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VB Forum / Controls / July 2008a syntax error when programming with MSComm
I'am a beginner in Visual Basic 6.0. Now I try to write a ActiveX control that is in charge of communication through COM1. So I decided to adopt MSComm control. I draged a button onto the usercontrol.Then I wrote some statements in its double-click event handler,like this: Private Sub Command1_Click() Dim MyComm As MSComm MyComm.CommPort = 1 MyComm.Settings = "9600,N,8,1" MyComm.PortOpen = True End Sub Then I started to run it in a web page by printing F5. When I double-clicked the button, a message box jumped out on which it says as following: Run-time error '91': Object variable or With block variable not set Please tell me why this happened? Where did I wrote incorrectly? Thank all of you! Adrian Chen > Private Sub Command1_Click() > Dim MyComm As MSComm > MyComm.CommPort = 1 > MyComm.Settings = "9600,N,8,1" > MyComm.PortOpen = True > End Sub > Run-time error '91': > Object variable or With block variable not set > > Please tell me why this happened? Where did I wrote incorrectly? Thank all > of you! The Dim statement tells VB what type of object the variable "MyComm" is capable of holding a reference to. (That's all) It does not actually create an object of that type. When you try to put a value into the ComPort property, VB notices that although "MyComm" has a type, it doesn't actually have a reference to an object. MyComm Is Nothing. So before you can use it, you need to create such an object and put a reference to that object into the variable. The easiest way to do both of these things would probably be: Set MyComm = New MSComm Bob Thank you, Bob! I was enlightened much through your words. But I run into another problem. When I replaced that statement with "Set MyComm = New MSComm", the error changed to "Compile error: Invalid use of New keyword" Why?? "Bob O`Bob" <filterbob@yahoogroups.com> ??????:%23GBzVmG5IHA.4344@TK2MSFTNGP03.phx.gbl... >> Private Sub Command1_Click() >> Dim MyComm As MSComm [quoted text clipped - 28 lines] > > Bob > Thank you, Bob! I was enlightened much through your words. > But I run into another problem. When I replaced that statement with "Set > MyComm = New MSComm", > the error changed to "Compile error: Invalid use of New keyword" > Why?? That's a harder question. I didn't actually check earlier, but I was pretty sure MSComm was one of the controls you can't easily use that way. What you ought to do is put the control on your form at design time, and then you won't need "New" at all. Since you're building a user control, there is probably no reason /not/ to have it there all the time. As for why that's really so, I don't think I actually know well enough to explain. There probably are replacement classes you could install to completely replace MSComm, if you were building something which had no UI at all, but I wouldn't recommend that to any beginner. Bob -- Bob, I've found the mistake! I was such a fool! When I design the axtivex, I drag the MSComm control from control panel onto usercontrol, a MSComm object has been generated automatically, so I needn't define a object myself. Sorry to cause you a lot of trouble! Thanks a lot! "Bob O`Bob" <filterbob@yahoogroups.com> ??????:u5Yu1eK5IHA.3804@TK2MSFTNGP03.phx.gbl... >> Thank you, Bob! I was enlightened much through your words. >> But I run into another problem. When I replaced that statement with "Set [quoted text clipped - 19 lines] > > Bob > Bob, I've found the mistake! I was such a fool! > > When I design the axtivex, I drag the MSComm control from control panel onto > usercontrol, a MSComm object has been generated automatically, so I needn't > define a object myself. > Sorry to cause you a lot of trouble! Thanks a lot! It's no trouble. This is exactly what some of us enjoy and choose to do, more or less as a hobby. To see the learning process take place is more than enough reward for the tiny bit of time I invested. Bob -- |
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