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• Succinct introduction to C++/CLI for C#/Haskell/F#/JS/C++/... programmer

  - by Henrik

  Hello everybody, I'm trying to write integrations with the operating system and with things like active directory and Ocropus. I know a bunch of programming languages, including those listed in the title. I'm trying to learn exactly how C++/CLI works, but can't find succinct, exact and accurate descriptions online from the searching that I have done. So I ask here. Could you tell me the pitfalls and features of C++/CLI? Assume I know all of C# and start from there. I'm not an expert in C++, so some of my questions' answers might be "just like C++", but could say that I am at C#. I would like to know things like: Converting C++ pointers to CLI pointers, Any differences in passing by value/doubly indirect pointers/CLI pointers from C#/C++ and what is 'recommended'. How do gcnew, __gc, __nogc work with Polymorphism Structs Inner classes Interfaces The "fixed" keyword; does that exist? Compiling DLLs loaded into the kernel with C++/CLI possible? Loaded as device drivers? Invoked by the kernel? What does this mean anyway (i.e. to load something into the kernel exactly; how do I know if it is?)? L"my string" versus "my string"? wchar_t? How many types of chars are there? Are we safe in treating chars as uint32s or what should one treat them as to guarantee language indifference in code? Finalizers (~ClassName() {}) are discouraged in C# because there are no garantuees they will run deterministically, but since in C++ I have to use "delete" or use copy-c'tors as to stack allocate memory, what are the recommendations between C#/C++ interactions? What are the pitfalls when using reflection in C++/CLI? How well does C++/CLI work with the IDisposable pattern and with SafeHandle, SafeHandleZeroOrMinusOneIsInvalid? I've read briefly about asynchronous exceptions when doing DMA-operations, what are these? Are there limitations you impose upon yourself when using C++ with CLI integration rather than just doing plain C++? Attributes in C++ similar to Attributes in C#? Can I use the full meta-programming patterns available in C++ through templates now and still have it compile like ordinary C++? Have you tried writing C++/CLI with boost? What are the optimal ways of interfacing the boost library with C++/CLI; can you give me an example of passing a lambda expression to an iterator/foldr function? What is the preferred way of exception handling? Can C++/CLI catch managed exceptions now? How well does dynamic IL generation work with C++/CLI? Does it run on Mono? Any other things I ought to know about?

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• Succinct introduction to C++/CLI for C#/Haskell/F#/JS/C++/... programmer

  - by Henrik

  Hello everybody, I'm trying to write integrations with the operating system and with things like active directory and Ocropus. I know a bunch of programming languages, including those listed in the title. I'm trying to learn exactly how C++/CLI works, but can't find succinct, exact and accurate descriptions online from the searching that I have done. So I ask here. Could you tell me the pitfalls and features of C++/CLI? Assume I know all of C# and start from there. I'm not an expert in C++, so some of my questions' answers might be "just like C++", but could say that I am at C#. I would like to know things like: Converting C++ pointers to CLI pointers, Any differences in passing by value/doubly indirect pointers/CLI pointers from C#/C++ and what is 'recommended'. How do gcnew, __gc, __nogc work with Polymorphism Structs Inner classes Interfaces The "fixed" keyword; does that exist? Compiling DLLs loaded into the kernel with C++/CLI possible? Loaded as device drivers? Invoked by the kernel? What does this mean anyway (i.e. to load something into the kernel exactly; how do I know if it is?)? L"my string" versus "my string"? wchar_t? How many types of chars are there? Are we safe in treating chars as uint32s or what should one treat them as to guarantee language indifference in code? Finalizers (~ClassName() {}) are discouraged in C# because there are no garantuees they will run deterministically, but since in C++ I have to use "delete" or use copy-c'tors as to stack allocate memory, what are the recommendations between C#/C++ interactions? What are the pitfalls when using reflection in C++/CLI? How well does C++/CLI work with the IDisposable pattern and with SafeHandle, SafeHandleZeroOrMinusOneIsInvalid? I've read briefly about asynchronous exceptions when doing DMA-operations, what are these? Are there limitations you impose upon yourself when using C++ with CLI integration rather than just doing plain C++? Attributes in C++ similar to Attributes in C#? Can I use the full meta-programming patterns available in C++ through templates now and still have it compile like ordinary C++? Have you tried writing C++/CLI with boost? What are the optimal ways of interfacing the boost library with C++/CLI; can you give me an example of passing a lambda expression to an iterator/foldr function? What is the preferred way of exception handling? Can C++/CLI catch managed exceptions now? How well does dynamic IL generation work with C++/CLI? Does it run on Mono? Any other things I ought to know about?

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• user generated / user specific functions

  - by pedalpete

  I'm looking for the most elegant and secure method to do the following. I have a calendar, and groups of users. Users can add events to specific days on the calendar, and specify how long each event lasts for. I've had a few requests from users to add the ability for them to define that events of a specific length include a break, of a certain amount of time, or require that a specific amount of time be left between events. For example, if event is 2 hours, include a 20min break. for each event, require 30 minutes before start of next event. The same group that has asked for an event of 2 hours to include a 20 min break, could also require that an event 3 hours include a 30 minute break. In the end, what the users are trying to get is an elapsed time excluding breaks calculated for them. Currently I provide them a total elapsed time, but they are looking for a running time. However, each of these requests is different for each group. Where one group may want a 30 minute break during a 2 hour event, and another may want only 10 minutes for each 3 hour event. I was kinda thinking I could write the functions into a php file per group, and then include that file and do the calculations via php and then return a calculated total to the user, but something about that doesn't sit right with me. Another option is to output the groups functions to javascript, and have it run client-side, as I'm already returning the duration of the event, but where the user is part of more than one group with different rules, this seems like it could get rather messy. I currently store the start and end time in the database, but no 'durations', and I don't think I should be storing the calculated totals in the db, because if a group decides to change their calculations, I'd need to change it throughout the db. Is there a better way of doing this? I would just store the variables in mysql, but I don't see how I can then say to mysql to calculate based on those variables. I'm REALLY lost here. Any suggestions? I'm hoping somebody has done something similar and can provide some insight into the best direction. If it helps, my table contains eventid, user, group, startDate, startTime, endDate, endTime, type The json for the event which I return to the user is {"eventid":"'.$eventId.'", "user":"'.$userId.'","group":"'.$groupId.'","type":"'.$type.'","startDate":".$startDate.'","startTime":"'.$startTime.'","endDate":"'.$endDate.'","endTime":"'.$endTime.'","durationLength":"'.$duration.'", "durationHrs":"'.$durationHrs.'"} where for example, duration length is 2.5 and duration hours is 2:30.

