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• Sharing rails fragments between formats

  - by Julian

  Hi I'm toying with mobile_fu and want to share some fragments between the different views. E.g. views/ item/ view.html.erb view.mobile.rb shared/ _common.erb In both view.html.erb and view.mobile.erb I want to share the same fragment '_common.erb' without having to specify the format (should you ever have to specify the format inside a fragment? It doesn't seem like The Rails Way?). Let's say for arguments's sake it's because it's in a helper or whatever -- the point is that I need to share fragments in a 'well-defined and Railsy way' across formats. Let's take this fairly innocuous snippet <% render :fragment => 'shared/common' %> I've tried 3 file name conventions: _common.html.erb only works for html /item/view/xx fails with 'shared/_common.erb not found') however _common.erb fails for html and works for mobile (maybe mobile_fu is doing something wacky?) -- same error as for .html.erb version above _common.rhtml does work for both I'm thinking that: that rhtml works for both is a legacy hack and I'm loathe to rename all the shared fragments .rhtml to get the behaviour I want. Any feedback gratefully welcome! Including 'you fundamentally don't understand how Rails works please RTFM here: http://....' :)

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• Is there a design pattern to cut down on code duplication when subclassing Activities in Android?

  - by Daniel Lew

  I've got a common task that I do with some Activities - downloading data then displaying it. I've got the downloading part down pat; it is, of course, a little tricky due to the possibility of the user changing the orientation or cancelling the Activity before the download is complete, but the code is there. There is enough code handling these cases such that I don't want to have to copy/paste it to each Activity I have, so I thought to create an abstract subclass Activity itself such that it handles a single background download which then launches a method which fills the page with data. This all works. The issue is that, due to single inheritance, I am forced to recreate the exact same class for any other type of Activity - for example, I use Activity, ListActivity and MapActivity. To use the same technique for all three requires three duplicate classes, except each extends a different Activity. Is there a design pattern that can cut down on the code duplication? As it stands, I have saved much duplication already, but it pains me to see the exact same code in three classes just so that they each subclass a different type of Activity.

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• File upload issue

  - by Varun

  I am working on a PHP based, ticket management system. While creating a ticket, one can upload an attachment. I want to put a limit (say 10 MB) per file upload. To implement this I plan the following- 1. In php.ini set post_max_size = 10M 2.In PHP script which receives the POST- Since the file is larger than post_max_size, $_FILES[] will be empty. But I can still check the content-length header and discard the upload, if size more than 10M. While testing this I tried uploading a file of 1 GB and analysed the http traffic and this is what I found. - the entire 1 GB data is first uploaded to a to the server temporarily and discarded once the http request completes. Though I couldn't exactly find out where the file was getting saved(as it was not there in the temporary directory in the server.), but my http traffic analyzer showed that the browser did send 1 GB data to the server. - the PHP script execution started only after completion of the http request(i.e after uploading the entire 1 GB) Now I have 2 concerns: a) People may exploit my server bandwidth by trying to upload large file, which I will have to discard anyways. b) Even worse, if someone starts uploading a huge file (say 100 GB), entire 100 GB data is first uploaded to the server temporarily, that means for that period, it will consume that much of memory on my server. What's the common solution for this. Am I missing something here?

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• TFS2010 API - Which server event fires when checkin notes are changed?

