ASP.NET Discussion Boards

Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

Nadia Monalisa13-Aug-07 11:31

13-Aug-07 11:31

Hi,

I have developed a custom server control for .NET Framework 2.0. The server control has a property named BinaryData of type byte[]. I marked this property to be data bindable. Now, I have varbinary(Max) type of field in my SQL Database and I have used SQLDataSource and bound this varbinary(Max) field with the property BinaryData (byte[]) of my control. It is working fine as long as the data value is not NULL. Now, In my control, I have handled the NULL value so that no Exception is thrown. Still, when I bind this property using the SQLDataSource, I get Error "Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'." I am not sure if I can do anything to stop this erro within my control. If it is not possible from the control, then what is the workaround that I can do in my ASPX page in order to stop this error ?

Thanks a lot in advance.

Re: Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

Michael Sync13-Aug-07 15:40

Michael Sync

13-Aug-07 15:40

What about checking DbNull.Value before binding?

maybe. You can check the SQLDataSource whether any null value included in it or not..

OR, Is there any place where you were trying to cast the type?

Thanks and Regards,
Michael Sync ( Blog: http://michaelsync.net)

If you want to thank me for my help, please vote my message by clicking one of numbers beside "Rate this message". Why vote? Plz Read it here. Thank you.

Re: Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

Nadia Monalisa13-Aug-07 17:09

Nadia Monalisa

13-Aug-07 17:09

Dear Michael,

Thanks a lot for your reply. Actually I am the control developer and I am supplying my control to my client. Now, within my code, i have the property of byte[] type. And this property is databoundable. Now, where can I place your snippet in the code of my control ? I mean, my code has following definition of the byte[] type property,

<br />
1           private byte[] binData;<br />
2    <br />
3            [Bindable(true)]<br />
4            [Category("Data Input fields")]<br />
5            [Localizable(true)]<br />
6            public byte[] BinData<br />
7            {<br />
8                get<br />
9                {<br />
10                   try<br />
11                   {<br />
12                    <br />
13                   }<br />
14                   catch<br />
15                   {<br />
                          binData = null;<br />
16                   }<br />
17   <br />
18                   return binData;<br />
19               }<br />
20               set<br />
21               {<br />
22                   try<br />
23                   {<br />
24                       binData = value;<br />
25                   }<br />
26                   catch<br />
27                   {<br />
28                       binData = null;<br />
29                   }<br />
30   <br />
37               }<br />
38           }<br />
39

Now, How can I access the datareader of the SQLDataSource or any datasource that has bound this property and override this error message ?

Regards.

Re: Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

Michael Sync13-Aug-07 17:44

Michael Sync

13-Aug-07 17:44

I don't think that it's your responsibility to prevent this error. Let's say one simple one.

Example 1 ~

You are the control developer. So, you create one control that has one property. The type of this property is "int". I'm your client and I'm using your control in my problem. I wanna set one value to the property of your control. then, I wrote like yourcontrol.IntProperty = "Mike";. so, i will be getting the error since I'm setting wrong string data type to int type. In that situration, this is my responsibility for checking the datatype. (your client in your case.)

Do you get what I mean?

Example 2 ~

But let's say there is one function called "SetDataSource(DataTable)" in your control.

You wrote like that in that function of control ~

public void SetDataSource(DataTable dt){<br />
  foreach(DataRow dr in dt.Rows){<br />
    string str = (string)dr[0];  <br />
  }<br />
}

When the user is passing the datatable that contains NULL values, your function will throw the error.
For that case, you have the responsibility for checking whether this value is null or not before casting the type.

So, you decide your case is like example 1 or 2. I think your case is like example 1. so, i don't think you need to do something about it.

Re: Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

Nadia Monalisa13-Aug-07 23:51

Nadia Monalisa

13-Aug-07 23:51

Dear Michael,
thanks a lot again for your kind reply.

Actually, I was confused and I thought, may be I could do something within my sourcecode which could check the NULL value for the databound property. Because, when I have a label's Text property bound to a SQL varchar(x) type and if the SQL contains NULL for that varchar(x), we dont get this "Unable to cast....." Exception, rather, the Label shows Empty String. Same thing like CheckBox. If I bind "Checked" property of a checkbox to a SQL bit type field, and if SQL contains NULL value for that bit field, we dont get Exception, rather we see unchecked state of the CheckBox. So, I thought, the control developer made some smart way to handle databound NULL values for the Label and CheckBox. If so, as a developer, I also could do something for my Byte[] property.

If it is really not possible to implement solution within my control, what workaround I can suggest my client to overcome this error ? Because it is very usual that, his or her SQL Database may contain NULL values for the VarBinary(x) field and he/she wont like to get error for that, so he/she would like to know from me about the workaround.

I appreciate your kind help. Thanks a lot.

