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• In C++, where are static, dynamic and local variables stored? How about in C and Java?

  - by user285109

  In C++, where are static, dynamic and local variables stored? How about in C and Java?

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• Updating resources in SharpDX - why can I not map a dynamic texture?

  - by sebf

  I am trying to map a Texture2D resource in DirectX11 via SharpDX. The resource is declared as a ShaderResource, with Default usage and the 'Write' CPU flag specified. My call however fails with a generic exception from SharpDX: _Parent.Context.MapSubresource(_Resource, 0, SharpDX.Direct3D11.MapMode.Write, SharpDX.Direct3D11.MapFlags.None, out stream); I see from this question that it is supported. The MSDN docs and this other question hint that instead of using Context.MapSubresource() I should be using Texture2D.Map(), however, the DirectX11 Texture2D class does not define Map() (though it does for the DX10 equivalent). If I call the above with MapMode.WriteDiscard, the call succeeds but in this case the previous content of the texture is lost, which is no good when I only want to update a section of it. Has the Map() method been removed in DirectX11 or am I looking in the wrong place? Is the MapSubresource() method unsuitable or am I using it wrong?

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• Is dynamic HTML layout good from an SEO perspective?

  - by sll

  Just wondering whether dynamically built HTML layout is fine from SEO perspectives? So let's assume e-commerce engine and its most popular page - products catalog. So 90% of the page is built using AJAX and MVVM library knockoutjs which builds HTML on the fly on the client side. So how search bots would parse such content? Is it fine indexed and would be such effective as server-side built HTML pages from the SEO perspectives?

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• .Net Reflector 6.5 EAP now available

  - by CliveT

  With the release of CLR 4 being so close, we’ve been working hard on getting the new C# and VB language features implemented inside Reflector. The work isn’t complete yet, but we have some of the features working. Most importantly, there are going to be changes to the Reflector object model, and we though it would be useful for people to see the changes and have an opportunity to comment on them. Before going any further, we should tell you what the EAP contains that’s different from the released version. A number of bugs have been fixed, mainly bugs that were raised via the forum. This is slightly offset by the fact that this EAP hasn’t had a whole lot of testing and there may have been new bugs introduced during the development work we’ve been doing. The C# language writer has been changed to display in and out co- and contra-variance markers on interfaces and delegates, and to display default values for optional parameters in method definitions. We also concisely display values passed by reference into COM calls. However, we do not change callsites to display calls using named parameters; this looks like hard work to get right. The forthcoming version of the C# language introduces dynamic types and dynamic calls. The new version of Reflector should display a dynamic call rather than the generated C#: dynamic target = MyTestObject(); target.Hello("Mum"); We have a few bugs in this area where we are not casting to dynamic when necessary. These have been fixed on a branch and should make their way into the next EAP. To support the dynamic features, we’ve added the types IDynamicMethodReferenceExpression, IDynamicPropertyIndexerExpression, and IDynamicPropertyReferenceExpression to the object model. These types, based on the versions without “Dynamic” in the name, reflect the fact that we don’t have full information about the method that is going to be called, but only have its name (as a string). These interfaces are going to change – in an internal version, they have been extended to include information about which parameter positions use runtime types and which use compile time types. There’s also the interface, IDynamicVariableDeclaration, that can be used to determine if a particular variable is used at dynamic call sites as a target. A couple of these language changes have also been added to the Visual Basic language writer. The new features are exposed only when the optimization level is set to .NET 4. When the level is set this high, the other standard language writers will simply display a message to say that they do not handle such an optimization level. Reflector Pro now has 4.0 as an optional compilation target and we have done some work to get the pdb generation right for these new features. The EAP version of Reflector no longer installs the add-in on startup. The first time you run the EAP, it displays the integration options dialog. You can use the checkboxes to select the versions of Visual Studio into which you want to install the EAP version. Note that you can only have one version of Reflector Pro installed in Visual Studio; if you install into a Visual Studio that has another version installed, the previous version will be removed. Please try it out and send your feedback to the EAP forum.

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• Do You Need a Static or a Dynamic Website?

