Hi
I have a factory class which I want to use to create new objects which
inherit a certain base type so I have a declaration
Public Class MyOwnFactory(Of T As MyOwnBase)
As I understand it, a new MyOwnFactory will get instantiated for every
different type of class implementing MyOwnBase. (This is what I want
anyway as the factory is holding a cache of previously created objects
of this type)
In the class, I have some methods :
Public Function GetMyObject(ByVal p_key As String, ByVal p_reload As
Boolean) As T
....
Dim l_def As T = CreateMyObject(l_dto)
...
Return l_def
End Function
Private Function CreateMyObject() As T
Dim l_def As T = New T()
If LoadCommonData(l_def, l_data) then
endif
Return l_def
End Function
I'm getting the error
"'New' cannot be used on a type parameter that does not have a 'New'
constraint." against the line
Dim l_def As T = New T()
Because it is a factory, I want to keep the New-ing local to the factory
(so I don't want public constructors on the types inheriting MyOwnBase)
and I wondering if someone could explain a way to do this or perhaps an
alternative way of looking at this.
Thx in advance
Simon
9  3785 
Public Class MyOwnFactory(Of T As {New, MyOwnBase})
"Simon Woods" <si*********@hotmail.comwrote in message
news:es**************@TK2MSFTNGP05.phx.gbl...
Hi
I have a factory class which I want to use to create new objects which
inherit a certain base type so I have a declaration
Public Class MyOwnFactory(Of T As MyOwnBase)
As I understand it, a new MyOwnFactory will get instantiated for every
different type of class implementing MyOwnBase. (This is what I want
anyway as the factory is holding a cache of previously created objects of
this type)
In the class, I have some methods :
Public Function GetMyObject(ByVal p_key As String, ByVal p_reload As
Boolean) As T
....
Dim l_def As T = CreateMyObject(l_dto)
...
Return l_def
End Function
Private Function CreateMyObject() As T
Dim l_def As T = New T()
If LoadCommonData(l_def, l_data) then
endif
Return l_def
End Function
I'm getting the error
"'New' cannot be used on a type parameter that does not have a 'New'
constraint." against the line
Dim l_def As T = New T()
Because it is a factory, I want to keep the New-ing local to the factory
(so I don't want public constructors on the types inheriting MyOwnBase)
and I wondering if someone could explain a way to do this or perhaps an
alternative way of looking at this.
Thx in advance
Simon
Thx Bill
When I introduce the New constraint, an error is generated
"'MyOwnClasses.MyOwnClass' must have a public parameterless instance
constructor to satisfy the 'New' constraint for type parameter 'T'."
where the factory is instantiated with
Dim l_factory As MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass) _
= MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass).Instance
(It's a singleton btw)
I'm not too sure how to get round this, as it seems that it is looking
for a public New constructor which I don't want to supply because I want
the factory to be doing all the newing
Thanks again
S
Bill McCarthy wrote:
Public Class MyOwnFactory(Of T As {New, MyOwnBase})
"Simon Woods" <si*********@hotmail.comwrote in message
news:es**************@TK2MSFTNGP05.phx.gbl...
>Hi
I have a factory class which I want to use to create new objects which
inherit a certain base type so I have a declaration
Public Class MyOwnFactory(Of T As MyOwnBase)
As I understand it, a new MyOwnFactory will get instantiated for every
different type of class implementing MyOwnBase. (This is what I want
anyway as the factory is holding a cache of previously created objects
of this type)
In the class, I have some methods :
Public Function GetMyObject(ByVal p_key As String, ByVal p_reload As
Boolean) As T
....
Dim l_def As T = CreateMyObject(l_dto)
...
Return l_def
End Function
Private Function CreateMyObject() As T
Dim l_def As T = New T()
If LoadCommonData(l_def, l_data) then
endif
Return l_def
End Function
I'm getting the error
"'New' cannot be used on a type parameter that does not have a 'New'
constraint." against the line
Dim l_def As T = New T()
Because it is a factory, I want to keep the New-ing local to the
factory (so I don't want public constructors on the types inheriting
MyOwnBase) and I wondering if someone could explain a way to do this
or perhaps an alternative way of looking at this.
