Threaing.Timer + Delegates = Headache?
Nov 11, 2010
I'm trying to learn how to work with Multithreading as well as Threading.Timers. So far I can only sum up my output as broken. I have read lots of information but none of it seems to be sinking in. I can't seem to find any information that is exactly relevant to what I want to do to make good sense of it.All I want to do is run two separate threads with a Threading.Timer on each. One will show the time elapsed and one will show the current time.
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Mar 27, 2009
What are Delegates and Multicast Delegates in VB.NET? How do I use them? provide a simple example to illustrate the concept.
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Jun 19, 2009
i have a field on my form that gives me a real headache. when i try my form, i push "TAB" to go from 1 field to the next. when i hit the nightmarish field, my program hangs. i cannot get out of the field and i cannot even close the program. i need to go to taskman and kill it to close it.
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Jun 16, 2009
I am very close to cracking a problem I've had in visual basic 2008 that i am running out of visual studio 2008. I would like to generate a graph on a form using MSChart. I have got the first bit sorted out ie i can get a graph to show on a form using the following code (I've only put the first tranche in for the purpose of this question:[code] I can't get the array or string to be compatible with the one dimensional, comma-delimited array that I need to populate the y-axis values of the chart.
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May 11, 2012
I'm trying to split a string at a period character and save the two halves. I want to later evaluate the length of these, but I can't get the Split function to work at all.
Dim myArray() As String = Split(myString, ".", , CompareMethod.Text)I thought that this would split the two halves into an array as the help documentation said it would, but I just get the "A first chance exception of type 'System.IndexOutOfRangeException' occurred" error. This is really bugging me, as I can't even do this as the documentation tells me to do it. I try to run their example and the same thing happens.
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Mar 14, 2011
OK, this is crazy - How do I format text in a text box, (or god forbid) a grid, so that if it is a number it will align right, and if it is Currency it will have a $ sign. Do I have to define a Data Template? Every Template example online seems to deal with drawing borders around ListBox items, or showing photos instead of Strings,. I found 20 links, and not one talked about Alignment of #s or Currency.I'm new to WPF, and can only say that ease of use has gone to hell with WPF. Some things that were straight forward in Winforms are (IMHO) arcane in WPF (and I come from Delphi, which makes both VS Winforms and WPF seem like Rubik's Cubes).
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Apr 13, 2010
I've found my life greatly eased by having given up on ListView. DataGridView is by far the better way to go. I wish I listened early on to the suggestion of someone here who recommended it. Chalk up another failure to my stubbornness.However, while I can set the ForeColor of an individual cell using GridV.Item(a, b).Style.ForeColor,[code]All these work without a hitch. But when I want to set the text of a given column to a desired color, GridV.Columns(a).DefaultCellStyle.ForeColor is completely ignored.Upon investigating further, I discovered that exactly the same behavior as described above is also true for setting the text and back color for Rows.If I have to, I'll succumb to using GridV.Item(a, b).Style.ForeColor, though this adds unnecessary complication to the code. But I'd like to know why I'm unable to set the text color of a column or row programmatically and get that working.
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Feb 10, 2010
I have a class that I want to be serializable but contains a public instance of delegate that, apparently can't be serialized: [Code] Is there a way to make it serializable however?
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Feb 3, 2012
Consider these two functions[code]...
My question is: what is the right way to accomplish this to resolve the ambiguity so that I can pass value or references types and get overload 2, but pass Functions and get overload 1? Can I constrain the types in some way to make this happen?
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Mar 27, 2011
I've been tinkering with Delegates, and now Multicast delegates. Every time I invoke two delegates It only displays one of the two delegates per invocation.
[Code]...
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Feb 17, 2011
[Code]....
So func is a function that accepts a string and return a string. In practice, internally, func also utilizez text1, text2. In fact, func can even be a member function with access the object that owns it (something like me or this operator).
And all that can be accomplished without changing the signature of func? How do the compiler do this?
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Dec 15, 2010
I am struggling to get the syntax for the reflection call GetCustomAttributes ... at least I don't seem to be able to get hold of the custom attribute which I've decorated a particular method with. The complicating factor maybe that I have passed that method into an extension method as a generic delegate. (The other, more likely, complicating factor is that I'm not sufficiently familiar with reflection or what happens when you pass a method as a parameter like this!)
The code appears to run, and when I step it, the count returned from the GetCustomAttributes is 1. I can't work out how to get hold of that custom parameter
[Code]...
