Search Results

Search found 26810 results on 1073 pages for 'fixed point'.

Page 650/1073 | < Previous Page | 646 647 648 649 650 651 652 653 654 655 656 657  | Next Page >

  • webbrowser control on form2 vb windows application

    - by user228058
    Hi, I have a vb windows application with 2 forms, where form2 is called from form1 using form2.showdialog() I added a web browser control to form2, and I'm getting the following error at the point where form2 is called: Current thread must be set to single thread apartment (STA) mode before OLE calls can be made. Ensure that your Main function has STAThreadAttribute marked on it. I tried: 1) adding STAThread() to the form_load() 2) I added a module to my application, and created a sub main(), with the STAThread attribute applied to it 3) I marked the sub startup() with STAThread() And none of this helped. Any tips on how to get around this issue? Thanks, rcpg

    Read the article

  • Looking for calculator source code, BSD-licensed

    - by Horace Ho
    I have an urgent project which need many functions of a calculator (plus a few in-house business rule formulas). As I won't have time to re-invent the wheel so I am looking for source code directly. Requirements: BSD licensed (GPL won't help) in c/c++ programming language 32-bit CPU minimum dependency on platform API/data structure best with both RPN and prefix notation supported emulator/simulator code also acceptable (if not impossible to add custom formula) with following functions (from wikipedia) Scientific notation for calculating large numbers floating point arithmetic logarithmic functions, using both base 10 and base e trigonometry functions (some including hyperbolic trigonometry) exponents and roots beyond the square root quick access to constants such as pi and e plus hexadecimal, binary, and octal calculations, including basic Boolean math fractions optional statistics and probability calculations complex numbers programmability equation solving

    Read the article

  • Intercept UITableView scroll touches

    - by Jonesy
    Is it possible to control when the UITableView scrolls in my own code. I am trying to get behaviour where a vertical swipe scrolls and a horizontal swipe gets passed through to my code (of which there are many example) BUT I want a DIAGONAL swipe to do nothing, i.e the UITableView should not even begin scrolling. I tried catching it in here - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView but the scrollView.contentOffset.x is always 0 so I cannot detect a horizontal movement. I also tried subclassing UITableView and implementing - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event - (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event etc.. but the UITableView (and I guess it's parent UIScrollView) start to scroll before the touches are notified? To re-iterate, I want the UITableView scrolling to be locked if a diagonal swipe is made, but to scroll vertically normally. (This behaviour can be seen in Tweetie(Twitter) for the iPhone) Thanks for any help!

    Read the article

  • Performance of std::pow - cache misses???

    - by Eamon Nerbonne
    I've been trying to optimize a numeric program of mine, and have run into something of a mystery. I'm looping over code that performs thousands of floating point operations, and just 1 call to pow nevertheless, that call takes 5% of the time... That's not necessarily a critical issue, but it is odd, so I'd like to understand what's happening. When I profiled for cache misses, VS.NET 2010RC's profiler reports that virtually all cache misses are occurring in std::pow... so... what's up with that? Is there a faster alternative? I tried powf, but that's only slightly faster; it's still responsible for an abnormal number of cache misses. Why would a basic function like pow cause cache-misses?

    Read the article

  • After minimizing app, on restore, windows pursues mouse pointer

    - by Nuno Silva
    Hi! I have an application in WPF C# where other than the purpose of what it's done, I customized the close and minimize buttons. The problem is that when I minimize, all is good, I cycle around all other apps, but, when I want to go back to the application, I click in the window in the taskbar, and the window pops up... But when it pops up, the window pursues the mouse pointer throughout the screen... The code i've implemented the the simplest it can be... private void Minimize_LeftMouseDown(object sender, MouseButtonEventArgs e) { this.WindowState = WindowState.Minimized; } Can you point me some directions? Thanks

    Read the article

  • F# currying efficiency?