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• What do you expect from a package manager for Emacs

  - by tarsius

  Although several hundred Emacs Lisp libraries exist GNU Emacs does not have an (internal) package manager. I guess that most users would agree that it is currently rather inconvenient to find, install and especially keep up-to-date Emacs Lisp libraries. These pages make life a bit easier Emacs Lisp List - Problem: I see dead people (links). Emacswiki - Problem: May contain traces of nuts (malicious code). These are some package managers XEmacs package manager package.el - ELPA pases install.el install-elisp.el plugin.el use-package.el jem-pkg.el epkg/elm - the one I am working. And this are some packages that provide functionality that might be useful in a package manager ell.el - Browse the Emacs Lisp List genauto.el - helps generate autoloads for your elisp packages date-calc.el - date calculation and parsing routines strptime.el - partial implementation of POSIX date and time parsing wikirel.el - Visit relevant pages on the Emacs Wiki loadhist.el, lib-requires.el, elisp-depend.el - Commands to list Emacs Lisp library dependencies. project-root.el - Define a project root and take actions based upon it So I would like to know from you what you consider important/unimportant/supplementary... in a package manager for Emacs. Some ideas Many packages (incorporate the Emacs Lisp List and other lists of libraries). Only packages that have been tested. Support for more than one package archive (so people can choose between many/tested packages). Dependency calculated based on required features only. Dependencies take particular versions into account. Only use versions that have been released upstream. Use versions from version control systems if available. Packages are categorized. Packages can be uninstalled and updated not only installed. Support creating fork of upstream version of packages. Support publishing these forks. Support choosing a fork. After installation packages are activated. Generate autoloads. Integration with Emacswiki (see wikirel.el). Users can tag, comment ... packages and share that information. Only FSF-assigned/GPL/FOSS software or don't care about license. Package manager should be integrated in Emacs. Support contacting author. Lots of metadata. Suggest alternatives before installing a particular package. Some discussions about the subject at hand emacs-devel 20080801 comp.emacs 20021121 RationalElispPackaging I am hoping for these kinds of answers Pointers to more implementations, discussions etc. Lengthy descriptions of a set of features that make up your ideal package manager. Descriptions of one particular disired/undisired feature. This has the advantage that the regular voting mechanism allows us to see what features are most welcomed. Feel free to elaborate on my ideas from above. Surprise me.

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• Handling file renames in git

  - by Greg K

  I'd read that when renaming files in git, you should commit any changes, perform your rename and then stage your renamed file. Git will recognise the file from the contents, rather than seeing it as a new untracked file, and keep the change history. However, doing just this tonight I ended up reverting to git mv. > $ git status # On branch master # Changes to be committed: # (use "git reset HEAD <file>..." to unstage) # # modified: index.html # Rename my stylesheet in Finder from iphone.css to mobile.css > $ git status # On branch master # Changes to be committed: # (use "git reset HEAD <file>..." to unstage) # # modified: index.html # # Changed but not updated: # (use "git add/rm <file>..." to update what will be committed) # (use "git checkout -- <file>..." to discard changes in working directory) # # deleted: css/iphone.css # # Untracked files: # (use "git add <file>..." to include in what will be committed) # # css/mobile.css So git now thinks I've deleted one CSS file, and added a new one. Not what I want, lets undo the rename and let git do the work. > $ git reset HEAD . Unstaged changes after reset: M css/iphone.css M index.html Back to where I began. > $ git status # On branch master # Changes to be committed: # (use "git reset HEAD <file>..." to unstage) # # modified: index.html # Lets use git mv instead. > $ git mv css/iphone.css css/mobile.css > $ git status # On branch master # Changes to be committed: # (use "git reset HEAD <file>..." to unstage) # # renamed: css/iphone.css -> css/mobile.css # # Changed but not updated: # (use "git add <file>..." to update what will be committed) # (use "git checkout -- <file>..." to discard changes in working directory) # # modified: index.html # Looks like we're good. So why didn't git recognise the rename the first time around when I used Finder?

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• Challenge: Neater way of currying or partially applying C#4's string.Join

  - by Damian Powell

  Background I recently read that .NET 4's System.String class has a new overload of the Join method. This new overload takes a separator, and an IEnumerable<T> which allows arbitrary collections to be joined into a single string without the need to convert to an intermediate string array. Cool! That means I can now do this: var evenNums = Enumerable.Range(1, 100) .Where(i => i%2 == 0); var list = string.Join(",",evenNums); ...instead of this: var evenNums = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .Select(i => i.ToString()) .ToArray(); var list = string.Join(",", evenNums); ...thus saving on a conversion of every item to a string, and then the allocation of an array. The Problem However, being a fan of the functional style of programming in general, and method chaining in C# in particular, I would prefer to be able to write something like this: var list = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .string.Join(","); This is not legal C# though. The closest I've managed to get is this: var list = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .ApplyTo( Functional.Curry<string, IEnumerable<object>, string> (string.Join)(",") ); ...using the following extension methods: public static class Functional { public static TRslt ApplyTo<TArg, TRslt>(this TArg arg, Func<TArg, TRslt> func) { return func(arg); } public static Func<T1, Func<T2, TResult>> Curry<T1, T2, TResult>(this Func<T1, T2, TResult> func) { Func<Func<T1, T2, TResult>, Func<T1, Func<T2, TResult>>> curried = f => x => y => f(x, y); return curried(func); } } This is quite verbose, requires explicit definition of the parameters and return type of the string.Join overload I want to use, and relies upon C#4's variance features because we are defining one of the arguments as IEnumerable rather than IEnumerable. The Challenge Can you find a neater way of achieving this using the method-chaining style of programming?

