I need your help for an issue about inheritance.
In a project of mine I am using a the SyndicationFeed .net class to read several feed a make a ul of its elements.
For every element I want to show the feed's image as well, so I wanted to assign the same ImageUrl property of the feed to the single item.
So I started by creating a derived class:
Public Class SyndicationItemWImage
Inherits SyndicationItem
Private mItemImage As Uri
Public Property ItemImage As Uri
Get
Return mItemImage
End Get
Set(value As Uri)
mItemImage = value
End Set
End Property
End Class
Then I would initialize the object and populate it
Dim BlogsPostsWImage As List(Of SyndicationItemWImage)
BlogsPostsWImage = New List(Of SyndicationItemWImage)
…
[initialize SyndFeed]
…
BlogsPostsWImage.AddRange(SyndFeed.Items.ToList.GetRange(0, 10))
Where SynFeed is a well working SyndicationFeed object.
Unfortunately I get an error that the cast is invalid:
System.InvalidCastException: Unable to cast object of type 'System.Collections.Generic.List1[System.ServiceModel.Syndication.SyndicationItem]' to type 'System.Collections.Generic.IEnumerable1[lucamauricom.SyndicationItemWImage]'. at lucamauricom._default.Page_Load(Object sender, EventArgs e)
I do not understand why: shouldn't the cast from a parent class to a child one be allowed?
I think I am missing something fundamental here… not sure what.
Thanks for any help you can provide.
Unfortunately nobody appears to be able to help me with this, so I went on attacking the problem from another angle: I now have an alternative method to accomplish the same goal. I am answering my own question here to document it.
Starting from the same SynFeed as above, I filled a temporary List and then I added an ElementExtension:
Dim TempItems As New List(Of SyndicationItem)
If SyndFeed.Items.Count >= CurrentFeed.TotalElements Then
TempItems.AddRange(SyndFeed.Items.ToList.GetRange(0, CurrentFeed.TotalElements))
Else
TempItems.AddRange(SyndFeed.Items.ToList)
End If
For Each CurrItem As SyndicationItem In TempItems
CurrItem.ElementExtensions.Add("favico", "", SingleFeed.Descendants("//bits.wikimedia.org/favicon/wikipedia.ico")
Next
FeedItems.AddRange(TempItems)
The ElementExtension is called favico, it contains no namespace and has value //bits.wikimedia.org/favicon/wikipedia.ico.
This way, I added the data as a sort of "custom field" that can be easily read on the ASPX page like this:
<img src='<%#CType(Container.DataItem, SyndicationItem).ElementExtensions.ReadElementExtensions(Of String)("favico", "").Item(0).ToString%>' height="16" />
I still cannot figure out what is wrong with the derived class of my original idea, but this second way of dealing with the issue is probably better within the context of Syndication class.
Related
So, i want to do what I feel should be such a simple task... pass in a parameter to a constructor using Autofac!
However, I have managed to get a work around working, but just dont think this is correct, I feel i am chaning too much of the recommended code from the Autofac guides
I am more than happy for answers in C# or VB.net it doesnt matter, the location of code is all the same
So, here is my setup (im not fussed about neatness, just trying to get this to work for now)
In my global.asax I have:
'***Note, the autofac guide had this a a private shared, see below for why i changed it***
' Provider that holds the application container.
Public Shared _containerProvider As IContainerProvider
' Instance property that will be used by Autofac HttpModules
' to resolve And inject dependencies.
Public ReadOnly Property ContainerProvider As IContainerProvider Implements IContainerProviderAccessor.ContainerProvider
Get
Return _containerProvider
End Get
End Property
then within my global.asax within application_start I have:
***again, note, originally I was using IMyClass when registering type... not sure this or that is correct***
Dim builder As New ContainerBuilder()
builder.RegisterType(Of MyClass)().As(Of MyClass)().InstancePerLifetimeScope()
'... continue registering dependencies...
' Once you're done registering things, set the container
' provider up with your registrations.
_containerProvider = New ContainerProvider(builder.Build())
As you can see, origianly the _containerProvider was just public, but I have had to make it "Shared" for this to work, this feels wrong right away!
so, now, in my webForm1.aspx.vb I have this:
Public Property MyClass2 As IMyClass
Private _myClass As IMyClass
Now, because I have adjusted the global to "registerType" to use the actual object, not the interface (which, again seems wrong having to change that too), means now my webform public property is not being set (but, because of my work around, i dont need that anyway)
Also, note the private _myClass... this is for my workaround
so, now in my Webform init method, i have the following:
WebForm1.aspx.vb*
_myClass = [Global]._containerProvider.RequestLifetime.Resolve(Of MyClass)(New TypedParameter(GetType(HttpRequest), Request))
which now instantiates my _myClass with the parameter correctly injected in... this is great, whoopadeedoo
...but... I dont think this is correct.
