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• How to update GUI thread/class from worker thread/class?

  - by user315182

  First question here so hello everyone. The requirement I'm working on is a small test application that communicates with an external device over a serial port. The communication can take a long time, and the device can return all sorts of errors. The device is nicely abstracted in its own class that the GUI thread starts to run in its own thread and has the usual open/close/read data/write data basic functions. The GUI is also pretty simple - choose COM port, open, close, show data read or errors from device, allow modification and write back etc. The question is simply how to update the GUI from the device class? There are several distinct types of data the device deals with so I need a relatively generic bridge between the GUI form/thread class and the working device class/thread. In the GUI to device direction everything works fine with [Begin]Invoke calls for open/close/read/write etc. on various GUI generated events. I've read the thread here (How to update GUI from another thread in C#?) where the assumption is made that the GUI and worker thread are in the same class. Google searches throw up how to create a delegate or how to create the classic background worker but that's not at all what I need, although they may be part of the solution. So, is there a simple but generic structure that can be used? My level of C# is moderate and I've been programming all my working life, given a clue I'll figure it out (and post back)... Thanks in advance for any help.

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• Java inheritance and super() isn't working as expected

  - by dwwilson66

  For a homework assignment, I'm working with the following. It's an assigned class structure, I know it's not the best design by a long shot. Class | Extends | Variables -------------------------------------------------------- Person | None | firstName, lastName, streetAddress, zipCode, phone CollegeEmployee | Person | ssn, salary,deptName Faculty | CollegeEmployee | tenure(boolean) Student | person | GPA,major So in the Faculty class... public class Faculty extends CollegeEmployee { protected String booleanFlag; protected boolean tenured; public Faculty(String firstName, String lastName, String streetAddress, String zipCode, String phoneNumber,String ssn, String department,double salary) { super(firstName,lastName,streetAddress,zipCode,phoneNumber, ssn,department,salary); String booleanFlag = JOptionPane.showInputDialog (null, "Tenured (Y/N)?"); if(booleanFlag.equals("Y")) tenured = true; else tenured = false; } } It was my understanding that super() in Faculty would allow access to the variables in CollegeEmployee as well as Person. With the code above, it compiles fine when I ONLY include the Person variables. As soon as I try to use ssn, department, or salary I get the following compile errors. Faculty.java:15: error: constructor CollegeEmployee in class CollegeEmployee can not be applied to the given types: super(firstName,lastName,streetAddress,zipCode,phoneNumber,ssn,department,salary); ^ Required: String,String,String,String,String Found: String,String,String,String,String,String,String,String reason: actual and formal argument lists differ in length I'm completely confused by this error...which is the actual and formal? Person has five arguments, CollegeEmployee has 3, so my guess is that something's funky with how the parameters are being passed...but I'm not quite sure where to begin fixing it. What am I missing?

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• table design for storing large number of rows

  - by hyperboreean

  I am trying to store in a postgresql database some unique identifiers along with the site they have been seen on. I can't really decide which of the following 3 option to choose in order to be faster and easy maintainable. The table would have to provide the following information: the unique identifier which unfortunately it's text the sites on which that unique identifier has been seen The amount of data that would have to hold is rather large: there are around 22 millions unique identifiers that I know of. So I thought about the following designs of the table: id - integer identifier - text seen_on_site - an integer, foreign key to a sites table This approach would require around 22 mil multiplied by the number of sites. id - integer identifier - text seen_on_site_1 - boolean seen_on_site_2 - boolean ............ seen_on_site_n - boolean Hopefully the number of sites won't go past 10. This would require only the number of unique identifiers that I know of, that is around 20 millions, but it would make it hard to work with it from an ORM perspective. one table that would store only unique identifiers, like in: id - integer unique_identifier - text, one table that would store only sites, like in: id - integer site - text and one many to many relation, like: id - integer, unique_id - integer (fk to the table storing identifiers) site_id - integer (fk to sites table) another approach would be to have a table that stores unique identifiers for each site So, which one seems like a better approach to take on the long run?

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• Why thread in background is not waiting for task to complete?

