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  • How to tell if a datareader is open on a connection and close it

    - by Earlz
    Hi, I'm setting up a little thing for connection pooling and on of the more common bugs that we have occur(its always an easy fix, but we just can't remember reader.Close()!) it is when we have a connection that is used by a lot of classes/methods and one method opens a data reader and forgets to close it. This isn't really bad cause a lot of times all you have to do is go into the debugger and go up one level and see the function before it was and check if it had an unclosed data reader. Now, here is the bigger problem. In this connection pool, if a datareader is open, then it's not known until a thread gets a connection and tries to use it and the thing that originally opened the data reader may no longer even be alive. So quite simply, how can you detect if a data reader is open on a connection and is there a way to close the reader without closing the connection?

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  • c# reading integer fields from database, returning empty string when reading integer type field

    - by arnoldino
    what is wrong with this code? field="id"; table="MInvMonth"; condition="machine_id=37"; public static String getConditionedField(String field, String table, String condition) try { if (cmd == null) getConnection(); cmd.CommandText = "Select " + field + " from " + table + " where " + condition; SQLiteDataReader reader = cmd.ExecuteReader(); if (reader.HasRows==true) { reader.Read(); string s = reader[0].ToString(); // return first element reader.Close(); return s; } reader.Close(); return null; } catch (Exception e) { MessageBox.Show("Caught exception: " + e.Message+"|"+cmd.CommandText); return null; } I checked the sql statement, it turns the right value. why can't I read it? the returnvalue is "".

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  • How to initialize F# list when size is unknown, using while..do loop

    - by James Black
    I have a function that will parse the results of a DataReader, and I don't know how many items are returned, so I want to use a while..do loop to iterate over the reader, and the outcome should be a list of a certain type. (fun(reader) -> [ while reader.Read() do new CityType(Id=(reader.GetInt32 0), Name=(reader.GetString 1), StateName=(reader.GetString 2)) ]) This is what I tried, but the warning I get is: This expression should have type 'unit', but has type 'CityType'. Use 'ignore' to discard the result of the expression, or 'let' to bind the result to a name. So what is the best way to iterate over a DataReader and create a list?

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  • How to read from an XmlReader without moving it forwards

    - by andy
    hey guys, I've got this scenario: while (reader.Read()) { if (reader.NodeType == XmlNodeType.Element && reader.Name == itemElementName) { XElement item = null; try { item = XElement.ReadFrom(reader) as XElement; } catch (XmlException ex) { //log line number and stuff from XmlException class } } } In the above loop I'm transforming a certain node (itemElementName) into an XElement. Some nodes will be good XML and will go into an XElement, however, some will not. In the CATCH, I'd like to now only catch the standard XmlException stuff... I'd also like to catch an extract of the current Xml and a string. However, if I do any kind of READ operation on the node before I pass it to the XElement, it moves the reader forward. How can get a "snapshot" of the contents of the OuterXml of the reader without interfering with it's position?

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  • c# reading integer fields from database

    - by arnoldino
    what is wrong with this code? try { if (cmd == null) getConnection(); cmd.CommandText = "Select id from HMonthInventary where machine_id=37"; SQLiteDataReader reader = cmd.ExecuteReader(); if (reader.HasRows==true) { reader.Read(); string s = reader[0].ToString(); // return first element reader.Close(); return s; } reader.Close(); return null; } catch (Exception e) { MessageBox.Show("Caught exception: " + e.Message+"|"+cmd.CommandText); return null; } I checked the sql statement, it turns the right value. why can't I read it? the returnvalue is "".

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  • Using the same CArchive object for archive and un-archive

    - by bdhar
    Following is a sample code: CFile serFile; serFile.Open(_T("Person.ser"), CFile::modeCreate | CFile::modeWrite); CArchive writer(&serFile, CArchive::store); me.Serialize(writer); writer.Close(); serFile.Close(); serFile.Open(_T("Person.ser"), CFile::modeRead); CArchive reader(&serFile, CArchive::load); CPerson clone; clone.Serialize(reader); reader.Close(); serFile.Close(); Here, I have a writer which archives the object me. Then, I use another CArchive object reader to un-archive it. Is it possible to re-construct or set any property of writer to make it, the reader instead of declaring another CArchive object reader? Thanks.

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  • Importing a spreadsheet, but having trouble.

    - by Chris Phelps
    I have a form that allows a user to import a spreadsheet. This spreadsheet is generally static when it comes to column headers, but now the users want to be able to include an optional column (called Notes). My code crashes when I try to read the column from the spreadsheet if it doesn't exist. Dim objCommand As New OleDbCommand() objCommand = ExcelConnection() 'function that opens spreadsheet and returns objCommand Dim reader As OleDbDataReader reader = objCommand.ExecuteReader() While reader.Read() Dim Employee As String = Convert.ToString(reader("User")) Dim SerialNUM As String = Convert.ToString(reader("serialno")) **Dim Notes As String = Convert.ToString(reader("notes"))** If the spreadsheet contains a Notes column, all goes well. If not, crash. How can I check to see if the Notes column exists in the spreadsheet to avoid the crash?

