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• Programatic re-evalutation of MVVM command's "can execute" state

  - by dzs

  Hello! I'm writing a WPF application using the MVVM pattern, based on the following article: WPF Apps With The Model-View-ViewModel Design Pattern I have two buttons on my View with the buttons' "Command" property bound (with data binding) to a given instance of the RelayCommand class (see "Figure 3 The RelayCommand Class" from the article above). The RelayCommand class has support for checking whether the given command can be executed. WPF automatically disables buttons whose command cannot be executed. Each of my commands (in the ViewModel class) start a background operation, and the command cannot be executed again until the background operation is finished. The RelayCommand instances have information whether the background operation is still working or it is finished. My problem is the following: after pressing the any of the buttons, the buttons automaticaly go disabled (which is OK) because the background operation started and the command cannot be executed until it is finished, but after the operation had finished, the buttons don't go enabled automatically because their command's "can be executed" predicate is not automatically reevaluated. The reevaluation can be manually triggered by having the application loose and regain focus (by pressing ALT+TAB). After doing this trick, the buttons get enabled once again. How can I programatically reevaluate the buttons' command's "can execute" state?

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• What would you like to correct and/or improve in this java implementation of Chain Of Responsibility

  - by Maciek Kreft

  package design.pattern.behavioral; import design.pattern.behavioral.ChainOfResponsibility.*; public class ChainOfResponsibility { public static class Chain { private Request[] requests = null; private Handler[] handlers = null; public Chain(Handler[] handlers, Request[] requests){ this.handlers = handlers; this.requests = requests; } public void start() { for(Request r : requests) for (Handler h : handlers) if(h.handle(r)) break; } } public static class Request { private int value; public Request setValue(int value){ this.value = value; return this; } public int getValue() { return value; } } public static class Handler<T1> { private Lambda<T1> lambda = null; private Lambda<T1> command = null; public Handler(Lambda<T1> condition, Lambda<T1> command) { this.lambda = condition; this.command = command; } public boolean handle(T1 request) { if (lambda.lambda(request)) command.lambda(request); return lambda.lambda(request); } } public static abstract class Lambda<T1>{ public abstract Boolean lambda(T1 request); } } class TestChainOfResponsibility { public static void main(String[] args) { new TestChainOfResponsibility().test(); } private void test() { new Chain(new Handler[]{ // chain of responsibility new Handler<Request>( new Lambda<Request>(){ // command public Boolean lambda(Request condition) { return condition.getValue() >= 600; } }, new Lambda<Request>(){ public Boolean lambda(Request command) { System.out.println("You are rich: " + command.getValue() + " (id: " + command.hashCode() + ")"); return true; } } ), new Handler<Request>( new Lambda<Request>(){ public Boolean lambda(Request condition) { return condition.getValue() >= 100; } }, new Lambda<Request>(){ public Boolean lambda(Request command) { System.out.println("You are poor: " + command.getValue() + " (id: " + command.hashCode() + ")"); return true; } } ), }, new Request[]{ new Request().setValue(600), // chaining method new Request().setValue(100), } ).start(); } }

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• How to avoid using this in a constructor

  - by Paralife

  I have this situation: interface MessageListener { void onMessageReceipt(Message message); } class MessageReceiver { MessageListener listener; public MessageReceiver(MessageListener listener, other arguments...) { this.listener = listener; } loop() { Message message = nextMessage(); listener.onMessageReceipt(message); } } and I want to avoid the following pattern: (Using the this in the Client constructor) class Client implements MessageListener { MessageReceiver receiver; MessageSender sender; public Client(...) { receiver = new MessageReceiver(this, other arguments...); sender = new Sender(...); } . . . @Override public void onMessageReceipt(Message message) { if(Message.isGood()) sender.send("Congrtulations"); else sender.send("Boooooooo"); } } The reason why i need the above functionality is because i want to call the sender inside the onMessageReceipt() function, for example to send a reply. But I dont want to pass the sender into a listener, so the only way I can think of is containing the sender in a class that implements the listener, hence the above resulting Client implementation. Is there a way to achive this without the use of 'this' in the constructor? It feels bizare and i dont like it, since i am passing myself to an object(MessageReceiver) before I am fully constructed. On the other hand, the MessageReceiver is not passed from outside, it is constructed inside, but does this 'purifies' the bizarre pattern? I am seeking for an alternative or an assurance of some kind that this is safe, or situations on which it might backfire on me.

