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  • How do I create rows with alternating colors for a UITableView on iPhone?

    - by Mat
    Hi all, i would to have alternate 2 colors of rows, like the first black, the second white, the third black, etc, etc... my approach is like a basic exercise of programming to calculate if a number is odd number or not: - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; cell = ((MainCell*)[tableView dequeueReusableCellWithIdentifier:CellIdentifier]); if (cell==nil) { NSArray *topLevelObjects=[[NSBundle mainBundle] loadNibNamed:@"MainCell" owner:self options:nil]; for (id currentObject in topLevelObjects){ if ([currentObject isKindOfClass:[UITableViewCell class]]){ if ((indexPath.row % 2)==0) { [cell.contentView setBackgroundColor:[UIColor purpleColor]]; }else{ [cell.contentView setBackgroundColor:[UIColor whiteColor]]; } cell = (MainCell *) currentObject; break; } } }else { AsyncImageView* oldImage = (AsyncImageView*) [cell.contentView viewWithTag:999]; [oldImage removeFromSuperview]; }return cell; The problem is that when i do a rapid scroll, the background of cells become like the last 2 cell black, the first 2 cell white or something like this, but if i scroll slow works fine. I think the problem is the cache of reusableCell. Any ideas? TIA

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  • strcmp() but with 0-9 AFTER A-Z? (C/C++)

    - by Aaron
    For reasons I completely disagree with but "The Powers (of Anti-Usability) That Be" continue to decree despite my objections, I have a sorting routine which does basic strcmp() compares to sort by its name. It works great; it's hard to get that one wrong. However, at the 11th hour, it's been decided that entries which begin with a number should come AFTER entries which begin with a letter, contrary to the ASCII ordering. They cite the EBCDIC standard has numbers following letters so the prior assumption isn't a universal truth, and I have no power to win this argument... but I digress. Therein lies my problem. I've replaced all appropriate references to strcmp with a new function call nonstd_strcmp, and now need to implement the modifications to accomplish the sort change. I've used a FreeBSD source as my base: http://freebsd.active-venture.com/FreeBSD-srctree/newsrc/libkern/strncmp.c.html if (n == 0) return (0); do { if (*s1 != *s2++) return (*(const unsigned char *)s1 - *(const unsigned char *)(s2 - 1)); if (*s1++ == 0) break; } while (--n != 0); return (0); I guess I might need to take some time away to really think about how it should be done, but I'm sure I'm not the only one who's experienced the brain-deadness of just-before-release spec changes.

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  • Treating differential operator as algebraic entity

    - by chappar
    I know that this question is offtopic and don't belong here. But i didn't know somewhere else to ask. So here is the question. I was reading e:the story of a number by Eli Maor, where he treats differential operator as just like any algebraic entity. For example if we have a differential equation like y’’ + 5y’ - 6y = 0. This can be treaed as (D^2 + 5D – 6)y = 0. So, either y = 0 (trivial solution) or (D^2 + 5D – 6) = 0. Factoring out above equation we get (D-1)(D+6)= 0 with solutions as D = 1 and D = -6. Since D does not have any meaning on its own, multiplying by y on both the sides we get Dy = y and Dy = -6y for which the solutions are Ae^x and Be^-6x. Combining these 2 solutions we get Ae^x + Be^-6x. Now my doubt is this approach break when we have an equation like D^2y = 0. Which means y = 0 (again trivial) or D^2 = 0 which means D = 0. Now Dy = y*0 = 0. That means y = C ( a constant). The actual answer should be Cx. I know that it is stupidity to treat D^2 = 0 as D = 0, it led me to doubt the entire process of treating differential equation as algebraic equation. Can someone throw light on this? Or any other site where i might get answer?

