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• How to use Mozilla ActiveX Control without registry

  - by Andrew McKinlay

  I've been using the IE Browser component that is part of Windows. But I'm running into problems with security settings. For example, users get security warnings on pages with Javascript. So I'm looking at using the Mozilla ActiveX control instead. It's especially nice because it has a compatible interface. It works well if I let it install the control in the registry. But my users don't always have administrator rights to install things in the registry. So I'm trying to figure out how to use the control without registry changes. I'm using DllGetClassObject to get the class factory (IID_ICLASSFACTORY) and then CoRegisterClassObject to register it. All the API calls appear to succeed. And when I create an AtlAxWin window with the CLSID, it also appears to work. But when I try to call Navigate on the AtlAxGetControl it doesn't work - the interface doesn't have Navigate. I would show the code but it's in an obscure language (Suneido) so it wouldn't mean much. An example in C or C++ would be easy for me to translate. Or an example in another dynamic language like Python or Ruby might be helpful. Obviously I'm doing something wrong. Maybe I'm passing the wrong thing to CoRegisterClassObject? The MSDN documentation isn't very clear on what to pass and I haven't found any good examples. Or if there is another approach, I'm ok with that too. Note: I'm using the AtlAxWin window class so I'm not directly creating the control and can't use this approach. Another option is registry free com with a manifest. But again, I couldn't find a good example, especially since I'm not using Visual Studio. I tried to use the MT manifest tool, but couldn't figure it out. I don't think I can use DLL redirection since that doesn't get around the registry issue AFAIK. Another possibility is using WebKit but it seems even harder to use.

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• Google Chart Number formatting

  - by MizAkita

  I need to format my pie and column charts to show the $ and comma in currency format ($###,###) when you hover over the charts. Right now, it is displaying the number and percentage but the number as #####.## here is my code. Any help would be appreciated. // Load the Visualization API and the piechart package. google.load('visualization', '1.0', {'packages':['corechart']}); // Set a callback to run when the Google Visualization API is loaded. google.setOnLoadCallback(drawChart); var formatter = new google.visualization.NumberFormat({ prefix: '$' }); formatter.format(data, 1); var options = { pieSliceText: 'value' }; // Callback that creates and populates a data table, // instantiates the pie chart, passes in the data and // draws it. function drawChart() { // REVENUE CHART - Create the data table. var data4 = new google.visualization.DataTable(); data4.addColumn('string', 'Status'); data4.addColumn('number', 'In Thousands'); data4.addRows([ ['Net tution & Fees', 213.818], ['Auxiliaries', 30.577], ['Government grants/contracts', 39.436], ['Private grants/gifts', 39.436], ['Investments', 10.083], ['Clinics', 14.353], ['Other', 5.337] ]); // EXPENSES CHART - Create the data table. var data5 = new google.visualization.DataTable(); data5.addColumn('string', 'Status'); data5.addColumn('number', 'Amount'); data5.addRows([ ['Instruction', 133.868], ['Sponsored Progams', 34.940], ['Auxiliaries', 30.064], ['Academic Support', 25.529], ['Depreciation & amortization', 18.548], ['Student Services', 22.626], ['Plant operations & maintenance', 18.105], ['Fundraising', 13.258], ['Geneal Administration', 11.628], ['Interest', 6.846], ['Student Aid', 1.886], ]); // ENDOWMENT CHART - Create the data table. var data6 = new google.visualization.DataTable(); data6.addColumn('string', 'Status'); data6.addColumn('number', 'In Millions'); data6.addRows([ ['2010', 178.7], ['2011', 211.693], ['2012', 199.3] ]); // Set REVENUE chart options var options4 = { is3D: true, fontName: 'Arial', colors:['#AFD8F8', '#F6BD0F', '#8BBA00', '#FF8E46', '#008E8E', '#CCCCCC', '#D64646', '#8E468E'], 'title':'', 'width':550, 'height':250}; // Set EXPENSES chart options var options5 = { is3D: true, fontName: 'Arial', colors:['#AFD8F8', '#F6BD0F', '#8BBA00', '#FF8E46', '#008E8E', '#CCCCCC', '#D64646', '#8E468E'], 'title':'', 'width':550, 'height':250}; // Set ENDOWMENT chart options var options6 = { is3D: true, fontName: 'Arial', colors:['#AFD8F8', '#F6BD0F', '#8BBA00', '#FF8E46', '#008E8E', '#CCCCCC', '#D64646', '#8E468E'], 'title':'', 'width':450, 'height':250}; // Instantiate and draw our chart, passing in some options. var chart4 = new google.visualization.PieChart(document.getElementById('chart_div4')); chart4.draw(data4, options4); var chart5 = new google.visualization.PieChart(document.getElementById('chart_div5')); chart5.draw(data5, options5); var chart6 = new google.visualization.ColumnChart(document.getElementById('chart_div6')); chart6.draw(data6, options6);}

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• A better UPDATE method in LINQ to SQL