Regards,
Nishat

Re: Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

Member 766318817-Aug-11 8:00

Member 7663188

17-Aug-11 8:00

Hi,
Did you ever find a solution to this problem? I'm struggling with the exact same issue.
Many thanks,
Andrew

Datagrid help

Ridge Howison13-Aug-07 10:48

Ridge Howison

13-Aug-07 10:48

Hello All,

Thanks for reading this. Here is my issue. I have a datagrid which needs to show 3 columns from my database stored procedure. Lets say the stored proc returns a dataset with 3 columns A,B,C. In my datagrid I want to show columns A and B and keep column C invisible. No big deal right ? Okay here is the tricky part. If value of the data row for column C="General" then i want to make the entire row color Red(or the text color to turn red preferably) for that record.If the value of column C="Personal" i want the rowtext to remain black..but now i want to show a "Delete" hyperlink there, lets say clicking on it makes it go to another page.The "delete" hyperlink should not appear when the column C value is "General". I know the "Delete" hyperlink we can add as a column which is not visible, but cannot seem to figure the mechanics of it. How do I go about it ? All help is greatly appreciated. Code samples much more appreciated !!!

Regards
RH

Re: Datagrid help

Fred_Smith13-Aug-07 12:39

Fred_Smith

13-Aug-07 12:39

You need to investigate teh ItemDataBound event of teh dataGrid class...

This site:
http://www.datagridgirl.com/articles.aspx[^]

has loads of links and articles on the datagrid.

So does this one (and a lot else besides):

http://www.4guysfromrolla.com/[^]

Access Asp.net control from client side javascript

Ali Rafiee13-Aug-07 9:28

Ali Rafiee

13-Aug-07 9:28

Hi,

I have been trying to change the active tab of a Asp.Net AJAX toolkit tab container all day and I haven't been able to do it. I am new to both asp.net and javascript. I have done a couple of searches but nothing.

Here is the javascript that I am calling from my asp.net button OnClientClick handler. OnClientClick="return SwitchTab('TabContainer1');"

function SwitchTab(TabID)
{
var MyTab = document.getElementById(TabID);
// MyTab.style.display = "none"; //this line worked
MyTab.setAttribute('ActiveTabIndex','0');
return false;
}

How can I access the active tab attribute?

Thanks
Ali

AliR.
Visual C++ MVP

RadioButtonList and Hover Balloon

janetb9913-Aug-07 9:22

janetb99

13-Aug-07 9:22

I need to do a registration form for eucation classes, but some of the classes have concurrent sessions. I would like to use a RadioButtonList for each group, but would also like to be have to have a alt-type property or hover balloon to expand/collapse descriptions for each item within each radioButtonList. Anybody seen anything like that or am I just nuts?

Thanks, Janet

Re: RadioButtonList and Hover Balloon

N a v a n e e t h13-Aug-07 21:05

N a v a n e e t h

13-Aug-07 21:05

janetb99 wrote:
have a alt-type property or hover balloon to expand/collapse descriptions for each item within each radioButtonList

I have not seen anything for RadioButtonList. But you can try this[^] article which explains how to do this for textbox. You can easily port this for RadiobuttonList.

Or are you planning to develop from scratch ? Then start with capturing MouseOver event using javascript. Create a div element and assign InnerText to div. Find the position of RadioButton and place your div near to that. This will work something like a tool tip.

My Website | Ask smart questions

Recursion

seemamltn13-Aug-07 8:11

seemamltn

13-Aug-07 8:11

1) What will the value of txt be after executing MyFunction?

public void Main()
{
string txt = MyFunction( “12345” );
}

public string MyFunction( string str )
{
if( str.Length == 1 )
return str;
else
return MyFunction(str.Substring(1, str.Length - 1)) + str.Substring(0,1);
}
Hint:
String.Substring( startIndex, length )

Ans54321.

seema

Re: Recursion

Christian Graus13-Aug-07 8:21

Christian Graus

13-Aug-07 8:21

1 - do your own homework, that's what it's for
2 - don't spam the boards
3 - certainly don't post in the ASP.NET forum, with a question that has nothing to do with ASP.NET.

Christian Graus - Microsoft MVP - C++

"I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )

Creating a pager application help needed

ski_freak13-Aug-07 7:55

ski_freak

13-Aug-07 7:55

I am trying to determine if this can be done or not. My company would like to try to use .Net to set up a pager application. A user would list all their information, group they are in, application(s) they support etc. When someone needs to page a person on call they would logon to this application, select the person to page and it would send out a page.

Currently it is written in ASP.Net front end, and MVS back end using Cobol/DB2.

We would like to try to have this all on the .Net platform.

2 things that we need to work

1 - Send out pages to 1 or more at a time
2 - Automatic pages
a - if one group gets paged, automatically page another group
b - automaticaly page at a certain date/time

Can all of this be accomplished?

If so can you please get me started on where to look, code examples etc.