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  • Capture and handling the tab/Textchanged event in a textbox in asp.net MVC

    - by Icerman
    I have the following code th handle a user name validation on the server side. But the event seems not firing since break points in js or C# code didn't hit. Can anyone point out where I did wrong? Here is the user control which has a user name textbox: <%: Html.TextBox("UserName", Model.Username, new { maxlength = "40", size = "20", tabindex = "1", @onchange = "CheckAvailability()" })% CheckAvailability() is defined in the User.Validation.js and included in the above user control: $(document).ready(function () { function CheckAvailability() { $.post("/Home/Survey/CheckAvailability", { Username: $("#UserName").val() }, function (data) { var myObject = eval('(' + data + ')'); var newid = myObject; if (newid == 0) { $("#usernamelookupresult").html("<font color='green'>Available :-D</font>") } else { $("#usernamelookupresult").html("<font color='red'>Taken :-(</font>") } }); } }); Here is the survey controller function which will have server side validation: [HttpPost] public ActionResult CheckAvailability(string Username) { int Taken = 0; // This is where you add your database lookup if (Username == "abc") { Taken = 1; } return Json(Taken); }

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  • LDAP query using Python: always no result

    - by Grey
    I am trying to use python to query LDAP server, and it always returns me no result. and anyone help me find what wrong with my python code? it runs fine without excpetions, and it always has no result. i played around with the filter like "cn=partofmyname" but just no luck. thanks for help import ldap try: l = ldap.open("server") l.protocol_version = ldap.VERSION3 l.set_option(ldap.OPT_REFERRALS, 0) output =l.simple_bind("cn=username,cn=Users,dc=domian, dc=net",'password$R') print output except ldap.LDAPError, e: print e baseDN = "DC=rim,DC=net" searchScope = ldap.SCOPE_SUBTREE ## retrieve all attributes - again adjust to your needs - see documentation for more options retrieveAttributes = None Filter = "(&(objectClass=user)(sAMAccountName=myaccount))" try: ldap_result_id = l.search(baseDN, searchScope, Filter, retrieveAttributes) print ldap_result_id result_set = [] while 1: result_type, result_data = l.result(ldap_result_id, 0) if len(result_data) == 0: print 'no reslut' break else: for i in range(len(result_set)): for entry in result_set[i]: try: name = entry[1]['cn'][0] email = entry[1]['mail'][0] phone = entry[1]['telephonenumber'][0] desc = entry[1]['description'][0] count = count + 1 print "%d.\nName: %s\nDescription: %s\nE-mail: %s\nPhone: %s\n" %\ (count, name, desc, email, phone) except: pass ## here you don't have to append to a list ## you could do whatever you want with the individual entry #if result_type == ldap.RES_SEARCH_ENTRY: # result_set.append(result_data) # print result_set except ldap.LDAPError, e: print e l.unbind()

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  • Optimizing a bin-placement algorithm

    - by user258651
    Alright, I've got two collections, and I need to place elements from collection1 into the bins (elements) of collection2, based on whether their value falls within a given bin's range. For a concrete example, assume I have a sorted collection objects (bins) which have an int range ([1...4], [5..10], etc). I need to determine the range an int falls in, and place it in the appropriate bin. foreach(element n in collection1) { foreach(bin m in collection2) { if (m.inRange(n)) { m.add(n); break; } } } So the obvious NxM complexity algorithm is there, but I really would like to see Nxlog(M). To do this I'd like to use BinarySearch in place of the inner foreach loop. To use BinarySearch, I need to implement an IComparer class to do the searching for me. The problem I'm running into is this approach would require me to make an IComparer.Compare function that compares two different types of objects (an element to its bin), and that doesn't seem possible or correct. So I'm asking, how should I write this algorithm?

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  • Which templating languages output HTML *as a tree of nodes*?

    - by alamar
    HTML is a tree of nodes, before all. It's not just a text. However, most templating engines handle their input and output as it was just a text; they don't care what happens around their tags, their {$foo}'s and <% bar() %>'s; also they don't care about what are they outputting. Sometimes they happen to produce a correct html, but that's just a coincidence; they didn't aim for that, all they wanted is to replace some funny marks in the text stream with their evaluation. There are a few templating engines which do treat their output as a set of nodes; XSLT and Haml come to mind. For some tasks, this has advantages: for example, you can automatically reformat (like, delete all empty text nodes; auto-indent; word-wrap). The result is guaranteed to be a correct xml/sgml unless you use a strict subset of operations that can break that. Also, such templating engine would automatically quote strings, differently in text nodes and in attributes, because it strictly knows whether you're writing an attribute or a text node. Moreover, it can conditionally remove a node from output because it knows where it does begin and end, which is useful, and do other non-trivial node operations. You might not like XSLT for its verbosiness or functionalness, but it's damn helps that your template is xmllint-able XML, and your output is a good sgml/xml. So the question is: Which template engines do you know that treat their output as a set of correct nodes, not just an unstructured text? I know XSLT, Haml and some obscure python-based one. Moar!