  - by Refracted Paladin

  The below is a typical, for me, Update method in L2S. I am still fairly new to a lot of this(L2S & business app development) but this just FEELs wrong. Like there MUST be a smarter way of doing this. Unfortunately, I am having trouble visualizing it and am hoping someone can provide an example or point me in the right direction. To take a stab in the dark, would I have a Person Object that has all these fields as Properties? Then what, though? Is that redundant since L2S already mapped my Person Table to a Class? Is this just 'how it goes', that you eventually end up passing 30 parameters(or MORE) to an UPDATE statement at some point? For reference, this is a business app using C#, WinForms, .Net 3.5, and L2S over SQL 2005 Standard. Here is a typical Update Call for me. This is in a file(BLLConnect.cs) with other CRUD methods. Connect is the name of the DB that holds tblPerson When a user clicks save() this is what is eventually called with all of these fields having, potentially, been updated-- public static void UpdatePerson(int personID, string userID, string titleID, string firstName, string middleName, string lastName, string suffixID, string ssn, char gender, DateTime? birthDate, DateTime? deathDate, string driversLicenseNumber, string driversLicenseStateID, string primaryRaceID, string secondaryRaceID, bool hispanicOrigin, bool citizenFlag, bool veteranFlag, short ? residencyCountyID, short? responsibilityCountyID, string emailAddress, string maritalStatusID) { using (var context = ConnectDataContext.Create()) { var personToUpdate = (from person in context.tblPersons where person.PersonID == personID select person).Single(); personToUpdate.TitleID = titleID; personToUpdate.FirstName = firstName; personToUpdate.MiddleName = middleName; personToUpdate.LastName = lastName; personToUpdate.SuffixID = suffixID; personToUpdate.SSN = ssn; personToUpdate.Gender = gender; personToUpdate.BirthDate = birthDate; personToUpdate.DeathDate = deathDate; personToUpdate.DriversLicenseNumber = driversLicenseNumber; personToUpdate.DriversLicenseStateID = driversLicenseStateID; personToUpdate.PrimaryRaceID = primaryRaceID; personToUpdate.SecondaryRaceID = secondaryRaceID; personToUpdate.HispanicOriginFlag = hispanicOrigin; personToUpdate.CitizenFlag = citizenFlag; personToUpdate.VeteranFlag = veteranFlag; personToUpdate.ResidencyCountyID = residencyCountyID; personToUpdate.ResponsibilityCountyID = responsibilityCountyID; personToUpdate.EmailAddress = emailAddress; personToUpdate.MaritalStatusID = maritalStatusID; personToUpdate.UpdateUserID = userID; personToUpdate.UpdateDateTime = DateTime.Now; context.SubmitChanges(); } }

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• Google Docs iphone library error reporting

  - by phil harris

  I'm in the process of adding a Google Docs interface to my iPhone app, and I'm largely following the example in the GoogleDocs.m file from Tom Saxton's example app. The objective-c library I'm using is from http://code.google.com/p/gdata-objectivec-client/wiki/GDataObjCIntroduction The library file used is from gdata-objectivec-client-1.10.0.zip. This service:username:password method is a slight variant of the one found in the Saxton file GoogleDocs.m starting at line 351: - (void)service:(NSString *)username password:(NSString *)password { if(service == nil) { service = [[[GDataServiceGoogleDocs alloc] init] autorelease]; [service setUserAgent:s_strUserAgent]; [service setShouldCacheDatedData:NO]; [service setServiceShouldFollowNextLinks:NO]; (void)[service authenticateWithDelegate:self didAuthenticateSelector:@selector(ticket:authenticatedWithError:)]; } // update the username/password each time the service is requested if (username != nil && [username length] && password != nil && [password length]) [service setUserCredentialsWithUsername:username password:password]; else [service setUserCredentialsWithUsername:nil password:nil]; } // associated callback for service:username:password: method - (void)ticket:(GDataServiceTicket *)ticket authenticatedWithError:(NSError *)error { NSLog(@"%@",@"authenticatedWithError called"); if(error == nil) [self selectBackupRestore]; else { NSLog(@"error code(%d)", [error code]); NSLog(@"error domain(%d)", [error domain]); NSLog(@"localizedDescription(%@)", error.localizedDescription); NSLog(@"localizedFailureReason(%@)", error.localizedFailureReason); NSLog(@"localizedRecoveryOptions(%@)", error.localizedRecoveryOptions); NSLog(@"localizedRecoverySuggestion(%@)", error.localizedRecoverySuggestion); } } Please note the service:username:password method and the callback compile and run fine. The problem is that the callback is passing a non-nil NSError object. I added an NSLog() for every error reporting attribute of NSError and the (Xcode) log output of a test run is below. [Session started at 2010-05-27 12:27:16 -0700.] 2010-05-27 12:27:38.778 iFilebox[74596:207] authenticatedWithError called 2010-05-27 12:27:38.779 iFilebox[74596:207] error code(-1) 2010-05-27 12:27:38.780 iFilebox[74596:207] error domain(499324) 2010-05-27 12:27:38.781 iFilebox[74596:207] localizedDescription(Operation could not be completed. (com.google.GDataServiceDomain error -1.)) 2010-05-27 12:27:38.782 iFilebox[74596:207] localizedFailureReason((null)) 2010-05-27 12:27:38.782 iFilebox[74596:207] localizedRecoveryOptions((null)) 2010-05-27 12:27:38.783 iFilebox[74596:207] localizedRecoverySuggestion((null)) My essential question is in the error reporting. I was hoping the localizedDescription would be more specific of the error. All I get for the error code value is -1, and the only description of the error is "Operation could not be completed. (com.google.GDataServiceDomain error -1.". Not very helpful. Does anyone know what a GDataServiceDomain error -1 is? Where can I find a full list of all error codes returned, and a description of what they mean?

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• WPF: Improving Performance for Running on Older PCs

  - by Phil Sandler

  So, I'm building a WPF app and did a test deployment today, and found that it performed pretty poorly. I was surprised, as we are really not doing much in the way of visual effects or animations. I deployed on two machines: the fastest and the slowest that will need to run the application (the slowest PC has an Intel Celeron 1.80GHz with 2GB RAM). The application ran pretty well on the faster machine, but was choppy on the slower machine. And when I say "choppy", I mean the cursor jumped even just passing it over any open window of the app that had focus. I opened the Task Manager Performance window, and could see that the CPU usage jumped whenever the app had focus and the cursor was moving over it. If I gave focus to another (e.g. Excel), the CPU usage went back down after a second. This happened on both machines, but the choppiness was only noticeable on the slower machine. I had very limited time to tinker on the deployment machines, so didn't do a lot of detailed testing. The app runs fine on my development machine, but I also see the CPU spiking up to 10% there, just running the cursor over the window. I downloaded the WPF performance tool from MS and have been tinkering with it (on my dev machine). The docs say this about the "Frame Rate" metric in the Perforator tool: For applications without animation, this value should be near 0. The app is not doing any heavy animation, but the frame rate stays near 50 when the cursor is over any window. The screens I tested on have column headers in a grid that "highlight" and buttons that change color and appearance when scrolled over. Even moving the mouse on blank areas of the windows cause the same Frame rate and CPU usage (doesn't seem to be related to these minor animations). (Also, I am unable to figure out how to get anything but the two default tools--Perforator and Visual Profiler--installed into the WPF performance tool. That is probably a separate question). I also have Redgate's profiling tool, but I'm not sure if that can shed any light on rendering performance. So, I realize this is not an easy thing to troubleshoot without specifics or sample code (which I can't post). My questions are: What are some general things to look for (or avoid) in the code to improve performance? What steps can I take using the WPF performance tool to narrow down the problem? Is the PC spec listed above (Intel Celeron 1.80GHz with 2GB RAM) too slow to be running even vanilla WPF applications?

