Which is the right way to add the Change Event for a FileSystemWatcher?

Question

Which is the proper way to add the Changed Event?

    public static void WatchFileForChange()
        {
            FileSystemWatcher fsw = new FileSystemWatcher();

            fsw.Path = Path.Join(System.Configuration.ConfigurationManager.AppSettings["AccessDBFolder"]);
            fsw.Changed += new FileSystemEventHandler(UpdateMDBChange);
            fsw.Filter = "*.mdb";
            fsw.NotifyFilter = NotifyFilters.FileName | NotifyFilters.LastWrite;
            fsw.EnableRaisingEvents = true;
            fsw.IncludeSubdirectories = true;
        }

        private static void UpdateMDBChange(object sender, FileSystemEventArgs e)
        {
            //https://stackoverflow.com/a/3042963/6067603
            DateTime lastWriteTime = File.GetLastWriteTime(e.FullPath);
            if (lastWriteTime.Ticks - lastRead.Ticks > 100000)
            {
                TestClient().Wait();
                lastRead = lastWriteTime;
            }
        }

Is it fsw.Changed += new FileSystemEventHandler(UpdateMDBChange); or fsw.Changed += UpdateMDBChange;

Both ways seem to fine. But I don't know if there's a technical issue that could occur. Or if a certain way is frowned upon.

score 5 · Accepted Answer · edited Mar 21 '22 at 03:53

They're identical under the hood.

Here's the disassembly:

            ed.MyEvent += Ed_MyEvent;
00007FFDF3D05F22  mov         rcx,7FFDF3DD4F00h  
00007FFDF3D05F2C  call        CORINFO_HELP_NEWSFAST (07FFE5384AF00h)  
00007FFDF3D05F31  mov         qword ptr [rbp+28h],rax  
00007FFDF3D05F35  mov         r8,offset CLRStub[MethodDescPrestub]@7ffdf3cfc768 (07FFDF3CFC768h)  
00007FFDF3D05F3F  mov         rcx,qword ptr [rbp+28h]  
00007FFDF3D05F43  xor         edx,edx  
00007FFDF3D05F45  mov         r9,offset CLRStub[StubLinkStub]@7ffdf3bcd070 (07FFDF3BCD070h)  
00007FFDF3D05F4F  call        Method stub for: System.MulticastDelegate.CtorOpened(System.Object, IntPtr, IntPtr) (07FFDF3CF4568h)  
00007FFDF3D05F54  mov         rcx,qword ptr [rbp+38h]  
00007FFDF3D05F58  mov         rdx,qword ptr [rbp+28h]  
00007FFDF3D05F5C  cmp         dword ptr [rcx],ecx  
00007FFDF3D05F5E  call        CLRStub[MethodDescPrestub]@7ffdf3d059b8 (07FFDF3D059B8h)  
00007FFDF3D05F63  nop  

            ed.MyEvent += new dlgEvent(Ed_MyEvent);
00007FFDF3D05F64  mov         rcx,7FFDF3DD4F00h  
00007FFDF3D05F6E  call        CORINFO_HELP_NEWSFAST (07FFE5384AF00h)  
00007FFDF3D05F73  mov         qword ptr [rbp+20h],rax  
00007FFDF3D05F77  mov         r8,offset CLRStub[MethodDescPrestub]@7ffdf3cfc768 (07FFDF3CFC768h)  
00007FFDF3D05F81  mov         rcx,qword ptr [rbp+20h]  
00007FFDF3D05F85  xor         edx,edx  
00007FFDF3D05F87  mov         r9,offset CLRStub[StubLinkStub]@7ffdf3bcd070 (07FFDF3BCD070h)  
00007FFDF3D05F91  call        Method stub for: System.MulticastDelegate.CtorOpened(System.Object, IntPtr, IntPtr) (07FFDF3CF4568h)  
00007FFDF3D05F96  mov         rcx,qword ptr [rbp+38h]  
00007FFDF3D05F9A  mov         rdx,qword ptr [rbp+20h]  
00007FFDF3D05F9E  cmp         dword ptr [rcx],ecx  
00007FFDF3D05FA0  call        CLRStub[MethodDescPrestub]@7ffdf3d059b8 (07FFDF3D059B8h)  
00007FFDF3D05FA5  nop  
}

I don't pretend to know what all those instructions are but you can see they're the same.

So the answer to your question is, "it doesn't matter".

score 4 · Answer 2 · answered Mar 01 '22 at 15:17

This is called method group conversion. It allows you to replace the more verbose

fsw.Changed += new FileSystemEventHandler(UpdateMDBChange);

by directly supplying the method name

fsw.Changed += UpdateMDBChange;

Basically, it's syntactic sugar, a feature added later on so you could type less. The type of the event handler can be inferred and doesn't need to be declared explicitly.

Which is the right way to add the Change Event for a FileSystemWatcher?

2 Answers2