  - by user3708981

  I've written a TFS plugin that impliments the ISubscribe interface, and creates an external ticket base off of the contents of a check-in note. What I would like to do, if when I go back through older TFS check-ins in VS and edit a check-in note, the plugin would process that event and create an external ticket retroactively. What event / SubscribedType do I need to subscribe to in order for ProcessEvents to fire? My stubbed out code - using Microsoft.TeamFoundation.Client; using Microsoft.TeamFoundation.Common; using Microsoft.TeamFoundation.VersionControl.Client; // From C:\Program Files\Microsoft Team Foundation Server 2010\Tools\ using Microsoft.TeamFoundation.Framework.Server; using Microsoft.TeamFoundation.VersionControl.Server; using Changeset = Microsoft.TeamFoundation.VersionControl.Server.Changeset; public class EmbeddedWorkItemEventHandler : ISubscriber { const string EVENT_NAME = "TicketEvent"; const string APP_LOG = "Application"; public Type[] SubscribedTypes() { return new Type[1] { typeof(CheckinNotification) }; // What else do I need here? } public string Name { get { return EVENT_NAME; } } public SubscriberPriority Priority { get { return SubscriberPriority.Normal; } } public EventNotificationStatus ProcessEvent(TeamFoundationRequestContext requestContext, NotificationType notificationType, object notificationEventArgs, out int statusCode, out string statusMessage, out ExceptionPropertyCollection properties) { // Create the event source, if it doesn't exist if (!System.Diagnostics.EventLog.SourceExists(EVENT_NAME)) { System.Diagnostics.EventLog.CreateEventSource(EVENT_NAME, APP_LOG); } statusCode = 0; properties = null; statusMessage = String.Empty; string ErrorLine = ""; try { // Here we'll validate the Ticket name if (notificationType == NotificationType.DecisionPoint && notificationEventArgs is CheckinNotification) { //Check-in blocking logic here. } else if (notificationType == NotificationType.Notification && notificationEventArgs is CheckinNotification) { // Tickets on check-in here. } } Catch { // Error checking } return EventNotificationStatus.ActionPermitted; }

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• How to accommodate for the different screen resolution of iPhone 4?

  - by mystify

  This is a programming question! Read on before you vote to close! According to Apple, iPhone 4 has a new screen resolution: 3.5-inch (diagonal) widescreen Multi-Touch display 960-by-640-pixel resolution at 326 ppi This little detail affects our apps in a heavy way. Most of the demo apps on the net have one thing in common: They position views in the believe that the screen has a fixed size of 320 x 480 pixels. So what most -if not all- developers do is: They designed everything in such a way, that a touchable area is -for example- 50 x 50 pixels big. Just enough to tap it. Things have been positioned relative to the upper left, to reach a specific position on screen - let's say the center, or somewhere at the bottom. Edit: It seems Apple has integrated an switch that allows to tell if an app is highRes or not. Nice. When we develop high-resolution apps, probably they won't work on older devices. And if they did, they would suffer a lot from 4-times the size of any image, having to scale them down in memory. This is community wiki. Just add anything that you think is relevant to this huge problem (constant screen res was one of the main reasons why I didn't go for Android!!).

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• avoiding code duplication in Rails 3 models

  - by Dustin Frazier

  I'm working on a Rails 3.1 application where there are a number of different enum-like models that are stored in the database. There is a lot of identical code in these models, as well as in the associated controllers and views. I've solved the code duplication for the controllers and views via a shared parent controller class and the new view/layout inheritance that's part of Rails 3. Now I'm trying to solve the code duplication in the models, and I'm stuck. An example of one of my enum models is as follows: class Format < ActiveRecord::Base has_and_belongs_to_many :videos attr_accessible :name validates :name, presence: true, length: { maximum: 20 } before_destroy :verify_no_linked_videos def verify_no_linked_videos unless self.videos.empty? self.errors[:base] << "Couldn't delete format with associated videos." raise ActiveRecord::RecordInvalid.new self end end end I have four or five other classes with nearly identical code (the association declaration being the only difference). I've tried creating a module with the shared code that they all include (which seems like the Ruby Way), but much of the duplicate code relies on ActiveRecord, so the methods I'm trying to use in the module (validate, attr_accessible, etc.) aren't available. I know about ActiveModel, but that doesn't get me all the way there. I've also tried creating a common, non-persistent parent class that subclasses ActiveRecord::Base, but all of the code I've seen to accomplish this assumes that you won't have subclasses of your non-persistent class that do persist. Any suggestions for how best to avoid duplicating these identical lines of code across many different enum models?

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• Client-Side caching on IIS7 doesn't seem to work

  - by thomasbtv

  I have set content caching on a specific folder by following the local web.config method. I don't think it works, and I would like to fix this. I activate the cache using the IIS / HTTP Headers / Common headers feature. I set them to 1 day of expiration. I opened a page with Google Chrome in private navigation, and then open the Network tab in the console. The first time I load the page, everything loads from the site, obviously. If I refresh the page, I see 2 types of loading in the Network console: the files from Google and Facebook and such have a status of 200, and a size of (from cache). the files from the folder for which I set the caching have a status of 304 and their size is displayed. So, I guess the caching setting doesn't work? Or does the 304 response means that it's loaded from the cache? If they aren't, how can I make it work ? Thanks !