  Web design industry is thriving despite the global economic slowdown. The boom in small home based businesses increased the demand of web design services. Today?s small businesses and home based busi... [Author: Emily Matthew - Web Design and Development - March 31, 2010]

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• What is the best approach to copy public dynamic pages?

  - by Renan

  Situation: the government is supposed to publish official information online such as acts and laws. Problem: they're using 90s expertise to do it. You can tell that by the constant use of deprecated html tags such as <table and the lack of any compression at all, which makes some documents go way over 700,000 bytes even though they're pure text. Side problem: some companies are actually editing and selling this content that should be public and free. What I need to know is the best approach to offer said official content in my own site for free. I've thought of setting up a mirror to copy the official pages from time to time, since some of them are updated frequently, which would automatically be compressed as all my pages are via htaccess.

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• Tab Sweep - State of Java EE, Dynamic JPA, Java EE performance, Garbage Collection, ...

  - by alexismp

  Recent Tips and News on Java EE 6 & GlassFish: • Java EE: The state of the environment (SDTimes) • Extend your Persistence Unit on the fly (EclipseLink blog) • Glassfish 3.1 - AccessLog Format (Ralph) • Java Enterprise Performance - Unburdended Applications (Lucas) • Java Garbage Collection and Heap Analysis (John) • Qu’attendez-vous de JMS 2.0? (Julien) • Dynamically registering WebFilter with Java EE 6 (Markus)

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• Would this be a good web application architecture?

  - by Gustav Bertram

  My problem Our MVC based framework does not allow us to cache only part of our output. Ideally we want to cahce static and semi-static bits, and run dynamic bits. In addition, we need to consider data caching that reacts to database changes. My idea The concept I came up with was to represent a page as a tree of XML fragment objects. (I say XML, but I mean XHTML). Some of the fragments are dynamic, and can pull their data directly from models or other sources, but most of the fragments are static scaffolding. If a subtree of fragments is completely static, then I imagine that they could unfold into pure XML that would then be cached as the text representation of their parent element. This process would ideally continue until we are left with a root element that contains all of the static XML, and has a couple of dynamic XML fragments that are resolved and attached to the relevant nodes of the XML tree just before the page is displayed. In addition to separating content into dynamic and static fragments, some fragments could be dynamic and cached. A simple expiry time which propagates up through the XML fragment tree would indicate that a specific fragment should periodically be refreshed. A newspaper section or front page does not need to be updated each second. Minutes or sometimes even longer is sufficient. Other fragments would be dynamic and uncached. Typically too many articles are viewed for them to be cached - the cache would overflow. Some individual articles may be cached if they are extremely popular. Functional notes The folding mechanism could be to be smart enough to judge when it would be more profitable to fold a dynamic cached fragment and propagate the expiry date to the parent fragment, or to keep it separate and simple attach to the XML tree when resolving the page. If some dynamic cached fragments are associated to database objects through mechanisms like a globally unique content id, then changes to the database could trigger changes to the output cache. If fragments store the identifiers of parent fragments, then they could trigger a refolding process that would then include the updated data. A set of pure XML with an ordered array of fragment objects (that each store the identifying information of the node to which they should be attached), can be resolved in a fairly simple way by walking the XML tree, and merging the data from the fragments. Because it is not necessary to parse and construct the entire tree in memory before attaching nodes, processing should be fairly fast. The identifiers of each fragment would be a combination of relevant identity data and the type of fragment object. Cached parent fragments would contain references to these identifiers, in order to then either pull them from the fragment cache, or to run their code. The controller's responsibility is reduced to making changes to the database, and telling the root XML fragment object to render itself. The Question My question has two parts: Is this a good design? Are there any obvious flaws I'm missing? Has somebody else thought of this before? References? Is there an existing alternative that I should consider? A cool templating engine maybe?

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• How can I set parameters in Google webmaster tools so that my dynamic content is indexed?

  - by Werewolf

  I have read questions about URL parameters in Google Webmaster Tools in this site and the Google Webmaster Help Center but I have a problem. My site searches in the database and show some information. These two URL display some data: http://mydomain.com/index.aspx?category=business http://mydomain.com/index.aspx?category=graphic&City=Paris In URL parameter section, I can only define parameter category, how Google can detect proper values (business, graphics, real estate...)? Every word is not valid for search. If My page name is default.aspx or anything else, where I should define it? If I use URL rewriting like http://mydomain.com/search/category/business, my settings must change?

