I have some Ajax on a web page that feeds some data to a server-side VB.Net method. Once that data is in the server-side method, I need to call another server-side method to use the data I just collected. Here is a really simplified example:
' This method gets the input from the Ajax code on the web page.
<System.Web.Services.WebMethod> _
Public Shared Sub GetAwesome(VBInputText As String)
Dim strTest As String = VBInputText
' Now that we have collected input from the user,
' we need to run a method that does a ton of other stuff.
DisplayAwesome(VBInputText)
End Sub
Protected Sub DisplayAwesome(AwesomeIn As String)
' The real app does a lot more than this. For this example, it
' just sets the text of a literal.
litAwesomeResult.Text = AwesomeIn
End Sub
Of course, in the above example DisplayAwesome(VBInputText) gives me the 'Cannot refer to an instance member...' error. So, is it possible now to call Protected Sub DisplayAwesome from Public Shared Sub GetAwesome? I'm hoping to stay close to this sort of solution because it would play very well with the app as it is already written by another coworker.
unfortunately you cannot do this, Since the page method DisplayAwesome is defined as Protected and you requires an instance of the class to access the Protected method. But changes in another instance will not reflect in the current UI. another thing you can do is Make DisplayAwesome as Shared, but this time you cannot access the UI elements inside the shared function.
The thing you can do in this situation is, return data to the called method(in front end) and handle the litAwesomeResult.Text there
Call sub with name of Form Class like this:
FormName.DisplayAwesome(VBInputText)
In VB.Net, you can call the method not shared from a shared method with Name of Form Class by default instance, because The default instance is an object Form type that the VB application framework create and manage it, when the form is added to the project.
For more info see this :
VB.NET Default Form Instances
Related
I have been banging my head against a wall all day and am starting to think this isnt possible so you guys are my last hope!
I have a user control which is used to create messages and then allows the message to be emailed or sent via SMS depending on what aspx page the user control is on. I have a fair amount of logic in the user control and was find I was doing alot of this:
If type="email" Then
'Logic for email
Exit Sub
End If
If type="sms" Then
'Logic for sms
Exit Sub
End If
And alot of the logic was similar so there was alot of duplication. I ended up abstracting out the similar logic for email and SMS into an Interface:
Public Interface IContactMessager(Of T)
Sub Delete(ref As String)
Function GetAll() As List(Of T)
Function GetByRef(ref As String) As T
Function MessageExists(ref As String) As Boolean
ReadOnly Property RefField() As String
Sub Save(ref As String, message As String)
Sub SendMessage(contact As String, message As String)
Sub Update(ref As String, message As String)
End Interface
I now have a sms and email manager classes that inherit from this interface. This should allow me to do something similar to the below in the user control
Dim handler As IContactMessager(Of Email)=if(type="sms",SMSHandler,EmailHandler)
Then instead of ifs I can just do handler.logic and it will run the correct logic.
Now heres my issue, and its due to the interface being generic. Ideally id like to do the following:
Public ReadOnly Property ContactMessagerHandler() As IContactMessager(Of T)
Get
Return If(MessageType.ToLower() = "email", New EmailContactMessager(), New SMSContactMessager())
End Get
End Property
However I cant have the (Of T) because obviously it has no idea what type to make this. I need to somehow dynamically set this type but I have run out of ideas.
A few things i have toyed with:
Trying to see if I can pass an the object from the calling aspx page
Making the interface a basepage instead then making the calling aspx page inherit from the base page and then trying to get the type from the usercontrols parent, but to no success
Attempting to make methods to set the type of the interface based on text passed through from the calling aspx page
None of these work. Does anyone else have any other ideas? Hopefully this makes sense, if not let me know if I can improve the question somehow
Given the following simple Web API (not part of an MVC project, just an empty ASP.NET site) which I've taken from a tutorial:
Public Class AwesomeController
Inherits ApiController
Public Function [Get]() As String
Return "Hello. The time is " & DateTime.Now.ToString
End Function
Public Function Post(<FromBody> yourName As String) As String
Return String.Format("Hi {0}, you posted here at {1}", yourName, DateTime.Now.ToString)
End Function
End Class
I am creating the Route within global.asax like this:
Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
GlobalConfiguration.Configuration.Routes.Add("default", New HttpRoute("{controller}"))
End Sub
This works fine, but I've read that WebAPI Routing should preferably be created using MapHttpRoute so that the service can exist in isolation. Is this true?