Thx in advance
Simon
From generic code the only constraint available for creating instances is
New
"Simon Woods" <si*********@hotmail.comwrote in message
news:u1**************@TK2MSFTNGP04.phx.gbl...
Thx Bill
When I introduce the New constraint, an error is generated
"'MyOwnClasses.MyOwnClass' must have a public parameterless instance
constructor to satisfy the 'New' constraint for type parameter 'T'."
where the factory is instantiated with
Dim l_factory As MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass) _
= MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass).Instance
(It's a singleton btw)
I'm not too sure how to get round this, as it seems that it is looking for
a public New constructor which I don't want to supply because I want the
factory to be doing all the newing
Thanks again
S
Bill McCarthy wrote:
>Public Class MyOwnFactory(Of T As {New, MyOwnBase})
"Simon Woods" <si*********@hotmail.comwrote in message
news:es**************@TK2MSFTNGP05.phx.gbl...
>>Hi
I have a factory class which I want to use to create new objects which
inherit a certain base type so I have a declaration
Public Class MyOwnFactory(Of T As MyOwnBase)
As I understand it, a new MyOwnFactory will get instantiated for every
different type of class implementing MyOwnBase. (This is what I want
anyway as the factory is holding a cache of previously created objects
of this type)
In the class, I have some methods :
Public Function GetMyObject(ByVal p_key As String, ByVal p_reload As
Boolean) As T
....
Dim l_def As T = CreateMyObject(l_dto)
...
Return l_def
End Function
Private Function CreateMyObject() As T
Dim l_def As T = New T()
If LoadCommonData(l_def, l_data) then
endif
Return l_def
End Function
I'm getting the error
"'New' cannot be used on a type parameter that does not have a 'New'
constraint." against the line
Dim l_def As T = New T()
Because it is a factory, I want to keep the New-ing local to the factory
(so I don't want public constructors on the types inheriting MyOwnBase)
and I wondering if someone could explain a way to do this or perhaps an
alternative way of looking at this.
Thx in advance
Simon
So is it a case of using Reflection to lookup the type of T and create
an object of that type and return it as a T ... or will I suffer from
the same problem that Reflection also needs a public constructor.
I have been looking at this approach, but have encountered a similar
problem (but this time at runtime presumably because of its latebound
nature) when trying to use the following - ...
Dim l_myOwnClass As T = CType(Activator.CreateInstance(GetType(T), _
'
System.Reflection.BindingFlags.NonPublic Or _
'
System.Reflection.BindingFlags.Instance), T)
Bill McCarthy wrote:
From generic code the only constraint available for creating instances
is New
"Simon Woods" <si*********@hotmail.comwrote in message
news:u1**************@TK2MSFTNGP04.phx.gbl...
>Thx Bill
When I introduce the New constraint, an error is generated
"'MyOwnClasses.MyOwnClass' must have a public parameterless instance
constructor to satisfy the 'New' constraint for type parameter 'T'."
where the factory is instantiated with
Dim l_factory As MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass) _
= MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass).Instance
(It's a singleton btw)
I'm not too sure how to get round this, as it seems that it is looking
for a public New constructor which I don't want to supply because I
want the factory to be doing all the newing
Thanks again
S
Bill McCarthy wrote:
>>Public Class MyOwnFactory(Of T As {New, MyOwnBase})
"Simon Woods" <si*********@hotmail.comwrote in message
news:es**************@TK2MSFTNGP05.phx.gbl...
Hi
I have a factory class which I want to use to create new objects
which inherit a certain base type so I have a declaration
Public Class MyOwnFactory(Of T As MyOwnBase)
As I understand it, a new MyOwnFactory will get instantiated for
every different type of class implementing MyOwnBase. (This is what
I want anyway as the factory is holding a cache of previously
created objects of this type)
In the class, I have some methods :
Public Function GetMyObject(ByVal p_key As String, ByVal p_reload
As Boolean) As T
....