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• How would you price a dynamic real estate property management website? [closed]

  - by user1217550

  Imagine, hypothetically of course, that you are being commissioned to develop a full-fledged real estate website that includes: 1) a search engine with ajax/json autofill, 2) google maps and geolocation integration, google streetview, 3) user registration, login and account management 4) administrative panels to control data input 5) search results page 6) user statistics 7) property inquiry to allow internal messaging between users How much would you charge? Suppose you are developing the most advanced and specific system in PhP/MySQL, and your total development time is roughly 1500 hours? Any suggestions?

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• How do I count Internal Logical Files (ILF) and External Inputs (EI) for a dynamic form entry page?

  - by DmytroL

  Assuming I have an applicant information entry screen, the number and types of fields on which can be defined by the system administrator, how do I go about counting the number of Internal Logical Files (ILFs) and Data Element Types (DETs) for the related data functions? So far I have come up with something like this: ILF #1 (control information): Field Metadata, 1 RET, ~3 DET (name, type, mandatory) ILF #2 (business data): Applicant Data, most likely 1 RET, but how many DET? Of course I could count it as 2 DET (Field ref, Value), but I am not sure that would be correct And when it comes to an External Input (EI), say, "Add New Applicant", things become even more complicated, because the number of DET corresponding to the user-editable fields is totally dependent on the control information in ILF #1, and I am out of ideas here... Anyone fancy to help with that? Thanks in advance!

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• How to dynamic add Google analytics track code using php?

  - by foodil2

  I would like to add track code for each link of in my email content So , i have register a google analytic accounts and found that there is only 1 track code therefore, how to use php , given a google analytics id and password given, register for a new track code add each code to a link (need to use php to add a 1px * 1 px image for each link?) Return the codes added Thank you Besides, if i have to track the result in Google analytic (traffic source -campaign) or i can use an api that can integrate the result panel in Google analytic to my system ? Thank you again for any kindly help

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• How to find optimal path visit every node with parallel workers complicated by dynamic edge costs?

  - by Aaron Anodide

  Say you have an acyclic directed graph with weighted edges and create N workers. My goal is to calculate the optimal way those workers can traverse the entire graph in parralel. However, edge costs may change along the way. Example: A -1-> B A -2-> C B -3-> C (if A has already been visited) B -5-> C (if A has not already been visited) Does what I describe lend itself to a standard algorithmic approach, or alternately can someone suggest if I'm looking at this in an inherently flawed way (i have an intuition I might be)?

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• How to build a dynamic grub on a usb-drive?

  - by 13east

  I would like to setup GRUB on a USB where it detects automatically the available OS installations on the machine that it is plugged into. This could be useful if you messed up your default GRUB menu on a computer and would like to boot into the machine w/out booting Live-OS. Or if you have multiple Live-OS installations on a USB-Drive and would like to add/remove different installations w/out needing to update grub manually. I know that Grub2 has a OS-prober feature that looks for other installations on the hard-drive, but will that work in either of the scenarios listed above?

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• To track or not to track user created images for display in a dynamic website?

  - by Question Overflow

  I have a website that allows user to upload and display images. Currently, I am not using a database to track these user images. A folder having the user id as the folder name is created for each user and under each folder, the image files are labelled numerically with filenames ranging from 01.jpg to 20.jpg. Up to 20 such images can be displayed on each user page. I am using javascript to hide these images in case of any of them is absent. I have seen many websites having user images with unique random filenames and possibly tracking these files with a database Since obscurity is not something that I need for these web accessible images, is there any reason why I should track them with a DB? I am not sure if a reduction of 404 errors is a good enough reason to justify the added complexity of maintaining a database or can anyone enlighten me?