If so, can anyone post the code to replace my global.asax version?
Update
I figured out the last bit, but would still appreciate knowing whether there is a 'correct' way?
RouteTable.Routes.MapHttpRoute("default", "{controller}")
The MapHttpRoute extension method is simply a convenient way to register HttpRoute instances in your routing table. It's perfectly okay to manually create and register an HttpRoute without making use of the shorthand method, though.
If you want to understand the inner workings of MapHttpRoute, take a look at the source code: HttpRouteCollectionExtensions.cs.
I am using this example I found to learn how to load class files and access variables through them. This is in a file called Class1.vb in the App_Code folder (this is not an app project):
Imports Microsoft.VisualBasic
Public Class my_class
Public Shared Sub my_sub()
Dim vartest As String
vartest = 10
HttpContext.Current.Session("myvar") = vartest
End Sub
End Class
This is the codebehind on the aspx file:
Imports my_class
Partial Public Class test
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
my_class.my_sub()
Label1.Text = HttpContext.Current.Session("myvar")
End Sub
End Class
How could I access the vartest variable without using a session, since if this is accessed by multiple functions at the same time the variable can be overwritten I assume. Is it possible to go the other way, where a variable is sent to a class file?
It sounds like you need a quick overview of some basic ASP.Net Webforms concepts. Up first I'll counter a common newbie misconception:
Your Page class does not hang around on the web server for very long
I think many new ASP.Net developers have this idea of the web server keeping a single instance of their page class for every user session that hits their site, and each postback or event uses this same page class instance. That's just not how it works. ASP.Net page class instances are nearly always created and destroyed again in well under a second, and most experienced developers see it as a big problem if it takes longer.
ASP.NET relies on the HTTP protocol
The thing to remember here is ASP.Net still relies on the HTTP protocol, and http boils down to requests and responses. When you view a web page, your browser first sends a request to a server. The server responds, usually with an html document. The browser will then parse the html; based on what it sees in the html the browser may send more requests to the server for additional resources, such as javascript, images, or css files. Each request results in a separate response, and the browser uses all these resources to render the page to the screen. However, the ASP.Net runtime normally does not have to process the additional requests (that would make things slower) — ony the initial html needs ASP.Net support; you want the other resources to be basic files that can be cached.
The ASP.Net runtime creates a new instance of your class for every request.
When the ASP.net runtime processes a request for a page, it will create a new instance of your page class. The runtime will follow the ASP.Net Page lifecycle (this should really be named the "ASP.Net Page Request Lifecycle"), and call certain methods or raise certain events in this class instance, in a specific order defined by the lifecycle.
This means every postback or event runs in a different instance of your class.
It also means every postback or event is rebuilding and transmitting all of the html the goes into your page, and not just the portions you want to change. For your server code, the consequence is the only thing class-level variables are really good for in ASP.Net is things that will be used within a single http request. For the browser, the consequence is you're working with a brand new DOM after every event.
To understand all of that, it's important here to also have a good understanding of the difference between a class and an instance of a class. A couple items in your question make me unsure whether you have this understanding yet.
The ASP.Net runtime shares one application instance among all users of your site
The web server typically only has one instance of your application for the entire web site and all it's users. Therefore, anything with a Shared/static scope is common to every user. It's rarely appropriate in ASP.Net for anything to be Shared/static.
So how do you handle data that should live with a single user or visit to your site?
This is exactly what the Session is for. A session will always be unique to an individual request at any given time. You're worried about multiple functions accessing the session at the same time, but this does not happen. The ASP.Net Page Lifecycle ensures that unless you manually spawn additional threads, only one function at a time is running for a given HttpContext and Session. If a user somehow sends two requests at about the same time that should have the same Session/HttpContext, one will be held by the ASP.Net runtime until the other is completed. If you don't want to reference the session all the time, you can build properties in your class that wrap session variables. See #Pankaj's answer for an example.
First, a Session has user-scope, so it will not be overwritten by another Request.