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• Scale background image to wrap content of layout

  - by bjg222

  I have a layout that contains some text fields and has a background image that's displayed at the top of my activity. I'd like the background image to scale to wrap the content (don't care about aspect ratio). However, the image is larger than content, so the layout instead wraps the background image. Here's my original code: <RelativeLayout android:layout_width="fill_parent" android:id="@+id/HeaderList" android:layout_gravity="top" android:layout_height="wrap_content" android:background="@drawable/header"> <TextView android:layout_height="wrap_content" android:layout_width="wrap_content" android:id="@+id/NameText" android:text="Jhn Doe" android:textColor="#FFFFFF" android:textSize="30sp" android:layout_alignParentLeft="true" android:layout_alignParentTop="true" android:paddingLeft="4dp" android:paddingTop="4dp" /> <TextView android:layout_height="wrap_content" android:layout_width="wrap_content" android:textColor="#FFFFFF" android:layout_alignParentLeft="true" android:id="@+id/HoursText" android:text="170 hours" android:textSize="23sp" android:layout_below="@+id/NameText" android:paddingLeft="4dp" /> </RelativeLayout> After searching through some other questions, I found these two: How to wrap content views rather than background drawable? Scale a Drawable or background image? Based on this, I created a FrameLayout w/ an ImageView showing the background. Unfortunately, I still can't get it to work. I want the height of the background image to shrink/expand w/ the size of the text views, but with the FrameLayout, the ImageView fits to the size of it's parent, and I can't find a way to make the parent fit to the size the text view layout. Here's my updated code: <FrameLayout android:layout_width="fill_parent" android:layout_height="wrap_content" > <ImageView android:src="@drawable/header" android:layout_width="fill_parent" android:scaleType="fitXY" android:layout_height="fill_parent" /> <RelativeLayout android:layout_width="fill_parent" android:id="@+id/HeaderList" android:layout_gravity="top" android:layout_height="wrap_content" > <TextView android:layout_height="wrap_content" android:layout_width="wrap_content" android:id="@+id/NameText" android:text="John Doe" android:textColor="#FFFFFF" android:textSize="30sp" android:layout_alignParentLeft="true" android:layout_alignParentTop="true" android:paddingLeft="4dp" android:paddingTop="4dp" /> <TextView android:layout_height="wrap_content" android:layout_width="wrap_content" android:textColor="#FFFFFF" android:layout_alignParentLeft="true" android:id="@+id/HoursText" android:text="170 hours" android:textSize="23sp" android:layout_below="@+id/NameText" android:paddingLeft="4dp" /> </RelativeLayout> </FrameLayout> Does anybody have any suggestions for how best to make an image scale to the size of the contents of some layout? I'm not concerned with the aspect ratio of the image, as it won't matter, I just want it to fill the background. Thanks!

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• Sharing a file from Android to Gmail or to Dropbox

  - by Calaf

  To share a simple text file, I started by copying verbatim from FileProvider's manual page: <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <provider android:name="android.support.v4.content.FileProvider" android:authorities="com.mycorp.helloworldtxtfileprovider.MainActivity" android:exported="false" android:grantUriPermissions="true" > <meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/my_paths" /> </provider> <activity android:name="com.mycorp.helloworldtxtfileprovider.MainActivity" ... Then I saved a text file and used, again nearly verbatim, the code under Sending binary content. (Notice that this applies more accurately in this case than "Sending text content" since we are sending a file, which happens to be a text file, rather than just a string of text.) For the convenience of duplication on your side, and since the code is in any case so brief, I'm including it here in full. public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); String filename = "hellow.txt"; String fileContents = "Hello, World!\n"; byte[] bytes = fileContents.getBytes(); FileOutputStream fos = null; try { fos = this.openFileOutput(filename, MODE_PRIVATE); fos.write(bytes); } catch (IOException e) { e.printStackTrace(); } finally { try { fos.close(); } catch (IOException e) { e.printStackTrace(); } } File file = new File(filename); Intent shareIntent = new Intent(); shareIntent.setAction(Intent.ACTION_SEND); shareIntent.putExtra(Intent.EXTRA_STREAM, Uri.fromFile(file)); shareIntent.setType("application/txt"); startActivity(Intent.createChooser(shareIntent, getResources().getText(R.string.send_to))); file.delete(); } } Aside from adding a value for send_to in res/values/strings.xml, the only other change I did to the generic Hello, World that Eclipse creates is to add the following in res/xml/my_paths.xml (as described on the page previously referenced. <paths xmlns:android="http://schemas.android.com/apk/res/android"> <Files-path name="files" path="." /> </paths> This code runs fine. It shows a list of intent recipients. But sending the text file to either Dropbox or to Gmail fails. Dropbox sends the notification "Uploading to Dropbox" followed by "Upload failed: my_file.txt". After "sending message.." Gmail sends "Couldn't send attachment". What is wrong?

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• How to limit JTextArea max Rows and Coloums?

  - by Billbo bug

  I am using JTextArea in JScrollPane I want to limit the maximum number of lines possible and the maximum chars in each line. I need that the string will be exactly like on the screen, each line will end with '\n' (if there another line after it) and the user will be able to insert only X lines and Y chars in each line. I tried to limit the lines but i don't know exactly how many lines do i have because of the line wrapping, The line wrapping is starting new line visualy on the screen(because of the width of the JTextArea) but in the string of the component it is really the same line with no '\n' to indicate new line. I do not have an idea how to limit the max chars in each line while typing. There are 2 stages: The typing of the string- keep that the user will not be able to type more then X lines and Y chars in each line. (even if the line wrap only visualy or the user typed '/n') Insert the string to the DB- after cliking 'OK' convert the string that every line will end with "/n" even if the user did not typed it and the line was wrapped only visualy. There are few problems if i will count the chars in the line and insert '/n' in the end of the line, thats why i decided to do it in two stages. In the first stage ehile the user is typing i would rather only limit it visualy and force line wrpping or something similar. Only in the second stage when i save string i will add the '/n' even if the user did not typed it in the end of the lines! Does anyone have an idea? I know that i will have to use DocumentFilter OR StyledDocument. Here is sample code that limit only the lines to 3:(but not the chars in row to 19) private JTextArea textArea ; textArea = new JTextArea(3,19); textArea .setLineWrap(true); textArea .setDocument(new LimitedStyledDocument(3)); JScrollPane scrollPane = new JScrollPane(textArea public class LimitedStyledDocument extends DefaultStyledDocument /** Field maxCharacters */ int maxLines; public LimitedStyledDocument(int maxLines) { maxCharacters = maxLines; } public void insertString(int offs, String str, AttributeSet attribute) throws BadLocationException { Element root = this.getDefaultRootElement(); int lineCount = getLineCount(str); if (lineCount + root.getElementCount() <= maxLines){ super.insertString(offs, str, attribute); } else { Toolkit.getDefaultToolkit().beep(); } } /** * get Line Count * * @param str * @return the count of '\n' in the String */ private int getLineCount(String str){ String tempStr = new String(str); int index; int lineCount = 0; while (tempStr.length() > 0){ index = tempStr.indexOf("\n"); if(index != -1){ lineCount++; tempStr = tempStr.substring(index+1); } else{ break; } } return lineCount; } }

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• How do I serialize an object to xml but not have it be the root element of the xml document

  - by mezoid

  I have the following object: public class MyClass { public int Id { get; set;} public string Name { get; set; } } I'm wanting to serialize this to the following xml string: <MyClass> <Id>1</Id> <Name>My Name</Name> </MyClass> Unfortunately, when I use the XMLSerializer I get a string which looks like: <?xml version="1.0" encoding="utf-8"?> <MyClass xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Id>1</Id> <Name>My Name</Name> </MyClass> I'm not wanting MyClass to be the root element the document, rather I'm eventually wanting to add the string with other similar serialized objects which will be within a larger xml document. i.e. Eventually I'll have a xml string which looks like this: <Classes> <MyClass> <Id>1</Id> <Name>My Name</Name> </MyClass> <MyClass> <Id>1</Id> <Name>My Name</Name> </MyClass> </Classes>" My first thought was to create a class as follows: public class Classes { public List<MyClass> MyClasses { get; set; } } ...but that just addes an additional node called MyClasses to wrap the list of MyClass.... My gut feeling is that I'm approaching this the wrong way and that my lack of experience with creating xml files isn't helping to point me to some part of the .NET framework or some other library that simplifies this.