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• Maintain List of Active Users for Web

  - by Bryan Marble

  Problem Statement - Would like to know if particular web app user is active (i.e. logged in and using site) and be able to query for list of active users or determine a user's activity status. Constraints - Doesn't need to be exact (i.e. if a user was active within a certain timeframe, that's ok to say that they're active even if they've closed their browser). I feel like there should be a design pattern for this type of problem but haven't been able to find anything here or elsewhere on the web. Approaches I'm considering: Maintain a table that is updated any time a user performs an action (or some subset of actions). Would then query for users that have performed an action within some threshold of time. Try to monitor session information and maintain a table that lists logged in users and times out after a certain period of time. Some other more standard way of doing this? How would you approach this problem (again, from a design pattern perspective)? Thanks!

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• Handling incremental Data Modeling Changes in Functional Programming

  - by Adam Gent

  Most of the problems I have to solve in my job as a developer have to do with data modeling. For example in a OOP Web Application world I often have to change the data properties that are in a object to meet new requirements. If I'm lucky I don't even need to programmatically add new "behavior" code (functions,methods). Instead I can declarative add validation and even UI options by annotating the property (Java). In Functional Programming it seems that adding new data properties requires lots of code changes because of pattern matching and data constructors (Haskell, ML). How do I minimize this problem? This seems to be a recognized problem as Xavier Leroy states nicely on page 24 of "Objects and Classes vs. Modules" - To summarize for those that don't have a PostScript viewer it basically says FP languages are better than OOP languages for adding new behavior over data objects but OOP languages are better for adding new data objects/properties. Are there any design pattern used in FP languages to help mitigate this problem? I have read Phillip Wadler's recommendation of using Monads to help this modularity problem but I'm not sure I understand how?

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• Represent multiple Null/Generic objects in an ActiveRecord association?

  - by slothbear

  I have a Casefile model that belongs_to a Doctor. In additional to all the "real" doctors, there are several generic Doctors: "self-treated", "not specified", and "removed" (it used to have a real doctor, but no longer does). I suspect there will be even more generic values in the future. I started with special "doctors" in the database, generated from seed. The generic Doctors only need to respond to the "name" and "real_doctor?" methods. This worked with one, was strained with two, and now feels completely broken. I want to change the behavior and can't figure out how to test it, a bad sign. Creating all the generic objects for testing is also trouble, including fake values to pass validation of the required Doctor attributes. The Null Object pattern works well for one generic object. The "name" method could check casefile.doctor.nil? and return "self-treated", as demonstrated by Craig Ambrose. What pattern should I use when there are multiple generic objects with very limited state?

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• How to remove the file suffix/extension (.jsp and .action) using the Stripes Framework?

  - by Dolph Mathews

  I'm looking to use pretty / clean URL's in my web app. I would like the following URL: http://mydomain.com/myapp/calculator .. to resolve to: com.mydomain.myapp.action.CalculatorActionBean I tried overwriting the NameBasedActionResolver with: public class CustomActionResolver extends NameBasedActionResolver { public static final String DEFAULT_BINDING_SUFFIX = "."; @Override protected String getBindingSuffix() { return DEFAULT_BINDING_SUFFIX; } @Override protected List<String> getActionBeanSuffixes() { List<String> suffixes = new ArrayList<String>(super.getActionBeanSuffixes()); suffixes.add(DEFAULT_BINDING_SUFFIX); return suffixes; } } And adding this to web.xml: <servlet-mapping> <servlet-name>StripesDispatcher</servlet-name> <url-pattern>*.</url-pattern> </servlet-mapping> Which gets me to: http://mydomain.com/myapp/Calculator. But: A stray "." is still neither pretty nor clean. The class name is still capitalized in the URL..? That still leaves me with *.jsp..? Is it even possible to get rid of both .action and .jsp?