Now, when I didnt need to pass in a parameter to the construtor, it all worked nice, didnt need to change any of the code from the autofac guide, it just worked, set the public property on my webform.aspx page fine, was really nice.
But, as soon as I start to work with a paramter being passed into the construtor, it seems everything needs to be tweaked so it will work? is this correct?
I have even tried the deligate guide from autofac, but that also doesnt work for me at all by doing this within my webForm.aspx page:
Dim container As ILifetimeScope = [Global]._containerProvider.RequestLifetime
Dim myClassFactory As MyClass = container.Resolve(Of MyClass.Factory)
Dim myClassholding As MyClass = myClassFactory.Invoke("ABC")
even tried without the "Invoke", but "cannot be indexed because it has no default property"
Just incase it helps, here is "myClass"
Private _myID as integer
Public Delegate Sub Factory(myID As integer)
Sub New()
End Sub
Sub New(myID As integer)
_myID = myID
End Sub
Public Sub DoSomething() Implements IDfCookieManager.DoSomething
'do something with myID
End Sub
I know I can pass the id in as a parameter to DoSomething, but i want to understand how to pass this into the constructor
so, my questions:
If this is not how to do this (which I am hoping its not correct), how would I do this without needing to change all the global setup??
Is it best to use a deligate factory or just resolve?
do I really need to change the global container to be shared/static, so that i can access the container from within my code?
So, there are two ways, but firstly, shouldnt need to mess around with how Autofac suggests setting up the ContainerProvider in global.asax... i can keep it as non shared (not static), and to access this value I do the following:
Dim cpa As IContainerProviderAccessor = (CType(HttpContext.Current.ApplicationInstance, IContainerProviderAccessor))
Dim scope As ILifetimeScope = cpa.ContainerProvider.RequestLifetime
Also, in our webform.aspx page, Public Property MyClass As IMyClass should not be added when we need to pass in parameters to the constructor when resolving (otherwise it will be resolved before we try to manually resolve it!
1: Passing in using TypedParameter
Here is my adjusted code to pass in the parameters using resolve (including the lines above):
Dim cpa As IContainerProviderAccessor = (CType(HttpContext.Current.ApplicationInstance, IContainerProviderAccessor))
Dim scope As ILifetimeScope = cpa.ContainerProvider.RequestLifetime
Dim myClass As MyClass = scope.Resolve(Of IMyClass)(New TypedParameter(GetType(Integer), 123))
Also, having the public property at the top of my WebForm1.aspx needed to be removed, because that will auto resolve, meaning, if i try to "resolve" the object manually, it has already been automatically resolved by autofac (which is why i thought my code wasnt working initially), and has already instantiated the object with the empty constructor!
2: Using a Deligate Factory
the line Public Delegate Sub Factory(myID As integer) isnt correct, it should use a function for Autofac to automaticly set this up! so should be: Public Delegate Function Factory(myID As integer) as MyClass
In Global.asax, I just need to add this builder.RegisterType(Of MyClass)().InstancePerLifetimeScope(), because we require a parameter and using a factory, we cant append the .As(Of IMyClass)
Finally, our webform1.aspx.vb just needs this:
Dim cpa As IContainerProviderAccessor = (CType(HttpContext.Current.ApplicationInstance, IContainerProviderAccessor))
Dim scope As ILifetimeScope = cpa.ContainerProvider.RequestLifetime
Dim myClassFactory As MyClass.Factory = scope.Resolve(Of MyClass.Factory)
_myClass = myClassFactory.Invoke(123)
however, I tweaked that slightly to this:
Dim cpa As IContainerProviderAccessor = (CType(HttpContext.Current.ApplicationInstance, IContainerProviderAccessor))
Dim scope As ILifetimeScope = cpa.ContainerProvider.RequestLifetime
Dim myClass As MyClass = scope.Resolve(Of MyClass.Factory).Invoke(123)
I have been building various web based programs and things for a while, but am quite new to .NET and doing things "properly." As I am completely self taught, with help from sites like this and so on, my understanding of fundamentals is limited.