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Nov 29, 2009
is there a way to create an interface of delegates? Sub dostuff(byval arg1 as dele1)works, problem is that i have 8 delegates, so i will have to give it 8 signatures. that isn't so bad, but the problem is that when there are various combinations of signatures it gets real real bad.
Sub dostuff(byval arg1 as [Delegate])works, but it allows me to accept delegates beyond the 8 that i wanted (it's like declarign arguments with base Object)could i be able to do this:
Sub dostuff(byval arg1 as Idele1to8)
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Apr 7, 2009
Is it possible to create anonymous delegates in vb.net version 8 or earlier? If so, could someone provide an example of the syntax?
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Jul 12, 2011
I have a VBNET app to scan my Active Directory using WMI calls and return some basic informaiton such as Dell Model name, current user logged on, Dell Service Tag etc my issue is the app becomes unresponsive whilst it scans and i have to wait for it to finish looping before i can work with it, in the past a do events used to suffice
I think Multithreading is the way i may need to go, whats the best approach? I tried to use Delegates but it doesnt seem to have made any difference
below is my for next loop code that calls the functions, the last section "Private Sub Button1_Click" down is the Delegate code i attempted
[Code]...
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Nov 15, 2010
Maybe I am just not reading the MSDN documentation correctly, but given a function that takes in one string parameter and returns type T, how can this be specifed as a shared function using Func()?
MSDN says Func(Of In T1, Out TResult), but all of their examples use the same data type, i.e., Func(Of String, String). I want to do Func(Of In String, Out T), where T is arbitrary (but I can constrain it if necessary by a base class). I want it shared/static at the class level, yet the encapsulating class will itself not be a generic class. It seems in this specific scenario, it's impossible to do what I want because the compiler would have no way of knowing what Type T is at runtime.
So is it possible to do generics on delegates or anonymous lambda expressions in VB.net (not C#)?
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May 7, 2009
I can come up with, if I understood the solution better, I could probably phrase a better subject line.[code]...
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Jun 4, 2010
I am having trouble with getting a delegate to work properly.Here's my
[Code]...
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Feb 11, 2010
What is the difference b/w Delegates and Events. I have little bit confusion. Where delegates are used, and when we have to used delegates. Can, you give some examples(both delebates and events) in vb.net.
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May 26, 2009
I was going through tutorials and found the topic of Events and Delegates. However, I fail to understand why should this be required ? Instead of having to raise events, can't one just call the necessary procedure ?Sorry for posing this basic question. Any replies or even links to existing posts are welcome. [Also not sure if this question strictly falls under VB.NET category.]
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Aug 2, 2010
What I need to do to make this code work for hours as well?[code]...
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Jan 15, 2009
I need an accurate timer to interface a Windows application to a piece of lab equipment.I used System.Timers.Timer() to create a timer that ticks every 10 msec, but this clock runs slow. For example 1000 ticks with an interval of 10 msec should take 10 wall-clock seconds, but it actually takes more like 20 wall-clock sec (on my PC). I am guessing this is because System.Timers.Timer() is an interval timer that is reset every time it elapses. Since it will always take some time between when the timer elapses and when it is reset (to another 10msec) the clock will run slow. This probably fine if the interval is large (seconds or minutes) but unacceptable for very short intervals.Is there a function on Windows that will trigger a procedure every time the system clock crosses a 10 msec (or whatever) boundary?
UPDATE: System.Timers.Timer() is extremely inaccurate for small intervals.I wrote a simple program that counted 10 seconds several ways:
Interval=1, Count=10000, Run time = 160 sec, msec per interval=16
Interval=10, Count=1000, Run time = 16 sec, msec per interval=15
Interval=100, Count=100, Run time = 11 sec, msec per interval=110
Interval=1000, Count=10, Run time = 10 sec, msec per interval=1000
It seems like System.Timers.Timer() cannot tick faster that about 15 msec, regardless of the interval setting.Note that none of these tests seemed to use any measurable CPU time, so the limit is not the CPU, just a .net limitation (bug?)For now I think I can live with an inaccurate timer that triggers a routine every 15 msec or so and the routine gets an accurate system time. Kinda strange, but...I also found a shareware product ZylTimer.NET that claims to be a much more accurate .net timer (resolution of 1-2 msec). This may be what I need. If there is one product there are likely others.