  - by Haris Hasan

  I am playing with async await feature of C#. Things work as expected when I use it with UI thread. But when I use it in a non-UI thread it doesn't work as expected. Consider the code below private void Click_Button(object sender, RoutedEventArgs e) { var bg = new BackgroundWorker(); bg.DoWork += BgDoWork; bg.RunWorkerCompleted += BgOnRunWorkerCompleted; bg.RunWorkerAsync(); } private void BgOnRunWorkerCompleted(object sender, RunWorkerCompletedEventArgs runWorkerCompletedEventArgs) { } private async void BgDoWork(object sender, DoWorkEventArgs doWorkEventArgs) { await Method(); } private static async Task Method() { for (int i = int.MinValue; i < int.MaxValue; i++) { var http = new HttpClient(); var tsk = await http.GetAsync("http://www.ebay.com"); } } When I execute this code, background thread don't wait for long running task in Method to complete. Instead it instantly executes the BgOnRunWorkerCompleted after calling Method. Why is that so? What am I missing here? P.S: I am not interested in alternate ways or correct ways of doing this. I want to know what is actually happening behind the scene in this case? Why is it not waiting?

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• MySQL Ratings From Two Tables

  - by DirtyBirdNJ

  I am using MySQL and PHP to build a data layer for a flash game. Retrieving lists of levels is pretty easy, but I've hit a roadblock in trying to fetch the level's average rating along with it's pointer information. Here is an example data set: levels Table: level_id | level_name 1 | Some Level 2 | Second Level 3 | Third Level ratings Table: rating_id | level_id | rating_value 1 | 1 | 3 2 | 1 | 4 3 | 1 | 1 4 | 2 | 3 5 | 2 | 4 6 | 2 | 1 7 | 3 | 3 8 | 3 | 4 9 | 3 | 1 I know this requires a join, but I cannot figure out how to get the average rating value based on the level_id when I request a list of levels. This is what I'm trying to do: SELECT levels.level_id, AVG(ratings.level_rating WHERE levels.level_id = ratings.level_id) FROM levels I know my SQL is flawed there, but I can't figure out how to get this concept across. The only thing I can get to work is returning a single average from the entire ratings table, which is not very useful. Ideal Output from the above conceptually valid but syntactically awry query would be: level_id | level_rating 1| 3.34 2| 1.00 3| 4.54 My main issue is I can't figure out how to use the level_id of each response row before the query has been returned. It's like I want to use a placeholder... or an alias... I really don't know and it's very frustrating. The solution I have in place now is an EPIC band-aid and will only cause me problems long term... please help!

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• Custom Solr sorting

  - by Tom

  Hello everyone, I've been asked to do an evaluation of Solr as an alternative for a commercial search engine. The application now has a very particular way of sorting results using something called "buckets". I'll try to explain with a bit of details: In the interface they have 2 fields: "what" and "where". Both fields are actually sets of fields (what = category, name, contact info... and where= country, state, region, city...) so the copyfield feature of Solr immediately comes to mind. Now based on the field generated the actual match the result should end up in a specific bucket. In particular the first bucket contains all the result documents that have an exact match on the category field, in the second bucket all exact matches on name, the third partial matches on category, the fourth partial matches on name, the fifth matches on contact info etc... Then within each of those first tier buckets all results are placed in second tier buckets depending on what location was matched: city, then region, then province and so on. To even complicate things more there is also a third tier bucket where results are placed according to the value of a ranking field: all documents with the value 1 in the ranking field go in bucket 1 and so on. And finally results should be randomized in the third tier bucket... On top of this they obviously want support for facets and paging. My apologies for the long mail but I would greatly appreciate feedback and/or suggestions. I'm aware that this that this is a very particular problem but everything that points me in the right direction is helpful. Cheers, Tom

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• How can I create a "dynamic" WHERE clause?

  - by TheChange

  Hello there, First: Thanks! I finished my other project and the big surprise: now everything works as it should :-) Thanks to some helpful thinkers of SO! So here I go with the next project. I'd like to get something like this: SELECT * FROM tablename WHERE field1=content AND field2=content2 ... As you noticed this can be a very long where-clause. tablename is a static property which does not change. field1, field2 , ... (!) and the contents can change. So I need an option to build up a SQL statement in PL/SQL within a recursive function. I dont really know what to search for, so I ask here for links or even a word to search for.. Please dont start to argue about wether the recursive function is really needed or what its disadvanteges - this is not in question ;-) If you could help me to create something like an SQL-String which will later be able to do a successful SELECT this would be very nice! Iam able to go through the recursive function and make a longer string each time, but I cannot make an SQL statement from it.. Oh, one additional thing: I get the fields and contents by a xmlType (xmldom.domdocument etc) I can get the field and the content for example in a clob from the xmltype

