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• XmlHttpRequest bug?

  - by valdo

  Hello all. I'm writing a program that among other things needs to download a file given its URL. I'm too lazy to implement the Http/Https protocols manually, so that I needed some library/object/function that'll do the job. Critical requirement: The download must be asynchronous. That is, the thread that issued the download must be able to do something else "while" downloading the file, plus the download must be able to be aborted anytime without any barbaric side effects (such as internal call to TerminateThread). Nice-to-have requirements: Should be able to download the file "into memory". Means - read the contents of the file as they arrive, not necessarily save it into some "file system" file. It'd be nice to have some convenient Win32 progress notification mechanism (waitable event, semahpore, completion port, etc.), rather than just periodically polling the download status. I've chosen the XmlHttpRequest COM object to do the work. It seemed to work fine enough, plus it supported asynchronous mode. However I noticed that after some period it just stops working. That is, after several successful file downloads it stops downloading anything. I periodically poll it to get its status, it reports "in-progress", but nothing actually happens, and there's no network activity. Moreover, when the same process creates another instance of XmlHttpRequest object to perform new downloads - the effect is the same. The object reports "in progress", whereas it doesn't even try to connect to the server (according to network sniffers and system TCP state). The only way to make this object work back is to restart the process. This makes me suspect that there's a sort of a bug (sorry, I meant undocumented feature) in the object. Also it's not a bug at the level of an individual object, since the problem persists when the object is destroyed and another one is created. It's probably some global state of the DLL that implements this object. Does anyone know something about this? Is this a known bug? I'm pretty sure there's no chance that I have another bug in my code, because of which it seems to me to be the bug is in the XmlHttpRequest. I've done enoughtests and spent time with the debugger to conclude without reasonable doubt that it's just the object stops working. BTW, while the object should work, I do all the waiting via MsgWaitXXXX API calls. So that if this object needs the message loop to work properly (for instance, it may create a hidden notification window and bind it to a socket via WSAAsyncSelect) - I give it the opportunity.

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• Why an object declared in method is subject to garbage collection before the method returns?

  - by SiLent SoNG

  Consider an object declared in a method: public void foo() { final Object obj = new Object(); // A long run job that consumes tons of memory and // triggers garbage collection } Will obj be subject to garbage collection before foo() returns? UPDATE: Previously I thought obj is not subject to garbage collection until foo() returns. However, today I find myself wrong. I have spend several hours in fixing a bug and finally found the problem is caused by obj garbage collected! Can anyone explain why this happens? And if I want obj to be pinned how to achieve it? Here is the code that has problem. public class Program { public static void main(String[] args) throws Exception { String connectionString = "jdbc:mysql://<whatever>"; // I find wrap is gc-ed somewhere SqlConnection wrap = new SqlConnection(connectionString); Connection con = wrap.currentConnection(); Statement stmt = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); ResultSet rs = stmt.executeQuery("select instance_id, doc_id from crawler_archive.documents"); while (rs.next()) { int instanceID = rs.getInt(1); int docID = rs.getInt(2); if (docID % 1000 == 0) { System.out.println(docID); } } rs.close(); //wrap.close(); } } After running the Java program, it will print the following message before it crashes: 161000 161000 ******************************** Finalizer CALLED!! ******************************** ******************************** Close CALLED!! ******************************** 162000 Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: And here is the code of class SqlConnection: class SqlConnection { private final String connectionString; private Connection connection; public SqlConnection(String connectionString) { this.connectionString = connectionString; } public synchronized Connection currentConnection() throws SQLException { if (this.connection == null || this.connection.isClosed()) { this.closeConnection(); this.connection = DriverManager.getConnection(connectionString); } return this.connection; } protected void finalize() throws Throwable { try { System.out.println("********************************"); System.out.println("Finalizer CALLED!!"); System.out.println("********************************"); this.close(); } finally { super.finalize(); } } public void close() { System.out.println("********************************"); System.out.println("Close CALLED!!"); System.out.println("********************************"); this.closeConnection(); } protected void closeConnection() { if (this.connection != null) { try { connection.close(); } catch (Throwable e) { } finally { this.connection = null; } } } }

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• Building a QueryExpression where name field is either A or B

  - by Mike

  I'm trying to build a Dynamics CRM 4 query so that I can get calendar events that are named either "Event A" or "Event B". A QueryByAttribute doesn't seem to do the job as I cannot specify a condition where the field called "event_name" = "Event A" of "event_name" = "Event B". When using the QueryExpression, I've found the FilterExpression applies to the Referencing Entity. I don't know if the FilterExpression can be used on the Referenced Entity at all. The example below is something like what I want to achieve, though this would return an empty result set as it will go looking in the entity called "my_event_response" for a "name" attribute. It's starting to look like I will need to run several queries to get this but this is less efficient than if I can submit it all at once. ColumnSet columns = new ColumnSet(); columns.Attributes = new string[]{ "event_name", "eventid", "startdate", "city" }; ConditionExpression eventname1 = new ConditionExpression(); eventname1.AttributeName = "event_name"; eventname1.Operator = ConditionOperator.Equal; eventname1.Values = new string[] { "Event A" }; ConditionExpression eventname2 = new ConditionExpression(); eventname2.AttributeName = "event_name"; eventname2.Operator = ConditionOperator.Equal; eventname2.Values = new string[] { "Event B" }; FilterExpression filter = new FilterExpression(); filter.FilterOperator = LogicalOperator.Or; filter.Conditions = new ConditionExpression[] { eventname1, eventname2 }; LinkEntity link = new LinkEntity(); link.LinkCriteria = filter; link.LinkFromEntityName = "my_event"; link.LinkFromAttributeName = "eventid"; link.LinkToEntityName = "my_event_response"; link.LinkToAttributeName = "eventid"; QueryExpression query = new QueryExpression(); query.ColumnSet = columns; query.EntityName = EntityName.mbs_event.ToString(); query.LinkEntities = new LinkEntity[] { link }; RetrieveMultipleRequest request = new RetrieveMultipleRequest(); request.Query = query; return (RetrieveMultipleResponse)crmService.Execute(request); I'd appreciate some advice on how to get the data I need.

