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• Problems with starting an activity in onStart

  - by Fizz

  Hello everyone. I'm trying to start a floating activity from onStart to retrieve some info from the user right when the initial activity begins. I have the following: @Override public void onStart(){ super.onStart(); callProfileDialog(); } And callProfileDialog() is just: private void callProfileDialog(){ Intent i = new Intent(this, com.utility.ProfileDialog.class); startActivityForResult(i, PROFDIALOG); } ProfileDialog.class returns a String from an input box. If the result returned is RESULT_CANCELED then I restart the activity. The problem I'm having is that when the program starts, the screen is just black. If I hit the Back button a RESULT_CANCELED is returned then the initial activity shows as well as the floating activity (since it recalled itself when it got a RESULT_CANCELED). Why can't I get the activities show by calling ProfileDialog.class from onStart()? I got the same result when I called it at the end of onCreate() which is way I switch over to use onStart(). Thanks for the help.

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• Complicated .NET factory design

  - by Tom W

  Hello SO; I'm planning to ask a fairly elaborate question that is also something of a musing here, so bear with me... I'm trying to design a factory implementation for a simulation application. The simulation will consist of different sorts of entities i.e. it is not a homogenous simulation in any respect. As a result, there will be numerous very different concrete implementations and only the very general properties will be abstracted at the top level. What I'd like to be able to do is create new simulation entities by calling a method on the model with a series of named arguments representing the parameters of the entity, and have the model infer what type of object is being described by the inbound parameters (from the names of the parameters and potentially the sequence they occur in) and call a factory method on the appropriate derived class. For example, if I pass the model a pair of parameters (Param1=5000, Param2="Bacon") I would like it to infer that the names Param1 and Param2 'belong' to the class "Blob1" and call a shared function "getBlob1" with named parameters Param1:=5000, Param2:="Bacon" whereas if I pass the model (Param1=5000, Param3=50) it would call a similar factory method for Blob2; because Param1 and Param3 in that order 'belong' to Blob2. I foresee several issues to resolve: Whether or not I can reflect on the available types with string parameter names and how to do this if it's possible Whether or not there's a neat way of doing the appropriate constructor inference from the combinatoric properties of the argument list or whether I'm going to have to bodge something to do it 'by hand'. If possible I'd like the model class to be able to accept parameters as parameters rather than as some collection of keys and values, which would require the model to expose a large number of parametrised methods at runtime without me having to code them explicitly - presumably one for every factory method available in the relevant namespace. What I'm really asking is how you'd go about implementing such a system, rather than whether or not it's fundamentally possible. I don't have the foresight or experience with .NET reflection to be able to figure out a way by myself. Hopefully this will prove an informative discussion.

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• JQuery: How to apply css to a .wrap element?

  - by Eamonn

  My code thus far: $(".lorem img:not(.full-img)").each(function() { $(this).addClass("inline-img"); var imgWidth = $(this).prop('width'); var imgHeight = $(this).prop('height'); var imgFloat = $(this).prop('float'); $(this).wrap('<div class="inline-img-wrap" />'); if ($(this).prop("title")!='') { $('<p class="inline-img-caption">').text($(this).prop('title')).insertAfter($(this)); } }); I am searching for images within a body of text, appending their title values as captions underneath, and wrapping both img and p in a div.inline-img-wrap. That works fine. What I need help with is applying the styling of the img to the new wrapping div instead. You can see I have created vars for just this, but cannot get applying them to work. $this will always apply to the image, and <div class="inline-img-wrap" style="width:'+imgWidth+'"> doesn't work. All advice appreciated!

