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asp.net : problem with "Object reference not set to an instance of an object"
class, so when you write: If mpg.FindControl("lkred").Visible = True Then you get the error because "mpg" has not been set to an instance of a MasterPage class. You need to either instantiate mpg: Dim mpg As NEW MasterPage or set mpg equal to an already created instance of a MasterPage: Dim foo As New MasterPage Dim mpg As MasterPage = foo -Scott [quoted text, click to view] "Chris" <????@nospam.dc> wrote in message news:elwnpXqXHHA.2640@TK2MSFTNGP06.phx.gbl... > Hi, > > I tried to create a class which must change the propety 'visible' of a > <link> tag in the masterpage into 'false' when the user is logged. But i > get the error: "Object reference not set to an instance of an object" > for the line 'If mpg.FindControl("lkred").Visible = True Then'. > > I couldn't find sofar the solution. > Any help would be appreciated ... > Thanks > Chris > > the class: > --------- > Imports Microsoft.VisualBasic > Public Class loginkl > Public Sub logkl() > Dim pg As New Page > Dim mpg As MasterPage > If pg.User.Identity.IsAuthenticated = True Then > If mpg.FindControl("lkred").Visible = True Then > .... > End If > End Sub > End Class > > code-behind: > ----------- > Partial Class MasterPage > Inherits System.Web.UI.MasterPage > Protected Sub Page_Init(ByVal sender As Object, ByVal e As > System.EventArgs) Handles Me.Init > Dim lg As New loginkl > lg.logkl() > End Sub > End Class > > masterpage.master: > ------------------ > <link runat="server" id="lkred" href="App_Themes/red.css" rel=Stylesheet > type="text/css" visible="true"/> > > >
Hi,
I tried to create a class which must change the propety 'visible' of a <link> tag in the masterpage into 'false' when the user is logged. But i get the error: "Object reference not set to an instance of an object" for the line 'If mpg.FindControl("lkred").Visible = True Then'. I couldn't find sofar the solution. Any help would be appreciated ... Thanks Chris the class: --------- Imports Microsoft.VisualBasic Public Class loginkl Public Sub logkl() Dim pg As New Page Dim mpg As MasterPage If pg.User.Identity.IsAuthenticated = True Then If mpg.FindControl("lkred").Visible = True Then .... End If End Sub End Class code-behind: ----------- Partial Class MasterPage Inherits System.Web.UI.MasterPage Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init Dim lg As New loginkl lg.logkl() End Sub End Class masterpage.master: ------------------ <link runat="server" id="lkred" href="App_Themes/red.css" rel=Stylesheet type="text/css" visible="true"/>
[quoted text, click to view]
Chris wrote: > Hi, > > I tried to create a class which must change the propety 'visible' of a > <link> tag in the masterpage into 'false' when the user is logged. But i get > the error: "Object reference not set to an instance of an object" > for the line 'If mpg.FindControl("lkred").Visible = True Then'. > > I couldn't find sofar the solution. > Any help would be appreciated ... > Thanks > Chris > > the class: > --------- > Imports Microsoft.VisualBasic > Public Class loginkl > Public Sub logkl() > Dim pg As New Page Here you are creating a completely new instance of the Page class. The Page class is the base class for pages and doesn't contain any controls at all. [quoted text, click to view] > Dim mpg As MasterPage > If pg.User.Identity.IsAuthenticated = True Then > If mpg.FindControl("lkred").Visible = True Then The FindControl method returns a null reference. As there are no controls in the page object, the control you are looking for can of course not be found. [quoted text, click to view] > .... > End If > End Sub > End Class > > code-behind: > ----------- > Partial Class MasterPage > Inherits System.Web.UI.MasterPage > Protected Sub Page_Init(ByVal sender As Object, ByVal e As > System.EventArgs) Handles Me.Init > Dim lg As New loginkl > lg.logkl() Here you should to pass a reference to the current Page into the method, so that it can use that to locate the control. Better yet, why not pass a reference to the control into the method. That way you don't have to use FindControl to locate it, and the method can be used to hide any control that you like, not only a control named "lkred". I am not sure, but the Init event of the master page might also occur too early to access the controls of the page. If the markup of the page has not yet been parsed, the page does not yet contain any controls. Then you have to use an even that occurs later in the cycle. [quoted text, click to view] > End Sub > End Class > > masterpage.master: > ------------------ > <link runat="server" id="lkred" href="App_Themes/red.css" rel=Stylesheet > type="text/css" visible="true"/> > > -- Göran Andersson _____