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  • Pricing options at O’Reilly

    - by Nick Harrison
    I was browsing through the new options for books on O'Reilly and Associates and noticed something kind of cool    If you buy the print edition of a book, you can get the ebook for just a couple dollars more.  This is pure genius marketing. I may question whether or not I want the ebook at 20 or the print copy at 25, but to get them both for 28, well that's a no brainer.  This is actually a strategy examined at great depth in Predictably Rational In all honesty, $20 is probably over priced for the ebook, but $3 if you are already buying the print edition is actually a pretty good deal  .

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  • New Java Tutorials Updated

    - by hinkmond
    The new Java Tutorials are here! The new Java Tutorials are here! So what? So, you can read them on your iPad thingie--if that's how you roll, that is... See: Read New Java Tutorials Here's a quote: What's New The Java Tutorials are continuously updated to keep up with changes to the Java Platform and to incorporate feedback from our readers. Recent updates include the following features: The Generics lesson has been completely reworked... The Java Tutorials are now available in two ebook formats: mobi ebook files for Kindle. ePub ebook files for iPad, Nook, and other eReaders that support the ePub format. Just kick back, open up your favorite tablet or eReader and learn all about the new things in the Java platform. Nice. All you need now is a cool drink and you're all set! Hinkmond

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  • Windows Phone 7 development: reading RSS feeds

    - by DigiMortal
    One limitation on Windows Phone 7 is related to System.Net namespace classes. There is no convenient way to read data from web. There is no WebClient class. There is no GetResponse() method – we have to do it all asynchronously because compact framework has limited set of classes we can use in our applications to communicate with internet. In this posting I will show you how to read RSS-feeds on Windows Phone 7. NB! This is my draft code and it may contain some design flaws and some questionable solutions. This code is intended to use as test-drive for Windows Phone 7 CTP developer tools and I don’t suppose you are going to use this code in production environment. Current state of my RSS-reader Currently my RSS-reader for Windows Phone 7 is very simple, primitive and uses almost all defaults that come out-of-box with Windows Phone 7 CTP developer tools. My first goal before going on with nicer user interface design was making RSS-reading work because instead of convenient classes from .NET Framework we have to use very limited classes from .NET Framework CE. This is why I took the reading of RSS-feeds as my first task. There are currently more things to solve regarding user-interface. As I am pretty new to all this Silverlight stuff I am not very sure if I can modify default controls easily or should I write my own controls that have better look and that work faster. The image on right shows you how my RSS-reader looks like right now. Upper side of screen is filled with list that shows headlines from this blog. The bottom part of screen is used to show description of selected posting. You can click on the image to see it in original size. In my next posting I will show you some improvements of my RSS-reader user interface that make it look nicer. But currently it is nice enough to make sure that RSS-feeds are read correctly. FeedItem class As this is most straight-forward part of the following code I will show you RSS-feed items class first. I think we have to stop on it because it is simple one. public class FeedItem {     public string Title { get; set; }     public string Description { get; set; }     public DateTime PublishDate { get; set; }     public List<string> Categories { get; set; }     public string Link { get; set; }       public FeedItem()     {         Categories = new List<string>();     } } RssClient RssClient takes feed URL and when asked it loads all items from feed and gives them back to caller through ItemsReceived event. Why it works this way? Because we can make responses only using asynchronous methods. I will show you in next section how to use this class. Although the code here is not very good but it works like expected. I will refactor this code later because it needs some more efforts and investigating. But let’s hope I find excellent solution. :) public class RssClient {     private readonly string _rssUrl;       public delegate void ItemsReceivedDelegate(RssClient client, IList<FeedItem> items);     public event ItemsReceivedDelegate ItemsReceived;       public RssClient(string rssUrl)     {         _rssUrl = rssUrl;     }       public void LoadItems()     {         var request = (HttpWebRequest)WebRequest.Create(_rssUrl);         var result = (IAsyncResult)request.BeginGetResponse(ResponseCallback, request);     }       void ResponseCallback(IAsyncResult result)     {         var request = (HttpWebRequest)result.AsyncState;         var response = request.EndGetResponse(result);           var stream = response.GetResponseStream();         var reader = XmlReader.Create(stream);         var items = new List<FeedItem>(50);           FeedItem item = null;         var pointerMoved = false;           while (!reader.EOF)         {             if (pointerMoved)             {                 pointerMoved = false;             }             else             {                 if (!reader.Read())                     break;             }               var nodeName = reader.Name;             var nodeType = reader.NodeType;               if (nodeName == "item")             {                 if (nodeType == XmlNodeType.Element)                     item = new FeedItem();                 else if (nodeType == XmlNodeType.EndElement)                     if (item != null)                     {                         items.Add(item);                         item = null;                     }                   continue;             }               if (nodeType != XmlNodeType.Element)                 continue;               if (item == null)                 continue;               reader.MoveToContent();             var nodeValue = reader.ReadElementContentAsString();             // we just moved internal pointer             pointerMoved = true;               if (nodeName == "title")                 item.Title = nodeValue;             else if (nodeName == "description")                 item.Description =  Regex.Replace(nodeValue,@"<(.|\n)*?>",string.Empty);             else if (nodeName == "feedburner:origLink")                 item.Link = nodeValue;             else if (nodeName == "pubDate")             {                 if (!string.IsNullOrEmpty(nodeValue))                     item.PublishDate = DateTime.Parse(nodeValue);             }             else if (nodeName == "category")                 item.Categories.Add(nodeValue);         }           if (ItemsReceived != null)             ItemsReceived(this, items);     } } This method is pretty long but it works. Now let’s try to use it in Windows Phone 7 application. Using RssClient And this is the fragment of code behing the main page of my application start screen. You can see how RssClient is initialized and how items are bound to list that shows them. public MainPage() {     InitializeComponent();       SupportedOrientations = SupportedPageOrientation.Portrait | SupportedPageOrientation.Landscape;     listBox1.Width = Width;       var rssClient = new RssClient("http://feedproxy.google.com/gunnarpeipman");     rssClient.ItemsReceived += new RssClient.ItemsReceivedDelegate(rssClient_ItemsReceived);     rssClient.LoadItems(); }   void rssClient_ItemsReceived(RssClient client, IList<FeedItem> items) {     Dispatcher.BeginInvoke(delegate()     {         listBox1.ItemsSource = items;     });            } Conclusion As you can see it was not very hard task to read RSS-feed and populate list with feed entries. Although we are not able to use more powerful classes that are part of full version on .NET Framework we can still live with limited set of classes that .NET Framework CE provides.

