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  • C#/.NET Little Wonders: Fun With Enum Methods

    - by James Michael Hare
    Once again lets dive into the Little Wonders of .NET, those small things in the .NET languages and BCL classes that make development easier by increasing readability, maintainability, and/or performance. So probably every one of us has used an enumerated type at one time or another in a C# program.  The enumerated types we create are a great way to represent that a value can be one of a set of discrete values (or a combination of those values in the case of bit flags). But the power of enum types go far beyond simple assignment and comparison, there are many methods in the Enum class (that all enum types “inherit” from) that can give you even more power when dealing with them. IsDefined() – check if a given value exists in the enum Are you reading a value for an enum from a data source, but are unsure if it is actually a valid value or not?  Casting won’t tell you this, and Parse() isn’t guaranteed to balk either if you give it an int or a combination of flags.  So what can we do? Let’s assume we have a small enum like this for result codes we want to return back from our business logic layer: 1: public enum ResultCode 2: { 3: Success, 4: Warning, 5: Error 6: } In this enum, Success will be zero (unless given another value explicitly), Warning will be one, and Error will be two. So what happens if we have code like this where perhaps we’re getting the result code from another data source (could be database, could be web service, etc)? 1: public ResultCode PerformAction() 2: { 3: // set up and call some method that returns an int. 4: int result = ResultCodeFromDataSource(); 5:  6: // this will suceed even if result is < 0 or > 2. 7: return (ResultCode) result; 8: } So what happens if result is –1 or 4?  Well, the cast does not fail, so what we end up with would be an instance of a ResultCode that would have a value that’s outside of the bounds of the enum constants we defined. This means if you had a block of code like: 1: switch (result) 2: { 3: case ResultType.Success: 4: // do success stuff 5: break; 6:  7: case ResultType.Warning: 8: // do warning stuff 9: break; 10:  11: case ResultType.Error: 12: // do error stuff 13: break; 14: } That you would hit none of these blocks (which is a good argument for always having a default in a switch by the way). So what can you do?  Well, there is a handy static method called IsDefined() on the Enum class which will tell you if an enum value is defined.  1: public ResultCode PerformAction() 2: { 3: int result = ResultCodeFromDataSource(); 4:  5: if (!Enum.IsDefined(typeof(ResultCode), result)) 6: { 7: throw new InvalidOperationException("Enum out of range."); 8: } 9:  10: return (ResultCode) result; 11: } In fact, this is often recommended after you Parse() or cast a value to an enum as there are ways for values to get past these methods that may not be defined. If you don’t like the syntax of passing in the type of the enum, you could clean it up a bit by creating an extension method instead that would allow you to call IsDefined() off any isntance of the enum: 1: public static class EnumExtensions 2: { 3: // helper method that tells you if an enum value is defined for it's enumeration 4: public static bool IsDefined(this Enum value) 5: { 6: return Enum.IsDefined(value.GetType(), value); 7: } 8: }   HasFlag() – an easier way to see if a bit (or bits) are set Most of us who came from the land of C programming have had to deal extensively with bit flags many times in our lives.  As such, using bit flags may be almost second nature (for a quick refresher on bit flags in enum types see one of my old posts here). However, in higher-level languages like C#, the need to manipulate individual bit flags is somewhat diminished, and the code to check for bit flag enum values may be obvious to an advanced developer but cryptic to a novice developer. For example, let’s say you have an enum for a messaging platform that contains bit flags: 1: // usually, we pluralize flags enum type names 2: [Flags] 3: public enum MessagingOptions 4: { 5: None = 0, 6: Buffered = 0x01, 7: Persistent = 0x02, 8: Durable = 0x04, 9: Broadcast = 0x08 10: } We can combine these bit flags using the bitwise OR operator (the ‘|’ pipe character): 1: // combine bit flags using 2: var myMessenger = new Messenger(MessagingOptions.Buffered | MessagingOptions.Broadcast); Now, if we wanted to check the flags, we’d have to test then using the bit-wise AND operator (the ‘&’ character): 1: if ((options & MessagingOptions.Buffered) == MessagingOptions.Buffered) 2: { 3: // do code to set up buffering... 4: // ... 5: } While the ‘|’ for combining flags is easy enough to read for advanced developers, the ‘&’ test tends to be easy for novice developers to get wrong.  First of all you have to AND the flag combination with the value, and then typically you should test against the flag combination itself (and not just for a non-zero)!  This is because the flag combination you are testing with may combine multiple bits, in which case if only one bit is set, the result will be non-zero but not necessarily all desired bits! Thanks goodness in .NET 4.0 they gave us the HasFlag() method.  This method can be called from an enum instance to test to see if a flag is set, and best of all you can avoid writing the bit wise logic yourself.  Not to mention it will be more readable to a novice developer as well: 1: if (options.HasFlag(MessagingOptions.Buffered)) 2: { 3: // do code to set up buffering... 