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• apply style to range of text with javascript in uiwebview

  - by drawnonward

  I am displaying some simple styled text as html in a UIWebView on iPhone. It is basically a series of paragraphs with the occasional strong or emphasized phrase. At runtime I need to apply styles to ranges of text. There are a few similar scenarios, one of which is highlighting search results. If the user has searched for "something" I would like to change the background color behind occurrences of the word, then later restore the original background. Is it possible to apply styles to ranges of text using javascript? A key part of this is also being able to unset the styles. There seem to be two likely paths to follow. One would be modifying some html in Objective-C and passing it through javascript as the new innerHTML of some container. The other would be to use javascript to directly manipulate DOM nodes. I could manipulate html, but that sounds tedious in Objective-C so I would rather manipulate the DOM if that is a reasonable approach. I am not that familiar with javascript and DOM so I do not know if it is a reasonable approach. I wrote some routines to translate between text ranges and node ranges with offsets. So if I start with text range 100-200 and that starts in one paragraph and ends in a third, I can get the text nodes and the offsets within the nodes that represent the given text range. I just need a way to split a text node at an offset in the text. Currently I just apply styles to the paragraphs containing the text range. A few notes: straight javascript please, no external frameworks like jquery. the changes never need to be written to disk. the changes should be undoable or at least removable. the styles to apply already exist in a css file. it needs to work in iPhone 3.0 and forward. all the source files are shipped with the app. please be verbose. Thanks for any suggestions.

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• Should I skip authorization, with CanCan, of an action that instantiates a resource?

  - by irkenInvader

  I am writing a web app to pick random lists of cards from larger, complete sets of cards. I have a Card model and a CardSet model. Both models have a full RESTful set of 7 actions (:index, :new, :show, etc). The CardSetsController has an extra action for creating random sets: :random. # app/models/card_set.rb class CardSet < ActiveRecord::Base belongs_to :creator, :class_name => "User" has_many :memberships has_many :cards, :through => :memberships # app/models/card.rb class Card < ActiveRecord::Base belongs_to :creator, :class_name => "User" has_many :memberships has_many :card_sets, :through => :memberships I have added Devise for authentication and CanCan for authorizations. I have users with an 'editor' role. Editors are allowed to create new CardSets. Guest users (Users who have not logged in) can only use the :index and :show actions. These authorizations are working as designed. Editors can currently use both the :random and the :new actions without any problems. Guest users, as expected, cannot. # app/controllers/card_sets_controller.rb class CardSetsController < ApplicationController before_filter :authenticate_user!, :except => [:show, :index] load_and_authorize_resource I want to allow guest users to use the :random action, but not the :new action. In other words, they can see new random sets, but not save them. The "Save" button on the :random action's view is hidden (as designed) from the guest users. The problem is, the first thing the :random action does is build a new instance of the CardSet model to fill out the view. When cancan tries to load_and_authorize_resource a new CardSet, it throws a CanCan::AccessDenied exception. Therefore, the view never loads and the guest user is served a "You need to sign in or sign up before continuing" message. # app/controllers/card_sets_controllers.rb def random @card_set = CardSet.new( :name => "New Set of 10", :set_type => "Set of 10" ) I realize that I can tell load_and_authorize_resource to skip the :random action by passing :except => :random to the call, but that just feels "wrong" for some reason. What's the "right" way to do this? Should I create the new random set without instantiating a new CardSet? Should I go ahead and add the exception?

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• Supporting multiple instances of a plugin DLL with global data

  - by Bruno De Fraine

  Context: I converted a legacy standalone engine into a plugin component for a composition tool. Technically, this means that I compiled the engine code base to a C DLL which I invoke from a .NET wrapper using P/Invoke; the wrapper implements an interface defined by the composition tool. This works quite well, but now I receive the request to load multiple instances of the engine, for different projects. Since the engine keeps the project data in a set of global variables, and since the DLL with the engine code base is loaded only once, loading multiple projects means that the project data is overwritten. I can see a number of solutions, but they all have some disadvantages: You can create multiple DLLs with the same code, which are seen as different DLLs by Windows, so their code is not shared. Probably this already works if you have multiple copies of the engine DLL with different names. However, the engine is invoked from the wrapper using DllImport attributes and I think the name of the engine DLL needs to be known when compiling the wrapper. Obviously, if I have to compile different versions of the wrapper for each project, this is quite cumbersome. The engine could run as a separate process. This means that the wrapper would launch a separate process for the engine when it loads a project, and it would use some form of IPC to communicate with this process. While this is a relatively clean solution, it requires some effort to get working, I don't now which IPC technology would be best to set-up this kind of construction. There may also be a significant overhead of the communication: the engine needs to frequently exchange arrays of floating-point numbers. The engine could be adapted to support multiple projects. This means that the global variables should be put into a project structure, and every reference to the globals should be converted to a corresponding reference that is relative to a particular project. There are about 20-30 global variables, but as you can imagine, these global variables are referenced from all over the code base, so this conversion would need to be done in some automatic manner. A related problem is that you should be able to reference the "current" project structure in all places, but passing this along as an extra argument in each and every function signature is also cumbersome. Does there exist a technique (in C) to consider the current call stack and find the nearest enclosing instance of a relevant data value there? Can the stackoverflow community give some advice on these (or other) solutions?