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• PHP OOP: Providing Domain Entities with "Identity"

  - by sunwukung

  Bit of an abstract problem here. I'm experimenting with the Domain Model pattern, and barring my other tussles with dependencies - I need some advice on generating Identity for use in an Identity Map. In most examples for the Data Mapper pattern I've seen (including the one outlined in this book: http://apress.com/book/view/9781590599099) - the user appears to manually set the identity for a given Domain Object using a setter: $UserMapper = new UserMapper; //returns a fully formed user object from record sets $User = $UserMapper->find(1); //returns an empty object with appropriate properties for completion $UserBlank = $UserMapper->get(); $UserBlank->setId(); $UserBlank->setOtherProperties(); Now, I don't know if I'm reading the examples wrong - but in the first $User object, the $id property is retrieved from the data store (I'm assuming $id represents a row id). In the latter case, however, how can you set the $id for an object if it has not yet acquired one from the data store? The problem is generating a valid "identity" for the object so that it can be maintained via an Identity Map - so generating an arbitrary integer doesn't solve it. My current thinking is to nominate different fields for identity (i.e. email) and demanding their presence in generating blank Domain Objects. Alternatively, demanding all objects be fully formed, and using all properties as their identity...hardly efficient. (Or alternatively, dump the Domain Model concept and return to DBAL/DAO/Transaction Scripts...which is seeming increasingly elegant compared to the ORM implementations I've seen...)

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• Setup SSL (self signed cert) with tomcat

  - by Danny

  I am mostly following this page: http://tomcat.apache.org/tomcat-6.0-doc/ssl-howto.html I used this command to create the keystore keytool -genkey -alias tomcat -keyalg RSA -keystore /etc/tomcat6/keystore and answered the prompts Then i edited my server.xml file and uncommented/edited this line <Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true" maxThreads="150" scheme="https" secure="true" clientAuth="false" sslProtocol="TLS" keystoreFile="/etc/tomcat6/keystore" keystorePass="tomcat" /> then I go to the web.xml file for my project and add this into the file <security-constraint> <web-resource-collection> <web-resource-name>Security</web-resource-name> <url-pattern>/*</url-pattern> </web-resource-collection> <user-data-constraint> <transport-guarantee>CONFIDENTIAL</transport-guarantee> </user-data-constraint> </security-constraint> When I try to run my webapp I am met with this: Unable to connect Firefox can't establish a connection to the server at localhost:8443. * The site could be temporarily unavailable or too busy. Try again in a few moments. * If you are unable to load any pages, check your computer's network connection. If I comment out the lines I've added to my web.xml file, the webapp works fine. My log file in /var/lib/tomcat6/logs says nothing. I can't figure out if this is a problem with my keystore file, my server.xml file or my web.xml file.... Any assistance is appreciated I am using tomcat 6 on ubuntu.

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• Syncing two separate structures to the same master data

  - by Mike Burton

  I've got multiple structures to maintain in my application. All link to the same records, and one of them could be considered the "master" in that it reflects actual relationships held in files on disk. The other structures are used to "call out" elements of the main design for purchase and work orders. I'm struggling to come up with a pattern that deals appropriately with changes to the master data. As an example, the following trees might refer to the same data: A |_ B |_ C |_ D |_ E |_ B |_ C |_ D A |_ B E C |_ D A |_ B C D E These secondary structures follow internal rules, but their overall structure is usually user-determined. In all cases (including the master), any element can be used in multiple locations and in multiple trees. When I add a child to any element in the tree, I want to either automatically build the secondary structure for each instance of the "master" element or at least advertise the situation to the user and allow them to manually generate the data required for the secondary trees. Is there any pattern which might apply to this situation? I've been treating it as a view problem, but it turns out to be more complicated than that when you look at the initial generation of the data.

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• Redirect website from http to https

  - by MaG3Stican

  I have a website stored on azure for which I got an SSL certificate. I am trying to redirect www.mywebsite.com to https://www.mywebsite.com but with no success. I am using the following code that should change the configuration of IIS where my project is deployed : <system.webServer> <rewrite> <rules> <rule name="Redirect to HTTPS"> <match url="(.*)" /> <conditions> <add input="{HTTPS}" pattern="off" ignoreCase="true" /> <add input="{URL}" pattern="/$" negate="true" /> <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" /> </conditions> <action type="Redirect" url="https://{SERVER_NAME}/{R:1}" redirectType="SeeOther" /> </rule> </rules> </rewrite> But when I type my URL it does not redirect to https. By the way, rewrite appears unrecorgnized by Intellisense.

