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  • Identifying the best pattern

    - by Daniel Grillo
    I'm developing a software to program a device. I have some commands like Reset, Read_Version, Read_memory, Write_memory, Erase_memory. Reset and Read_Version are fixed. They don't need parameters. Read_memory and Erase_memory need the same parameters that are Length and Address. Write_memory needs Lenght, Address and Data. For each command, I have the same steps in sequence, that are something like this sendCommand, waitForResponse, treatResponse. I'm having difficulty to identify which pattern should I use. Factory, Template Method, Strategy or other pattern.

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  • Pattern for performing game actions

    - by Arkiliknam
    Is there a generally accepted pattern for performing various actions within a game? A way a player can perform actions and also that an AI might perform actions, such as move, attack, self-destruct, etc. I currently have an abstract BaseAction which uses .NET generics to specify the different objects that get returned by the various actions. This is all implemented in a pattern similar to the Command, where each action is responsible for itself and does all that it needs. My reasoning for being abstract is so that I may have a single ActionHandler, and AI can just queue up different action implementing the baseAction. And the reason it is generic is so that the different actions can return result information relevant to the action (as different actions can have totally different outcomes in the game), along with some common beforeAction and afterAction implementations. So... is there a more accepted way of doing this, or does this sound alright?

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  • Making Class Diagram for MVC Pattern Project

    - by iMohammad
    I have a question about making a class diagram for an MVC based college senior project. If we have 2 actors of users in my system, lets say Undergrad and Graduate students are the children of abstract class called User. (Generalisation) Each actor has his own features. My question, in such case, do we need to have these two actors in separate classes which inherits from the abstract class User? even though, I'm going to implement them as roles using one Model called User Model ? I think you can see my confusion here. I code using MVC pattern, but I've never made a class diagram for this pattern. Thank you in advance!

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  • how to generate number pattern in triangular form

    - by Vignesh Vicky
    I want to print this pattern like right angled triangle 0 909 89098 7890987 678909876 56789098765 4567890987654 345678909876543 23456789098765432 1234567890987654321 I wrote following code # include<stdio.h> # include<conio.h> void main() { clrscr(); int i,j,x,z,k,f=1; for ( i=10;i>=1;i--,f++) { for(j=1;j<=f;j++,k--) { k=i; if(k!=10) { printf("%d",k); } if(k==10) { printf("0"); } } for(x=1;x<f;x++,z--) { z=9; printf("%d",z); } printf("%d/n"); } getch(); } what is wrong with this code? when i check manually it seems correct but when compiled gives different pattern

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  • Clarification on the Strategy Pattern

    - by Holly
    I've just been reading through some basic design patterns, Could someone tell me if the term "strategy pattern" only applies if your implementing a completely abstract interface? What about when your children (concretes?) inherit from a parent class (the strategy?) with some implemented methods and some virtual and/or abstract functions? Otherwise the rest of the implementation, the idea that you can switch between different children at run time, is identical. This is something i'm quite familiar with, i was wondering if you would still call it the Strategy Pattern or if that term only applies to using an interface. Apologies if this question is not appropriate! Or if this is just nitpicking :) I'm still learning and i'm not really sure if design patterns are quite heavily defined within the industry or just a concept to be implemented as you like.

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  • Tester/Doer pattern: Assume the caller conforms to the pattern or be defensive and repeat the check?

    - by Daniel Hilgarth
    Assume a simple class that implements the Tester/Doer pattern: public class FooCommandHandler : ICommandHandler { public bool CanHandle(object command) { return command is FooCommand; } public void Handle(object command) { var fooCommand = (FooCommand)command; // Do something with fooCommand } } Now, if someone doesn't conform to the pattern and calls Handle without verifying the command via CanHandle, the code in Handle throws an exception. However, depending on the actual implementation of Handle this can be a whole range of different exceptions. The following implementation would check CanHandle again in Handle and throw a descriptive exception: public void Handle(object command) { if(!CanHandle(command)) throw new TesterDoerPatternUsageViolationException("Please call CanHandle first"); // actual implementation of handling the command. } This has the advantage that the exception is very descriptive. It has the disadvantage that CanHandle is called twice for "good" clients. Is there a consensus on which variation should be used?

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  • Implementing Command Pattern in Web Application

    - by KingOfHypocrites
    I'm looking to implement the command pattern in a web application (asp.net c#)... Since the commands come in text format from the client, what is the best way to translate the string to a command object? Should I use reflection? Currently I just assume the command that comes in matches the file name of a user control. This is a bit of a hack. Rather than have a select case statement that says if string = "Dashboard" then call Dashboard.Execute(), is there a pattern for working with commands that originate as strings?