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• Extracting DCT coefficients from encoded images and video

  - by misha

  Is there a way to easily extract the DCT coefficients (and quantization parameters) from encoded images and video? Any decoder software must be using them to decode block-DCT encoded images and video. So I'm pretty sure the decoder knows what they are. Is there a way to expose them to whomever is using the decoder? I'm implementing some video quality assessment algorithms that work directly in the DCT domain. Currently, the majority of my code uses OpenCV, so it would be great if anyone knows of a solution using that framework. I don't mind using other libraries (perhaps libjpeg, but that seems to be for still images only), but my primary concern is to do as little format-specific work as possible (I don't want to reinvent the wheel and write my own decoders). I want to be able to open any video/image (H.264, MPEG, JPEG, etc) that OpenCV can open, and if it's block DCT-encoded, to get the DCT coefficients. In the worst case, I know that I can write up my own block DCT code, run the decompressed frames/images through it and then I'd be back in the DCT domain. That's hardly an elegant solution, and I hope I can do better. Presently, I use the fairly common OpenCV boilerplate to open images: IplImage *image = cvLoadImage(filename); // Run quality assessment metric The code I'm using for video is equally trivial: CvCapture *capture = cvCaptureFromAVI(filename); while (cvGrabFrame(capture)) { IplImage *frame = cvRetrieveFrame(capture); // Run quality assessment metric on frame } cvReleaseCapture(&capture); In both cases, I get a 3-channel IplImage in BGR format. Is there any way I can get the DCT coefficients as well?

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• Determine asymmetric latencies in a network

  - by BeeOnRope

  Imagine you have many clustered servers, across many hosts, in a heterogeneous network environment, such that the connections between servers may have wildly varying latencies and bandwidth. You want to build a map of the connections between servers my transferring data between them. Of course, this map may become stale over time as the network topology changes - but lets ignore those complexities for now and assume the network is relatively static. Given the latencies between nodes in this host graph, calculating the bandwidth is a relative simply timing exercise. I'm having more difficulty with the latencies - however. To get round-trip time, it is a simple matter of timing a return-trip ping from the local host to a remote host - both timing events (start, stop) occur on the local host. What if I want one-way times under the assumption that the latency is not equal in both directions? Assuming that the clocks on the various hosts are not precisely synchronized (at least that their error is of the the same magnitude as the latencies involved) - how can I calculate the one-way latency? In a related question - is this asymmetric latency (where a link is quicker in direction than the other) common in practice? For what reasons/hardware configurations? Certainly I'm aware of asymmetric bandwidth scenarios, especially on last-mile consumer links such as DSL and Cable, but I'm not so sure about latency. Added: After considering the comment below, the second portion of the question is probably better off on serverfault.

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• How to use a TFileStream to read 2D matrices into dynamic array?

  - by Robert Frank

  I need to read a large (2000x2000) matrix of binary data from a file into a dynamic array with Delphi 2010. I don't know the dimensions until run-time. I've never read raw data like this, and don't know IEEE so I'm posting this to see if I'm on track. I plan to use a TFileStream to read one row at a time. I need to be able to read as many of these formats as possible: 16-bit two's complement binary integer 32-bit two's complement binary integer 64-bit two's complement binary integer IEEE single precision floating-point For 32-bit two's complement, I'm thinking something like the code below. Changing to Int64 and Int16 should be straight forward. How can I read the IEEE? Am I on the right track? Any suggestions on this code, or how to elegantly extend it for all 4 data types above? Since my post-processing will be the same after reading this data, I guess I'll have to copy the matrix into a common format when done. I have no problem just having four procedures (one for each data type) like the one below, but perhaps there's an elegant way to use RTTI or buffers and then move()'s so that the same code works for all 4 datatypes? Thanks! type TRowData = array of Int32; procedure ReadMatrix; var Matrix: array of TRowData; NumberOfRows: Cardinal; NumberOfCols: Cardinal; CurRow: Integer; begin NumberOfRows := 20; // not known until run time NumberOfCols := 100; // not known until run time SetLength(Matrix, NumberOfRows); for CurRow := 0 to NumberOfRows do begin SetLength(Matrix[CurRow], NumberOfCols); FileStream.ReadBuffer(Matrix[CurRow], NumberOfCols * SizeOf(Int32)) ); end; end;