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• validation before ajax form submission

  - by ZX12R

  How do i introduce validation before remote_form_for submits? I have javascript function called validateForm(). I am able to call it before the AJAX request process. I tried to use return false and event.preventDefault. But there seems to be no effect. Here is what my code looks like <% remote_form_for :customer, :update =>"uxScreenLoaderDiv", :url => {:action => "login", :controller => "site"}, :html => {:id => "uxLoginForm"}, :onsubmit => "validateForm(event)" do |f| %> User name : <%= f.text_field "uxUserName", :class => "TextBox", :style => "width:100px;" %>&nbsp;* &nbsp;Password : <%= f.password_field "uxPassword", :class => "TextBox", :style => "width:100px;" %>&nbsp;* <%= f.submit "Go!", :class => "Button-Simple", :id => "uxSubmitButton" %> <% end %> the javascript function is simple as follows function validateForm(event){ return false; //event.preventDefault(); }

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• How can I qualify an autowired property with a variable from a config file using annotations?

  - by jiggy

  My specific problem is that I have configured two beans that implement the same interface and I have a third bean that has a property of that interface's type. I inject the property using a config property. So, assuming RemoteDataSource and LocalDataSource implement IDataSource and dao1 has a property of type IDataSource, my XML config might look like this: <bean id="datasource1" class="com.foo.RemoteDataSource"> <property name="url">${url}</property> </bean> <bean id="datasource2" class="com.foo.LocalDataSource"> <property name="path">${filepath}</property> </bean> <bean id="dao1" class="com.foo.MyDAO"> <property name="dataSource">${datasource}</property> </bean> With url, filepath and datasource being defined in an included properties file. We are now making a push for annotation-driven configuration and I'm not sure how to annotate my dao to put the data source configured in the property file. I want to do something like this, but it is evidently not allowed: @Autowired @Qualifier("${datasource}") public void setDataSource(IDataSource datasource) {...}

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• Passing functor and function pointers interchangeably using a templated method in C++

  - by metroxylon

  I currently have a templated class, with a templated method. Works great with functors, but having trouble compiling for functions. Foo.h template <typename T> class Foo { public: // Constructor, destructor, etc... template <typename Func> void bar(T x, Func f); }; template <typename T> template <typename Func> Foo::bar(T x, Func f) { /* some code here */ } Main.cpp #include "Foo.h" template <typename T> class Functor { public: Functor() {} void operator()(T x) { /* ... */ } private: /* some attributes here */ }; void Function(T x) { /* ... */ } int main() { Foo<int> foo; foo.bar(2, Functor); // No problem foo.bar(2, Function); // <unresolved overloaded function type> return 0; }

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• Use CSS3 nth-child to alternate the float of images within DIV tags...

  - by Aaron Rodgers

  Basically, what I'm trying to create is a page of div tags, each has an image inside them and I'm trying to use CSS3's nth-child to alternate the float of that specific image. But for the life of me, I can't get the nth-child to locate those images. Here is my code so far... CSS .featureBlock img:nth-of-type(even) { float: left; } .featureBlock img:nth-of-type(odd) { float: right; } This is the HTML of one of those div tags.... <div class="featureBlock"> <h1>Multisize Players</h1> <div class="featureHelpBlock"><a href="#">More help with this</a></div> <img src="http://office2.vzaar.com/images/features/ft_multisize_players.png"> <span class="featureContent"><p>A variety of player sizes is important as we recognise the fact that no two videos or websites are ever the same and you will want something that suits your site&#8217;s look. So if you record your video in 4x3 (not widescreen) or 16x9 (widescreen) we have the range of player sizes to suit your exact needs.</p> <p>We encode the video at the time of uploading in the size that you choose so that the picture and sound quality is retained throughout. Users can choose from the following sizes:</p></span> <br style="clear:both"> </div> Hope this makes sense...

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• Can foreground threads be aborted on application shutdown in C#.Net?

