really common.) From my experience with several software metrics, Function Point is really not a lightweight metric. If the hour/FP thing fluctuates so much, then what's the point, maybe I could have gone with User Story Points which is a lot faster to get and arguably almost as uncertain. What would be the FP experts' answers to this?

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• How Can I Populate Default Form Data with a ManyToMany Field?

  - by b14ck

  Ok, I've been crawling google and Django documentation for over 2 hours now (as well as the IRC channel on freenode), and haven't been able to figure this one out. Basically, I have a model called Room, which is displayed below: class Room(models.Model): """ A `Partyline` room. Rooms on the `Partyline`s are like mini-chatrooms. Each room has a variable amount of `Caller`s, and usually a moderator of some sort. Each `Partyline` has many rooms, and it is common for `Caller`s to join multiple rooms over the duration of their call. """ LIVE = 0 PRIVATE = 1 ONE_ON_ONE = 2 UNCENSORED = 3 BULLETIN_BOARD = 4 CHILL = 5 PHONE_BOOTH = 6 TYPE_CHOICES = ( ('LR', 'Live Room'), ('PR', 'Private Room'), ('UR', 'Uncensored Room'), ) type = models.CharField('Room Type', max_length=2, choices=TYPE_CHOICES) number = models.IntegerField('Room Number') partyline = models.ForeignKey(Partyline) owner = models.ForeignKey(User, blank=True, null=True) bans = models.ManyToManyField(Caller, blank=True, null=True) def __unicode__(self): return "%s - %s %d" % (self.partyline.name, self.type, self.number) I've also got a forms.py which has the following ModelForm to represent my Room model: from django.forms import ModelForm from partyline_portal.rooms.models import Room class RoomForm(ModelForm): class Meta: model = Room I'm creating a view which allows administrators to edit a given Room object. Here's my view (so far): def edit_room(request, id=None): """ Edit various attributes of a specific `Room`. Room owners do not have access to this page. They cannot edit the attributes of the `Room`(s) that they control. """ room = get_object_or_404(Room, id=id) if not room.is_owner(request.user): return HttpResponseForbidden('Forbidden.') if is_user_type(request.user, ['admin']): form_type = RoomForm elif is_user_type(request.user, ['lm']): form_type = LineManagerEditRoomForm elif is_user_type(request.user, ['lo']): form_type = LineOwnerEditRoomForm if request.method == 'POST': form = form_type(request.POST, instance=room) if form.is_valid(): if 'owner' in form.cleaned_data: room.owner = form.cleaned_data['owner'] room.save() else: defaults = {'type': room.type, 'number': room.number, 'partyline': room.partyline.id} if room.owner: defaults['owner'] = room.owner.id if room.bans: defaults['bans'] = room.bans.all() ### this does not work properly! form = form_type(defaults, instance=room) variables = RequestContext(request, {'form': form, 'room': room}) return render_to_response('portal/rooms/edit.html', variables) Now, this view works fine when I view the page. It shows all of the form attributes, and all of the default values are filled in (when users do a GET)... EXCEPT for the default values for the ManyToMany field 'bans'. Basically, if an admins clicks on a Room object to edit, the page they go to will show all of the Rooms default values except for the 'bans'. No matter what I do, I can't find a way to get Django to display the currently 'banned users' for the Room object. Here is the line of code that needs to be changed (from the view): defaults = {'type': room.type, 'number': room.number, 'partyline': room.partyline.id} if room.owner: defaults['owner'] = room.owner.id if room.bans: defaults['bans'] = room.bans.all() ### this does not work properly! There must be some other syntax I have to use to specify the default value for the 'bans' field. I've really been pulling my hair out on this one, and would definitely appreciate some help. Thanks!