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• Difference between MVC FilterAttribute and Filter

  - by zaaaaphod

  I'm trying to write my own custom AuthorizationAttribute that uses DI. I'm using the MUNQ IoC provider for it's speed and have decided to use constructor injection on all my classes as opposed to post instatiation property binding (because I prefer it). I'm trying to write a custom IFilterProvider that will use my IoC container to return requests for filters (so that I can map concrete classes using the container). I've come up with the following. public class FilterProvider : IFilterProvider { private readonly IocContainer _container; public FilterProvider(IocContainer container) { _container = container; } public IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor) { var x = Enumerable.Union<Object>(_container.ResolveAll<IActionFilter>(), _container.ResolveAll<IAuthorizationFilter>()); foreach (Filter actionFilter in x) yield return new Filter(actionFilter, FilterScope.First, null); } } The above code will fail during the foreach because my objects that implement IAuthorizationFilter are based on FilterAttribute and not Filter My question is, what is the difference between Filter and FilterAttribute? I would have thought that there would have been a common link between them, unless I'm missing something. Another deeper question is, how come there is no IFilterAttributeProvider that would support IEnumerable GetFilters(...) Is there some other way that I should be using to resolve IAuthorizationFilter via my IoC container? Thank you very much for your help. Z

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• Obfuscator for .NET assembly (Maybe just a C++ obfuscator?)

  - by Pirate for Profit

  The software company I work for is using a ton of open source LGPL/BSD/MIT C++ code that we have written wrappers around to port "helper classes" into a .NET assembly, via C++/CLI. These libraries have wrapped old cryptic APIs into easy-to-use ones based on common sense, and will be very helpful for a lot of different tasks will be included in many future client's applications, and we might even license it to other software companies in the same field. So naturally we are tasked with looking into solutions for securing the code from prying eyes. What we're trying to do is stop the casual observer from seeing what's going on. Now I have hacked some crazy shit in EverQuest and other video games in my day so I know with enough tireless effort anything can be done. But we don't want to make it easy for whomever. To the point, besides the Visual Studio compiler's optimizations, is there's a C++ obfuscator or .NET assembly obfuscator (after it's been built o.O) or something that would scramble everything up, re-arrange data structures, string constants, etc. idk? And if such a thing exists, we'd be curious to know how that would impact performance, as some sections of code are time critical (funny saying that using a managed M$ framework).

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• Eclipse > Javascript > Code highlighting not working with Object Notation

  - by Redsandro

  I am using Eclipse Helios with PDT, and when I am editing JavaScript files with the default JavaScript Editor (JSDT), code highlighting (Mark Occurrences) is not working for half of the code, for example JSON-style (or Object Literal if you will) declarations. Little example: Foo = {}; Foo.Bar = Foo.Bar || {}; Foo.Bar = { bar: function(str) { alert(str) }, baz: function(str) { this.bar(str); // This bar *is* highlighted though } }; Foo.Bar.baz('text'); No Bar, bar or baz is highlighted. For now, I humbly edit the JavaScript part of projects in Notepad++ because it just highlights every occurrence of whatever is currently selected. Is there a common practice for Eclipse JavaScript developers to get code highlighting work correctly, using the popular Object Literal notation? An option or update I missed? -update- I have found that code highlighting depends on the code being properly outlined. Altough commonly used, Object Literal outlining still seems rare in javascript editors. the Spket Javascript Editor does partial Object Literal outlining, and the Aptana Javascript Editor does full Object Literal outlining. But both loses other important functionality. A quest for the editor with the least loss of functionality is currently in progress in this question.

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• Javascript inheritance: call super-constructor or use prototype chain?

  - by Jeremy S.