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• Please help me debug this little C program on dynamic two-dimensional array? [migrated]

  - by azhi

  I am a newbie here. I have written a little C program, which is to create a two-dimensional matrix. Here is the code: #include <stdio.h> #include <stdlib.h> int **CreatMatrix(int m,int n){ int **Matrix; int i; Matrix=(int**)malloc(m*sizeof(int*)); for(i=0;i<m;i++){ Matrix[i]=(int*)malloc(n*sizeof(int)); } return Matrix; } int main(){ int m,n; int **A; printf("Please input the size of the Matrix: "); scanf("%d%d",&m,&n); A=CreatMatrix(m,n); printf("Please input the entries of the Matrix, which should be integers!\n"); int i,j; for(i=0;i<m;i++){ for(j=0;j<n;j++){ scanf("%d",&A[i][j]); } } printf("The Matrix that you input is:\n"); for(i=0;i<m;i++){ for(j=0;j<n;j++){ printf("%3d ",A[i][j]); } printf("\n"); } for(i=0;i<m;i++) free(A[i]); free(A); } I have run it, and it works fine. But I am not sure if it is right? Can anyone help me debug it?

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• Static vs. dynamic memory allocation - lots of constant objects, only small part of them used at runtime

  - by k29

  Here are two options: Option 1: enum QuizCategory { CATEGORY_1(new MyCollection<Question>() .add(Question.QUESTION_A) .add(Question.QUESTION_B) .add...), CATEGORY_2(new MyCollection<Question>() .add(Question.QUESTION_B) .add(Question.QUESTION_C) .add...), ... ; public MyCollection<Question> collection; private QuizCategory(MyCollection<Question> collection) { this.collection = collection; } public Question getRandom() { return collection.getRandomQuestion(); } } Option 2: enum QuizCategory2 { CATEGORY_1 { @Override protected MyCollection<Question> populateWithQuestions() { return new MyCollection<Question>() .add(Question.QUESTION_A) .add(Question.QUESTION_B) .add...; } }, CATEGORY_2 { @Override protected MyCollection<Question> populateWithQuestions() { return new MyCollection<Question>() .add(Question.QUESTION_B) .add(Question.QUESTION_C) .add...; } }; public Question getRandom() { MyCollection<Question> collection = populateWithQuestions(); return collection.getRandomQuestion(); } protected abstract MyCollection<Question> populateWithQuestions(); } There will be around 1000 categories, each containing 10 - 300 questions (100 on average). At runtime typically only 10 categories and 30 questions will be used. Each question is itself an enum constant (with its fields and methods). I'm trying to decide between those two options in the mobile application context. I haven't done any measurements since I have yet to write the questions and would like to gather more information before committing to one or another option. As far as I understand: (a) Option 1 will perform better since there will be no need to populate the collection and then garbage-collect the questions; (b) Option 1 will require extra memory: 1000 categories x 100 questions x 4 bytes for each reference = 400 Kb, which is not significant. So I'm leaning to Option 1, but just wondered if I'm correct in my assumptions and not missing something important? Perhaps someone has faced a similar dilemma? Or perhaps it doesn't actually matter that much?

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• Building Reducisaurus URLs

  - by Alix Axel

  I'm trying to use Reducisaurus Web Service to minify CSS and Javascript but I've run into a problem... Suppose I've two unminified CSS at: http:/domain.com/dynamic/styles/theme.php?color=red http:/domain.com/dynamic/styles/typography.php?font=Arial According to the docs I should call the web service like this: http:/reducisaurus.appspot.com/css?url=http:/domain.com/dynamic/styles/theme.php?color=red And if I want to minify both CSS files at once: http:/reducisaurus.appspot.com/css?url1=http:/domain.com/dynamic/styles/theme.php?color=red&url2=http:/domain.com/dynamic/styles/theme.php?color=red If I wanted to specify a different number of seconds for the cache (3600 for instance) I would use: http:/reducisaurus.appspot.com/css?url=http:/domain.com/dynamic/styles/theme.php?color=red&expire_urls=3600 And again for both CSS files at once: http:/reducisaurus.appspot.com/css?url1=http:/domain.com/dynamic/styles/theme.php?color=red&url2=http:/domain.com/dynamic/styles/theme.php?color=red&expire_urls=3600 Now my question is, how does Reducisaurus knows how to separate the URLs I want? How does it know that &expire_urls=3600 is not part of my URL? And how does it know that &url2=... is not a GET argument of url1? I'm I doing this right? Do I need to urlencode my URLs? I took a peek into the source code and although my Java is very poor it seems that the methods acquireFromRemoteUrl() and getSortedParameterNames() from the BaseServlet.java file hold the answers to my question - if a GET argument name contains - or _ they should be ignored?! What about multiple &url(n)s?