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• MVVM Binding Orthogonal Aspects in Views e.g. Application Settings

  - by chibacity

  I have an application which I am developing using WPF\Prism\MVVM. All is going well and I have some pleasing MVVM implementations. However, in some of my views I would like to be able to bind application settings e.g. when a user reloads an application, the checkbox for auto-scrolling a grid should be checked in the state it was last time the user used the application. My view needs to bind to something that holds the "auto-scroll" setting state. I could put this on the view-model, but applications settings are orthogonal to the purpose of the view-model. The "auto-scroll" setting is controlling an aspect of the view. This setting is just an example. There will be quite a number of them and splattering my view-models with properties to represent application settings (so I can bind them) feels decidedly yucky. One view-model per view seems to be de rigeuer... What is best\usual practice here? Splatter my view-models with application settings? Have multiple view-models per view so settings can be represented in their own right? Split views so that controls can bind to an ApplicationSettingsViewModel? = too many views? Something else? Edit 1 To add a little more context, I am developing a UI with a tabbed interface. Each tab will host a single widget and there a variety of widgets. Each widget is a Prism composition of individual views. Some views are common amongst widgets e.g. a file picker view. Whilst each widget is composed of several views, as a whole, conceptually a widget has a single set of user settings e.g. last file selected, auto-scroll enabled, etc. These need to be persisted and retrieved\applied when the application starts again, and the widget views are created. My question is focused on the fact that conceptually a widget has a single set of user settings which is at right-angles to the fact that a widget consists of many views. Each view in the widget has it's own view-model (which works nicely and logically) but if I stick to a one view-model per view, I would have to splatter each view-model with user settings appropriate to it. This doesn't sound right ?!?

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• Where can I find information on the Get, Set and Address methods for multidimensional System.Array i

  - by Rob Smallshire

  System.Array serves as the base class for all arrays in the Common Language Runtime (CLR). According to this article, For each concrete array type, [the] runtime adds three special methods: Get/Set/Address. and indeed if I disassemble this C# code, int[,] x = new int[1024,1024]; x[0,0] = 1; x[1,1] = 2; x[2,2] = 3; Console.WriteLine(x[0,0]); Console.WriteLine(x[1,1]); Console.WriteLine(x[2,2]); into CIL I get, IL_0000: ldc.i4 0x400 IL_0005: ldc.i4 0x400 IL_000a: newobj instance void int32[0...,0...]::.ctor(int32, int32) IL_000f: stloc.0 IL_0010: ldloc.0 IL_0011: ldc.i4.0 IL_0012: ldc.i4.0 IL_0013: ldc.i4.1 IL_0014: call instance void int32[0...,0...]::Set(int32, int32, int32) IL_0019: ldloc.0 IL_001a: ldc.i4.1 IL_001b: ldc.i4.1 IL_001c: ldc.i4.2 IL_001d: call instance void int32[0...,0...]::Set(int32, int32, int32) IL_0022: ldloc.0 IL_0023: ldc.i4.2 IL_0024: ldc.i4.2 IL_0025: ldc.i4.3 IL_0026: call instance void int32[0...,0...]::Set(int32, int32, int32) IL_002b: ldloc.0 IL_002c: ldc.i4.0 IL_002d: ldc.i4.0 IL_002e: call instance int32 int32[0...,0...]::Get(int32, int32) IL_0033: call void [mscorlib]System.Console::WriteLine(int32) IL_0038: ldloc.0 IL_0039: ldc.i4.1 IL_003a: ldc.i4.1 IL_003b: call instance int32 int32[0...,0...]::Get(int32, int32) IL_0040: call void [mscorlib]System.Console::WriteLine(int32) IL_0045: ldloc.0 IL_0046: ldc.i4.2 IL_0047: ldc.i4.2 IL_0048: call instance int32 int32[0...,0...]::Get(int32, int32) IL_004d: call void [mscorlib]System.Console::WriteLine(int32) where the calls to the aforementioned Get and Set methods can be clearly seen. It seems the arity of these methods is related to the dimensionality of the array, which is presumably why they are created by the runtime and are not pre-declared. I couldn't locate any information about these methods on MSDN and their simple names makes them resistant to Googling. I'm writing a compiler for a language which supports multidimensional arrays, so I'd like to find some official documentation about these methods, under what conditions I can expect them to exist and what I can expect their signatures to be. In particular, I'd like to know whether its possible to get a MethodInfo object for Get or Set for use with Reflection.Emit without having to create an instance of the array with correct type and dimensionality on which to reflect, as is done in the linked example.