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Jul 9, 2009
I have a timer on a page in ASP.NET.
After a certain period of time elapses, I want to disable the timer.
I want to put a static variable in the timers tick event that will track how many seconds have elapsed.
My question is, will this work?
If user X and Y are viewing the page will they both have separate local static variables?
What is the best method of shutting down an ASP.NET timer after a certain elapsed time?
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Apr 23, 2009
I have a windows application that need to process som quite time consuming jobs. In my first try i did all processing under
the form thread. The result was bad response and update of the form due to the heavy jobs.To get around the problem with bad response from the form i created a new class "processing" where i put all the data processing. Then i instanciated a background worker where i in the "doWork" sub created a new instance of "processing".The "processing" class creates a timer from system.timer, and the timer drives the processing.On the Timer event Elapsed the timer starts a new thread from the thread pool.
My problem is now when i want to asynchronously close the background worker (with the corresponding function call what ever it is called ...) there is still a timer thread out there that causes exceptions for me.
1. How can i close my background worker and at the same time have the timer to be stopped?
2. Is there a way to synchronize the timer event so that the timer executes from the background worker thread?
3. Is there a better approach for me to adapt?
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Jan 11, 2011
I want to create an array of timer in vb.net. My problem is that how will i raise the tick event for a particular timer, say mytimer(x).tick and inside the tick event there is also a button, say mybutton(x) which changes location every interval. for example:
public class blah
dim mybuttons(20) as button
dim mytimer(20) as timer
private sub form_load(....) handles me.load
for x as integer = 0 to 20
[Code]...
i dont know what to do next, all i want is to pass the button mybuttons(x) to mytimer(x) tick event, in which their index number are the same. i want to create one timer per button. how to do that? please help me and post example codes. i've researched the net but i cant understand passing variables, addhandlers, etc. i'm just new to programming object oriented.
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Jul 4, 2011
How can I incorporate the timer so once a page loads the timer activates, waits a few seconds then I tell my program what to do next.I tried this code but it didnt work:
Timer1.Interval = 5000
Timer1.Enabled = True
Timer1.Start()
[code]....
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Aug 6, 2010
However, I am wondering if there are any workarounds or plans for incorporating this feature into VB.NET in the future?What I'd like to do:
Public Delegate Function Deserializer(Of T)(ByRef Buffer() As Byte, optional ByRef BufferPosition As Integer = 0) As T
'Implementation of a func that matches the delegate'
Class A
Public Function Deserialize(Byref Buffer() as Byte, optional Byref BufferPosition as integer = 0)
....
In the absence of specifying "optional" inside the actual delegate itself, it'd at least be nice to be able to do it in the function implementation only:
Public Delegate Function Deserializer(Of T)(ByRef Buffer() As Byte, ByRef BufferPosition As Integer) As T
'Implementation of a func that matches the delegate'
Class A
Public Function Deserialize(Byref Buffer() as Byte, optional Byref BufferPosition as integer = 0)
....
At least this second way, the functions for the delegate will always have a value mapped to each parameter, although some may come from the function side and not the calling side.
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Jan 30, 2010
is there a way to check how many delegates are attached to an event, let's saymybutton.Click has 10 handlers, 5 by using the Handles keyword and another 5 added by using the AddHandler method (well this is not the point, then point is that i do not know how many handlers there will be). and i would want to create another button that had all 10 handlers of mybutton.Click attached to its Click event as well.
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Dec 3, 2009
I'm looking for a reference that can explain the concept and use of the DataReceived event and Delegates subject.The reference has to be pretty simple as I'm an "old dog attempting to learn a new trick". I'm not ignorant of things programming, but am ignorant of things dealing with serial communication in VB2005.I already have a couple of O'Rielly books ("VB2005 Cookbook", "VB2005 Desktop Reference") and I have a book that deals with serial communication from a Jan Axle-something. Neither O'Rielly books have any info, and the Axle-someting book's remotely related examples are too confusing for this slow learner.
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Oct 7, 2009
I find myself calling functions from lambdas frequently as the provided delegate does not match or does not have sufficient parameters. It is irritating that I cannot do lambda on subroutines. Each time I want to do this I have to wrap my subroutine in a function which returns nothing. Not pretty, but it works.
Is there another way of doing this that makes this smoother/prettier? I have read that this whole lambda inadequacy will probably be fixed in VS2010/VB10 so my question is more out of curiosity.
[Code]...
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