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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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  • jquery: how to append elements to emtpy object

    - by John
    I want to create a set of options, that will be appended to every select in grid column <option> option 1 </option> <option> option 2 </option> ... <option> option N </option> but I don't know how to create a set of elements without parent element. appending to an empty jquery object doesn't work var options = $(''); options.append('<option></option>')

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  • Why aren't operator conversions implicitly called for templated functions? (C++)

    - by John Gordon
    I have the following code: template <class T> struct pointer { operator pointer<const T>() const; }; void f(pointer<const float>); template <typename U> void tf(pointer<const float>); void g() { pointer<float> ptr; f(ptr); tf(ptr); } When I compile the code with gcc 4.3.3 I get a message (aaa.cc:17: error: no matching function for call to ‘tf(pointer<float>&)’) indicating that the compiler called 'operator pointer<const T>' for the non-templated function f(), but didn't for the templated function tf(). Why and is there any workaround short of overloading tf() with a const and non-const version? Thanks in advance for any help.

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  • Change user control appearance based on state

    - by John
    I have a user control that consists of four overlapping items: 2 rectangles, an ellipse and a lable <UserControl x:Class="UserControl" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Width="50.1" Height="45.424" Background="Transparent" FontSize="24"> <Grid> <Grid.RowDefinitions> <RowDefinition Height="3.303*" /> <RowDefinition Height="40*" /> <RowDefinition Height="2.121*" /> </Grid.RowDefinitions> <Grid.ColumnDefinitions> <ColumnDefinition Width="5.344*" /> <ColumnDefinition Width="40.075*" /> <ColumnDefinition Width="4.663*" /> </Grid.ColumnDefinitions> <Rectangle Name="Rectangle1" RadiusX="5" RadiusY="5" Fill="DarkGray" Grid.ColumnSpan="3" Grid.RowSpan="3" /> <Ellipse Name="ellipse1" Fill="{Binding State}" Margin="0.016,0.001,4.663,0" Grid.Row="1" Grid.Column="1" Grid.ColumnSpan="2" Stroke="Black" IsEnabled="True" Panel.ZIndex="2" /> <Label Name="lblNumber" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Foreground="White" FontWeight="Bold" FontSize="24" Grid.Column="1" Grid.Row="1" Padding="0" Panel.ZIndex="3">9</Label> <Rectangle Grid.Column="1" Grid.Row="1" Margin="0.091,0,4.663,0" Fill="Blue" Name="rectangle2" Stroke="Black" Grid.ColumnSpan="2" Panel.ZIndex="1" /> </Grid> Here is my business object that I want to control the state of my user control: Imports System.Data Imports System.ComponentModel Public Class BusinessObject Implements INotifyPropertyChanged 'Public logger As log4net.ILog Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged Private _state As States Public Enum States State1 State2 State3 End Enum Public Property State() As States Get Return _state End Get Set(ByVal value As States) If (value <> _state) Then _state = value RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("State")) End If End Set End Property Protected Sub OnPropertyChanged(ByVal name As String) RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(name)) End Sub I want to be able to change the state of a business object in the code behind and have that change the colors of multiple shapes in my usercontrol. I'm not sure about how to do the binding. I set the datacontext of the user control in the code behind but not sure if that's right. I'm new to WPF and programming in general and I'm stuck on where to go from here. Any recommendations would be greatly appreciated!!

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  • What to keep in mind when creating your own custom web services API?

    - by John Conde
    I have created a website which allows users to sign up for, and use, an online service. To help promote the website we will be have resellers who will be offering their own branded services through us. The initial plan is to allow resellers to place registration, login, and lost password forms on their own website and use an API created by us to handle these requests. I have begun outlining how I expect the API to work (and starting documenting it as well) and I want to make sure I get it right, or as close to right, as I can from the beginning as I know once you have declared a public API you want to avoid changing that API at all costs. So far I have decided: To have the user pass their account credentials with each request To require SSL for all requests What else should I be keeping in mind?