So, I have a series of functions which return data that I want depending on parameters put in, this is very basic stuff, and obviously all works. However, I am trying to make it easier to call these functions by using Classes.
So, say I have a function which returns a populated DropDownList converted to an HTML string
Function GetList(ListRequired as String) as String
' Do stuff to return a dropdownlist whos contend is determined by `ListRequired`, converted to an HTML string
End Function
In this example, it works fine, but to use it I must know what to enter for "ListRequired" to get what I want.
So, let's say, the options for the ListRequired para are "mastercategory", "brandlist", "priceranges" to return a different set of lists - each option would send the code off the retrieve information from a database and return accordingly.
Suppose I want a third party developer to be able to call this function with the most basic amount of "instruction" required, and not even have to tell him the list of available ListRequired by making it available as a Class.
Public Class DropDownLists
Public Property MasterCategory
Public Property BrandList
Sub New()
Me.MasterCategory = HTMLControls.RenderSearchFilters("mastercategory")
Me.BrandList = HTMLControls.RenderSearchFilters("brandList")
End Sub
End Class
A developer can then call this from Visual Studio/VWD etc very simply:
Dim dd As New DropDownLists
Dim list1Html as String = dd.MasterCategory
Dim list2Html as String = dd.BrandList
Because VWD etc creates all the handy helpers and displays which properties the Class exposes, it is very easy to use this code without have to constantly refer to a manual.
However... when creating a new instance of the Class:
Dim dd As New DropDownLists
This will cause the server to process all the functions within the class which create the Properties, which would be desperately inefficient if there are lots of properties.
So I have tried using my own interpretation of the logic and written this:
Public Class DropDownLists
Shared Property Master
Shared Property Brand
Sub New()
End Sub
Public Class MasterCategory
Sub New()
DropDownLists.Master = HTMLControls.RenderSearchFilters("mastercategory")
End Sub
End Class
Public Class BrandList
Sub New()
DropDownLists.Brand = HTMLControls.RenderSearchFilters("brandList")
End Sub
End Class
End Class
Hoping I'd be able to create the HTML for a Master Category drop down like:
Dim dd as New DropDownLists.MasterCategory
But that doesn't work, and upon reflection I think I can see why... it's not returning the string, but creating a new type.
So... my question is...
What is the correct way to achieve what I am looking for, which is, to be able to create these string outputs by typing
Dim dd As New DropDownLists
Dim list1Html as String = dd.MasterCategory
Dim list2Html as String = dd.BrandList
Without having to pass potentially unknown string parameters, or causing ALL properties to be created each time the DropDownLists Class is created, ie, only run the code for the output I need.
I'm expanding my comment to give you a clearer idea of what I meant:
Public Class DropDownLists
Enum ListType
Undefined
MasterCategory
Brandlist
End Enum
Public Shared Function GetList(ListRequired As ListType) As String
Select Case ListRequired
Case ListType.Brandlist
Return . . .
Case ListType.MasterCategory
Return . . .
Case ListType.Undefined
Throw New . . . .
End Select
End Function
End Class
I am trying to rename a button from a string. Sounds simple enough? Well I have scowered the internet and tried many things however I keep coming up with the same errors.
I have 2 forms and one class file. I am using object orientation to pass a string from a textbox to form1 where upon the "button1.Text" can be change passing it through my "Reference class" (I don't think it can be done any other way)
private void button1_Click_1(object sender, EventArgs e)
{
Refclass Ref = new Refclass();
String but1 = Ref.but1;
String btn = "button1"; this.Controls[btn].Text = but1;
}
I am sure this is probably wrong but I hope by this might be able to understand what I am trying to do. I am calling a string from the "Ref" class and calling the string "hell"
Needless to say I am either getting a debugging error and totally crashing visual studio or I get an error saying "Object reference not set to an instance of an object."
I know I am going wrong somewhere does anyone know where? Thank you.
there is no need of create the object for class.if your class in same assembly.just call like this.
button1.text=ref.but1;
where but1 is a const string in that class.
I have two classes in two separate libraries (one VB, one C#):
Public Class Item
...
Public Overridable ReadOnly Property TotalPrice() As String
Get
Return FormatCurrency(Price + SelectedOptionsTotal())
End Get
End Property
End Class
and
public class DerivedItem : Item {
...
public new Decimal TotalPrice
{
get { return Price + OptionsPrice; }
}
}
As you can see, the DerivedItem.TotalPrice shadows the Item.TotalPrice property. However, when trying to retrieve the DerivedItem.TotalPrice value, I'm still getting the base object's TotalPrice value.