Dim l_def As T = CreateMyObject(l_dto)
...
Return l_def
End Function
Private Function CreateMyObject() As T
Dim l_def As T = New T()
If LoadCommonData(l_def, l_data) then
endif
Return l_def
End Function
I'm getting the error
"'New' cannot be used on a type parameter that does not have a 'New'
constraint." against the line
Dim l_def As T = New T()
Because it is a factory, I want to keep the New-ing local to the
factory (so I don't want public constructors on the types inheriting
MyOwnBase) and I wondering if someone could explain a way to do this
or perhaps an alternative way of looking at this.
Thx in advance
Simon
The reflection call should work. You want to include the
System.Reflection.BindingFlags.CreateInstance flag
"Simon Woods" <si*********@hotmail.comwrote in message
news:ua**************@TK2MSFTNGP04.phx.gbl...
So is it a case of using Reflection to lookup the type of T and create an
object of that type and return it as a T ... or will I suffer from the
same problem that Reflection also needs a public constructor.
I have been looking at this approach, but have encountered a similar
problem (but this time at runtime presumably because of its latebound
nature) when trying to use the following - ...
Dim l_myOwnClass As T = CType(Activator.CreateInstance(GetType(T), _
' System.Reflection.BindingFlags.NonPublic Or _
' System.Reflection.BindingFlags.Instance), T)
Bill McCarthy wrote:
> From generic code the only constraint available for creating instances
is New
"Simon Woods" <si*********@hotmail.comwrote in message
news:u1**************@TK2MSFTNGP04.phx.gbl...
>>Thx Bill
When I introduce the New constraint, an error is generated
"'MyOwnClasses.MyOwnClass' must have a public parameterless instance
constructor to satisfy the 'New' constraint for type parameter 'T'."
where the factory is instantiated with
Dim l_factory As MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass) _
= MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass).Instance
(It's a singleton btw)
I'm not too sure how to get round this, as it seems that it is looking
for a public New constructor which I don't want to supply because I want
the factory to be doing all the newing
Thanks again
S
Bill McCarthy wrote:
Public Class MyOwnFactory(Of T As {New, MyOwnBase})
"Simon Woods" <si*********@hotmail.comwrote in message
news:es**************@TK2MSFTNGP05.phx.gbl...
Hi
>
I have a factory class which I want to use to create new objects which
inherit a certain base type so I have a declaration
>
Public Class MyOwnFactory(Of T As MyOwnBase)
>
As I understand it, a new MyOwnFactory will get instantiated for every
different type of class implementing MyOwnBase. (This is what I want
anyway as the factory is holding a cache of previously created objects
of this type)
>
>
In the class, I have some methods :
>
>
Public Function GetMyObject(ByVal p_key As String, ByVal p_reload As
Boolean) As T
>
....
>
Dim l_def As T = CreateMyObject(l_dto)
>
...
>
Return l_def
End Function
>
Private Function CreateMyObject() As T
>
Dim l_def As T = New T()
>
If LoadCommonData(l_def, l_data) then
>
endif
>
Return l_def
>
End Function
>
I'm getting the error
>
"'New' cannot be used on a type parameter that does not have a 'New'
constraint." against the line
>
Dim l_def As T = New T()
>
Because it is a factory, I want to keep the New-ing local to the
factory (so I don't want public constructors on the types inheriting
MyOwnBase) and I wondering if someone could explain a way to do this
or perhaps an alternative way of looking at this.
>
Thx in advance
>
Simon
>
>
>
>
Ok ... thx very much Bill
So I've tried this cmd with a protected, private and friend constructor
on MyOwnClass
Return CType(Activator.CreateInstance(GetType(T), _
System.Reflection.BindingFlags.NonPublic Or
_
System.Reflection.BindingFlags.CreateInstance), T)
but it's erroring with
System.MissingMethodException: Constructor on type
'MyOwnClasses.MyOwnClass' not found..
