取消订阅活动仍然会多次被解雇，如何阻止它？ [英] Unsubscribing from an event still it's getting fired many times, how to stop it?
问题描述
首先我正在订阅一个事件，然后在该事件发生时将执行的方法我取消订阅它。但我仍然认为它被解雇了很多次。
我尝试过：
使用System;
使用System.Collections.Generic;
使用System.IO;
使用System.IO.Ports;
使用System.Linq;
使用System.Text;
使用System.Threading.Tasks;
namespace SerialPortHexCommunication
{
public class Program
{
private static bool unsubscribe = false;
static void Main（string [] args）
{
SerialPort port = new SerialPort（）;
port.PortName =COM5;
port.Parity = Parity.None;
port.BaudRate = 9600;
port.DataBits = 8;
port.StopBits = StopBits.One;
if（port.IsOpen）
{
port.Close（）;
port.Dispose（）;
}
port.Open（）;
byte [] bytesToSend = new byte [6] {0xD0,0xF2,0xFF，0x00,0x06,0xC7};
port.Write（bytesToSend，0，bytesToSend.Length）;
port.DataReceived + = new SerialDataReceivedEventHandler（new cEventHandler（）。DataReceivedHandler）;
port.DataReceived - = new SerialDataReceivedEventHandler（new cEventHandler（）。DataReceivedHandler）;
Console.ReadKey（）;
port.Close（）;
port.Dispose（）;
}
}
}
使用System;
使用System.Collections.Generic;
使用System.IO.Ports;
使用System.Linq;
使用System.Text;
使用System.Threading.Tasks;
namespace SerialPortHexCommunication
{
public class cEventHandler
{
public void DataReceivedHandler（object sender，SerialDataReceivedEventArgs e）
{// this In
//应该只打印一次数据接收消息，因为我取消订阅但是多次打印。
Console.WriteLine（在数据接收中）;
SerialPort port =（SerialPort）sender;
port.DataReceived - = new SerialDataReceivedEventHandler（DataReceivedHandler）;
int bytes = port.BytesToRead;
byte [] buffer = new byte [bytes];
if（port.BytesToRead> 1）
{
port.Read（buffer，0，bytes）;
}
foreach（缓冲区中的字节项）
{
Console.WriteLine（item）;
}
port.DataReceived - = new SerialDataReceivedEventHandler（new cEventHandler（）。DataReceivedHandler）;
//Console.ReadKey（）;
}
}
}
请看看你的代码！
为什么要这样写：
SerialPort port = new SerialPort（）;
...
if（port.IsOpen）
{
port.Close（）;
port.Dispose（）;
}
port.Open（）;如果它是一个新端口，它就无法打开 - 这也是一样，因为你的应用程序会立即崩溃试图成熟你刚刚处置过的一个端口......
第二点要注意的是，多个DataReceived事件正是你应该期待的：串行数据被称为因为它以串行方式逐字节到达，而不是作为信息的托管包：每个字节都可能导致单独的DataReceived事件被触发。
I两天前告诉你这个！
DataReceived事件应该在调用
Open（）方法SerialPort类。
根据您的结果事件被多次调用 - 在我的只有在来自另一个配对端口的任何响应的情况下才会调用case事件。
对于ex。配对端口是 - COM5< - > COM3所以当任何响应来自COM3端口时，将调用DataReceived事件。
无需取消订阅该事件。
Quote：
port .DataReceived + = new SerialDataReceivedEventHandler（new cEventHandler（）。DataReceivedHandler）;
port.DataReceived - = new SerialDataReceivedEventHandler（new cEventHandler（）。DataReceivedHandler）;
您已为事件添加了两个处理程序。因此，每次引发事件时，您的事件处理程序都会被调用两次。
引用：
port.DataReceived - = new SerialDataReceivedEventHandler（new cEventHandler（）。DataReceivedHandler）;
该行将有没有效果。
当从事件中删除指向实例方法的委托时，委托指向的对象引用将作为其标识的一部分包含在内。由于您正在创建类的新实例，因此您创建的委托不等于该事件的任何已注册处理程序，因此删除它不会执行任何操作。
之前的port.DataReceived - =新的SerialDataReceivedEventHandler（DataReceivedHandler）;行应该已经删除了处理程序，所以你可以删除这一行。
First I am subscribing to an event and then in the method which will be executed when that event occurs i am unsubscribing it.But still I think it is getting fired many times.