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  • Using callback functions for error handling in C

    - by Earlz
    Hi, I have been thinking about the difficulty incurred with C error handling.. like who actually does if(printf("hello world")==-1){exit(1);} But you break common standards by not doing such verbose, and usually useless coding. Well what if you had a wrapper around the libc? like so you could do something like.. //main... error_catchall(my_errors); printf("hello world"); //this will automatically call my_errors on an error of printf ignore=1; //this makes it so the function will return like normal and we can check error values ourself if(fopen.... //we want to know if the file opened or not and handle it ourself. } int my_errors(){ if(ignore==0){ _exit(1); //exit if we aren't handling this error by flagging ignore } return 0; //this is called when there is an error anywhere in the libc } ... I am considering making such a wrapper as I am synthesizing my own BSD licensed libc(so I already have to touch the untouchable..), but I would like to know what people think about it.. would this actually work in real life and be more useful than returning -1?

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  • Android How to get position of selected item from gridview without using onclicklistner, using ontouchlistner instead

    - by zonemikel
    I have a gridview, I need to do stuff on motioneven.action_down and do something for motioneven.action_up ... using onclicklistener is great but does not give me this needed functionality. Is there anyway to easily call the gridview and get its selected item in a ontouchlistener ? I've been having limited success with making my own implementation. Its hard to get the right x,y because if i call the child it gives me the x and y relative to the child so a button would be 0,0 to 48,48 but it does not tell you the actual location on the screen relative to the gridview or the screen itself. this is what i've been doing, its partially working so far. Grid.setOnTouchListener(new OnTouchListener() { public boolean onTouch(View v, MotionEvent event) { if (event.getAction() == MotionEvent.ACTION_DOWN) { int x = (int)event.getX(); int y = (int)event.getY(); int position = 0; int childCount = Grid.getChildCount(); Message msg = new Message(); Rect ButtonRect = new Rect(); Grid.getChildAt(0).getDrawingRect(ButtonRect); int InitialLeft = ButtonRect.left + 10; ButtonRect.offsetTo(InitialLeft, ButtonRect.top); // while(position < childCount){ if(ButtonRect.contains(x,y)){break;} if(ButtonRect.right + ButtonRect.width() > Grid.getWidth()) { ButtonRect.offsetTo(InitialLeft, ButtonRect.bottom);} position++; ButtonRect.offsetTo(ButtonRect.right, ButtonRect.top); } msg.what = position; msg.arg1 = ButtonRect.bottom; msg.arg2 = y; cHandler.sendMessage(msg); }// end if action up if (event.getAction() == MotionEvent.ACTION_UP) { } return false; } });

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  • database connection OK,result not appear

    - by klox
    hi..all.for now i'm already connected to database but the result not appear at Tuner range is"+res+"this is my code: var str=data[0]; var matches=str.match(/[EE|EJU].*D/i); $.ajax({ type:"post", url:"process1.php", data:"tversion="+matches+"&action=tunermatches", cache:false, async:false, success: function(res){ $('#value').replacewith("<div id='value'><h6>Tuner range is"+res+".</h6></div>"); } }); }); and this is my process file: //connect to database $dbc=mysql_connect(_SRV,_ACCID,_PWD) or die(_ERROR15.": ".mysql_error()); $db=mysql_select_db("qdbase",$dbc) or die(_ERROR17.": ".mysql_error()); switch(postVar('action')) { case 'tunermatches' : tunermatches(postVar('tversion')); break; function tunermatches($tversion)){ $Tuner=mysql_real_escape_string($tversion); $sql= "SELECT remark FROM settingdata WHERE itemname='Tuner_range' AND itemdata='".$Tunermatches."'"; $res=mysql_query($sql) or die (_ERROR26.":".mysql_error()); $dat=mysql_fetch_array($res,MYSQL_NUM); if($dat[0]>0) { echo $dat[0]; } mysql_close($dbc); }

