problem with getter and setter not working

[Adam Sandler]

Hi all,

I hope this is an easy one... Using VWD 2005. When I call my accessor
method (getName) I always receive an empty string back. Debugging
shows there should be something there but I cannot figure out where the
problem is actually occurring.

The first couple of lines of my code behind:

Partial Class _Default
Inherits System.Web.UI.Page

Dim sName As String ' for getter and setter

Here's my getter and setter:

Function getName()
Return sName
End Function

Sub setName(ByVal s As String)
sName = s
End Sub

Here's the code which calls the setter:

Protected Sub Button2_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button2.Click
Try
setName(Me.GridView1.SelectedRow.Cells(2).Text)
Catch nre As NullReferenceException
MsgBox("Please select a row.")
End Try
End Sub

Lastly, here's some code which calls the getter:

Protected Sub Button4_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button4.Click
MsgBox(getName())
End Sub


When Button4 is clicked, the message box pops up but there's nothing in
it... where am I going wrong here?

Thanks!

 

[Jimi200478]

the reason that you are getting this is because once you have clicked
button4, the value of sName is no longer there because a post back has
occured. what you want to do is something like this:

private string SetName
{
set{ViewState["sName"] = value;}
}

private string GetName
{
get{return ViewState["sName"].ToString();}
}

Notice also that I am using the "getter" and "setter" as they are
intended to be used. they should be properties, not methods.

 

[sloan]

C# and VB.net... don't really go with the java setters/getters

In VB, you do a

Public Property LastName
Set
Me.m_lastName = Value
End Set
Get
return Me.m_lastName
End Get
End Property

where m_lastName is a member variable.

Yeah, stuff "disappears" on the PostBack, you have to be aware of objects
called in Page_Load, aren't around on a button click.

I have a "smart" object holder at my blog:

http://spaces.msn.com/sholliday/ 10/24/2005

that should help if you want to go fancy.
Or learn how to perist items in the Session["mykeyname"] format.

 

[Jimi200478]

i would just use viewstate. that way you dont have to create variables
that you dont need, and you're not carrying around unescessary data in
session. if you're using this value on only one page...use viewstate,
if you need it on other pages, then you can use session. code i posted
above is in c#. translation is fairly easy.

 

[Adam Sandler]

Thanks all... As sloan guessed, I'm a Java guy that's been thrown in to
the deep end of the ASP.NET pool without knowing how to swim.

But I don't exactly find the translation easy... probably because it's
a bit of a paradigm shift and Googling the terms: property, viewstate,
and vb isn't yeilding results I think I can use.

http://www.codeguru.com/csharp/.net/net_asp/controls/article.php/c11971/
is the same thing as above and in C#

Either I've translated from C# incorrectly or the the post back still
over writes what was sent to the setter.

If I got this working and I actually want to work with the data, do I
do that by typing this LastName.Get (sloan's example) or GetName
(Jimi200478's example)?

 

[sloan]

Are you trying to Display the value in the Page (somewhere in the html
output)?

Or are you trying to use it in the code_behind page (where the actualy
vb.net code resides)

?

 

[Adam Sandler]

Are you trying to Display the value in the Page (somewhere in the html
output)?

Or are you trying to use it in the code_behind page (where the actualy
vb.net code resides)

In the code behind... In the past 15 minutes I tried this in my class
declaration:

Private _myname As String

Public Property MyName() As String
Get
Return _myname
End Get
Set(ByVal value As String)
_myname = value
End Set
End Property

And then in my event handlers:

Protected Sub Button2_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button2.Click
MyName = Me.GridView1.SelectedRow.Cells(2).Text
End Sub

Protected Sub Button4_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button4.Click
MsgBox(MyName)
End Sub

And I get the same result... an empty string returned.

Thanks for your help thus far!!!

 

[Jimi200478]

Adam Sandler:

You are going to have to store "MyName" in either ViewState or Session
if you want it to survive a PostBack. Both mine and Sloan's examples
are the same, just different syntax. Sloans example demonstrates how to
use a property in .NET, but it doesnt answer base question which is
"how do i make the value survive a postback". The answer to that
question is viewstate or session. if you do want to have a variable on
your page called myname, you will have to do something like this:

in C#:

private string _MyName;

public string MyName
{
get
{
_MyName = ViewState["MyName"].ToString();
return _MyName;
}
set
{
_MyName = value;
ViewState["MyName"] = _MyName;
}
}

if the property is followed by an equals sign, then it knows to "set"
the value. if it is called without an equals sign, the property knows
to "get" the value. see below:

Setting MyName :

MyName = "John"

Getting MyName :

MsgBox(MyName)

Truthfully, at the end of it all, it doesnt matter how you do it, all
that matters is that you use viewstate or session to keep your value
alive. well, good luck!

 

[sloan]

Yeah... I wrote an example up before seeing Jimi's example.

But here is mine... Same bat time, same bat channel.



