How to get rid of this invalid cast exception?

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So, I've been continously working on my little project with more or less success but find myself in front of a problem I seemingly can't solve on my own. I get thrown an InvalidCastException when I'm basically just reusing a function that works already.

What I have tried:

var c = (customerDB)comboBox1.SelectedItem;
newContact.Name = textBox_Contact_Name.Text.Trim();
newContact.Vorname = textbox_Contact_Firstname.Text.Trim();
newContact.FKKunde = c.PKCustomer;

db.Contacts.Add(newContact);
db.SaveChanges();
Close();

The above code is the snippet that works, below is the one that doesn't.

var b = (TArticle)comboBox_Article.SelectedItem;
TPosition newPosition = new TPosition();


newPosition.FKArticle = b.PKArticle;
newPosition.Quantity = (int)numericUpDown_Menge.Value;
newPosition.Position = textBox_Position.Text;
db.TPosition.Add(newPosition);
db.SaveChanges();
Close();

It seems like the same to me, yet the second one doesn't run properly. The exception is thrown when declaring var b.

Posted 7-May-18 21:11pm

Member 13783935

Updated 8-May-18 0:04am

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Maciej Los 8-May-18 4:36am

Check what type of object is stored in comboBox_Article.SelectedItem.

var b = comboBox_Article.SelectedItem;
if(typeof(TArticle)==b.GetType())
{
    //further instructions
}

I'm pretty sure that comboBox_Article.SelectedItem is type of object (or null).

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OriginalGriff · Answer 1 · 2018-05-07T21:33:00

The item in the ComboBox is an instance of a customerDB in the first case, but it isn't an instance of a TArticle or a class derived from TArticle in the second. If the instance is of a class that cannot be cast to the required type, you will get an invalid cast exception.

Start by using the debugger to find out exactly what the selected item actually is: when you know that, you can start looking at why it isn't what you thought it was, or work out what class you should be converting it to.

Maciej Los · Answer 2 · 2018-05-08T00:05:00

The simplest way to get rid InvalidCastException message is to use try-catch (C# Reference) | Microsoft Docs[^] block.

For further details, please see:
Casting and Type Conversions (C# Programming Guide) | Microsoft Docs[^]
How to: Safely Cast by Using as and is Operators (C# Programming Guide) | Microsoft Docs[^]
Boxing and Unboxing (C# Programming Guide) | Microsoft Docs[^]

How to get rid of this invalid cast exception?

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