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• Java and dynamic variables

  - by Arvanem

  Hi folks, I am wondering whether it is possible to make dynamic variables in Java. In other words, variables that change depending on my instructions. FYI, I am making a trading program. A given merchant will have an array of items for sale for various prices. The dynamism I am calling for comes in because each category of items for sale has its own properties. For example, a book item has two properties: int pages, and boolean hardCover. In contrast, a bookmark item has one property, String pattern. Here are skeleton snippets of code so you can see what I am trying to do: public class Merchants extends /* certain parent class */ { // only 10 items for sale to begin with Stock[] itemsForSale = new Stock[10]; // Array holding Merchants public static Merchants[] merchantsArray = new Merchants[maxArrayLength]; // method to fill array of stock goes here } and public class Stock { int stockPrice; int stockQuantity; String stockType; // e.g. book and bookmark // Dynamic variables here, but they should only be invoked depending on stockType int pages; boolean hardCover; String pattern; }

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• Liferay hook: filter url giving filterstart error and current url generates exception null

  - by jack

  I'm trying to make an autologinfilter in Eclipse using a liferay hook. Now I've added the: <filter> <filter-name>myautologinfilter</filter-name> <filter-class>bla.bla.xyz</filter-class> </filter> <filter-mapping> <filter-name>myautologinfilter</filter-name> <url-pattern>/c/login/myurl</url-pattern> </filter-mapping> To the liferay hook's web.xml. In the liferay-hook.xml I added: portal.properties And in that hook.xml I added: auto.login.hooks=bla.bla.xyz bla.bla.xyz implements AutoLogin, but for now it's pretty gutted: @Override public String[] login(HttpServletRequest request, HttpServletResponse response) throws AutoLoginException { Object parameters = request.getAttribute("javax.servlet.forward.query_string"); Map<String, String> x = parserClass.parsing(parameters.toString()); System.out.println("voornaam: " + geparsdeParameters.get("tokenvalue1")); try { return null; } catch (Exception e) { throw new AutoLoginException(e); } } Since the hook doesn't start when I add the filtering I removed it and just tried: http://localhost:8080/c/portal/login?tokenvalue1=55 but when I check my tomcat I see: Error XYZ Url: url myUsedUrl exception null Also I tried adding some util classes but I got: classnotfoundexceptions. Is there anything specific I have to do when I add extra classes in a hook? Any advice/input would be appreciated. Or someone's ear I could lend so I could mail them a little bit so I could pick their brain a bit would be really appreciated since I don't know anyone who programs for liferay.

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• Are there scenarios where the ViewModel needs to invoke methods on the View w.r.t. MVVM in WPF?

  - by Gishu

  As per the pattern, the ViewModel exposes Properties(with change notification) and Commands (to notify the VM of user actions) that the View binds to. The only communication that flows from the VM to the View is the property change notifications (so that the View can refresh itself with updated data). In MVP or PresentationModel form of the pattern (if I'm not mistaken), the View implements a plain vanilla interface (consisting of methods, properties and/or events). With MVVM, it feels methods on the IView have been outlawed (along with IView itself). One scenario I could think of was to set the focus to a certain control in the View. (When the user does ActionX, the focus should immediately be set to FieldY). In MVP, I'd write this as IView.ActivateField(NameConstant), which the presenter or PM would invoke. In MVVM, this seems to be a fringe case that needs a workaround / little bit of code-behind. The VM implements an ActiveField Property, which it sets to NameConstant. The view picks up the change notification event and in a code-behind event handler, activates the Name control. Is the above just an exception to the norm? Or are there other such scenarios, where the VM needs to invoke a method on the View ?

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• Backreferences syntax in replacement strings (why dollar sign?)