4: // ... 5: } It is much more concise and unambiguous, thus increasing your maintainability and readability. It would be nice to have a corresponding SetFlag() method, but unfortunately generic types don’t allow you to specialize on Enum, which makes it a bit more difficult.  It can be done but you have to do some conversions to numeric and then back to the enum which makes it less of a payoff than having the HasFlag() method.  But if you want to create it for symmetry, it would look something like this: 1: public static T SetFlag<T>(this Enum value, T flags) 2: { 3: if (!value.GetType().IsEquivalentTo(typeof(T))) 4: { 5: throw new ArgumentException("Enum value and flags types don't match."); 6: } 7:  8: // yes this is ugly, but unfortunately we need to use an intermediate boxing cast 9: return (T)Enum.ToObject(typeof (T), Convert.ToUInt64(value) | Convert.ToUInt64(flags)); 10: } Note that since the enum types are value types, we need to assign the result to something (much like string.Trim()).  Also, you could chain several SetFlag() operations together or create one that takes a variable arg list if desired. Parse() and ToString() – transitioning from string to enum and back Sometimes, you may want to be able to parse an enum from a string or convert it to a string - Enum has methods built in to let you do this.  Now, many may already know this, but may not appreciate how much power are in these two methods. For example, if you want to parse a string as an enum, it’s easy and works just like you’d expect from the numeric types: 1: string optionsString = "Persistent"; 2:  3: // can use Enum.Parse, which throws if finds something it doesn't like... 4: var result = (MessagingOptions)Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result == MessagingOptions.Persistent) 7: { 8: Console.WriteLine("It worked!"); 9: } Note that Enum.Parse() will throw if it finds a value it doesn’t like.  But the values it likes are fairly flexible!  You can pass in a single value, or a comma separated list of values for flags and it will parse them all and set all bits: 1: // for string values, can have one, or comma separated. 2: string optionsString = "Persistent, Buffered"; 3:  4: var result = (MessagingOptions)Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 7: { 8: Console.WriteLine("It worked!"); 9: } Or you can parse in a string containing a number that represents a single value or combination of values to set: 1: // 3 is the combination of Buffered (0x01) and Persistent (0x02) 2: var optionsString = "3"; 3:  4: var result = (MessagingOptions) Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 7: { 8: Console.WriteLine("It worked again!"); 9: } And, if you really aren’t sure if the parse will work, and don’t want to handle an exception, you can use TryParse() instead: 1: string optionsString = "Persistent, Buffered"; 2: MessagingOptions result; 3:  4: // try parse returns true if successful, and takes an out parm for the result 5: if (Enum.TryParse(optionsString, out result)) 6: { 7: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 8: { 9: Console.WriteLine("It worked!"); 10: } 11: } So we covered parsing a string to an enum, what about reversing that and converting an enum to a string?  The ToString() method is the obvious and most basic choice for most of us, but did you know you can pass a format string for enum types that dictate how they are written as a string?: 1: MessagingOptions value = MessagingOptions.Buffered | MessagingOptions.Persistent; 2:  3: // general format, which is the default, 4: Console.WriteLine("Default : " + value); 5: Console.WriteLine("G (default): " + value.ToString("G")); 6:  7: // Flags format, even if type does not have Flags attribute. 8: Console.WriteLine("F (flags) : " + value.ToString("F")); 9:  10: // integer format, value as number. 11: Console.WriteLine("D (num) : " + value.ToString("D")); 12:  13: // hex format, value as hex 14: Console.WriteLine("X (hex) : " + value.ToString("X")); Which displays: 1: Default : Buffered, Persistent 2: G (default): Buffered, Persistent 3: F (flags) : Buffered, Persistent 4: D (num) : 3 5: X (hex) : 00000003 Now, you may not really see a difference here between G and F because I used a [Flags] enum, the difference is that the “F” option treats the enum as if it were flags even if the [Flags] attribute is not present.  Let’s take a non-flags enum like the ResultCode used earlier: 1: // yes, we can do this even if it is not [Flags] enum. 2: ResultCode value = ResultCode.Warning | ResultCode.Error; And if we run that through the same formats again we get: 1: Default : 3 2: G (default): 3 3: F (flags) : Warning, Error 4: D (num) : 3 5: X (hex) : 00000003 Notice that since we had multiple values combined, but it was not a [Flags] marked enum, the G and default format gave us a number instead of a value name.  This is because the value was not a valid single-value constant of the enum.  However, using the F flags format string, it broke out the value into its component flags even though it wasn’t marked [Flags]. So, if you want to get an enum to display appropriately for whether or not it has the [Flags] attribute, use G which is the default.  If you always want it to attempt to break down the flags, use F.  For numeric output, obviously D or  X are the best choice depending on whether you want decimal or hex. Summary Hopefully, you learned a couple of new tricks with using the Enum class today!  I’ll add more little wonders as I think of them and thanks for all the invaluable input!   Technorati Tags: C#,.NET,Little Wonders,Enum,BlackRabbitCoder