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  • What Design Pattern is seperating transform converters

    - by RevMoon
    For converting a Java object model into XML I am using the following design: For different types of objects (e.g. primitive types, collections, null, etc.) I define each its own converter, which acts appropriate with respect to the given type. This way it can easily extended without adding code to a huge if-else-then construct. The converters are chosen by a method which tests whether the object is convertable at all and by using a priority ordering. The priority ordering is important so let's say a List is not converted by the POJO converter, even though it is convertable as such it would be more appropriate to use the collection converter. What design pattern is that? I can only think of a similarity to the command pattern.

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  • Looking for feedback on design pattern for simple 2D environment

    - by Le Mot Juiced
    I'm working in iOS. I am trying to make a very simple 2D environment where there are some basic shapes you can drag around with your finger. These shapes should interact in various ways when dropped on each other, or when single-tapped versus double-tapped, etc. I don't know the name for the design pattern I'm thinking of. Basically, you have a bunch of arrays named after attributes, such as "double-tappable" or "draggable" or "stackable". You assign these attributes to the shapes by putting the shapes in the arrays. So, if there's a double-tap event, the code gets the location of it, then iterates through the "double-tappable" array to see if any of its members are in that location. And so on: every interactive event causes a scan through the appropriate array or arrays. It seems like that should work, but I'm wondering if there's a better pattern for the purpose.

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  • What Design Pattern is separating transform converters

    - by RevMoon
    For converting a Java object model into XML I am using the following design: For different types of objects (e.g. primitive types, collections, null, etc.) I define each its own converter, which acts appropriate with respect to the given type. This way it can easily extended without adding code to a huge if-else-then construct. The converters are chosen by a method which tests whether the object is convertable at all and by using a priority ordering. The priority ordering is important so let's say a List is not converted by the POJO converter, even though it is convertable as such it would be more appropriate to use the collection converter. What design pattern is that? I can only think of a similarity to the command pattern.

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  • Design Pattern for Data Validation

    - by melodui
    What would be the best design pattern for this problem: I have an Object A. Object A can either be registered or deleted from the database depending on the user request. Data validation is performed before registration or deletion of the object. There are a set of rules to be checked before the object can be registered and another set of rules for deletion. Some of these rules are common for both operations. So far, I think the Chain of Responsibility design pattern fits the most but I'm having trouble implementing it.

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  • SOA Anti-pattern: Nanoservices

    After a long hiatus, I guess it is time for another SOA anti-pattern to see the light. It is probably also a good time to remind you that I am looking for your insights on this project. In any event I hope youd find this anti-pattern useful and as always comments are more than welcomed (do keep in mind this is an unedited draft :) ) ------------------------------------- There are many unsolved mysteries, youve probably heard about some of them like the Loch...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • RewriteRule applying pattern even though 1 of the RewriteCond's failed

    - by BHare
    #www. domain . tld RewriteCond %{HTTP_HOST} (?:.*\.)?([^.]+)\.(?:[^.]+)$ RewriteCond /home/%1/ -d RewriteRule ^(.+) %{HTTP_HOST}$1 RewriteRule (?:.*\.)?([^.]+)\.(?:[^.]+)/media/(.*)$ /home/$1/client/media/$2 [L] RewriteRule (?:.*\.)?([^.]+)\.(?:[^.]+)/(.*)$ /home/$1/www/$2 [L] Here is rewritelog output: #(4) RewriteCond: input='tfnoo.mydomain.org' pattern='(?:.*\.)?([^.]+)\.(?:[^.]+)$' [NC] => matched #(4) RewriteCond: input='/home/mydomain/' pattern='-d' => not-matched #(3) applying pattern '(?:.*\.)?([^.]+)\.(?:[^.]+)/media/(.*)$' to uri 'http://www.mydomain.org/files/images/logo.png' #(3) applying pattern '(?:.*\.)?([^.]+)\.(?:[^.]+)/(.*)$' to uri 'http://www.mydomain.org/files/images/logo.png' #(2) rewrite 'http://www.mydomain.org/files/images/logo.png' -> '/home/mydomain/www/logo.png' If you note on the 2nd 4 it failed the -d (if directory exists) pattern. Which is correct. mydomain does not have a /home/. Therefore it should never rewrite, atleast according to my understanding that all rewriterules are subject to rewriteconds as logical ANDs.