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• System.Timers.Timer leaking due to "direct delegate roots"

  - by alimbada

  Apologies for the rather verbose and long-winded post, but this problem's been perplexing me for a few weeks now so I'm posting as much information as I can in order to get this resolved quickly. We have a WPF UserControl which is being loaded by a 3rd party app. The 3rd party app is a presentation application which loads and unloads controls on a schedule defined by an XML file which is downloaded from a server. Our control, when it is loaded into the application makes a web request to a web service and uses the data from the response to display some information. We're using an MVVM architecture for the control. The entry point of the control is a method that is implementing an interface exposed by the main app and this is where the control's configuration is set up. This is also where I set the DataContext of our control to our MainViewModel. The MainViewModel has two other view models as properties and the main UserControl has two child controls. Depending on the data received from the web service, the main UserControl decides which child control to display, e.g. if there is a HTTP error or the data received is not valid, then display child control A, otherwise display child control B. As you'd expect, these two child controls bind two separate view models each of which is a property of MainViewModel. Now child control B (which is displayed when the data is valid) has a RefreshService property/field. RefreshService is an object that is responsible for updating the model in a number of ways and contains 4 System.Timers.Timers; a _modelRefreshTimer a _viewRefreshTimer a _pageSwitchTimer a _retryFeedRetrievalOnErrorTimer (this is only enabled when something goes wrong with retrieving data). I should mention at this point that there are two types of data; the first changes every minute, the second changes every few hours. The controls' configuration decides which type we are using/displaying. If data is of the first type then we update the model quite frequently (every 30 seconds) using the _modelRefreshTimer's events. If the data is of the second type then we update the model after a longer interval. However, the view still needs to be refreshed every 30 seconds as stale data needs to be removed from the view (hence the _viewRefreshTimer). The control also paginates the data so we can see more than we can fit on the display area. This works by breaking the data up into Lists and switching the CurrentPage (which is a List) property of the view model to the right List. This is done by handling the _pageSwitchTimer's Elapsed event. Now the problem My problem is that the control, when removed from the visual tree doesn't dispose of it's timers. This was first noticed when we started getting an unusually high number of requests on the web server end very soon after deploying this control and found that requests were being made at least once a second! We found that the timers were living on and not stopping hours after the control had been removed from view and that the more timers there were the more requests piled up at the web server. My first solution was to implement IDisposable for the RefreshService and do some clean up when the control's UnLoaded event was fired. Within the RefreshServices Dispose method I've set Enabled to false for all the timers, then used the Stop() method on all of them. I've then called Dispose() too and set them to null. None of this worked. After some reading around I found that event handlers may hold references to Timers and prevent them from being disposed and collected. After some more reading and researching I found that the best way around this was to use the Weak Event Pattern. Using this blog and this blog I've managed to work around the shortcomings in the Weak Event pattern. However, none of this solves the problem. Timers are still not being disabled or stopped (let alone disposed) and web requests are continuing to build up. Mem Profiler tells me that "This type has N instances that are directly rooted by a delegate. This can indicate the delegate has not been properly removed" (where N is the number of instances). As far as I can tell though, all listeners of the Elapsed event for the timers are being removed during the cleanup so I can't understand why the timers continue to run. Thanks for reading. Eagerly awaiting your suggestions/comments/solutions (if you got this far :-p)

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• Advice/suggestions for my first project PHP Classes

  - by Philip

  Hi guys, Any advice is welcome! I have a very limited understanding of php classes but below is my starting point for the route I would like to take. The code is a reflection of what I see in my head and how I would like to go about business. Does my code even look ok, or am I way off base? What are your thoughts, how would you go about achieving such a task as form-validate-insertquery-sendmail-return messages and errors? Please try and keep your answers simple enough for me to digest as for me its about understanding whats going on and not just a copy/paste job. Kindest regards, Phil. Note: This is a base structure only, no complete code added. <?php //======================================= //class.logging.php //======================================== class logging { public $data = array(); public $errors = array(); function __construct() { array_pop($_POST); $this->data =($this->_logging)? is_isset(filterStr($_POST) : ''; foreach($this->data as $key=> $value) { $this->data[$key] = $value; } //print_r($this->data); de-bugging } public function is_isset($str) { if(isset($str)) ? true: false; } public function filterStr($str) { return preg_match(do somthing, $str); } public function validate_post() { try { if(!is_numeric($data['cardID'])) ? throw new Exception('CardID must be numeric!') : continue; } catch (Exception $e) { return $errors = $e->getCode(); } } public function showErrors() { foreach($errors as $error => $err) { print('<div class="notok"></div><br />'); } } public function insertQ() { $query = ""; } } //======================================= //Usercp.php //======================================== if(isset($_GET['mode'])) { $mode = $_GET['mode']; } else { $mode = 'usercp'; } switch($mode) { case 'usercp': echo 'Welcome to the User Control Panel'; break; case 'logging': require_once 'class.logging.php'; $logger = new logging(); if(isset($_POST['submit']) { if($logger->validate_post === true) { $logger->insertQ(); require_once '/scripts/PHPMailer/class.phpmailer.php'; $mailer = new PHPMailer(); $mailer->PHPMailer(); } else { echo ''.$logger->showErrors.''; } } else { echo ' <form action="'.$_SERVER['PHP_SELF'].'?mode=logging" method="post"> </form> '; } break; case 'user_logout': // do somthing break; case 'user_settings': // do somthing break; ?>

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• How to learn proper C++?

  - by Chris

  While reading a long series of really, really interesting threads, I've come to a realization: I don't think I really know C++. I know C, I know classes, I know inheritance, I know templates (& the STL) and I know exceptions. Not C++. To clarify, I've been writing "C++" for more than 5 years now. I know C, and I know that C and C++ share a common subset. What I've begun to realize, though, is that more times than not, I wind up treating C++ something vaguely like "C with classes," although I do practice RAII. I've never used Boost, and have only read up on TR1 and C++0x - I haven't used any of these features in practice. I don't use namespaces. I see a list of #defines, and I think - "Gracious, that's horrible! Very un-C++-like," only to go and mindlessly write class wrappers for the sake of it, and I wind up with large numbers (maybe a few per class) of static methods, and for some reason, that just doesn't seem right lately. The professional in me yells "just get the job done," the academic yells "you should write proper C++ when writing C++" and I feel like the point of balance is somewhere in between. I'd like to note that I don't want to program "pure" C++ just for the sake of it. I know several languages. I have a good feel for what "Pythonic" is. I know what clean and clear PHP is. Good C code I can read and write better than English. The issue is that I learned C by example, and picked up C++ as a "series of modifications" to C. And a lot of my early C++ work was creating class wrappers for C libraries. I feel like my own personal C-heavy background while learning C++ has sort of... clouded my acceptance of C++ in it's own right, as it's own language. Do the weathered C++ lags here have any advice for me? Good examples of clean, sharp C++ to learn from? What habits of C does my inner-C++ really need to break from? My goal here is not to go forth and trumpet "good" C++ paradigm from rooftops for the sake of it. C and C++ are two different languages, and I want to start treating them that way. How? Where to start? Thanks in advance! Cheers, -Chris