Is it safe to access asp.net session variables through static properties of a static object?
You could encapsulate the access into a property:
Public Shared Property MyVar() As String
Get
If HttpContext.Current.Session("MyVar") Is Nothing Then
HttpContext.Current.Session("MyVar") = ""
End If
Return DirectCast(HttpContext.Current.Session("MyVar"), String)
End Get
Set(value As String)
HttpContext.Current.Session("MyVar") = value
End Set
End Property
Then you can get the variable by:
Label1.Text = my_class.MyVar
In addition to the "Tim Schmelter" reply....
You can create a BaseClass which will inherit from
System.Web.UI.Page
Place the property as suggested by "Tim". The only change you need to do is to change the access modifier to Protected and you should remove Public and Shared
You can also keep other common functions, properties that can we reused in other classes also... Similarly you can create BaseControls as well for your User controls
Finally, inherit this class in the web form....
Hope this will help you...
Base Class code
Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web
Public Class BaseClass
Inherits System.Web.UI.Page
Protected Property MyVar() As String
Get
If HttpContext.Current.Session("MyVar") Is Nothing Then
HttpContext.Current.Session("MyVar") = ""
End If
Return Convert.ToString(HttpContext.Current.Session("MyVar"))
End Get
Set
HttpContext.Current.Session("MyVar") = value
End Set
End Property
End Class
Sample Code "Behind Code" - Showing the usage of Protected member Data from Base Class
Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls
Public Partial Class Default5
Inherits BaseClass
Protected Sub Page_Load(sender As Object, e As EventArgs)
If Not Page.IsPostBack Then
Dim str As String = Me.MyVar
End If
End Sub
End Class
Generally you can use different places to store application state: Application (application wide, saves state into application domain), Session (there can be saved everything what will be accessed by current browser session), ViewState (variables stored in hidden input field and will be posted on every postback). Of course you can also save state to database or file. I'm not sure what you want to achieve, but looks like you looking for something like ViewState.
Read ASP.NET State Management
In ASP.Net, is it possible to pass parameters to the "New" constructor of a User Control class? In VB.Net:
Public Sub New(ByVal pRequiredParam As String)
'Do something with required Param
End Sub
When I use this user control in a generic ASP.Net page, it doesn't prompt me for "pRequiredParam". Of course, if this was a "normal" class, I would have to supply "pRequiredParam" when I instantiate the object. Is this not possible with a User Control?
While you can certainly create a custom constructor like the one you show in your code sample, you cannot force the designer to make use of it. How would it determine what to send as argument to the constructor?
However, you can load the control dynamically in your code-behind file, and then use whatever parameters it defines. Note though that if you want the control to also work well with the graphical designer, I think that the control need to have a public constructor that takes no parameters (but I think you get that automatically in VB.NET?)
What's the best way to view the data that LoadPostData event is loading to the controls in ASP.NET?
It's actually really simple. The NameValueCollection that get's passed to this method of EVERY control that implements the IPostbackDataHandler interface is the contents of Page.Request.Form. So you can access it at any time by getting a Watch on HttpContext.Current.Request.Form.
Ugh... I would suggest setting your IDE environment up to debug the .net framework, and set a breakpoint on the LoadPostData() method of Control. That's a bit heavy-handed, but if you're willing to wade through the recursive calls to the Control class (perhaps set a conditional breakpoint on the method?), you will be able to get to the data that way.
Good luck!
If you want to be sure you're looking at the data going into a particular control, you can subclass its control type and break during a custom implementation of IPostBackDataHandler.LoadPostData.
For example, you have a programmatically added control to collect the user's city. Change:
Public City As Textbox
to
Public City As BreakableLoadPostDataTextBox
Public Class BreakableLoadPostDataTextBox
Inherits TextBox
Protected Overrides Function LoadPostData( _
ByVal postDataKey As String, _
ByVal postCollection As System.Collections.Specialized.NameValueCollection) _
As Boolean
Return MyBase.LoadPostData(postDataKey, postCollection) ' Break here
End Function
End Class
Set a breakpoint on the Return call. When execution breaks, you should be able to see the postDataKey that's being used to read the control's new value out of the postCollection. You can of course augment this method to your heart's content with Trace calls and whatnot.