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  • GetAccessControl error with NTAccount

    - by Adam Witko
    private bool HasRights(FileSystemRights fileSystemRights_, string fileName_, bool isFile_) { bool hasRights = false; WindowsIdentity WinIdentity = System.Security.Principal.WindowsIdentity.GetCurrent(); WindowsPrincipal WinPrincipal = new WindowsPrincipal(WinIdentity); AuthorizationRuleCollection arc = null; if (isFile_) { FileInfo fi = new FileInfo(@fileName_); arc = fi.GetAccessControl().GetAccessRules(true, true, typeof(NTAccount)); } else { DirectoryInfo di = new DirectoryInfo(@fileName_); arc = di.GetAccessControl().GetAccessRules(true, true, typeof(NTAccount)); } foreach (FileSystemAccessRule rule in arc) { if (WinPrincipal.IsInRole(rule.IdentityReference.Value)) { if (((int)rule.FileSystemRights & (int)fileSystemRights_) > 0) { if (rule.AccessControlType == AccessControlType.Allow) hasRights = true; else if (rule.AccessControlType == AccessControlType.Deny) { hasRights = false; break; } } } } return hasRights; } The above code block is causing me problems. When the WinPrincipal.IsInRole(rule.IdentityReference.Value) is executed the following exception occurs: "The trust relationship between the primary domain and the trusted domain failed.". I'm very new to using identities, principles and such so I don't know what's the problem. I'm assuming it's with the use of NTAccount? Thanks

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  • vector <T *> destructor

    - by Daniel.Z
    I have a class defined like: Class A { public: int num; A *parent; vector<A *> children; ... // constructor without parameters A(void) { this->num = 3; this->parent = 0; for (int i=0;i<num;++i) children.push_back(new A(this,num-1)); } // constructor with parameters A(A *a,int n) { this->num = n; this->children->parent = a; for (int i=0;i<num;++i) this->children.push_back(new A(this,this->num-1)); } }; now, the constructor works fine. there are some problem with destructor. currently, the destructor is defined as: A::~A(void) { if (this->parent!=0) this->parent = 0; for (int i=0;i<(int)children.size();++i) this->children[i]->~A(); vector <A *> ().swap(this->children); } but every time when I debug it, it will break at: void deallocate(pointer _Ptr, size_type) { // deallocate object at _Ptr, ignore size ::operator delete(_Ptr); } it looks like I cannot delete the pointer in the vector of this-children, is there any way that I can de-construct the class successfully?

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  • iOS Simulator is black on app execution