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  • Print SSRS Report / PDF automatically from SQL Server agent or Windows Service

    - by Jeremy Ramos
    Originally posted on: http://geekswithblogs.net/JeremyRamos/archive/2013/10/22/print-ssrs-report--pdf-from-sql-server-agent-or.aspxI have turned the Web upside-down to find a solution to this considering the least components and least maintenance as possible to achieve automated printing of an SSRS report. This is for the reason that we do not have a full software development team to maintain an app and we have to minimize the support overhead for the support team.Here is my setup:SQL Server 2008 R2 in Windows Server 2008 R2PDF format reports generated by SSRS Reports subscriptions to a Windows File ShareNetwork printerColoured reports with logo and brandingI have found and tested the following solutions to no avail:ProsConsCalling Adobe Acrobat Reader exe: "C:\Program Files (x86)\Adobe\Reader 11.0\Reader\acroRd32.exe" /n /s /o /h /t "C:\temp\print.pdf" \\printserver\printername"Very simple optionAdobe Acrobat reader requires to launch the GUI to send a job to a printer. Hence, this option cannot be used when printing from a service.Calling Adobe Acrobat Reader exe as a process from a .NET console appA bit harder than above, but still a simple solutionSame as cons abovePowershell script(Start-Process -FilePath "C:\temp\print.pdf" -Verb Print)Very simple optionUses default PDF client in quiet mode to Print, but also requires an active session.    Foxit ReaderVery simple optionRequires GUI same as Adobe Acrobat Reader Using the Reporting Services Web service to run and stream the report to an image object and then passed to the printerQuite complexThis is what we're trying to avoid  After pulling my hair out for two days, testing and evaluating the above solutions, I ended up learning more about printers (more than ever in my entire life) and how printer drivers work with PostScripts. I then bumped on to a PostScript interpreter called GhostScript (http://www.ghostscript.com/) and then the solution starts to get clearer and clearer.I managed to achieve a solution (maybe not be the simplest but efficient enough to achieve the least-maintenance-least-components goal) in 3-simple steps:Install GhostScript (http://www.ghostscript.com/download/) - this is an open-source PostScript and PDF interpreter. Printing directly using GhostScript only produces grayscale prints using the laserjet generic driver unless you save as BMP image and then interpret the colours using the imageInstall GSView (http://pages.cs.wisc.edu/~ghost/gsview/)- this is a GhostScript add-on to make it easier to directly print to a Windows printer. GSPrint automates the above  PDF -> BMP -> Printer Driver.Run the GSPrint command from SQL Server agent or Windows Service:"C:\Program Files\Ghostgum\gsview\gsprint.exe" -color -landscape -all -printer "printername" "C:\temp\print.pdf"Command line options are here: http://pages.cs.wisc.edu/~ghost/gsview/gsprint.htmAnother lesson learned is, since you are calling the script from the Service Account, it will not necessarily have the Printer mapped in its Windows profile (if it even has one). The workaround to this is by adding a local printer as you normally would and then map this printer to the network printer. Note that you may need to install the Printer Driver locally in the server.So, that's it! There are many ways to achieve a solution. The key thing is how you provide the smartest solution!