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  • Html.hiddenfor does not return value

    - by jackma1210
    Hi I have a template partial view, which used to render a model named VerificationCode, this model has a element 'CaptchaGeneratedText' which is hidden in the view and set value by Html.HiddenFor(m=m.CaptchaGeneratedText, captchaText), the problem is when view post, in the model validation the value of element 'CaptchaGeneratedText' is null, but it should not be as varant 'captchaText' has some value. meanwhile, the other element 'CaptchaUserInput' of this model does have value. Anybody have experienced similiar problem? Sorry I was unable to submit script file.

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  • Read a variable in bash with a default value

    - by rmarimon
    I need to read a value from the terminal in a bash script. I would like to be able to provide a default value that the user can change. # Please enter your name: Ricardo^ In this script the prompt is "Please enter your name: " the default value is "Ricardo" and the cursor would be after the default value. Is there a way to do this in a bash script?

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  • C# - Getting a RawFraction Performance Counter to show a persistant value

    - by jacko
    I've created a performance counter that shows a fraction of an incremeted value (RawFraction type) over a base value (RawBase). Unfortunately, when monitoring this value, it only shows the percentage when one of the counters is incremented. At all other times it it is sampled, it shows 0. Is there some way to tell the counter to hold onto the last value until the next time it needs to recalculate the fraction?

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  • Extracting value in Beautifulsoup

    - by Seth
    I have the following code: f = open(path, 'r') html = f.read() # no parameters => reads to eof and returns string soup = BeautifulSoup(html) schoolname = soup.findAll(attrs={'id':'ctl00_ContentPlaceHolder1_SchoolProfileUserControl_SchoolHeaderLabel'}) print schoolname which gives: [<span id="ctl00_ContentPlaceHolder1_SchoolProfileUserControl_SchoolHeaderLabel">A B Paterson College, Arundel, QLD</span>] when I try and access the value (i.e. 'A B Paterson College, Arundel, QLD) by using schoolname['value'] I get the following error: print schoolname['value'] TypeError: list indices must be integers, not str What am I doing wrong to get that value?

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  • how to clear the gmdatepicker value in the textbox

    - by Ranjana
    how to clear the gmdatepicker value in the textbox i have a Datepicker where i pass the value while inserting into the table as frmdate.Date it will store my date which im selecting in the datepicker but how to clear this selected value in the textbox once the value is inserted???????

