I'm new to Ada but not new to programming in general. I have a problem with protected data objects. As I understood from examples and books is that you can make a call for a member in the protected data object just as you would with a task.
Here is my code :
procedure ass4 is
protected type Signal_Object is
entry Wait;
procedure Signal;
function Is_Open return Boolean;
private
Open : Boolean := False;
end Signal_Object;
protected body Signal_Object is
entry Wait when Open is
begin
Open := False;
end Wait;
procedure Signal is
begin
Open := True;
end Signal;
function Is_Open return Boolean is
begin
return Open;
end Is_Open;
end Signal_Object;
begin
Signal_Object.Signal;
end;
However the compiler doesn't like the call Signal_Object.Signal; and I get the following error
invalid use of subtype mark in expression or call
So what am I missing ?
You have a protected type, not a protected object. Either change the declaration from
protected type Signal_Object is
to
protected Signal_Object is
or declare an object of the type
My_Signal_Object : Signal_Object;
and then make your call to the object
My_Signal_Object.Signal
Related
I need to call a function when an Ajax page method function returns success and without button click as protected sub. I couldn't include the ClientScript directly in the method or in shared function and the Method doesn't allow calling Public Sub UpdateText() without Shared ... any ideas?
'''' Method for Ajax with SQL and other functions
'''' ----------------------------------------------------------
<WebMethod()> _
Public Shared Function SendOrder(ByVal fulldata As String,
_ByVal id As Integer) As String
Try
UpdateText()
Return "Success"
Catch ex As Exception
Return "failure"
End Try
End Function
And here is the function I need to call
'''' Function to call only on success
'''' ----------------------------------------------------------
Public Sub UpdateText()
Dim jsUpdate As String
Dim cstype As Type
Dim cs As ClientScriptManager = Page.ClientScript
Dim jsUpdateTxt As String = "<script language='javascript'>...</script>"
ClientScript.RegisterStartupScript(cstype, jsUpdate, jsUpdateTxt)
End Sub
Page method calls have to be static.They cannot interact with the instance properties and methods of your Page class, because a page method call creates no instance of the Page or any of its controls.
after return either Success or failure, you can coding ajax methods in the client side like that
PageMethods.SendOrder(fulldata,id,OnRequestComplete, OnError);
function OnRequestComplete(result) {
//ToDo
}
function OnError(result) {
//ToDo
}
Here is class I reference in this question:
Public Class Enums
Public Enum Subscription As Byte
Vendor = 1
FreeTrial = 2
Standard = 3
Enterprise = 4
End Enum
End Class
In a VB.NET class I have the following property:
Private _optionSelection1 As String 'added by StackOverflow EDIT
Public Property OptionSelection() As String
Get
Return If(IsNothing(_optionSelection1), String.Empty, _optionSelection1)
End Get
Set(ByVal value As String)
_optionSelection1 = value
End Set
End Property
The property gets set from a Request.Form variable as follows: 'added by StackOverflow EDIT
Me.OptionSelection = HttpContext.Current.Request.Form("option_selection1") 'added by StackOverflow EDIT
I use this value later in a function:
Dim choiceMade As Enums.Subscription = SubscriptionOptionSelected(Me.OptionSelection)
I'm thinking the function might be stronger if its parameter could be "stronger" than String:
Private Function SubscriptionOptionSelected(ByVal value As String) As Enums.Subscription
Select Case value
Case "S10"
Return Enums.Subscription.Standard
Case "ENT"
Return Enums.Subscription.Enterprise
End Select
End Function
I've tried writing the function like the following but the compiler immediately complains:
Private Function SubscriptionOptionSelected(ByVal value As OptionSelection) As Enums.Subscription
Is there a way to use the Property as a type passed to this little function ?
What you are asking is redundant. OptionSelection is a string and the function you are calling is taking a string as an input. By saying you want the type of the parameter to be the property you are saying you want a string to be a string.
Now if that string had certain business logic that needed to be applied to it to be a valid string, then you need to create a class that can contain that business logic:
Public Class OptionSelection
Private _OptionString As String
Private _validStrings As String() = New String() {"S10", "ENT"}
Public Sub New(Optional ByVal AnOption As String = "S10")
If _validStrings.Contains(AnOption) Then
_OptionString = AnOption
Else
Throw New Exception("Value must be in the list of acceptable strings")
End If
End Sub
Public Property OptionSelection() As String
Get
Return _OptionString
End Get
Set(ByVal value As String)
If _validStrings.Contains(value) Then
_OptionString = value
Else
Throw New Exception("Value must be in the list of acceptable strings")
End If
End Set
End Property
Public Shared Narrowing Operator CType(ByVal input As String) As OptionSelection
Return New OptionSelection(input)
End Operator
End Class
Then your property changes to:
Private _optionSelection1 As OptionSelection
Public Property OptionSelection() As OptionSelection
Get
Return _optionSelection1
End Get
Set(ByVal value As OptionSelection)
_optionSelection1 = value
End Set
End Property
Your assignment changes to:
Me.OptionSelection = CType(HttpContext.Current.Request.Form("option_selection1"),OptionSelection)
And your function is then:
Private Function SubscriptionOptionSelected(ByVal value As OptionSelection) As Enums.Subscription
Select Case value.OptionSelection
Case "S10"
Return Enums.Subscription.Standard
Case "ENT"
Return Enums.Subscription.Enterprise
End Select
End Function
What all this code does for you is allow you to enforce what kind of strings are being stored in the OptionSelection. You can extend the allowed strings by including them in the array _validStrings.