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  • eBooks on iPad vs. Kindle: More Debate than Smackdown

    - by andrewbrust
    When the iPad was presented at its San Francisco launch event on January 28th, Steve Jobs spent a significant amount of time explaining how well the device would serve as an eBook reader. He showed the iBooks reader application and iBookstore and laid down the gauntlet before Amazon and its beloved Kindle device. Almost immediately afterwards, criticism came rushing forth that the iPad could never beat the Kindle for book reading. The curious part of that criticism is that virtually no one offering it had actually used the iPad yet. A few weeks later, on April 3rd, the iPad was released for sale in the United States. I bought one on that day and in the few additional weeks that have elapsed, I’ve given quite a workout to most of its capabilities, including its eBook features. I’ve also spent some time with the Kindle, albeit a first-generation model, to see how it actually compares to the iPad. I had some expectations going in, but I came away with conclusions about each device that were more scenario-based than absolute. I present my findings to you here.   Vital Statistics Let’s start with an inventory of each device’s underlying technology. The iPad has a color, backlit LCD screen and an on-screen keyboard. It has a battery which, on a full charge, lasts anywhere from 6-10 hours. The Kindle offers a monochrome, reflective E Ink display, a physical keyboard and a battery that on my first gen loaner unit can go up to a week between charges (Amazon claims the battery on the Kindle 2 can last up to 2 weeks on a single charge). The Kindle connects to Amazon’s Kindle Store using a 3G modem (the technology and network vary depending on the model) that incurs no airtime service charges whatsoever. The iPad units that are on-sale today work over WiFi only. 3G-equipped models will be on sale shortly and will command a $130 premium over their WiFi-only counterparts. 3G service on the iPad, in the U.S. from AT&T, will be fee-based, with a 250MB plan at $14.99 per month and an unlimited plan at $29.99. No contract is required for 3G service. All these tech specs aside, I think a more useful observation is that the iPad is a multi-purpose Internet-connected entertainment device, while the Kindle is a dedicated reading device. The question is whether those differences in design and intended use create a clear-cut winner for reading electronic publications. Let’s take a look at each device, in isolation, now.   Kindle To me, what’s most innovative about the Kindle is its E Ink display. E Ink really looks like ink on a sheet of paper. It requires no backlight, it’s fully visible in direct sunlight and it causes almost none of the eyestrain that LCD-based computer display technology (like that used on the iPad) does. It’s really versatile in an all-around way. Forgive me if this sounds precious, but reading on it is really a joy. In fact, it’s a genuinely relaxing experience. Through the Kindle Store, Amazon allows users to download books (including audio books), magazines, newspapers and blog feeds. Books and magazines can be purchased either on a single-issue basis or as an annual subscription. Books, of course, are purchased singly. Oddly, blogs are not free, but instead carry a monthly subscription fee, typically $1.99. To me this is ludicrous, but I suppose the free 3G service is partially to blame. Books and magazine issues download quickly. Magazine and blog subscriptions cause new issues or posts to be pushed to your device on an automated basis. Available blogs include 9000-odd feeds that Amazon offers on the Kindle Store; unless I missed something, arbitrary RSS feeds are not supported (though there are third party workarounds to this limitation). The shopping experience is integrated well, has an huge selection, and offers certain graphical perks. For example, magazine and newspaper logos are displayed in menus, and book cover thumbnails appear as well. A simple search mechanism is provided and text entry through the physical keyboard is relatively painless. It’s very easy and straightforward to enter the store, find something you like and start reading it quickly. If you know what you’re looking for, it’s even faster. Given Kindle’s high portability, very reliable battery, instant-on capability and highly integrated content acquisition, it makes reading on whim, and in random spurts of downtime, very attractive. The Kindle’s home screen lists all of your publications, and easily lets you select one, then start reading it. Once opened, publications display in crisp, attractive text that is adjustable in size. “Turning” pages is achieved through buttons dedicated to the task. Notes can be recorded, bookmarks can be saved and pages can be saved as clippings. I am not an avid book reader, and yet I found the Kindle made it really fun, convenient and soothing to read. There’s something about the easy access to the material and the simplicity of the display that makes the Kindle seduce you into chilling out and reading page after page. On the other hand, the Kindle has an awkward navigation interface. While menus are displayed clearly on the screen, the method of selecting menu items is tricky: alongside the right-hand edge of the main display is a thin column that acts as a second display. It has a white background, and a scrollable silver cursor that is moved up or down through the use of the device’s scrollwheel. Picking a menu item on the main display involves scrolling the silver cursor to a position parallel to that menu item and pushing the scrollwheel in. This navigation technique creates a disconnect, literally. You don’t really click on a selection so much as you gesture toward it. I got used to this technique quickly, but I didn’t love it. It definitely created a kind of anxiety in me, making me feel the need to speed through menus and get to my destination document quickly. Once there, I could calm down and relax. Books are great on the Kindle. Magazines and newspapers much less so. I found the rendering of photographs, and even illustrations, to be unacceptably crude. For this reason, I expect that reading textbooks on the Kindle may leave students wanting. I found that the original flow and layout of any publication was sacrificed on the Kindle. In effect, browsing a magazine or newspaper was almost impossible. Reading the text of individual articles was enjoyable, but having to read this way made the whole experience much more “a la carte” than cohesive and thematic between articles. I imagine that for academic journals this is ideal, but for consumer publications it imposes a stripped-down, low-fidelity experience that evokes a sense of deprivation. In general, the Kindle is great for reading text. For just about anything else, especially activity that involves exploratory browsing, meandering and short-attention-span reading, it presents a real barrier to entry and adoption. Avid book readers will enjoy the Kindle (if they’re not already). It’s a great device for losing oneself in a book over long sittings. Multitaskers who are more interested in periodicals, be they online or off, will like it much less, as they will find compromise, and even sacrifice, to be palpable.   