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• JavaScript Resource Management Design Pattern

  - by Adam

  As a web developer, a common problem I find myself tackling is waiting for something to load before doing something else. In particular, I often hide (using either display: none; or visibility: hidden; depending on the situation) elements while waiting for a background image or a CSS file to load. Consider this example from Last.FM. They overlay a semi-transparant PNG over each album art image so that it looks like it's inside a jewel-case. They let it load when it loads, so depending on your internet speed, you may see the art image by itself (without the overlay) temporarily. In this case, the album art looks fine without the jewel-case effect. But in similar situations, I have found that I don't want the user to see the site's design mangled as resources incrementally load. So, in rare cases I have hidden everything from the user until the whole kit and kaboodle has loaded. But this is often a pain to write out, and may force the user to wait for a pretty long time to see anything (besides "loading..." text). I can think of (and have used on occasion) some obvious solutions/compromises: Use some inline CSS so that as certain parts of the DOM load and render, they will immediately have the correct size/position/etc. Immediately render the navigation part of the site, so that if the user wanted to use the current page purely to get somewhere else, they don't have to wait for the rest to load. Load pixelated images first as placeholders for layout while lazy-loading higher quality images as replacements. Something quirky like using a cute animated gif to distract the user during a "loading..." phase. Show useful information as a reference while loading the full UI. (Something akin to Gmail Inbox Preview, etc.) (Sorry if my question was basically just asked and answered...) Despite all of these ideas, I still find myself hoping there are better ways of doing some of these things. So I guess what I'm looking for is some inspiration and/or any creative ways of dealing with this problem that you guys may have seen out in the wild.

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• Is READ UNCOMMITTED / NOLOCK safe in this situation?

  - by Ben Challenor

  I know that snapshot isolation would fix this problem, but I'm wondering if NOLOCK is safe in this specific case so that I can avoid the overhead. I have a table that looks something like this: drop table Data create table Data ( Id BIGINT NOT NULL, Date BIGINT NOT NULL, Value BIGINT, constraint Cx primary key (Date, Id) ) create nonclustered index Ix on Data (Id, Date) There are no updates to the table, ever. Deletes can occur but they should never contend with the SELECT because they affect the other, older end of the table. Inserts are regular and page splits to the (Id, Date) index are extremely common. I have a deadlock situation between a standard INSERT and a SELECT that looks like this: select top 1 Date, Value from Data where Id = @p0 order by Date desc because the INSERT acquires a lock on Cx (Date, Id; Value) and then Ix (Id, Date), but the SELECT acquires a lock on Ix (Id, Date) and then Cx (Date, Id; Value). This is because the SELECT first seeks on Ix and then joins to a seek on Cx. Swapping the clustered and non-clustered index would break this cycle, but it is not an acceptable solution because it would introduce cycles with other (more complex) SELECTs. If I add NOLOCK to the SELECT, can it go wrong in this case? Can it return: More than one row, even though I asked for TOP 1? No rows, even though one exists and has been committed? Worst of all, a row that doesn't satisfy the WHERE clause? I've done a lot of reading about this online, but the only reproductions of over- or under-count anomalies I've seen (one, two) involve a scan. This involves only seeks. Jeff Atwood has a post about using NOLOCK that generated a good discussion. I was particularly interested in a comment by Rick Townsend: Secondly, if you read dirty data, the risk you run is of reading the entirely wrong row. For example, if your select reads an index to find your row, then the update changes the location of the rows (e.g.: due to a page split or an update to the clustered index), when your select goes to read the actual data row, it's either no longer there, or a different row altogether! Is this possible with inserts only, and no updates? If so, then I guess even my seeks on an insert-only table could be dangerous. Update: I'm trying to figure out how snapshot isolation works. It seems to be row-based, where transactions read the table (with no shared lock!), find the row they are interested in, and then see if they need to get an old version of the row from the version store in tempdb. But in my case, no row will have more than one version, so the version store seems rather pointless. And if the row was found with no shared lock, how is it different to just using NOLOCK?

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• Java: omitting a data member from the equals method.