If your application where to try and assign a string that did not exist in the _validStrings array, then an exception would be generated. So you get a kind of Business logic type safety.
Define your property as Enums.Subscription instead of String. An alternative could be to use Enum.TryParse() to validate the input for SubscriptionOptionSelected and throw an exception if the parsing fails. Here's an example of the property as the enum, although if the sole purpose of SubscriptionOptionSelected is to parse a string to an enum value then it isn't really necessary anymore.
Private _optionSelection1 As Enums.Subscription
Public Property OptionSelection() As Enums.Subscription
Get
Return _optionSelection1
End Get
Set(ByVal value As String)
_optionSelection1 = value
End Set
End Property
Private Function SubscriptionOptionSelected(ByVal value As Enums.Subscription) As Enums.Subscription
...
End Function
Here's an example where you use Enum.TryParse instead...
Private Function SubscriptionOptionSelected(ByVal value As String) As Enums.Subscription
Dim retVal As Enums.Subscription
If Not System.Enum.TryParse(Of Enums.Subscription)(value, retVal) Then
' Deal with invalid value... throw Exception maybe?
End If
Return retVal
End Function
So in your code (based on your updates) you could change your property to an enum and do this:
Me.OptionSelection = Me.SubscriptionOptionSelected(HttpContext.Current.Request.Form("option_selection1"))
This assumes that the value of Form("option_selection1") will be either the string or numeric equivalent value of your Enum elements. If the form submission values don't match, then I'm afraid you are stuck doing things as they are.
We are developing a webservice for a client. We are not supose to throw SoapExceptions, so instead, we catch every exception server side, and return a custom Exception class.
Public Class Order
...
End Class
Public Class MyException
...
End Class
And then in my webservice a function (webmethod):
Public Function GetOrder(ByVal id As Integer) As Object
Try
...
Return New Order()
Catch ex As Exception
Return New MyException(ex.Message)
End Try
End Function
The problem now is, that since my webmethod is returning the type [Object]. The wdsl that is generated does not contain the order, or the exception.
I can change the [Object] to [Order] Or [MyException], but only one of them is generated in the wsdl.
So does anybody have an idea of how i should handle this? I want both the MyException type and the Order type in my wsdl, but i just cant get it working.
Thank you all.
If your definition of MyException
Public Class MyException
inherits System.Exception
...
End Class
then you shouldn't need to return the Custom Exception just throw it.
then you can define
Public Function GetOrder(ByVal id As Integer) As Order
Try
...
Return New Order()
Catch ex As Exception
Throw New MyException(ex.Message)
End Try
End Function
As I recall (and it's been a while) trying to return multiple objects from a web method can prove to be extremely troublesome
If you really want to return multiple objects, then maybe you should create a "wrapper" object, e.g something like this:
'please note: I don't normally use VB.NET, so there might be some errors
Public Class OrderResponse
Public Property Order() As Order
Get
Return m_Order
End Get
Set
m_Order = Value
End Set
End Property
Private m_Order As Order
Public Property Exception() As MyException
Get
Return m_Exception
End Get
Set
m_Exception = Value
End Set
End Property
Private m_Exception As MyException
End Class
Then change your method to return an instance of that class, with either the property Order or Exception set to the respective value:
Public Function GetOrder(ByVal id As Integer) As OrderResponse
...
End Function
So hopefully this is a silly question (that would make it easily answered).
I'm trying to make a composite server control that encapsulates a TextBox, some validators and other stuff, depending on the type of field required.
My control has a "DataType" value that lets me determine what to display. For example if DataType is "Date" I render a AjaxControlToolkit.CalendarExtender, etc.
My generic "Value" property is an object and will return whatever the DataType property calls for, so in the above example the Value would be a Date type.
So here's my problem, I need to convert my incoming Value property to whatever the DataType calls for at runtime.
