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• How to sync client and server at the first frame

  - by wheelinlight

  I'm making a game where an authoritative server sends information to all clients about states and positions for objects in a 3d world. The player can control his character by clicking on the screen to set a destination for the character, much like in the Diablo series. I've read most information I can find online about interpolation, reconciliation, and general networking architecture (Valve's for instance). I think I understand everything but one thing seems to be missing in every article I read. Let say we have an interpolation delay of 100ms, server tickrate=50ms, latency=200ms; How do I know when 100ms has past on the client? If the server sends the first update on t=0, can I assume it arrives at t=200, therefore assuming that all packets takes the same amount of time to reach the client? What if the first packet arrives a little quick, for instance at t=150. I would then be starting the client with t=150 and at t=250 it will think it has past 100ms since its connect to the server when it in fact only 50ms has past. Hopefully the above paragraph is understandable. The summarized question would be: How do I know at what tick to start simulating the client? EDIT: This is how I ended up doing it: The client keeps a clock (approximately) in sync with the server. The client then simulates the world at simulationTime = syncedTime - avg(RTT)/2 - interpolationTime The round-trip time can fluctuate so therefore I average it out over time. By only keeping the most recent values when calculating the average I hope to adapt to more permanent changes in latency. It's still to early to draw any conclusion. I'm currently simulating bad network connections, but it's looking good so far. Anyone see any possible problems?

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• Python Web Applications: What is the way and the method to handle Registrations, Login-Logouts and Cookies? [on hold]

  - by Phil

  I am working on a simple Python web application for learning purposes. I have chosen a very minimalistic and simple framework. I have done a significant amount of research but I couldn't find a source clearly explaining what I need, which is as follows: I would like to learn more about: User registration User Log-ins User Log-outs User auto-logins I have successfully handled items 1 and 3 due to their simple nature. However, I am confused with item 2 (log-ins) and item 4 (auto-logins). When a user enters username and password, and after hashing with salts and matching it in the DB; What information should I store in the cookies in order to keep the user logged in during the session? Do I keep username+password but encrypt them? Both or just password? Do I keep username and a generated key matching their password? If I want the user to be able to auto-login (when they leave and come back to the web page), what information then is kept in the cookies? I don't want to use modules or libraries that handle these things automatically. I want to learn basics and why something is the way it is. I would also like to point out that I do not mind reading anything you might offer on the topic that explains hows and whys. Possibly with algorithm diagrams to show the process. Some information: I know about setting headers, cookies, encryption (up to some level, obviously not an expert!), request objects, SQLAlchemy etc. I don't want any data kept in a single web application server's store. I want multiple app-servers to be handle a user, and whatever needs to be kept on the server to be done with a Postgres/MySQL via SQLAlchemy (I think, this is called stateless?) Thank you.

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• Architecture : am I doing things right?

  - by Jeremy D

  I'm trying to use a '~classic' layered arch using .NET and Entity Framework. We are starting from a legacy database which is a little bit crappy: Inconsistent naming Unneeded views (view referencing other views, select * views etc...) Aggregated columns Potatoes and Carrots in the same table etc... So I ended with fully isolating my database structure from my domain model. To do so EF entities are hidden from presentation layer. The goal is to permit an easier database refactoring while lowering the impact of it on applications. I'm now facing a lot of challenges and I'm starting to ask myself if I'm doing things right. My Domain Model is highly volatile, it keeps evolving with apps as new fields needs are arising. Complexity of it keeps raising and class it contains start to get a lot of properties. Creating include strategy and reprojecting to EF is very tricky (my domain objects don't have any kind of lazy/eager loading relationship properties): DomainInclude<Domain.Model.Bar>.Include("Customers").Include("Customers.Friends") // To... IFooContext.Bars.Include(...).Include(...).Where(...) Some framework are raping the isolation levels (Devexpress Grids which needs either XPO or IQueryable for filtering and paging large data sets) I'm starting to ask myself if : the isolation of EF auto-generated entities is an unneeded cost. I should allow frameworks to hit IQueryable? Slow slope to hell? (it's really hard to isolate DevExpress framework, any successful experience?) the high volatility of my domain model is normal? Did you have similar difficulties? Any advice based on experience?