  - by cchampion

  public class GamePiece { public GamePiece(char cLetter, int nPointValue) { m_cLetter=cLetter; m_nPointValue=nPointValue; m_nTurnPlaced=0; //has not been placed on game board yet. } public char GetLetter() {return m_cLetter;} public int GetPointValue() {return m_nPointValue;} public int GetTurnPlaced() {return m_nTurnPlaced;} public void SetTurnPlaced(int nTurnPlaced) { m_nTurnPlaced=nTurnPlaced; } @Override public boolean equals(Object obj) { /*NOTE to keep this shorter I omitted some of the null checking and instanceof stuff. */ GamePiece other = (GamePiece) obj; //not case sensitive, and I don`t think we want it to be here. if(m_cLetter != other.m_cLetter) { return false; } if(m_nPointValue != other.m_nPointValue) { return false; } /* NOTICE! m_nPointValue purposely omitted. It does not affect hashcode or equals */ return true; } @Override public int hashCode() { /* NOTICE! m_nPointValue purposely omitted. It should not affect hashcode or equals */ final int prime = 41; return prime * (prime + m_nPointValue + m_cLetter); } private char m_cLetter; private int m_nPointValue; private int m_nTurnPlaced;//turn which the game piece was placed on the game board. Does not affect equals or has code! } Consider the given piece of code. This object has been immutable until the introduction of the m_nTurnPlaced member (which can be modified by the SetTurnPlaced method, so now GamePiece becomes mutable). GamePiece is used in an ArrayList, I call contains and remove methods which both rely on the equals method to be implemented. My question is this, is it ok or common practice in Java for some members to not affect equals and hashcode? How will this affect its use in my ArrayList? What type of java Collections would it NOT be safe to use this object now that it is mutable? I've been told that you're not supposed to override equals on mutable objects because it causes some collections to behave "strangely" (I read that somewhere in the java documentation).

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• Silverlight? WPF? or Windows Form?

  - by Amit

  After Silverlight 4.0 has been released with new WPF, I am kind of confused with these technologies: Silverlight? WPF? Windows Form? The main motive that we want to achieve for BIG business project is following: Performance Security And platform independent** If I consider all above three points then only Silverlight is the option as I don’t want people buying emulator on MacOS for WPF or Windows Form. Now how good the Silverlight is for Business applications, I was completely against when Silverlight 2.0 was in the market but now it is Silverlight 4.0 and they have provided many new features (but still basics) that is required in any challenging business applications. Comparing Silverlight and WPF -* Silverlight and WPF are very new technology and if I'd to compare from these two then I'd prefer WPF because it can be considered stable and mature. But it is not same as Windows Form. -* If I go with Silverlight then I am sure about keep updating to the latest version of Silverlight. I remembered when we were developing software for version 2.0 then we'd to create our own framework with dynamic loading DLL, and then Navigation concept. But everything was got changed once Silverlight 3.0 came. I don't want this to be happening with this new product. -* If we go with WPF then we don't get the platform independence. Now, why not we just focus on making WPF and then move to Silverlght. As someone (Tim?) from Microsoft has said that the idea is to make Silverlight as close as WPF. But if that is the case then why XAML structure is different; I will not be convinced with by saying that .Net framework for SL is too small.. well the difference is coming from the namespace ? I was searching on this subject and found "Microsoft WPF-Silverlight Comparison Whitepaper v1.1.pdf". This guide is very good that gives you ins-outs about how can we build common apps that runs on both. But again, it is comparing Silverlight 2 and not 4. I am sure many architect/ developers/ project managers must be facing similar kind of questions in their premises and wants to initiate this discussion, if it has not been :). We've still got 2 weeks to make this decision, so I'm expecting everyone to participate, gurus?

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• how to implement a "soft barrier" in multithreaded c++