What I have tried:
using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Ports;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace SerialPortHexCommunication
{
public class Program
{
private static bool unsubscribe=false;
static void Main(string[] args)
{
SerialPort port = new SerialPort();
port.PortName = "COM5";
port.Parity = Parity.None;
port.BaudRate = 9600;
port.DataBits = 8;
port.StopBits = StopBits.One;
if (port.IsOpen)
{
port.Close();
port.Dispose();
}
port.Open();
byte[] bytesToSend = new byte[6] { 0xD0, 0xF2, 0xFF, 0x00, 0x06, 0xC7 };
port.Write(bytesToSend, 0, bytesToSend.Length);
port.DataReceived += new SerialDataReceivedEventHandler(new cEventHandler().DataReceivedHandler);
port.DataReceived -= new SerialDataReceivedEventHandler(new cEventHandler().DataReceivedHandler);
Console.ReadKey();
port.Close();
port.Dispose();
}
}
}
using System;
using System.Collections.Generic;
using System.IO.Ports;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace SerialPortHexCommunication
{
public class cEventHandler
{
public void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
{//this In data receive message should be printed only once
//as i am unsubscribing but it get printed many times.
Console.WriteLine("In data receive");
SerialPort port = (SerialPort)sender;
port.DataReceived -= new SerialDataReceivedEventHandler(DataReceivedHandler);
int bytes = port.BytesToRead;
byte[] buffer = new byte[bytes];
if (port.BytesToRead > 1)
{
port.Read(buffer, 0, bytes);
}
foreach (byte item in buffer)
{
Console.WriteLine(item);
}
port.DataReceived -= new SerialDataReceivedEventHandler(new cEventHandler().DataReceivedHandler);
//Console.ReadKey();
}
}
}Please, look at your code!
Why would you write this:
SerialPort port = new SerialPort(); ... if (port.IsOpen) { port.Close(); port.Dispose(); } port.Open();If it's a new port, it can't be open - which is just as well, as your app would then crash immediately as you tried to oipen a port you had just Disposed...
The second thing to note is that multiple DataReceived events are exactly what you should expect: Serial data is called that because it arrives in a serial fashion, byte by byte instead of as a "managed packet" of information: each byte can cause a separate DataReceived event to fire.
I told you this two days ago!
DataReceivedevent should be subscribed before calling
Open()method of
SerialPortclass.
As per your result event is called many times- In my case event will be called only in case of any response comes from another paired port.
For ex. Paired ports are - "COM5" <-> "COM3" so when any response will come from "COM3" port then theDataReceivedevent will be called.
There is no need to unsubscribe the event.
Quote:
port.DataReceived += new SerialDataReceivedEventHandler(new cEventHandler().DataReceivedHandler); port.DataReceived -= new SerialDataReceivedEventHandler(new cEventHandler().DataReceivedHandler);
You've added two handlers to the event. Therefore, every time the event is raised, your event handler will be called twice.
Quote:port.DataReceived -= new SerialDataReceivedEventHandler(new cEventHandler().DataReceivedHandler);
That line will have no effect.
When a delegate pointing to an instance method is removed from an event, the object reference to which the delegate points is included as part of its identity. Since you're creating a new instance of your class, the delegate you create is not equal to any of the registered handlers for the event, so removing it doesn't do anything.
The previousport.DataReceived -= new SerialDataReceivedEventHandler(DataReceivedHandler);line should already remove the handler, so you can just delete this line.
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