    - by Eamon Nerbonne
    I have a function that looks as follows: let isInSet setElems normalize p = normalize p |> (Set.ofList setElems).Contains This function can be used to quickly check whether an element is semantically part of some set; for example, to check if a file path belongs to an html file: let getLowerExtension p = (Path.GetExtension p).ToLowerInvariant() let isHtmlPath = isInSet [".htm"; ".html"; ".xhtml"] getLowerExtension However, when I use a function such as the above, performance is poor since evaluation of the function body as written in "isInSet" seems to be delayed until all parameters are known - in particular, invariant bits such as (Set.ofList setElems).Contains are reevaluated each execution of isHtmlPath. How can best I maintain F#'s succint, readable nature while still getting the more efficient behavior in which the set construction is preevaluated. The above is just an example; I'm looking for a general pattern that avoids bogging me down in implementation details - where possible I'd like to avoid being distracted by details such as the implementation's execution order since that's usually not important to me and kind of undermines a major selling point of functional programming.

    Read the article

  • CSS margin collapsing?

    - by Seth P
    I'm working with Google Chrome on OS X, and I seem to be running into a margin collapse issue. I have two divs stacked on top of each other, both with a margin-top of 2px and a margin-bottom of 5px, and both with a 1px border. According to my arithmetic, there should be 1+1+2+5=7px of space between the "content" areas of the divs, since the border prevents the margins from collapsing? More confusing is that, in a location where I have a div with a 3px border and a 0 margin-top underneath one of the previously described divs, I end up with 9px of space (as I so dearly desire). The only difference between the divs is the additional class that shrinks the border and redefines the margins, so both divs have the same padding (only padding-bottom is 0). Can anyone point out where I've gone wrong?

    Read the article

  • Visual studio 2003 web projects.

    - by swapna
    Hi, I have a requirement to work on a VS2003 web project. I have VS2008,vs2010,vs2003 installed in my system Other System details are Windows Xp professional version 2 service pack 3. IIS 5.1 When i am trying to create a VS 2003 web project giving the localhost as path i am getting the following error. "visual studio noted that specified web server is not running under asp .net 1.1 version.You will be unable to run asp .net web applications or services". I have used aspnet_regiis commands as well as a tool(ASPNETVersionSwitcher.exe ) to swith versions and in iis also default web site asp.net version chosen as asp .net 1.14322. Still i am getting the error. same error i get ,if i point a virtual directory in the existing 1.1 .net web application and trying to open it. Please advise since i have to work on this project as soon as possible. Thanks SNA

    Read the article

  • What is in scala-android.jar?

    - by synic
    I've been trying to experiment with developing Android applications with Scala. I've gotten to the point where I can get the app to compile, but there are no helper functions for things like: button.setOnClickListener( () => { text.setText("test") }) (I'm talking about the closure there) I see lots of references to scala-android.jar, and have this file in my project, but I'm not sure what it does, or how to use it. I get the feeling it has these helper conversion functions, but I'm not sure. Running jar -tvf scala-android.jar on the file gives me this: 401 Sun Jun 06 10:06:02 MDT 2010 scala/Function0$class.class 431 Sun Jun 06 10:06:02 MDT 2010 scala/Function0.class 572 Sun Jun 06 10:06:02 MDT 2010 scala/Function1.class 282 Sun Jun 06 10:06:02 MDT 2010 scala/ScalaObject$class.class 271 Sun Jun 06 10:06:02 MDT 2010 scala/ScalaObject.class 458 Sun Jun 06 10:06:02 MDT 2010 scala/runtime/BoxedUnit.class If this isn't what I'm looking for, is there a simple library that'll do conversions for this kind of stuff?

    Read the article

  • java.lang.NoSuchMethodError: main when starting HelloWorld with Eclipse Scala plugin

    - by Matt Sheppard
    I've just been playing with Scala, and installed the Eclipse plugin as described at http://www.scala-lang.org/node/94, but after entering the "Hello World" test example and setting up the run configuration as described, I get the following error Exception in thread "main" java.lang.NoSuchMethodError: main For reference the code is package hello object HelloWorld extends Application { println("Hello World!") } I've tinkered a bit with the obvious solutions (adding a main method, adding a singleton object with a main method) but I'm clearly doing something wrong. Can anyone get their test example to work, or point out what I am doing wrong?