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• How to query MySQL for exact length and exact UTF-8 characters

  - by oskarae

  I have table with words dictionary in my language (latvian). CREATE TABLE words ( value varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci; And let's say it has 3 words inside: INSERT INTO words (value) VALUES ('teja'); INSERT INTO words (value) VALUES ('vejš'); INSERT INTO words (value) VALUES ('feja'); What I want to do is I want to find all words that is exactly 4 characters long and where second character is 'e' and third character is 'j' For me it feels that correct query would be: SELECT * FROM words WHERE value LIKE '_ej_'; But problem with this query is that it returs not 2 entries ('teja','vejš') but all three. As I understand it is because internally MySQL converts strings to some ASCII representation? Then there is BINARY addition possible for LIKE SELECT * FROM words WHERE value LIKE BINARY '_ej_'; But this also does not return 2 entries ('teja','vejš') but only one ('teja'). I believe this has something to do with UTF-8 2 bytes for non ASCII chars? So question: What MySQL query would return my exact two words ('teja','vejš')? Thank you in advance

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• UIAlertView choice causing resignFirstResponder to fail

  - by Chazbot

  Hi everyone. I'm having a similar issue to Anthony Chan's question, and after trying every suggested solution, I'm still stuck. Somehow, only after interacting with my UIAlertView, I'm unable to dismiss the keyboard in another view of my app. It's as though the Alert is breaking my UITextField's ability to resignFirstResponder. Below I instantiate my UIAlertView, which then calls its didDismissWIthButtonIndex method. Then, I call the showInfo method, which loads another UIViewController. UIAlertView *emailFailAlert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"error message text." delegate:self cancelButtonTitle:@"Not now" otherButtonTitles:@"Settings", nil]; [emailFailAlert setTag:2]; [emailFailAlert show]; [emailFailAlert release]; Once the 'Settings' option is pressed, I'm calling this method: - (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex { if ([alertView tag] == 2) { if (buttonIndex == 1){ [self showInfo:nil]; } } } My showInfo method loads the other ViewController, via the code below: - (IBAction)showInfo:(id)sender { FlipsideViewController *fscontroller = [[FlipsideViewController alloc] initWithNibName:@"FlipsideView" bundle:nil]; fscontroller.delegate = self; fscontroller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal; [self presentModalViewController:fscontroller animated:YES]; [fscontroller release]; } Upon clicking any textField in this Flipside VC, I'm unable to dismiss the keyboard as I normally can with - (BOOL)textFieldShouldReturn:(UITextField *)textField, and [textField resignFirstResponder]. I've omitted this code bc this question is getting long, but I'm happy to post if necessary. The interesting part is that if I comment out the [self showInfo:nil] call made when the button is clicked and call it by clicking a test button (outside the alertView didDismissWithButtonIndex: method), everything works fine. Any idea what's happening here? Thanks in advance!

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• mysqldb interfaceError

  - by Johanna

  I have a very weird probleme with mysqldb (mysql module for python). I have a file with queries for inserting records in tables. If I call the functions from the file, it works just fine. But when I try to call one of the functions from another file it throws me a _mysql_exception.InterfaceError: (0, '') I really don't get what I'm doing wrong here.. I call the function from buildDB.py : import create create.newFormat("HD", 0,0,0) The function newFormat(..) is in create.py (imported) : from Database import Database db = Database() def newFormat(name, width=0, height=0, fps=0): format_query = "INSERT INTO Format (form_name, form_width, form_height, form_fps) VALUES ('"+name+"',"+str(width)+","+str(height)+","+str(fps)+");" db.execute(format_query) And the class Databse is the following : import MySQLdb from MySQLdb.constants import FIELD_TYPE class Database(): def __init__(self): server = "localhost" login = "seq" password = "seqmanager" database = "Sequence" my_conv = { FIELD_TYPE.LONG: int } self.conn = MySQLdb.connection(host=server, user=login, passwd=password, db=database, conv=my_conv) # self.cursor = self.conn.cursor() def close(self): self.conn.close() def execute(self, query): self.conn.query(query) (I put only relevant code) Traceback : Z:\sequenceManager\mysql>python buildDB.py D:\ProgramFiles\Python26\lib\site-packages\MySQLdb\__init__.py:34: DeprecationWa rning: the sets module is deprecated from sets import ImmutableSet INSERT INTO Format (form_name, form_width, form_height, form_fps) VALUES ('HD',0 ,0,0); Traceback (most recent call last): File "buildDB.py", line 182, in <module> create.newFormat("HD") File "Z:\sequenceManager\mysql\create.py", line 52, in newFormat db.execute(format_query) File "Z:\sequenceManager\mysql\Database.py", line 19, in execute self.conn.query(query) _mysql_exceptions.InterfaceError: (0, '') The warning has never been a problem before so I don't think it's related.