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• Python 3, urllib ... Reset Connection Possible?

  - by Rhys

  In the larger scale of my program the goal of the below code is to filter out all dynamic html in a web-page source code code snippet: try: deepreq3 = urllib.request.Request(deepurl3) deepreq3.add_header("User-Agent","etc......") deepdata3 = urllib.request.urlopen(deepurl3).read().decode("utf8", 'ignore') The following code is looped 3 times in order to identify whether the target web-page is Dynamic (source code is changed at intervals) or not. If the page IS dynamic, the above code loops another 15 times and attempts to filter out the dynamic content. QUESTION: While this filtering method works 80% of the time, some pages will reload ALL 15 times and STILL contain dynamic code. HOWEVER. If I manually close down the Python Shell and re-execute my program, the dynamic html that my 'refresh-page method' could not shake off is no longer there ... it's been replaced with new dynamic html that my 'refresh-page method' cannot shake off. So I need to know, what is going on here? How is re-running my program causing the dynamic content of a page to change. AND, is there any way, any 'reset connection' command I can use to recreate this ... without manually restarting my app. Thanks for your response.

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• PHP Warning: PHP Startup: Unable to load dynamic library php_mysql.dll, Mac 10.6, Apache 2.2, php 5

  - by munchybunch

  I'm trying to use the PHP CLI, and when I enter something like php test.php in the command line it returns: PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php/extensions/no-debug-non-zts-20090626/php_mysql.dll' - dlopen(/usr/lib/php/extensions/no-debug-non-zts-20090626/php_mysql.dll, 9): image not found in Unknown on line 0 something test.php contains: <?php echo 'something'; ?> I checked /usr/lib/php/extensions/no-debug-non-zts-20090626/, and as expected the .dll file isn't there. I'm a complete beginner when it comes to this - what is happening, and how can I fix it? A search of my system for "php_msyql.dll" reveals nothing. Does it have to do with how I compiled it? I don't have the original version of php that came with the mac, I think - I may have reinstalled it somewhere along the way. Any help would be appreciated!

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• Does kern.hz still have any relevance in FreeBSD if "dynamic tick mode" is enabled?

  - by Frerich Raabe

  I'm running a FreeBSD 9.0 setup as a virtual machine in a KVM setup. In previous versions of FreeBSD it was common to force the kern.hz setting to a lower value so that the virtual machine does not keep the host busy because it's handling timer interrupts without having any work to do - the FreeBSD Handbook explains: The most important step is to reduce the kern.hz tunable to reduce the CPU utilization of FreeBSD under the Parallels environment. This is accomplished by adding the following line to /boot/loader.conf: kern.hz=100 Without this setting, an idle FreeBSD Parallels guest OS will use roughly 15% of the CPU of a single processor iMac®. After this change the usage will be closer to a mere 5%. However, in FreeBSD 9, the "dynamic tick mode" (aka "tickless mode") is the default, controlled by the kern.eventtimer.periodic setting which defaults to 0 (read: tickless mode). This makes me wonder - does the tip of lowering kern.hz still have any relevance for making FreeBSD 9 play nicely in a virtual machine setup?

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• How to create dynamic Scatter Plot/Matrix with labels and categories on both axis in Excel 2010?

  - by user1581900

  Let us consider a following data set: Name | Age | Hair Color ----------------------------- John | Young | Brown Sophie | Old | Blond Adam | Mature| Blond Mark | Teen | Dark Jeremy | Old | Grey Alex | Young | Brown etc... Both Age and Hair Color, can take only defined values(Young/teen/mature/old and Blond/brown/Dark/Grey). Name is the only real variable here. I want to create a Scatter Plot / Matrix that will look something like that: I know that I schould use this tool to add labels to the scatter plot. I also found this youtube video that explains how to display categories on Y-axis Moreover I need the chart to be dynamic as explained in another youtube video. How do I combine all these approaches to get a Scatter Plot with categories as values on both axis?