    Read the article

  • Java Audit table logging, MySQL equivalent of CONTEXT_INFO.

    - by Julia
    Hi, I am looking for the MySQL equivalent of CONTEXT_INFO that is present in SQL Server. Or any other session variable like thing using which I can pass the username to the trigger. I am currently working on logging table data for audit. I need to pass the username of the logged in user to the delete trigger. Any ideas? We are deleting the rows from the table in a few cases and marking them as deleted in others. Any alternate solutions are welcome. I thought of using AOP but it could prove problematic when deleting a cascade. I want to look into Hibernate Interceptors, not sure at this point if that works. If I can find the MySQL equivalent of CONTEXT_INFO, my job is done and elegant as well. Thanks, Julia.

    Read the article

  • WPF tabcontrol styling

    - by BrettRobi
    I've got a UI with a fairly standard look and feel. It has a column of icons on the left side which when clicked open a different user control on the right side. Currently I'm using separate controls for the selection icons and the usercontrol containment. I'm having strange focus issues that I am tired of trying to mitigate and am wondering if I could style a tabcontrol to look like my UI (under the assumption a tabcontrol would not have focus issues when navigating tabs). Here is a screenshot of the basic UI. The styling is mostly about how to get the tabcontrols page selection to look like my column of icons. Anyone want to throw their hat in the ring as to how I might accomplish this with a tabcontrol? My xaml is pretty weak at this point.

    Read the article

  • Modifying Bresenham's line algorithm

    - by sphennings
    I'm trying to use Bresenham's line algorithm to compute Field of View on a grid. The code I'm using calculates the lines without a problem but I'm having problems getting it to always return the line running from start point to endpoint. What do I need to do so that all lines returned run from (x0,y0) to (x1,y1) def bresenham_line(self, x0, y0, x1, y1): steep = abs(y1 - y0) > abs(x1 - x0) if steep: x0, y0 = y0, x0 x1, y1 = y1, x1 if x0 > x1: x0, x1 = x1, x0 y0, y1 = y1, y0 if y0 < y1: ystep = 1 else: ystep = -1 deltax = x1 - x0 deltay = abs(y1 - y0) error = -deltax / 2 y = y0 line = [] for x in range(x0, x1 + 1): if steep: line.append((y,x)) else: line.append((x,y)) error = error + deltay if error > 0: y = y + ystep error = error - deltax return line

    Read the article

  • StreamReader.ReadToEnd() returning an empty string

    - by axk
    I have a method private static String DecompressAndDecode(byte[] data) { GZipStream decompressor = new GZipStream(new MemoryStream(data), CompressionMode.Decompress); StreamReader decompressed = new StreamReader(decompressor, Encoding.UTF8); String result = decompressed.ReadToEnd(); return result; } I have some GZipped text as input and the result is supposed to be a String representation of this text. The problem is that the method returns an empty string. What is puzzling me is that when I step trough the method in debug mode and reach the return statement the result variable is an empty string but if I create a watch for the decompressed.ReadToEnd() expression it returns me the text. What I would expect at this point is the result variable to contain the text and the decompressed.ReadToEnd() expression evaluating to an empty string. (Reevaluating the decompressed.ReadToEnd() expression returns an empty string as expected). There must be something obvious I'm missing here.

    Read the article

  • MS SQL Bridge Table Constraints

    - by greg
    Greetings - I have a table of Articles and a table of Categories. An Article can be used in many Categories, so I have created a table of ArticleCategories like this: BridgeID int (PK) ArticleID int CategoryID int Now, I want to create constraints/relationships such that the ArticleID-CategoryID combinations are unique AND that the IDs must exist in the respective primary key tables (Articles and Categories). I have tried using both VS2008 Server Explorer and Enterprise Manager (SQL-2005) to create the FK relationships, but the results always prevent Duplicate ArticleIDs in the bridge table, even though the CategoryID is different. I am pretty sure I am doing something obviously wrong, but I appear to have a mental block at this point. Can anyone tell me please how should this be done? Greaty appreciated!

