C# 仅将唯一项目添加到列表
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Only Add Unique Item To List
提问by Oli
I'm adding remote devices to a list as they announce themselves across the network. I only want to add the device to the list if it hasn't previously been added.
我正在将远程设备添加到列表中，因为它们通过网络宣布自己。如果之前未添加设备，我只想将其添加到列表中。
The announcements are coming across an async socket listener so the code to add a device can be run on multiple threads. I'm not sure what I'm doing wrong but no mater what I try I end up with duplications. Here is what I currently have.....
公告是通过异步套接字侦听器发出的，因此添加设备的代码可以在多个线程上运行。我不确定我做错了什么，但无论我尝试什么，我最终都会重复。这是我目前拥有的......
lock (_remoteDevicesLock)
{
RemoteDevice rDevice = (from d in _remoteDevices
where d.UUID.Trim().Equals(notifyMessage.UUID.Trim(), StringComparison.OrdinalIgnoreCase)
select d).FirstOrDefault();
if (rDevice != null)
{
//Update Device.....
}
else
{
//Create A New Remote Device
rDevice = new RemoteDevice(notifyMessage.UUID);
_remoteDevices.Add(rDevice);
}
}
采纳答案by Austin Salonen
If your requirements are to have no duplicates, you should be using a HashSet.
如果您的要求是没有重复项，则应该使用HashSet。
HashSet.Addwill return falsewhen the item already exists (if that even matters to you).
当项目已经存在时，HashSet.Add将返回false（如果这对你很重要的话）。
You can use the constructor that @pstrjds links to below (or here) to define the equality operator or you'll need to implement the equality methods in RemoteDevice(GetHashCode& Equals).
您可以使用@pstrjds 链接到下面（或此处）的构造函数来定义相等运算符，或者您需要在RemoteDevice( GetHashCode& Equals) 中实现相等方法。
回答by Luke Eckley
Just like the accepted answer says a HashSet doesn't have an order. If order is important you can continue to use a List and check if it contains the item before you add it.
就像接受的答案说 HashSet 没有订单一样。如果顺序很重要，您可以继续使用 List 并在添加之前检查它是否包含该项目。
if (_remoteDevices.Contains(rDevice))
_remoteDevices.Add(rDevice);
Performing List.Contains() on a custom class/object requires implementing IEquatable<T>on the custom class or overriding the Equals. It's a good idea to also implement GetHashCodein the class as well. This is per the documentation at https://msdn.microsoft.com/en-us/library/ms224763.aspx
在自定义类/对象上执行 List.Contains() 需要IEquatable<T>在自定义类上实现或覆盖Equals. GetHashCode在类中也实现也是一个好主意。这是根据https://msdn.microsoft.com/en-us/library/ms224763.aspx 上的文档
public class RemoteDevice: IEquatable<RemoteDevice>
{
private readonly int id;
public RemoteDevice(int uuid)
{
id = id
}
public int GetId
{
get { return id; }
}
// ...
public bool Equals(RemoteDevice other)
{
if (this.GetId == other.GetId)
return true;
else
return false;
}
public override int GetHashCode()
{
return id;
}
}
回答by RavinderReddy Seelam
//HashSet allows only the unique values to the list
HashSet<int> uniqueList = new HashSet<int>();
var a = uniqueList.Add(1);
var b = uniqueList.Add(2);
var c = uniqueList.Add(3);
var d = uniqueList.Add(2); // should not be added to the list but will not crash the app
//Dictionary allows only the unique Keys to the list, Values can be repeated
Dictionary<int, string> dict = new Dictionary<int, string>();
dict.Add(1,"Happy");
dict.Add(2, "Smile");
dict.Add(3, "Happy");
dict.Add(2, "Sad"); // should be failed // Run time error "An item with the same key has already been added." App will crash
//Dictionary allows only the unique Keys to the list, Values can be repeated
Dictionary<string, int> dictRev = new Dictionary<string, int>();
dictRev.Add("Happy", 1);
dictRev.Add("Smile", 2);
dictRev.Add("Happy", 3); // should be failed // Run time error "An item with the same key has already been added." App will crash
dictRev.Add("Sad", 2);