  Hi folks, quite recently I read about javascript call usage in MDC https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/call one linke of the example shown below, I still don't understand. Why are they using inheritance here like this Prod_dept.prototype = new Product(); is this necessary? Because there is a call to the super-constructor in Prod_dept() anyway, like this Product.call is this just out of common behaviour? When is it better to use call for the super-constructor or use the prototype chain? function Product(name, value){ this.name = name; if(value >= 1000) this.value = 999; else this.value = value; } function Prod_dept(name, value, dept){ this.dept = dept; Product.call(this, name, value); } Prod_dept.prototype = new Product(); // since 5 is less than 1000, value is set cheese = new Prod_dept("feta", 5, "food"); // since 5000 is above 1000, value will be 999 car = new Prod_dept("honda", 5000, "auto"); Thanks for making things clearer

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• Memory mapping of files and system cache behavior in WinXP

  - by Canopus

  Our application is memory intensive and deals with reading a large number of disk files. The total load can be more than 3 GB. There is a custom memory manager that uses memory mapped files to achieve reading of such a huge data. The files are mapped into the process memory space only when needed and with this the process memory is well under control. But what is observed is, with memory mapping, the system cache keeps on increasing until it occupies the available physical memory. This leads to the slowing down of the entire system. My question is how to prevent system cache from hogging the physical memory? I attempted to remove the file buffering (by using FILE_FLAG_NO_BUFFERING ), but with this, the read operations take considerable amount of time and slows down the application performance. How to achieve the scalability without sacrificing much on performance. What are the common techniques used in such cases? I dont have a good understanding of the WinXP OS caching behavior. Any good links explaining the same would also be helpful.

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• How can I make this simple C# generics factory work?

  - by Kevin Brassen

  I have this design: public interface IFactory<T> { T Create(); T CreateWithSensibleDefaults(); } public class AppleFactory : IFactory<Apple> { ... } public class BananaFactory : IFactory<Banana> { ... } // ... The fictitious Apple and Banana here do not necessarily share any common types (other than object, of course). I don't want clients to have to depend on specific factories, so instead, you can just ask a FactoryManager for a new type. It has a FactoryForType method: IFactory<T> FactoryForType<T>(); Now you can invoke the appropriate interface methods with something like FactoryForType<Apple>().Create(). So far, so good. But there's a problem at the implementation level: how do I store this mapping from types to IFactory<T>s? The naive answer is an IDictionary<Type, IFactory<T>>, but that doesn't work since there's no type covariance on the T (I'm using C# 3.5). Am I just stuck with an IDictionary<Type, object> and doing the casting manually?

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• SELECT product from subclass: How many queries do I need?

  - by Stefano

  I am building a database similar to the one described here where I have products of different type, each type with its own attributes. I report a short version for convenience product_type ============ product_type_id INT product_type_name VARCHAR product ======= product_id INT product_name VARCHAR product_type_id INT -> Foreign key to product_type.product_type_id ... (common attributes to all product) magazine ======== magazine_id INT title VARCHAR product_id INT -> Foreign key to product.product_id ... (magazine-specific attributes) web_site ======== web_site_id INT name VARCHAR product_id INT -> Foreign key to product.product_id ... (web-site specific attributes) This way I do not need to make a huge table with a column for each attribute of different product types (most of which will then be NULL) How do I SELECT a product by product.product_id and see all its attributes? Do I have to make a query first to know what type of product I am dealing with and then, through some logic, make another query to JOIN the right tables? Or is there a way to join everything together? (if, when I retrieve the information about a product_id there are a lot of NULL, it would be fine at this point). Thank you

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• breaking datetime into constituent parts ASP.NET MVC form

  - by nick

  hi guys, i have searched the web relentlessly for this and have not found anything - which is surprising because i would think it is such a common scenario! Basically, on my model i have a DateTime field which i wish the user to populate through a form. I am using the Html helper to render all other parts of the form (along with validation) So this question is in two parts... Html Helper Firstly, is there any way to use the Html helper to split the DateTime field to be rendered as the three constituent parts of a date: day, month, year (since i do not care about the time part). This could be rendered as text boxes, drop down lists or a combination of both. Model Binding And then when the form is posted, what is the best approach for binding back up to the model? I have seen Scott Hanselmann's solution to this, but it seems a little bloated for what i need - i was hoping for a slightly more elegant solution. Is it recommended to extend DefaultModelBinder and set that as default binder (since all dates would be handled in this way) or write a class that implements IModelBionder and set it as the default binder for the DateTime type? Thanks for all the help in advance :-) i'm loving MVC but it's infuriating me that something so trivial is causing so much headaches!