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  • Test for absence of an input tag's value attribute

    - by Jeff
    How can I confirm the absence of a HTML attribute in a Rails RSpec test? I can verify that an input tag has a value attribute and that it is an empty string like so: response.should have_tag("input[name=?][value=?]", "user[password]", "") response.should have_tag("input[name=?][value=?]", "user[password_confirmation]", "") But what I want to do is verify that my input fields do not have a value attribute at all (i.e., a blank field).

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  • Parametrizing max value of a jQuery ui slider

    - by Gandalf StormCrow
    I'm trying to create this slider http://jqueryui.com/demos/slider/#rangemax Is it possible to parametrize the max value? For ex: $("#slider-range-max").slider({ range: "max", min: 1, max: maxValue, value: 2, slide: function(event, ui) { $("#amount").val(ui.value); } }); Is it possible to pass maxValue value, when I click on something? After its been initialized? Not on document ready function, but even after that?

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  • function parameter used to store value

    - by user248247
    Hi, I have to define an interface. The API in my homework is stated below: int generate_codes(char * ssn, char * student_id); int denotes 0 or 1 for pass or fail. studentid is an output param should return a 6 digit id. ssn is a 9 digit input param they school program will take ssn's and use my code to generate the student id. now from an API perspective should I not be using const char * for both parameters. should the studentid not be passed in by reference? rather than by pointer? can someone tell me how i can easily use the pointer in my test app which uses my api to get the pointer such that it prints a std::string from a char *? my app code looks something like const char * ssn = "987098765" const char * studnt_id = new char [7]; int value = -1; value = generate_codes(ssn,studnt_id); std::string test(studnt_id); std::cout<<"student id= "<<test<<" Pass/fail= "<<value<<std::endl; delete [] studnt_id; return 0; I basically got an error about << not being compatible with the right hand side of the operand. When i changed the code to std::cout<<"student id= "<<test.c_str()<<" Pass/fail= "<<value<<std::endl; then it worked but i get garbage for the value. not sure how to do get the value form the pointer. THe value inside the function prints just fine. but when i try to print it outside of the function it prints garbage. Inside the above function I do set the studndt_id like so std::string str_studnt_id = studnt_id; should that make the address of the str_studnt point to the address of studnt_id and thus any changes I make to the value that its pointing to it should reflect outside the function?

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  • COGNOS 8 Bi value prompt

    - by Rahul Kadam
    Currently I have a value prompt added to my report (with UI selected as List-Box) and the date item used is name 'YEAR'. Now when I run the report the values in the value prompt are seen as below: YEAR 2004 2005 2006 What I want to do is get rid of the year tag that is present in the output of the value prompt box, more clearly the output in the value prompt box should be as below: 2004 2005 2006 Can someone let me know how that can be achieved?

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  • Get Value from thick box control

    - by Muhammad Akhtar
    I have hidden field on thick box, when I close thick I need to get the value of my hidden field, when close thick box this method calls function tb_remove(parent_func_callback) { parent.document.getElementById('hdf').value// I need value of hidden field here please tell me how can I get hidden field value that is on thick box? Thanks

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  • NSTableViewCell uses value from other cells

    - by Michael Z
    Hi Guys: I have problem with using dequeueReusableCellWithIdentifier method. Whenever I use this one, one cell would display its own value and value that does not belong to it. This first and second images show the problem, while the third image shows the proper data.The problem seems to be caused by old value not being wiped off and the new value being added on top if it. Which seems very strange.