  - by Cartman

  I inherited a c# winforms app (.NET 2.0) which creates a thread upon startup in a singleton class. This thread handles messages from a messaging topic (Tibco EMS). When the app is shutdown, the thread doesn't remain the the background? How is this possible? Is there something else happening that can abort this thread? Code snippet: public class Startup { public static void main(string [] args) { MySingletonClass.Instance.Init(); // do other things below Application.Run(new MainForm()); } public class MySingletonClass { // singleton code //.. //.. private Thread t; public void Init() { t = new Thread(new ThreadStart(poll)); } private void poll() { while(true} { // listen for messages and process but there is no break clause // exceptions are also handled within to ensure control doesnt go out } } Pls. don't write to tell me this is bad code. I know it and i was going to refactor it when i realised that the app actually shutdowns correctly inspite of this aberration. So i want to understand how this is possible. Thanks for your help

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• Using boost::iterator_adaptor

  - by Neil G

  I wrote a sparse vector class (see #1, #2.) I would like to provide two kinds of iterators: The first set, the regular iterators, can point any element, whether set or unset. If they are read from, they return either the set value or value_type(), if they are written to, they create the element and return the lvalue reference. Thus, they are: Random Access Traversal Iterator and Readable and Writable Iterator The second set, the sparse iterators, iterate over only the set elements. Since they don't need to lazily create elements that are written to, they are: Random Access Traversal Iterator and Readable and Writable and Lvalue Iterator I also need const versions of both, which are not writable. I can fill in the blanks, but not sure how to use boost::iterator_adaptor to start out. Here's what I have so far: class iterator : public boost::iterator_adaptor< iterator // Derived , value_type* // Base , boost::use_default // Value , boost::?????? // CategoryOrTraversal > class sparse_iterator : public boost::iterator_adaptor< iterator // Derived , value_type* // Base , boost::use_default // Value , boost::random_access_traversal_tag? // CategoryOrTraversal >

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• throwing exception from APCProc crashes program

  - by lazy_banana

  I started to do some research on how terminate a multithreaded application properly and I found those 2 post(first, second) about how to use QueueUserAPC to signal other threads to terminate. I thought I should give it a try, and the application keeps crashing when I throw the exception from the APCProc. Code: #include <stdio.h> #include <windows.h> class ExitException { public: char *desc; DWORD exit_code; ExitException(char *desc,int exit_code): desc(desc), exit_code(exit_code) {} }; //I use this class to check if objects are deconstructed upon termination class Test { public: char *s; Test(char *s): s(s) { printf("%s ctor\n",s); } ~Test() { printf("%s dctor\n",s); } }; DWORD CALLBACK ThreadProc(void *useless) { try { Test t("thread_test"); SleepEx(INFINITE,true); return 0; } catch (ExitException &e) { printf("Thread exits\n%s %lu",e.desc,e.exit_code); return e.exit_code; } } void CALLBACK exit_apc_proc(ULONG_PTR param) { puts("In APCProc"); ExitException e("Application exit signal!",1); throw e; return; } int main() { HANDLE thread=CreateThread(NULL,0,ThreadProc,NULL,0,NULL); Sleep(1000); QueueUserAPC(exit_apc_proc,thread,0); WaitForSingleObject(thread,INFINITE); puts("main: bye"); return 0; } My question is why does this happen? I use mingw for compilation and my OS is 64bit. Can this be the reason?I read that you shouldn't call QueueApcProc from a 32bit app for a thread which runs in a 64bit process or vice versa, but this shouldn't be the case.

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• How to: StructureMap and configuration based on runtime parameters?