As you can see I attempted to write a TypeConverter for it but it doesn't seem to work, I end up with this error during compile:
Unable to generate code for a value of type 'System.Object'. This error occurred while trying to generate the property value for Value.
Any help would be much appreciated!
Here is how I'm attempting to call my control:
<custom:SomeTextControl ID="dateFoo" runat="server" DataType="Date" Value="08/11/2009" />
Here is my class:
Public Class SomeTextControl
Inherits Control
Private _Value as Object
<Bindable(True), TypeConverter(GetType(ObjectConverter))> _
Public Property Value() As Object
Get
Return _Value
End Get
Set(ByVal value As Object)
_Value = value
End Set
End Property
End Class
Public Class ObjectConverter
Inherits TypeConverter
Public Overrides Function ConvertFrom(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, ByVal value As Object) As Object
Dim o As Object
o = value
Return o
End Function
Public Overrides Function CanConvertFrom(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal sourceType As System.Type) As Boolean
If sourceType Is GetType(String) Then
Return True
End If
Return MyBase.CanConvertFrom(context, sourceType)
End Function
Public Overrides Function CanConvertTo(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal destinationType As System.Type) As Boolean
If destinationType Is GetType(String) Then
Return True
End If
Return MyBase.CanConvertTo(context, destinationType)
End Function
End Class
So seems that I semi figured it out myself... so much for overzealously asking questions.
Anyway, seems I had forgotten to check if the destinationType is a InstanceDescriptor (duh). Once I got that it was a few more mins to figure out I had to set my Object to a String (or something else, but I'm opting for a String since I'm just going to spit it back out into a TextBox anyway) since an Object doesn't take a constructor.
Let me know if you guys have any better ideas.
So I ended up with this TypeConverter:
Friend Class ObjectConverter
Inherits TypeConverter
Public Overrides Function ConvertFrom(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, ByVal value As Object) As Object
Return value
End Function
Public Overrides Function CanConvertFrom(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal sourceType As System.Type) As Boolean
If sourceType Is GetType(String) Then
Return True
ElseIf sourceType Is GetType(InstanceDescriptor) Then
Return True
End If
Return MyBase.CanConvertFrom(context, sourceType)
End Function
Public Overrides Function CanConvertTo(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal destinationType As System.Type) As Boolean
If destinationType Is GetType(String) Then
Return True
ElseIf destinationType Is GetType(InstanceDescriptor) Then
Return True
End If
Return MyBase.CanConvertTo(context, destinationType)
End Function
Public Overrides Function ConvertTo(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, ByVal value As Object, ByVal destinationType As System.Type) As Object
If destinationType Is GetType(InstanceDescriptor) Then
Dim constructor As ConstructorInfo = GetType(String).GetConstructor(New Type() {GetType(Char())})
Dim instance As New InstanceDescriptor(constructor, New Object() {CType(value.ToString, Char())})
Return instance
End If
Return MyBase.ConvertTo(context, culture, value, destinationType)
End Function
End Class
I'm building a decent sized application in ASP.NET/VB.NET with various objects... I've never used interfaces before, and a fellow programmer balked when I mentioned this to him. Can anyone give me a quick overview on how they're used, what they're used for, and why I would use them? Maybe I don't need to use them for this project, but if they would help, I surely would love to try.
Thanks so much!
Once you "get" interfaces, OOP really falls into place. To put it simply, an interface defines a set of public method signatures, you create a class which implements those methods. This allows you generalize functions for any class which implements a particular interface (i.e. classes which have the same methods), even if those classes don't necessarily descend from one another.
Module Module1
Interface ILifeform
ReadOnly Property Name() As String
Sub Speak()
Sub Eat()
End Interface
Class Dog
Implements ILifeform
Public ReadOnly Property Name() As String Implements ILifeform.Name
Get
Return "Doggy!"
End Get
End Property
Public Sub Speak() Implements ILifeform.Speak
Console.WriteLine("Woof!")
End Sub
Public Sub Eat() Implements ILifeform.Eat
Console.WriteLine("Yum, doggy biscuits!")
End Sub
End Class
Class Ninja
Implements ILifeform
Public ReadOnly Property Name() As String Implements ILifeform.Name
Get
Return "Ninja!!"
End Get
End Property
Public Sub Speak() Implements ILifeform.Speak
Console.WriteLine("Ninjas are silent, deadly killers")
End Sub
Public Sub Eat() Implements ILifeform.Eat
Console.WriteLine("Ninjas don't eat, they wail on guitars and kick ass")
End Sub
End Class
Class Monkey
Implements ILifeform
Public ReadOnly Property Name() As String Implements ILifeform.Name
Get
Return "Monkey!!!"
End Get
End Property
Public Sub Speak() Implements ILifeform.Speak
Console.WriteLine("Ook ook")
End Sub
Public Sub Eat() Implements ILifeform.Eat
Console.WriteLine("Bananas!")