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• Synchronized IEnumerator<T>

  - by Dan Bryant

  I'm putting together a custom SynchronizedCollection<T> class so that I can have a synchronized Observable collection for my WPF application. The synchronization is provided via a ReaderWriterLockSlim, which, for the most part, has been easy to apply. The case I'm having trouble with is how to provide thread-safe enumeration of the collection. I've created a custom IEnumerator<T> nested class that looks like this: private class SynchronizedEnumerator : IEnumerator<T> { private SynchronizedCollection<T> _collection; private int _currentIndex; internal SynchronizedEnumerator(SynchronizedCollection<T> collection) { _collection = collection; _collection._lock.EnterReadLock(); _currentIndex = -1; } #region IEnumerator<T> Members public T Current { get; private set;} #endregion #region IDisposable Members public void Dispose() { var collection = _collection; if (collection != null) collection._lock.ExitReadLock(); _collection = null; } #endregion #region IEnumerator Members object System.Collections.IEnumerator.Current { get { return Current; } } public bool MoveNext() { var collection = _collection; if (collection == null) throw new ObjectDisposedException("SynchronizedEnumerator"); _currentIndex++; if (_currentIndex >= collection.Count) { Current = default(T); return false; } Current = collection[_currentIndex]; return true; } public void Reset() { if (_collection == null) throw new ObjectDisposedException("SynchronizedEnumerator"); _currentIndex = -1; Current = default(T); } #endregion } My concern, however, is that if the Enumerator is not Disposed, the lock will never be released. In most use cases, this is not a problem, as foreach should properly call Dispose. It could be a problem, however, if a consumer retrieves an explicit Enumerator instance. Is my only option to document the class with a caveat implementer reminding the consumer to call Dispose if using the Enumerator explicitly or is there a way to safely release the lock during finalization? I'm thinking not, since the finalizer doesn't even run on the same thread, but I was curious if there other ways to improve this. EDIT After thinking about this a bit and reading the responses (particular thanks to Hans), I've decided this is definitely a bad idea. The biggest issue actually isn't forgetting to Dispose, but rather a leisurely consumer creating deadlock while enumerating. I now only read-lock long enough to get a copy and return the enumerator for the copy.

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• J: Self-reference in bubble sort tacit implementation

  - by Yasir Arsanukaev

  Hello people! Since I'm beginner in J I've decided to solve a simple task using this language, in particular implementing the bubblesort algorithm. I know it's not idiomatically to solve such kind of problem in functional languages, because it's naturally solved using array element transposition in imperative languages like C, rather than constructing modified list in declarative languages. However this is the code I've written: (((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # Let's apply it to an array: (((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # 5 3 8 7 2 2 3 5 7 8 The thing that confuses me is $: referring to the statement within the outermost parentheses. Help says that: $: denotes the longest verb that contains it. The other book (~ 300 KiB) says: 3+4 7 5*20 100 Symbols like + and * for plus and times in the above phrases are called verbs and represent functions. You may have more than one verb in a J phrase, in which case it is constructed like a sentence in simple English by reading from left to right, that is 4+6%2 means 4 added to whatever follows, namely 6 divided by 2. Let's rewrite my code snippet omitting outermost ()s: ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) ^: # 5 3 8 7 2 2 3 5 7 8 Reuslts are the same. I couldn't explain myself why this works, why only ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) is treated as the longest verb for $: but not the whole expression ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) ^: # and not just (<./@(2&{.)), $:@((>./@(2&{.)),2&}.), because if ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) is a verb, it should also form another verb after conjunction with #, i. e. one might treat the whole sentence (first snippet) as a verb. Probably there's some limit for the verb length limited by one conjunction. Look at the following code (from here): factorial =: (* factorial@<:) ^: (1&<) factorial 4 24 factorial within expression refers to the whole function, i. e. (* factorial@<:) ^: (1&<). Following this example I've used a function name instead of $:: bubblesort =: (((<./@(2&{.)), bubblesort@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # bubblesort 5 3 8 7 2 2 3 5 7 8 I expected bubblesort to refer to the whole function, but it doesn't seem true for me since the result is correct. Also I'd like to see other implementations if you have ones, even slightly refactored. Thanks.

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• Adding UIView animation mysteriously changes starting frame

  - by clozach

  I'm working on an app that shows a thumbnail of a photo taken by the user. In order to show a seemless transition from the full-screen image shown in the UIImagePickerController to the thumbnail, I set the frame on my copy of the image to [[UIScreen mainScreen] bounds] and then change the frame to match the frame of an invisible button. (The button allows users to re-take their photo by tapping the thumbnail image.) The trouble is that the starting x-origin of my UIImageView (imageView) is mysteriously starting nearly offscreen to the left: As you can see from the alert, the imageView purports to be located at (0,0), yet it's displaying at something like (-255,0). Here's the code: CGRect frame = [[UIScreen mainScreen] bounds]; imageView.frame = frame; [[[[UIAlertView alloc] initWithTitle:@"Yo!" message:[NSString stringWithFormat:@"starting frame:%@",NSStringFromCGRect(imageView.frame)] delegate:nil cancelButtonTitle:@"K." otherButtonTitles:nil] autorelease] show]; // Slide the enlarged image seamlessly "onto" the photo button [UIView beginAnimations:nil context:nil]; [UIView setAnimationDuration:1000]; [UIView setAnimationDelay:.5]; imageView.frame = pictureButton.frame; [UIView commitAnimations]; As if to taunt me, the image actually does go full screen if I comment out the animation code: CGRect frame = [[UIScreen mainScreen] bounds]; imageView.frame = frame; [[[[UIAlertView alloc] initWithTitle:@"Yo!" message:[NSString stringWithFormat:@"starting frame:%@",NSStringFromCGRect(imageView.frame)] delegate:nil cancelButtonTitle:@"K." otherButtonTitles:nil] autorelease] show]; // Slide the enlarged image seamlessly "onto" the photo button // [UIView beginAnimations:nil context:nil]; // [UIView setAnimationDuration:1000]; // [UIView setAnimationDelay:.5]; // // imageView.frame = pictureButton.frame; // // [UIView commitAnimations]; (Note: animationDuration will of course be set to something more like .5 in production, not 1000 seconds.) Update — Other weirdness worth mentioning in case it's relevant: It turns out the offset changes depending on the orientation of the camera when the photo was taken. If I take the picture with the phone upside-down, for instance, then the image gets offset vertically as well as horizontally. The picker seems to be filling the image's imageOrientation incorrectly: I have to hold the phone sideways, Home button on the left, to get an image with UIImageOrientationUp. At one point I experimented with setting imageView.clipsToBounds = YES;, which revealed that my image view's frame is in fact correct. Rather, it's the UIImage's placement within the UIImageView that gets offset. Fwiw, the image view's contentMode is the default, UIViewContentModeScaleToFill.