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• Using Core Data Concurrently and Reliably

  - by John Topley

  I'm building my first iOS app, which in theory should be pretty straightforward but I'm having difficulty making it sufficiently bulletproof for me to feel confident submitting it to the App Store. Briefly, the main screen has a table view, upon selecting a row it segues to another table view that displays information relevant for the selected row in a master-detail fashion. The underlying data is retrieved as JSON data from a web service once a day and then cached in a Core Data store. The data previous to that day is deleted to stop the SQLite database file from growing indefinitely. All data persistence operations are performed using Core Data, with an NSFetchedResultsController underpinning the detail table view. The problem I am seeing is that if you switch quickly between the master and detail screens several times whilst fresh data is being retrieved, parsed and saved, the app freezes or crashes completely. There seems to be some sort of race condition, maybe due to Core Data importing data in the background whilst the main thread is trying to perform a fetch, but I'm speculating. I've had trouble capturing any meaningful crash information, usually it's a SIGSEGV deep in the Core Data stack. The table below shows the actual order of events that happen when the detail table view controller is loaded: Main Thread Background Thread viewDidLoad Get JSON data (using AFNetworking) Create child NSManagedObjectContext (MOC) Parse JSON data Insert managed objects in child MOC Save child MOC Post import completion notification Receive import completion notification Save parent MOC Perform fetch and reload table view Delete old managed objects in child MOC Save child MOC Post deletion completion notification Receive deletion completion notification Save parent MOC Once the AFNetworking completion block is triggered when the JSON data has arrived, a nested NSManagedObjectContext is created and passed to an "importer" object that parses the JSON data and saves the objects to the Core Data store. The importer executes using the new performBlock method introduced in iOS 5: NSManagedObjectContext *child = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; [child setParentContext:self.managedObjectContext]; [child performBlock:^{ // Create importer instance, passing it the child MOC... }]; The importer object observes its own MOC's NSManagedObjectContextDidSaveNotification and then posts its own notification which is observed by the detail table view controller. When this notification is posted the table view controller performs a save on its own (parent) MOC. I use the same basic pattern with a "deleter" object for deleting the old data after the new data for the day has been imported. This occurs asynchronously after the new data has been fetched by the fetched results controller and the detail table view has been reloaded. One thing I am not doing is observing any merge notifications or locking any of the managed object contexts or the persistent store coordinator. Is this something I should be doing? I'm a bit unsure how to architect this all correctly so would appreciate any advice.

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• Unable to read data from the transport connection: the connection was closed

  - by webdreamer

  The exception is Remoting Exception - Authentication Failure. The detailed message says "Unable to read data from the transport connection: the connection was closed." I'm having trouble with creating two simple servers that can comunicate as remote objects in C#. ServerInfo is just a class I created that holds the IP and Port and can give back the address. It works fine, as I used it before, and I've debugged it. Also the server is starting just fine, no exception is thrown, and the channel is registered without problems. I'm using Forms to do the interfaces, and call some of the methods on the server, but didn't find any problems in passing the parameters from the FormsApplication to the server when debugging. All seems fine in that chapter. public ChordServerProgram() { RemotingServices.Marshal(this, "PADIBook"); nodeInt = 0; } public void startServer() { try { serverChannel = new TcpChannel(serverInfo.Port); ChannelServices.RegisterChannel(serverChannel, true); } catch (Exception e) { Console.WriteLine(e.ToString()); } } I run two instances of this program. Then startNode is called on one of the instances of the application. The port is fine, the address generated is fine as well. As you can see, I'm using the IP for localhost, since this server is just for testing purposes. public void startNode(String portStr) { IPAddress address = IPAddress.Parse("127.0.0.1"); Int32 port = Int32.Parse(portStr); serverInfo = new ServerInfo(address, port); startServer(); //node = new ChordNode(serverInfo,this); } Then, in the other istance, through the interface again, I call another startNode method, giving it a seed server to get information from. This is where it goes wrong. When it calls the method on the seedServer proxy it just got, a RemotingException is thrown, due to an authentication failure. (The parameter I'll want to get is the node, I'm just using the int to make sure the ChordNode class has nothing to do with this error.) public void startNode(String portStr, String seedStr) { IPAddress address = IPAddress.Parse("127.0.0.1"); Int32 port = Int32.Parse(portStr); serverInfo = new ServerInfo(address, port); IPAddress addressSeed = IPAddress.Parse("127.0.0.1"); Int32 portSeed = Int32.Parse(seedStr); ServerInfo seedInfo = new ServerInfo(addressSeed, portSeed); startServer(); ChordServerProgram seedServer = (ChordServerProgram)Activator.GetObject(typeof(ChordServerProgram), seedInfo.GetFullAddress()); // node = new ChordNode(serverInfo,this); int seedNode = seedServer.nodeInt; // node.chordJoin(seedNode.self); }

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• Java DriverManager Always Assigns My Driver

  - by JGB146

  I am writing a driver to act as a wrapper around two separate MySQL connections (to distributed databases). Basically, the goal is to enable interaction with my driver for all applications instead of requiring the application to sort out which database holds the desired data. Most of the code for this is in place, but I'm having a problem in that when I attempt to create connections via the MySQL Driver, the DriverManager is returning an instance of my driver instead of the MySQL Driver. I'd appreciate any tips on what could be causing this and what could be done to fix it! Below is a few relevant snippets of code. I can provide more, but there's a lot, so I'd need to know what else you want to see. First, from MyDriver.java: public MyDriver() throws SQLException { DriverManager.registerDriver(this); } public Connection connect(String url, Properties info) throws SQLException { try { return new MyConnection(info); } catch (Exception e) { return null; } } public boolean acceptsURL(String url) throws SQLException { if (url.contains("jdbc:jgb://")) { return true; } return false; } It is my understanding that this acceptsURL function will dictate whether or not the DriverManager deems my driver a suitable fit for a given URL. Hence it should only be passing connections from my driver if the URL contains "jdbc:jgb://" right? Here's code from MyConnection.java: Connection c1 = null; Connection c2 = null; /** *Constructors */ public DDBSConnection (Properties info) throws SQLException, Exception { info.list(System.out); //included for testing Class.forName("com.mysql.jdbc.Driver").newInstance(); String url1 = "jdbc:mysql://server1.com/jgb"; String url2 = "jdbc:mysql://server2.com/jgb"; this.c1 = DriverManager.getConnection( url1, info.getProperty("username"), info.getProperty("password")); this.c2 = DriverManager.getConnection( url2, info.getProperty("username"), info.getProperty("password")); } And this tells me two things. First, the info.list() call confirms that the correct user and password are being sent. Second, because we enter an infinite loop, we see that the DriverManager is providing new instances of my connection as matches for the mysql URLs instead of the desired mysql driver/connection. FWIW, I have separately tested implementations that go straight to the mysql driver using this exact syntax (al beit only one at a time), and was able to successfully interact with each database individually from a test application outside of my driver.