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• Static DataTable or DataSet in a class - bad idea?

  - by Superbest

  I have several instances of a class. Each instance stores data in a common database. So, I thought "I'll make the DataTable table field static, that way every instance can just add/modify rows to its own table field, but all the data will actually be in one place!" However, apparently it's a bad idea to do use static fields, especially if it's databases: Don't Use "Static" in C#? Is this a bad idea? Will I run into problems later on if I use it? This is a small project so I can accept no testing as a compromise if that is the only drawback. The benefit of using a static database is that there can be many objects of type MyClass, but only one table they all talk to, so a static field seems to be an implementation of exactly this, while keeping syntax concise. I don't see why I shouldn't use a static field (although I wouldn't really know) but if I had to, the best alternative I can think of is creating one DataTable, and passing a reference to it when creating each instance of MyClass, perhaps as a constructor parameter. But is this really an improvement? It seems less intuitive than a static field.

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• SQL language drawbacks, The Third Manifesto

  - by David Portabella

  Sometime ago I read about SQL language drawbacks (the basic language specification, not vendor specific), and one of the drawbacks was that the language does not allow to create a set of tuples that don't come from a table. For instance, SELECT firstName, lastName from people; this creates a set of tuples coming from the table people. Now, if I don't have this table people, and I want to return a constant, I'd need something like this to return a set of two tuples (this would not require to have a table): SELECT VALUES('james', 'dean'), ('tom', 'cruisse'); Why I would need that? Because of the same reasons that we can define constants (not only basic types, but objects and arrays also) in any advanced programming language. Workarounds, Yes, I could create a temporal table, fill the data, and SELECT from that table. This is a hack, to overcome the drawbacks of the poor SQL language. I think that I read about this somewhere in "The Third Manifesto", but I don't find the paragraph/example talking about this concrete drawback anymore. Do you know a reference about it?

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• Where should "display functions" live in an MVC web app?

  - by User

  I'm using the Yii Framework which is an MVC php framework that is pretty similar to your standard web-based MVC framework. I want to display the related data from a many-to-many table as a list of strings in my view. Assuming a table schema like: tag { id, name } post { id, title, content, date } post_tag { post_id, tag_id } A post will display like: Date: 9/27/2012 Title: Some Title Content: blah blah blah... Tags: Smart Funny Cool Informative I can achieve this by doing something like this in my Post view: <?php echo join(' ', array_map(function($tag) { return $tag->name; }, $model->tags)); ?> (where $model->tags is an array of Tag objects associated with my model) My questions are: Is this amount of code/logic okay in the view? (Personally I think I'd rather just reference a property or call a single function.) If not, where should this code live? In the model? the controller? a helper? Potentially I may want to use in in other views as well. Ultimately I think its purely a display issue which would make me think it should be in the view, but then I have to repeat the code in any view I want to use it in.

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• Places to store basic data

  - by Ella

  I am using PHP. I'm building a fully modular CMS, which is destined for the public. Some people might view this as a framework, but I intend to write a set of extensions for it, extensions that will make it a CMS :P Because it's completely modular I have a problem figuring out how to load extensions. Practically I need to get the list of active extensions, so I can load them inside my base class. I load them by reading some file headers, which contain a "dependency" field. That field decides the order in which I have to instantiate the objects. The problem is that when the CMS starts I have no database interface, because that's an extension too, so I can't store the active extensions list in the database :) You might ask how are extensions activated in the first place. Well - in the administration interface, which is an extension as well (obviously on first install of the CMS there will be some extensions active by default). Could writing that list inside a text file be a solution? The problem is that a lot of hosts are not very nice with scripts when they write files. And since this CMS is public I might have a problem here?