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• Dumb IE6 resize behaviour - hope it rings some bells with someone

  - by Ollie2893

  Hi, I'm having no end of fun (sic) with jQuery.tabs. The widget is quite crafty in that it turns basic HTML like so <div> <ul> <li>Tab #1</li> ... </ul> <div for panel #1> </div> <div for panel #2> </div> ... </div> into a cute tabbed dialogue. (It does so by restyling the UL and then toggling the "display" attribute for the panel DIVs to show/not show whatever panel is selected.) Now I found that I can spare myself a lot of trouble in my JS project if I insert a scrollable IFRAME into each panel. One usability problem I'm trying to ameliorate is that when the tabbed panel becomes larger than the browser's window, then the user ends up with too many scrollbars. I am trying to avoid this situation by linking the size of the tabbed panel to that of $(window). That is, I trap and process the resize event on $(window). To make my life bearable, all components are relatively sized. This is also true, in particular, of the IFRAMEs (100% width, 100% height). The only exception are the panel DIVs, which are of fixed height (in px). And this is the only dimension css attribute that I manipulate during my resize action. All of this works a treat in FF and Chrome, but IE6 is doing something rather cute: So long as I do not affect the width of the browser window (but only change its height), only the panel DIV changes in height; the IFRAME contained will not change. As a result of this behaviour, it is not possible to shorten the tabbed panel below the height of the IFRAME. I can lengthen the DIV, yes. But the IFRAME will not fill the panel in that case. All becomes good the moment I make the slightest change to the width of the browser window. In that moment, the IFRAME expands to catch up with the extended DIV or DIV and IFRAME contract in tandem. Bizarre. I inserted useless CSS instructions like "position: relative" and "zoom: 1". Also nudged the display with "display: block". No joy so far. Any ideas? Thanks.

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• Lightbox image / link URL

  - by GSTAR

  Basically I have a slightly non-standard implementation of FancyBox. By default you have to include a link to the large version of the image so that the Lightbox can display it. However, in my implementation, the image link URLs point to a script rather than directly to the image file. So for example, instead of: <a href="mysite/images/myimage.jpg" rel="gallery"> I have: <a href="mysite/photos/view/abc123" rel="gallery"> The above URL points to a function: public function actionPhotos($view) { $photo=Photo::model()->find('name=:name', array(':name'=>$view)); if(!empty($photo)) { $this->renderPartial('_photo', array('photo'=>$photo, true)); } } The "$this-renderPartial()" bit simply calls a layout file which includes a standard HTML tag to output. Now when the user clicks on a thumbnail, the above function is called and the large image is displayed in the Lightbox. Now if the user right clicks on the thumbnail and selects "open in new tab/window" then the image is displayed in the browser as per normal, i.e. just the image. I want to change this so that it displays the image within a layout. In the above code I can include the following and put it in an IF statement: $this->render('photos', array('photo'=>$photo)); This will call the layout file "photos" which contains the layout to display the image in. I have a specific limitation for this - the image URL must remain the same, i.e. no additional GET variables in the URL. However if we can pass in a GET variable in the background then that is OK. I will most likely need to change my function above so that it calls a different file for this functionality. EDIT: To demonstrate exactly what I am trying to do, check out the following: http://www.starnow.co.uk/KimberleyMarren Go to the photos tab and hover over a thumbnail - note the URL. Click the thumbnail and it will open up in the Lightbox. Next right click on that same thumbnail and select "open in new tab/new window". You will notice that the image is now displayed in a layout. So that same URL is used for displaying the image in the Lightbox and on its own page. The way StarNow have done this is using some crazy long JavaScript functionality, which I'm not too keen on replicating.

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• Java Nimbus LAF with transparent text fields

  - by Software Monkey

  I have an application that uses disabled JTextFields in several places which are intended to be transparent - allowing the background to show through instead of the text field's normal background. When running the new Nimbus LAF these fields are opaque (despite setting setOpaque(false)), and my UI is broken. It's as if the LAF is ignoring the opaque property. Setting a background color explicitly is both difficult in several places, and less than optimal due to background images actually doesn't work - it still paints it's LAF default background over the top, leaving a border-like appearance (the splash screen below has the background explicitly set to match the image). Any ideas on how I can get Nimbus to not paint the background for a JTextField? Note: I need a JTextField, rather than a JLabel, because I need the thread-safe setText(), and wrapping capability. Note: My fallback position is to continue using the system LAF, but Nimbus does look substantially better. See example images below. Conclusions The surprise at this behavior is due to a misinterpretation of what setOpaque() is meant to do - from the Nimbus bug report: This is a problem the the orginal design of Swing and how it has been confusing for years. The issue is setOpaque(false) has had a side effect in exiting LAFs which is that of hiding the background which is not really what it is ment for. It is ment to say that the component my have transparent parts and swing should paint the parent component behind it. It's unfortunate that the Nimbus components also appear not to honor setBackground(null) which would otherwise be the recommended way to stop the background painting. Setting a fully transparent background seems unintuitive to me. In my opinion, setOpaque()/isOpaque() is a faulty public API choice which should have been only: public boolean isFullyOpaque(); I say this, because isOpaque()==true is a contract with Swing that the component subclass will take responsibility for painting it's entire background - which means the parent can skip painting that region if it wants (which is an important performance enhancement). Something external cannot directly change this contract (legitimately), whose fulfillment may be coded into the component. So the opacity of the component should not have been settable using setOpaque(). Instead something like setBackground(null) should cause many components to "no long have a background" and therefore become not fully opaque. By way of example, in an ideal world most components should have an isOpaque() that looks like this: public boolean isOpaque() { return (background!=null); }