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• Retain a list of objects and pass it to the create/edit view when validation fails in ASP.NET MVC 2

  - by brainnovative

  I am binding a Foreign key property in my model. I am passing a list of possible values for that property in my model. The model looks something like this: public class UserModel { public bool Email { get; set; } public bool Name { get; set; } public RoleModel Role { get; set; } public IList<RoleModel> Roles { get; set; } } public class RoleModel { public string RoleName { get; set; } } This is what I have in the controller: public ActionResult Create() { IList<RoleModel> roles = RoleModel.FromArray(_userService.GetAllRoles()); UserModel model = new UserModel() { Roles = roles }; return View(model); } In the view I have: <div class="editor-label"> <%= Html.LabelFor(model => model.Role) %> </div> <div class="editor-field"> <%= Html.DropDownListFor(model => model.Role, new SelectList(Model.Roles, "RoleName", "RoleName", Model.Role))%> <%= Html.ValidationMessageFor(model => model.Role)%> </div> What do I need to do to get the list of roles back to my controller to pass it again to the view when validation fails. This is what I need: [HttpPost] public ActionResult Create(UserModel model) { if (ModelState.IsValid) { // insert logic here } //the validation fails so I pass the model again to the view for user to update data but model.Roles is null :( return View(model); } As written in the comments above I need to pass the model with the list of roles again to my view but model.Roles is null. Currently I ask the service again for the roles (model.Roles = RoleModel.FromArray(_userService.GetAllRoles());) but I don't want to add an extra overhead of getting the list from DB when I have already done that.. Anyone knows how to do it?

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• template pass by const reference

  - by 7vies

  Hi, I've looked over a few similar questions, but I'm still confused. I'm trying to figure out how to explicitly (not by compiler optimization etc) and C++03-compatible avoid copying of an object when passing it to a template function. Here is my test code: #include <iostream> using namespace std; struct C { C() { cout << "C()" << endl; } C(const C&) { cout << "C(C)" << endl; } ~C() { cout << "~C()" << endl; } }; template<class T> void f(T) { cout << "f<T>" << endl; } template<> void f(C c) { cout << "f<C>" << endl; } // (1) template<> void f(const C& c) { cout << "f<C&>" << endl; } // (2) int main() { C c; f(c); return 0; } (1) accepts the object of type C, and makes a copy. Here is the output: C() C(C) f<C> ~C() ~C() So I've tried to specialize with a const C& parameter (2) to avoid this, but this simply doesn't work (apparently the reason is explained in this question). Well, I could "pass by pointer", but that's kind of ugly. So is there some trick that would allow to do that somehow nicely? EDIT: Oh, probably I wasn't clear. I already have a templated function template<class T> void f(T) {...} But now I want to specialize this function to accept a const& to another object: template<> void f(const SpecificObject&) {...} But it only gets called if I define it as template<> void f(SpecificObject) {...}

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• How do I call a function name that is stored in a hash in Perl?

  - by Ether

  I'm sure this is covered in the documentation somewhere but I have been unable to find it... I'm looking for the syntactic sugar that will make it possible to call a method on a class whose name is stored in a hash (as opposed to a simple scalar): use strict; use warnings; package Foo; sub foo { print "in foo()\n" } package main; my %hash = (func => 'foo'); Foo->$hash{func}; If I copy $hash{func} into a scalar variable first, then I can call Foo->$func just fine... but what is missing to enable Foo->$hash{func} to work? (EDIT: I don't mean to do anything special by calling a method on class Foo -- this could just as easily be a blessed object (and in my actual code it is); it was just easier to write up a self-contained example using a class method.) EDIT 2: Just for completeness re the comments below, this is what I'm actually doing (this is in a library of Moose attribute sugar, created with Moose::Exporter): # adds an accessor to a sibling module sub foreignTable { my ($meta, $table, %args) = @_; my $class = 'MyApp::Dir1::Dir2::' . $table; my $dbAccessor = lcfirst $table; eval "require $class" or do { die "Can't load $class: $@" }; $meta->add_attribute( $table, is => 'ro', isa => $class, init_arg => undef, # don't allow in constructor lazy => 1, predicate => 'has_' . $table, default => sub { my $this = shift; $this->debug("in builder for $class"); ### here's the line that uses a hash value as the method name my @args = ($args{primaryKey} => $this->${\$args{primaryKey}}); push @args, ( _dbObject => $this->_dbObject->$dbAccessor ) if $args{fkRelationshipExists}; $this->debug("passing these values to $class -> new: @args"); $class->new(@args); }, ); } I've replaced the marked line above with this: my $pk_accessor = $this->meta->find_attribute_by_name($args{primaryKey})->get_read_method_ref; my @args = ($args{primaryKey} => $this->$pk_accessor); PS. I've just noticed that this same technique (using the Moose meta class to look up the coderef rather than assuming its naming convention) cannot also be used for predicates, as Class::MOP::Attribute does not have a similar get_predicate_method_ref accessor. :(

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• Android onActivityResult is always 0

  - by Dean

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

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• Calculate minimum moves to solve a puzzle

  - by Luke

  I'm in the process of creating a game where the user will be presented with 2 sets of colored tiles. In order to ensure that the puzzle is solvable, I start with one set, copy it to a second set, then swap tiles from one set to another. Currently, (and this is where my issue lies) the number of swaps is determined by the level the user is playing - 1 swap for level 1, 2 swaps for level 2, etc. This same number of swaps is used as a goal in the game. The user must complete the puzzle by swapping a tile from one set to the other to make the 2 sets match (by color). The order of the tiles in the (user) solved puzzle doesn't matter as long as the 2 sets match. The problem I have is that as the number of swaps I used to generate the puzzle approaches the number of tiles in each set, the puzzle becomes easier to solve. Basically, you can just drag from one set in whatever order you need for the second set and solve the puzzle with plenty of moves left. What I am looking to do is after I finish building the puzzle, calculate the minimum number of moves required to solve the puzzle. Again, this is almost always less than the number of swaps used to create the puzzle, especially as the number of swaps approaches the number of tiles in each set. My goal is to calculate the best case scenario and then give the user a "fudge factor" (i.e. 1.2 times the minimum number of moves). Solving the puzzle in under this number of moves will result in passing the level. A little background as to how I currently have the game configured: Levels 1 to 10: 9 tiles in each set. 5 different color tiles. Levels 11 to 20: 12 tiles in each set. 7 different color tiles. Levels 21 to 25: 15 tiles in each set. 10 different color tiles. Swapping within a set is not allowed. For each level, there will be at least 2 tiles of a given color (one for each set in the solved puzzle). Is there any type of algorithm anyone could recommend to calculate the minimum number of moves to solve a given puzzle?