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• How to redirect page

  - by sharun

  Hi i created one java application in which i tried to open my company's standard login page and i planned to redirect the link to open my own design page. Standard login page is displayed, instead of going to my own design page as usual its going to mail page. After sign out the mail page i'm gettting my own design page. But my need is, when i sign in the standard login page it should diplay my own design page. Is it possible? Please Help me. And this is code that i followed import java.io.IOException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.google.appengine.api.users.UserService; import com.google.appengine.api.users.UserServiceFactory; import com.google.appengine.api.users.User; public class New extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException { resp.setHeader("Cache-Control", "no-store, no-cache, must-revalidate"); resp.setContentType("text/html"); UserService userService = UserServiceFactory.getUserService(); User user = userService.getCurrentUser(); if (user != null) { if(user.getEmail().equals("[email protected]")) { resp.getWriter().println("done"); resp.sendRedirect("/login.jsp"); } else { resp.getWriter().println("Hello, " + user.getNickname()+"<br>"); resp.getWriter().println("Thanks for your interest. But this application is still not available to everybody."); resp.getWriter().println("<a href="+UserServiceFactory.getUserService().createLogoutURL(userService.createLoginURL(req.getRequestURI()))+">Log out</a>"); } } else { resp.sendRedirect(userService.createLoginURL("http://mail.yyy.edu.in")); } } } Thanks in advance Regards Sharun.

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• MMS2R and Multiple Images Rails

  - by Maletor

  Here's my code: require 'mms2r' class IncomingMailHandler < ActionMailer::Base ## # Receives email(s) from MMS-Email or regular email and # uploads that content the user's photos. # TODO: Use beanstalkd for background queueing and processing. def receive(email) begin mms = MMS2R::Media.new(email) ## # Ok to find user by email as long as activate upon registration. # Remember to make UI option that users can opt out of registration # and either not send emails or send them to a [email protected] # type address. ## # Remember to get SpamAssasin if (@user = User.find_by_email(email.from) && email.has_attachments?) mms.media.each do |key, value| if key.include?('image') value.each do |file| @user.photos.push Photo.create!(:uploaded_data => File.open(file), :title => email.subject.empty? ? "Untitled" : email.subject) end end end end ensure mms.purge end end end and here's my error: /usr/local/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/commands/runner.rb:48: undefined method photos' for true:TrueClass (NoMethodError) from /usr/home/xxx/app/models/incoming_mail_handler.rb:23:in each' from /usr/home/xxx/app/models/incoming_mail_handler.rb:23:in receive' from /usr/home/xxx/app/models/incoming_mail_handler.rb:21:in each' from /usr/home/xxx/app/models/incoming_mail_handler.rb:21:in receive' from /usr/local/lib/ruby/gems/1.8/gems/actionmailer-2.3.4/lib/action_mailer/base.rb:419:in receive' from (eval):1 from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in eval' from /usr/local/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/commands/runner.rb:48 from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in gem_original_require' from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' from /home/xxx/script/runner:3 I sent an email to the server with two image attachments. Upon receiving the email the server runs "| ruby /xxx/script/runner 'IncomingMailHandler.receive STDIN.read'" What is going on? What am I doing wrong? MMS2R docs are here: http://mms2r.rubyforge.org/mms2r/

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• Why does first call to java.io.File.createTempFile(String,String,File) take 5 seconds on Citrix?