  - by user981375

  In a nutshell - I want to be able to instantiate object based on runtime parameters. In this particular case there are only two parameters but the problem is that I'm facing different permutations of these parameters and it gets messy. Here is the situation: I want to get an instance of an object specific to, say, given country and then, say, specific state/province. So, considering the US, there are 50 possible combinations. In reality it's less than that but that's the max. Think of it this way, I want to find out what's the penalty for smoking pot in a given country/state, I pass this information in and I get instantiated object telling me what it is. To the code (for reference only): interface IState { string Penalty { get; } } interface ICountry { IState State { get; set; } string Name { get; } } class BasePenalty : IState { virtual public string Penalty { get { return "Slap on a wrist"; } } } class USA : ICountry { public USA(IState state) { State = state; } public IState State { get; set; } public string Name { get { return "USA"; } } } class Florida: BasePenalty { public override string Penalty { get { return "Public beheading"; } } } // and so on ... I defined other states // which have penalties other than the "Slap on a wrist" How do I configure my container that when given country and state combination it will return the penalty? I tried combinations of profile and contextual binding but that configuration was directly proportional to the number of classes I've created. I have already gone thru trouble of defining different combinations. I'd like to avoid having to do the same during container configuration. I want to inject State into the Country. Also, I'd like to return UsaBasePenalty value in case state is not specified. Is that possible? Perhaps these is something wrong with the design.

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• Hibernate HQL m:n join problem

  - by smallufo

  I am very unfamiliar with SQL/HQL , and am currently stuck with this 'maybe' simple problem : I have two many-to-many Entities , with a relation table : Car , CarProblem , and Problem . One Car may have many Problems , One Problem may appear in many Cars, CarProblem is the association table with other properties . Now , I want to find Car(s) with specified Problem , how do I write such HQL ? All ids are Long type . I've tried a lot of join / inner-join combinations , but all in vain.. -- updated : Sorry , forget to mention : Car has many CarProblem Problem has many CarProblem Car and Problem are not directly connected in Java Object. -- update , java code below -- @Entity public class Car extends Model{ @OneToMany(mappedBy="car" , cascade=CascadeType.ALL) public Set<CarProblem> carProblems; } @Entity public class CarProblem extends Model{ @ManyToOne public Car car; @ManyToOne public Problem problem; ... other properties } @Entity public class Problem extends Model { other properties ... // not link to CarProblem , It seems not related to this problem // **This is a very stupid query , I want to get rid of it ...** public List<Car> findCars() { List<CarProblem> list = CarProblem.find("from CarProblem as cp where cp.problem.id = ? ", id).fetch(); Set<Car> result = new HashSet<Car>(); for(CarProblem cp : list) result.add(cp.car); return new ArrayList<Car>(result); } } The Model is from Play! framework , so these properties are all public .

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• Javascript/Jquery pop-up window in Asp.Net MVC4

  - by Mark

  Below I have a "button" (just a span with an icon) that creates a pop-up view of a div in my application to allow users to compare information in seperate windows. However, I get and Asp.Net Error as follows: **Server Error in '/' Application. The resource cannot be found. Requested URL: /Home/[object Object]** Does anyone have an Idea of why this is happending? Below is my code: <div class="module_actions"> <div class="actions"> <span class="icon-expand2 pop-out"></span> </div> </div> <script> $(document).ajaxSuccess(function () { var Clone = $(".pop-out").click(function () { $(this).parents(".module").clone().appendTo("#NewWindow"); }); $(".pop-out").click(function popitup(url) { LeftPosition = (screen.width) ? (screen.width - 400) / 1 : 0; TopPosition = (screen.height) ? (screen.height - 700) / 1 : 0; var sheight = (screen.height) * 0.5; var swidth = (screen.width) * 0.5; settings = 'height=' + sheight + ',width=' + swidth + ',top=' + TopPosition + ',left=' + LeftPosition + ',scrollbars=yes,resizable=yes,toolbar=no,status=no,menu=no, directories=no,titlebar=no,location=no,addressbar=no' newwindow = window.open(url, '/Index', settings); if (window.focus) { newwindow.focus() } return false; }); });

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• Importing a div's content from a Static HTML file using PHP or jQuery or Ajax?

  - by Vikram

  Hello friends a newbie question... The Issue is like this: I have a static HTML file and I want to import just a portion of that file into another page. How can I do that. Example Code: <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Some title here</title> <link rel="stylesheet" type="text/css" href="styles.css" /> </head> <body> <div id="box-1"> <div class="block"> <!-- Some code here --> </div> </div> <div id="box-2"> <div class="block"> <!-- Some code here --> </div> </div> <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script> <script src="script.js"></script> </body> </html> Now what I want is to read this HTML file and import just this bit: <div id="box-1"> <div class="block"> <!-- Some code here --> </div> </div> Is there a way of doing it? Kindly help. Even a PHP, jQuery, Ajax or any other solution will also do. Please help me.