iPad The iPad is a very different device from the Kindle. While the Kindle is oriented to pages of text, the iPad orbits around applications and their interfaces. Be it the pinch and zoom experience in the browser, the rich media features that augment content on news and weather sites, or the ability to interact with social networking services like Twitter, the iPad is versatile. While it shares a slate-like form factor with the Kindle, it’s effectively an elegant personal computer. One of its many features is the iBook application and integration of the iBookstore. But it’s a multi-purpose device. That turns out to be good and bad, depending on what you’re reading. The iBookstore is great for browsing. It’s color, rich animation-laden user interface make it possible to shop for books, rather than merely search and acquire them. Unfortunately, its selection is rather sparse at the moment. If you’re looking for a New York Times bestseller, or other popular titles, you should be OK. If you want to read something more specialized, it’s much harder. Unlike the awkward navigation interface of the Kindle, the iPad offers a nearly flawless touch-screen interface that seduces the user into tinkering and kibitzing every bit as much as the Kindle lulls you into a deep, concentrated read. It’s a dynamic and interactive device, whereas the Kindle is static and passive. The iBook reader is slick and fun. Use the iPad in landscape mode and you can read the book in 2-up (left/right 2-page) display; use it in portrait mode and you can read one page at a time. Rather than clicking a hardware button to turn pages, you simply drag and wipe from right-to-left to flip the single or right-hand page. The page actually travels through an animated path as it would in a physical book. The intuitiveness of the interface is uncanny. The reader also accommodates saving of bookmarks, searching of the text, and the ability to highlight a word and look it up in a dictionary. Pages display brightly and clearly. They’re easy to read. But the backlight and the glare made me less comfortable than I was with the Kindle. The knowledge that completely different applications (including the Web and email and Twitter) were just a few taps away made me antsy and very tempted to task-switch. The knowledge that battery life is an issue created subtle discomfort. If the Kindle makes you feel like you’re in a library reading room, then the iPad makes you feel, at best, like you’re under fluorescent lights at a Barnes and Noble or Borders store. If you’re lucky, you’d be on a couch or at a reading table in the store, but you might also be standing up, in the aisles. Clearly, I didn’t find this conducive to focused and sustained reading. But that may have more to do with my own tendency to read periodicals far more than books, and my neurotic . And, truth be known, the book reading experience, when not explicitly compared to Kindle’s, was still pleasant. It is also important to point out that Kindle Store-sourced books can be read on the iPad through a Kindle reader application, from Amazon, specific to the device. This offered a less rich experience than the iBooks reader, but it was completely adequate. Despite the Kindle brand of the reader, however, it offered little in terms of simulating the reading experience on its namesake device. When it comes to periodicals, the iPad wins hands down. Magazines, even if merely scanned images of their print editions, read on the iPad in a way that felt similar to reading hard copy. The full color display, touch navigation and even the ability to render advertisements in their full glory makes the iPad a great way to read through any piece of work that is measured in pages, rather than chapters. There are many ways to get magazines and newspapers onto the iPad, including the Zinio reader, and publication-specific applications like the Wall Street Journal’s and Popular Science’s. The New York Times’ free Editors’ Choice application offers a Times Reader-like interface to a subset of the Gray Lady’s daily content. The completely Web-based but iPad-optimized Times Skimmer site (at www.nytimes.com/timesskimmer) works well too. Even conventional Web sites themselves can be read much like magazines, given the iPad’s ability to zoom in on the text and crop out advertisements on the margins. While the Kindle does have an experimental Web browser, it reminded me a lot of early mobile phone browsers, only in a larger size. For text-heavy sites with simple layout, it works fine. For just about anything else, it becomes more trouble than it’s worth. And given the way magazine articles make me think of things I want to look up online, I think that’s a real liability for the Kindle.   Summing Up What I came to realize is that the Kindle isn’t so much a computer or even an Internet device as it is a printer. While it doesn’t use physical paper, it still renders its content a page at a time, just like a laser printer does, and its output appears strikingly similar. You can read the rendered text, but you can’t interact with it in any way. That’s why the navigation requires a separate cursor display area. And because of the page-oriented rendering behavior, turning pages causes a flash on the display and requires a sometimes long pause before the next page is rendered. The good side of this is that once the page is generated, no battery power is required to display it. That makes for great battery life, optimal viewing under most lighting conditions (as long as there is some light) and low-eyestrain text-centric display of content. The Kindle is highly portable, has an excellent selection in its store and is refreshingly distraction-free. All of this is ideal for reading books. And iPad doesn’t offer any of it. What iPad does offer is versatility, variety, richness and luxury. It’s flush with accoutrements even if it’s low on focused, sustained text display. That makes it inferior to the Kindle for book reading. But that also makes it better than the Kindle for almost everything else. As such, and given that its book reading experience is still decent (even if not superior), I think the iPad will give Kindle a run for its money. True book lovers, and people on a budget, will want the Kindle. People with a robust amount of discretionary income may want both devices. Everyone else who is interested in a slate form factor e-reading device, especially if they also wish to have leisure-friendly Internet access, will likely choose the iPad exclusively. One thing is for sure: iPad has reduced Kindle’s market, and may have shifted its mass market potential to a mere niche play. If Amazon is smart, it will improve its iPad-based Kindle reader app significantly. It can then leverage the iPad channel as a significant market for the Kindle Store. After all, selling the eBooks themselves is what Amazon should care most about.