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• Data access pattern

  - by andlju

  I need some advice on what kind of pattern(s) I should use for pushing/pulling data into my application. I'm writing a rule-engine that needs to hold quite a large amount of data in-memory in order to be efficient enough. I have some rather conflicting requirements; It is not acceptable for the engine to always have to wait for a full pre-load of all data before it is functional. Only fetching and caching data on-demand will lead to the engine taking too long before it is running quickly enough. An external event can trigger the need for specific parts of the data to be reloaded. Basically, I think I need a combination of pushing and pulling data into the application. A simplified version of my current "pattern" looks like this (in psuedo-C# written in notepad): // This interface is implemented by all classes that needs the data interface IDataSubscriber { void RegisterData(Entity data); } // This interface is implemented by the data access class interface IDataProvider { void EnsureLoaded(Key dataKey); void RegisterSubscriber(IDataSubscriber subscriber); } class MyClassThatNeedsData : IDataSubscriber { IDataProvider _provider; MyClassThatNeedsData(IDataProvider provider) { _provider = provider; _provider.RegisterSubscriber(this); } public void RegisterData(Entity data) { // Save data for later StoreDataInCache(data); } void UseData(Key key) { // Make sure that the data has been stored in cache _provider.EnsureLoaded(key); Entity data = GetDataFromCache(key); } } class MyDataProvider : IDataProvider { List<IDataSubscriber> _subscribers; // Make sure that the data for key has been loaded to all subscribers public void EnsureLoaded(Key key) { if (HasKeyBeenMarkedAsLoaded(key)) return; PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } // Force all subscribers to get a new version of the data for key public void ForceReload(Key key) { PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } void PublishDataToSubscribers(Key key) { Entity data = FetchDataFromStore(key); foreach(var subscriber in _subscribers) { subscriber.RegisterData(data); } } } // This class will be spun off on startup and should make sure that all data is // preloaded as quickly as possible class MyPreloadingThread { IDataProvider _provider; MyPreloadingThread(IDataProvider provider) { _provider = provider; } void RunInBackground() { IEnumerable<Key> allKeys = GetAllKeys(); foreach(var key in allKeys) { _provider.EnsureLoaded(key); } } } I have a feeling though that this is not necessarily the best way of doing this.. Just the fact that explaining it seems to take two pages feels like an indication.. Any ideas? Any patterns out there I should have a look at?

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• "RFC 2833 RTP Event" Consecutive Events and the E "End" Bit

  - by brian_d

  Hello, I can send out a RFC 2833 dtmf event as outlined at http://www.ietf.org/rfc/rfc2833.txt When I do set the E "End" bit, but leave it as 0, I get the following behaviour: If for example keys 7874556332111111145855885#3 were pressed, then ALL events would be sent and show up in a program like wireshark, however only 87456321458585#3 would sound. So the first key (which I figure could be a separate issue) and any repeats of an event (ie 11111) are failing to sound. In section 3.9, figure 2 of the above linked document, they give a 911 example. Here all but the last event have the E bit set. When I set the bit for all numbers, I never get an event to sound. I have thought of a couple possible thing but do not know if they are the reason: 1) figure 2 shows payload types of 96 and 97 sent. I have not nor know how to exactly. In section 3.8, codes 96 and 97 are described as "the dynamic payload types 96 and 97 have been assigned for the redundancy mechanism and the telephone event payload respectively" 2) In section 3.5, "E:", "A sender MAY delay setting the end bit until retransmitting the last packet for a tone, rather than on its first transmission" Does anyone have an idea of how to actually do this? I have also fiddled around with timestamp intervals and the RTP marker. Any help is greatly appreciated. Here is a sample wireshark event capture of the relevant areas: 6590 31.159045000 xx.x.x.xxx --.--.---.-- RTP EVENT Payload type=RTP Event, DTMF Pound # (end) Real-Time Transport Protocol Stream setup by SDP (frame 6225) Setup frame: 6225 Setup Method: SDP 10.. .... = Version: RFC 1889 Version (2) ..0. .... = Padding: False ...0 .... = Extension: False .... 0000 = Contributing source identifiers count: 0 0... .... = Marker: False Payload type: telephone-event (101) Sequence number: 0 Extended sequence number: 65536 Timestamp: 0 Synchronization Source identifier: 0x15f27104 (368210180) RFC 2833 RTP Event Event ID: DTMF Pound # (11) 1... .... = End of Event: True .0.. .... = Reserved: False ..00 0000 = Volume: 0 Event Duration: 2048

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• SimpleXML not pulling correct link

  - by kylex

  My code does not pull the proper link for the item. Instead it's getting the previous item's link. Any suggestions? Thanks! <?php // Load the XML data from the specified file name. // The second argument (NULL) allows us to specify additional libxml parameters, // we don't need this so we'll leave it as NULL. The third argument however is // important as it informs simplexml to handle the first parameter as a file name // rather than a XML formatted string. $pFile = new SimpleXMLElement("http://example.blogspot.com/feeds/posts/default?alt=rss", null, true); // Now that we've loaded our XML file we can begin to parse it. // We know that a channel element should be available within the, // document so we begin by looping through each channel foreach ($pFile->channel as $pChild) { // Now we want to loop through the items inside this channel { foreach ($pFile->channel->item as $pItem) { // If this item has child nodes as it should, // loop through them and print out the data foreach ($pItem->children() as $pChild) { // We can check the name of this node using the getName() method. // We can then use this information, to, for example, embolden // the title or format a link switch ($pChild->getName()) { case 'pubDate': $date = date('l, F d, Y', strtotime($pChild)); echo "<p class=\"blog_time\">$date</p>"; break; case 'link': $link = $pChild; break; case 'title': echo "<p class=\"blog_title\"><a href=\"$link\">$pChild</a></p>"; break; case 'description': // echo substr(strip_tags($pChild), 0 , 270) . "..."; break; case 'author': echo ""; break; case 'category': echo ""; break; case 'guid': echo ""; break; default: // echo strip_tags($pChild) . "<br />\n"; break; } } } } } ?>

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• How can arguments to variadic functions be passed by reference in PHP?