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• Reference remotely located assembly (web uri) from locally installed application?

  - by moonground.de

  Hi Stackoverflowers! :) We have a .NET application for Windows which is installed locally by Microsoft Installer. Now we have the need to use additional assemblies which are located online at our Web Servers. We'd like to refer to a remote uri like https://www.ourserver.com/OurProductName/ExternalLib.dll and reveal additional functionality, which is described roughly by a known common ("AddIn/Plugin") Interface. These are not 3rd Party Plugins, we just want be able to exchange parts of the application frequently, without the need to have frequent software updates. Our first idea was to add some kind of "remote refence" in Visual Studio by setting the path to the remote assembly uri. But Visual Studio downloaded the assembly immediately to a temporary directory, adding a reference to it. Our second attempt then, is simply using a WebRequest (or WebClient) to retrieve a binary stream of the Assembly, loading it "from image" by using Assembly.Load(...). This actually works, but is not very elegant and requires more additional programming for verification etc. We hoped Clickonce would provide useful techniques but apparently it's suitable for standalone applications only. (Correct me?) Is there a way (.net native or by framework/api) to reference remotely located assemblies? Thanks in advance and have a happy easter!

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• multi-threading in MFC

  - by kiddo

  Hello all,in my application there is a small part of function,in which it will read files to get some information,the number of filecount would be utleast 50,So I thought of implementing threading.Say if the user is giving 50 files,I wanted to separate it as 5 *10, 5 thread should be created,so that each thread can handle 10 files which can speed up the process.And also from the below code you can see that some variables are common.I read some articles about threading and I am aware that only one thread should access a variable/contorl at a me(CCriticalStiuation can be used for that).For me as a beginner,I am finding hard to imlplement what I have learned about threading.Somebody please give me some idea with code shown below..thanks in advance file read function:// void CMyClass::GetWorkFilesInfo(CStringArray& dataFilesArray,CString* dataFilesB, int* check,DWORD noOfFiles,LPWSTR path) { CString cFilePath; int cIndex =0; int exceptionInd = 0; wchar_t** filesForWork = new wchar_t*[noOfFiles]; int tempCheck; int localIndex =0; for(int index = 0;index < noOfFiles; index++) { tempCheck = *(check + index); if(tempCheck == NOCHECKBOX) { *(filesForWork+cIndex) = new TCHAR[MAX_PATH]; wcscpy(*(filesForWork+cIndex),*(dataFilesB +index)); cIndex++; } else//CHECKED or UNCHECKED { dataFilesArray.Add(*(dataFilesB+index)); *(check + localIndex) = *(check + index); localIndex++; } } WorkFiles(&cFilePath,dataFilesArray,filesForWork, path, cIndex); dataFilesArray.Add(cFilePath); *(check + localIndex) = CHECKED; }

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• How to accommodate for the next iPhones totally different screen resolution?

  - by mystify

  This is a programming question! Read on before you vote to close! According to Gizmodo, the next iPhone will have a new screen resolution: The 3.5-inch screen has a resolution of 960?×?640 pixels This little detail affects our apps in a heavy way. Most of the demo apps on the net have one thing in common: They position views in the believe that the screen has a fixed size of 320 x 480 pixels. So what most -if not all- developers do is: They designed everything in such a way, that a touchable area is -for example- 50 x 50 pixels big. Just enough to tap it. Things have been positioned relative to the upper left, to reach a specific position on screen - let's say the center, or somewhere at the bottom. So the big question is: How will the developers compensate their layout and graphics? Are there already solutions which can be used to calculate coordinates and sizes in a normalized manner, which then appear to be exactly the same when viewing them on a screen of any resolution, assuming at least that the aspect ration won't change? This is community wiki. Just add anything that you think is relevant to this huge problem (constant screen res was one of the main reasons why I didn't go for Android!!).

