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Delete the current element in an array

How can I delete the current element of an array inside a foreach-loop?
My program gets data form a DB and sends it to a new one via HTTP requests. Now I want to post a JSON string to my new DB. If it was a success I want to delete the current array item which I'm working with. Something like this.
foreach(var item in array)
{
bool decide = method.DoSomething();
if(decide == true)
{
//delete current item
}
}

since you cannot delete items from an array and change the size of it here is a loop approach using a second collection
List<itemClass> keepCollection = new List<itemClass>();
foreach(var item in array)
{
bool decide = method.DoSomething();
if(decide == false)
{
keepCollection.Add(item);
}
}
If you need it again in array form just call ToArray()
var finalResult = keepCollection.ToArray();

appraoch with Linq which creates a new array with valid elements and overwrites the existing array
array = array.Where(x => !method.DoSomething(x)).ToArray(); //select valid elements

there are 2 ways (both were tested)
foreach (var item in array.ToList())
{
bool decide = method.DoSomething();
if (decide == true)
{
item.Remove();
}
}
and
for ( i=0; i < array.Length; i++)
{
bool decide = method.DoSomething();
if (decide == true)
{
array[i].Remove();
}
}

Whenever you want to delete entries from a collection, you should never loop through that collection from beginning to end, but always from end back to beginning.
By the way, C# does not allow you deleting entries from a collection while looping through that collection using a foreach loop.

Can not find index of combobox item when using a List as datasource

I'm populating a list from a LINQ Query, then I am using the list as the data source for a combo box.
I am then trying to select items within the combo box but it doesn't seem to be able to find the index
using (var db = new CruxEntities())
{
var query = from q in db.Businesses
where q.BusinessID == BusinessId
select q;
var B = query.FirstOrDefault();
if (B != null)
{
// other form controls populated
var sites = B.TblBusinessSites.ToList();
this.comboBox.DisplayMember = "SiteName";
this.comboBox.ValueMember = "BusinessSiteID";
this.comboBox.DataSource = sites;
int index = comboBox.FindString(B.IdFromLinq);
}
}
index always has the value of -1 assigned to it but i've stepped through the code and I know that the value exists in the list... it seems to be that the rest of the code is not recognising that the combo box has the values.
What am I missing?
Edit
I got the index fine... but something I missed out from my initial post is that there are 2 combo boxes bound to the list... I get the indexes for both of them fine when I step through the code but the combo boxes seem linked so I assigning the index to either one seems to assign it to both...
index = sites.FindIndex(s => s.BusinessSiteID == B.PrimarySiteDeliveryID);
comboBox_DefaultDeliverySite.SelectedIndex = index;
index = sites.FindIndex(s => s.BusinessSiteID == B.PrimarySiteInvoiceID);
comboBox_DefaultInvoiceSite.SelectedIndex = index;

You can't find site index because FindString method checks item's displayed text (site name in your case), but you are trying to search by ID, which is item's value.
Actually you even don't need to touch combobox here, because items will be added in same order as you have them in sites collection. To get index of some site you can just search index of site in sites list:
int index = sites.FindIndex(s => s.BusinessSiteID == B.IdFromLinq);

The FindString method is not a good choice, since you are binding with objects, so stick to object, not string.
You can loop on your item instead :
foreach(var item in comboBox.Items)
{
var businessSite = item as BusinessSite;
if(businessSite != null && businessSite.BusinessSiteID == B.IdFromLinq)
{
// your item here
}
}
Or index based:
for(int index = 0; index < comboBox.Items.Count; index++)
{
var item = comboBox.Items[index];
var businessSite = item as BusinessSite;
if(businessSite != null && businessSite.BusinessSiteID == B.IdFromLinq)
{
return index;
}
}

Removing Item from List<DBTables> in C# [duplicate]