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• manipulate variable made up of html before adding it to the dom (new in jQuery 1.4???)

  - by pedalpete

  I thought I had seen this in the first announcement of jQuery 1.4, but can't seem to find anything now. I have a calendar table which is built dynamically from a json ajax response. The table is built in a variable called putHtml. Currently, once the table is added to the DOM, I run a showEvents function which takes each event and adds it to the appropriate cell in the table. Unfortunately, when I have 100 events, that means I am updating the DOM 100 seperate times. Which is getting rather slow. I use the showEvents function to add events dynamically, so it would be really nice if I could just use the same function, and specify to look in the DOM for the cell to add the event to, or look in the variable (assuming I've got it right, and you can actually do this with jQuery). The code I use currenlty is this jQuery('div#calendars').append('putHtml.join('')); for(var e in thisCal.events){ showEvent(thisCal.events[e]); } What I had attempted to do instead was for(var e in thisCal.events){ showEvent(thisCal.events[e],putHtml); } jQuery('div#calendars').append('putHtml.join('')); the showEvents function looks like this function showEvents(event){ var eventDate=event.date; var eventTime=event.time; var eventGroup=event.group; var eventName=event.name; var eventType=event.type; var whereEvent=jQuery('div.a'+eventDate, 'table.'+eventGroup); var putEvent='<div class="event" id="a+'eventDate+'_'+eventTime+'">'+eventName+'</div>' jQuery(whereEvent, 'div#calendar').append(putEvent); if(eventType2){ jQuery(whereEvent, 'div#listings').append(putEvent); } } when attempting to manipulate the variable putHtml before adding to the dom, I was passing putHtml into the showEvent function, so instead of '(whereEvent, 'div#calendar'), I had (whereEvent, putHtml), but that didn't work. of course, the other method to accomplish this would be that when I make each cell, I iterate over the events json, and apply the appropriate html to the cell at the time, but that means repetitively running over the entire json in order to get the event to put in the cell. Is there another/better way to do something like this?

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• Linker Issues with boost::thread under linux using Eclipse and CMake

  - by OcularProgrammer

  I'm in the process of attempting to port some code across from PC to Ubuntu, and am having some issues due to limited experience developing under linux. We use CMake to generate all our build stuff. Under windows I'm making VS2010 projects, and under Linux I'm making Eclipse projects. I've managed to get my OpenCV stuff ported across successfully, but am having major headaches trying to port my threaded boost apps. Just so we're clear, the steps I have followed so-far on a clean Ubuntu 12 installation. (I've done 2 clean re-installs to try and fix potential library cock-ups, now I'm just giving up and asking): Install Eclipse and Eclipse CDT using my package manager Install CMake and CMake Gui using my package manager Install libboost-all-dev using my package manager So-far that's all I've done. I can create the eclipse project using CMake with no errors, so CMake is successfully finding my boost install. When I try and build through eclipse is when I get issues; The app I'm attempting to build uses boost::asio for some UDP I/O and boost::thread to create worker threads for the asio I/O services. I can successfully compile each module, but when I come to link I get spammed with errors such as: /usr/bin/c++ CMakeFiles/RE05DevelopmentDemo.dir/main.cpp.o CMakeFiles/RE05DevelopmentDemo.dir/RE05FusionListener/RE05FusionListener.cpp.o CMakeFiles/RE05DevelopmentDemo.dir/NewEye/NewEye.cpp.o -o RE05DevelopmentDemo -rdynamic -Wl,-Bstatic -lboost_system-mt -lboost_date_time-mt -lboost_regex-mt -lboost_thread-mt -Wl,-Bdynamic /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libboost_thread-mt.a(thread.o): In function `void boost::call_once<void (*)()>(boost::once_flag&, void (*)()) [clone .constprop.98]': make[2]: Leaving directory `/home/david/Code/Build/Support/RE05DevDemo' (.text+0xc8): undefined reference to `pthread_key_create' /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libboost_thread-mt.a(thread.o): In function `boost::this_thread::interruption_enabled()': (.text+0x540): undefined reference to `pthread_getspecific' make[1]: Leaving directory `/home/david/Code/Build/Support/RE05DevDemo' /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libboost_thread-mt.a(thread.o): In function `boost::this_thread::disable_interruption::disable_interruption()': (.text+0x570): undefined reference to `pthread_getspecific' /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libboost_thread-mt.a(thread.o): In function `boost::this_thread::disable_interruption::disable_interruption()': (.text+0x59f): undefined reference to `pthread_getspecific' Some Gotchas that I have collected from other StackOverflow posts and have already checked: The boost libs are all present at /usr/lib I am not getting any compile errors for inability to find the boost headers, so they must be getting found. I am trying to link statically, but I believe eclipse should be passing the correct arguments to make that happen since my CMakeLists.txt includes SET(Boost_USE_STATIC_LIBS ON) I'm officially out of ideas here, I have tried doing local builds of boost and a bunch of other stuff with no more success. I even re-installed Ubuntu to ensure I haven't completely fracked the libs directories and links with multiple weird versions or anything else. Any help would be muchly appreciated.

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• Specializing a template on a lambda in C++0x

  - by Tony A.

  I've written a traits class that lets me extract information about the arguments and type of a function or function object in C++0x (tested with gcc 4.5.0). The general case handles function objects: template <typename F> struct function_traits { template <typename R, typename... A> struct _internal { }; template <typename R, typename... A> struct _internal<R (F::*)(A...)> { // ... }; typedef typename _internal<decltype(&F::operator())>::<<nested types go here>>; }; Then I have a specialization for plain functions at global scope: template <typename R, typename... A> struct function_traits<R (*)(A...)> { // ... }; This works fine, I can pass a function into the template or a function object and it works properly: template <typename F> void foo(F f) { typename function_traits<F>::whatever ...; } int f(int x) { ... } foo(f); What if, instead of passing a function or function object into foo, I want to pass a lambda expression? foo([](int x) { ... }); The problem here is that neither specialization of function_traits<> applies. The C++0x draft says that the type of the expression is a "unique, unnamed, non-union class type". Demangling the result of calling typeid(...).name() on the expression gives me what appears to be gcc's internal naming convention for the lambda, main::{lambda(int)#1}, not something that syntactically represents a C++ typename. In short, is there anything I can put into the template here: template <typename R, typename... A> struct function_traits<????> { ... } that will allow this traits class to accept a lambda expression?