Any other suggestions ? I also tried putting an explicit constructor on
MyOwnBase Because MyOwnClass is inheriting it but got the same error
thx again
Bill McCarthy wrote:
The reflection call should work. You want to include the
System.Reflection.BindingFlags.CreateInstance flag
"Simon Woods" <si*********@hotmail.comwrote in message
news:ua**************@TK2MSFTNGP04.phx.gbl...
>So is it a case of using Reflection to lookup the type of T and create
an object of that type and return it as a T ... or will I suffer from
the same problem that Reflection also needs a public constructor.
I have been looking at this approach, but have encountered a similar
problem (but this time at runtime presumably because of its latebound
nature) when trying to use the following - ...
Dim l_myOwnClass As T = CType(Activator.CreateInstance(GetType(T), _
' System.Reflection.BindingFlags.NonPublic Or _
' System.Reflection.BindingFlags.Instance), T)
Bill McCarthy wrote:
>> From generic code the only constraint available for creating
instances is New
"Simon Woods" <si*********@hotmail.comwrote in message
news:u1**************@TK2MSFTNGP04.phx.gbl...
Thx Bill
When I introduce the New constraint, an error is generated
"'MyOwnClasses.MyOwnClass' must have a public parameterless instance
constructor to satisfy the 'New' constraint for type parameter 'T'."
where the factory is instantiated with
Dim l_factory As MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass) _
= MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass).Instance
(It's a singleton btw)
I'm not too sure how to get round this, as it seems that it is
looking for a public New constructor which I don't want to supply
because I want the factory to be doing all the newing
Thanks again
S
Bill McCarthy wrote:
Public Class MyOwnFactory(Of T As {New, MyOwnBase})
>
>
"Simon Woods" <si*********@hotmail.comwrote in message
news:es**************@TK2MSFTNGP05.phx.gbl.. .
>Hi
>>
>I have a factory class which I want to use to create new objects
>which inherit a certain base type so I have a declaration
>>
> Public Class MyOwnFactory(Of T As MyOwnBase)
>>
>As I understand it, a new MyOwnFactory will get instantiated for
>every different type of class implementing MyOwnBase. (This is
>what I want anyway as the factory is holding a cache of previously
>created objects of this type)
>>
>>
>In the class, I have some methods :
>>
>>
> Public Function GetMyObject(ByVal p_key As String, ByVal
>p_reload As Boolean) As T
>>
> ....
>>
> Dim l_def As T = CreateMyObject(l_dto)
>>
> ...
>>
> Return l_def
> End Function
>>
> Private Function CreateMyObject() As T
>>
> Dim l_def As T = New T()
>>
> If LoadCommonData(l_def, l_data) then
>>
> endif
>>
> Return l_def
>>
> End Function
>>
>I'm getting the error
>>
>"'New' cannot be used on a type parameter that does not have a
>'New' constraint." against the line
>>
> Dim l_def As T = New T()
>>
>Because it is a factory, I want to keep the New-ing local to the
>factory (so I don't want public constructors on the types
>inheriting MyOwnBase) and I wondering if someone could explain a
>way to do this or perhaps an alternative way of looking at this.
>>
>Thx in advance
>>
>Simon
>>
>>
>>
>>
>
Simon Woods wrote:
Ok ... thx very much Bill
Actually Bill, ... I'm not going with the Reflection approach because it
seems noticably slower even to report an error compare to the New T()
approach ... so I'll have a rethink about how to re-engineer this so I
get all early binding.
thx very much again...
Simon
Right as it should. There is no overload that matches that .
CType(Activator.CreateInstance(GetType(T), CreateInstance Or [Public] Or
Instance, Nothing, Nothing, Nothing), T)
"Simon Woods" <si*********@hotmail.comwrote in message
news:e%****************@TK2MSFTNGP06.phx.gbl...
