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Insert object into list in c #

I have a list of class objects UserData

. I am getting an object from this list using the methodwhere 

UserData.Where(s => s.ID == IDKey).ToList(); //ID is unique

I would like to make some changes to the object and paste at the same place in the list. However, I do not have an index of this object.

Any idea how to do this?

thank

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5 answers


When you get an item from LIST of its reference type, if you update something, it automatically changes the values ​​in LIST. After updating, check your identity ...........

The item you get from



UserData.Where(s => s.ID == IDKey).ToList();

is a reference type.

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You can get the index using the method UserData.FindIndex(s => s.ID == IDKey)

It will return int.



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While it UserData

is a reference type, the list contains only references to instances of that object. This way you can change your properties without needing to delete / insert (and obviously don't need the index of that object).

I also suggest that you use the method Single

(instead of ToList()

) as long as the id is unique.

Example

public void ChangeUserName(List<UserData> users, int userId, string newName)
{
     var user = users.Single(x=> x.UserId == userId);
     user.Name = newName;  // here you are changing the Name value of UserData objects, which is still part of the list
}
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just select the object with SingleOrDefault

and make the appropriate changes; you no longer need to add it to the list; you just change the same instance that is the list item.

var temp = UserData.SingleOrDefault(s => s.ID == IDKey);
// apply changes
temp.X = someValue;
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If I don't understand you, then please correct me, but I think you are saying that you essentially want to iterate over the elements of the list, and if that matches the condition, then you want to modify it in some way and add it to another list ...

If so, then please see the code below to see how to write an anonymous method using the Where clause. The Where clause just wants an anonymous function or delegate that matches the following:

: ElementType, int index - return: bool result

which allows you to either select or ignore an item based on a boolean return. This allows us to represent a simple boolean expression or a more complex function with additional steps:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace StackOverflow
{
    class Program
    {
        static void Main(string[] args)
        {
            int IDKey = 1;
            List<SomeClass> UserData = new List<SomeClass>()
            {
                new SomeClass(),
                new SomeClass(1),
                new SomeClass(2)
            };
            //This operation actually works by evaluating the condition provided and adding the
            //object s if the bool returned is true, but we can do other things too
            UserData.Where(s => s.ID == IDKey).ToList();
            //We can actually write an entire method inside the Where clause, like so:
            List<SomeClass> filteredList = UserData.Where((s) => //Create a parameter for the func<SomeClass,bool> by using (varName)
                {
                    bool theBooleanThatActuallyGetsReturnedInTheAboveVersion =
                        (s.ID == IDKey);
                    if (theBooleanThatActuallyGetsReturnedInTheAboveVersion) s.name = "Changed";
                    return theBooleanThatActuallyGetsReturnedInTheAboveVersion;
                }
            ).ToList();

            foreach (SomeClass item in filteredList)
            {
                Console.WriteLine(item.name);
            }
        }
    }
    class SomeClass
    {
        public int ID { get; set; }
        public string name { get; set; }
        public SomeClass(int id = 0, string name = "defaultName")
        {
            this.ID = id;
            this.name = name;
        }
    }
}
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