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• Few doubts regarding Bitmaps , Images & `using` blocks

  - by imageWorker

  I caught up in this problem. http://stackoverflow.com/questions/2559826/garbage-collector-not-doing-its-job-memory-consumption-1-5gb-outofmemory-exc I feel that there is something wrong in my understanding. Please clarify these things. Destructor & IDisposable.Dispose are two methods for freeing resources that are not not under the control of .NET. Which means, everything except memory. right? using blocks are just better way of calling IDisposable.Dispose() method of an object. This is the main code I'm referring to. class someclass { static someMethod(Bitmap img) { Bitmap bmp = new Bitmap(img); //statement1 // some code here and return } } here is class I'm using for testing: class someotherClass { public static voide Main() { foreach (string imagePath in imagePathsArray) { using (Bitmap img1 = new Bitmap(imagePath)) { someclass.someMethod(img1); // does some more processing on `img1` } } } } Is there any memory leak with statement1? Question1: If each image size is say 10MB. Then does this bmp object occupy atleast 10MB? What I mean is, will it make completely new copy of entire image? or just refer to it? Question2:should I or should I not put the statement1 in using block? My Argument: We should not. Because using is not for freeing memory but for freeing the resources (file handle in this case). If I use it in using block. It closes file handle here encapsulated by this bmp object. It means we are also closing filehandle for the caller's img1 object. Which is not correct? As of the memory leak. No there is no scope of memory leak here. Because reference bmp is destroyed when this method is returned. Which leaves memory it refered without any pointer. So, its garbage collected. Am I right? Edit: class someclass { static Bitmap someMethod(Bitmap img) { Bitmap bmp = new Bitmap(img); //can I use `using` block on this enclosing `return bmp`; ??? // do some processing on bmp here return bmp; } }

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• Working with friends. Poor career choice?

  - by a_person

  Hi all, Hope you can help me solve somewhat of a moral dilemma. Some time ago, after just a few years of living in U.S. and having to take any job I could get my hands on a friend of mine submitted recommended me for an open position at the company that he was working for. I could have not been happier. I do not have a degree of any sort, however, by being passionate about CS and with constant drive for self education I've became a somewhat of a strong generalist. Every place I worked for recognized me for that quality and used me on various projects where set of technology in hand had no overlap with set of knowledge of the team members. Rapidly I've advanced to Sr. Programmer position and the trend of me following a friend from one place to another have started and continued on for a few years. My friend's goal always been to become an IT Director, mine is to become the best programmer I can be. To my knowledge I've accommodated his goals as much as I could by taking a back seat, and letting him take the lead. Fast forward to today. He's a manager, and I am on his team. I am unhappy and I in considerable amount of suffering. I am not being utilized to my potential, it's almost exact opposite, I am being micromanaged to an unhealthy extent, my decisions, and suggestions are constantly met with negative connotation. Last week I had to hear about how my friend is a better programmer than I am. My ego was ecstatic about this one /s. In addition to that working in the field of BI have exhausted itself for most parts. The only pleasure of my work is being derived from making everything as dynamic and parameter driven as possible. This is the only area where a friend of mine does not feel competent enough to actually micromanage. Because of my situation I feel a fair amount of guilt and ever growing resentment. I need your advice, maybe you've dealt with this expression of ego before, needs of self vs the needs of your friend. Is working with a friend a poor choice? Thank you for reading in.

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• How can I group an array of rectangles into "Islands" of connected regions?

  - by Eric

  The problem I have an array of java.awt.Rectangles. For those who are not familiar with this class, the important piece of information is that they provide an .intersects(Rectangle b) function. I would like to write a function that takes this array of Rectangles, and breaks it up into groups of connected rectangles. Lets say for example, that these are my rectangles (constructor takes the arguments x, y, width,height): Rectangle[] rects = new Rectangle[] { new Rectangle(0, 0, 4, 2), //A new Rectangle(1, 1, 2, 4), //B new Rectangle(0, 4, 8, 2), //C new Rectangle(6, 0, 2, 2) //D } A quick drawing shows that A intersects B and B intersects C. D intersects nothing. A tediously drawn piece of ascii art does the job too: +-------+ +---+ ¦A+---+ ¦ ¦ D ¦ +-+---+-+ +---+ ¦ B ¦ +-+---+---------+ ¦ +---+ C ¦ +---------------+ Therefore, the output of my function should be: new Rectangle[][]{ new Rectangle[] {A,B,C}, new Rectangle[] {D} } The failed code This was my attempt at solving the problem: public List<Rectangle> getIntersections(ArrayList<Rectangle> list, Rectangle r) { List<Rectangle> intersections = new ArrayList<Rectangle>(); for(Rectangle rect : list) { if(r.intersects(rect)) { list.remove(rect); intersections.add(rect); intersections.addAll(getIntersections(list, rect)); } } return intersections; } public List<List<Rectangle>> mergeIntersectingRects(Rectangle... rectArray) { List<Rectangle> allRects = new ArrayList<Rectangle>(rectArray); List<List<Rectangle>> groups = new ArrayList<ArrayList<Rectangle>>(); for(Rectangle rect : allRects) { allRects.remove(rect); ArrayList<Rectangle> group = getIntersections(allRects, rect); group.add(rect); groups.add(group); } return groups; } Unfortunately, there seems to be an infinite recursion loop going on here. My uneducated guess would be that java does not like me doing this: for(Rectangle rect : allRects) { allRects.remove(rect); //... } Can anyone shed some light on the issue?

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• How to cache queries in EJB and return result efficient (performance POV)

  - by Maxym

  I use JBoss EJB 3.0 implementation (JBoss 4.2.3 server) At the beginning I created native query all the time using construction like Query query = entityManager.createNativeQuery("select * from _table_"); Of couse it is not that efficient, I performed some tests and found out that it really takes a lot of time... Then I found a better way to deal with it, to use annotation to define native queries: @NamedNativeQuery( name = "fetchData", value = "select * from _table_", resultClass=Entity.class ) and then just use it Query query = entityManager.createNamedQuery("fetchData"); the performance of code line above is two times better than where I started from, but still not that good as I expected... then I found that I can switch to Hibernate annotation for NamedNativeQuery (anyway, JBoss's implementation of EJB is based on Hibernate), and add one more thing: @NamedNativeQuery( name = "fetchData2", value = "select * from _table_", resultClass=Entity.class, readOnly=true) readOnly - marks whether the results are fetched in read-only mode or not. It sounds good, because at least in this case of mine I don't need to update data, I wanna just fetch it for report. When I started server to measure performance I noticed that query without readOnly=true (by default it is false) returns result with each iteration better and better, and at the same time another one (fetchData2) works like "stable" and with time difference between them is shorter and shorter, and after 5 iterations speed of both was almost the same... The questions are: 1) is there any other way to speed query using up? Seems that named queries should be prepared once, but I can't say it... In fact if to create query once and then just use it it would be better from performance point of view, but it is problematic to cache this object, because after creating query I can set parameters (when I use ":variable" in query), and it changes query object (isn't it?). well, is here any way to cache them? Or named query is the best option I can use? 2) any other approaches how to make results retrieveng faster. I mean, for instance I don't need those Entities to be attached, I won't update them, all I need is just fetch collection of data. Maybe readOnly is the only available way, so I can't speed it up, but who knows :) P.S. I don't ask about DB performance, all I need now is how not to create query all the time, so use it efficient, and to "allow" EJB to do less job with the same result concerning data returning.