    Read the article

  • jquery dataTables plugin: dynamically modify ajaxSource

    - by Anthony Koval'
    hello! on my page i have dataTable, which was initialized with, for example, sAjaxSource url like "/api/reports". when we're doing sorting, filtering it appends to url additional query-keys. I want do add keys "date_from" and "date_to" to sAjaxSource url (date intervals could be changed after table initialization). is there any entry-point function, before table reload, so i can do there smth like: var oSettings = rtbl.fnSettings(); oSettings.sAjaxSource = "/api/reports/?type=sites&date_from=" + $("#date_from").text() + "&date_to=" + $("#date_to").text(); thanks for your help!

    Read the article

  • Workflow Foundation: How to create Receive activity with custom message in xaml designer?

    - by Petr Felzmann
    I need to have Receive activity which can receive my custom data. I found examples, but all use coded workflows like such public class ProcessRequest : Activity { public ProcessRequest() { Variable request = new Variable { Name = "request" }; Receive receiveRequest = new Receive { ServiceContractName = "IProcessRequest", OperationName = "Foo", CanCreateInstance = true, Content = ReceiveContent.Create(new OutArgument(request)) }; } } The main point is that Receive.Content property. It is not clear for me how I can do it in XAML designer. What I have to set in the dialog of the Content property - Message or Parameters and what to set inside those options? Thanks for the light!

    Read the article

  • Symfony user authentication using Active Directory

    - by Radu Dragomir
    Is there a way to authenticate users in symfony apps using Active Directory? Can you please point out some documentation? edit What i need is to have a transparent login in my application. The user authenticates once at windows logon, then all applications should be accessed with the same credentials without being asked for the domain\username and password again. I tried the following in a simple php script: if (!isset($_SERVER['PHP_AUTH_USER'])) { header('WWW-Authenticate: Basic realm="my realm"'); header('HTTP/1.0 401 Unauthorized'); exit; } else { echo "<p>Hello {$_SERVER['PHP_AUTH_USER']}.</p>"; echo "<p>You entered {$_SERVER['PHP_AUTH_PW']} as your password.</p>"; } but then i get the authentication form popped up. Is there any way to pass the header the credentials used at windows logon? Thanks, Radu.

