Casting generic lists - C# Discussion Boards

24-Oct-06 1:00

Is there a way of casting a generic list to another one, best way to explain what I want is, imagine the following scenario

public class Customer : Person { ... }
public class Criminal : Person { ... }

Now there's a dictionary object to provide a lookup table:

Dictionary<Type, List<Person>> lists;

And I'd like this dictioanry to contain a list of Customers and Criminals so...

lists.Add(typeof(Customer), new List<Customer>());
lists.Add(typeof(Criminal), new List<Criminal>());

However this complains that there's no conversion between List<Customer> and List<Person>.

This code will be accessed later on, for arguments sake through a method like this:

public List<T> GetList<T>() where T : Person
{
    return lists[typeof(T)];
}

Anybody have any ideas on how to accomplish this. The objects (Customer and Criminal) can be cast to Person and back again but it does not like casting the lists. Any ideas on "fooling" the compiler into doing what I want?

Sig cops got me...

Ed.Poore24-Oct-06 1:16

24-Oct-06 1:16

I've found a work-around (not very nice but it works), declare Dictionary<Type, object> lists;

Sig cops got me...

Not Active24-Oct-06 3:07

Not Active

24-Oct-06 3:07

You could use a Converter

<code>

List<Customer> customers = new Converter<Customer, Person>( CustomerToPerson )

private Person CustomerToPerson(Customer c)
{
return (Person)c; // More complicated I know, but you get the idea
}</code>

only two letters away from being an asset

Ed.Poore24-Oct-06 3:47

24-Oct-06 3:47

I did think of something along those lines but doing that would result in potentially thousands of casts. (Maybe I'm being stupid though), but the way I'm doing it at the moment only has one cast and it's hidden in the internal implementation anyway so I'll go with that for the time being until I can think of a better way, or MS decide to fix the "problem".

Sig cops got me...

Daniel Grunwald24-Oct-06 5:21

Daniel Grunwald

24-Oct-06 5:21

You cannot cast a List<customer> to List<person> because List<person> supports .Add(person), but you then you could add criminals to your customers list.

Ed.Poore24-Oct-06 5:36

Newbie: Porblem with ListView...

24-Oct-06 5:36

Yep, I agree, that's why it's complaining, but then again it won't let me add a List<Criminal> to the dictionary in the first place which would have solved these "problems".

I think that the only half-decent way around this is to use the dictionary to store objects. I just have to make sure that it never returns the wrong object to cast.

Sig cops got me...

Phillip Hodges24-Oct-06 0:10

Phillip Hodges

24-Oct-06 0:10

Hello all, I am having a little trouble with a ListView. I am trying to update an item but it isn't doing what it should...

To explain: I have a list containing about 20 items. I can find the index location for the item I want to update. I am then removing the old item at the found index location, and then inserting the new item at the same point. It works, but with one problem...

It isn't inserting the new item at the correct index position. Instead it is putting it at the bottom of the list... And I can't work out why??

I am viewing the list in 'tile' view.

Can anybody help?

Thanks in advance,

Phil

"Rules are for the obedience of fools and the guidance of wise men"

Re: Newbie: Porblem with ListView...

baerten24-Oct-06 2:34

baerten

24-Oct-06 2:34

Hello,

You tried already :

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemwindowsformslistviewlistviewitemcollectionclassinserttopic.asp

Creates a new item and inserts it into the collection at the specified index.

[C#] public ListViewItem Insert(int, string);

that doesn't work?

You have some code ?

Re: Newbie: Porblem with ListView...

Phillip Hodges24-Oct-06 22:03

Phillip Hodges

24-Oct-06 22:03

Thanks for the reply...

I can insert the item. It is just not being inserted where I asked it to be...

Here is the code:

// Find location of original item in listview<br />
                    ListViewItem temp = new ListViewItem();<br />
                    temp = listView_main.FindItemWithText(item_text, true, 0);<br />
                    int location = temp.Index;<br />
<br />
                    // Create listview item<br />
                    ListViewItem lvItem = new ListViewItem(item_text, icon);<br />
                    lvItem.SubItems.Add("Name:" + name + "(" + aka + ")");<br />
                    lvItem.SubItems.Add("Data:" + data);<br />
                    lvItem.ToolTipText = item.ToString();<br />
                    lvItem.Group = listView_main.Groups[0];<br />
<br />
                    // Remove old item in listview<br />
                    listView_main.Items.RemoveAt(location);<br />
<br />
                    // Add new item to listview<br />
                    listView_main.Items.Insert(location, lvItem);

Hope that helps...