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• Problems with making a simple UNIX shell

  - by Kodemax

  Hai, I am trying to create a simple shell in UNIX. I read a lot and found that everybody uses the strtok a lot. But i want to do without any special functions. So i wrote the code but i cant seem to get it to work. Can anybody point out what i am doing wrong here? void process(char**); int arg_count; char **splitcommand(char* input) { char temp[81][81] ,*cmdptr[40]; int k,done=0,no=0,arg_count=0; for(int i=0 ; input[i] != '\0' ; i++) { k=0; while(1) { if(input[i] == ' ') { arg_count++; break; } if(input[i] == '\0') { arg_count++; done = 1; break; } temp[arg_count][k++] = input[i++]; } temp[arg_count][k++] = '\0'; if(done == 1) { break; } } for(int i=0 ; i<arg_count ; i++) { cmdptr[i] = temp[i]; cout<<endl; } cout<<endl; } void process(char* cmd[]) { int pid = fork(); if(pid < 0) { cout << "Fork Failed" << endl; exit(-1); } else if( pid == 0) { cout<<endl<<"in pid"; execvp(cmd[0], cmd); } else { wait(NULL); cout << "Job's Done" << endl; } } int main() { cout<<"Welcome to shell !!!!!!!!!!!"<<endl; char input[81]; cin.getline(input,81); splitcommand(input); }

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• Getting 404 when attempting to POST file to Google Cloud Storage from service account

  - by klactose

  I'm wondering if anyone can tell me the proper syntax & formatting for a service account to send a POST Object to bucket request? I'm attempting it programmatically using the HttpComponents library. I manage to get a token from my GoogleCredential, but every time I construct the POST request, I get: HTTP/1.1 403 Forbidden <?xml version='1.0' encoding='UTF-8'?><Error><Code>AccessDenied</Code><Message>Access denied.</Message><Detailsbucket-name</Details></Error The Google documentation that describes the request methods, mentions posting using html forms, but I'm hoping that wasn't suggesting the ONLY way to get the job done. I know that HttpComponents has a way to explicitly create form data by using UrlEncodedFormEntity, but it doesn't support multipart data. Which is why I went with using the MultipartEntity class. My code is below: MultipartEntity entity = new MultipartEntity( HttpMultipartMode.BROWSER_COMPATIBLE ); String token = credential.getAccessToken(); entity.addPart("Authorization", new StringBody("OAuth " + token)); String date = formatDate(new Date()); entity.addPart("Date", new StringBody(date)); entity.addPart("Content-Encoding", new StringBody("UTF-8")); entity.addPart("Content-Type", new StringBody("multipart/form-data")); entity.addPart("bucket", new StringBody(bucket)); entity.addPart("key", new StringBody("fileName")); entity.addPart("success_action_redirect", new StringBody("/storage")); File uploadFile = new File("pathToFile"); FileBody fileBody = new FileBody(uploadFile, "text/xml"); entity.addPart("file", fileBody); httppost.setEntity(entity); System.out.println("Posting URI = "+httppost.toString()); HttpResponse response = client.execute(httppost); HttpEntity resp_entity = response.getEntity(); As I mentioned, I am able to get an actual token, so I'm pretty sure the problem is in how I've formed the request as opposed to not being properly authenticated. Keep in mind: This is being performed by a service account. Which means that it does have Read/Write access Thanks for reading, and I appreciate any help!

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• Is it possible to create a service like Feed My Inbox on my own server?

  - by Mark Bowen

  I was just wondering if it's at all possible to create a service like Feed My Inbox on my own server using PHP? Basically I have a site which has RSS feeds which are dynamic in nature and can search from thousands of posts based on many different criteria. I have the RSS feed working fine and bringing back data dynamically for whatever criteria I want so that bits fine. I am using the ExpressionEngine CMS to handle the site and there will be thousands of users on the site (currently there are around 2,0000) but that number is exponentially growing every single day. What I want to be able to do is allow the users to choose from certain criteria which will then build a dynamic RSS URL which will then be stored in a database table (one row for each user). This bit I will be able to do myself but then I want to be able to send out new RSS feed items via e-mail to each user. This is the part I'm a little stuck on. I'm guessing I would somehow need to run a cron job to hit a page which would check each users RSS feed and then if there are new items to send them to the user via e-mail. That's where I am totally stuck though and I'm just wondering what the best way to go about it would be? That or any software in PHP that already does this sort of thing would be great. I tried out phpList but it has severe problems working with RSS and I only ever got it to work once and now never again and I've read that lots of people have had this same problem so unfortunately it's not just me :-( I know there are services such as Feed My Inbox which I could easily set up so that users click a link and their RSS feed URL is added to go and use that service but I want to keep users from seeing the dynamic nature of the feed or they will easily be able to modify it to get at other items in the feed. I need this so that I can charge for access to the feeds but if people can see the URL of the feed then I will be totally unstuck as they will be able to get at whatever they want very easily. Therefore I'd like to be able to send the items out to them. Would really love to hear if anyone knows if this kind of thing is possible at all and what would be involved?

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• Can I avoid a threaded UDP socket in Python dropping data?