    - by Terryn
    I am running xcode 5.1.1 and have been trying to learn objective C / iOS development. Right now whenever I try to run my code on the emulator (I do not have an actual device atm) it comes up with a black screen. Code can be found here. Compiling and running gives me the following error: 2014-08-23 10:42:57.429 Calculator[1862:60b] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<XYZViewController 0xe436640> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key didgetPressed.' *** First throw call stack: ( 0 CoreFoundation 0x017ed1e4 __exceptionPreprocess + 180 1 libobjc.A.dylib 0x0156c8e5 objc_exception_throw + 44 2 CoreFoundation 0x0187cfe1 -[NSException raise] + 17 3 Foundation 0x0122cd9e -[NSObject(NSKeyValueCoding) setValue:forUndefinedKey:] + 282 4 Foundation 0x011991d7 _NSSetUsingKeyValueSetter + 88 5 Foundation 0x01198731 -[NSObject(NSKeyValueCoding) setValue:forKey:] + 267 6 Foundation 0x011fab0a -[NSObject(NSKeyValueCoding) setValue:forKeyPath:] + 412 7 UIKit 0x004e31f4 -[UIRuntimeOutletConnection connect] + 106 8 libobjc.A.dylib 0x0157e7de -[NSObject performSelector:] + 62 9 CoreFoundation 0x017e876a -[NSArray makeObjectsPerformSelector:] + 314 10 UIKit 0x004e1d4d -[UINib instantiateWithOwner:options:] + 1417 11 UIKit 0x0034a6f5 -[UIViewController _loadViewFromNibNamed:bundle:] + 280 12 UIKit 0x0034ae9d -[UIViewController loadView] + 302 13 UIKit 0x0034b0d3 -[UIViewController loadViewIfRequired] + 78 14 UIKit 0x0034b5d9 -[UIViewController view] + 35 15 UIKit 0x0026b267 -[UIWindow addRootViewControllerViewIfPossible] + 66 16 UIKit 0x0026b5ef -[UIWindow _setHidden:forced:] + 312 17 UIKit 0x0026b86b -[UIWindow _orderFrontWithoutMakingKey] + 49 18 UIKit 0x002763c8 -[UIWindow makeKeyAndVisible] + 65 19 UIKit 0x00226bc0 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 2097 20 UIKit 0x0022b667 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824 21 UIKit 0x0023ff92 -[UIApplication handleEvent:withNewEvent:] + 3517 22 UIKit 0x00240555 -[UIApplication sendEvent:] + 85 23 UIKit 0x0022d250 _UIApplicationHandleEvent + 683 24 GraphicsServices 0x037e2f02 _PurpleEventCallback + 776 25 GraphicsServices 0x037e2a0d PurpleEventCallback + 46 26 CoreFoundation 0x01768ca5 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53 27 CoreFoundation 0x017689db __CFRunLoopDoSource1 + 523 28 CoreFoundation 0x0179368c __CFRunLoopRun + 2156 29 CoreFoundation 0x017929d3 CFRunLoopRunSpecific + 467 30 CoreFoundation 0x017927eb CFRunLoopRunInMode + 123 31 UIKit 0x0022ad9c -[UIApplication _run] + 840 32 UIKit 0x0022cf9b UIApplicationMain + 1225 33 Calculator 0x00002c8d main + 141 34 libdyld.dylib 0x01e34701 start + 1 35 ??? 0x00000001 0x0 + 1 ) libc++abi.dylib: terminating with uncaught exception of type NSException (lldb) I have attempted the following things, and so far nothing has worked 1) checked the deployment info, it has the main interface set to main 2) double checked all break points to turn them off and disabled all of them through Debug-Disable Breakpoints 3) Reset Content and Settings on the iOS Simulator. 4) Checked the issue with the LLDB Debugger, however from what I have read the issue is no longer present with the 5.1.1 xcode. 5) checked the local host is still set to 127.0.0.1 Thanks! - Terryn

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  • maximum memory which malloc can allocate!

    - by Vikas
    I was trying to figure out how much memory I can malloc to maximum extent on my machine (1 Gb RAM 160 Gb HD Windows platform). I read that maximum memory malloc can allocate is limited to physical memory.(on heap) Also when a program exceeds consumption of memory to a certain level, the computer stops working because other applications do not get enough memory that they require. So to confirm,I wrote a small program in C, int main(){ int *p; while(1){ p=(int *)malloc(4); if(!p)break; } } Hoping that there would be a time when memory allocation will fail and loop will be breaked. But my computer hanged as It was an infinite loop. I waited for about an hour and finally I had to forcely shut down my computer. Some questions: Does malloc allocate memory from HD also? What was the reason for above behaviour? Why didn't loop breaked at any point of time.? Why wasn't there any allocation failure?

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  • MySQL " identify storage engine statement"