  - by Jason

  I have some multithreaded c++ code with the following structure: do_thread_specific_work(); update_shared_variables(); //checkpoint A do_thread_specific_work_not_modifying_shared_variables(); //checkpoint B do_thread_specific_work_requiring_all_threads_have_updated_shared_variables(); What follows checkpoint B is work that could have started if all threads have reached only checkpoint A, hence my notion of a "soft barrier". Typically multithreading libraries only provide "hard barriers" in which all threads must reach some point before any can continue. Obviously a hard barrier could be used at checkpoint B. Using a soft barrier can lead to better execution time, especially since the work between checkpoints A and B may not be load-balanced between the threads (i.e. 1 slow thread who has reached checkpoint A but not B could be causing all the others to wait at the barrier just before checkpoint B). I've tried using atomics to synchronize things and I know with 100% certainty that is it NOT guaranteed to work. For example using openmp syntax, before the parallel section start with: shared_thread_counter = num_threads; //known at compile time #pragma omp flush Then at checkpoint A: #pragma omp atomic shared_thread_counter--; Then at checkpoint B (using polling): #pragma omp flush while (shared_thread_counter > 0) { usleep(1); //can be removed, but better to limit memory bandwidth #pragma omp flush } I've designed some experiments in which I use an atomic to indicate that some operation before it is finished. The experiment would work with 2 threads most of the time but consistently fail when I have lots of threads (like 20 or 30). I suspect this is because of the caching structure of modern CPUs. Even if one thread updates some other value before doing the atomic decrement, it is not guaranteed to be read by another thread in that order. Consider the case when the other value is a cache miss and the atomic decrement is a cache hit. So back to my question, how to CORRECTLY implement this "soft barrier"? Is there any built-in feature that guarantees such functionality? I'd prefer openmp but I'm familiar with most of the other common multithreading libraries. As a workaround right now, I'm using a hard barrier at checkpoint B and I've restructured my code to make the work between checkpoint A and B automatically load-balancing between the threads (which has been rather difficult at times). Thanks for any advice/insight :)

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• Do Websites need Local Databases Anymore?

  - by viatropos

  If there's a better place to ask this, please let me know. Every time I build a new website/blog/shopping-cart/etc., I keep trying to do the following: Extract out common functionality into reusable code (Rubygems and jQuery plugins mostly) If possible, convert that gem into a small service so I never have to deal with a database for the objects involved (by service, I mean something lean and mean, usually built with the Sinatra Web Framework with a few core models). My assumption is, if I can remove dependencies on local databases, that will make it easier and more scalable in the long run (scalable in terms of reusability and manageability, not necessarily database/performance). I'm not sure if that's a good or bad assumption yet. What do you think? I've made this assumption because of the following reason: Most serious database/model functionality has been built on the internet somewhere. Just to name a few: Social Network API: Facebook Messaging API: Twitter Mailing API: Google Event API: Eventbrite Shopping API: Shopify Comment API: Disqus Form API: Wufoo Image API: Picasa Video API: Youtube ... Each of those things are fairly complicated to build from scratch and to make as optimized, simple, and easy to use as those companies have made them. So if I build an app that shows pictures (picasa) on an Event page (eventbrite), and you can see who joined the event (facebook events), and send them emails (google apps api), and have them fill out monthly surveys (wufoo), and watch a video when they're done (youtube), all integrated into a custom, easy to use website, and I can do that without ever creating a local database, is that a good thing? I ask because there's two things missing from the puzzle that keep forcing me to create that local database: Post API RESTful/Pretty Url API While there's plenty of Blogging systems and APIs for them, there is no one place where you can just write content and have it part of some massive thing. For every app, I have to use code for creating pretty/restful urls, and that saves posts. But it seems like that should be a service! Question is, is that what the website is? ...That place to integrate the worlds services for my specific cause... and, sigh, to store posts that only my site has access to. Will everyone always need "their own blog"? Why not just have a profile and write lots of content on an established platform like StackOverflow or Facebook? ... That way I can write apps entirely without a database and know that I'm doing it right. Note: Of course at some point you'd need a database, if you were doing something unique or new. But for the case where you're just rewiring information or creating things like videos, events, and products, is it really necessary anymore??

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• Would a Centralized Blogging Service Work?