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  • Python regex look-behind requires fixed-width pattern

    - by invictus
    Hi When trying to extract the title of a html-page I have always used the following regex: (?<=<title.*>)([\s\S]*)(?=</title>) Which will extract everything between the tags in a document and ignore the tags themselves. However, when trying to use this regex in Python it raises the following Exception: Traceback (most recent call last): File "test.py", line 21, in pattern = re.compile('(?<=)([\s\S]*)(?=)') File "C:\Python31\lib\re.py", line 205, in compile return _compile(pattern, flags) File "C:\Python31\lib\re.py", line 273, in _compile p = sre_compile.compile(pattern, flags) File "C:\Python31\lib\sre_compile.py", line 495, in compile code = _code(p, flags) File "C:\Python31\lib\sre_compile.py", line 480, in _code _compile(code, p.data, flags) File "C:\Python31\lib\sre_compile.py", line 115, in _compile raise error("look-behind requires fixed-width pattern") sre_constants.error: look-behind requires fixed-width pattern The code I am using is: pattern = re.compile('(?<=<title.*>)([\s\S]*)(?=</title>)') m = pattern.search(f) if I do some minimal adjustments it works: pattern = re.compile('(?<=<title>)([\s\S]*)(?=</title>)') m = pattern.search(f) This will, however, not take into account potential html titles that for some reason have attributes or similar. Anyone know a good workaround for this issue? Any tips are appreciated.

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  • I don't understand the definition of side effects

    - by Chris Okyen
    I don't understand the wikipedia article on Side Effects: In computer science, a function or expression is said to have a side effect if, in addition to returning a value, it also 1.) Modifies some state or 2.) Has an observable interaction with calling functions or the outside world. I know an example of the first thing that causes a function or expression to have side effects - modifying a state Function and Expression modifying a state : 1.) foo(int X) { return x = x % x; } a = a + 1; What does 2.) - Has an observable interaction with calling functions or the outside world," mean? - Please give an example. The article continues on to say, "For example, a function might modify a global or static variable, modify one of its arguments, raise an exception, write data to a display or file, read data, or call other side-effecting functions...." Are all these examples, examples of 1.) - Modifiying some state , or are they also part of 2.) - Has an observable interaction with calling functions or the outside world?

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  • How do you handle animations that are for transitioning between states?

    - by yaj786
    How does one usually handle animations that are for going between a game object's states? For example, imagine a very simple game in which a character can only crouch or stand normally. Currently, I use a custom Animation class like this: class Animation{ int numFrames; int curFrame; Bitmap spriteSheet; //... various functions for pausing, returning frame, etc. } and an example Character class class Character{ int state; Animation standAni; Animation crouchAni; //... etc, etc. } Thus, I use the state of the character to draw the necessary animation. if(state == STATE_STAND) draw(standAni.updateFrame()); else if(state == STATE_CROUCH) draw(crouchAni.updateFrame()); Now I've come to the point where I want to draw "in-between" animations, because right now the character will just jump immediately into a crouch instead of bending down. What is a good way to handle this? And if the way that I handle storing Animations in the Character class is not a good way, what is? I thought of creating states like STATE_STANDING_TO_CROUCHING but I feel like that may get messy fast.

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  • Trying to backup system state on server 2003 sp2, getting "Faulting application vssvc.exe - system state backup failed" in applciation log

    - by IT_Fixr
    Trying to backup system state on Windows Server 2003 (SP2), getting "Faulting application vssvc.exe - system state backup failed" in application log. Volume shadow copy creation: Attempt 1. "MSDEWriter" has reported an error 0x800423f2. This is part of System State. The volume shadow copy operation can be retried. "Event Log Writer" has reported an error 0x800423f2. This is part of System State. The volume shadow copy operation can be retried. "Registry Writer" has reported an error 0x800423f2. This is part of System State. The volume shadow copy operation can be retried. "COM+ REGDB Writer" has reported an error 0x800423f2. This is part of System State. The volume shadow copy operation can be retried. "Removable Storage Manager" has reported an error 0x0. This is part of System State. The backup cannot continue. Error returned while creating the volume shadow copy:800423f2 Aborting Backup.

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  • How does pattern matching work behind the scenes in F#?

    - by kryptic
    Hello Everyone, I am completely new to F# (and functional programming in general) but I see pattern matching used everywhere in sample code. I am wondering for example how pattern matching actually works? For example, I imagine it working the same as a for loop in other languages and checking for matches on each item in a collection. This is probably far from correct, how does it actually work behind the scenes?