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• Recommended Free DNS hosting for my webserve on a dynamic IP? [closed]

  - by JSchwartz

  I have finished a webserver project (for school) and the professor wants to be able to "test it" from home whenever he is free - this means I need to provide his with the URL to my webserver (which is fine). The only issue is that my IP-Address is dynamic (changes almost everyday) and I would rather not have to email him everytime - nor do I want him to try when it isn't working ... So I was looking into alternative solutions like DNS hosting (I hope that is the right terminology), so I could provide something static for him to connect to ... problem is I have never done this before... Are there any recommeneded free ones? Does Google or someone provide something good? I found http://www.no-ip.com/ which seems like it does what I want... Any feedback would be appreciated. Thanks,

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• Want to Receive dynamic length data from a message queue in IPC?

  - by user1089679

  Here I have to send and receive dynamic data using a SysV message queue. so in structure filed i have dynamic memory allocation char * because its size may be varies. so how can i receive this type of message at receiver side. Please let me know how can i send dynamic length of data with message queue. I am getting problem in this i posted my code below. send.c /*filename : send.c *To compile : gcc send.c -o send */ #include <stdio.h> #include <stdlib.h> #include <errno.h> #include <string.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> struct my_msgbuf { long mtype; char *mtext; }; int main(void) { struct my_msgbuf buf; int msqid; key_t key; static int count = 0; char temp[5]; int run = 1; if ((key = ftok("send.c", 'B')) == -1) { perror("ftok"); exit(1); } printf("send.c Key is = %d\n",key); if ((msqid = msgget(key, 0644 | IPC_CREAT)) == -1) { perror("msgget"); exit(1); } printf("Enter lines of text, ^D to quit:\n"); buf.mtype = 1; /* we don't really care in this case */ int ret = -1; while(run) { count++; buf.mtext = malloc(50); strcpy(buf.mtext,"Hi hello test message here"); snprintf(temp, sizeof (temp), "%d",count); strcat(buf.mtext,temp); int len = strlen(buf.mtext); /* ditch newline at end, if it exists */ if (buf.mtext[len-1] == '\n') buf.mtext[len-1] = '\0'; if (msgsnd(msqid, &buf, len+1, IPC_NOWAIT) == -1) /* +1 for '\0' */ perror("msgsnd"); if(count == 100) run = 0; usleep(1000000); } if (msgctl(msqid, IPC_RMID, NULL) == -1) { perror("msgctl"); exit(1); } return 0; } receive.c /* filename : receive.c * To compile : gcc receive.c -o receive */ #include <stdio.h> #include <stdlib.h> #include <errno.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> struct my_msgbuf { long mtype; char *mtext; }; int main(void) { struct my_msgbuf buf; int msqid; key_t key; if ((key = ftok("send.c", 'B')) == -1) { /* same key as send.c */ perror("ftok"); exit(1); } if ((msqid = msgget(key, 0644)) == -1) { /* connect to the queue */ perror("msgget"); exit(1); } printf("test: ready to receive messages, captain.\n"); for(;;) { /* receive never quits! */ buf.mtext = malloc(50); if (msgrcv(msqid, &buf, 50, 0, 0) == -1) { perror("msgrcv"); exit(1); } printf("test: \"%s\"\n", buf.mtext); } return 0; }

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• Adventures in MVVM &ndash; My ViewModel Base