  - by 666craig

  First off, I'm new to Python and learning on the job, so be gentle! I'm trying to write a threaded Python app for Windows that reads data from a UDP socket (thread-1), writes it to file (thread-2), and displays the live data (thread-3) to a widget (gtk.Image using a gtk.gdk.pixbuf). I'm using queues for communicating data between threads. My problem is that if I start only threads 1 and 3 (so skip the file writing for now), it seems that I lose some data after the first few samples. After this drop it looks fine. Even by letting thread 1 complete before running thread 3, this apparent drop is still there. Apologies for the length of code snippet (I've removed the thread that writes to file), but I felt removing code would just prompt questions. Hope someone can shed some light :-) import socket import threading import Queue import numpy import gtk gtk.gdk.threads_init() import gtk.glade import pygtk class readFromUDPSocket(threading.Thread): def __init__(self, socketUDP, readDataQueue, packetSize, numScans): threading.Thread.__init__(self) self.socketUDP = socketUDP self.readDataQueue = readDataQueue self.packetSize = packetSize self.numScans = numScans def run(self): for scan in range(1, self.numScans + 1): buffer = self.socketUDP.recv(self.packetSize) self.readDataQueue.put(buffer) self.socketUDP.close() print 'myServer finished!' class displayWithGTK(threading.Thread): def __init__(self, displayDataQueue, image, viewArea): threading.Thread.__init__(self) self.displayDataQueue = displayDataQueue self.image = image self.viewWidth = viewArea[0] self.viewHeight = viewArea[1] self.displayData = numpy.zeros((self.viewHeight, self.viewWidth, 3), dtype=numpy.uint16) def run(self): scan = 0 try: while True: if not scan % self.viewWidth: scan = 0 buffer = self.displayDataQueue.get(timeout=0.1) self.displayData[:, scan, 0] = numpy.fromstring(buffer, dtype=numpy.uint16) self.displayData[:, scan, 1] = numpy.fromstring(buffer, dtype=numpy.uint16) self.displayData[:, scan, 2] = numpy.fromstring(buffer, dtype=numpy.uint16) gtk.gdk.threads_enter() self.myPixbuf = gtk.gdk.pixbuf_new_from_data(self.displayData.tostring(), gtk.gdk.COLORSPACE_RGB, False, 8, self.viewWidth, self.viewHeight, self.viewWidth * 3) self.image.set_from_pixbuf(self.myPixbuf) self.image.show() gtk.gdk.threads_leave() scan += 1 except Queue.Empty: print 'myDisplay finished!' pass def quitGUI(obj): print 'Currently active threads: %s' % threading.enumerate() gtk.main_quit() if __name__ == '__main__': # Create socket (IPv4 protocol, datagram (UDP)) and bind to address socketUDP = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) host = '192.168.1.5' port = 1024 socketUDP.bind((host, port)) # Data parameters samplesPerScan = 256 packetsPerSecond = 1200 packetSize = 512 duration = 1 # For now, set a fixed duration to log data numScans = int(packetsPerSecond * duration) # Create array to store data data = numpy.zeros((samplesPerScan, numScans), dtype=numpy.uint16) # Create queue for displaying from readDataQueue = Queue.Queue(numScans) # Build GUI from Glade XML file builder = gtk.Builder() builder.add_from_file('GroundVue.glade') window = builder.get_object('mainwindow') window.connect('destroy', quitGUI) view = builder.get_object('viewport') image = gtk.Image() view.add(image) viewArea = (1200, samplesPerScan) # Instantiate & start threads myServer = readFromUDPSocket(socketUDP, readDataQueue, packetSize, numScans) myDisplay = displayWithGTK(readDataQueue, image, viewArea) myServer.start() myDisplay.start() gtk.gdk.threads_enter() gtk.main() gtk.gdk.threads_leave() print 'gtk.main finished!'

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• ajaxSubmit and Other Code. Can someone help me determine what this code is doing?

  - by Matt Dawdy

  I've inherited some code that I need to debug. It isn't working at present. My task is to get it to work. No other requirements have been given to me. No, this isn't homework, this is a maintenance nightmare job. ASP.Net (framework 3.5), C#, jQury 1.4.2. This project makes heavy use of jQuery and AJAX. There is a drop down on a page that, when an item is chosen, is supposed to add that item (it's a user) to an object in the database. To accomplish this, the previous programmer first, on page load, dynamically loads the entire page through AJAX. To do this, he's got 5 div's, and each one is loaded from a jquery call to a different full page in the website. Somehow, the HTML and BODY and all the other stuff is stripped out and the contents of the div are loaded with the content of the aspx page. Which seems incredibly wrong to me since it relies on the browser to magically strip out html, head, body, form tags and merge with the existing html head body form tags. Also, as the "content" page is returned as a string, the previous programmer has this code running on it before it is appended to the div: function CleanupResponseText(responseText, uniqueName) { responseText = responseText.replace("theForm.submit();", "SubmitSubForm(theForm, $(theForm).parent());"); responseText = responseText.replace(new RegExp("theForm", "g"), uniqueName); responseText = responseText.replace(new RegExp("doPostBack", "g"), "doPostBack" + uniqueName); return responseText; } When the dropdown itself fires it's onchange event, here is the code that gets fired: function SubmitSubForm(form, container) { //ShowLoading(container); $(form).ajaxSubmit( { url: $(form).attr("action"), success: function(responseText) { $(container).html(CleanupResponseText(responseText, form.id)); $("form", container).css("margin-top", "0").css("padding-top", "0"); //HideLoading(container); } } ); } This blows up in IE, with the message that "Microsoft JScript runtime error: Object doesn't support this property or method" -- which, I think, has to be that $(form).ajaxSubmit method doesn't exist. What is this code really trying to do? I am so turned around right now that I think my only option is to scrap everything and start over. But I'd rather not do that unless necessary. Is this code good? Is it working against .Net, and is that why we are having issues?

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• What is a good generic sibling control Javascript communication strategy?

  - by James

  I'm building a webpage that is composed of several controls, and trying to come up with an effective somewhat generic client side sibling control communication model. One of the controls is the menu control. Whenever an item is clicked in here I wanted to expose a custom client side event that other controls can subscribe to, so that I can achieve a loosely coupled sibling control communication model. To that end I've created a simple Javascript event collection class (code below) that acts as like a hub for control event registration and event subscription. This code certainly gets the job done, but my question is is there a better more elegant way to do this in terms of best practices or tools, or is this just a fools errand? /// Event collection object - acts as the hub for control communication. function ClientEventCollection() { this.ClientEvents = {}; this.RegisterEvent = _RegisterEvent; this.AttachToEvent = _AttachToEvent; this.FireEvent = _FireEvent; function _RegisterEvent(eventKey) { if (!this.ClientEvents[eventKey]) this.ClientEvents[eventKey] = []; } function _AttachToEvent(eventKey, handlerFunc) { if (this.ClientEvents[eventKey]) this.ClientEvents[eventKey][this.ClientEvents[eventKey].length] = handlerFunc; } function _FireEvent(eventKey, triggerId, contextData ) { if (this.ClientEvents[eventKey]) { for (var i = 0; i < this.ClientEvents[eventKey].length; i++) { var fn = this.ClientEvents[eventKey][i]; if (fn) fn(triggerId, contextData); } } } } // load new collection instance. var myClientEvents = new bsdClientEventCollection(); // register events specific to the control that owns it, this will be emitted by each respective control. myClientEvents.RegisterEvent("menu-item-clicked"); Here is the part where this code above is consumed by source and subscriber controls. // menu control $(document).ready(function() { $(".menu > a").click( function(event) { //event.preventDefault(); myClientEvents.FireEvent("menu-item-clicked", $(this).attr("id"), null); }); }); <div style="float: left;" class="menu"> <a id="1" href="#">Menu Item1</a><br /> <a id="2" href="#">Menu Item2</a><br /> <a id="3" href="#">Menu Item3</a><br /> <a id="4" href="#">Menu Item4</a><br /> </div> // event subscriber control $(document).ready(function() { myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged); myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged2); myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged3); }); function menuItemChanged(id, contextData) { alert('menuItemChanged ' + id); } function menuItemChanged2(id, contextData) { alert('menuItemChanged2 ' + id); } function menuItemChanged3(id, contextData) { alert('menuItemChanged3 ' + id); }