This question already has answers here:
What is the best way to modify a list in a 'foreach' loop?
(11 answers)
Closed 9 years ago.
I am currently working on a C# WPF project. I have a list which uses a class to store multiple values. The class is called DBTables and has the following inside:
class DBTables
{
public string selDatabase { get; set; }
public string selTable { get; set; }
}
I am creating a new instance of the list with the following code
List<DBTables> tableArr = new List<DBTables>();
I am adding new items to the List without any problems but the problem I am having is when it comes to removing an item from the list.
A an item is added to the list when a checkbox is selected the item is added and when the checkbox is unchecked the item needs to be removed. Each time the checkbox is checked two values are added using the following code:
private void addBackupArray(string table)
{
backupArr.Add(new DBTables
{
selDatabase = selectedDatabase,
selTable = table
});
}
When the check box is unchecked the values at the position need to be removed and I have sort of got it working but after it has removed the item it then displays the error 'InvalidOperationException, collection was modified; enumeration may not execute'.
Below is the code that I am currently using to remove the item from the list.
private void removeBackupArray(string table)
{
int i = 0;
foreach (DBTables tables in backupArr)
{
if (selectedDatabase == tables.selDatabase && table == tables.selTable)
{
backupArr.RemoveAt(i);
i = 0;
}
i++;
}
}
The code above iterates through the values in the list and based on an if statement of whether the two variables match the value found in the list it removes it at the current position of the counter i.
How can I get round this issue so I can remove the item without getting the error.
Thanks for any help you can provide.

Change the foreach to normal for loop will fix the issue:
for (int tablesIndex = 0; tablesIndex < backupArr.Count; tablesIndex++)
{
var tables = backupArr[tablesIndex];
if (selectedDatabase == tables.selDatabase && table == tables.selTable)
{
backupArr.RemoveAt(tablesIndex);
tablesIndex--;
}
}

Changed your foreach to a for loop. The foreach uses an enumerator to iterate over all of the objects in the List. You can't change the contents of the enumerator within the foreach or you'll get the error you see.
Give this a try instead
int i;
for (i = 0; i < backupArr.Count; i++)
{
DBTables tables = backupArr[i];
if (selectedDatabase == tables.selDatabase && table == tables.selTable)
{
break;
}
}
backupArr.RemoveAt(i);

A neater solution could be to use a linq like so:
DBTables tables = backupArr.Where(t => t.selDatabase == selectedDatabase && t.selTable == table).SingleOrDefault();
if (tables != null)
backupArr.Remove(tables);

Update List element at specified list item position

I am trying to do this:
foreach (Settings sets in MySets)
{
if (sets.pName == item.SubItems[2].Text)
{
var ss = new SettingsForm(sets);
if (ss.ShowDialog() == DialogResult.OK)
{
if (ss.ResultSave)
{
sets = ss.getSettings();
}
}
return;
}
}
But since the sets spawned variable is readonly, I cant override it.
I would also like to do something like this
foreach (Settings sets in MySets)
{
if(sets.pName == someName)
sets.RemoveFromList();
}
How can I accomplish this? Lists have a very nice Add() method, but they forgot the rest :(

You can use:
MySets.RemoveAll(sets => sets.pName == someName);
to remove all the items that satisfy a specific condition.
If you want to grab all the items satisfying a condition without touching the original list, you can try:
List<Settings> selectedItems = MySets.FindAll(sets => sets.pName == someName);
foreach loops don't work here as trying to change the underlying list will cause an exception in the next iteration of the loop. Of course, you can use a for loop and manually index the list. However, you should be very careful not to miss any items in the process of removing an item from the list (since the index of all the following items will get decremented if an element is removed):
for (int i = 0; i < MySets.Count; ++i) {
var sets = MySets[i]; // simulate `foreach` current variable
// The rest of the code will be pretty much unchanged.
// Now, you can set `MySets[i]` to a new object if you wish so:
// MySets[i] = new Settings();
//
// If you need to remove the item from a list and need to continue processing
// the next item: (decrementing the index var is important here)
// MySets.RemoveAt(i--);
// continue;
if (sets.pName == item.SubItems[2].Text)
{
var ss = new SettingsForm(sets);
if (ss.ShowDialog() == DialogResult.OK)
{
if (ss.ResultSave)
{
// Assigning to `sets` is not useful. Directly modify the list:
MySets[i] = ss.getSettings();
}
}
return;
}
}

You can't do it in a 'regular' for loop?