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  • in Python find number of same elements in 2 lists

    - by John
    Hi, In Python if I have 2 lists say: l1 = ['a', 'b', 'c', 'd'] l2 = ['c', 'd', 'e'] is there a way to find out how many elements they have the same. In the case about it would be 2 (c and d) I know I could just do a nested loop but is there not a built in function like in php with the array_intersect function Thanks

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  • Thoughts on streamlining multiple .Net apps

    - by John Virgolino
    We have a series of ASP.Net applications that have been written over the course of 8 years. Mostly in the first 3-4 years. They have been running quite well with little maintenance, but new functionality is being requested and we are running into IDE and platform issues. The apps were written in .Net 1.x and 2.x and run in separate spaces but are presented as a single suite of applications which use a common navigation toolbar (implemented as a user control). Every time we want to add something to a menu in the nav we have to modify it in all the apps which is a pain. Also, the various versions of Crystal reports and that we used tables to organize the visual elements and we end up with a mess, especially with all the multi-platform .Net versions running. We need to streamline the suite of apps and make it easier to add on new apps without a hassle. We also need to bring all these apps under one .Net platform and IDE. In addition, there is a WordPress blog styled to match the style of the application suite "integrated" into the UI and a link to a MediaWiki Wiki application as well. My current thinking is to use an open source content management system (CMS) like Joomla (PHP based unfortunately, but it works well) as the user interface framework for style templating and menu management. Joomla's article management would allow us to migrate the Wiki content into articles which could be published without interfering with the .Net apps. Then essentially use an IFrame within an "article" to "host" the .Net application, then... Upgrade the .Net apps to VS2010, strip out all the common header/footer controls and migrate the styles to use the style sheets used in the CMS. As I write this, I certainly realize this is a lot of work and there are optimization issues which this may cause as well as using IFrames seems a bit like cheating and I've read about issues with IFrames. I know that we could use .Net application styling, but it seems like a lot more work (not sure really). Also, the use of a CMS to handle the blog and wiki also seems appealing, unless there is a .Net CMS out there that can handle all of these requirements. Given this information, I am looking to know if I am totally going in the wrong direction? We tried to use open source and integrate it over time, but not this has become hard to maintain. Am I not aware of some technology out there that will meet our requirements? Did we do this right and should we just focus on getting the .Net streamlined? I understand that no matter what we do, it's going to be a lot of work. The communities considerable experience would be helpful. Thanks!! PS - A complete rewrite is not an option.

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  • R: how can I concatenate a list?

    - by John
    I'm trying to produce a single variable which is a concatenation of two chars e.g to go from "p30s4" "p28s4" to "p30s4 p28s4". I've tried cat and paste as shown below. Both return empty variables. What am I doing wrong? > blah = c("p30s4","p28s4") > blah [1] "p30s4" "p28s4" > foo = cat(blah) p30s4 p28s4 > foo NULL > foo = paste(cat(blah)) p30s4 p28s4 > foo character(0)

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  • R: How to update a package and keep it from reverting to the original?

    - by John
    I want to upgrade the package ggplot2: library(ggplot2) packageDescription("ggplot2")["Version"] > 0.8.3 But the current version is 0.8.7. I tried update.packages(), which seemed to work OK. But it still returned older version 0.8.3. So I downloaded and installed the package source from Cran, which says 0.8.7 in the download page. I then install it via the GUI menu in R. It returns ** building package indices ... * DONE (ggplot2) I then run: packageDescription("ggplot2")["Version"] > 0.8.3 And still I have the older version! I don't know why this is not working, what's more I had already come across this problem before and solved it (I can't remember exactly what) but now it has gone back to the older version! What's the easiest way to keep packages like this updated automatically and not have them refer back to older packages?

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  • Easiest way to convert json data into objects with methods attached?