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  • Send regular keyboard samples OR keyboard state changes over network

    - by Ciaran
    Building a multi player asteroids game where ships compete with each other. Using UDP. Wanted to minimize traffic sent to server. Which would you do: Send periodic keyboard state samples every from client every to match server physics update rate e.g. 50 times per second. Highly resilient to packet loss and other reliabilty problems. Out of date packets disacarded by server. Generates a lot of unnuecessary traffic. Only send keyboard state when it changes (key up, key down). Radically less traffic sent from client to server. However, UDP can lose packets without you being informed. So the latter method could result in the vital packet never being resent unless I detect and resend this in a timely manner.

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  • Enum driving a Visual State change via the ViewModel

    - by Chris Skardon
    Exciting title eh? So, here’s the problem, I want to use my ViewModel to drive my Visual State, I’ve used the ‘DataStateBehavior’ before, but the trouble with it is that it only works for bool values, and the minute you jump to more than 2 Visual States, you’re kind of screwed. A quick search has shown up a couple of points of interest, first, the DataStateSwitchBehavior, which is part of the Expression Samples (on Codeplex), and also available via Pete Blois’ blog. The second interest is to use a DataTrigger with GoToStateAction (from the Silverlight forums). So, onwards… first let’s create a basic switch Visual State, so, a DataObj with one property: IsAce… public class DataObj : NotifyPropertyChanger { private bool _isAce; public bool IsAce { get { return _isAce; } set { _isAce = value; RaisePropertyChanged("IsAce"); } } } The ‘NotifyPropertyChanger’ is literally a base class with RaisePropertyChanged, implementing INotifyPropertyChanged. OK, so we then create a ViewModel: public class MainPageViewModel : NotifyPropertyChanger { private DataObj _dataObj; public MainPageViewModel() { DataObj = new DataObj {IsAce = true}; ChangeAcenessCommand = new RelayCommand(() => DataObj.IsAce = !DataObj.IsAce); } public ICommand ChangeAcenessCommand { get; private set; } public DataObj DataObj { get { return _dataObj; } set { _dataObj = value; RaisePropertyChanged("DataObj"); } } } Aaaand finally – hook it all up to the XAML, which is a very simple UI: A Rectangle, a TextBlock and a Button. The Button is hooked up to ChangeAcenessCommand, the TextBlock is bound to the ‘DataObj.IsAce’ property and the Rectangle has 2 visual states: IsAce and NotAce. To make the Rectangle change it’s visual state I’ve used a DataStateBehavior inside the Layout Root Grid: <i:Interaction.Behaviors> <ei:DataStateBehavior Binding="{Binding DataObj.IsAce}" Value="true" TrueState="IsAce" FalseState="NotAce"/> </i:Interaction.Behaviors> So now we have the button changing the ‘IsAce’ property and giving us the other visual state: Great! So – the next stage is to get that to work inside a DataTemplate… Which (thankfully) is easy money. All we do is add a ListBox to the View and an ObservableCollection to the ViewModel. Well – ok, a little bit more than that. Once we’ve got the ListBox with it’s ItemsSource property set, it’s time to add the DataTemplate itself. Again, this isn’t exactly taxing, and is purely going to be a Grid with a Textblock and a Rectangle (again, I’m nothing if not consistent). Though, to be a little jazzy I’ve swapped the rectangle to the other side (living the dream). So, all that’s left is to add some States to the template.. (Yes – you can do that), these can be the same names as the others, or indeed, something else, I have chosen to stick with the same names and take the extra confusion hit right on the nose. Once again, I add the DataStateBehavior to the root Grid element: <i:Interaction.Behaviors> <ei:DataStateBehavior Binding="{Binding IsAce}" Value="true" TrueState="IsAce" FalseState="NotAce"/> </i:Interaction.Behaviors> The key difference here is the ‘Binding’ attribute, where I’m now binding to the IsAce property directly, and boom! It’s all gravy!   So far, so good. We can use boolean values to change the visual states, and (crucially) it works in a DataTemplate, bingo! Now. Onwards to the Enum part of this (finally!). Obviously we can’t use the DataStateBehavior, it' only gives us true/false options. So, let’s give the GoToStateAction a go. Now, I warn you, things get a bit complex from here, instead of a bool with 2 values, I’m gonna max it out and bring in an Enum with 3 (count ‘em) 3 values: Red, Amber and Green (those of you with exceptionally sharp minds will be reminded of traffic lights). We’re gonna have a rectangle which also has 3 visual states – cunningly called ‘Red’, ‘Amber’ and ‘Green’. A new class called DataObj2: public class DataObj2 : NotifyPropertyChanger { private Status _statusValue; public DataObj2(Status