  - by Ben Roling

  While debugging slow startup of an Eclipse RCP app on a Citrix server, I came to find out that java.io.createTempFile(String,String,File) is taking 5 seconds. It does this only on the first execution and only for certain user accounts. Specifically, I am noticing it Citrix anonymous user accounts. I have not tried many other types of accounts, but this behavior is not exhibited with an administrator account. Also, it does not matter if the user has access to write to the given directory or not. If the user does not have access, the call will take 5 seconds to fail. If they do have access, the call with take 5 seconds to succeed. This is on a Windows 2003 Server. I've tried Sun's 1.6.0_16 and 1.6.0_19 JREs and see the same behavior. I googled a bit expecting this to be some sort of known issue, but didn't find anything. It seems like someone else would have had to have run into this before. The Eclipse Platform uses File.createTempFile() to test various directories to see if they are writeable during initialization and this issue adds 5 seconds to the startup time of our application. I imagine somebody has run into this before and might have some insight. Here is sample code I executed to see that it is indeed this call that is consuming the time. I also tried it with a second call to createTempFile and notice that subsequent calls return nearly instantaneously. public static void main(final String[] args) throws IOException { final File directory = new File(args[0]); final long startTime = System.currentTimeMillis(); File file = null; try { file = File.createTempFile("prefix", "suffix", directory); System.out.println(file.getAbsolutePath()); } finally { System.out.println(System.currentTimeMillis() - startTime); if (file != null) { file.delete(); } } } Sample output of this program is the following: C:\java.exe -jar filetest.jar C:/Temp C:\Temp\prefix8098550723198856667suffix 5093

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• Weird camera Intent behavior

  - by David Erosa

  Hi all. I'm invoking the MediaStore.ACTION_IMAGE_CAPTURE intent with the MediaStore.EXTRA_OUTPUT extra so that it does save the image to that file. On the onActivityResult I can check that the image is being saved in the intended file, which is correct. The weird thing is that anyhow, the image is also saved in a file named something like "/sdcard/Pictures/Camera/1298041488657.jpg" (epoch time in which the image was taken). I've checked the Camera app source (froyo-release branch) and I'm almost sure that the code path is correct and wouldn't have to save the image, but I'm a noob and I'm not completly sure. AFAIK, the image saving process starts with this callback (comments are mine): private final class JpegPictureCallback implements PictureCallback { ... public void onPictureTaken(...){ ... // This is where the image is passed back to the invoking activity. mImageCapture.storeImage(jpegData, camera, mLocation); ... public void storeImage(final byte[] data, android.hardware.Camera camera, Location loc) { if (!mIsImageCaptureIntent) { // Am i an intent? int degree = storeImage(data, loc); // THIS SHOULD NOT BE CALLED WITHIN THE CAPTURE INTENT!! ....... // An finally: private int storeImage(byte[] data, Location loc) { try { long dateTaken = System.currentTimeMillis(); String title = createName(dateTaken); String filename = title + ".jpg"; // Eureka, timestamp filename! ... So, I'm receiving the correct data, but it's also being saved in the "storeImage(data, loc);" method call, which should not be called... It'd not be a problem if I could get the newly created filename from the intent result data, but I can't. When I found this out, I found about 20 image files from my tests that I didn't know were on my sdcard :) I'm getting this behavior both with my Nexus One with Froyo and my Huawei U8110 with Eclair. Could please anyone enlight me? Thanks a lot.

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• JavaScript onchange, onblur, and focus weirdness in Firefox

  - by typoknig

  On my form I have a discount field that accepts a dollar amount to be taken off of the total bill (HTML generated in PHP): echo "<input id=\"discount\" class=\"text\" type=\"text\" name=\"discount\" onkeypress=\"return currency(this, event)\" onchange=\"currency_format(this)\" onfocus=\"on_focus(this)\" onblur=\"on_blur(this); calculate_bill()\"/><br/><br/>\n"; The JavaScript function calculate_bill calculates the bill and takes off the discount amount as long as the discount amount is less than the total bill: if(discount != ''){ if(discount - 0.01 > total_bill){ window.alert('Discount Cannot Be Greater Than Total Bill'); document.form.discount.focus(); } else{ total_bill -= discount; } } The problem is that even that when the discount is more than the total bill focus is not being returned to the discount field. I have tried calling the calculate_bill function with onchange but neither IE or Firefox will return focus to the discount field when I do it like that. When I call calculate_bill with onblur it works in IE, but still does not work in Firefox. I have attempted to use a confirmation box instead of an alert box as well, but that didn't work either (plus I don't want two buttons, I only an "OK" button). How can I ensure focus is returned to the discount field after a user has left that field by clicking on another field or tabbing IF the discount amount is larger than the total bill?