  - by polygenelubricants

  In Java, and it seems in a few other languages, backreferences in the pattern is preceded by a slash (e.g. \1, \2, \3, etc), but in a replacement string it's preceded by a dollar sign (e.g. $1, $2, $3, and also $0). Here's a snippet to illustrate: System.out.println( "left-right".replaceAll("(.*)-(.*)", "\\2-\\1") // WRONG!!! ); // prints "2-1" System.out.println( "left-right".replaceAll("(.*)-(.*)", "$2-$1") // CORRECT! ); // prints "right-left" System.out.println( "You want million dollar?!?".replaceAll("(\\w*) dollar", "US\\$ $1") ); // prints "You want US$ million?!?" System.out.println( "You want million dollar?!?".replaceAll("(\\w*) dollar", "US$ \\1") ); // throws IllegalArgumentException: Illegal group reference Questions: Is the use of $ for backreferences in replacement strings unique to Java? If not, what language started it? What flavors use it and what don't? Why is this a good idea? Why not stick to the same pattern syntax? Wouldn't that lead to a more cohesive and an easier to learn language? Wouldn't the syntax be more streamlined if statements 1 and 4 in the above were the "correct" ones instead of 2 and 3?

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• Best way to split a string by word (SQL Batch separator)

  - by Paul Kohler

  I have a class I use to "split" a string of SQL commands by a batch separator - e.g. "GO" - into a list of SQL commands that are run in turn etc. ... private static IEnumerable<string> SplitByBatchIndecator(string script, string batchIndicator) { string pattern = string.Concat("^\\s*", batchIndicator, "\\s*$"); RegexOptions options = RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.Multiline; foreach (string batch in Regex.Split(script, pattern, options)) { yield return batch.Trim(); } } My current implementation uses a Regex with yield but I am not sure if it's the "best" way. It should be quick It should handle large strings (I have some scripts that are 10mb in size for example) The hardest part (that the above code currently does not do) is to take quoted text into account Currently the following SQL will incorrectly get split: var batch = QueryBatch.Parse(@"-- issue... insert into table (name, desc) values('foo', 'if the go is on a line by itself we have a problem...')"); Assert.That(batch.Queries.Count, Is.EqualTo(1), "This fails for now..."); I have thought about a token based parser that tracks the state of the open closed quotes but am not sure if Regex will do it. Any ideas!?

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• Double Click and Resize on an Ipad

  - by Luke

  Thanks to the great post at OranLooney.com I was able to get a java/icefaces web-app to resize nicely on the ipad, however the code provided for double click doesn't seem to work without further customization. Has anybody had any experience with getting this to work? there seems to be little documentation on google. the donnothing(); in the window.orientationchange is there as it seems sometimes without it the resize will (sometimes) not work // a function to parse the user agent string; useful for // detecting lots of browsers, not just the iPad. function checkUserAgent(vs) { var pattern = new RegExp(vs, 'i'); return !!pattern.test(navigator.userAgent); } if ( checkUserAgent('iPad') ) { // iPad specific stuff here window.onorientationchange = function() { donnothing(); }; document.body.addEventListener('touchstart', function(e) { touch = e.touches[0]; if ( !touch ) return; var me = document.createEvent("MouseEvents"); me.initMouseEvent('dblclick', true, true, window, 1, // detail / mouse click count touch.screenX, touch.screenY, touch.clientX, touch.clientY, false, false, false, false, // key modifiers 0, // primary mouse button null // related target not used for dblclick event ); touch.target.dispatchEvent(me); }); }

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• Web application date time localization best practice at 201x

  - by Hieu Lam

  Hi all, I have worked for various web projects but correct date time localization have not been done and considered throroughly so I want to ask this very typical problem here and I want to hear comments from expert in this problem What is the correct strategy for storing a date/time value from client from server As I understand, because of locale and timezone so we have to do the conversion, I have heard about GMT or UTC time and after do some search it seems that UTC is more accurate ? so we will convert from client time - UTC+0 when saving and when we read the value from server to client, we convert from server time back to client time again ? However, I see in some website, at the bottom have the sentence "All times are in UTC", "All times are in GMT" and also "All times are in your local time". So maybe not all the sites do the convertion back and forth ? And in that case the user has to manually do the date/time conversion ? How to display the date/time convenient to user based on his locale and region How to provide personalization on date/time value ? I had one time depends on vbscript to do the display and the format is read from windows regional and format settings automatically. But without vbscript how can we determine a date/time pattern for a user of a specific locale. Do we have to store a mapping between a locale and pattern somewhere and do the conversion at the server side ? Although date/time conversion is needed in most case, there's situation where only date matter for example if my birthday is 2 Feb 1980, it should be the same for all locale and no conversion should be done. How can we address this issue.

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• Does Java have dynamic variables for class members?