End Sub
End Class
Sub Main()
Dim lifeforms As ILifeform() = New ILifeform() {New Dog(), New Ninja(), New Monkey()}
For Each x As ILifeform In lifeforms
HandleLifeform(x)
Next
Console.ReadKey(True)
End Sub
Sub HandleLifeform(ByVal x As ILifeform)
Console.WriteLine("Handling lifeform '{0}'", x.Name)
x.Speak()
x.Eat()
Console.WriteLine()
End Sub
End Module
None of the classes above descend from one another, but my HandleLifeform method is generalized to operate on all of them -- or really any class which implements the ILifeform interface.
Since the basics have already been covered, lets move on to practical examples.
Say I'm going to have a Dictionary that stores String keys and Person objects and I'm going to pass this dictionary (actually, the reference to it) to some methods I have.
Now, my receiving method would look something like
Imports System.Collections.Generic
Public Sub DoSomething(ByVal myDict As Dictionary(Of String, Person))
' Do something with myDict here
End Sub
right?
But what if someone invents some new high performance dictionary class? I have to turn around and change every reference to Dictionary to FastDictionary!
However, if I had coded to the interface in the first place, I wouldn't have this problem:
Imports System.Collections.Generic
Public Sub DoSomething(ByVal myDict As IDictionary(Of String, Person))
' Do something with myDict here
End Sub
Now it takes any dictionary!
Interfaces basically allow you to define a type's contract without specifying its implementation.
The idea is that if you know that a given type implements a certain interface it is guaranteeing that certain methods and properties are members of that type.
So any type that implements the following interface:
Interface ISpinnable
Sub Spin()
End Interface
Would have to implement the Spin method. But the caller of this type that implements ISpinnable does not care about how it is implemented, it just cares that the method is there. Here is a type that implements ISpinnable:
Class Top Implements ISpinnable
Sub Spin()
' do spinning stuff
End Sub
End Class
The benefit to this is that you can create method arguments of type ISpinner and allow the caller of these methods to pass any type to you as long as it implements the interface. Your method is no longer tightly coupled to the concrete type that the caller is using.
An interface is a contract without an implementation. It allows you to define what a type will look like without indicating what the implementation of that type is.
This allows you to have various implementations of an interface, which would suit your particular needs.
A good example is the IComparer(Of T) interface. You can have one implementation that will compare two items based on which is greater, and then another which will return a value based on which is lesser.
Then, you could pass one or the other to the static Sort method on the Array class to sort your items in ascending, or descending order, respectively.
One of the things interfaces can be useful is browsing through the array of objects of different types but which share the same interface.
Can't say for VB, but in C# you can use the handy "is" operator to determine if object's type implements the given interface and it's safe to access methods of that interface by casting. Sorry for C#, but i'll try to put some comments in =))
//we declare 3 different interfaces each requiring to implement one method
interface IProgrammer
{
void WriteCode();
}
interface ITester
{
void FindBugs();
}
interface IWorker
{
void StartShift();
}
// each programmer will be able to start his shift and write code
class Programmer : IWorker, IProgrammer
{
public void StartShift()
{
// ...
}
public void WriteCode()
{
// ...
}
}
// each tester will be able to start his shift and find bugs
class Tester : IWorker, ITester
{
public void StartShift()
{
// ...
}
public void FindBugs()
{
// ...
}
}
//then in code you can rely on objects implementing the interface to
// be able to do tasks interface requires to do
static void Main()
{
IWorker[] workers = new IWorker[3];
workers[0] = new Programmer();
workers[1] = new Tester();
workers[2] = new Tester();
// now we can browse through array of different workers because they all share
// the IWorker interface
foreach(IWorker worker in workers)
{
// All IWorkers can StartShift so we access its methods without casts
worker.StartShift();
if(worker is IProgrammer)
{
// Since that worker also implements IProgrammer
// we cast worker as IProgrammer and access IProgrammer method(s)
(worker as IProgrammer).WriteCode();
}
if(worker is ITester)
{
// Same,
// we cast worker as ITester and access ITester method(s)
// handy! =)
(worker as ITester).FindBugs();
}
}
A classic example is the Data Layer where you use it to support multiple database format. This was actually very useful before ORMappers came into the picture in mainstream programming.
Your interface just tells what type of method and properties your object has, the object itself then has to implement these methods.
IMyDatabase myDb;
switch case myDbFormat {
case "mysql":
myDb = new MyDbMySql();
break;
case "mssql" :
myDb = new MyDbMsSql();
break;
}
myDb.SaveToDatabase(some data)
Ofcourse the myDb classes have to implement the ImyDatabase Interface. I assume you can see how useful this is :).