  - by outis

  Assuming it's possible, how would one pass arguments by reference to a variadic function without generating a warning in PHP? We can no longer use the '&' operator in a function call, otherwise I'd accept that (even though it would be error prone, should a coder forget it). What inspired this is are old MySQLi wrapper classes that I unearthed (these days, I'd just use PDO). The only difference between the wrappers and the MySQLi classes is the wrappers throw exceptions rather than returning FALSE. class DBException extends RuntimeException {} ... class MySQLi_throwing extends mysqli { ... function prepare($query) { $stmt = parent::prepare($query); if (!$stmt) { throw new DBException($this->error, $this->errno); } return new MySQLi_stmt_throwing($this, $query, $stmt); } } // I don't remember why I switched from extension to composition, but // it shouldn't matter for this question. class MySQLi_stmt_throwing /* extends MySQLi_stmt */ { protected $_link, $_query, $_delegate; public function __construct($link, $query, $prepared) { //parent::__construct($link, $query); $this->_link = $link; $this->_query = $query; $this->_delegate = $prepared; } function bind_param($name, &$var) { return $this->_delegate->bind_param($name, $var); } function __call($name, $args) { //$rslt = call_user_func_array(array($this, 'parent::' . $name), $args); $rslt = call_user_func_array(array($this->_delegate, $name), $args); if (False === $rslt) { throw new DBException($this->_link->error, $this->errno); } return $rslt; } } The difficulty lies in calling methods such as bind_result on the wrapper. Constant-arity functions (e.g. bind_param) can be explicitly defined, allowing for pass-by-reference. bind_result, however, needs all arguments to be pass-by-reference. If you call bind_result on an instance of MySQLi_stmt_throwing as-is, the arguments are passed by value and the binding won't take. try { $id = Null; $stmt = $db->prepare('SELECT id FROM tbl WHERE ...'); $stmt->execute() $stmt->bind_result($id); // $id is still null at this point ... } catch (DBException $exc) { ... } Since the above classes are no longer in use, this question is merely a matter of curiosity. Alternate approaches to the wrapper classes are not relevant. Defining a method with a bunch of arguments taking Null default values is not correct (what if you define 20 arguments, but the function is called with 21?). Answers don't even need to be written in terms of MySQL_stmt_throwing; it exists simply to provide a concrete example.

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• Can LINQ-to-SQL omit unspecified columns on insert so a database default value is used?

  - by Todd Ropog

  I have a non-nullable database column which has a default value set. When inserting a row, sometimes a value is specified for the column, sometimes one is not. This works fine in TSQL when the column is omitted. For example, given the following table: CREATE TABLE [dbo].[Table1]( [id] [int] IDENTITY(1,1) NOT NULL, [col1] [nvarchar](50) NOT NULL, [col2] [nvarchar](50) NULL, CONSTRAINT [PK_Table1] PRIMARY KEY CLUSTERED ([id] ASC) ) GO ALTER TABLE [dbo].[Table1] ADD CONSTRAINT [DF_Table1_col1] DEFAULT ('DB default') FOR [col1] The following two statements will work: INSERT INTO Table1 (col1, col2) VALUES ('test value', '') INSERT INTO Table1 (col2) VALUES ('') In the second statement, the default value is used for col1. The problem I have is when using LINQ-to-SQL (L2S) with a table like this. I want to produce the same behavior, but I can't figure out how to make L2S do that. I want to be able to run the following code and have the first row get the value I specify and the second row get the default value from the database: var context = new DataClasses1DataContext(); var row1 = new Table1 { col1 = "test value", col2 = "" }; context.Table1s.InsertOnSubmit(row1); context.SubmitChanges(); var row2 = new Table1 { col2 = "" }; context.Table1s.InsertOnSubmit(row2); context.SubmitChanges(); If the Auto Generated Value property of col1 is False, the first row is created as desired, but the second row fails with a null error on col1. If Auto Generated Value is True, both rows are created with the default value from the database. I've tried various combinations of Auto Generated Value, Auto-Sync and Nullable, but nothing I've tried gives the behavior I want. L2S does not omit the column from the insert statement when no value is specified. Instead it does something like this: INSERT INTO Table1 (col1, col2) VALUES (null, '') ...which of course causes a null error on col1. Is there some way to get L2S to omit a column from the insert statement if no value is given? Or is there some other way to get the behavior I want? I need the default value at the database level because not all row inserts are done via L2S, and in some cases the default value is a little more complex than a hard coded value (e.g. creating the default based on another field) so I'd rather avoid duplicating that logic.

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• JSON Feed Appears to be XHR when it should be JS

  - by Oscar Godson

  I don't get why it'd doing this with the 2nd feed (appearing as a XHR call rather than just JS [looking at it in Firefox/Firebug]). The 2nd feed has the exact same MIME type as Flickr's JSON feed, yet the PortlandOregon.gov one shows as XHR and i get a NULL callback when using $.getJSON and if i use $.ajax with a 'json' or 'jsonp' type i get nothing at all. If i do the Flickr one i get the normal "[object Object]" callback. Whats going on? Please help! This has been such a headache for about a week. And i have authorization to change the feed, but i have to request the change, so if anyone knows for absolute sure let me know that! Response Headers from Flickr's API ( http://api.flickr.com/services/feeds/photos_public.gne?tags=cat&tagmode=any&format=json&jsoncallback=? ) [JS]: Date Mon, 15 Mar 2010 21:56:06 GMT P3P policyref="http://p3p.yahoo.com/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA POL HEA PRE GOV" Expires Mon, 26 Jul 1997 05:00:00 GMT Last-Modified Mon, 15 Mar 2010 21:52:17 GMT Cache-Control no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma no-cache Vary Accept-Encoding Content-Encoding gzip Content-Length 3647 Connection close Content-Type application/x-javascript; charset=utf-8 Request Headers Host api.flickr.com User-Agent Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 Accept */* Accept-Language en-us,en;q=0.5 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 115 Connection keep-alive Referer http://oscargodson.com/dev/addWidget/test.html Cookie BX=4lflj455amesp&b=3&s=iv; fltoto=0%2C0%2C0%2C0%2C1%2C0%3B0%2C0%2C0%2C0%2C0%2C0%2C0%2C0%2C0%2C0%2C0%2C0%2C0%3B1%3B0%3B; search_z=t; localization=en-us%3Bus%3Bus PortlandOregon.gov ( http://www.portlandonline.com/shared/cfm/json.cfm?c=27321 ) [XHR]: Response Headers Connection close Date Mon, 15 Mar 2010 21:57:49 GMT Server Microsoft-IIS/6.0 Set-Cookie CONTACT_ID=0;path=/ LAST_USER=;path=/ BIGipServercgis_pol_web_pool-http=1191537418.20480.0000; path=/ Content-Type application/x-javascript; charset=utf-8 Request Headers Host www.portlandonline.com User-Agent Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 Accept application/json, text/javascript, */* Accept-Language en-us,en;q=0.5 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 115 Connection keep-alive Referer http://oscargodson.com/dev/addWidget/test.html Origin http://oscargodson.com

