Csharp 为什么这个 lambda 表达式对构造函数参数有效

这种方法

o => _server.Connect()个

与此方法相同

void Anon(object o) 
{
    // argument o is ignored
    _server.Connect();
}

使此代码等同于您的代码:

private Server _server;
public RelayCommand ConnectToServerCommand {get; set;}

// un-lambda-ed
void Anon(object o) 
{
    _server.Connect();
}

public MainViewModel() // constructor
{
    _server = new Server();

    // no confusion
    ConnectToServerCommand = new(Anon);
}

让我们在构造函数中有两个调用:

public MainViewModel() // constructor
{
    _server = new Server();

    ConnectToServerCommand = new(o => _server.Connect());
    // no confusion
    ConnectToServerCommand = new(Anon);
}

然后比较生成的中间语言:

MainViewModel:
IL_0000:  ldarg.0     
IL_0001:  newobj      UserQuery+Server..ctor
IL_0006:  stfld       UserQuery._server              // _server = new Server();
IL_000B:  ldarg.0     
IL_000C:  ldarg.0     
IL_000D:  ldftn       UserQuery.<MainViewModel>b__0  // our lamda function, see below
IL_0013:  newobj      System.Action<System.Object>..ctor
IL_0018:  newobj      UserQuery+RelayCommand..ctor
IL_001D:  call        UserQuery.set_ConnectToServerCommand
IL_0022:  ldarg.0     
IL_0023:  ldarg.0     
IL_0024:  ldftn       UserQuery.Anon                 // our Anon call
IL_002A:  newobj      System.Action<System.Object>..ctor
IL_002F:  newobj      UserQuery+RelayCommand..ctor
IL_0034:  call        UserQuery.set_ConnectToServerCommand
IL_0039:  ret         

<MainViewModel>b__0:  // generated by the compiler for us, the lambda
IL_0000:  ldarg.0     // object o, nothing gets done with that
IL_0001:  ldfld       UserQuery._server
IL_0006:  callvirt    UserQuery+Server.Connect
IL_000B:  ret         

Anon:
IL_0000:  ldarg.0     // object o, nothing gets done with that
IL_0001:  ldfld       UserQuery._server
IL_0006:  callvirt    UserQuery+Server.Connect
IL_000B:  ret         

这是惊人的相似.