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• SAX parser does not resolve filename

  - by phantom-99w

  Another day, another strange error with SAX, Java, and friends. I need to iterate over a list of File objects and pass them to a SAX parser. However, the parser fails because of an IOException. However, the various File object methods confirm that the file does indeed exist. The output which I get: 11:53:57.838 [MainThread] DEBUG DefaultReactionFinder - C:\project\trunk\application\config\reactions\TestReactions.xml 11:53:57.841 [MainThread] ERROR DefaultReactionFinder - C:\project\trunk\application\config\reactions\null (The system cannot find the file specified) So the problem is obviously that null in the second line. I've tried nearly all variations of passing the file as a parameter to the parser, including as a String (both from getAbsolutePath() and entered by hand), as a URI and, even more weirdly, as a FileInputStream (for this I get the same error, except that the entire relative path gets reported as null, so C:\project\trunk\null). All that I can think of is that the SAXParserFactory is incorrectly configured. I have no idea what is wrong, though. Here is the code concerned: SAXParserFactory factory = SAXParserFactory.newInstance(); factory.setValidating(true); try { parser = factory.newSAXParser(); } catch (ParserConfigurationException e) { throw new InstantiationException("Error configuring an XML parser. Given error message: \"" + e.getMessage() + "\"."); } catch (SAXException e) { throw new InstantiationException("Error creating a SAX parser. Given error message: \"" + e.getMessage() + "\"."); } ... for (File f : fileLister.getFileList()) { logger.debug(f.getAbsolutePath()); try { parser.parse(f, new ReactionHandler(input)); //FileInputStream fs = new FileInputStream(f); //parser.parse(fs, new ReactionHandler(input)); //fs.close(); } catch (IOException e) { logger.error(e.getMessage()); throw new ReactionNotFoundException("An error occurred processing file \"" + f + "\"."); } ... } I have made no special provisions to provide a custom SAX parser implementation: I use the system default. Any help would be greatly appreciated!

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• How do you programmatically set a Style on a View?

  - by Greg

  I would like to do something like this: <Button android:id="@+id/button" android:layout_width="wrap_content" android:layout_height="wrap_cotent" style="@style/SubmitButtonType" /> But in code The xml approach works fine provided that SubmitButtonType is defined. Now what I assume happens is that the appt parser runs through this xml, generates an AttributeSet. That AttributeSet when passed to context/theme#obtainStyledAttributes() will have the style ref mask anything that is not written inline in this tag. Great that's fine! Now how do we do this programmatically. Button, as well as other View types, has a constructor that has the form: <Widget>(Context context, AttributeSet set, int defStyle). So I thought this would work. Button button = new Button(context, null, R.style.SubmitButtonType); However, I am finding that defStyle is badly documented as it really should be written to be a resourceId to an attribute (from R.attrs) that will be passed to obtainStyledAttributes() as the attribute resource, and not the style resource. After looking at the code, all the view implementations seem to pass 0 as the styleRef. I don't see the harm in having it passed as both the attr and the style resource (more flexible and negligible overhead) However I might be approaching this all wrong. How do you do this in code then other than by setting each individual element of the style to the specific widget you want to style (only possible by looking a the code to see what param maps to which method or set of methods). The only way I have found to do this is: <declare-styleable> <attr name="totallyAdhoc_attribute_just_for_this_case" format="reference"> </declare-styleable> <style name="MyAlreadyExistantTheme" > ... ... <item name="totallyAdhoc_attribute_just_for_this_case">@style/SubmitButtonType</item> </style> And instead of passing R.style.SubmitButtonType as defStyle, I pass the new R.attr.totallyAdhoc_attribute_just_for_this_case. Button button = new Button(context, null, R.attr.totallyAdhoc_attribute_just_for_this_case); This works but sounds way too complicated.

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• jQuery ajax multiline "script" response

  - by Rendrik

  I'm designing a template creation tool, which uses a jQuery Ajax request that posts parameters to a PHP file. The PHP does the actual generation of the template's HTML. // Send for processing. Expect JS back to execute. function generate() { $.ajax({ type: "POST", url: "generate.php", data: $('#genform :input').serialize(), dataType: "script", beforeSend: function() { $("#loading").html("<img src='images/loadbar.gif' />"); $("#loading") .dialog({ height: 80, width: 256, autoOpen: true, modal: true }); }, success: function(data) { $("#loading").dialog('close'); } }); } My trouble is that I have the ajax dataType: set to "script". Using this, the PHP file generates some jQuery dialogs for any errors which works nicely. However, after I generate the HTML, i'm having trouble passing it back. So I have probably 100 lines of generated HTML and javascript which i'd like to work with. In the PHP file, i've tried: echo('$("#result").html("'.$html.'");'); This does actually work if there are NO line breaks in $html. As soon as there are any line breaks, the Chrome debugger reports "gen.html:1 Uncaught SyntaxError: Unexpected token ILLEGAL". It's obvious that it's trying to eval the returned response headers, but is stopping at any line break. So, to be clear, when I pass $html back, if the contents are this: $html = "<div>hi there</div>"; It works fine (all of my error message dialogs are one line). But if it's: $html = "<div> hi there </div>"; It blows up. I'm really not sure how to get around this, or if there's a better way to go about it. It's important to me to keep the formatting so people can copy the HTML template. I may just break down and display the template file on the PHP page if I can't solve this, but I was really hoping to keep everything within the confines of the HTML page.

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• How can i maintain last cookie value in flex with jsp?