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  • Detecting that a MemberExpression has a value

    - by cs
    How do I detect if a MemberExpression has a value that needs to be compiled/evaluated? I have two separate member expression outputs, the first which has a value, and the second which doesn't. What is the best way to differentiate between the two? exp **{value(Microsoft.Connect.Api.Client.Tests.SearchQueryUnitTests+<>c__DisplayClass6).handle}** [System.Linq.Expressions.MemberExpression]: **{value(Microsoft.Connect.Api.Client.Tests.SearchQueryUnitTests+<>c__DisplayClass6).handle}** NodeType: MemberAccess Type: {Name = "String" FullName = "System.String"} vs exp {x.CreatedBy} [System.Linq.Expressions.MemberExpression]: {x.CreatedBy} NodeType: MemberAccess Type: {Name = "String" FullName = "System.String"}

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  • Parameterizing max value of a jQuery ui slider

    - by Gandalf StormCrow
    I'm trying to create this slider http://jqueryui.com/demos/slider/#rangemax Is it possible to parametrize the max value? For ex: $("#slider-range-max").slider({ range: "max", min: 1, max: maxValue, value: 2, slide: function(event, ui) { $("#amount").val(ui.value); } }); Is it possible to pass maxValue value, when I click on something? After its been initialized? Not on document ready function, but even after that?

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  • How to exclude hidden row vaue from total value SSRS

    - by Annmarie
    I have an SSRS project and I want to exclude a row that I have hidden from the total. I have hidden the row based on an expression on the row visibility, where the row is hidden if: =IIF(IIF(ReportItems!CUST_CNT2.Value = 0, 0, ReportItems!Total_Contribution5.Value / IIF(ReportItems!CUST_CNT2.Value = 0, 1, ReportItems!CUST_CNT2.Value)) > 0, True, False) So basically the column totals for the report just total up all rows including this above row that I have hidden, and I need the total to exclude this row. Any ideas?

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  • Validationattribute only when value is changed?

    - by boris callens
    I want to write a custom ValidationAttribute that checks if the given value is unique or not. The problem is that in the edit screen, it is not guaranteed that the user actually changed the value, resulting in a false error. Is there a way to check in my attribute whether the value actually changed? Or can I trigger the attribute only when the value has changed? I'm getting the feeling this requirement maybe just doesn't belong in an attribute?

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  • regular expression for challenge value

    - by Salman
    Hi what will be the regular expression to extract challenge var value i am interested in this vlaue 03AHJ_Vut9LJLOJuCsjF9PbSSMncTyUe7Y4dHX11eRLae3LGfDZ0hSfDR7jZq2ZrKJxyC-LRSSppv72oHKaQMsd-EnoVNL6p7liTh7siN26zzTA_E2rcC_JQ15613Azz4qm8HjPtAyksUdc7QZydszwolk92hBPrAAig this value changes every time we refresh it so the expression has to be generic enough to pick up what ever is the value var RecaptchaState = { site : '6LeKCL8SAAAAADV5Dr-lfY2eOEV8rubeN25BAKp2', challenge : '03AHJ_Vut9LJLOJuCsjF9PbSSMncTyUe7Y4dHX11eRLae3LGfDZ0hSfDR7jZq2ZrKJxyC-LRSSppv72oHKaQMsd-EnoVNL6p7liTh7siN26zzTA_E2rcC_JQ15613Azz4qm8HjPtAyksUdc7QZydszwolk92hBPrAAig', is_incorrect : false, programming_error : '', error_message : '', server : 'http://www.google.com/recaptcha/api/', timeout : 18000}; any help will be appreciated, or any method to extract this value in any server side lang

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  • Listview...how to conditionally replace a value with a string

    - by GaryAmundson
    Hi, my app presents a listview, from a database cursor and XML, that needs to replace the values in a column with various words based on the integer value contained in the cursor. For example, if the value is -1, replace it with the word "Invalid", but if the value is = 0 then just display the value. I was under the impression this could magically be done via XML... TIA.

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  • Set value of textarea in jquery

    - by GONeale
    I am attempting to set a value in a textarea field using jquery with the following code: $("textarea#ExampleMessage").attr("value", result.exampleMessage); The issue is, once this code executes, it is not altering the text in the textarea? However when performing an alert($("textarea#ExampleMessage").attr("value")) the newly set value is returned?

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  • One value display two columns in data grid

    - by Nair
    I have a XML with 3 values, they are 'name', 'department', 'value'. I want to display a data grid with four columns like Name, department, credit and debit. When I have a value positive in 'value' column I want to enter the value in debit column and 0 in credit column and vice versa.

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