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• hibernate empty collection in component

  - by Jurgen H

  I have a component mapped using Hibernate. If all fields in the component in the database are null, the component itself is set to null by hibernate. This is the expected behavior and also what I need. The problem I have, is that when I add a bag to that component, the bag is initialized to an empty list. This means the component has a non null value... resulting in the component being created. Any idea how to fix this? <class name="foo.bar.Entity" table="Entity"> <id name="id" column="id"> <generator class="native" /> </id> <property name="departure" column="departure_time" /> <property name="arrival" column="arrival_time" /> <component name="statistics"> <bag name="linkStatistics" lazy="false" cascade="all" > <key column="entity_id" not-null="true" /> <one-to-many class="foo.bar.LinkStatistics" /> </bag> <property name="loggedTime" column="logged_time" /> ... </component> A criteria with Restirctions.isNull("statistics") does return the expected values.

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• CodeModel help needed for right-hand singleton.getinstance() assignment.

  - by antarti

  I've been able to generate 99% of what I need with the CodeModel API, but I am stumped here... Using the various "directXX" methods does not add import statements to the generated code, and I can work without the "directXXX" type of methods except for one place in a generated class. Suppose I desire a generated method like: /** * Copies data from this Value-Obj instance, to the returned PERSON instance. * * @return PERSON * */ public PERSON mapVOToPERSON() throws MappingException { Mapper mapper = (com.blah.util.MapperSingleton.getMapperInstance()); return mapper.map(this, PERSON.class); } You can see the right hand of the Mapper assignment in parens. Emitting the entire package+class was the only way I could find to just declare "SomeSingleton.someMethod()" on the right hand side and have the generated code compile. Without the MapperSingleton being added to the object model, there is no import generated... Questions: 1) Is there a way to force an import to be generated? 2) How to declare an expression that gives me the right side of the Mapper assignment within the object model (so that an import of MapperSingleton gets generated. Any help appreciated...

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• photo upload with codeigniter

  I know there are many tutorials online, but I could not make them work :( maybe something particularly wrong with my system :/ My Controller localpath is: /localhost/rl/applications/backend/controller/ Controller: function do_upload() { $config['upload_path'] = './uploads/'; $config['allowed_types'] = 'gif|jpg|png'; $config['max_size'] = '100'; $config['max_width'] = '1024'; $config['max_height'] = '768'; $this->load->library('upload', $config); if ( ! $this->upload->do_upload()) { $error = array('error' => $this->upload->display_errors()); $this->load->view('add_image', $error); } else { $data = array('upload_data' => $this->upload->data()); $data['id'] = $this->input->post['id_work']; $this->load->view('add_image', $data); } } My View localpath is: /localhost/rl/applications/backend/view/ View: echo form_open_multipart('do_upload'); <ul class="frm"> <li><label>File: *</label><input type="file" name="userfile" class="frmlmnt" size="50" /></li> <li><label></label><input type="submit" class="btn" value="Upload" /></li> </ul> </form> Maybe I do something wrong with path

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• auto div height

  - by Geln

  <html><head><title>Test</title> <style> .main{width:600px;border:1px solid red; } .main .left{background:lightblue; width:100px;clear:both; float:left;} .main .right{margin-left:100px;background:lightyellow; } </style> </head><body> <div class="main"> <div class="left"> title </div> <div class="right"> <div id="item">item</div> <div id="item">item</div> <div id="item">item</div> <div id="item">item</div> <div id="item">item</div> <div id="item">item</div> <div id="item">item</div> </div> </div> </body></html> How to change the CSS to make the page display like the dialog shows? PS,I think it's a way that to make the "left" div's height auto expend when the height of the "right" div or parent div expend, but I don't know how.