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• Creating a Function in SQL Server with a Phone Number as a parameter and returns a Random Number

  - by Emer

  Hi Guys, I am hoping someone can help me here as google is not being as forthcoming as I would have liked. I am relatively new to SQL Server and so this is the first function I have set myself to do. The outline of the function is that it has a Phone number varchar(15) as a parameter, it checks that this number is a proper number, i.e. it is 8 digits long and contains only numbers. The main character I am trying to avoid is '+'. Good Number = 12345678 Bad Number = +12345678. Once the number is checked I would like to produce a random number for each phone number that is passed in. I have looked at substrings, the like operator, Rand(), left(), Right() in order to search through the number and then produce a random number. I understand that Rand() will produce the same random number unless alterations are done to it but right now it is about actually getting some working code. Any hints on this would be great or even point me towards some more documentation. I have read books online and they haven't helped me, maybe I am not looking in the right places. Here is a snippet of code I was working on the Rand declare @Phone Varchar (15) declare @Counter Varchar (1) declare @NewNumber Varchar(15) set @Phone = '12345678' set @Counter = len(@Phone) while @Counter > 0 begin select case when @Phone like '%[0-9]%' then cast(rand()*100000000 as int) else 'Bad Number' end set @counter = @counter - 1 end return Thanks for the help in advance Emer

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• Stream PDF to another local App

  - by Nathan

  Hi, I'm currently trying to optimize a small firefox extension that will grab a pdf off the current document and send it to a port that another local application is listening on. Right now it uses a terrifying hackjob of cache viewer. The way I'm getting it is loading the cache, searching through it using the current URL and grabbing the file and saving it to a temp directory. Then I stream the file in, delete the temp, and send it through the socket. Now, my new design, ideally I'd want to build it from scratch and cut out saving it to the local machine at all, and just stream it through the socket. I've been looking at doing something like, //check page to ensure its a pdf //init in/out streams //stream through sock //flush Now, this would be vastly superior to the 400 line hacked up mess I have now, but I'm new to building FF extensions, and after reading a lot about URIs and the file streaming and such I'm probably more confused than when I started trying to fix this three hours ago. I'm okay with sending things through the sockets and whatnot, I understand that, I'm mainly confused about what multitude of interfaces I want to use. Gah! Thanks! Also, long time reader, first time poster!

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• Unable to persist objects in GAE JDO

  - by Basil Dsouza

  Hello Guys, I am completely fresh to both JDO and GAE, and have been struggling to get my data layer to persist any code at all! The issues I am facing may be very simple, but I just cant seem to find any a way no matter what solution I try. Firstly the problem: (Slightly simplified, but still contains all the info necessary) My data model is as such: User: (primary key) String emailID String firstName Car: (primary key) User user (primary key) String registration String model This was the initial datamodel. I implemented a CarPK object to get a composite primary key of the User and the registration. However that ran into a variety of issues. (Which i will save for another time/question) I then changed the design as such: User: (Unchanged) Car: (primary key) String fauxPK (here fauxPK = user.getEmailID() + SEP + registration) User user String registration String model This works fine for the user, and it can insert and retrieve user objects. However when i try to insert a Car Object, i get the following error: "Cannot have a java.lang.String primary key and be a child object" Found the following helpful link about it: http://stackoverflow.com/questions/2063467/persist-list-of-objects Went to the link suggested there, that explains how to create Keys, however they keep talking about "Entity Groups" and "Entity Group Parents". But I cant seem to find any articles or sites that explain what are "Entity Group"s or an "Entity Group Parents" I could try fiddling around some more to figure out if i can store an object somehow, But I am running sort on patience and also would rather understand and implement than vice versa. So i would appreciate any docs (even if its huge) that covers all these points, and preferably has some examples that go beyond the very basic data modeling. And thanks for reading such a long post :)

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• Problem writing a snippet containing Emacs Lisp code