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• I'm searching for a messaging platform (like XMPP) that allows tight integration with a web applicat

  - by loxs

  Hi, At the company I work for, we are building a cluster of web applications for collaboration. Things like accounting, billing, CRM etc. We are using a RESTfull technique: For database we use CouchDB Different applications communicate with one another and with the database via http. Besides, we have a single sign on solution, so that when you login in one application, you are automatically logged to the other. For all apps we use Python (Pylons). Now we need to add instant messaging to the stack. We need to support both web and desktop clients. But just being able to chat is not enough. We need to be able to achieve all of the following (and more similar things). When somebody gets assigned to a task, they must receive a message. I guess this is possible with some system daemon. There must be an option to automatically group people in groups by lots of different properties. For example, there must be groups divided both by geographical location, by company division, by job type (all the programers from different cities and different company divisions must form a group), so that one can send mass messages to a group of choice. Rooms should be automatically created and destroyed. For example when several people visit the same invoice, a room for them must be automatically created (and they must auto-join). And when all leave the invoice, the room must be destroyed. Authentication and authorization from our applications. I can implement this using custom solutions like hookbox http://hookbox.org/docs/intro.html but then I'll have lots of problems in supporting desktop clients. I have no former experience with instant messaging. I've been reading about this lately. I've been looking mostly at things like ejabberd. But it has been a hard time and I can't find whether what I want is possible at all. So I'd be happy if people with experience in this field could help me with some advice, articles, tales of what is possible etc.

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• DB Design Pattern - Many to many classification / categorised tagging.

  - by Robin Day

  I have an existing database design that stores Job Vacancies. The "Vacancy" table has a number of fixed fields across all clients, such as "Title", "Description", "Salary range". There is an EAV design for "Custom" fields that the Clients can setup themselves, such as, "Manager Name", "Working Hours". The field names are stored in a "ClientText" table and the data stored in a "VacancyClientText" table with VacancyId, ClientTextId and Value. Lastly there is a many to many EAV design for custom tagging / categorising the vacancies with things such as Locations/Offices the vacancy is in, a list of skills required. This is stored as a "ClientCategory" table listing the types of tag, "Locations, Skills", a "ClientCategoryItem" table listing the valid values for each Category, e.g., "London,Paris,New York,Rome", "C#,VB,PHP,Python". Finally there is a "VacancyClientCategoryItem" table with VacancyId and ClientCategoryItemId for each of the selected items for the vacancy. There are no limits to the number of custom fields or custom categories that the client can add. I am now designing a new system that is very similar to the existing system, however, I have the ability to restrict the number of custom fields a Client can have and it's being built from scratch so I have no legacy issues to deal with. For the Custom Fields my solution is simple, I have 5 additional columns on the Vacancy Table called CustomField1-5. This removes one of the EAV designs. It is with the tagging / categorising design that I am struggling. If I limit a client to having 5 categories / types of tag. Should I create 5 tables listing the possible values "CustomCategoryItems1-5" and then an additional 5 many to many tables "VacancyCustomCategoryItem1-5" This would result in 10 tables performing the same storage as the three tables in the existing system. Also, should (heaven forbid) the requirements change in that I need 6 custom categories rather than 5 then this will result in a lot of code change. Therefore, can anyone suggest any DB Design Patterns that would be more suitable to storing such data. I'm happy to stick with the EAV approach, however, the existing system has come across all the usual performance issues and complex queries associated with such a design. Any advice / suggestions are much appreciated. The DBMS system used is SQL Server 2005, however, 2008 is an option if required for any particular pattern.

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• Proper HTML technique to create an web form out of an image

  - by Lars

  I plan to create an interactive golf score card for my website (XHTML). (Btw. thats how such a scorecard looks like: ScoreCard). So at the end one should be able to insert a score for each hole in the appropriated input field in the virtual scorecard on the website. For me it is very important that the interactive scorecard really looks the same as the original (paper-) scorecard does and so my first approach was to scan and slice the scorecard image to reach that appearance. Here you can see the way I sliced the image: The idea was to insert HTML text input for each score field ending up with something like this: After I sliced the image I reconstructed it using the HTML . To do that I put the image slices as the cell background. <table> <tr> <td style="background: url("slice1.jpg") width="58px" height="25px"> <input type="text"></inputText> </td> </tr> ... </table> At the first moment this worked fine (as Gimp offers quite a nice feature for this). Then the problem was that I had to create a HTML table to create the exact layout. As you can see the lower part of the layout is split up into 3 columns. The middle column is split up into several (for each hole) rows. So the left and right column have to be spanned over those rows. Ok finally that worked, but it lead to some kind of scaling problem. If I zoom in or out on the table the middle column (and only that one) is not scaled the right way. Iam not able to fix this, and so I start doubting if this is the right technique for html image virtualization. Iam really no specialist in the area of creating websites, so I would really appriciate any help on this. Maybe there is a complete other and better technique to do that, as I think it is a common job in webcreation. I couldnt find any nice examples or tuts on that.