  - by Arvanem

  Hi folks, I am wondering whether it is possible to make dynamic variables in Java. In other words, variables that change depending on my instructions. FYI, I am making a trading program. A given merchant will have an array of items for sale for various prices. The dynamism I am calling for comes in because each category of items for sale has its own properties. For example, a book item has two properties: int pages, and boolean hardCover. In contrast, a bookmark item has one property, String pattern. Here are skeleton snippets of code so you can see what I am trying to do: public class Merchants extends /* certain parent class */ { // only 10 items for sale to begin with Stock[] itemsForSale = new Stock[10]; // Array holding Merchants public static Merchants[] merchantsArray = new Merchants[maxArrayLength]; // method to fill array of stock goes here } and public class Stock { int stockPrice; int stockQuantity; String stockType; // e.g. book and bookmark // Dynamic variables here, but they should only be invoked depending on stockType int pages; boolean hardCover; String pattern; }

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• Where to Store ID Field In Silverlight

  - by Blake Blackwell

  I am trying to use the MVVM pattern, and I am wondering where I place an ID value. Do I create a TextBlock that has its visibility property set to collapsed? Or is there a better place to store this kind of data? Currently the command parameter is set to: CommandParameter="{Binding ElementName=Name,Path=Text}" But I'd rather it be something like: CommandParameter="{Binding ElementName=Id,Path=Text}" I'm totally up for suggestions on what the best way there is to do this, since I'm new to this pattern and presentation language. <ListBox x:Name="MyListBox" ItemsSource="{Binding MyData, Mode=TwoWay}" BorderThickness="0"> <ListBox.ItemTemplate> <DataTemplate> <StackPanel Orientation="Horizontal"> <CheckBox x:Name="Visible" IsChecked="{Binding Visible, Mode=TwoWay}" Command="{Binding ElementName=MyListBox, Path=DataContext.MyCommand}" CommandParameter="{Binding ElementName=Name,Path=Text}" /> <TextBlock Text="{Binding Name}" /> </StackPanel> </DataTemplate> </ListBox.ItemTemplate> </ListBox> EDIT: Option 1 <CheckBox x:Name="Visible" IsChecked="{Binding Visible, Mode=TwoWay}" Command="{Binding ElementName=MyListBox, Path=DataContext.MyCommand}" CommandParameter="{Binding Id}" /> This option gives me just the Id, which is useful in many situations. EDIT: Option 2 <CheckBox x:Name="Visible" IsChecked="{Binding Visible, Mode=TwoWay}" Command="{Binding ElementName=MyListBox, Path=DataContext.MyCommand}" CommandParameter="{Binding}" /> This option gives me the full model, which is even useful for my particular situation.

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• R:how to get grep to return the match, rather than the whole string

  - by Mike Dewar

  Hi, I have what is probably a really dumb grep in R question. Apologies, because this seems like it should be so easy - I'm obviously just missing something. I have a vector of strings, let's call it alice. Some of alice is printed out below: T.8EFF.SP.OT1.D5.VSVOVA#4 T.8EFF.SP.OT1.D6.LISOVA#1 T.8EFF.SP.OT1.D6.LISOVA#2 T.8EFF.SP.OT1.D6.LISOVA#3 T.8EFF.SP.OT1.D6.VSVOVA#4 T.8EFF.SP.OT1.D8.VSVOVA#3 T.8EFF.SP.OT1.D8.VSVOVA#4 T.8MEM.SP#1 T.8MEM.SP#3 T.8MEM.SP.OT1.D106.VSVOVA#2 T.8MEM.SP.OT1.D45.LISOVA#1 T.8MEM.SP.OT1.D45.LISOVA#3 I'd like grep to give me the number after the D that appears in some of these strings, conditional on the string containing "LIS" and an empty string or something otherwise. I was hoping that grep would return me the value of a capturing group rather than the whole string. Here's my R-flavoured regexp: pattern <- (?<=\\.D)([0-9]+)(?=.LIS) nothing too complicated. But in order to get what I'm after, rather than just using grep(pattern, alice, value = TRUE, perl = TRUE) I'm doing the following, which seems bad: reg.out <- regexpr( "(?<=\\.D)[0-9]+(?=.LIS)", alice, perl=TRUE ) substr(alice,reg.out,reg.out + attr(reg.out,"match.length")-1) Looking at it now it doesn't seem too ugly, but the amount of messing about it's taken to get this utterly trivial thing working has been embarrassing. Anyone any pointers about how to go about this properly? Bonus marks for pointing me to a webpage that explains the difference between whatever I access with $,@ and attr.

