IEnumerable<XElement>.Value() Extension Method Available In .Net But Not C#?
Jun 5, 2012
In VB.Net you can easily get the text value of the first child element of an XElement like so:Dim sChildValue = xeParent.<MyChild>.Value()Of course that syntax is not supported in C#, but it produces the same IEnumerable(Of XElement) result as the Elements() method. So we can rewrite the above like so:
Dim sChildValue = xeParent.Elements("MyChild").Value()This Value() extension method is handy because often you are working with small XML documents and you just want the first node that matches. (One thing that annoys me about this method is that it seems to return Nothing/null if the IEnumerable list is empty due to the specified element not being found. To work around this I have created my own ValueOrBlank() method that returns an empty string in that situation instead.)
My problem is that I can't do the same thing in C#:var sChildValue = xeParent.Elements("MyChild").Value(); // won't compile, can't find Value() method
I checked my references/imports and they match the VB.Net project where the same call works. Fortunately I am able to use my custom ValueOrBlank() extension method to accomplish the same thing. But I'm curious as to what's missing in my C# project. I tried right-clicking on the Value() method call in Visual Studio and clicking "Go To Definition" to see if the Object Browser could tell me where the extension method is kept, but it just shows the System.String class. Does that mean this is one of those sneaky VB.Net-only features that the compiler itself supports, like the XML Axis < MyChild > syntax?
why the next example throws a System.ArrayTypeMismatchException?New Int16(){4,5,6}.Cast(of UInt16).ToArray()I expected that this line returned a UInt16 array containing 4,5 and 6.
Why would I use an extension method instead of just creating non-extension sub or function?
For ex, I could have an extension function called IsNullOrEmptyOrAllSpaces on String, which does a check as its name implies. Or I can write a stand alone function that does the same thing. Other than having the extension show up in Intellisense, is there any advantage? Is a call to the extension quicker/more efficient than a call to a regular function?
I saw this post and I want to know if this is possible in VB. So like extension method, do extension properties exists in VB.Net? Here I've read they do, but cannot find any examples.
I'm working with a class that inherits the XElement class.The new class is called MXElement.It adds some new functionality to it for navigating through the XML tree, as well as some more information regarding attributes, but that's not particularly important.My problem is that I have an XML Tree filled with XElement objects.However, when I create a new MXElement object from the XElement object before, it is just a copy of that object. This means that any changes that I make to this object will not effect the original tree.I suppose what I'm asking for is a way to build in the functionality for my MXElement class and keep references to the original XElement objects.If possible, I would really prefer to keep MXElement a child class instead of building a lot of extension methods for XElement.
I am using XElement to manipulate my xml file: to find target node and then add child node to it. But now I have one problem. Let's say my xml file looks like this:
The second <ReportItem> is the newly-added one, but sadly this is not a valid file (my parser is complaining in the further processing of xml file). So how can I make this new item look exactly like the existing one, without any namespace? This has been driving me crazy. I spent a whole day to figure out that I need to add the curly brackets so that it will find the target node (it doesn't work like what the link above says that it adds and searches the default NS automatically), but now it adds something unnecessary?
Extension methods are useful for types that you don't own and can't/don't want to derive from and extend (e.g. reference types and interfaces). Obviously, interfaces should be kept as short and to-the-point as possible, so extension methods for interfaces are particularly useful (e.g. LINQ).For classes, especially classes that you own, they're still useful - but I'm wondering how you determine what should be an extension method or what should be a method in the class itself.Personally, every time I think about it, I keep going round in circles with the following thoughts:If it's useful enough, it should be in the class.It's not part of the core responsibility of the class, it should be an extension method - but if it's useful enough, surely it should be the responsibility of the class...
I'm binding a DataGridView to a BindingSource to a LINQ IEnumerable, I found that the BindingSource.Find method throws an exception because .Find isn't implemented in IEnumerable (and the BindingSource just passes the call to it's DataSource). I need to use BindingSource.Find to select/highlight a particular row in the DataGridView.
Is there a feasable way to extend my DataContext to support this behavior w/o breaking anything else? I expected to find the code out there already, but I've searched exaustively with no luck.Without it, I cannot "move" the BindingSource using .Position and that's a pretty common use of the BindingSource I think.
I'm trying figure out if this is possible. Basically, I need to create an XElement and then add one or more siblings to that XElement, but without a parent. I'll add that list of XElements to a Parent later, but need some flexibility in building this and other lists of XElements before doing so. Is this possible?