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• Android onActivityResult is always 0

  - by Dean

  This has been killing me for two days now. I have a main Activity A which calls a second Activity B. Activity B simply presents the user with a listview. When I press an item on the list view I want a couple of strings to be passed back to the main Activity A and Activiy B will finish. The problem is I always get a resultcode of 0 and the data bundle is null. I really don't understand why this is happening. Here is my code. Start Activity B for result; Test.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent i = new Intent(recipeActivity.this, BrowseLoadRecipes.class); startActivityForResult(i, RECIPE_CHOOSER); } }); This starts the second Activity fine. Activity B populates a listview and when I click an item I'm trying to send some data back to the calling Activity A. Any text at the moment, so I used the following in Activity B; lv.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> a, View v, int position, long id) { Bundle bundle = new Bundle(); bundle.putString("TEXT", "Please work... pleeeeaasee"); Intent mIntent = new Intent(); mIntent.putExtras(bundle); setResult(RESULT_OK, mIntent); finish(); } }); In the calling activity I have the following listening for the return as follows; protected void onActivityResult(int requestCode, int resultCode, Intent data) { switch(requestCode) { //TODO case RECIPE_CHOOSER: Toast.makeText(getApplicationContext(), "In recipe return", Toast.LENGTH_SHORT).show(); Toast.makeText(getApplicationContext(), "resultCode is " + String.valueOf(resultCode), Toast.LENGTH_SHORT).show(); if (resultCode == RESULT_OK) { Bundle b = getIntent().getExtras(); Toast.makeText(getApplicationContext(), "Returned " + b.getString("TEXT"), Toast.LENGTH_LONG).show(); } if (resultCode == RESULT_CANCELED) { } break; } } } I can see that the request code is correctly returned, but the resultcode is always a 0 and the data is always a null. I've ran through the debug and the setResult is doing its job and the bundle does indeed have the data I'm passing, but it's lost at some point along the way. Is there something in the manifest I'm missing or something. It's killed my progress on this project so far. Any help would truly be appreciated. Thanks, Dean

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• How to get colliding effect or bouncy when ball hits the track.

  - by Chandan Shetty SP

  I am using below formula to move the ball circular, where accelX and accelY are the values from accelerometer, it is working fine. But the problem in this code is mRadius (I fixed its value to 50), i need to change mRadius according to accelerometer values and also i need bouncing effect when it touches the track. Currently i am developing code by assuming only one ball is on the board. float degrees = -atan2(accelX, accelY) * 180 / 3.14159; int x = cCentrePoint.x + mRadius * cos(degreesToRadians(degrees)); int y = cCentrePoint.y + mRadius * sin(degreesToRadians(degrees)); Here is the snap of the game i want to develop: Updated: I am sending the updated code... mRadius = 5; mRange = NSMakeRange(0,60); -(void) updateBall: (UIAccelerationValue) accelX withY:(UIAccelerationValue)accelY { float degrees = -atan2(accelX, accelY) * 180 / 3.14159; int x = cCentrePoint.x + mRadius * cos(degreesToRadians(degrees)); int y = cCentrePoint.y + mRadius * sin(degreesToRadians(degrees)); //self.targetRect is rect of ball Object self.targetRect = CGRectMake(newX, newY, 8, 9); self.currentRect = self.targetRect; //http://books.google.co.in/books?id=WV9glgdrrrUC&pg=PA455#v=onepage&q=&f=false static NSDate *lastDrawTime; if(lastDrawTime!=nil) { NSTimeInterval secondsSinceLastDraw = -([lastDrawTime timeIntervalSinceNow]); ballXVelocity = ballXVelocity + (accelX * secondsSinceLastDraw) * [self isTouchedTrack:mRadius andRange:mRange]; ballYVelocity = ballYVelocity + -(accelY * secondsSinceLastDraw) * [self isTouchedTrack:mRadius andRange:mRange]; distXTravelled = distXTravelled + secondsSinceLastDraw * ballXVelocity * 50; distYTravelled = distYTravelled + secondsSinceLastDraw * ballYVelocity * 50; CGRect temp = self.targetRect; temp.origin.x += distXTravelled; temp.origin.y += distYTravelled; int radius = (temp.origin.x - cCentrePoint.x) / cos(degreesToRadians(degrees)); if( !NSLocationInRange(abs(radius),mRange)) { //Colided with the tracks...Need a better logic here ballXVelocity = -ballXVelocity; } else { // Need a better logic here self.targetRect = temp; } //NSLog(@"angle = %f",degrees); } [lastDrawTime release]; lastDrawTime = [ [NSDate alloc] init]; } In the above code i have initialized mRadius and mRange(indicate track) to some constant for testing, i am not getting the moving of the ball as i expected( bouncing effect when Collided with track ) with respect to accelerometer. Help me to recognize where i went wrong or send some code snippets or links which does the similar job. I am searching for better logic than my code, if you found share with me.

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• SpringBatch Jaxb2Marshaller: different name of class and xml attribute

  - by user588961

  I try to read an xml file as input for spring batch: Java Class: package de.example.schema.processes.standardprocess; @XmlAccessorType(XmlAccessType.FIELD) @XmlType(name = "Process", namespace = "http://schema.example.de/processes/process", propOrder = { "input" }) public class Process implements Serializable { @XmlElement(namespace = "http://schema.example.de/processes/process") protected ProcessInput input; public ProcessInput getInput() { return input; } public void setInput(ProcessInput value) { this.input = value; } } SpringBatch dev-job.xml: <bean id="exampleReader" class="org.springframework.batch.item.xml.StaxEventItemReader" scope="step"> <property name="fragmentRootElementName" value="input" /> <property name="resource" value="file:#{jobParameters['dateiname']}" /> <property name="unmarshaller" ref="jaxb2Marshaller" /> </bean> <bean id="jaxb2Marshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller"> <property name="classesToBeBound"> <list> <value>de.example.schema.processes.standardprocess.Process</value> <value>de.example.schema.processes.standardprocess.ProcessInput</value> ... </list> </property> </bean> Input file: <?xml version="1.0" encoding="UTF-8"?> <process:process xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:process="http://schema.example.de/processes/process"> <process:input> ... </process:input> </process:process> It fires the following exception: [javax.xml.bind.UnmarshalException: unexpected element (uri:"http://schema.example.de/processes/process", local:"input"). Expected elements are <<{http://schema.example.de/processes/process}processInput] at org.springframework.oxm.jaxb.JaxbUtils.convertJaxbException(JaxbUtils.java:92) at org.springframework.oxm.jaxb.AbstractJaxbMarshaller.convertJaxbException(AbstractJaxbMarshaller.java:143) at org.springframework.oxm.jaxb.Jaxb2Marshaller.unmarshal(Jaxb2Marshaller.java:428) If I change to in xml it work's fine. Unfortunately I can change neither the xml nor the java class. Is there a possibility to make Jaxb2Marshaller map the element 'input' to the class 'ProcessInput'?

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• Tab Bar and Nav Controller: Where did I go wrong in my Interface Builder wiring?