  - by Brian Genisio's House Of Bilz

  More Adventures in MVVM First, I’d like to say: THIS IS NOT A NEW MVVM FRAMEWORK. I tend to believe that MVVM support code should be specific to the system you are building and the developers working on it.  I have yet to find an MVVM framework that does everything I want it to without doing too much.  Don’t get me wrong… there are some good frameworks out there.  I just like to pick and choose things that make sense for me.  I’d also like to add that some of these features only work in WPF.  As of Silveright 4, they don’t support binding to dynamic properties, so some of the capabilities are lost. That being said, I want to share my ViewModel base class with the world.  I have had several conversations with people about the problems I have solved using this ViewModel base.  A while back, I posted an article about some experiments with a “Rails Inspired ViewModel”.  What followed from those ideas was a ViewModel base class that I take with me and use in my projects.  It has a lot of features, all designed to reduce the friction in writing view models. I have put the code out on Codeplex under the project: ViewModelSupport. Finally, this article focuses on the ViewModel and only glosses over the View and the Model.  Without all three, you don’t have MVVM.  But this base class is for the ViewModel, so that is what I am focusing on. Features: Automatic Command Plumbing Property Change Notification Strongly Typed Property Getter/Setters Dynamic Properties Default Property values Derived Properties Automatic Method Execution Command CanExecute Change Notification Design-Time Detection What about Silverlight? Automatic Command Plumbing This feature takes the plumbing out of creating commands.  The common pattern for commands in a ViewModel is to have an Execute method as well as an optional CanExecute method.  To plumb that together, you create an ICommand Property, and set it in the constructor like so: Before public class AutomaticCommandViewModel { public AutomaticCommandViewModel() { MyCommand = new DelegateCommand(Execute_MyCommand, CanExecute_MyCommand); } public void Execute_MyCommand() { // Do something } public bool CanExecute_MyCommand() { // Are we in a state to do something? return true; } public DelegateCommand MyCommand { get; private set; } } With the base class, this plumbing is automatic and the property (MyCommand of type ICommand) is created for you.  The base class uses the convention that methods be prefixed with Execute_ and CanExecute_ in order to be plumbed into commands with the property name after the prefix.  You are left to be expressive with your behavior without the plumbing.  If you are wondering how CanExecuteChanged is raised, see the later section “Command CanExecute Change Notification”. After public class AutomaticCommandViewModel : ViewModelBase { public void Execute_MyCommand() { // Do something } public bool CanExecute_MyCommand() { // Are we in a state to do something? return true; } }   Property Change Notification One thing that always kills me when implementing ViewModels is how to make properties that notify when they change (via the INotifyPropertyChanged interface).  There have been many attempts to make this more automatic.  My base class includes one option.  There are others, but I feel like this works best for me. The common pattern (without my base class) is to create a private backing store for the variable and specify a getter that returns the private field.  The setter will set the private field and fire an event that notifies the change, only if the value has changed. Before public class PropertyHelpersViewModel : INotifyPropertyChanged { private string text; public string Text { get { return text; } set { if(text != value) { text = value; RaisePropertyChanged("Text"); } } } protected void RaisePropertyChanged(string propertyName) { var handlers = PropertyChanged; if(handlers != null) handlers(this, new PropertyChangedEventArgs(propertyName)); } public event PropertyChangedEventHandler PropertyChanged; } This way of defining properties is error-prone and tedious.  Too much plumbing.  My base class eliminates much of that plumbing with the same functionality: After public class PropertyHelpersViewModel : ViewModelBase { public string Text { get { return Get<string>("Text"); } set { Set("Text", value);} } }   Strongly Typed Property Getters/Setters It turns out that we can do better than that.  We are using a strongly typed language where the use of “Magic Strings” is often frowned upon.  Lets make the names in the getters and setters strongly typed: A refinement public class PropertyHelpersViewModel : ViewModelBase { public string Text { get { return Get(() => Text); } set { Set(() => Text, value); } } }   Dynamic Properties In C# 4.0, we have the ability to program statically OR dynamically.  This base class lets us leverage the powerful dynamic capabilities in our ecosystem. (This is how the automatic commands are implemented, BTW)  By calling Set(“Foo”, 1), you have now created a dynamic property called Foo.  It can be bound against like any static property.  The opportunities are endless.  One great way to exploit this behavior is if you have a customizable view engine with templates that bind to properties defined by the user.  