    - by sammysmall
    This IS NOT a Homework question! While building my current student database project I realized that I may want to identify comprehensive information about a database design in the future. More-so if I am fortunate enough to get a job in this field and were handed a database project how could I break down certain elements for identification... In all of my previous designs I have been using MySQL Community Server (GPL) 5.1.42, I thought (duh) that I was using the MyISAM based on most of my text-book instruction and MySQL 5.0 Reference Manual :: 13 Storage Engines :: 13.1 The MyISAM Storage Engine I determined that this was in fact incorrect for this version and the use of "SHOW ENGINES" at the console... No problem, figured out why they have "versions" the need to pay attention to what version is being used, and the need for a means to determine what I am about to mess up "if" I do not pay attention to detail... Q1. Specifically what statement will identify the version used by someone elses initial database creation? (since I created my own databases I know what version I used) Q2. Specifically what statement will identify the storage engine that the developer used when creating the database. (I specified a particular database in my collection then tried SHOW Engine, did not work, then tried to just get the metadata from one table in that database: mysql SELECT duck_cust, table_type, engine - FROM INFORMATION_SCHEMA.tables - WHERE table_schema = 'tp' - ORDER BY table_type ASC, table_name DESC; as this was not really what I wanted (and did not work) I am looking for some direction from the pros... Q3. (If you really have the inclination to continue helping) If I were to access a database from an earlier/later "version" are there backward/forward compatibility issues for maintaining/updating data between versions? Please and Thank you in advance for your time and efforts! sammysmall

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  • 500 internal server error at form connection

    - by klox
    hi..all..i've a problem i can't connect to database what's wrong with my code?this is my code: $("#mod").change(function() { var barcode; barCode=$("#mod").val(); var data=barCode.split(" "); $("#mod").val(data[0]); $("#seri").val(data[1]); var str=data[0]; var matches=str.match(/(EE|[EJU]).*(D)/i); $.ajax({ type:"post", url:"process1.php", data:"value="+matches+"action=tunermatches", cache:false, async:false, success: function(res){ $('#rslt').replaceWith( "<div id='value'><h6>Tuner range is" + res + " .</h6></div>" ); } }); }); and this is my process file: switch(postVar('action')) { case 'tunermatches' : tunermatches(postVar('tuner')); break; function tunermatches($tuner)){ $Tuner=mysql_real_escape_string($tuner); $sql= "SELECT remark FROM settingdata WHERE itemname="Tuner_range" AND itemdata="$Tunermatches"; $res=mysql_query($sql); $dat=mysql_fetch_array($res,MYSQL_NUM); if($dat[0]>0) { echo $dat[0]; } mysql_close($dbc); }

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  • Why does this asp.net mvc unit test fail?

    - by Brian McCord
    I have this unit test: [TestMethod] public void Delete_Post_Passes_With_State_4() { //Arrange ViewResult result = stateController.Delete( 4 ) as ViewResult; var model = (State)result.ViewData.Model; //Act RedirectToRouteResult redirectResult = stateController.Delete( model ) as RedirectToRouteResult; var newresult = stateController.Delete( 4 ) as ViewResult; var newmodel = (State)newresult.ViewData.Model; //Assert Assert.AreEqual( redirectResult.RouteValues["action"], "Index" ); Assert.IsNull( newmodel ); } Here are the two controller actions that handle deleting: // // GET: /State/Delete/5 public ActionResult Delete(int id) { var x = _stateService.GetById( id ); return View(x); } // // POST: /State/Delete/5 [HttpPost] public ActionResult Delete(State model) { try { if( model == null ) { return View( model ); } _stateService.Delete( model ); return RedirectToAction("Index"); } catch { return View( model ); } } What I can't figure out is why this test fails. I have verified that the record actually gets deleted from the list. If I set a break point in the Delete method on the line: var x = _stateService.GetById( id ); The GetById does indeed return a null just as it should, but when it gets back to the newresult variable in the test, the ViewData.Model is the deleted model. What am I doing wrong?

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  • Best practices for withstanding launch day traffic burst

    - by Sam McAfee
    We are working on a website for a client that (for once) is expected to get a fair amount of traffic on day one. There are press releases, people are blogging about it, etc. I am a little concerned that we're going to fall flat on our face on day one. What are the main things you would look at to ensure (in advance without real traffic data) that you can stay standing after a big launch. Details: This is a L/A/M/PHP stack, using an internally developed MVC framework. This is currently being launched on one server, with Apache and MySQL both on it, but we can break that up if need be. We are already installing memcached and doing as much PHP-level caching as we can think of. Some of the pages are rather query intensive, and we are using Smarty as our template engine. Keep in mind there is no time to change any of these major aspects--this is the just the setup. What sorts of things should we watch out for?