Correction: I see now that you look for the control in the MasterPage
object, not in the Page object. The same appplies, though, but the actual error occurs because you have just declared a reference to a master page, and haven't assign any value to it. When you try to use the reference, it's null. (Are you sure that this is the actual code that you are using? I would expect a compiler error as you are trying to use a variable that hasn't been assigned any value.) You have to send a reference into the method, either a reference to the actual master page, or a reference to the control. The base class for master pages can not be used to access controls in any specific master page. -- Göran Andersson _____
Hi, thanks to you too. i did what you told me:but i still have the same
error for the same line "'If mpg.FindControl("lkred").Visible = True Then'. I show you the whole code to be sure ...(i also tried with Protected Sub Page_Load instead of Protected Sub Page_Init). masterpage: ----------- <head runat="server"> <link runat="server" id="Lkred" href="App_Themes/red/red.css" rel=Stylesheet type="text/css" visible="true"/> <link runat="server" id="lkgreen" href="App_Themes/green/green.css" rel=Stylesheet type="text/css" visible="false" /> </head> classe: ------- Imports Microsoft.VisualBasic Public Class loginkl Public Sub logkl() Dim pg As New Page Dim foo As New MasterPage Dim mpg As MasterPage = foo If pg.User.Identity.IsAuthenticated = True Then If mpg.FindControl("lkred").Visible = True Then mpg.FindControl("lkred").Visible = False mpg.FindControl("lkgreen").Visible = True Else mpg.FindControl("lkred").Visible = True mpg.FindControl("lkgreen").Visible = False End If End If End Sub End Class code-behind of masterpage: --------------------------- Partial Class MasterPage Inherits System.Web.UI.MasterPage Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init Dim lg As New loginkl lg.logkl() End Sub End Class
In the masterpage, the id of the control is Lkred and not lkred.
mpg.FindControl("lkred") returns nothing becuase it should be mpg.FindControl("Lkred") [quoted text, click to view] "Chris" <????@nospam.dc> wrote in message
news:%23CtWczvXHHA.4396@TK2MSFTNGP06.phx.gbl... > Hi, thanks to you too. i did what you told me:but i still have the same > error for the same line "'If mpg.FindControl("lkred").Visible = True > Then'. > I show you the whole code to be sure ...(i also tried with Protected Sub > Page_Load instead of Protected Sub Page_Init). > > > masterpage: > ----------- > <head runat="server"> > <link runat="server" id="Lkred" href="App_Themes/red/red.css" > rel=Stylesheet type="text/css" visible="true"/> > <link runat="server" id="lkgreen" href="App_Themes/green/green.css" > rel=Stylesheet type="text/css" visible="false" /> > </head> > > classe: > ------- > Imports Microsoft.VisualBasic > > Public Class loginkl > Public Sub logkl() > Dim pg As New Page > Dim foo As New MasterPage > Dim mpg As MasterPage = foo > If pg.User.Identity.IsAuthenticated = True Then > If mpg.FindControl("lkred").Visible = True Then > mpg.FindControl("lkred").Visible = False > mpg.FindControl("lkgreen").Visible = True > Else > mpg.FindControl("lkred").Visible = True > mpg.FindControl("lkgreen").Visible = False > End If > End If > End Sub > End Class > > code-behind of masterpage: > --------------------------- > Partial Class MasterPage > Inherits System.Web.UI.MasterPage > Protected Sub Page_Init(ByVal sender As Object, ByVal e As > System.EventArgs) Handles Me.Init > Dim lg As New loginkl > lg.logkl() > End Sub > End Class >
Hi,
It's true but it doesn't matter, i thing ... it's not case sensitive (VB.net) (i tried with both lower and uppercase). Still same error. "Stephany Young" <noone@localhost> schreef in bericht news:%23UWPf8vXHHA.4000@TK2MSFTNGP02.phx.gbl... [quoted text, click to view] > In the masterpage, the id of the control is Lkred and not lkred. > > mpg.FindControl("lkred") returns nothing becuase it should be > mpg.FindControl("Lkred") > > > > "Chris" <????@nospam.dc> wrote in message > news:%23CtWczvXHHA.4396@TK2MSFTNGP06.phx.gbl... >> Hi, thanks to you too. i did what you told me:but i still have the same >> error for the same line "'If mpg.FindControl("lkred").Visible = True >> Then'. >> I show you the whole code to be sure ...