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• iPhone scrolling the view up when keyboard is open

  - by Rob

  I understand that this problem is incredibly common and I have read through quite a few answers but am having trouble understanding how the code works. This works: -(void)textFieldDidBeginEditing:(UITextField *)sender { if ([sender isEqual:txtLeaveAddyLine1]) { //move the main view, so that the keyboard does not hide it. if (self.view.frame.origin.y >= 0) { [self setViewMovedUp:YES]; } } } In this example, txtLeaveAddy is the very first UITextField that is hidden by the keyboard and it works like a charm. As I cycle through the text fields on the screen it scrolls up when the user enters into that txtLeaveAddyLine1 field. However, when I try to add the fields below the txtLeaveAddyLine1 field - nothing happens. For example: -(void)textFieldDidBeginEditing:(UITextField *)sender { if ([sender isEqual:txtLeaveAddyLine1]) { //move the main view, so that the keyboard does not hide it. if (self.view.frame.origin.y >= 0) { [self setViewMovedUp:YES]; } } if ([sender isEqual:txtLeaveAddyLine2]) { //move the main view, so that the keyboard does not hide it. if (self.view.frame.origin.y >= 0) { [self setViewMovedUp:YES]; } } } Am I not using this function correctly?

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• multiple models in Rails with a shared interface

  - by dfondente

  I'm not sure of the best structure for a particular situation in Rails. We have several types of workshops. The administration of the workshops is the same regardless of workshop type, so the data for the workshops is in a single model. We collect feedback from participants about the workshops, and the questionnaire is different for each type of workshop. I want to access the feedback about the workshop from the workshop model, but the class of the associated model will depend on the type of workshop. If I was doing this in something other than Rails, I would set up an abstract class for WorkshopFeedback, and then have subclasses for each type of workshop: WorkshopFeedbackOne, WorkshopFeedbackTwo, WorkshopFeedbackThree. I'm unsure how to best handle this with Rails. I currently have: class Workshop < ActiveRecord::Base has_many :workshop_feedbacks end class Feedback < ActiveRecord::Base belongs_to :workshop has_many :feedback_ones has_many :feedback_twos has_many :feedback_threes end class FeedbackOne < ActiveRecord::Base belongs_to :feedback end class FeedbackTwo < ActiveRecord::Base belongs_to :feedback end class FeedbackThree < ActiveRecord::Base belongs_to :feedback end This doesn't seem like to the cleanest way to access the feedback from the workshop model, as accessing the correct feedback will require logic investigating the Workshop type and then choosing, for instance, @workshop.feedback.feedback_one. Is there a better way to handle this situation? Would it be better to use a polymorphic association for feedback? Or maybe using a Module or Mixin for the shared Feedback interface? Note: I am avoiding using Single Table Inheritance here because the FeedbackOne, FeedbackTwo, FeedbackThree models do not share much common data, so I would end up with a large sparsely populated table with STI.

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• Can I strictly evaluate a boolean expression stored as a string in Java?

  - by D Lawson

  I would like to be able to evaluate an boolean expression stored as a string, like the following: "hello" == "goodbye" && 100 < 101 I know that there are tons of questions like this on SO already, but I'm asking this one because I've tried the most common answer to this question, BeanShell, and it allows for the evaluation of statements like this one "hello" == 100 with no trouble at all. Does anyone know of a FOSS parser that throws errors for things like operand mismatch? Or is there a setting in BeanShell that will help me out? I've already tried Interpreter.setStrictJava(true). Here's the code that I'm using currently: Interpreter interpreter = new Interpreter(); interpreter.setStrictJava(true); String testableCondition = "100 == \"hello\""; try { interpreter.eval("boolean result = ("+ testableCondition + ")"); System.out.println("result: "+interpreter.get("result")); if(interpreter.get("result") == null){ throw new ValidationFailure("Result was null"); } } catch (EvalError e) { e.printStackTrace(); throw new ValidationFailure("Eval error while parsing the condition"); }

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• Type-safe generic data structures in plain-old C?

  - by Bradford Larsen

  I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

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