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

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最佳答案

使用 Linq 查找您可以执行的对象:

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

但在这种情况下，您可能希望将 List 保存到 Dictionary 中，然后使用以下命令:

// ... 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;

小开

或者没有 Linq

foreach(MyObject obj in myList)
{
if(obj.prop == someValue)
{
obj.otherProp = newValue;
break;
}
}

小开

只是为了加强柯尼格的回应。只要您正在处理的类是引用类型(比如类) ，他的答案就会有效。如果自定义对象是一个 struct，那么这就是一个值类型，并且 .FirstOrDefault的结果会给你一个它的本地副本，这意味着它不会持久地返回到集合中，如下例所示:

struct MyStruct
{
public int TheValue { get; set; }
}

测试代码:

List<MyStruct> coll = new List<MyStruct> {
new MyStruct {TheValue = 10},
new MyStruct {TheValue = 1},
new MyStruct {TheValue = 145},
};
var found = coll.FirstOrDefault(c => c.TheValue == 1);
found.TheValue = 12;


foreach (var myStruct in coll)
{
Console.WriteLine(myStruct.TheValue);
}
Console.ReadLine();

输出是10,1,145

将 struct 更改为类，输出为10、12、145

高温

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也可以试试。

 _lstProductDetail.Where(S => S.ProductID == "")
.Select(S => { S.ProductPcs = "Update Value" ; return S; }).ToList();

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var itemIndex = listObject.FindIndex(x => x == SomeSpecialCondition());
var item = listObject.ElementAt(itemIndex);
item.SomePropYouWantToChange = "yourNewValue";

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你可以这样做:

if (product != null) {
var products = Repository.Products;
var indexOf = products.IndexOf(products.Find(p => p.Id == product.Id));
Repository.Products[indexOf] = product;
// or
Repository.Products[indexOf].prop = product.prop;
}

小开

这是今天的一个新发现——在学习了 class/struct 参考课之后！

如果您的知道项目将被找到，您可以使用 Linq 和“ Single”，因为 Single 返回一个变量..。

myList.Single(x => x.MyProperty == myValue).OtherProperty = newValue;

小开

//Find whether the element present in the existing list


if (myList.Any(x => x.key == "apple"))
{
//Get that Item
var item = myList.FirstOrDefault(x => x.key == ol."apple");
//update that item
item.Qty = "your new value";
}

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我找到了一种不用 LINQ 的一行代码就能做到的方法:

yourList.Where(yourObject => yourObject.property == "yourSearchProperty").Select(yourObject => { yourObject.secondProperty = "yourNewProperty"; return yourObject; }).ToList();

小开

var index = yourList.FindIndex(x => x.yourProperty == externalProperty);
if (index > -1)
{
yourList[index] = yourNewObject;
}

yourlist now has the updated object inside of it.

小开

同样值得一提的是，Matt Roberts 所说的应用于类内的结构。

So even when you have a class (which will pass by reference, theoretically), a property which is a list of structs inside it will pass by value when you try to find it and change a value inside a given struct (on the list).

For instance (using the same code as Matt proposed):

ParentClass instance = new ParentClass();


var found = instance.ListofStruct.FirstOrDefault(c => c.TheValue == 1);
found.TheValue = 12;


foreach (var myStruct in instance.ListofStruct)
{
Console.WriteLine(myStruct.TheValue);
}
Console.ReadLine();


public class ParentClass
{
public List<MyStruct> ListofStruct { get; set; }
public struct MyStruct
{
public int TheValue { get; set; }
}


public ParentClass()
{
ListofStruct = new List<MyStruct>()
{
new MyStruct {TheValue = 10},
new MyStruct {TheValue = 1},
new MyStruct {TheValue = 145}
};
}
}

将输出: 10,1,145

而将 struct (在 ParentClass 内部)更改为类，如下所示:

public class ParentClass
{
public List<MySubClass> ListofClass { get; set; }
public class MySubClass
{
public int TheValue { get; set; }
}


public ParentClass()
{
ListofClass = new List<MySubClass>()
{
new MySubClass {TheValue = 10},
new MySubClass {TheValue = 1},
new MySubClass {TheValue = 145}
};
}
}

将输出: 10,12,145