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• Photoshop alternative with same keyboard shorcuts

  - by user292254

  tldr; Is there a program with the same keyboard shortcuts and/or user interface as PS. I know the "photoshop alternative" question has been asked so many times, but I feel this variant is worth the time to ask. I am a web designer and have been using PS daily on a windows or mac machine for about 10 years, but I do most of my development in linux. The only thing that has been keeping me from the full switch to linux is PS. I have tried many alternatives, including GIMP, but I feel the barrier to entry is too high for one reason and one reason only, the keyboard shortcuts. Over the years I have become very adept and quick in the use of PS because of keyboard shortcuts and muscle memory. I realize that many shortcuts can be customized, but many actions are just too different from PS. So my question is what programs are out there that are the closest to PS in keyboard shortcuts and interface. I don't care if I have to do a bunch of customization to get it as close as possible, but I just can't take too much time to learn a completely new workflow. Of course I realize that any software will take time and effort, I just want to make that time/effort as minimal as possible. Thanks in advance for your responses. edit I should tell you the most important features and workflow I use on a daily basis are, Smart objects, linked documents, save for web and devises.

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• Error when installing ubuntu-zfs

  - by ubiquibacon

  I'm switching from FreeNAS to Ubuntu 12.04 LTS. After a vanilla install of Ubuntu has been completed I run the following commands in the order shown to install ZFS: apt-get install python-software-properties add-apt-repository ppa:zfs-native/stable apt-get -y -q update && apt-get -y -q upgrade apt-get install ubuntu-zfs When the last command is run ZFS is installed and seems to be working correctly... mostly (more on that later). However, when the last command is run I get this error (full log here): configure: error: *** Please make sure the kmod spl devel <kernel> package for your *** distribution is installed then try again. If that fails you *** can specify the location of the spl objects with the *** '--with-spl-obj=PATH' option. What is this error and how do I fix it? Now I said mostly earlier because my pool's don't auto mount when the server restarts the way they should. All my reading (mostly from this page) indicates that mountall should just take care of the mounting. I have followed the instructions on that page and I cannot get mountall to work correctly. My pools will only auto mount on restart if I edit /etc/fstab or change the ZFS_MOUNT and ZFS_UNMOUNT options in /etc/default/zfs.

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• C++ and SDL Trouble Creating a STL Vector of a Game Object

  - by Jackson Blades

  I am trying to create a Space Invaders clone using C++ and SDL. The problem I am having is in trying to create Waves of Enemies. I am trying to model this by making my Waves a vector of 8 Enemy objects. My Enemy constructor takes two arguments, an x and y offset. My Wave constructor also takes two arguments, an x and y offset. What I am trying to do is have my Wave constructor initialize a vector of Enemies, and have each enemy given a different x offset so that they are spaced out appropriately. Enemy::Enemy(int x, int y) { box.x = x; box.y = y; box.w = ENEMY_WIDTH; box.h = ENEMY_HEIGHT; xVel = ENEMY_WIDTH / 2; } Wave::Wave(int x, int y) { box.x = x; box.y = y; box.w = WAVE_WIDTH; box.y = WAVE_HEIGHT; xVel = (-1)*ENEMY_WIDTH; yVel = 0; std::vector<Enemy> enemyWave; for (int i = 0; i < enemyWave.size(); i++) { Enemy temp(box.x + ((ENEMY_WIDTH + 16) * i), box.y); enemyWave.push_back(temp); } } I guess what I am asking is if there is a cleaner, more elegant way to do this sort of initialization with vectors, or if this is right at all. Any help is greatly appreciated.

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• How can I replicate the look and limitations of the Super NES?

  - by Mikalichov

  I am looking to produce graphics with the same limitations / look that in the Super Nes era. I am specifically looking for graphics similar to Chrono Trigger / FF6. It would be a lot easier to do if I had an idea of the resolution / dpi I am supposed to use. I found that the technical specs for the SNES are: Progressive: 256 × 224, 512 × 224, 256 × 239, 512 × 239 Interlaced: 512 × 448, 512 × 478 But even by using these resolutions, it is pointless if I set it at 72dpi, as I will still have possibly very detailed graphics (that is the main thing, I don't want detailed graphics, I want to go pixelated). I figured it might be related to the sprite size limit, i.e.: Sprites can be 8 × 8, 16 × 16, 32 × 32, or 64 × 64 pixels, each using one of eight 16-color palettes and tiles from one of two blocks of 256 in VRAM. Up to 32 sprites and 34 8 × 8 sprite tiles may appear on any one line. This would work for sprites (characters, objects), but what about maps? Are they built entirely from 8x8 tiles? And then, at what resolution is the end result displayed? It might seem like I am giving the question and answers at the same time, but all of these are suppositions I am making, so could someone confirm or correct them?