(i also tried with Protected Sub >> Page_Load instead of Protected Sub Page_Init). >> >> >> masterpage: >> ----------- >> <head runat="server"> >> <link runat="server" id="Lkred" href="App_Themes/red/red.css" >> rel=Stylesheet type="text/css" visible="true"/> >> <link runat="server" id="lkgreen" href="App_Themes/green/green.css" >> rel=Stylesheet type="text/css" visible="false" /> >> </head> >> >> classe: >> ------- >> Imports Microsoft.VisualBasic >> >> Public Class loginkl >> Public Sub logkl() >> Dim pg As New Page >> Dim foo As New MasterPage >> Dim mpg As MasterPage = foo >> If pg.User.Identity.IsAuthenticated = True Then >> If mpg.FindControl("lkred").Visible = True Then >> mpg.FindControl("lkred").Visible = False >> mpg.FindControl("lkgreen").Visible = True >> Else >> mpg.FindControl("lkred").Visible = True >> mpg.FindControl("lkgreen").Visible = False >> End If >> End If >> End Sub >> End Class >> >> code-behind of masterpage: >> --------------------------- >> Partial Class MasterPage >> Inherits System.Web.UI.MasterPage >> Protected Sub Page_Init(ByVal sender As Object, ByVal e As >> System.EventArgs) Handles Me.Init >> Dim lg As New loginkl >> lg.logkl() >> End Sub >> End Class >> >
As I have explained already, you can not access the controls of a
specific master page by creating an instance of the base class for master pages. You need a reference to the actual master page that contains the control. Read what I have written in my other posts in this thread about sending a reference to the method. [quoted text, click to view] Chris wrote: > Hi, thanks to you too. i did what you told me:but i still have the same > error for the same line "'If mpg.FindControl("lkred").Visible = True Then'. > I show you the whole code to be sure ...(i also tried with Protected Sub > Page_Load instead of Protected Sub Page_Init). > > > masterpage: > ----------- > <head runat="server"> > <link runat="server" id="Lkred" href="App_Themes/red/red.css" > rel=Stylesheet type="text/css" visible="true"/> > <link runat="server" id="lkgreen" href="App_Themes/green/green.css" > rel=Stylesheet type="text/css" visible="false" /> > </head> > > classe: > ------- > Imports Microsoft.VisualBasic > > Public Class loginkl > Public Sub logkl() > Dim pg As New Page > Dim foo As New MasterPage > Dim mpg As MasterPage = foo > If pg.User.Identity.IsAuthenticated = True Then > If mpg.FindControl("lkred").Visible = True Then > mpg.FindControl("lkred").Visible = False > mpg.FindControl("lkgreen").Visible = True > Else > mpg.FindControl("lkred").Visible = True > mpg.FindControl("lkgreen").Visible = False > End If > End If > End Sub > End Class > > code-behind of masterpage: > --------------------------- > Partial Class MasterPage > Inherits System.Web.UI.MasterPage > Protected Sub Page_Init(ByVal sender As Object, ByVal e As > System.EventArgs) Handles Me.Init > Dim lg As New loginkl > lg.logkl() > End Sub > End Class > -- Göran Andersson _____
Hi, thanks
I changed this line in the class: Dim mpg As New MasterPage I have no error anymore, but instead of changing the theme from red into green, it remains red. So at least one test remains false: If pg.User.Identity.IsAuthenticated = True Then If mpg.FindControl("lkred").Visible = True Then Could you please give me the right code for doing what you told me? The same appplies, though, but the actual error occurs because you have just declared a reference to a master page, and haven't assign any value to it. and You have to send a reference into the method, either a reference to the actual master page, or a reference to the control thanks again
[quoted text, click to view]
Chris wrote: > Hi, thanks > > I changed this line in the class: > Dim mpg As New MasterPage > > I have no error anymore, but instead of changing the theme from red into > green, it remains red. So at least one test remains false: > If pg.User.Identity.IsAuthenticated = True Then > If mpg.FindControl("lkred").Visible = True Then > > Could you please give me the right code for doing what you told me? > The same appplies, though, but the actual error occurs because you have > just declared a reference to a master page, and haven't assign any value > to it. > > and > > You have to send a reference into the method, either a reference to the > actual master page, or a reference to the control > > thanks again > Here's an example of how you send a reference to a control into a method: SomeMethod(theControl) Here's how you declare the method to accept the reference: Public Sub SomeMethod(link As Control) -- Göran Andersson _____
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