  - by viatropos

  If there's a better place to ask this, please let me know. Every time I build a new website/blog/shopping-cart/etc., I keep trying to do the following: Extract out common functionality into reusable code (Rubygems and jQuery plugins mostly) If possible, convert that gem into a small service so I never have to deal with a database for the objects involved (by service, I mean something lean and mean, usually built with the Sinatra Web Framework with a few core models. My assumption is, if I can remove dependencies on local databases, that will make it easier and more scalable in the long run (scalable in terms of reusability and manageability, not necessarily database/performance). I'm not sure if that's a good or bad assumption yet. What do you think? I've made this assumption because of the following reason: Most serious database/model functionality has been built on the internet somewhere. Just to name a few: Social Network API: Facebook Messaging API: Twitter Mailing API: Google Event API: Eventbrite Shopping API: Shopify Comment API: Disqus Form API: Wufoo Image API: Picasa Video API: Youtube ... Each of those things are fairly complicated to build from scratch and to make as optimized, simple, and easy to use as those companies have. So if I build an app that shows pictures (picasa) on an Event page (eventbrite), and you can see who joined the event (facebook events), and send them emails (google apps api), and have them fill out monthly surveys (wufoo), and watch a video when they're done (youtube), all integrated into a custom, easy to use website, and I can do that without ever creating a local database, is that a good thing? I ask because there's two things missing from the puzzle that keep forcing me to create that local database: Post API RESTful/Pretty Url API While there's plenty of Blogging systems and APIs for them, there is no one place where you can just write content and have it part of some massive thing. For every app, I have to use code for creating pretty/restful urls, and that saves posts. But it seems like that should be a service! Question is, is that the main point of a website? Will everyone always need "their own blog"? Why not just have a profile and write lots of content on an established platform like StackOverflow or Facebook?

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• Constructor Injection and when to use a Service Locator

  - by Simon

  I'm struggling to understand parts of StructureMap's usage. In particular, in the documentation a statement is made regarding a common anti-pattern, the use of StructureMap as a Service Locator only instead of constructor injection (code samples straight from Structuremap documentation): public ShippingScreenPresenter() { _service = ObjectFactory.GetInstance<IShippingService>(); _repository = ObjectFactory.GetInstance<IRepository>(); } instead of: public ShippingScreenPresenter(IShippingService service, IRepository repository) { _service = service; _repository = repository; } This is fine for a very short object graph, but when dealing with objects many levels deep, does this imply that you should pass down all the dependencies required by the deeper objects right from the top? Surely this breaks encapsulation and exposes too much information about the implementation of deeper objects. Let's say I'm using the Active Record pattern, so my record needs access to a data repository to be able to save and load itself. If this record is loaded inside an object, does that object call ObjectFactory.CreateInstance() and pass it into the active record's constructor? What if that object is inside another object. Does it take the IRepository in as its own parameter from further up? That would expose to the parent object the fact that we're access the data repository at this point, something the outer object probably shouldn't know. public class OuterClass { public OuterClass(IRepository repository) { // Why should I know that ThingThatNeedsRecord needs a repository? // that smells like exposed implementation to me, especially since // ThingThatNeedsRecord doesn't use the repo itself, but passes it // to the record. // Also where do I create repository? Have to instantiate it somewhere // up the chain of objects ThingThatNeedsRecord thing = new ThingThatNeedsRecord(repository); thing.GetAnswer("question"); } } public class ThingThatNeedsRecord { public ThingThatNeedsRecord(IRepository repository) { this.repository = repository; } public string GetAnswer(string someParam) { // create activeRecord(s) and process, returning some result // part of which contains: ActiveRecord record = new ActiveRecord(repository, key); } private IRepository repository; } public class ActiveRecord { public ActiveRecord(IRepository repository) { this.repository = repository; } public ActiveRecord(IRepository repository, int primaryKey); { this.repositry = repository; Load(primaryKey); } public void Save(); private void Load(int primaryKey) { this.primaryKey = primaryKey; // access the database via the repository and set someData } private IRepository repository; private int primaryKey; private string someData; } Any thoughts would be appreciated. Simon

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• Django Multi-Table Inheritance VS Specifying Explicit OneToOne Relationship in Models