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  • Asynchronous Streaming in ASP.NET WebApi

    - by andresv
     Hi everyone, if you use the cool MVC4 WebApi you might encounter yourself in a common situation where you need to return a rather large amount of data (most probably from a database) and you want to accomplish two things: Use streaming so the client fetch the data as needed, and that directly correlates to more fetching in the server side (from our database, for example) without consuming large amounts of memory. Leverage the new MVC4 WebApi and .NET 4.5 async/await asynchronous execution model to free ASP.NET Threadpool threads (if possible).  So, #1 and #2 are not directly related to each other and we could implement our code fulfilling one or the other, or both. The main point about #1 is that we want our method to immediately return to the caller a stream, and that client side stream be represented by a server side stream that gets written (and its related database fetch) only when needed. In this case we would need some form of "state machine" that keeps running in the server and "knows" what is the next thing to fetch into the output stream when the client ask for more content. This technique is generally called a "continuation" and is nothing new in .NET, in fact using an IEnumerable<> interface and the "yield return" keyword does exactly that, so our first impulse might be to write our WebApi method more or less like this:           public IEnumerable<Metadata> Get([FromUri] int accountId)         {             // Execute the command and get a reader             using (var reader = GetMetadataListReader(accountId))             {                 // Read rows asynchronously, put data into buffer and write asynchronously                 while (reader.Read())                 {                     yield return MapRecord(reader);                 }             }         }   While the above method works, unfortunately it doesn't accomplish our objective of returning immediately to the caller, and that's because the MVC WebApi infrastructure doesn't yet recognize our intentions and when it finds an IEnumerable return value, enumerates it before returning to the client its values. To prove my point, I can code a test method that calls this method, for example:        [TestMethod]         public void StreamedDownload()         {             var baseUrl = @"http://localhost:57771/api/metadata/1";             var client = new HttpClient();             var sw = Stopwatch.StartNew();             var stream = client.GetStreamAsync(baseUrl).Result;             sw.Stop();             Debug.WriteLine("Elapsed time Call: {0}ms", sw.ElapsedMilliseconds); } So, I would expect the line "var stream = client.GetStreamAsync(baseUrl).Result" returns immediately without server-side fetching of all data in the database reader, and this didn't happened. To make the behavior more evident, you could insert a wait time (like Thread.Sleep(1000);) inside the "while" loop, and you will see that the client call (GetStreamAsync) is not going to return control after n seconds (being n == number of reader records being fetched).Ok, we know this doesn't work, and the question would be: is there a way to do it?Fortunately, YES!  and is not very difficult although a little more convoluted than our simple IEnumerable return value. Maybe in the future this scenario will be automatically detected and supported in MVC/WebApi.The solution to our needs is to use a very handy class named PushStreamContent and then our method signature needs to change to accommodate this, returning an HttpResponseMessage instead of our previously used IEnumerable<>. The final code will be something like this: public HttpResponseMessage Get([FromUri] int accountId)         {             HttpResponseMessage response = Request.CreateResponse();             // Create push content with a delegate that will get called when it is time to write out              // the response.             response.Content = new PushStreamContent(                 async (outputStream, httpContent, transportContext) =>                 {                     try                     {                         // Execute the command and get a reader                         using (var reader = GetMetadataListReader(accountId))                         {                             // Read rows asynchronously, put data into buffer and write asynchronously                             while (await reader.ReadAsync())                             {                                 var rec = MapRecord(reader);                                 var str = await JsonConvert.SerializeObjectAsync(rec);                                 var buffer = UTF8Encoding.UTF8.GetBytes(str);                                 // Write out data to output stream                                 await outputStream.WriteAsync(buffer, 0, buffer.Length);                             }                         }                     }                     catch(HttpException ex)                     {                         if (ex.ErrorCode == -2147023667) // The remote host closed the connection.                          {                             return;                         }                     }                     finally                     {                         // Close output stream as we are done                         outputStream.Close();                     }                 });             return response;         } As an extra bonus, all involved classes used already support async/await asynchronous execution model, so taking advantage of that was very easy. Please note that the PushStreamContent class receives in its constructor a lambda (specifically an Action) and we decorated our anonymous method with the async keyword (not a very well known technique but quite handy) so we can await over the I/O intensive calls we execute like reading from the database reader, serializing our entity and finally writing to the output stream.  Well, if we execute the test again we will immediately notice that the a line returns immediately and then the rest of the server code is executed only when the client reads through the obtained stream, therefore we get low memory usage and far greater scalability for our beloved application serving big chunks of data.Enjoy!Andrés.        

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  • How to add a blank page to a pdf using iTextSharp?