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• Strategies for managing use of types in Python

  - by dave

  I'm a long time programmer in C# but have been coding in Python for the past year. One of the big hurdles for me was the lack of type definitions for variables and parameters. Whereas I totally get the idea of duck typing, I do find it frustrating that I can't tell the type of a variable just by looking at it. This is an issue when you look at someone else's code where they've used ambiguous names for method parameters (see edit below). In a few cases, I've added asserts to ensure parameters comply with an expected type but this goes against the whole duck typing thing. On some methods, I'll document the expected type of parameters (eg: list of user objects), but even this seems to go against the idea of just using an object and let the runtime deal with exceptions. What strategies do you use to avoid typing problems in Python? Edit: Example of the parameter naming issues: If our code base we have a task object (ORM object) and a task_obj object (higher level object that embeds a task). Needless to say, many methods accept a parameter named 'task'. The method might expect a task or a task_obj or some other construct such as a dictionary of task properties - it is not clear. It is them up to be to look at how that parameter is used in order to work out what the method expects.

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• Correct way to use Farseer Physics in XNA

  - by user1640602

  I am using Farseer Physics for my 2D sidescroller game and I'm not sure how to proceed with it. I currently have a Sprite class (handles nothing but graphics), a GameObject class (contains specific object info like hit points), a World object which contains the list of Bodies, and a Level object which contains all of these objects. Originally I was trying to keep track of the Sprites, GameObjects, and Bodies separately because I felt that would provide loose coupling but it quickly became a headache. So my new idea was to add a Sprite member to the GameObject class but I'm still not sure how to maintain the Bodies because they have to communicate with GameObject. Specifically, my issue is this: The position of the Body is used to draw the Sprite inside of the Level. In order to do that I would have to maintain a link between GameObjects and Bodies. Is this correct or is there a better way to architect my game? If any of this is unclear please ask and I'll try to clarify. Thank you in advance for any help.

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• Player & Level class structure in 2D python console game?

  - by Markus Meskanen

  I'm trying to create a 2D console game, where I have a player who can freely move around in a level (~map, but map is a reserved keyword) and interfere with other objects. Levels construct out of multiple Blocks, such as player(s), rocks, etc. Here's the Block class: class Block(object): def __init__(self, x=0, y=0, char=' ', solid=False): self.x = x self.y = y self.char = char self.solid = solid As you see, each block has a position (x, y) and a character to represent the block when it's printed. Each block also has a solid attribute, defining whether it can overlap with other solids or not. (Two solid blocks cannot overlap) I've now created few subclasses from Block (Rock might be useless for now) class Rock(Block): def __init__(self, x=0, y=0): super(Rock, self).__init__(x, y, 'x', True) class Player(Block): def __init__(self, x=0, y=0): super(Player, self).__init__(x, y, 'i', True) def move_left(self, x=1): ... # How do I make sure Player wont overlap with rocks? self.x -= x And here's the Level class: class Level(object): def __init__(self, name='', blocks=None): self.name = name self.blocks = blocks or [] Only way I can think of is to store a Player instance into Level's attributes (self.player=Player(), or so) and then give Level a method: def player_move_left(self): for block in self.blocks: if block.x == self.player.x - 1 and block.solid: return False But this doesn't really make any sense, why have a Player class if it can't even be moved without Level? Imo. player should be moved by a method inside Player. Am I wrong at something here, if not, how could I implement such behavior?