So I would have something like:
Public items As XElement = <ItemA>Something</ItemA>
And then I need to add an element so that the result looks like:
I'm building XML based on some data pulled from a database, and thought to try building the XML with LINQ2XML. The data is coming from a few different places, so I've been building the XML by sections, based on what I have populated in DataTable objects. Using the XElements and XAttributes, I can get one or the other, but I was wondering if anyone had insight in how to make the determination of whether to use XElement or XAttribute at the point where the XML is being built.[code]So it's in that LINQ query that I need to determine if ValueToParse, for example, has a valid value (non-empty). If it does, then I can add the node and it's value. If it DOES NOT, I need to add that named node, but with an attribute of 'xsi:nil="true"',The caveats are that that there are some descendants which repeat over different parents (for example, there's an AddressDetails section which contains AddressDetail elements. These AddressDetail elements can contain 0 or 1 Contacts groups of Contact elements, so adding a node to the Contacts node isn't a straightforward option as it would be if there was only ONE Contacts element).I don't usually USE LINQ, but it SEEMED like a good idea at the time XD
I have an object called Result<T> that has a constructor which accepts an argument of IEnumerable<T>. I'd like to be able to pass in a datatable if possible.
I tried datatable.AsEnumerable(), but where I bind to the data it was complaining that 'MyProperty' is not a field or property on type 'DataRow' - which makes sense since 'MyProperty' isn't a property on 'DataRow', but it was a column in my datatable.Is there a way to convert a datatable to something that I can pass into the Result object and still have it bind to, say, a gridview?
I tried using the linq Zip method on IEnumerable but it does not work for more than 2 arrays.Here is an example in Python of what I am trying to do(I got p - nested IEnumerable - and need q - another nested IEnumerable):
I know how to add extension method Like (Date.Now.MyExtensionFunction()),But I can NOT find how to add such methods and functions in class (not in module) with vb.net
I ran into a strange issue over the weekend while I was working on an asp.net mvc project in vb.net. I created an extension method to convert an integer to the corresponding month it is associated with. I tested the extension method in a console application so I know it is working.
In my asp.net mvc project I have a view and want to call the extension method but I get an error that the extension method is not recognized. I imported the namespace it was contained in and still couldn't shake the error.
I created a module to add some Extension Methods to a Class. This Class inherits from another parent Class. In the code of my Extension Methods, I would like to refer to the base Class using MyBase. This doesn't seems to be allowed (Error message : "'MyBase' is not valid within a Module.")
I am starting to play with extension methods and i came across with this problem:In the next scenario i get a: "extension method has a type constraint that can never be satisfied"
Public Interface IKeyedObject(Of TKey As IEquatable(Of TKey)) ReadOnly Property InstanceKey() As TKey End Interface
I'm trying to create an extension method that returns an IEqualityComparer based on a lambda function. Heres the extension method:
<Extension()> Public Function Comparer(Of T)(Func As Func(Of T, T, Boolean)) As IEqualityComparer(Of T) Return New GenericComparer(Of T)(Func) End Function
Public Enum Direction Left Right Top Bottom End Enum
And Sometimes I need to get the inverse, so it seems nice to write:
SomeDirection.Inverse()
But I can't put a method on an enum! However, I can add an Extension Method (VS2008+) to it.
In VB, Extension Methods must be inside Modules. I really don't like modules that much, and I'm trying to write a (moderately) simple class that I can share in a single file to be plugged into other projects.
Modules can only reside in the file/namespace level so I have one in the bottom of the file now:
Public Class MyClass '...' End Class
[Code]....
It works, and "if it ain't broke, don't fix it", but I'd love to know if I'm doing it wrong and there's a better way with less boilerplate. Maybe in .NET 4?
Finally, I know I could write a structure that behaves like an enum, but that seems even more backwards.
I've created a MyFunc extension (in Module Extensions) for all the base types as well as generic arrays, ICollection(Of T) and Dictionary(Of String,T):
Function MyFunc(Of T)(a() As T) As String Function MyFunc(Of T)(collection As ICollection(Of T)) As String Function MyFunc(Of T)(dict As Dictionary(Of String,T)) As String
Can I access values in application settings of web.config in extension method?I have the below code but it is not working:
<Extension()> _ Public Function DocCountExt(ByVal value As Collection) As Integer Dim maxOffSet As Integer = Integer.Parse(ConfigurationManager.AppSettings(APP_SETTINGS_OFFSET)) return maxOffSet End Function
i want to extend the integer class to a method that increments current integer value by 2. I create a console application and a second module which contains the extension method.
and everything works fine. The extension method module can be imported to any other project (Project-->add existing item --> select the vb file that contains the extension method module) and works fine too. But the code is accessible to other users. Is there a method to convert the extension method module to a dll and adding it to other projects as a reference. I tried to do it with creating a class project and pasting the code of the extension method module and compile the dll and then added it as reference to another project and imported the class with the keyword imports, but it didn't work.
I wanna create extension method for IEnumerable(Of FileSystemInfo). However, compiler says "'Sort' is not a member of'System.Collections. Generic. IEnumerable(Of System.IO.FileSystemInfo)". What is strange is that IntelliSense shows this method. Where's error? [code]
In our .aspx pages, we've got lots of this code:<%= CType(GetLocalResourceObject("key"), String)) %>I'd like to add an extension method that I can use in our .aspx views that allows me to do this:<%= GetLocalResourceString("key") %>The code isn't working, though:Imports System.Runtime.CompilerServices