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• Hovering a div shows hidden div - jquery to prototype conversion

  - by phil

  I may get killed for this but I have been trying for a few days using Prototype to show a hidden div when hovering over another div. I have this working fine in jquery but I could use some help porting it over to prototype. The code sample: <script type="text/javascript"> $(document).ready(function(){ $(".recent-question").hover(function(){ $(this).find(".interact").fadeIn(2.0); }, function(){ $(this).find(".interact").fadeOut(2.0); }); }); </script> <div class="recent-question"> <img src="images/new/img-sample.gif" alt="" width="70" height="60" /> <div class="question-text"> <h3>Heading</h3> <p><a href="#">Yadda Yadda Yadda</p> </div> <div class="interact" style="display:none;"> <ul> <li><a href="#">Choice1</a></li> <li><a href="#">Choice2</a></li> <li><a href="#">Choice3</a></li> </ul> </div> </div> So basically when I hover over a recent-question div i would like the div.interact to fade in or appear at all. The above code is for jquery but I am required to use prototype for this project. Any help converting would be greatly appreciated. Thanks!

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• Adding cancel ability and exception handling to async code.

  - by Rob

  I have this sample code for async operations (copied from the interwebs) public class LongRunningTask { public LongRunningTask() { //do nowt } public int FetchInt() { Thread.Sleep(2000); return 5; } } public delegate TOutput SomeMethod<TOutput>(); public class GoodPerformance { public void BeginFetchInt() { LongRunningTask lr = new LongRunningTask(); SomeMethod<int> method = new SomeMethod<int>(lr.FetchInt); // method is state object used to transfer result //of long running operation method.BeginInvoke(EndFetchInt, method); } public void EndFetchInt(IAsyncResult result) { SomeMethod<int> method = result.AsyncState as SomeMethod<int>; Value = method.EndInvoke(result); } public int Value { get; set; } } Other async approaches I tried required the aysnc page attribute, they also seemed to cancel if other page elements where actioned on (a button clicked), this approach just seemed to work. I’d like to add a cancel ability and exception handling for the longRunningTask class, but don’t erm, really know how.

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• How to create anonymous objects of type IQueryable using LINQ

  - by Soham Dasgupta

  Hi, I'm working in an ASP.NET MVC project where I have created a two LinqToSQL classes. I have also created a repository class for the models and I've implemented some methods like LIST, ADD, SAVE in that class which serves the controller with data. Now in one of the repository classes I have pulled some data with LINQ joins like this. private HerculesCompanyDataContext Company = new HerculesCompanyDataContext(); private HerculesMainDataContext MasterData = new HerculesMainDataContext(); public IQueryable TRFLIST() { var info = from trfTable in Company.TRFs join exusrTable in MasterData.ex_users on trfTable.P_ID equals exusrTable.EXUSER select new { trfTable.REQ_NO, trfTable.REQ_DATE, exusrTable.USER_NAME, exusrTable.USER_LNAME, trfTable.FROM_DT, trfTable.TO_DT, trfTable.DESTN, trfTable.TRAIN, trfTable.CAR, trfTable.AIRPLANE, trfTable.TAXI, trfTable.TPURPOSE, trfTable.STAT, trfTable.ROUTING }; return info; } Now when I call this method from my controller I'm unable to get a list. What I want to know is without creating a custom data model class how can I return an object of anonymous type like IQueryable. And because this does not belong to any one data model how can refer to this list in the view.