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• Good design for class with similar constructors

  - by RustyTheBoyRobot

  I was reading this question and thought that good points were made, but most of the solutions involved renaming one of the methods. I am refactoring some poorly written code and I've run into this situation: public class Entity { public Entity(String uniqueIdentifier, boolean isSerialNumber) { if (isSerialNumber) { this.serialNumber = uniqueIdentifier; //Lookup other data } else { this.primaryKey = uniqueIdentifier; // Lookup other data with different query } } } The obvious design flaw is that someone needed two different ways to create the object, but couldn't overload the constructor since both identifiers were of the same type (String). Thus they added a flag to differentiate. So, my question is this: when this situation arises, what are good designs for differentiating between these two ways of instantiating an object? My First Thoughts You could create two different static methods to create your object. The method names could be different. This is weak because static methods don't get inherited. You could create different objects to force the types to be different (i.e., make a PrimaryKey class and a SerialNumber class). I like this because it seems to be a better design, but it also is a pain to refactor if serialNumber is a String everywhere else.

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• Being stupid to get better productivity?

  - by loki2302

  I've spent a lot of time reading different books about "good design", "design patterns", etc. I'm a big fan of the SOLID approach and every time I need to write a simple piece of code, I think about the future. So, if implementing a new feature or a bug fix requires just adding three lines of code like this: if(xxx) { doSomething(); } It doesn't mean I'll do it this way. If I feel like this piece of code is likely to become larger in the nearest future, I'll think of adding abstractions, moving this functionality somewhere else and so on. The goal I'm pursuing is keeping average complexity the same as it was before my changes. I believe, that from the code standpoint, it's quite a good idea - my code is never long enough, and it's quite easy to understand the meanings for different entities, like classes, methods, and relations between classes and objects. The problem is, it takes too much time, and I often feel like it would be better if I just implemented that feature "as is". It's just about "three lines of code" vs. "new interface + two classes to implement that interface". From a product standpoint (when we're talking about the result), the things I do are quite senseless. I know that if we're going to work on the next version, having good code is really great. But on the other side, the time you've spent to make your code "good" may have been spent for implementing a couple of useful features. I often feel very unsatisfied with my results - good code that only can do A is worse than bad code that can do A, B, C, and D. Are there any books, articles, blogs, or your ideas that may help with developing one's "being stupid" approach?

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• The idea of functionN in Scala / Functionaljava

  - by Luke Murphy

  From brain driven development It turns out, that every Function you’ll ever define in Scala, will become an instance of an Implementation which will feature a certain Function Trait. There is a whole bunch of that Function Traits, ranging from Function1 up to Function22. Since Functions are Objects in Scala and Scala is a statically typed language, it has to provide an appropriate type for every Function which comes with a different number of arguments. If you define a Function with two arguments, the compiler picks Function2 as the underlying type. Also, from Michael Froh's blog You need to make FunctionN classes for each number of parameters that you want? Yes, but you define the classes once and then you use them forever, or ideally they're already defined in a library (e.g. Functional Java defines classes F, F2, ..., F8, and the Scala standard library defines classes Function1, ..., Function22) So we have a list of function traits (Scala), and a list of interfaces (Functional-java) to enable us to have first class funtions. I am trying to understand exactly why this is the case. I know, in Java for example, when I write a method say, public int add(int a, int b){ return a + b; } That I cannot go ahead and write add(3,4,5); ( error would be something like : method add cannot be applied to give types ) We simply have to define an interface/trait for functions with different parameters, because of static typing?

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• How to make the members of my Data Access Layer object aware of their siblings

  - by Graham

  My team currently has a project with a data access object composed like so: public abstract class DataProvider { public CustomerRepository CustomerRepo { get; private set; } public InvoiceRepository InvoiceRepo { get; private set; } public InventoryRepository InventoryRepo { get; private set; } // couple more like the above } We have non-abstract classes that inherit from DataProvider, and the type of "CustomerRepo" that gets instantiated is controlled by that child class. public class FloridaDataProvider { public FloridaDataProvider() { CustomerRepo = new FloridaCustomerRepo(); // derived from base CustomerRepository InvoiceRepo = new InvoiceRespository(); InventoryRepo = new InventoryRepository(); } } Our problem is that some of the methods inside a given repo really would benefit from having access to the other repo's. Like, a method inside InventoryRepository needs to get to Customer data to do some determinations, so I need to pass in a reference to a CustomerRepository object. Whats the best way for these "sibling" repos to be aware of each other and have the ability to call each other's methods as-needed? Virtually all the other repos would benefit from having the CustomerRepo, for example, because it is where names/phones/etc are selected from, and these data elements need to be added to the various objects that are returned out of the other repos. I can't just new-up a plain "CustomerRepository" object inside a method within a different repo, because it might not be the base CustomerRepository that actually needs to run.