  - by user388346

  Hi all, I've been trying to make use of a cool feature of YASnippet: write snippets containing embedded Emacs Lisp code. There is a snippet for rst-mode that surrounds the entered text with "=" that is as long as the text such as in ==== Text ==== Based on this snippet, I decided to slightly modify it (with Elisp) so that it comments out these three lines depending on the major mode you are in (I thought that such a snippet would be useful to organize the source code). So I wrote this: ${1:`(insert comment-start)`} ${2:$(make-string (string-width text) ?\-)} $1 ${2:Text} $1 ${2:$(make-string (string-width text) ?\-)} $0 This code works relatively well except for one problem: the indentation of these three lines gets mixed up, depending on the major mode I'm in (e.g., in emacs-lisp-mode, the second and the third lines move more to the right than the first line). I think the source of the problem might have something to do with what comes after the string ${1: on the first line. If I add a character, I have no problem (i.e., all three lines are correctly aligned at the end of the snippet expansion). If I add a single space after this string, the misalignment problem still continues though. So my question is: do you know of any way of rewriting this snippet so that this misalignment does not arise? Do you know what's the source of this behaviour? Cheers,

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• C# Late Binding for Parameterized Property

  - by optim

  I'm trying to use late binding to connect to a COM automation API provided by a program called Amibroker, using a C# WinForms project. So far I've been able to connect to everything in the API except one item, which I believe to be a "parameterized property" based on extensive Googling. Here's what the API specification looks like according to the docs (Full version here: http://www.amibroker.com/guide/objects.html): Property Filter(ByVal nType As Integer, ByVal pszCategory As String) As Long [r/w] A javascript snippet to update the value looks like this: AB = new ActiveXObject("Broker.Application"); AA = AB.Analysis; AA.Filter( 0, "market" ) = 0; Using the following C# late-binding code, I can get the value of the property, but I can't for the life of me figure out how to set the value: object[] parameter = new object[2]; parameter[0] = Number; parameter[1] = Type; object filters = _analysis.GetType().InvokeMember("Filter", BindingFlags.GetProperty, null, _analysis, parameter); So far I have tried: using BindingFlags.SetProperty, BindingFlags.SetField casting the returned object to a PropertyInfo object and trying to update the value using it adding extra object containing the value to the parameters object various other things as last-ditch efforts From what I can see, this should be straight-forward, but I'm finding the late binding in C# to be cumbersome at best. The property looks like a method call to me, which is what is throwing me off. How does one assign a value to a method, and what would the prototype for late-binding C# code look like for it? Hopefully that explains it well enough, but feel free to ask if I've left anything unclear. Thanks in advance for any help! Daniel

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• JQuery UI drag and drop doesn't notice DOM changes happening during the dragging ?

  - by user315677

  Hi everybody, I have a html table in which each line (<tr>) represents a group of client computers. Each line can be expanded to show the clients belonging to the group. The <tr> containing the clients are always generated but hidden and showed when clicking the plus button at the beginning of each line. The clients themselves (they are <div>) can be dragged and dropped in another group as long as this group is already expanded. So far it works fine. What I am trying to achieve now is that the client can be dragged to a collapsed group and after a second or so hovering the group it will be expanded and the client can be dropped amongst the other clients of the group. I programmed the hover using the in and outevents of the droppable and it expands the group all right, but (and now it starts to be hard to explain with words ;) the behavior of the droppable (the client) is still as if the table line that appeared were not there : the in out and drop events of the droppable are fired on the old position of the elements, and the in out and drop events of the newly appeared <tr> are never fired. It looks as if JQuery memorizes the position, size etc. of the elements when the drag starts, and these values are not updated if there is a change in the DOM before the drop happens... Can someone confirm this behavior is normal, or can it be caused by another problem in my own code ? Any workaround ? (the question is quite bloated already so I don't include any code but I'll gladly upload it if required)

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• How can the Three-Phase Commit Protocol (3PC) guarantee atomicity?

