c# - 如何创建新的订阅以删除任何以前的订阅者 C# Visual Studio

Question

我正在备考，遇到了一道我想不出来的题。它要求为 Radio 类创建一个 TurnOnRadio 方法。此方法应删除远程控制对象的任何电视订阅者。我以为我可以只用 = 而不用 += 或 -= 来做到这一点。当我这样做时说此事件“RemoteControl.channelChange ”只能位于 += 或 -= 的左侧(除非在“远程控制”类型中使用)完成此任务的任何帮助都是赞赏。代码贴在下面。

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

namespace RemoteControlApp2
{
class RemoteControl
{
    public delegate void ChannelChanged(object remote, RemoteEventsArgs re);
    public event ChannelChanged channelChange;
    private int currentChannel;

    public void ChangeTheCrrentChannel(int newChannel)
    {
        RemoteEventsArgs newRe = new RemoteEventsArgs(newChannel);

        if (channelChange!=null)
        {
            channelChange(this, newRe);
         }
    }
}

class RemoteEventsArgs : EventArgs
{
    public int newChannel;

    public RemoteEventsArgs(int nc)
    {
        this.newChannel = nc;
    }
}

class Television
{
    private int tvChannel;
    //Your code here
    public void TurnOnTV(RemoteControl Remote)
    {
        Remote.channelChange += new RemoteControl.ChannelChanged(TVChannelChanged);
        Console.WriteLine(Remote.ToString() + " is detected");
    }
    public void TurnOffTV(RemoteControl Remote)
    {
        Remote.channelChange -= new RemoteControl.ChannelChanged(TVChannelChanged);
        Console.WriteLine(Remote.ToString() + " is no longer detected");
    }
    public void TVChannelChanged(Object Remote, RemoteEventsArgs nc)
    {
        Console.WriteLine("The TV channel is changed. New channel is: {0}", nc.newChannel);
    }
}

class Radio
{
    private int radioChannel;
    //Your code here
    public void TurnOnRadio(RemoteControl Remote)
    {
        Remote.channelChange = new RemoteControl.ChannelChanged(TVChannelChanged);
        Console.WriteLine(Remote.ToString() + " is deteceted")
    }
    //May need to write RadioChannelChanged method

}

class Program
{
    static void Main(string[] args)
    {
        RemoteControl rc = new RemoteControl();
        Television tv = new Television();
        tv.TurnOnTV(rc);
        rc.ChangeTheCrrentChannel(29);
        rc.ChangeTheCrrentChannel(32);
        tv.TurnOffTV(rc);
        Console.ReadKey();
    }
}

Answer 1

我从公共(public)事件 ChannelChanged channelchange 中取出事件； 所以现在是 public ChannelChanged channelchange； 接下来我完成了 radio 类和 TurnOnRadio 方法，现在该事件已被删除，我可以使用 = 删除所有其他订阅，现在订阅 Remote 在 main 中更改到的任何 channel 。下面发布 radio 类代码。

class Radio
{
    private int radioChannel;
    //Your code here
    public void TurnOnRadio(RemoteControl Remote)
    {
        Remote.channelChange = new RemoteControl.ChannelChanged(RadioChannelChanged);
        //Console.WriteLine(Remote.ToString() + " is deteceted");
    }
    public void RadioChannelChanged(object Remote,RemoteEventsArgs re)
    {
        radioChannel = re.newChannel;
        Console.WriteLine("Radio channel is changed. New channel is :{0}", re.newChannel);
    }
    //May need to write RadioChannelChanged method

}