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• How can I read a portion of one Minecraft world file and write it into another?

  - by RapierMother

  I'm looking to read block data from one Minecraft world and write the data into certain places in another. I have a Minecraft world, let's say "TemplateWorld", and a 2D list of Point objects. I'm developing an application that should use the x and y values of these Points as x and z reference coordinates from which to read constant-sized areas of blocks from the TemplateWorld. It should then write these blocks into another Minecraft world at constant y coordinates, with x & z coordinates determined based on each Point's index in the 2D list. The issue is that, while I've found a decent amount of information online regarding Minecraft world formats, I haven't found what I really need: more of a breakdown by hex address of where/what everything is. For example, I could have the TemplateWorld actually be a .schematic file rather than a world; I just need to be able to read the bytes of the file, know that the actual block data starts always at a certain address (or after a certain instance of FF, etc.), and how it's stored. Once I know that, it's easy as pie to just read the bytes and store them.

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• How to handle the different frame rate on different devices?

  - by Fenwick

  I am not quite sure how frame per second works on a web page. I have a Canvas game that involves in moving an image from point A to B, and measuring the time elapsed. The code can be as simple as: var timeStamp = Date.now(); function update(){ obj.y += obj.speed; text = "Time: "+ (Date.now() - timeStamp) + "ms"; } The function update() is called every frame. The problem is that the time elapsed is different from device to device. It is pretty short on my PC, but get longer on my iPad, and is much longer on my cell phone. I thought it is because the FPS is smaller on mobile devices, so instead of calling update() every frame, I call it every 1ms by using a setInterval. But this does not solve the problem. In my understanding, the function for setInterval is invoked based on the increment in system time, other than frame rate, so it should fix the problem. Am I missing anything here? If the setInterval function is called based on FPS, is there any way to get around with the FPS difference across devices? On a side note, I have sort of a "water simulator" on the same canvas. It involves in redrawing about 60 objects which can be 600x600 pixels for every frame, so it could be a frame rate killer. I am using Phaser.js but not really using much of its functionalities, if that helps.

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• Traverse tree with results. Maybe type in Java?

  - by Angelo.Hannes

  I need to check a tree's node state. It can either be OK or NOT_OK. But that state is dependent on its children. So for a node to be OK, every of its children needs to be OK. If one or more of its children is NOT_OK the whole node is NOT_OK. To determine the state of a node I need to aggregate some properties of the node. So I thought of two possible implementations. And they are more or less covered in this question: Why is Option/Maybe considered a good idea and checked exceptions are not? Exception I could pass the properties up the recursion path, and throw an exception if something went wrong. Maybe I implement an Maybe type and let it either hold an error or the aggregated properties. Maybe it is more an Either. I tend towards the last option. And I'm thinking of an enum with two objects. Where I can additionally set those aggregated properties. Am I on the right track? I'm not familiar with the new JDK8 functional stuff. But I'm stuck on JDK7 anyway, so please focus on JDK7.

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• How to perform game object smoothing in multiplayer games

  - by spaceOwl

  We're developing an infrastructure to support multiplayer games for our game engine. In simple terms, each client (player) engine sends some pieces of data regarding the relevant game objects at a given time interval. On the receiving end, we step the incoming data to current time (to compensate for latency), followed by a smoothing step (which is the subject of this question). I was wondering how smoothing should be performed ? Currently the algorithm is similar to this: Receive incoming state for an object (position, velocity, acceleration, rotation, custom data like visual properties, etc). Calculate a diff between local object position and the position we have after previous prediction steps. If diff doesn't exceed some threshold value, start a smoothing step: Mark the object's CURRENT POSITION and the TARGET POSITION. Linear interpolate between these values for 0.3 seconds. I wonder if this scheme is any good, or if there is any other common implementation or algorithm that should be used? (For example - should i only smooth out the position? or other values, such as speed, etc) any help will be appreciated.

