Hi I Get This Eror Cast Not Valid

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morining all im trying to display data from a table into a combo box(usernames in a combo box) but i sorted most errors that i got .
"my error" System.InvalidCastException: Specified cast is not valid.
also i only get this message when i debug the program and open that form

my code>
private void add_user_Load(object sender, EventArgs e)
{
DataSet Ds = new DataSet();

string strConnectionString = "Data Source=JAMES-PC\\SQLEXPRESS;Initial Catalog=login1;Integrated Security=True";

SqlConnection objconnection = new SqlConnection(strConnectionString);
using (SqlCommand cmd = new SqlCommand("SELECT [username] FROM [user1]",
objconnection))
{
using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))
{
adapter.Fill(Ds);
}
}

var empList = Ds.Tables[0].AsEnumerable().Select(dataRow =>

dataRow.Field<int>("username")).ToList();
comboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
comboBox1.DataSource = empList;

comboBox1.SelectedIndex = 0;

C#

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            textBox1.Text = comboBox1.SelectedItem.ToString();
        }

any help would be much apreciated,thanks in advance

Posted 4-Aug-15 21:21pm

jamesmc1535

Updated 4-Aug-15 21:29pm

v2

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Comments

Sergey Alexandrovich Kryukov 5-Aug-15 3:34am

In what line?
—SA

jamesmc1535 5-Aug-15 3:37am

i dont know visual studios starts perfectly , its when i run the program and open that form (add user) that i get that error

2 solutions

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Animesh Datta · Accepted Answer · 2015-08-04T21:37:00

Solution 1

Hello ,
This type of error comes for Invalid casting or explicit conversion.Check whether "username" is Integer or other datatype.

Posted 4-Aug-15 21:37pm

Animesh Datta

OriginalGriff · Accepted Answer · 2015-08-04T21:41:00

Solution 2

Run the application in the debugger: when the exception occurs, it will stop and VS will show you the line it picked up the problem with.
The chances are that it's to do with your Linq Select anonymous method, and that your usernames are not all integers. So when the breakpoint hits, look at the data in your DataTable and check.

We can't do that for you - we can't run your code, and we don;t have access to your database!

BTW: If you are going to use using blocks - and it's a damn good idea - then put one round the SqlConnection object as well!

Posted 4-Aug-15 21:41pm

OriginalGriff

Comments

jamesmc1535 5-Aug-15 3:47am

thanks for the advice i will check quickly , when i run it and i get te eror i have the options,, details and continue,and quit but when i quit it doesnt show the line thats faulty, if i say continue the combobox is still emty XD (oviously) but the details shows this

See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.InvalidCastException: Specified cast is not valid.
at System.Data.DataRowExtensions.UnboxT`1.ValueField(Object value)
at login_form.add_user.<>c.<add_user_load>b__2_0(DataRow dataRow) in C:\Users\james\New folder\POS\pos\login form\add user.cs:line 53
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at login_form.add_user.add_user_Load(Object sender, EventArgs e) in C:\Users\james\New folder\POS\pos\login form\add user.cs:line 51
at System.Windows.Forms.Form.OnLoad(EventArgs e)
at System.Windows.Forms.Form.OnCreateControl()
at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
at System.Windows.Forms.Control.CreateControl()
at System.Windows.Forms.Control.WmShowWindow(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.Form.WmShowWindow(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

************** Loaded Assemblies **************
mscorlib
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/mscorlib.dll
----------------------------------------
login form
Assembly Version: 1.0.0.0
Win32 Version: 1.0.0.0
CodeBase: file:///C:/Users/james/New%20folder/POS/pos/login%20form/bin/Debug/login%20form.exe
----------------------------------------
System.Windows.Forms
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Windows.Forms/v4.0_4.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System/v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Drawing
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Drawing/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
System.Configuration
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Configuration/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
System.Core
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Core/v4.0_4.0.0.0__b77a5c561934e089/System.Core.dll
----------------------------------------
System.Xml
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Xml/v4.0_4.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
Accessibility
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/Accessibility/v4.0_4.0.0.0__b03f5f7f11d50a3a/Accessibility.dll
----------------------------------------
System.Data
Assembly Version: 4.0.0.0
Win32 Version: 4.6.81.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_64/S

OriginalGriff 5-Aug-15 4:02am

And when you get that box, it is showing the line in your source.
So. Put a breakpoint on the line
var empList = Ds.Tables[0].AsEnumerable().Select(dataRow => dataRow.Field<int>("username")).ToList();
and look at the DataTable content before it is executed.
Or even - look at the user1 table in SSMS! :laugh:

jamesmc1535 5-Aug-15 4:18am

lol XD this sqls doesnt like me, struggle alot with it -_- my mind just doesnt want to learn thanks il go do a quick check :)

jamesmc1535 5-Aug-15 4:48am

i entered it as u said but my datarow says does not exist , shud i create it or am i missing a refrence?

OriginalGriff 5-Aug-15 5:41am

Share the exact code you used, and the exact error message.

jamesmc1535 5-Aug-15 5:48am

my code >DataSet Ds = new DataSet();

string strConnectionString = "Data Source=JAMES-PC\\SQLEXPRESS;Initial Catalog=login1;Integrated Security=True";

SqlConnection objconnection = new SqlConnection(strConnectionString);
using (SqlCommand cmd = new SqlCommand("SELECT [username] FROM [user1]",
objconnection))
{
using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))
{
adapter.Fill(Ds);
}
}

var empList = Ds.Tables[0].AsEnumerable().Select(dataRow => dataRow.Field("username")).ToList();

dataRow.Field<int>("username")).ToList();
comboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
comboBox1.DataSource = empList;

comboBox1.SelectedIndex = 0;
my errors>The name 'dataRow' does not exist in the current context
The name 'ToList' does not exist in the current context
The type arguments for method
'DataRowExtensions.Field<t>(DataRow, string)'
cannot be inferred from the usage. Try specifying the type
arguments explicitly.

OriginalGriff 5-Aug-15 5:52am

:sigh:
Look at your code:

var empList = Ds.Tables[0].AsEnumerable().Select(dataRow => dataRow.Field("username")).ToList();

dataRow.Field("username")).ToList();

Why do you have the second bit there at all?

jamesmc1535 5-Aug-15 6:02am

thanks didnt notice i did it there, sorry if im asking stupid questions, but i might ask 1 more :) i remove the second part but i stil do get this>
The type arguments for method 'DataRowExtensions.Field<t>(DataRow, string)' cannot be inferred from the usage. Try specifying the type arguments explicity
code>var empList = Ds.Tables[0].AsEnumerable().Select(dataRow => dataRow.Field("username")).ToList();

comboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
comboBox1.DataSource = empList;

OriginalGriff 5-Aug-15 6:27am

Ah...yes...DataRow.Field(string name) is a generic extension method returns an type which depends on the content - so the appropriate datatype can't be determined at compile time to assign the var empList correctly.
Cast the field to the appropriate datatype (probably string) and it should work.

jamesmc1535 5-Aug-15 6:42am

its working, thanks alot man i apreciate it alot

OriginalGriff 5-Aug-15 6:56am

You're welcome!