Ok ... thx very much Bill
So I've tried this cmd with a protected, private and friend constructor on
MyOwnClass
Return CType(Activator.CreateInstance(GetType(T), _
System.Reflection.BindingFlags.NonPublic Or _
System.Reflection.BindingFlags.CreateInstance), T)
but it's erroring with
System.MissingMethodException: Constructor on type
'MyOwnClasses.MyOwnClass' not found..
Any other suggestions ? I also tried putting an explicit constructor on
MyOwnBase Because MyOwnClass is inheriting it but got the same error
thx again
Bill McCarthy wrote:
>The reflection call should work. You want to include the
System.Reflection.BindingFlags.CreateInstance flag
"Simon Woods" <si*********@hotmail.comwrote in message
news:ua**************@TK2MSFTNGP04.phx.gbl...
>>So is it a case of using Reflection to lookup the type of T and create
an object of that type and return it as a T ... or will I suffer from
the same problem that Reflection also needs a public constructor.
I have been looking at this approach, but have encountered a similar
problem (but this time at runtime presumably because of its latebound
nature) when trying to use the following - ...
Dim l_myOwnClass As T = CType(Activator.CreateInstance(GetType(T), _
' System.Reflection.BindingFlags.NonPublic Or _
' System.Reflection.BindingFlags.Instance), T)
Bill McCarthy wrote:
From generic code the only constraint available for creating instances
is New
"Simon Woods" <si*********@hotmail.comwrote in message
news:u1**************@TK2MSFTNGP04.phx.gbl...
Thx Bill
>
When I introduce the New constraint, an error is generated
>
"'MyOwnClasses.MyOwnClass' must have a public parameterless instance
constructor to satisfy the 'New' constraint for type parameter 'T'."
where the factory is instantiated with
>
Dim l_factory As MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass) _
= MyOwnClasses.Factory(Of MyOwnClasses.MyOwnClass).Instance
>
(It's a singleton btw)
>
I'm not too sure how to get round this, as it seems that it is looking
for a public New constructor which I don't want to supply because I
want the factory to be doing all the newing
>
Thanks again
>
S
>
>
Bill McCarthy wrote:
>Public Class MyOwnFactory(Of T As {New, MyOwnBase})
>>
>>
>"Simon Woods" <si*********@hotmail.comwrote in message
>news:es**************@TK2MSFTNGP05.phx.gbl. ..
>>Hi
>>>
>>I have a factory class which I want to use to create new objects
>>which inherit a certain base type so I have a declaration
>>>
>> Public Class MyOwnFactory(Of T As MyOwnBase)
>>>
>>As I understand it, a new MyOwnFactory will get instantiated for
>>every different type of class implementing MyOwnBase. (This is what
>>I want anyway as the factory is holding a cache of previously
>>created objects of this type)
>>>
>>>
>>In the class, I have some methods :
>>>
>>>
>> Public Function GetMyObject(ByVal p_key As String, ByVal p_reload
>>As Boolean) As T
>>>
>> ....
>>>
>> Dim l_def As T = CreateMyObject(l_dto)
>>>
>> ...
>>>
>> Return l_def
>> End Function
>>>
>> Private Function CreateMyObject() As T
>>>
>> Dim l_def As T = New T()
>>>
>> If LoadCommonData(l_def, l_data) then
>>>
>> endif
>>>
>> Return l_def
>>>
>> End Function
>>>
>>I'm getting the error
>>>
>>"'New' cannot be used on a type parameter that does not have a 'New'
>>constraint." against the line
>>>
>> Dim l_def As T = New T()
>>>
>>Because it is a factory, I want to keep the New-ing local to the
>>factory (so I don't want public constructors on the types inheriting
>>MyOwnBase) and I wondering if someone could explain a way to do this
>>or perhaps an alternative way of looking at this.
>>>
>>Thx in advance
>>>
>>Simon
>>>
>>>
>>>
>>>
>>
Bill McCarthy wrote:
Right as it should. There is no overload that matches that .
CType(Activator.CreateInstance(GetType(T), CreateInstance Or [Public] Or
Instance, Nothing, Nothing, Nothing), T)
That did it ... thx (I was in a vb6 mode thinking the params were optional!) This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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