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• What's wrong with circular references?

  - by dash-tom-bang

  I was involved in a programming discussion today where I made some statements that basically assumed axiomatically that circular references (between modules, classes, whatever) are generally bad. Once I got through with my pitch, my coworker asked, "what's wrong with circular references?" I've got strong feelings on this, but it's hard for me to verbalize concisely and concretely. Any explanation that I may come up with tends to rely on other items that I too consider axioms ("can't use in isolation, so can't test", "unknown/undefined behavior as state mutates in the participating objects", etc.), but I'd love to hear a concise reason for why circular references are bad that don't take the kinds of leaps of faith that my own brain does, having spent many hours over the years untangling them to understand, fix, and extend various bits of code. Edit: I am not asking about homogenous circular references, like those in a doubly-linked list or pointer-to-parent. This question is really asking about "larger scope" circular references, like libA calling libB which calls back to libA. Substitute 'module' for 'lib' if you like. Thanks for all of the answers so far!

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• Single-Click Checkbox in RadGridView

  - by Anthony Trudeau

  Originally posted on: http://geekswithblogs.net/tonyt/archive/2014/06/05/156809.aspxThe Telerik RadGridView for WPF is a flexible visual control for displaying and manipulating tables of data. It’s not without it’s quirks though. I ran into one of those quirks recently. The behavior of the RadGridView requires that you first activate the cell for editing. That enables the editing controls underneath. Although that provides better editing capabilities, it also can be unintuitive. In my case I don’t want my users to have to click a checkbox value twice in order to change the value. This can be solved easily by setting the EditTriggers and AutoSelectOnEdit properties to CellClick and True respectively. Unfortunately, the story doesn’t end there. You would think you could set those properties in a style with a TargetType of GridViewCheckBoxColumn. You’d be wrong. <!-- This works --> <telerik:GridViewCheckBoxColumn Header="Flag #1"       DataMemberBinding="{Binding Flag1}"       EditTriggers="CellClick" AutoSelectOnEdit="True"/> <!-- This doesn’t work --> <Style TargetType="{x:Type telerik:GridViewCheckBoxColumn}">       <Setter Property="EditTriggers" Value="CellClick" />       <Setter Property="AutoSelectOnEdit" Value="True" /> </Style> Telerik told me that is the correct, expected behavior, because the columns in the RadGridView are not visual elements. Their explanation is that the Style property comes from the base class FrameworkContentElement, but the column objects aren’t visual elements. That may be an implementation truth, but that doesn’t make the behavior correct or expected. It’s unintuitive that the GridViewCheckBoxColumn exposes a Style property that cannot be used properly, but there it is. At least there’s a way to get the desired effect.

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• Using visitor pattern with large object hierarchy

  - by T. Fabre

  Context I've been using with a hierarchy of objects (an expression tree) a "pseudo" visitor pattern (pseudo, as in it does not use double dispatch) : public interface MyInterface { void Accept(SomeClass operationClass); } public class MyImpl : MyInterface { public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } } This design was, however questionnable, pretty comfortable since the number of implementations of MyInterface is significant (~50 or more) and I didn't need to add extra operations. Each implementation is unique (it's a different expression or operator), and some are composites (ie, operator nodes that will contain other operator/leaf nodes). Traversal is currently performed by calling the Accept operation on the root node of the tree, which in turns calls Accept on each of its child nodes, which in turn... and so on... But the time has come where I need to add a new operation, such as pretty printing : public class MyImpl : MyInterface { // Property does not come from MyInterface public string SomeProperty { get; set; } public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } public void Accept(SomePrettyPrinter printer) { printer.PrettyPrint(this.SomeProperty); } } I basically see two options : Keep the same design, adding a new method for my operation to each derived class, at the expense of maintainibility (not an option, IMHO) Use the "true" Visitor pattern, at the expense of extensibility (not an option, as I expect to have more implementations coming along the way...), with about 50+ overloads of the Visit method, each one matching a specific implementation ? Question Would you recommand using the Visitor pattern ? Is there any other pattern that could help solve this issue ?

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