    - by Russell
    I am trying to do something I thought would be quite simple, however it is not so straight forward and google has not helped. I am using iTextSharp to merge PDF documents (letters) together so they can all be printed at once. If a letter has an odd number of pages I need to append a blank page, so we can print the letters double-sided. Here is the basic code I have at the moment for merging all of the letters: // initiaise MemoryStream pdfStreamOut = new MemoryStream(); Document document = null; MemoryStream pdfStreamIn = null; PdfReader reader = null; int numPages = 0; PdfWriter writer = null; for int(i = 0;i < letterList.Count; i++) { byte[] myLetterData = ...; pdfStreamIn = new MemoryStream(myLetterData); reader = new PdfReader(pdfStreamIn); numPages = reader.NumberOfPages; // open the streams to use for the iteration if (i == 0) { document = new Document(reader.GetPageSizeWithRotation(1)); writer = PdfWriter.GetInstance(document, pdfStreamOut); document.Open(); } PdfContentByte cb = writer.DirectContent; PdfImportedPage page; int importedPageNumber = 0; while (importedPageNumber < numPages) { importedPageNumber++; document.SetPageSize(reader.GetPageSizeWithRotation(importedPageNumber)); document.NewPage(); page = writer.GetImportedPage(reader, importedPageNumber); cb.AddTemplate(page, 1f, 0, 0, 1f, 0, 0); } } I have tried using: document.SetPageSize(reader.GetPageSizeWithRotation(1)); document.NewPage(); at the end of the for loop for an odd number of pages without success. Any help would be much appreciated!

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  • C# - InvalidCastException when fetching double from sqlite

    - by Irro
    I keep getting a InvalidCastException when I'm fetching any double from my SQLite database in C#. The exception says "Specified cast is not valid." I am able to see the value in a SQL manager so I know it exists. It is possible to fetch Strings (VARCHARS) and ints from the database. I'm also able to fetch the value as an object but then I get "66.0" when it's suppose to be "66,8558604947586" (latitude coordination). Any one who knows how to solve this? My code: using System.Data.SQLite; ... SQLiteConnection conn = new SQLiteConnection(@"Data Source=C:\\database.sqlite; Version=3;"); conn.Open(); SQLiteDataReader reader = getReader(conn, "SELECT * FROM table"); //These are working String name = reader.GetString(1); Int32 value = reader.GetInt32(2); //This is not working Double latitude = reader.getDouble(3); //This gives me wrong value Object o = reader[3]; //or reader["latitude"] or reader.getValue(3)

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  • Isolated storage misunderstand

    - by Costa
    Hi this is a discussion between me and me to understand isolated storage issue. can you help me to convince me about isolated storage!! This is a code written in windows form app (reader) that read the isolated storage of another win form app (writer) which is signed. where is the security if the reader can read the writer's file, I thought only signed code can access the file! If all .Net applications born equal and have all permissions to access Isolated storage, where is the security then? If I can install and run Exe from isolated storage, why I don't install a virus and run it, I am trusted to access this area. but the virus or what ever will not be trusted to access the rest of file system, it only can access the memory, and this is dangerous enough. I cannot see any difference between using app data folder to save the state and using isolated storage except a long nasty path!! I want to try give low trust to Reader code and retest, but they said "Isolated storage is actually created for giving low trusted application the right to save its state". Reader code: private void button1_Click(object sender, EventArgs e) { String path = @"C:\Documents and Settings\All Users\Application Data\IsolatedStorage\efv5cmbz.ewt\2ehuny0c.qvv\StrongName.5v3airc2lkv0onfrhsm2h3uiio35oarw\AssemFiles\toto12\ABC.txt"; StreamReader reader = new StreamReader(path); var test = reader.ReadLine(); reader.Close(); } Writer: private void button1_Click(object sender, EventArgs e) { IsolatedStorageFile isolatedFile = IsolatedStorageFile.GetMachineStoreForAssembly(); isolatedFile.CreateDirectory("toto12"); IsolatedStorageFileStream isolatedStorage = new IsolatedStorageFileStream(@"toto12\ABC.txt", System.IO.FileMode.Create, isolatedFile); StreamWriter writer = new StreamWriter(isolatedStorage); writer.WriteLine("Ana 2akol we ashrab kai a3eesh wa akbora"); writer.Close(); writer.Dispose(); }

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  • Encapsulate update method inside of object or have method which accepts an object to update

    - by Tom
    Hi, I actually have 2 questions related to each other: I have an object (class) called, say MyClass which holds data from my database. Currently I have a list of these objects ( List < MyClass ) that resides in a singleton in a "communal area". I feel it's easier to manage the data this way and I fail to see how passing a class around from object to object is beneficial over a singleton (I would be happy if someone can tell me why). Anyway, the data may change in the database from outside my program and so I have to update the data every so often. To update the list of the MyClass I have a method called say, Update, written in another class which accepts a list of MyClass. This updates all the instances of MyClass in the list. However would it be better instead to encapulate the Update() method inside the MyClass object, so instead I would say foreach(MyClass obj in MyClassList) { obj.update(); } What is a better implementation and why? The update method requires a XML reader. I have written an XML reader class which is basically a wrapper over the standard XML reader the language natively provides which provides application specific data collection. Should the XML reader class be in anyway in the "inheritance path" of the MyClass object - the MyClass objects inherits from the XML reader because it uses a few methods. I can't see why it should. I don't like the idea of declaring an instance of the XML Reader class inside of MyClass and an MyClass object is meant to be a simple "record" from the database and I feel giving it loads of methods, other object instances is a bit messy. Perhaps my XML reader class should be static but C#'s native XMLReader isn't static.? Any comments would be greatly appreciated Thanks Thomas