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  • Handling close-to-impossible collisions on should-be-unique values

    - by balpha
    There are many systems that depend on the uniqueness of some particular value. Anything that uses GUIDs comes to mind (eg. the Windows registry or other databases), but also things that create a hash from an object to identify it and thus need this hash to be unique. A hash table usually doesn't mind if two objects have the same hash because the hashing is just used to break down the objects into categories, so that on lookup, not all objects in the table, but only those objects in the same category (bucket) have to be compared for identity to the searched object. Other implementations however (seem to) depend on the uniqueness. My example (that's what lead me to asking this) is Mercurial's revision IDs. An entry on the Mercurial mailing list correctly states The odds of the changeset hash colliding by accident in your first billion commits is basically zero. But we will notice if it happens. And you'll get to be famous as the guy who broke SHA1 by accident. But even the tiniest probability doesn't mean impossible. Now, I don't want an explanation of why it's totally okay to rely on the uniqueness (this has been discussed here for example). This is very clear to me. Rather, I'd like to know (maybe by means of examples from your own work): Are there any best practices as to covering these improbable cases anyway? Should they be ignored, because it's more likely that particularly strong solar winds lead to faulty hard disk reads? Should they at least be tested for, if only to fail with a "I give up, you have done the impossible" message to the user? Or should even these cases get handled gracefully? For me, especially the following are interesting, although they are somewhat touchy-feely: If you don't handle these cases, what do you do against gut feelings that don't listen to probabilities? If you do handle them, how do you justify this work (to yourself and others), considering there are more probable cases you don't handle, like a supernonva?

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  • How do you tell that your unit tests are correct?

    - by Jacob Adams
    I've only done minor unit testing at various points in my career. Whenever I start diving into it again, it always troubles me how to prove that my tests are correct. How can I tell that there isn't a bug in my unit test? Usually I end up running the app, proving it works, then using the unit test as a sort of regression test. What is the recommended approach and/or what is the approach you take to this problem? Edit: I also realize that you could write small, granular unit tests that would be easy to understand. However, if you assume that small, granular code is flawless and bulletproof, you could just write small, granular programs and not need unit testing. Edit2: For the arguments "unit testing is for making sure your changes don't break anything" and "this will only happen if the test has the exact same flaw as the code", what if the test overfits? It's possible to pass both good and bad code with a bad test. My main question is what good is unit testing since if your tests can be flawed you can't really improve your confidence in your code, can't really prove your refactoring worked, and can't really prove that you met the specification?

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  • Using group_by with fields_for and accepts_nested_attributes_for

    - by Derek
    I have a the following rails models: class Release < ActiveRecord::Base has_many :release_questionnaires, :dependent => :destroy accepts_nested_attributes_for :release_questionnaires ... end class class ReleaseQuestionnaire < ActiveRecord::Base belongs_to :release belongs_to :milestone ... end class In my view code, I have the following form. <% form_for @release, ... do |f| %> ... <table class="questionnaires"> <% f.fields_for :release_questionnaires, @release.release_questionnaires.sort_by{|ra| ra.questionnaire.name} do |builder| %> ... <% end %> </table> <% end %> This works and allows me to view and edit the questionnaires as desired. However, I have an additional requirement to break the questionnaires out into their own tables grouped by the milestone they are associated to, rather than in a single table. It appears as though the group_by method is design to accomplish this, but I cannot get it to work as desired inside the tag. It may be that I'm missing something obvious, as I am a beginner... Any help is appreciated.

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  • Doctrine - get the offset of an object in a collection (implementing an infinite scroll)