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• JSF works only with the .xhtml ending

  - by ThreeFingerMark

  Hello, i start with the programming of a JSF Website. At the moment all files have the .xhtml ending. When i go to http://localhost:8080/myProject/start.jsf everything is all right. But when i rename the file from start.xhtml to start.jsf i became a NoClassDefFound Error. What is my mistake? <servlet-name>Faces Servlet</servlet-name> <servlet-class>javax.faces.webapp.FacesServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>Faces Servlet</servlet-name> <url-pattern>*.jsf</url-pattern> </servlet-mapping> <context-param> <param-name>javax.faces.PROJECT_STAGE</param-name> <param-value>Development</param-value> </context-param>

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• Am I abusing Policies?

  - by pmr

  I find myself using policies a lot in my code and usually I'm very happy with that. But from time to time I find myself confronted with using that pattern in situations where the Policies are selected and runtime and I have developed habbits to work around such situations. Usually I start with something like that: class DrawArrays { protected: void sendDraw() const; }; class DrawElements { protected: void sendDraw() const; }; template<class Policy> class Vertices : public Policy { using Policy::sendDraw(); public: void render() const; }; When the policy is picked at runtime I have different choices of working around the situation. Different code paths: if(drawElements) { Vertices<DrawElements> vertices; } else { Vertices<DrawArrays> vertices; } Inheritance and virtual calls: class PureVertices { public: void render()=0; }; template<class Policy> class Vertices : public PureVertices, public Policy { //.. }; Both solutions feel wrong to me. The first creates an umaintainable mess and the second introduces the overhead of virtual calls that I tried to avoid by using policies in the first place. Am I missing the proper solutions or do I use the wrong pattern to solve the problem?

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• Conventions for the behavior of double or triple "click to select text" features?

  - by John Sullivan

  Almost any mature program that involves text implements "double click to select the word" and, in some cases, "triple click to select additional stuff like an entire line" as a feature. I find these features useful but they are often inconsistent between programs. Example - some programs' double clicks do not select the ending space after a word, but most do. Some recognize the - character as the end of a word, others do not. SO likes to select the entire paragraph as I write this post when I triple click it, VS web developer 2005 has no triple click support, and ultra-edit 32 will select one line upon triple clicking. We could come up with innumerable inconsistencies about how double and triple click pattern matching is implemented across programs. I am concerned about how to implement this behavior in my program if nobody else has achieved a convention about how the pattern matching should work. My question is, does a convention (conventions? maybe an MS or Linux convention?) exist that dictates how these features are supposed to behave to the end user? What, if any, are they?

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• howto distinguish composition and self-typing use-cases

  - by ayvango

  Scala has two instruments for expressing object composition: original self-type concept and well known trivial composition. I'm curios what situations I should use which in. There are obvious differences in their applicability. Self-type requires you to use traits. Object composition allows you to change extensions on run-time with var declaration. Leaving technical details behind I can figure two indicators to help with classification of use cases. If some object used as combinator for a complex structure such as tree or just have several similar typed parts (1 car to 4 wheels relation) than it should use composition. There is extreme opposite use case. Lets assume one trait become too big to clearly observe it and it got split. It is quite natural that you should use self-types for this case. That rules are not absolute. You may do extra work to convert code between this techniques. e.g. you may replace 4 wheels composition with self-typing over Product4. You may use Cake[T <: MyType] {part : MyType} instead of Cake { this : MyType => } for cake pattern dependencies. But both cases seem counterintuitive and give you extra work. There are plenty of boundary use cases although. One-to-one relations is very hard to decide with. Is there any simple rule to decide what kind of technique is preferable? self-type makes you classes abstract, composition makes your code verbose. self-type gives your problems with blending namespaces and also gives you extra typing for free (you got not just a cocktail of two elements but gasoline-motor oil cocktail known as a petrol bomb). How can I choose between them? What hints are there? Update: Let us discuss the following example: Adapter pattern. What benefits it has with both selt-typing and composition approaches?

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