    - by John Mee
    What's the quickest and easiest way to convert my json, containing the data of the objects, into actual objects with methods attached? By way of example, I get data for a fruitbowl with an array of fruit objects which in turn contain an array of seeds thus: {"fruitbowl": [{ "name": "apple", "color": "red", "seeds": [] },{ "name": "orange", "color": "orange", "seeds": [ {"size":"small","density":"hard"}, {"size":"small","density":"soft"} ]} } That's all nice and good but down on the client we do stuff with this fruit, like eat it and plant trees... var fruitbowl = [] function Fruit(name, color, seeds){ this.name = name this.color = color this.seeds = seeds this.eat = function(){ // munch munch } } function Seed(size, density){ this.size = size this.density = density this.plant = function(){ // grow grow } } My ajax's success routine currently is currently looping over the thing and constructing each object in turn and it doesn't handle the seeds yet, because before I go looping over seed constructors I'm thinking Is there not a better way? success: function(data){ fruitbowl.length = 0 $.each(data.fruitbowl, function(i, f){ fruitbowl.push(new Fruit(f.name, f.color, f.seeds)) }) I haven't explored looping over the objects as they are and attaching all the methods. Would that work?

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  • WPF: How to efficiently update an Image 30 times per second

    - by John
    Hello, I'm writing a WPF application that uses a component, and this component returns a pointer (IntPtr) to pixels of a bitmap (stride * height). I know in advance that the bitmap is a 24bits rgb, its width and height. Updating the Image control with these bitmaps makes up a video to the user, but I'm not sure what's the most efficient way to do that, most of the time the CPU usage goes to 75%+ and memory changing from 40mb to 500mb and the nI think GC starts to work and then it drops again to 40mm. The app starts to not be responsive. What shoud I do? thanks!

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  • Rails: unexpected behavior updating a shared instance

    - by Pascal Lindelauf
    I have a User object, that is related to a Post object via two different association paths: Post --(has_many)-- comments --(belongs to)-- writer (of type User) Post --(belongs to)-- writer (of type User) Say the following hold: user1.name == "Bill" post1.comments[1].writer == user1 post1.writer == user1 Now when I retrieve the post1 and its comments from the database and I update post1.comments[1].writer like so: post1.comments[1].writer.name = "John" I would expect post1.writer to equal "John" too. But it doesn't! It still equals "Bill". So there seems to be some caching going on, but the kind I would not expect. I would expect Rails to be clever enough to load exactly one instance of the user with name "Bill"; instead is appears to load two individual ones: one for each association path. Can someone explain how this works exactly and how I am to handle these types of situations the "Rails way"?

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  • [solved] IE6 PNG-transparency CSS hack not working

    - by John
    I looked around and decided to use a CSS approach rather than rely on JS... I figure the kind of corporate users stuck with IE6 might also have JS disabled by IT departments. So In my HTML I have: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html;charset=utf-8" /> <title>My Page</title> <link rel="stylesheet" type="text/css" href="default.css" /> <!--[if IE 6]><link rel="stylesheet" type="text/css" href="ie6.css"><![endif]--> </head> <body> <img src="media/logo.png"/> </body> Then my ie6.css consists simply of: img { filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(...); } However none of this makes the slightest difference, no transparency. I commented out all the rest of the page so it is literally that one and still no luck. I removed the default.css stylesheet and still no difference. EDIT: I now got it working, using the .htc method, loading that file in a conditional IE6 test block. It turned out the problem I was having was that Windows 7 had 'locked' the file (I don't even know what this means) and this blocked IE from loading/using it.

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  • getcwd for current location based on ftp account permission

    - by John Doe
    Hello. I'm trying to make a small script that's changing the permission for specific file using a ftp connection. My problem is the absolute path. I have a ftp account wich land on the script directory (/script/). If i'm using getcwd, it will return the whole path (/home/user/public_html/script) but i need only the difference between the full path and the current path (getcwd path: /home/user/public_html/script/ ftp landing path: /script). So, how can i use getcwd to get the current directory for a ftp account? For example, if the user is landing in public_html, the path to the script will be /script/, or if he is landing inside /user, the path will be /public_html/script. Thanks

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  • Javascript Split: without losing character

    - by Rohan
    I want to split certain text using JavaSscript. The text looks like: 9:30 pm The user did action A. 10:30 pm Welcome, user John Doe. 11:30 am Messaged user John Doe Now, I want to split the string into events. i.e.: 9:30 pm The user did action A. would be one event. I'm using RegEx for this: var split = journals.split(/\d*\d:/); Thing is, the first two characters are getting lost. The split appears like this: 30 pm The user did action A. How do I split so that the split maintains the first two/three characters (ie 9: or 10:) etc? Thanks!