    - by dan
    I am using Doctrine and trying to implement an infinite scroll on a collection of notes displayed on the user's browser. The application is very dynamic, therefore when the user submits a new note, the note is added to the top of the collection straightaway, besides being sent (and stored) to the server. Which is why I can't use a traditional pagination method, where you just send the page number to the server and the server will figure out the offset and the number of results from that. To give you an example of what I mean, imagine there are 20 notes displayed, then the user adds 2 more notes, therefore there are 22 notes displayed. If I simply requests "page 2", the first 2 items of that page will be the last two items of the page currently displayed to the user. Which is why I am after a more sophisticated method, which is the one I am about to explain. Please consider the following code, which is part of the server code serving an AJAX request for more notes: // $lastNoteDisplayedId is coming from the AJAX request $lastNoteDisplayed = $repository->findBy($lastNoteDisplayedId); $allNotes = $repository->findBy($filter, array('createdAt' => 'desc')); $offset = getLastNoteDisplayedOffset($allNotes, $lastNoteDisplayedId); // retrieve the page to send back so that it can be appended to the listing $notesPerPage = 30 $notes = $repository->findBy( array(), array('createdAt' => 'desc'), $notesPerPage, $offset ); $response = json_encode($notes); return $response; Basically I would need to write the method getLastNoteDisplayedOffset, that given the whole set of notes and one particoular note, it can give me its offset, so that I can use it for the pagination of the previous Doctrine statement. I know probably a possible implementation would be: getLastNoteDisplayedOffset($allNotes, $lastNoteDisplayedId) { $i = 0; foreach ($allNotes as $note) { if ($note->getId() === $lastNoteDisplayedId->getId()) { break; } $i++; } return $i; } I would prefer not to loop through all notes because performance is an important factor. I was wondering if Doctrine has got a method itself or if you can suggest a different approach.

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  • Exercise for exam about comparing string on file

    - by Telmo Vaz
    I'm trying to do this exercise for my exam tomorrow. I need to compare a string of my own input and see if that string is appearing on the file. This needs to be done directly on the file, so I cannot extract the string to my program and compare them "indirectly". I found this way but I'm not getting it right, and I don't know why. The algorithm sounds good to me. Any help, please? I really need to focus on this one. Thanks in advance, guys. #include<stdio.h> void comp(); int main(void) { comp(); return 0; } void comp() { FILE *file = fopen("e1.txt", "r+"); if(!file) { printf("Not possible to open the file"); return; } char src[50], ch; short i, len; fprintf(stdout, "What are you looking for? \nwrite: "); fgets(src, 200, stdin); len = strlen(src); while((ch = fgetc(file)) != EOF) { i = 0; while(ch == src[i]) { if(i <= len) { printf("%c - %c", ch, src[i]); fseek(file, 0, SEEK_CUR + 1); i++; } else break; } } }

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  • How to create and display a list in Java?

    - by lox
    i have to create a list of ,let's say 50 people, (in Java) and display the list, and i don't really know how to do that. so this is what i have tried to do so far . please correct and complete some of my code . public class Person { String name; String stuff; } public class CreatePerson { public static void ang() { ArrayList<Person> thing=new ArrayList<Person>(); Scanner diskScanner = new Scanner(in); for(int i=0; i<50; i++){ Person pers = new Person(); out.print("name: "); pers.name=diskScanner.nextLine(); out.print("stuff: "); pers.stuff=diskScanner.nextLine(); thing.add(pers); break; } // Display people for (int i=0; i<50; i++) { out.println(??);{ } } }}

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  • Constraint to array dimension in C language

    - by Summer_More_More_Tea
    int KMP( const char *original, int o_len, const char *substring, int s_len ){ if( o_len < s_len ) return -1; int k = 0; int cur = 1; int fail[ s_len ]; fail[ k ] = -1; while( cur < s_len ){ k = cur - 1; do{ if( substring[ cur ] == substring[ k ] ){ fail[ cur ] = k; break; }else{ k = fail[ k ] + 1; } }while( k ); if( !k && ( substring[ cur ] != substring[ 0 ] ) ){ fail[ cur ] = -1; }else if( !k ){ fail[ cur ] = 0; } cur++; } k = 0; cur = 0; while( ( k < s_len ) && ( cur < o_len ) ){ if( original[ cur ] == substring[ k ] ){ cur++; k++; }else{ if( k == 0 ){ cur++; }else{ k = fail[ k - 1 ] + 1; } } } if( k == s_len ) return cur - k; else return -1; } This is a KMP algorithm I once coded. When I reviewed it this morning, I find it strange that an integer array is defined as int fail[ s_len ]. Does the specification requires dimesion of arrays compile-time constant? How can this code pass the compilation? By the way, my gcc version is 4.4.1. Thanks in advance!

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