  - by AndiDog

  I'm currently exploring worst case scenarios of atomic commit protocols like 2PC and 3PC and am stuck at the point that I can't find out why 3PC can guarantee atomicity. That is, how does it guarantee that if cohort A commits, cohort B also commits? Here's the simplified 3PC from the Wikipedia article: Now let's assume the following case: Two cohorts participate in the transaction (A and B) Both do their work, then vote for commit Coordinator now sends precommit messages... A receives the precommit message, acknowledges, and then goes offline for a long time B doesn't receive the precommit message (whatever the reason might be) and is thus still in "uncertain" state The results: Coordinator aborts the transaction because not all precommit messages were sent and acknowledged successfully A, who is in precommit state, is still offline, thus times out and commits B aborts in any case: He either stays offline and times out (causes abort) or comes online and receives the abort command from the coordinator And there you have it: One cohort committed, another aborted. The transaction is screwed. So what am I missing here? In my understanding, if the automatic commit on timeout (in precommit state) was replaced by infinitely waiting for a coordinator command, that case should work fine.

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• Insert data in an object to a database.

  - by paul

  I am facing the following design/implementation dilemma. I have a class Customer which is below with getters and setters. I would like to insert the value of the Customer into a "Customer" table of a database. But Customer has an address which is of type "Address". How do I go about inserting this field into the database?(I am using sqlite3). I thought of writing a separate table "Address(customerId,doorNo,city,state,country,pinCode)". But I am having second thoughts about generating the primary key(customerId) which should be same for both the "customer" and "Address" table. Sqlite3 faq states that I can do "Integer Primary Key" to use the field to generate an auto number. But if I do that in customer table, I would have to retrieve the same Id to be used in Address table. This kinda looks wrong to me :-?. There should be an elegant method to solve this. Any ideas would be much appreciated. Thanks in advance. import java.io.*; import java.sql.*; class Customer { private String id; private String name; private Address address; private Connection connection; private ResultSet resultSet; private PreparedStatement preparedStatement; public void insertToDatabase(){ } } class Address{ private String doorNumber; private String streetName; private String cityName; private String districtName; private String stateName; private String countryName; private long pinCode; }

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• Byte-Pairing for data compression

  - by user1669533

  Question about Byte-Pairing for data compression. If byte pairing converts two byte values to a single byte value, splitting the file in half, then taking a gig file and recusing it 16 times shrinks it to 62,500,000. My question is, is byte-pairing really efficient? Is the creation of a 5,000,000 iteration loop, to be conservative, efficient? I would like some feed back on and some incisive opinions please. Dave, what I read was: "The US patent office no longer grants patents on perpetual motion machines, but has recently granted at least two patents on a mathematically impossible process: compression of truly random data." I was not inferring the Patent Office was actually considering what I am inquiring about. I was merely commenting on the notion of a "mathematically impossible process." If someone has, in some way created a method of having a "single" data byte as a placeholder of 8 individual bytes of data, that would be a consideration for a patent. Now, about the mathematically impossibility of an 8 to 1 compression method, it is not so much a mathematically impossibility, but a series of rules and conditions that can be created. As long as there is the rule of 8 or 16 bit representation of storing data on a medium, there are ways to manipulate data that mirrors current methods, or creation by a new way of thinking.

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• Factorial in Prolog and C++

  - by Joshua Green

  I would like to work out a number's factorial. My factorial rule is in a Prolog file and I am connecting it to a C++ code. Can someone tell me what is wrong with my C++ interface please? % factorial.pl factorial( 1, 1 ):- !. factorial( X, Fac ):- X > 1, Y is X - 1, factorial( Y, New_Fac ), Fac is X * New_Fac. // factorial.cpp # headerfiles term_t t1; term_t t2; term_t goal_term; functor_t goal_functor; int main( int argc, char** argv ) { argc = 4; argv[0] = "libpl.dll"; argv[1] = "-G32m"; argv[2] = "-L32m"; argv[3] = "-T32m"; PL_initialise(argc, argv); if ( !PL_initialise(argc, argv) ) PL_halt(1); PlCall( "consult(swi('plwin.rc'))" ); PlCall( "consult('factorial.pl')" ); cout << "Enter your factorial number: "; long n; cin >> n; PL_put_integer( t1, n ); t1 = PL_new_term_ref(); t2 = PL_new_term_ref(); goal_term = PL_new_term_ref(); goal_functor = PL_new_functor( PL_new_atom("factorial"), 2 ); PL_put_atom( t1, t2 ); PL_cons_functor( goal_term, goal_functor, t1, t2 ); PL_halt( PL_toplevel() ? 0 : 1 ); }

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