    Read the article

  • CLR via C# 3rd Edition is out

    - by Abhijeet Patel
    Time for some book news update. CLR via C#, 3rd Edition seems to have been out for a little while now. The book was released in early Feb this year, and needless to say my copy is on it’s way. I can barely wait to dig in and chew on the goodies that one of the best technical authors and software professionals I respect has in store. The 2nd edition of the book was an absolute treat and this edition promises to be no less. Here is a brief description of what’s new and updated from the 2nd edition. Part I – CLR Basics Chapter 1-The CLR’s Execution Model Added about discussion about C#’s /optimize and /debug switches and how they relate to each other. Chapter 2-Building, Packaging, Deploying, and Administering Applications and Types Improved discussion about Win32 manifest information and version resource information. Chapter 3-Shared Assemblies and Strongly Named Assemblies Added discussion of TypeForwardedToAttribute and TypeForwardedFromAttribute. Part II – Designing Types Chapter 4-Type Fundamentals No new topics. Chapter 5-Primitive, Reference, and Value Types Enhanced discussion of checked and unchecked code and added discussion of new BigInteger type. Also added discussion of C# 4.0’s dynamic primitive type. Chapter 6-Type and Member Basics No new topics. Chapter 7-Constants and Fields No new topics. Chapter 8-Methods Added discussion of extension methods and partial methods. Chapter 9-Parameters Added discussion of optional/named parameters and implicitly-typed local variables. Chapter 10-Properties Added discussion of automatically-implemented properties, properties and the Visual Studio debugger, object and collection initializers, anonymous types, the System.Tuple type and the ExpandoObject type. Chapter 11-Events Added discussion of events and thread-safety as well as showing a cool extension method to simplify the raising of an event. Chapter 12-Generics Added discussion of delegate and interface generic type argument variance. Chapter 13-Interfaces No new topics. Part III – Essential Types Chapter 14-Chars, Strings, and Working with Text No new topics. Chapter 15-Enums Added coverage of new Enum and Type methods to access enumerated type instances. Chapter 16-Arrays Added new section on initializing array elements. Chapter 17-Delegates Added discussion of using generic delegates to avoid defining new delegate types. Also added discussion of lambda expressions. Chapter 18-Attributes No new topics. Chapter 19-Nullable Value Types Added discussion on performance. Part IV – CLR Facilities Chapter 20-Exception Handling and State Management This chapter has been completely rewritten. It is now about exception handling and state management. It includes discussions of code contracts and constrained execution regions (CERs). It also includes a new section on trade-offs between writing productive code and reliable code. Chapter 21-Automatic Memory Management Added discussion of C#’s fixed state and how it works to pin objects in the heap. Rewrote the code for weak delegates so you can use them with any class that exposes an event (the class doesn’t have to support weak delegates itself). Added discussion on the new ConditionalWeakTable class, GC Collection modes, Full GC notifications, garbage collection modes and latency modes. I also include a new sample showing how your application can receive notifications whenever Generation 0 or 2 collections occur. Chapter 22-CLR Hosting and AppDomains Added discussion of side-by-side support allowing multiple CLRs to be loaded in a single process. Added section on the performance of using MarshalByRefObject-derived types. Substantially rewrote the section on cross-AppDomain communication. Added section on AppDomain Monitoring and first chance exception notifications. Updated the section on the AppDomainManager class. Chapter 23-Assembly Loading and Reflection Added section on how to deploy a single file with dependent assemblies embedded inside it. Added section comparing reflection invoke vs bind/invoke vs bind/create delegate/invoke vs C#’s dynamic type. Chapter 24-Runtime Serialization This is a whole new chapter that was not in the 2nd Edition. Part V – Threading Chapter 25-Threading Basics Whole new chapter motivating why Windows supports threads, thread overhead, CPU trends, NUMA Architectures, the relationship between CLR threads and Windows threads, the Thread class, reasons to use threads, thread scheduling and priorities, foreground thread vs background threads. Chapter 26-Performing Compute-Bound Asynchronous Operations Whole new chapter explaining the CLR’s thread pool. This chapter covers all the new .NET 4.0 constructs including cooperative cancelation, Tasks, the aralle class, parallel language integrated query, timers, how the thread pool manages its threads, cache lines and false sharing. Chapter 27-Performing I/O-Bound Asynchronous Operations Whole new chapter explaining how Windows performs synchronous and asynchronous I/O operations. Then, I go into the CLR’s Asynchronous Programming Model, my AsyncEnumerator class, the APM and exceptions, Applications and their threading models, implementing a service asynchronously, the APM and Compute-bound operations, APM considerations, I/O request priorities, converting the APM to a Task, the event-based Asynchronous Pattern, programming model soup. Chapter 28-Primitive Thread Synchronization Constructs Whole new chapter discusses class libraries and thread safety, primitive user-mode, kernel-mode constructs, and data alignment. Chapter 29-Hybrid Thread Synchronization Constructs Whole new chapter discussion various hybrid constructs such as ManualResetEventSlim, SemaphoreSlim, CountdownEvent, Barrier, ReaderWriterLock(Slim), OneManyResourceLock, Monitor, 3 ways to solve the double-check locking technique, .NET 4.0’s Lazy and LazyInitializer classes, the condition variable pattern, .NET 4.0’s concurrent collection classes, the ReaderWriterGate and SyncGate classes.