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• Jquery Double clicking on link removing div content

  - by ram

  I wrote this code to load the content of a DIV ,when some one clicks on a link. Now,if you click on a link twice,it is removing the content. Here is the code $('a').click(function() { var id = $(this).attr('class'); if(id == 'first') { $('.active').removeClass('active'); $('a.first').addClass('active'); } else if(id == 'second') { $('.active').removeClass('active'); $('a.second').addClass('active'); } $('#first').toggle(id == 'first'); $('#second').toggle(id == 'second'); });? <a class="first">one</a> <a class="second">two</a> <div> <li id="first"> <h2>pen</h2> <div> <div>parker</div> </div> </li> <li id="second" style="display: none;"> <h2>car</h2> <div>Bugatti</div> </div> </li> </div>? .active { color: green; }

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• Doesn't (didn't) Scala have automatically generated setters?

  - by Malvolio

  Google and my failing memory are both giving me hints that it does, but every attempt is coming up dry. class Y { var y = 0 } var m = new Y() m.y_(3) error: value y_ is not a member of Y Please tell me I am doing something wrong. (Also: please tell me what it is I am doing wrong.) EDIT The thing I am not doing wrong, or at least not the only thing I am doing wrong, is the way I am invoking the setter. The following things also fail, all with the same error message: m.y_ // should be a function valued expression m.y_ = (3) // suggested by Google and by Mchl f(m.y_) // where f takes Int => Unit as an argument f(m.y) // complains that I am passing in Int not a function I am doing this all through SimplyScala, because I'm too lazy and impatient to set up Scala on my tiny home machine. Hope it isn't that... And the winner is ... Fabian, who pointed out that I can't have a space between the _ and the =. I thought out why this should be and then it occurred to me: The name of the setter for y is not y_, it is y_= ! Observe: class Y { var y = 0 } var m = new Y() m.y_=(3) m.y res1: Int = 3 m.y_= error: missing arguments for method y_= in class Y; follow this method with `_` if you want to treat it as a partially applied function m.y_= ^ m.y_=_ res2: (Int) => Unit = def four(f : Int => Unit) = f(4) four(m.y_=) m.y res3: Int = 4 Another successful day on StackExchange.

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• How to write curiously recurring templates with more than 2 layers of inheritance?

  - by Kyle

  All the material I've read on Curiously Recurring Template Pattern seems to one layer of inheritance, ie Base and Derived : Base<Derived>. What if I want to take it one step further? #include <iostream> using std::cout; template<typename LowestDerivedClass> class A { public: LowestDerivedClass& get() { return *static_cast<LowestDerivedClass*>(this); } void print() { cout << "A\n"; } }; template<typename LowestDerivedClass> class B : public A<LowestDerivedClass> { public: void print() { cout << "B\n"; } }; class C : public B<C> { public: void print() { cout << "C\n"; } }; int main() { C c; c.get().print(); // B b; // Intentionally bad syntax, // b.get().print(); // to demonstrate what I'm trying to accomplish return 0; } How can I rewrite this code to compile without errors (and output "C\nB\n")?

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• Why Is the sender type null when dealing with events

  - by ChloeRadshaw

  From C# Via CLR: Note A lot of people wonder why the event pattern requires the sender parameter to always be of type Object After all, since the MailManager will be the only type raising an event with a NewMail EventArgs object, it makes more sense for the callback method to be prototyped like this: void MethodName(Mai l Manager sender, NewMail EventArgs e); The pattern requires the sender parameter to be of type Object mostly because of inheritance What if Mai lManager were used as a base class for SmtpMailManager? In this case, the callback method should have the sender parameter prototyped as SmtpMailManager instead of Mail Manager, but this can’t happen because SmtpMai lManager just inherited the NewMai l event So the code that was expecting SmtpMail Manager to raise the event must still have to cast the sender argument to SmtpMailManager In other words, the cast is still required, so the sender parameter might as well be typed as Obj ect The next reason for typing the sender parameter as Obj ect is just fexibility It allows the delegate to be used by multiple types that offer an event that passes a NewMail EventArgs object For example, a PopMai lManager class could use the delegate even if this class were not derived from Mail Manager I just simply cannot understand why the sender is an object - Why can it not be generified? so most of the time we do not need to do generic casts

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