Updating an Object from a List in C#

How to update an object in a List<> in C#

Using Linq to find the object you can do:

var obj = myList.FirstOrDefault(x => x.MyProperty == myValue);
if (obj != null) obj.OtherProperty = newValue;

But in this case you might want to save the List into a Dictionary and use this instead:

// ... define after getting the List/Enumerable/whatever
var dict = myList.ToDictionary(x => x.MyProperty);
// ... somewhere in code
MyObject found;
if (dict.TryGetValue(myValue, out found)) found.OtherProperty = newValue;

C# update object in list

No because item is just a local variable, but you can use the indexer of the list:

int index = list.FindIndex(m => m.Id == viewModel.Id);
if(index >= 0)
    list[index] = viewModel;

Update items in List<T> c#

Since your list contains a mutable type, all you need to do is get a reference to the specific item you want to update.

That can be done in a number of ways - using it's index, using the Find method, or using linq are the first three that comes to mind.

Using index:

userData[0]?.Name = "CBA";

Using Find:

userData.Find(u => u.Name = "Abc")?.Name = "CBA";

Using linq (FirstOrDefault is not the only option):

userData.FirstOrDefault(u => u.Name = "Abc")?.Name = "CBA";

Note the use of null conditional operator (]? and .?) it prevents a null reference exception in case the item is not found.

Updating An object In A Collection C#

"How should I update the existingPepe"

There is no need to create a new instance of Person, you can update the property Age on the existing found instance directly. That mutates the actual instance itself. Doing that also means there is no need to swap the item in the List<Person>.

// note that SingleOrDefault will throw an exception if there is more than one match
var foundPerson = people.SingleOrDefault(a => a.id ==someId);
if(foundPerson != null)
  foundPerson.Age = 65;
// else person with that id does not exist in the list

If you want to have an exception thrown if there is no match then use Single instead.

var foundPerson = people.Single(a => a.id ==someId);
foundPerson.Age = 65;

Updating an object within a List of objects in C#

In the Update() function copycomp is referring to the object within
collection variable, so any changes made to the copycomp variable
doesn't need to assign it back to the collection like this :

The value of copycomp is a reference to the object collection.subComponent1, which is a List<SubComponent1>. When you call a method and pass copycomp as an argument (without the use of ref) you actually pass a copy of this reference, this is the default behavior in C# and in many other high level programming languages. Hence you still have a reference to the original object and you can alter any value there. Specifically in your case you can remove items from the list, add other items, change the value of a property of an item etc.

If the above is that you want you don't need the ref keyword. You should use the ref keyword if you want to change the reference that copycomp holds and then use the new reference for another purpose. In this case you could do any of the actions mentioned previously, which would result in the mutation of the object state that copycomp points to and in addition to this you could change even the actual reference that copycomp holds.

C# updating an object within a list

You are likely sharing the same object (reference) between 2 lists, so the price / name / or anything else will be reflected in both lists (as it's the same object).

You can think of a reference as a piece of paper which has the address of a physical location of stuff. When you are adding the reference to a list, or copy it. You are just coping the that piece of paper (the address). When you change a property, it looks up the actual physical location and it changes the stuff for everyone.

What you will need to do is clone your product. There are lots of ways to do this, some easier than others. However the most fundamental way is just copy the properties and state. Such that the internal state is the same.

var newProduk = new Produk() 
                     {
                         Price = produk.Price,
                         Name = produk.Name,
                         ...
                         // the rest of your state and properties
                     };

Tempuser._produk.Add(newProduk );

Update a List's object using Linq

You cannot replace the value in the list using LINQ, because LINQ is a projection of a collection.

You can get your item and then find it in the list using IndexOf:

var item = Items.Single(i => i.Code == line.Code);
int index = Items.IndexOf(item);
Items[index] = new Item(); // replace the value

However, this approach is far from optimal in terms of algorithmic complexity, because it has to read through your list multiple times.

You can try to read more on Dictionary to find, add or replace items by key (in your case, Code) efficiently.

Update an item in the list not working

Doing this:

var userToUpdate = userList.FirstOrDefault(r => r.IdUser == 3);

you get copy of reference that points to needed user. So, there are two different references pointing to this user: userToUpdate and reference inside userList.

When you assign newUser to userToUpdate you have one reference from list still pointing to the old user and you get reference userToUpdate pointing to newUser.

To update user you should do something like this:

var index = userList.FindIndex(r => r.IdUser == 3);

if (index != -1)
{
    userList[index].Id = newUser.Id,
    //set all other properties from newUser
}

OR

simpler way:

var index = userList.FindIndex(r => r.IdUser == 3);

if (index != -1)
{
    userList[index] = newUser;        
}

Update an Object by Matching with other Object Values depend on a Condition in C#

Thanks for those who tried to answer my question following solution worked for me

if (!string.IsNullOrWhiteSpace(caller) && !string.IsNullOrWhiteSpace(now) && !string.IsNullOrWhiteSpace(callee))
{
    var recentChannel = activeChannels.FirstOrDefault(c => c.CallerExt == caller && c.CalleeExt == callee);
    if (recentChannel != null)
        recentChannel.ChannelName = now;
}                                      

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