The base class just needs to create the dynamic properties at runtime from information in the model, and the custom template can bind even though the static properties do not exist. All dynamic properties still benefit from the notifiable capabilities that static properties do. For any nay-sayers out there that don’t like using the dynamic features of C#, just remember this: the act of binding the View to a ViewModel is dynamic already.  Why not exploit it?  Get over it :) Just declare the property dynamically public class DynamicPropertyViewModel : ViewModelBase { public DynamicPropertyViewModel() { Set("Foo", "Bar"); } } Then reference it normally <TextBlock Text="{Binding Foo}" />   Default Property Values The Get() method also allows for default properties to be set.  Don’t set them in the constructor.  Set them in the property and keep the related code together: public string Text { get { return Get(() => Text, "This is the default value"); } set { Set(() => Text, value);} }   Derived Properties This is something I blogged about a while back in more detail.  This feature came from the chaining of property notifications when one property affects the results of another, like this: Before public class DependantPropertiesViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); RaisePropertyChanged("Percentage"); RaisePropertyChanged("Output"); } } public int Percentage { get { return (int)(100 * Score); } } public string Output { get { return "You scored " + Percentage + "%."; } } } The problem is: The setter for Score has to be responsible for notifying the world that Percentage and Output have also changed.  This, to me, is backwards.    It certainly violates the “Single Responsibility Principle.” I have been bitten in the rear more than once by problems created from code like this.  What we really want to do is invert the dependency.  Let the Percentage property declare that it changes when the Score Property changes. After public class DependantPropertiesViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); } } [DependsUpon("Score")] public int Percentage { get { return (int)(100 * Score); } } [DependsUpon("Percentage")] public string Output { get { return "You scored " + Percentage + "%."; } } }   Automatic Method Execution This one is extremely similar to the previous, but it deals with method execution as opposed to property.  When you want to execute a method triggered by property changes, let the method declare the dependency instead of the other way around. Before public class DependantMethodsViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); WhenScoreChanges(); } } public void WhenScoreChanges() { // Handle this case } } After public class DependantMethodsViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); } } [DependsUpon("Score")] public void WhenScoreChanges() { // Handle this case } }   Command CanExecute Change Notification Back to Commands.  One of the responsibilities of commands that implement ICommand – it must fire an event declaring that CanExecute() needs to be re-evaluated.  I wanted to wait until we got past a few concepts before explaining this behavior.  You can use the same mechanism here to fire off the change.  In the CanExecute_ method, declare the property that it depends upon.  When that property changes, the command will fire a CanExecuteChanged event, telling the View to re-evaluate the state of the command.  The View will make appropriate adjustments, like disabling the button. DependsUpon works on CanExecute methods as well public class CanExecuteViewModel : ViewModelBase { public void Execute_MakeLower() { Output = Input.ToLower(); } [DependsUpon("Input")] public bool CanExecute_MakeLower() { return !string.IsNullOrWhiteSpace(Input); } public string Input { get { return Get(() => Input); } set { Set(() => Input, value);} } public string Output { get { return Get(() => Output); } set { Set(() => Output, value); } } }   Design-Time Detection If you want to add design-time data to your ViewModel, the base class has a property that lets you ask if you are in the designer.  You can then set some default values that let your designer see what things might look like in runtime. Use the IsInDesignMode property public DependantPropertiesViewModel() { if(IsInDesignMode) { Score = .5; } }   What About Silverlight? Some of the features in this base class only work in WPF.  As of version 4, Silverlight does not support binding to dynamic properties.  This, in my opinion, is a HUGE limitation.  Not only does it keep you from using many of the features in this ViewModel, it also keeps you from binding to ViewModels designed in IronRuby.  Does this mean that the base class will not work in Silverlight?  No.  Many of the features outlined in this article WILL work.  All of the property abstractions are functional, as long as you refer to them statically in the View.  This, of course, means that the automatic command hook-up doesn’t work in Silverlight.  You need to plumb it to a static property in order for the Silverlight View to bind to it.  Can I has a dynamic property in SL5?     Good to go? So, that concludes the feature explanation of my ViewModel base class.  Feel free to take it, fork it, whatever.  It is hosted on CodePlex.  When I find other useful additions, I will add them to the public repository.  I use this base class every day.  It is mature, and well tested.  If, however, you find any problems with it, please let me know!  Also, feel free to suggest patches to me via the CodePlex site.  :)

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