  - by chefsmart

  Hope all this makes sense :) I'll clarify via comments if necessary. Also, I am experimenting using bold text in this question, and will edit it out if I (or you) find it distracting. With that out of the way... Using django.contrib.auth gives us User and Group, among other useful things that I can't do without (like basic messaging). In my app I have several different types of users. A user can be of only one type. That would easily be handled by groups, with a little extra care. However, these different users are related to each other in hierarchies / relationships. Let's take a look at these users: - Principals - "top level" users Administrators - each administrator reports to a Principal Coordinators - each coordinator reports to an Administrator Apart from these there are other user types that are not directly related, but may get related later on. For example, "Company" is another type of user, and can have various "Products", and products may be supervised by a "Coordinator". "Buyer" is another kind of user that may buy products. Now all these users have various other attributes, some of which are common to all types of users and some of which are distinct only to one user type. For example, all types of users have to have an address. On the other hand, only the Principal user belongs to a "BranchOffice". Another point, which was stated above, is that a User can only ever be of one type. The app also needs to keep track of who created and/or modified Principals, Administrators, Coordinators, Companies, Products etc. (So that's two more links to the User model.) In this scenario, is it a good idea to use Django's multi-table inheritance as follows: - from django.contrib.auth.models import User class Principal(User): # # # branchoffice = models.ForeignKey(BranchOffice) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalmodifier") # # # Or should I go about doing it like this: - class Principal(models.Model): # # # user = models.OneToOneField(User, blank=True) branchoffice = models.ForeignKey(BranchOffice) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="principalmodifier") # # # Please keep in mind that there are other user types that are related via foreign keys, for example: - class Administrator(models.Model): # # # principal = models.ForeignKey(Principal, help_text="The supervising principal for this Administrator") user = models.OneToOneField(User, blank=True) province = models.ForeignKey( Province) landline = models.CharField(blank=True, max_length=20) mobile = models.CharField(blank=True, max_length=20) created_by = models.ForeignKey(User, editable=False, blank=True, related_name="administratorcreator") modified_by = models.ForeignKey(User, editable=False, blank=True, related_name="administratormodifier") I am aware that Django does use a one-to-one relationship for multi-table inheritance behind the scenes. I am just not qualified enough to decide which is a more sound approach.

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• Excel string manipulation to check data consistency

  - by chefsmart

  Background information: - There are nearly 7000 individuals and there is data about their performances in one, two or three tests. Every individual has taken the 1st test (let's call it Test M). Some of those who have taken Test M have also taken Test I, and some of those who have taken Test I have also taken Test B. For the first two tests (M and I), students can score grades I, II, or III. Depending on the grades they are awarded points -- 3 for grade I, 2 for II, 1 for III. The last Test B is just a pass or a fail result with no grades. Those passing this test get 1 point, with no points for failure. (Well actually, grades are awarded, but all grades are given a common 1 point). An amateur has entered data to represent these students and their grades in an Excel file. Problem is, this person has done the worst thing possible - he has developed his own notation and entered all test information in a single cell --- and made my life hell. The file originally had two text columns, one for individual's id, and the second for test info, if one could call it that. It's horrible, I know, and I am suffering. In the image, if you see "M-II-2 I-III-1" it means the person got grade II in Test M for 2 points and grade III in Test I for 1 point. Some have taken only one test, some two, and some three. When the file came to me for processing and analyzing the performance of students, I sent it back with instructions to insert 3 additional columns with only the grades for the three tests. The file now looks as follows. Columns C and D represent grades I, II, and III using 1,2 and 3 respectively. Column C is for Test M, column D for Test I. Column E says BA (B Achieved!) if the individual has passed Test B. Now that you have the above information, let's get to the problem. I don't trust this and want to check whether data in column B matches with data in columns C,D and E. That is, I want to examine the string in column B and find out whether the figures in columns C,D and E are correct. All help is really appreciated. P.S. - I had exported this to MySQL via ODBC and that is why you are seeing those NULLs. I tried doing this in MySQL too, and really will accept a MySQL or an Excel solution, I don't have a preference. Edit : - See file with sample data

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• How to initiate chatting between two clients and two clients only, using applets and servlets?