  - by praveen

  Hi All, my login form in flex when I login I have created a cookie in jsp like this name setValueCookie.jsp <%@ page language="java" import="java.util.* , javax.net.*" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <% String username = request.getParameter("value"); System.out.println("Email got in cookieSet = " + username); if(username==null) username=""; Date now = new Date(); String timestamp = now.toString(); Cookie cookie = new Cookie("username",username); cookie.setMaxAge(365 * 24 * 60 * 60); response.addCookie(cookie); %> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>DashBoard-Cookie</title> </head> <body> </body> </html> now using Http service request parameter i am passing username 'Value' to this jsp. and i am reading cookie value from getValueCookie.jsp like this <% String cookieName = "username"; Cookie cookies [] = request.getCookies (); Cookie myCookie = null; String result; if (cookies != null) { for (int i = 0; i < cookies.length; i++) { if (cookies [i].getName().equals (cookieName)) { myCookie = cookies[i]; break; } } } %> <data> <status><%=myCookie.getValue().toString()%></status> </data> through the httpservice value i am getting but if i open a new window or any new tab cookie value is not getting how can i solve this? Thanks in advance.

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• g++ linker error--typeinfo, but not vtable

  - by James

  I know the standard answer for a linker error about missing typeinfo usually also involves vtable and some virtual function that I forgot to actually define. I'm fairly certain that's not the situation this time. Here's the error: UI.o: In function boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::Resource::GroupByState>(boost::shared_ptr<Graphics::Resource::GroupByState> const&, boost::detail::dynamic_cast_tag)': UI.cpp:(.text._ZN5boost10shared_ptrIN8Graphics7Widgets9WidgetSetEEC1INS1_8Resource12GroupByStateEEERKNS0_IT_EENS_6detail16dynamic_cast_tagE[boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::Resource::GroupByState>(boost::shared_ptr<Graphics::Resource::GroupByState> const&, boost::detail::dynamic_cast_tag)]+0x30): undefined reference totypeinfo for Graphics::Widgets::WidgetSet' Running c++filt on the obnoxious mangled name shows that it actually is looking at .boost::shared_ptr::shared_ptr(boost::shared_ptr const&, boost::detail::dynamic_cast_tag) The inheritance hierarchy looks something like class AbstractGroup { typedef boost::shared_ptr<AbstractGroup> Ptr; ... }; class WidgetSet : public AbstractGroup { typedef boost::shared_ptr<WidgetSet> Ptr; ... }; class GroupByState : public AbstractGroup { ... }; Then there's this: class UI : public GroupByState { ... void LoadWidgets( GroupByState::Ptr resource ); }; Then the original implementation: void UI::LoadWidgets( GroupByState::Ptr resource ) { WidgetSet::Ptr tmp( boost::dynamic_pointer_cast< WidgetSet >(resource) ); if( tmp ) { ... } } Stupid error on my part (trying to cast to a sibling class with a shared parent), even if the error is kind of cryptic. Changing to this: void UI::LoadWidgets( AbstractGroup::Ptr resource ) { WidgetSet::Ptr tmp( boost::dynamic_pointer_cast< WidgetSet >(resource) ); if( tmp ) { ... } } (which I'm fairly sure is what I actually meant to be doing) left me with a very similar error: UI.o: In function boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::_Drawer::Group>(boost::shared_ptr<Graphics::_Drawer::Group> const&, boost::detail::dynamic_cast_tag)': UI.cpp:(.text._ZN5boost10shared_ptrIN8Graphics7Widgets9WidgetSetEEC1INS1_7_Drawer5GroupEEERKNS0_IT_EENS_6detail16dynamic_cast_tagE[boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::_Drawer::Group>(boost::shared_ptr<Graphics::_Drawer::Group> const&, boost::detail::dynamic_cast_tag)]+0x30): undefined reference totypeinfo for Graphics::Widgets::WidgetSet' collect2: ld returned 1 exit status dynamic_cast_tag is just an empty struct in boost/shared_ptr.hpp. It's just a guess that boost might have anything at all to do with the error. Passing in a WidgetSet::Ptr totally eliminates the need for a cast, and it builds fine (which is why I think there's more going on than the standard answer for this question). Obviously, I'm trimming away a lot of details that might be important. My next step is to cut it down to the smallest example that fails to build, but I figured I'd try the lazy way out and take a stab on here first. TIA!

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• Marshalling non-Blittable Structs from C# to C++

  - by Greggo

  I'm in the process of rewriting an overengineered and unmaintainable chunk of my company's library code that interfaces between C# and C++. I've started looking into P/Invoke, but it seems like there's not much in the way of accessible help. We're passing a struct that contains various parameters and settings down to unmanaged codes, so we're defining identical structs. We don't need to change any of those parameters on the C++ side, but we do need to access them after the P/Invoked function has returned. My questions are: What is the best way to pass strings? Some are short (device id's which can be set by us), and some are file paths (which may contain Asian characters) Should I pass an IntPtr to the C# struct or should I just let the Marshaller take care of it by putting the struct type in the function signature? Should I be worried about any non-pointer datatypes like bools or enums (in other, related structs)? We have the treat warnings as errors flag set in C++ so we can't use the Microsoft extension for enums to force a datatype. Is P/Invoke actually the way to go? There was some Microsoft documentation about Implicit P/Invoke that said it was more type-safe and performant. For reference, here is one of the pairs of structs I've written so far: C++ /** Struct used for marshalling Scan parameters from managed to unmanaged code. */ struct ScanParameters { LPSTR deviceID; LPSTR spdClock; LPSTR spdStartTrigger; double spinRpm; double startRadius; double endRadius; double trackSpacing; UINT64 numTracks; UINT32 nominalSampleCount; double gainLimit; double sampleRate; double scanHeight; LPWSTR qmoPath; //includes filename LPWSTR qzpPath; //includes filename }; C# /// <summary> /// Struct used for marshalling scan parameters between managed and unmanaged code. /// </summary> [StructLayout(LayoutKind.Sequential)] public struct ScanParameters { [MarshalAs(UnmanagedType.LPStr)] public string deviceID; [MarshalAs(UnmanagedType.LPStr)] public string spdClock; [MarshalAs(UnmanagedType.LPStr)] public string spdStartTrigger; public Double spinRpm; public Double startRadius; public Double endRadius; public Double trackSpacing; public UInt64 numTracks; public UInt32 nominalSampleCount; public Double gainLimit; public Double sampleRate; public Double scanHeight; [MarshalAs(UnmanagedType.LPWStr)] public string qmoPath; [MarshalAs(UnmanagedType.LPWStr)] public string qzpPath; }

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