    Read the article

  • msysgit bash shell- how to troubleshoot "cannot find command"

    - by Frank Schwieterman
    I need help getting git extensions to run with msysgit. I have had bad luck with extensions git-tfs and git-fetchall, in both cases it is the same problem. The addon will require a file to be placed where git can find it (git-tfs.exe and git-fetchall.sh). I understand this to mean the files need to be in a directory that is in the 'PATH' environment variable. In both cases I get stuck at this point: $ git-diffall bash: git-diffall: command not found or: $ git-tfs bash: git-tfs: command not found When I run echo %PATH% from a regular command shell, it shows my path variable includes the directories where git-diffall and git-tfs are. How can I debug this, or am I missing something? Is there a way within msysgit to verify the command search path is what I expect?

    Read the article

  • Are there some general Network programming best practices?

    - by uriDium
    I am implementing some networking stuff in our project. It has been decided that the communication is very important and we want to do it synchronously. So the client sends something the server acknowledges. Are there some general best practices for the interaction between the client and the server. For instance if there isn't an answer from the server should the client automatically retry? Should there be a timeout period before it retries? What happens if the acknowledgement fails? At what point do we break the connection and reconnect? Is there some material? I have done searches but nothing is really coming up. I am looking for best practices in general. I am implementing this in c# (probably with sockets) so if there is anything .Net specific then please let me know too.

    Read the article

  • How is GroupOn website programmed?

    - by Maxi Garcia
    Hello world! This is my first time on Stackoverflow.com and it's great to be here! I need some expert programmer out there to tell me how the GroupOn's platform operates, from the programming point of view. Which are the most complex features it has and what technology do they use? If I were about to start learning programming languages, what should I learn to create a site like GroupOn.com? Is there any website where I can learn the basic principles for free? I appreciate your advices. Thanks in advance!

    Read the article

  • Getting "Object is read only" error when setting ClientCredentials in WCF

    - by Paul Mrozowski
    I have a proxy object generated by Visual Studio (client side) named ServerClient. I am attempting to set ClientCredentials.UserName.UserName/Password before opening up a new connection using this code: InstanceContext context = new InstanceContext(this); m_client = new ServerClient(context); m_client.ClientCredentials.UserName.UserName = "Sample"; As soon as the code hits the UserName line it fails with an "Object is read-only" error. I know this can happen if the connection is already open or faulted, but at this point I haven't called context.Open() yet. I have configured the Bindings (which uses netTcpBinding) to use Message as it's security mode, and MessageClientCredentialType is set to UserName. Any ideas?