  - by mithun1538

  Hello everyone, I first need to apologize for my earlier questions. (You can check my profile for them)They seemed to ask more questions than give answers. Hence, I am laying down the actual question that started all them absurd questions. I am trying to design a chat applet. Till now, I have coded the applet, servlet and communication between the applet and the servlet. The code in the servlet side is such that I was able to establish chatting between clients using the applets, but the code was more like a broadcast all feature, i.e. all clients would be chatting with each other. That was my first objective when I started designing the chat applet. The second step is chatting between only two specific users, much like any other chat application we have. So this was my idea for it: I create an instance of the servlet that has the 'broadcast-all' code. I then pass the address of this instance to the respective clients. 2 client applets use the address to then chat. Technically the code is 'broadcast-all', but since only 2 clients are connected to it, it gives the chatting between two clients feature. Thus, groups of 2 clients have different instances of the same servlet, and each instance handles chatting between two clients at a max. However, as predicted, the idea didn't materialize! I tried to create an instance of the servlet but the only solution for that was using sessions on the servlet side, and I don't know how to use this session for later communications. I then tried to modify my broadcast-all code. In that code, I was using classes that implemented Observer and Observable interfaces. So the next idea that I got was: Create a new object of the Observable class(say class_1). This object be common to 2 clients. 2 clients that wish to chat will use same object of the class_1. 2 other clients will use a different object of class_1. But the problem here lies with the class that implements the Observer interface(say class_2). Since this has observers monitoring the same type of class, namely class_1, how do I establish an observer monitoring one object of class_1 and another observer monitoring another object of the same class class_1 (Because notifyObservers() would notify all the observers and I can't assign a particular observer to a particular object)? I first decided to ask individual problems, like how to create instances of servlets, using objects of observable and observer and so on in stackoverflow... but I got confused even more. Can anyone give me an idea how to establish chatting between two clients only?(I am using Http and not sockets or RMI). Regards, Mithun. P.S. Thanks to all who replied to my previous (absurd) queries. I should have stated the purpose earlier so that you guys could help me better.

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• Under what circumstances would a LINQ-to-SQL Entity "lose" a changed field?

  - by John Rudy

  I'm going nuts over what should be a very simple situation. In an ASP.NET MVC 2 app (not that I think this matters), I have an edit action which takes a very small entity and makes a few changes. The key portion (outside of error handling/security) looks like this: Todo t = Repository.GetTodoByID(todoID); UpdateModel(t); Repository.Save(); Todo is the very simple, small entity with the following fields: ID (primary key), FolderID (foreign key), PercentComplete, TodoText, IsDeleted and SaleEffortID (foreign key). Each of these obviously corresponds to a field in the database. When UpdateModel(t) is called, t does get correctly updated for all fields which have changed. When Repository.Save() is called, by the time the SQL is written out, FolderID reverts back to its original value. The complete code to Repository.Save(): public void Save() { myDataContext.SubmitChanges(); } myDataContext is an instance of the DataContext class created by the LINQ-to-SQL designer. Nothing custom has been done to this aside from adding some common interfaces to some of the entities. I've validated that the FolderID is getting lost before the call to Repository.Save() by logging out the generated SQL: UPDATE [Todo].[TD_TODO] SET [TD_PercentComplete] = @p4, [TD_TodoText] = @p5, [TD_IsDeleted] = @p6 WHERE ([TD_ID] = @p0) AND ([TD_TDF_ID] = @p1) AND /* Folder ID */ ([TD_PercentComplete] = @p2) AND ([TD_TodoText] = @p3) AND (NOT ([TD_IsDeleted] = 1)) AND ([TD_SE_ID] IS NULL) /* SaleEffort ID */ -- @p0: Input BigInt (Size = -1; Prec = 0; Scale = 0) [5] -- @p1: Input BigInt (Size = -1; Prec = 0; Scale = 0) [1] /* this SHOULD be 4 and in the update list */ -- @p2: Input TinyInt (Size = -1; Prec = 0; Scale = 0) [90] -- @p3: Input NVarChar (Size = 4000; Prec = 0; Scale = 0) [changing text] -- @p4: Input TinyInt (Size = -1; Prec = 0; Scale = 0) [0] -- @p5: Input NVarChar (Size = 4000; Prec = 0; Scale = 0) [changing text foo] -- @p6: Input Bit (Size = -1; Prec = 0; Scale = 0) [True] -- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 4.0.30319.1 So somewhere between UpdateModel(t) (where I've validated in the debugger that FolderID updated) and the output of this SQL, the FolderID reverts. The other fields all save. (Well, OK, I haven't validated SaleEffortID yet, because that subsystem isn't really ready yet, but everything else saves.) I've exhausted my own means of research on this: Does anyone know of conditions which would cause a partial entity reset (EG, something to do with long foreign keys?), and/or how to work around this?

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