Phil

"Rules are for the obedience of fools and the guidance of wise men"

Re: Newbie: Porblem with ListView...

baerten25-Oct-06 0:07

baerten

25-Oct-06 0:07

namespace codepro
{
///

/// Zusammenfassung für Form1.
///

public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.ListView TheList;
private System.Windows.Forms.ColumnHeader columnHeader1;
private System.Windows.Forms.ColumnHeader columnHeader2;
private System.Windows.Forms.Button button1;
///

/// Erforderliche Designervariable.
///

private System.ComponentModel.Container components = null;

public Form1()
{
//
// Erforderlich für die Windows Form-Designerunterstützung
//
InitializeComponent();

//
// TODO: Fügen Sie den Konstruktorcode nach dem Aufruf von InitializeComponent hinzu
//
}

///

/// Die verwendeten Ressourcen bereinigen.
///

protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Vom Windows Form-Designer generierter Code
///

/// Erforderliche Methode für die Designerunterstützung.
/// Der Inhalt der Methode darf nicht mit dem Code-Editor geändert werden.
///

private void InitializeComponent()
{
System.Windows.Forms.ListViewItem listViewItem1 = new System.Windows.Forms.ListViewItem(new string[] {
"One",
"1.2.",
"1.3.",
"1.4."}, -1);
System.Windows.Forms.ListViewItem listViewItem2 = new System.Windows.Forms.ListViewItem(new string[] {
"Two",
"2.1.",
"2.2.",
"2.3."}, -1);
System.Windows.Forms.ListViewItem listViewItem3 = new System.Windows.Forms.ListViewItem(new string[] {
"Four",
"4.1.",
"4.2.",
"4.3."}, -1);
this.TheList = new System.Windows.Forms.ListView();
this.columnHeader1 = new System.Windows.Forms.ColumnHeader();
this.columnHeader2 = new System.Windows.Forms.ColumnHeader();
this.button1 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// TheList
//
this.TheList.Columns.AddRange(new System.Windows.Forms.ColumnHeader[] {
this.columnHeader1,
this.columnHeader2});
this.TheList.Items.AddRange(new System.Windows.Forms.ListViewItem[] {
listViewItem1,
listViewItem2,
listViewItem3});
this.TheList.Location = new System.Drawing.Point(24, 16);
this.TheList.Name = "TheList";
this.TheList.Size = new System.Drawing.Size(200, 232);
this.TheList.TabIndex = 0;
this.TheList.View = System.Windows.Forms.View.List;
this.TheList.SelectedIndexChanged += new System.EventHandler(this.TheList_SelectedIndexChanged);
//
// columnHeader1
//
this.columnHeader1.Text = ":: 1 ::";
//
// columnHeader2
//
this.columnHeader2.Text = ":: 2 ::";
//
// button1
//
this.button1.Location = new System.Drawing.Point(240, 80);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(48, 64);
this.button1.TabIndex = 1;
this.button1.Text = "button1";
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(292, 266);
this.Controls.Add(this.button1);
this.Controls.Add(this.TheList);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);

}
#endregion

///

/// Der Haupteinstiegspunkt für die Anwendung.
///

[STAThread]
static void Main()
{
Application.Run(new Form1());
}

private void TheList_SelectedIndexChanged(object sender, System.EventArgs e)
{

}

private void button1_Click(object sender, System.EventArgs e)
{
System.Windows.Forms.ListViewItem listViewItemIns = new System.Windows.Forms.ListViewItem(new string[] {
"Three",
"3.1.",
"3.2.",
"3.3."}, -1);
TheList.Items.Insert(2,listViewItemIns);
Refresh();
}
}
}

The button1_Click inserts the Item "Three" at the correct place

So i doesn't see a mistake in you code Sigh | :sigh:

Date Of Birth

bhanu1234523-Oct-06 23:33

bhanu12345

23-Oct-06 23:33

I am using a textbox which takes date of birth as input
I want to use regular expression validator for that textbox
The Date Format Should Be mm/dd/yyyy
and valid date
Can Enyone Hel me Out

Jon Hulatt23-Oct-06 23:48

Jon Hulatt

23-Oct-06 23:48

http://regexlib.com/

using System.Beer;

V.24-Oct-06 0:43

24-Oct-06 0:43

You can use a Masked Textbox?

V.

Stop smoking so you can: Enjoy longer the money you save.
Moviereview Archive

Ed.Poore24-Oct-06 1:02

24-Oct-06 1:02

If you want a regex the following should work

\d{2}/\d{2}/\d{4}

Not very advanced, just checks for 2 digits followed by a slash and 2 more digits, then a slash then a group of four digits.

Sig cops got me...

Guffa24-Oct-06 1:02

Guffa

24-Oct-06 1:02

You can use a pattern like "\d{2}/\d{2}/\d{4}" to validate only the format. You can rule out dates that clearly are invalid with a pattern like "(0[1-9]|[12]\d|3[01])/(0[1-9]|1[0-2])/(19|20)\d\d", but a pattern that would actually check if the date is valid would be extremely complex. Just imagine all the combinations to validate the correct number of days in the different months, then imagine leap years on top of that...

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