Writing to ListBox from multiple threads
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Hi Bruce, I think that the problem might be with the:
if (InvokeRequired)line. Try:if (this.lb.InvokeRequired)and thenlb.BeginInvoke(new LogDelegate(log), new object[] { message });Hope this helps. :)Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.”
The Form and ListBox both run on the same ( UI ) thread, so it doesn't matter which you use. Nick
---------------------------------- Be excellent to each other :)
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Hi Bruce, I think that the problem might be with the:
if (InvokeRequired)line. Try:if (this.lb.InvokeRequired)and thenlb.BeginInvoke(new LogDelegate(log), new object[] { message });Hope this helps. :)Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.”
Thanks Henry. That is still throwing compile errors. I am beginning to suspect that the problem is because the two background threads are each in their own class file and that they cannot see the log(message) method in Form1 unless I make that method a static. Having made it a static the compiler is having trouble with pretty much every line of the method as follows: Error 2 An object reference is required for the non-static field, method, or property 'System.Windows.Forms.Control.Invoke(System.Delegate, params object[])' \\Server1\srvr\Code\PC Programs\SYSTest\SYSTest\Form1.cs 60 17 SYSTest Can anybody confirm whether I can make the log(message) a static or do I have to restructure my solution to put the background threads inside the Form1 class so I do not have to make the function into a static? Many thanks for all your valuable input, Bruce
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Thanks Henry. That is still throwing compile errors. I am beginning to suspect that the problem is because the two background threads are each in their own class file and that they cannot see the log(message) method in Form1 unless I make that method a static. Having made it a static the compiler is having trouble with pretty much every line of the method as follows: Error 2 An object reference is required for the non-static field, method, or property 'System.Windows.Forms.Control.Invoke(System.Delegate, params object[])' \\Server1\srvr\Code\PC Programs\SYSTest\SYSTest\Form1.cs 60 17 SYSTest Can anybody confirm whether I can make the log(message) a static or do I have to restructure my solution to put the background threads inside the Form1 class so I do not have to make the function into a static? Many thanks for all your valuable input, Bruce
The two background threads certainly need to be able to 'see' Form1, the best bet is probably as Nick suggested by passing a reference to Form1 in the constructor of the threads. The problems caused by making
log()static are thatlog()itself will not be able to see the listbox.Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.”
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The Form and ListBox both run on the same ( UI ) thread, so it doesn't matter which you use. Nick
---------------------------------- Be excellent to each other :)
Yes, of course! How dumb. :-O
Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.”
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The two background threads certainly need to be able to 'see' Form1, the best bet is probably as Nick suggested by passing a reference to Form1 in the constructor of the threads. The problems caused by making
log()static are thatlog()itself will not be able to see the listbox.Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.”
"The problems caused by making log() static are that log() itself will not be able to see the listbox." That makes sense. The compiler errors when the method is static could very well be caused by that. I will try Nick's suggestion and let you know. Many, many thanks Bruce
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I have a fairly standard Form1.cs with a listbox to display comms traffic. The comms traffic comes from two different interfaces each of which is handled by it's own background thread. I want to log the traffic in the listbox on Form1 and have set up a delegate / Invoke routine as below in the Form1 class:
//\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* // public void log(string message) // This function appends the message to the list box //\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* public delegate void LogDelegate(string s); public void log(string message) { if (InvokeRequired) { Invoke(new LogDelegate(log), new object\[\] { message }); } else { lb.Items.Add(message); lb.TopIndex = lb.Items.Count - 1; } } // End of void log()When I try to call log(string) from either of the backgound threads the compiler isn't finding this function and I cant for the life of me see why not. I did try making it a static but that threw lots of errors so I took that away. What am I doing wrong please? Many thanks, Bruce :confused:
What is spawning the threads? If it's the same class then you shouldn't be having an issue. If it's a seperate class then the easiest way is to raise an event in that class, that the form can subscribe to, and in the handler invoke the method required.
Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
Why are you using VB6? Do you hate yourself? (Christian Graus) -
Hi Nick, Thanks for your response. The thread will see Form1.log() if I make the log method a static. However if I make it a static the compiler kicks on just about every line of log() with "Object refernece required for ..." I just am not sure what it is looking for that I haven't provided. Cheers, Bruce
Yep, that is why Nick said
myForm1.log, not Form1.log. myForm1 should be a variable pointing to your Form1 instance. :)Luc Pattyn [Forum Guidelines] [My Articles]
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I have a fairly standard Form1.cs with a listbox to display comms traffic. The comms traffic comes from two different interfaces each of which is handled by it's own background thread. I want to log the traffic in the listbox on Form1 and have set up a delegate / Invoke routine as below in the Form1 class:
//\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* // public void log(string message) // This function appends the message to the list box //\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* public delegate void LogDelegate(string s); public void log(string message) { if (InvokeRequired) { Invoke(new LogDelegate(log), new object\[\] { message }); } else { lb.Items.Add(message); lb.TopIndex = lb.Items.Count - 1; } } // End of void log()When I try to call log(string) from either of the backgound threads the compiler isn't finding this function and I cant for the life of me see why not. I did try making it a static but that threw lots of errors so I took that away. What am I doing wrong please? Many thanks, Bruce :confused:
Hi Bruce, the code shown is perfect. However the problem is elsewhere. You have to help those threads to find and use your log method. Especially for logging purposes I tend to do that with static events, like so (incomplete and unchecked code):
class Form1 : Form {
public Form() {
...
Class2.Logger+=log; // one statement per "log client" class
}public void log(string s) {...}}
and the "log clients" look like this:
class Class2 {
public static event Action<string> Logger;
private void log(string s) {
if (Logger!=null) Logger(s);
}
}BTW: the event does not have to be static, but it allows for doing Logger+=log before the actual client objects have been created. PS: I always like to have a log(Exception) method too; I either solve that by doing the above stuff twice, or by adding the following code in every log client class:
private void log(Exception exc) {
foreach(string s in exc.ToString().Split('\r','\n')) if (s.Length!=0) log(s);
}:)
Luc Pattyn [Forum Guidelines] [My Articles]
- before you ask a question here, search CodeProject, then Google - the quality and detail of your question reflects on the effectiveness of the help you are likely to get - use the code block button (PRE tags) to preserve formatting when showing multi-line code snippets
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Hi Bruce, the code shown is perfect. However the problem is elsewhere. You have to help those threads to find and use your log method. Especially for logging purposes I tend to do that with static events, like so (incomplete and unchecked code):
class Form1 : Form {
public Form() {
...
Class2.Logger+=log; // one statement per "log client" class
}public void log(string s) {...}}
and the "log clients" look like this:
class Class2 {
public static event Action<string> Logger;
private void log(string s) {
if (Logger!=null) Logger(s);
}
}BTW: the event does not have to be static, but it allows for doing Logger+=log before the actual client objects have been created. PS: I always like to have a log(Exception) method too; I either solve that by doing the above stuff twice, or by adding the following code in every log client class:
private void log(Exception exc) {
foreach(string s in exc.ToString().Split('\r','\n')) if (s.Length!=0) log(s);
}:)
Luc Pattyn [Forum Guidelines] [My Articles]
- before you ask a question here, search CodeProject, then Google - the quality and detail of your question reflects on the effectiveness of the help you are likely to get - use the code block button (PRE tags) to preserve formatting when showing multi-line code snippets
Don't want to hijack the thread but... I experimented briefly with static events a while ago and came across a slight issue of objects not getting disposed. Normally, if a ClassA instance subscribes to an event in a ClassB instance, when ClassB instance goes out of scope, it will allow ClassA instance to be disposed if there are no other references. With a static event in ClassB, that never happens of course and ClassA instance will continue to exist for the application's lifetime unless it explicitly unsubscribes from the static event. Worth bearing in mind as otherwise unexpected things can happen, as well as potential memory pressures.
Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
Why are you using VB6? Do you hate yourself? (Christian Graus) -
Don't want to hijack the thread but... I experimented briefly with static events a while ago and came across a slight issue of objects not getting disposed. Normally, if a ClassA instance subscribes to an event in a ClassB instance, when ClassB instance goes out of scope, it will allow ClassA instance to be disposed if there are no other references. With a static event in ClassB, that never happens of course and ClassA instance will continue to exist for the application's lifetime unless it explicitly unsubscribes from the static event. Worth bearing in mind as otherwise unexpected things can happen, as well as potential memory pressures.
Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
Why are you using VB6? Do you hate yourself? (Christian Graus)Hi Dave, IMO your remark is perfectly valid in general; however in this situation the form implementing the log functionality is assumed to be the main form, and to live for as long as the app is running. If not, one should consider implementing the log server in a separate class, or drop the statics. :)
Luc Pattyn [Forum Guidelines] [My Articles]
- before you ask a question here, search CodeProject, then Google - the quality and detail of your question reflects on the effectiveness of the help you are likely to get - use the code block button (PRE tags) to preserve formatting when showing multi-line code snippets