Why is the DerivedItem's property not being returned?
EDIT
I've actually found the problem! I am getting the wrong value in the JSON string being returned via AJAX. It turns out that the TotalPrice is being returned correctly, it's just being overwritten by the shadowed property call being made later in the JSON string. My new question, then, is how to I prevent the shadowed property from being serialized?
(This question has been rescoped here)
It may depend on how you are instantiating the object.
For example:
DerivedItem i = new DerivedItem();
i.TotalPrice();
Will call the shadowed version.
However:
Item i = new DerivedItem();
i.TotalPrice();
Will actually call the base.
Here's a nice explanation.
Of course if at all possible I would avoid shadowing.... :-)
Are you referecing TotalPrice from a reference to the base type?
Item item = new DerivedItem;
string s = item.TotalPrice;
Does setting <NonSerialized()> attribute on the base class property work?
am trying to implement fluent nhibernate in MVC project...there were no build errors... but when i run the project i get this exception
System.Xml.Schema.XmlSchemaValidationException: The element 'class' in namespace 'urn:nhibernate-mapping-2.2' has incomplete content. List of possible elements expected: 'meta, subselect, cache, synchronize, comment, tuplizer, id, composite-id' in namespace 'urn:nhibernate-mapping-2.2'.
have no idea what am doing wrong here... the following is the code for opening session factory...
Private Function CreateSessionFactory() As ISessionFactory
Dim sessionFactoryObject As ISessionFactory
sessionFactoryObject = Fluently.Configure().Database(FluentNHibernate.Cfg.Db.MsSqlConfiguration.MsSql2005.ConnectionString("Data Source=.\sqlexpress;Initial Catalog=Designs;User ID=sa;Password=root")).Mappings(Function(x) x.FluentMappings.Add(GetType(DesignMap))).BuildSessionFactory()
Return sessionFactoryObject
End Function
this is really driving me nuts....thanks in advance...:)
update-the mappings
the design table map
Public Class DesignMap
Inherits ClassMap(Of Design)
Public Sub DesignMap()
Table("DesignList")
Id(Function(x) x.DesignId)
Map(Function(x) x.DesignType)
References(Function(x) x.Designer, "DesignerId")
End Sub
End Class
the designer table map
Public Class DesignerMap
Inherits ClassMap(Of Designer)
Public Sub DesignerMap()
Table("DesignerList")
Id(Function(x) x.DesignerId)
Map(Function(x) x.DesignerName)
Map(Function(x) x.DesignerCompany)
HasMany(Function(x) x.DesignersDesigns)
End Sub
End Class
new edit-- the entity property looks like this
Public Overridable Property Name() As String
Get
Return _name
End Get
Protected Set(ByVal value As String)
_name = value
End Set
End Property
am i going the right way..?
I'm not quite sure as the mappings seem ok. I can see one error tough, you have only mapped one of your classes:
.Mappings(Function(x) x.FluentMappings.Add(GetType(DesignMap)))
That should not cause this type of error tough. If you add both your mappings and call the method .ExportTo(#"C:\your\export\path") you will get the actual xml mappings. This way it's easier to see the error. You can do that like this:
.Mappings(Function(x) x.FluentMappings.Add(GetType(DesignMap)).Add(GetType(DesignerMap
).ExportTo(#"C:\your\export\path"))
You can also use the method AddFromAssemblyOf (or some other. There is a few choices) if you don't want to add the mappings one by one.
Try exporting the mappings and see if you can find any error. Or you can post the xml mappings and someone else might find something.
There are several things that can cause this. When using automappings, you will get this if you incorrectly specify the assemblies and namespaces to look in. Other things (more likely in your case) that could cause it, are entity properties that aren't marked as public virtual, having an entity constructor with arguments, but neglecting to make a default constructor, or inheriting your entities from a base class.
I would probably first check to make sure all of your entity properties are "public virtual".
found the problem...the constructor for the map was wrong...it should be like this...
Public Class DesignMap
Inherits ClassMap(Of Design)
Public Sub New()
Table("DesignList")
Id(Function(x) x.DesignId)
Map(Function(x) x.DesignType)
References(Function(x) x.Designer, "DesignerId")
End Sub
End Class
problems of working in both C# and vb.net at the same time i guess..!!
and "Matthew Talbert" was correct...making all the properties Overrideable is important..
thanks guys...:)