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  • PHP XMLREADER - QUESTION

    - by Matias
    Hi Guys, I am pretty new to xml parsing and I am using XMLREADER to parse a huge file. Given the following XML (sample): <hotels> <hotel> <name>Bla1</name> </hotel> <hotel> <name>Bla2</name> </hotel> </hotels> And then the XMLREADER in PHP which pulls up the values to my Database: $reader = new XMLReader(); $reader->open('hotels.xml'); while ($reader->read()) { if ($reader->name == "name") { $reader->read(); mysql_query("INSERT INTO MyHotels (hotelName) VALUES (\"$reader->value\")"); } } $reader->close(); The problem is that I've got a single empty row between each of the parsed nodes!! Not sure why this happens! | ID | hotelName | | 1 | Bla1 | | 2 | | | 3 | Bla2 | | 4 | | Help is greatly appreciated.

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  • Compare system date with a date field in SQL

    - by JeT_BluE
    I am trying to compare a date record in SQL Server with the system date. In my example the user first register with his name and date of birth which are then stored in the database. The user than logs into the web application using his name only. After logging in, his name is shown on the side where it says "Welcome "player name" using Sessions. What I am trying to show in addition to his name is a message saying "happy birthday" if his date of birth matches the system date. I have tried working with System.DateTime.Now, but what I think is that it is also comparing the year, and what I really want is the day and the month only. I would really appreciate any suggestion or help. CODE In Login page: protected void Button1_Click(object sender, EventArgs e) { String name = TextBox1.Text; String date = System.DateTime.Today.ToShortDateString(); SqlConnection myconn2 = new SqlConnection(ConfigurationManager.ConnectionStrings["User"].ToString()); SqlCommand cmd2 = new SqlCommand(); SqlDataReader reader; myconn2.Open(); cmd2 = new SqlCommand("Select D_O_B from User WHERE Username = @username", myconn2); cmd2.Parameters.Add("@username", SqlDbType.NVarChar).Value = name; cmd2.Connection = myconn2 cmd2.ExecuteNonQuery(); reader = cmd2.ExecuteReader(); while (reader.Read().ToString() == date) { Session["Birthday"] = "Happy Birthday"; } } Note: I using the same reader in the code above this one, but the reader here is with a different connection. Also, reader.Read() is different than reader.HasRows? Code in Web app Page: string date = (string)(Session["Birthday"]); // Retrieving the session Label6.Text = date;

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  • Adding a Way To preserve A Comma In A CSV To DataTable Function

    - by Nick LaMarca
    I have a function that converts a .csv file to a datatable. One of the columns I am converting is is a field of names that have a comma in them i.e. "Doe, John" when converting the function treats this as 2 seperate fields because of the comma. I need the datatable to hold this as one field Doe, John in the datatable. Function CSV2DataTable(ByVal filename As String, ByVal sepChar As String) As DataTable Dim reader As System.IO.StreamReader Dim table As New DataTable Dim colAdded As Boolean = False Try ''# open a reader for the input file, and read line by line reader = New System.IO.StreamReader(filename) Do While reader.Peek() >= 0 ''# read a line and split it into tokens, divided by the specified ''# separators Dim tokens As String() = System.Text.RegularExpressions.Regex.Split _ (reader.ReadLine(), sepChar) ''# add the columns if this is the first line If Not colAdded Then For Each token As String In tokens table.Columns.Add(token) Next colAdded = True Else ''# create a new empty row Dim row As DataRow = table.NewRow() ''# fill the new row with the token extracted from the current ''# line For i As Integer = 0 To table.Columns.Count - 1 row(i) = tokens(i) Next ''# add the row to the DataTable table.Rows.Add(row) End If Loop Return table Finally If Not reader Is Nothing Then reader.Close() End Try End Function

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  • How to "pin" C++/CLI pointers

    - by Kumar
    I am wrapping up a class which reading a custom binary data file and makes the data available to a .net/c# class However a couple of lines down the code, i start getting the memory access violation error which i believe is due to the GC moving memory around, the class is managed Here's the code if ( ! reader.OpenFile(...) ) return ; foreach(string fieldName in fields) { int colIndex = reader.GetColIndex( fieldName ); int colType = reader.GetColType( colIndex ); // error is raised here on 2nd iteration } for ( int r = 0 ; r < reader.NumFields(); r++ ) { foreach(string fieldName in fields) { int colIndex = reader.GetColIndex( fieldName ); int colType = reader.GetColType( colIndex ); // error is raised here on 2nd iteration switch ( colType ) { case 0 : // INT processField( r, fieldName, reader.GetInt(r,colIndex) ); break ; .... } } } .... i've looked at interior_ptr, pin_ptr but they give an error c3160 cannot be in a managed class Any workaround ? BTW, this is my 1st C++ program in a very long time !

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