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• ItemsControl ItemTemplate Binding

  - by Wonko the Sane

  Hi All, In WPF4.0, I have a class that contains other class types as properties (combining multiple data types for display). Something like: public partial class Owner { public string OwnerName { get; set; } public int OwnerId { get; set; } } partial class ForDisplay { public Owner OwnerData { get; set; } public int Credit { get; set; } } In my window, I have an ItemsControl with the following (clipped for clarity): <ItemsControl ItemsSource={Binding}> <ItemsControl.ItemTemplate> <DataTemplate> <local:MyDisplayControl OwnerName={Binding OwnerData.OwnerName} Credit={Binding Credit} /> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> I then get a collection of display information from the data layer, and set the DataContext of the ItemsControl to this collection. The "Credit" property gets displayed correctly, but the OwnerName property does not. Instead, I get a binding error: Error 40: BindingExpression path error: 'OwnerName' property not found on 'object' ''ForDisplay' (HashCode=449124874)'. BindingExpression:Path=OwnerName; DataItem='ForDisplay' (HashCode=449124874); target element is 'TextBlock' (Name=txtOwnerName'); target property is 'Text' (type 'String') I don't understand why this is attempting to look for the OwnerName property in the ForDisplay class, rather than in the Owner class from the ForDisplay OwnerData property. Edit It appears that it has something to do with using the custom control. If I bind the same properties to a TextBlock, they work correctly. <ItemsControl ItemsSource={Binding}> <ItemsControl.ItemTemplate> <DataTemplate> <StackPanel> <local:MyDisplayControl OwnerName={Binding OwnerData.OwnerName} Credit={Binding Credit} /> <TextBlock Text="{Binding OwnerData.OwnerName}" /> <TextBlock Text="{Binding Credit}" /> </StackPanel> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> Thanks, wTs

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• Calculating multiple column average in SQLite3

  - by Benjamin Oakes

  I need to average some values in a row-wise fashion, rather than a column-wise fashion. (If I were doing a column-wise average, I could just use avg()). My specific application of this requires me ignore NULLs in averaging. It's pretty straightforward logic, but seems awfully difficult to do in SQL. Is there an elegant way of doing my calculation? I'm using SQLite3, for what it's worth. Details If you need more details, here's an illustration: I have a a table with a survey: | q1 | q2 | q3 | ... | q144 | |----|-------|-------|-----|------| | 1 | 3 | 7 | ... | 2 | | 4 | 2 | NULL | ... | 1 | | 5 | NULL | 2 | ... | 3 | (Those are just some example values and simple column names. The valid values are 1 through 7 and NULL.) I need to calculate some averages like so: q7 + q33 + q38 + q40 + ... + q119 / 11 as domain_score_1 q10 + q11 + q34 + q35 + ... + q140 / 13 as domain_score_2 ... q2 + q5 + q13 + q25 + ... + q122 / 12 as domain_score_14 ...but i need to pull out the nulls and average based on the non-nulls. So, for domain_score_1 (which has 11 items), I would need to do: Input: 3, 5, NULL, 7, 2, NULL, 3, 1, 5, NULL, 1 (3 + 5 + 7 + 2 + 3 + 1 + 5 + 1) / (11 - 3) 27 / 8 3.375 A simple algorithm I'm considering is: Input: 3, 5, NULL, 7, 2, NULL, 3, 1, 5, NULL, 1 Coalesce each value to 0 if NULL: 3, 5, 0, 7, 2, 0, 3, 1, 5, 0, 1 Sum: 27 Get the number of non-zeros by converting values 0 to 1 and sum: 3, 5, 0, 7, 2, 0, 3, 1, 5, 0, 1 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1 8 Divide those two numbers 27 / 8 3.375 But that seems like a lot more programming than this should take. Is there an elegant way of doing this that I'm not aware of? Update: Unless I'm misunderstanding something, avg() won't work for this. Example of what I would want to do: select avg(q7, q33, q38, ..., q119) from survey; Output: SQL error near line 3: wrong number of arguments to function avg()

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• With sqlalchemy how to dynamically bind to database engine on a per-request basis

  - by Peter Hansen

  I have a Pylons-based web application which connects via Sqlalchemy (v0.5) to a Postgres database. For security, rather than follow the typical pattern of simple web apps (as seen in just about all tutorials), I'm not using a generic Postgres user (e.g. "webapp") but am requiring that users enter their own Postgres userid and password, and am using that to establish the connection. That means we get the full benefit of Postgres security. Complicating things still further, there are two separate databases to connect to. Although they're currently in the same Postgres cluster, they need to be able to move to separate hosts at a later date. We're using sqlalchemy's declarative package, though I can't see that this has any bearing on the matter. Most examples of sqlalchemy show trivial approaches such as setting up the Metadata once, at application startup, with a generic database userid and password, which is used through the web application. This is usually done with Metadata.bind = create_engine(), sometimes even at module-level in the database model files. My question is, how can we defer establishing the connections until the user has logged in, and then (of course) re-use those connections, or re-establish them using the same credentials, for each subsequent request. We have this working -- we think -- but I'm not only not certain of the safety of it, I also think it looks incredibly heavy-weight for the situation. Inside the __call__ method of the BaseController we retrieve the userid and password from the web session, call sqlalchemy create_engine() once for each database, then call a routine which calls Session.bind_mapper() repeatedly, once for each table that may be referenced on each of those connections, even though any given request usually references only one or two tables. It looks something like this: # in lib/base.py on the BaseController class def __call__(self, environ, start_response): # note: web session contains {'username': XXX, 'password': YYY} url1 = 'postgres://%(username)s:%(password)s@server1/finance' % session url2 = 'postgres://%(username)s:%(password)s@server2/staff' % session finance = create_engine(url1) staff = create_engine(url2) db_configure(staff, finance) # see below ... etc # in another file Session = scoped_session(sessionmaker()) def db_configure(staff, finance): s = Session() from db.finance import Employee, Customer, Invoice for c in [ Employee, Customer, Invoice, ]: s.bind_mapper(c, finance) from db.staff import Project, Hour for c in [ Project, Hour, ]: s.bind_mapper(c, staff) s.close() # prevents leaking connections between sessions? So the create_engine() calls occur on every request... I can see that being needed, and the Connection Pool probably caches them and does things sensibly. But calling Session.bind_mapper() once for each table, on every request? Seems like there has to be a better way. Obviously, since a desire for strong security underlies all this, we don't want any chance that a connection established for a high-security user will inadvertently be used in a later request by a low-security user.

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