status) { StatusValue = status; } public Status StatusValue { get { return _statusValue; } set { _statusValue = value; RaisePropertyChanged("StatusValue"); } } } Where ‘Status’ is my enum. Good times are here! Ok, so let’s get to the beefy stuff. So, we’ll start off in the same manner as the last time, we will have a single DataObj2 instance available to the Page and bind to that. Let’s add some Triggers (these are in the LayoutRoot again). <i:Interaction.Triggers> <ei:DataTrigger Binding="{Binding DataObject2.StatusValue}" Value="Amber"> <ei:GoToStateAction StateName="Amber" UseTransitions="False" /> </ei:DataTrigger> <ei:DataTrigger Binding="{Binding DataObject2.StatusValue}" Value="Green"> <ei:GoToStateAction StateName="Green" UseTransitions="False" /> </ei:DataTrigger> <ei:DataTrigger Binding="{Binding DataObject2.StatusValue}" Value="Red"> <ei:GoToStateAction StateName="Red" UseTransitions="False" /> </ei:DataTrigger> </i:Interaction.Triggers> So what we’re saying here is that when the DataObject2.StatusValue is equal to ‘Red’ then we’ll go to the ‘Red’ state. Same deal for Green and Amber (but you knew that already). Hook it all up and start teh project. Hmm. Just grey. Not what I wanted. Ok, let’s add a ‘ChangeStatusCommand’, hook that up to a button and give it a whirl: Right, so the DataTrigger isn’t picking up the data on load. On the plus side, changing the status is making the visual states change. So. We’ll cross the ‘Grey’ hurdle in a bit, what about doing the same in the DataTemplate? <Codey Codey/> Grey again, but if we press the button: (I should mention, pressing the button sets the StatusValue property on the DataObj2 being represented to the next colour). Right. Let’s look at this ‘Grey’ issue. First ‘fix’ (and I use the term ‘fix’ in a very loose way): The Dispatcher Fix This involves using the Dispatcher on the View to call something like ‘RefreshProperties’ on the ViewModel, which will in turn raise all the appropriate ‘PropertyChanged’ events on the data objects being represented. So, here goes, into turdcode-ville – population – me: First, add the ‘RefreshProperties’ method to the DataObj2: internal void RefreshProperties() { RaisePropertyChanged("StatusValue"); } (shudder) Now, add it to the hosting ViewModel: public void RefreshProperties() { DataObject2.RefreshProperties(); if (DataObjects != null && DataObjects.Count > 0) { foreach (DataObj2 dataObject in DataObjects) dataObject.RefreshProperties(); } } (double shudder) and now for the cream on the cake, adding the following line to the code behind of the View: Dispatcher.BeginInvoke(() => ((MoreVisualStatesViewModel)DataContext).RefreshProperties()); So, what does this *ahem* code give us: Awesome, it makes the single bound data object show the colour, but frankly ignores the DataTemplate items. This (by the way) is the same output you get from: Dispatcher.BeginInvoke(() => ((MoreVisualStatesViewModel)DataContext).ChangeStatusCommand.Execute(null)); So… Where does that leave me? What about adding a button to the Page to refresh the properties – maybe it’s a timer thing? Yes, that works. Right, what about using the Loaded event then eh? Loaded += (s, e) => ((MoreVisualStatesViewModel) DataContext).RefreshProperties(); Ahhh No. What about converting the DataTemplate into a UserControl? Anything is worth a shot.. Though – I still suspect I’m going to have to ‘RefreshProperties’ if I want the rectangles to update. Still. No. This DataTemplate DataTrigger binding is becoming a bit of a pain… I can’t add a ‘refresh’ button to the actual code base, it’s not exactly user friendly. I’m going to end this one now, and put some investigating into the use of the DataStateSwitchBehavior (all the ones I’ve found, well, all 2 of them are working in SL3, but not 4…)

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  • Design patterns frequently seen in embedded systems programming

    - by softwarelover
    I don't have any question related to coding. My concerns are about embedded systems programming independent of any particular programming language. Because I am new in the realm of embedded programming, I would quite appreciate responses from those who consider themselves experienced embedded systems programmers. I basically have 2 questions. Of the design patterns listed below are there any seen frequently in embedded systems programming? Abstraction-Occurrence pattern General Hierarchy pattern Player-Role pattern Singleton pattern Observer pattern Delegation pattern Adapter pattern Facade pattern Immutable pattern Read-Only Interface pattern Proxy pattern As an experienced embedded developer, what design patterns have you, as an individual, come across? There is no need to describe the details. Only the pattern names would suffice. Please share your own experience. I believe the answers to the above questions would work as a good starting point for any novice programmers in the embedded world.

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