Prevent double entries in ListView using C#?

How can we access the items added to a ListView?
The thing I have to do is: add an item to the list view. I want to check if the item to add to the listview is already present in the ListView.
I'm using C# and Visual Studio 2005.

The ListView class provides a few different methods to determine if an item exists:
Using Contains on the Items collection
Using one of the FindItemWithText methods
They can be used in the following manner:
// assuming you had a pre-existing item
ListViewItem item = ListView1.FindItemWithText("test");
if (!ListView1.Items.Contains(item))
{
// doesn't exist, add it
}
// or you could find it by the item's text value
ListViewItem item = ListView1.FindItemWithText("test");
if (item != null)
{
// it exists
}
else
{
// doesn't exist
}
// you can also use the overloaded method to match sub items
ListViewItem item = ListView1.FindItemWithText("world", true, 0);

Just add your items and make sure you assign a name. Then
just use the ContainsKey method of the Items collection to
determine if it's there, like this.
for (int i = 0; i < 20; i++)
{
ListViewItem item = new ListViewItem("Item" + i.ToString("00"));
item.Name = "Item"+ i.ToString("00");
listView1.Items.Add(item);
}
MessageBox.Show(listView1.Items.ContainsKey("Item00").ToString()); // True
MessageBox.Show(listView1.Items.ContainsKey("Item20").ToString()); // False

You could do something like this:
ListViewItem itemToAdd;
bool exists = false;
foreach (ListViewItem item in yourListView.Items)
{
if(item == itemToAdd)
exists=true;
}
if(!exists)
yourListView.Items.Add(itemToAdd);

The following will help to locate a ListViewItem within the ListView control once you've added it:
string key = <some generated value that defines the key per item>;
if (!theListViewControl.Items.ContainsKey(key))
{
item = theListViewControl.Items.Add(key, "initial text", -1);
}
// now we get the list item based on the key, since we already
// added it if it does not exist
item = theListViewControl.Items[key];
...
Note
The key used to add the item to the ListView items collection can be any unique value that can identify the ListViewItem within the collection of items. For example, it could be a hashcode value or some property on an object attached to the ListViewItem.

A small correction in Robban's answer
ListViewItem itemToAdd;
bool exists = false;
foreach (ListViewItem item in yourListView.Items)
{
if(item == itemToAdd)
{
exists=true;
break; // Break the loop if the item found.
}
}
if(!exists)
{
yourListView.Items.Add(itemToAdd);
}
else
{
MessageBox.Show("This item already exists");
}

In case of multicolumn ListView, you can use following code to prevent duplicate entry according to any column:
Let us suppose there is a class Judge like this
public class Judge
{
public string judgename;
public bool judgement;
public string sequence;
public bool author;
public int id;
}
And i want to add unique object of this class in a ListView. In this class id is unique field, so I can check unique record in ListView with the help of this field.
Judge judge = new Judge
{
judgename = comboName.Text,
judgement = checkjudgement.Checked,
sequence = txtsequence.Text,
author = checkauthor.Checked,
id = Convert.ToInt32(comboName.SelectedValue)
};
ListViewItem lvi = new ListViewItem(judge.judgename);
lvi.SubItems.Add(judge.judgement ? "Yes" : "No");
lvi.SubItems.Add(string.IsNullOrEmpty(judge.sequence) ? "" : txtsequence.Text);
lvi.SubItems.Add(judge.author ? "Yes" : "No");
lvi.SubItems.Add((judge.id).ToString());
if (listView1.Items.Count != 0)
{
ListViewItem item = listView1.FindItemWithText(comboName.SelectedValue.ToString(), true, 0);
if (item != null)
{
// it exists
}
else
{
// doesn't exist
}
}