  - by editor

  Even if you don't know how I've shot myself in the foot, a story which I've tried to lay out below, if you think I've done a good job showing the parameters of my problem I'd appreciate an upvote so that I might be able to grab some attention for my question. I've been working on an iPhone application in XCode and Interface Builder of the Tab Bar project type. After getting a table view of topics (business sectors) working fine I realized that I would need to add a Navigation Control to allow the user to drill into a subtopics (subsectors) table. As a green Objective-C developer, that was confusing, but I managed to get it working by reading various documentation trying out a few different IB options. My current setup is a Tab Bar Controller with Tab 1 as a Navigation Controller and Tab 2 a plain view with a Table View placed into it. The wiring works: I can log when table rows are selected and I'm ready to push a new View Controller onto the stack so that I can display the subtopics Table View. My problem: For some reason the first tab's Table View is a delegate and dataSource of the second ta. It doesn't make sense to me and I can't figure out why that's the only setup that works. Here is the wiring: Navigation Controller (Sectors) is a delegate of Tab Bar Navigation Bar is a delegate of Navigation Controller (Sectors) View Contoller (Sectors) has a view of Table View Table View (in Navigation Controller (Sectors)) is a delegate of First View Controller (Companies) Table View (in Navigation Controller (Sectors)) is a dataSource outlet of First View Controller (Companies) First View Controller (Companies) First View Contoller (Sectors) has a view of Table View Table View (in First View Controller (Companies)) is not hooked up to a dataSource outlet and is not a delegate When I click the tab buttons and look at the Inspector I see that the first tab is correctly hooked up to my MainWindow.xib and the second tab has selected a nib called SecondView.xib. It's in the File's Owner of MainWindow.xib where I inherit UITableViewDataSource and UITableViewDelegate (and also UITabBarControllerDelegate) in the .h, and in the .m where I implement the delegate methods. Why does this setup only work when the Table View in my first tab (View Controller (Sectors)) is a delegate and dataSource of the second tab? I'm confused: why wouldn't it need to be hooked up to the Navigation Controller-enabled tab in which the Table View is seen (Navigation Controller (Sectors))? The Table View seen on the second tab has neither dataSource and is not a delegate. I'm having trouble getting a pushViewController to fire (self.navigationController is not nil but the new View Controller still doesn't load) and I suspect that I need to work out this IB wiring issue before I can troubleshoot why the Nav Controller won't push a new View Controller onto the stack. if(nil == self.navigationController) { NSLog(@"self.navigationController is nil."); } else { NSLog(@"self.navigationController is not nil."); SectorList *subsectorViewController = [[SectorList alloc] initWithNibName:@"SectorList" bundle:nil]; subsectorViewController.title = @"Subsectors"; [[self navigationController] pushViewController:subsectorViewController animated:YES]; [subsectorViewController release]; }

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• How do I hide the text links over a toggleable horizontal list with background images.

  - by Sivakanesh

  I'm trying to create a UL/LI horizontal list with background images only, with no text link visible. The reason for this is so that when I over over a list item, the background would rollover and when I click on it the current item would toggle. basically it is a horizontal menu with background images that can be toggled; mimicking the job of a radio button. I have done it like this; <div id="options"> <ul id="list"> <li class="active"><a href="#" class="option1 active" id="link1"><span>XXXXX</span></a></li> <li><a href="#" class="option2" id="link2"><span>XXXXX</span></a></li> <li><a href="#" class="option3" id="link3"><span>XXXXX</span></a></li> </ul> </div> The CSS for option1, option2 and option3 simply define the background image. #options LI{list-style-type: none; display : inline} a.option1{ background:url('../images/option1.png') no-repeat;} a.option2{ background:url('../images/option2.png') no-repeat;} a.option3{ background:url('../images/option3.png') no-repeat;} a.option1, a.option2, a.option3{ background-position:top; display:inline; width:230px; height:40px; } And the hover & active css part simply sets the background position like so- a.option1:hover, a.option2:hover, a.option3:hover{ background-position:bottom; } a.active{ background-position:bottom !important; } This works fine, however on top of the background I get the words "XXXXX" as text links and I'm struggling to hide them. They are interfering with the hover action and preventing rollover (even if I replace XXXXX with a period or something short). I can't just remove the text from the link as it would hide the whole LI element. I have tried to use display:none; or text-indent:-999px but then the whole UI element becomes invisible. I can't understand what I'm doing wrong. Are you able to help? Thanks

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• Postgresql count+sort performance

  - by invictus

  I have built a small inventory system using postgresql and psycopg2. Everything works great, except, when I want to create aggregated summaries/reports of the content, I get really bad performance due to count()'ing and sorting. The DB schema is as follows: CREATE TABLE hosts ( id SERIAL PRIMARY KEY, name VARCHAR(255) ); CREATE TABLE items ( id SERIAL PRIMARY KEY, description TEXT ); CREATE TABLE host_item ( id SERIAL PRIMARY KEY, host INTEGER REFERENCES hosts(id) ON DELETE CASCADE ON UPDATE CASCADE, item INTEGER REFERENCES items(id) ON DELETE CASCADE ON UPDATE CASCADE ); There are some other fields as well, but those are not relevant. I want to extract 2 different reports: - List of all hosts with the number of items per, ordered from highest to lowest count - List of all items with the number of hosts per, ordered from highest to lowest count I have used 2 queries for the purpose: Items with host count: SELECT i.id, i.description, COUNT(hi.id) AS count FROM items AS i LEFT JOIN host_item AS hi ON (i.id=hi.item) GROUP BY i.id ORDER BY count DESC LIMIT 10; Hosts with item count: SELECT h.id, h.name, COUNT(hi.id) AS count FROM hosts AS h LEFT JOIN host_item AS hi ON (h.id=hi.host) GROUP BY h.id ORDER BY count DESC LIMIT 10; Problem is: the queries runs for 5-6 seconds before returning any data. As this is a web based application, 6 seconds are just not acceptable. The database is heavily populated with approximately 50k hosts, 1000 items and 400 000 host/items relations, and will likely increase significantly when (or perhaps if) the application will be used. After playing around, I found that by removing the "ORDER BY count DESC" part, both queries would execute instantly without any delay whatsoever (less than 20ms to finish the queries). Is there any way I can optimize these queries so that I can get the result sorted without the delay? I was trying different indexes, but seeing as the count is computed it is possible to utilize an index for this. I have read that count()'ing in postgresql is slow, but its the sorting that are causing me problems... My current workaround is to run the queries above as an hourly job, putting the result into a new table with an index on the count column for quick lookup. I use Postgresql 9.2.

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