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  • I want just the insert query for a temp table.

    - by John Stephen
    Hi..I am using C#.Net and Sql Server ( Windows Application ). I had created a temporary table. When a button is clicked, temporary table (#tmp_emp_details) is created. I am having another button called "insert Values" and also 5 textboxes. The values that are entered in the textbox are used and whenever com.ExecuteNonQuery(); line comes, it throws an error message Invalid object name '#tbl_emp_answer'.. Below is the set of code.. Please give me a solution. Code for insert (in insert value button): private void btninsertvalues_Click(object sender, EventArgs e) { username = txtusername.Text; examloginid = txtexamloginid.Text; question = txtquestion.Text; answer = txtanswer.Text; useranswer = txtanswer.Text; SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=tempdb;Integrated Security=True;"); SqlCommand com = new SqlCommand("Insert into #tbl_emp_answer values('"+username+"','"+examloginid+"','"+question+"','"+answer+"','"+useranswer+"')", con); con.Open(); com.ExecuteNonQuery(); con.Close(); }

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  • Coping with weak typing

    - by John Leonard
    I'm a front end Flex developer peeking over the wall at html. One of the things I have a hard time with is weak typing in Javascript. I know many developers say they prefer it. How do I stop worrying and learn to love the weak typing? Are there best practices for variable naming that help make var types human readable? Another thing I have trouble with is getting by without my trusted compiler errors and warnings. I'm getting along with firebug. Is there anything else I should have in my toolkit?

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  • When are sqlite3 views updated?

    - by John Smith
    I have a database on the iPhone which as a view. When I update the dependent tables the view is not updated. It's only updated when I close and reopen the application. From there onwards things are okay: updates reflect immediately. Is there something I need to do to force update of a VIEW?

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  • For-Each and Pointers in Java

    - by John
    Ok, so I'm tyring to iterate through an ArrayList and remove a specefic element. However, I am having some trouble using the For-Each like structure. When I run the following code: ArrayList<String> arr = new ArrayList<String>(); //... fill with some values (doesn't really matter) for(String t : arr) { t = " some other value "; //hoping this would change the actual array } for(String t : arr) { System.out.println(t); //however, I still get the same array here } My question in, how can I make 't' a pointer to 'arr' so that I am able to change the values in a for-each loop? I know I could loop through the ArrayList using a different structure, but this one looks so clean and readable, it would just be nice to be able to make 't' a pointer. All comments are appreciated! Even if you say I should just suck it up and use a different construct.

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  • can't explain NullPointerException

    - by John Pope
    In the following code, i have a method to get a Vector of persons with the same zodiac sign. persoane is a Vector. I keep getting a NullPointerException at the if condition (persoane is definetly not null). I am unable to see why. Any help would be greatly appreciated public Vector<Persoana> cautaDupaZodie(String zodie) { Vector<Persoana> rezultat= new Vector<Persoana>(); for(int i=0; i<persoane.size(); i++) { if(persoane.get(i).getData().getZodie().equals(zodie)) //the exception occurs here { rezultat.add(persoane.get(i)); } } return rezultat; }

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  • Is it good practice to name variables differently when defining more than one function?

    - by John
    For example, in this simple function where fun1 takes as input two numbers, adds them together and passes them to function 2 for printing the output. var1_in is local to each function, so is it OK to use the name var1_in in both functions, or is it better practice to call them different things? fun1 <- function (var1_in, var2_in) { var3 = var1_in + var2_in fun2(var3) } fun2 <- function (var1_in) { var4 = var1_in print(var4) }

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