nPath Ltd. » Linq

Copy a generic list, List, by ref, by value wierdness

B.Harding — Mon, 19 Oct 2009 17:45:00 +0000

Here is my latest weird problem.

I had a generic list, I wanted to make a copy of it. So the aproach I used was to make the new list = the first one.

Enter the wierdness; any mods to the second list showed up in the first one. So I guess it used a pointer or passed it by reference instead of making a copy like I expected.

Live and learn I guess. The work around was to initialize it blank and call the add range function passing it the first list.

Here is an example of what I’m talking about. You can past this into Linqpad as C# Statements and play around more.

List<string> s1 = new List<string>{“one”,“two”,“three”,“four”,“five”};

List<string> s2 = s1;

s2.Add(“six”);

s2.Add(“seven”);

s1.Dump();

s2.Dump();
List<string> s3 = new List<string>{};

s3.AddRange(s1);

s3.Add(“eight”);

s3.Add(“nine”);

s3.Add(“ten”);

s1.Dump();

s3.Dump();

Returns:

5List (7 items)

one

two

three

four

five

six

seven

5List (7 items)

one

two

three

four

five

six

seven

5List (7 items)

one

two

three

four

five

six

seven

5List (10 items)

one

two

three

four

five

six

seven

eight

nine

ten

Insert with FormView using Linq

B.Harding — Thu, 05 Feb 2009 17:05:40 +0000

I had a wierd error trying to insert data using a formview today.

The jist is this: the formview was trying to use an empty string for an int field instead of Nothing.
Here is the error I saw, helpful huh?

Failed to set one or more properties on type xxxxxxx Ensure that the input values are valid and can be converted to the corresponding property types.

The fields are allowed to be null but the formview just isn’t smart enough to use nothing instead of “”.

My workaround was simple and flexible enough to be re-used so I figured I would post it here.
I simply hijack the formview’s onInserting and replaced “” with Nothing for each field.

Protected Sub formView1_ItemInserting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.FormViewInsertEventArgs)

For Each o As DictionaryEntry In e.Values
If o.Value = “” Then e.Values(o.Key) = Nothing
Next

End Sub

Operator ‘==’ incompatible with operand types ‘Int32′ and ‘Object’

B.Harding — Thu, 05 Feb 2009 16:49:52 +0000

I had this error pop up on me recently.

Operator ‘==’ incompatible with operand types ‘Int32′ and ‘Object’

I had an good grasp on why but the stack track would not tell me where!

The issue is that a null object was being used in a where clause somewhere. Linq translated the null as “” and could not be compared the the ID field which is an int.

My solution was to simply check each key and cancel the action if there is a null value.

Since I couldn’t tell which Linq Data source was crashing I wired up on selecting events for them ALL and put the following code in:

foreach (KeyValuePair<string, object> kvp in e.WhereParameters)
{

if (kvp.Value == null){

e.Cancel = true;

return;

}

Problem solved.