ASPX
<HTML>
<HEAD>
<title>ViewStateTest</title>
<meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR">
<meta content="C#" name="CODE_LANGUAGE">
<meta content="JavaScript" name="vs_defaultClientScript">
<meta content="http://schemas.microsoft.com/intellisense/ie5"
name="vs_targetSchema">
</HEAD>
<body>
<form id="Form1" method="post" runat="server">
<P><asp:textbox id="TextBox1" runat="server"></asp:textbox>&nbsp;(Put a
Number In
Here, and click the Button Below)</P>
<P><asp:button id="Button1" runat="server"
Text="ButtonONE"></asp:button></P>
<P><asp:button id="Button2" runat="server" Text="ButtonTWO"
Visible="False"></asp:button></P>

</form>
</body>
</HTML>


..cs code behind:


public int SelectedRecordID

{

get

{

if (ViewState["SelectedRecordID"] != null)

return Convert.ToInt32(ViewState["SelectedRecordID"]);

else

return -1;

}

set

{

ViewState["SelectedRecordID"] = value;

}

}

private void Button1_Click(object sender, System.EventArgs e)

{


int whatsMyValue = this.SelectedRecordID;



this.SelectedRecordID = int.Parse(this.TextBox1.Text);



this.Button1.Visible = false;

this.Button2.Visible = true;



}

private void Button2_Click(object sender, System.EventArgs e)

{

int whatsMyValue = this.SelectedRecordID;



this.SelectedRecordID = int.Parse(this.TextBox1.Text);



}



private void Page_Load(object sender, System.EventArgs e)

{

// Put user code to initialize the page here

if (!Page.IsPostBack)

{

this.SelectedRecordID = -999; // use -999 for the PageLoad

}



}

Adam Sandler:

You are going to have to store "MyName" in either ViewState or Session
if you want it to survive a PostBack. Both mine and Sloan's examples
are the same, just different syntax. Sloans example demonstrates how to
use a property in .NET, but it doesnt answer base question which is
"how do i make the value survive a postback". The answer to that
question is viewstate or session. if you do want to have a variable on
your page called myname, you will have to do something like this:

in C#:

private string _MyName;

public string MyName
{
get
{
_MyName = ViewState["MyName"].ToString();
return _MyName;
}
set
{
_MyName = value;
ViewState["MyName"] = _MyName;
}
}

if the property is followed by an equals sign, then it knows to "set"
the value. if it is called without an equals sign, the property knows
to "get" the value. see below:

Setting MyName :

MyName = "John"

Getting MyName :

MsgBox(MyName)

Truthfully, at the end of it all, it doesnt matter how you do it, all
that matters is that you use viewstate or session to keep your value
alive. well, good luck!

 

[Adam Sandler]

Adam Sandler:

You are going to have to store "MyName" in either ViewState or Session
if you want it to survive a PostBack. Both mine and Sloan's examples
are the same, just different syntax. Sloans example demonstrates how to
use a property in .NET, but it doesnt answer base question which is
"how do i make the value survive a postback". The answer to that
question is viewstate or session. if you do want to have a variable on
your page called myname, you will have to do something like this:

in C#:

private string _MyName;

public string MyName
{
get
{
_MyName = ViewState["MyName"].ToString();
return _MyName;
}
set
{
_MyName = value;
ViewState["MyName"] = _MyName;
}
}

if the property is followed by an equals sign, then it knows to "set"
the value. if it is called without an equals sign, the property knows
to "get" the value. see below:

Setting MyName :

MyName = "John"

Getting MyName :

MsgBox(MyName)

Truthfully, at the end of it all, it doesnt matter how you do it, all
that matters is that you use viewstate or session to keep your value
alive. well, good luck!

Jimi... thatnks for the help. Here's what I have so far...

Private _MyName As String

Public Property MyName() As String
Get
_MyName = Me.ViewState(MyName).ToString
End Get
Set(ByVal value As String)
_MyName = value
Me.ViewState(MyName) = _MyName
End Set
End Property

The compiler doesn't like this code above but it will run. However,
the first time I click the button which has this in its handler:

MyName = someComponent.Text

It throws an error with "The string parameter 'key' cannot be null or
empty." as the message. This is why I assumed earlier that my
translation from C# to VB was incorrect. I'm positing it here now so
you can indeed see that I am very interested in what you have posted
but for whatever reason, I haven't been able to successfully implement
your advice.

Thanks!

 

[Jimi200478]

you're almost there. you just need to change the code a little bit:

change the code in the get to:
*notice that the viewstate key is a string

_MyName = Me.ViewState("MyName").ToString
Return _MyName

change the code in the set to:
*notice that the viewstate key is a string

_MyName = value
Me.ViewState("MyName") = _MyName

 

[Adam Sandler]

That was it... Thanks gents for the help!!!!

 

[Jimi200478]

you're very welcome. Happy Programming.