Thanks,
Mark

Re: Creating a pager application help needed

ToddHileHoffer13-Aug-07 8:09

ToddHileHoffer

13-Aug-07 8:09

Your first step should be contacting your wireless service provider. You'll need to check with them on how to send a page. They may have a web service, or a website you can write an http request to. They'll also let you know if you can find out if a page was responded to.

As for paging at a certain date and time. You can do that in .net code, but not via a web application. You'll need to code a windows service or use a sql server job or something. But that is still easy enough to do.

I didn't get any requirements for the signature

Persist Gridview Data

kjosh13-Aug-07 6:33

kjosh

13-Aug-07 6:33

Hi,

I have a Gridview. I am adding new row to Gridview with a button click which is outside gridview. User can add as many rows and I need to update all the rows with one button click. The user add row to gridview and enter some information in the new row and again when he adds new row the previously entered information is erasing. How to persist the gridview rows data.

Thanks

Re: Persist Gridview Data

ToddHileHoffer13-Aug-07 7:55

ToddHileHoffer

13-Aug-07 7:55

What you can do is store a dataTable in viewstate.
You can write code to update the dataTable from grid or add new rows to the table and rebind. Then iterate through the gidview to save to database.

If you need a code example I might be able to track it down for you.

I didn't get any requirements for the signature

Re: Persist Gridview Data

kjosh14-Aug-07 3:36

kjosh

14-Aug-07 3:36

Hi,
Thanks for your answer. I am storing the Data Table in Viewstate and adding the new row to Datatable. But I am not updating the Datatable. How to update the datatable.If you can Please provide me the example.

Thanks in advance

Gridview with validation

kjosh13-Aug-07 5:15

kjosh

13-Aug-07 5:15

Hi,
I have a gridview which contains the one ID column the user enters a new row to Gridview he enter some value to the ID column. On the ID TextChanged event I have to check whether this ID is exist in the database table or not. I am able to check the entered id against database table value. But here my question is if the entered id value not exist in the database then I am returing some 999 value. Then I have to provide validation error messages like “the Entered id doesnot exist” How to provide this validation.

Thanks

Access parent page controls from Iframe [modified]

rana7813-Aug-07 4:42

rana78

13-Aug-07 4:42

Hi All,
Can anybody let me know as to how can one access the parent page controls (textbox control value in my case) from within an iframe. I need to access the textbox control value on the parent page, for some logic impementation in my iframe code behind (.cs ). Can somebody answer me quick.

Thanks in Advance,
Rana78

-- modified at 10:56 Monday 13th August, 2007

s k bhuyan

Re: Access parent page controls from Iframe

Michael Sync13-Aug-07 5:49

Michael Sync

13-Aug-07 5:49

Use "top" keyword for accessing parent page.

Re: Access parent page controls from Iframe [modified]

rana7813-Aug-07 5:54

rana78

13-Aug-07 5:54

Michael ,can u please elaborate a little more(how do i use this keyword) more over i'am trying to access the parent page from server side code and not client end javascript !
Thanks,
Rana

-- modified at 12:04 Monday 13th August, 2007

Rana78

Re: Access parent page controls from Iframe

Michael Sync13-Aug-07 6:28

Michael Sync

13-Aug-07 6:28

AFAIK, you can't access the control of parent page from Code-behind. So, you have to use Javascript for accessing the parent page. After that, you have to look a tick to access this client-side value from Code-behind..

For example: There are one textbox called Textbox1 and IFRAME in Default.aspx. There is another page called Default2.aspx which suppose to be shown in IFRAME of Default.aspx page. We add one button called Button1 in Default2.aspx (ChildPage). We wanna get the value of Textbox1 that is placed in Default.aspx (parent page) from Default2.aspx (childpage).

So, we have to write the following ocde in Form_load event of default2.aspx.

Button1.Attributes.Add ("onclick", "alert(top.document.getElementById('TextBox1').value);");

Yeah. I know that it's not exactly what you want. But the idea is that you have to get the value of controls of the parent page by using Javascript. Then, try to find the way to access the those values from Code-behind. (Using Server-side hidden field is one of the communication between client-side script and server-side script. )

Hope it helps.

Re: Access parent page controls from Iframe

Nick.cheng.liu13-Aug-07 6:21

Nick.cheng.liu

13-Aug-07 6:21

You can do it with javascript.

For example:
add the following code on the child page

<br />
		<script language="javascript"><br />
		function Test()<br />
		{<br />
			var parentTextBox = parent.document.getElementById("TextBox1");<br />
//TextBox1 is the ID of TextBox on ParentPage.<br />
			<br />
			alert(parentTextBox.value);<br />
		}<br />
		</script><br />

I am learning english

Re: Access parent page controls from Iframe

Michael Sync13-Aug-07 6:31

Michael Sync

13-Aug-07 6:31

yeah. I agree with cheng.liu. Javascript is the only way you go.. Rana..

cheng.liu wrote:
I am learning english

Oh. yeah. Me too..

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