    Read the article

  • Liskov Substitution Principle and the Oft Forgot Third Wheel

    - by Stacy Vicknair
    Liskov Substitution Principle (LSP) is a principle of object oriented programming that many might be familiar with from the SOLID principles mnemonic from Uncle Bob Martin. The principle highlights the relationship between a type and its subtypes, and, according to Wikipedia, is defined by Barbara Liskov and Jeanette Wing as the following principle:   Let be a property provable about objects of type . Then should be provable for objects of type where is a subtype of .   Rectangles gonna rectangulate The iconic example of this principle is illustrated with the relationship between a rectangle and a square. Let’s say we have a class named Rectangle that had a property to set width and a property to set its height. 1: Public Class Rectangle 2: Overridable Property Width As Integer 3: Overridable Property Height As Integer 4: End Class   We all at some point here that inheritance mocks an “IS A” relationship, and by gosh we all know square IS A rectangle. So let’s make a square class that inherits from rectangle. However, squares do maintain the same length on every side, so let’s override and add that behavior. 1: Public Class Square 2: Inherits Rectangle 3:  4: Private _sideLength As Integer 5:  6: Public Overrides Property Width As Integer 7: Get 8: Return _sideLength 9: End Get 10: Set(value As Integer) 11: _sideLength = value 12: End Set 13: End Property 14:  15: Public Overrides Property Height As Integer 16: Get 17: Return _sideLength 18: End Get 19: Set(value As Integer) 20: _sideLength = value 21: End Set 22: End Property 23: End Class   Now, say we had the following test: 1: Public Sub SetHeight_DoesNotAffectWidth(rectangle As Rectangle) 2: 'arrange 3: Dim expectedWidth = 4 4: rectangle.Width = 4 5:  6: 'act 7: rectangle.Height = 7 8:  9: 'assert 10: Assert.AreEqual(expectedWidth, rectangle.Width) 11: End Sub   If we pass in a rectangle, this test passes just fine. What if we pass in a square?   This is where we see the violation of Liskov’s Principle! A square might "IS A” to a rectangle, but we have differing expectations on how a rectangle should function than how a square should! Great expectations Here’s where we pat ourselves on the back and take a victory lap around the office and tell everyone about how we understand LSP like a boss. And all is good… until we start trying to apply it to our work. If I can’t even change functionality on a simple setter without breaking the expectations on a parent class, what can I do with subtyping? Did Liskov just tell me to never touch subtyping again? The short answer: NO, SHE DIDN’T. When I first learned LSP, and from those I’ve talked with as well, I overlooked a very important but not appropriately stressed quality of the principle: our expectations. Our inclination is to want a logical catch-all, where we can easily apply this principle and wipe our hands, drop the mic and exit stage left. That’s not the case because in every different programming scenario, our expectations of the parent class or type will be different. We have to set reasonable expectations on the behaviors that we expect out of the parent, then make sure that those expectations are met by the child. Any expectations not explicitly expected of the parent aren’t expected of the child either, and don’t register as a violation of LSP that prevents implementation. You can see the flexibility mentioned in the Wikipedia article itself: A typical example that violates LSP is a Square class that derives from a Rectangle class, assuming getter and setter methods exist for both width and height. The Square class always assumes that the width is equal with the height. If a Square object is used in a context where a Rectangle is expected, unexpected behavior may occur because the dimensions of a Square cannot (or rather should not) be modified independently. This problem cannot be easily fixed: if we can modify the setter methods in the Square class so that they preserve the Square invariant (i.e., keep the dimensions equal), then these methods will weaken (violate) the postconditions for the Rectangle setters, which state that dimensions can be modified independently. Violations of LSP, like this one, may or may not be a problem in practice, depending on the postconditions or invariants that are actually expected by the code that uses classes violating LSP. Mutability is a key issue here. If Square and Rectangle had only getter methods (i.e., they were immutable objects), then no violation of LSP could occur. What this means is that the above situation with a rectangle and a square can be acceptable if we do not have the expectation for width to leave height unaffected, or vice-versa, in our application. Conclusion – the oft forgot third wheel Liskov Substitution Principle is meant to act as a guidance and warn us against unexpected behaviors. Objects can be stateful and as a result we can end up with unexpected situations if we don’t code carefully. Specifically when subclassing, make sure that the subclass meets the expectations held to its parent. Don’t let LSP think you cannot deviate from the behaviors of the parent, but understand that LSP is meant to highlight the importance of not only the parent and the child class, but also of the expectations WE set for the parent class and the necessity of meeting those expectations in order to help prevent sticky situations.   Code examples, in both VB and C# Technorati Tags: LSV,Liskov Substitution Principle,Uncle Bob,Robert Martin,Barbara Liskov,Liskov

    Read the article

  • TypeConverter for serialization

    - by Cat
    Is it normal practice to use a TypeConverter for serialization? There is a class that I do not own that has a "lossy" TypeConverter. When converting to a string, it formats its floating point data with "G4", so that when this type is displayed in a PropertyGrid, it's easily readable. I would like to also use this TypeConverter to convert from a string, creating an instance of this class. Right now I am checking the CultureInfo passed to TypeConverter.ConvertTo and only using the pretty, lossy conversion if the CultureInfo is not InvariantCulture. I'd like to know if I'm going about this the wrong way.

    Read the article

< Previous Page | 646 647 648 649 650 651 652 653 654 655 656 657  | Next Page >