Re: How to update a class property with a timer - C# Discussion Boards

3-Jul-07 3:03

In my class I have to update a property every second until the user stops this task.
I choose a System.Threading.Timer to do the job but the timer runs on its own thread so it cannot update the class property.
My question:
Is it possible to implement something like Control class's Invoke method or do I have to choose another approach?

Luc Pattyn3-Jul-07 3:06

Luc Pattyn

3-Jul-07 3:06

Hi,

you could use the InvokeRequired and Invoke members of Control.

But it is much simpler to use a Forms.Timer; that one ticks on the GUI thread.

Smile | :)

Luc Pattyn

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pusch3-Jul-07 5:13

3-Jul-07 5:13

Thanks Luc for your quick response!
I think I have to go in more detail:
I developed a class which accesses my tv card only for radio stations so I do not have a gui thread.
But I would like to send the signal level of the station by calling a method of a com interface every second within the radio class..
Now using a timer who makes the call to the interface, I get an error, this is because the timers thread is not the thread which created the radio class
As far as all com objects and interfaces are part of a windows forms application I was able to use this.Invoke((MethodInvoker)delegate()... to make a call to the com interface method in the timers TimerCallback.
Of course I can solve my problem using a timer in the windows forms application, but I would like to use the timer in my radio class.

Luc Pattyn3-Jul-07 5:30

Luc Pattyn

3-Jul-07 5:30

Hi,

if you have a "TVCard" class in C#, it should probably not be concerned by GUI stuff at all;
but it might offer a "Station" property getting/setting the current station selected.

Then an app using the TVCard class could periodically read and display the Station property
using the right thread, and based on its own requirements.

Alternatively, but I dont like this as much, the TVCard class could offer an event that
periodically reports the Station setting; then the app can subscribe to that event,
and must itself take care of the threading issues. The reason I dont like this that much
is that now the TVCard is deciding on how often something happens in the app, normally
the app is in charge !

Of course you could give the TVCard an Interval property as well,
so it really starts to look like a timer.

And yes, you could teach your TVCard to always raise the event on the GUI thread too,
but that would not be needed when an app wants to know but not display the Station setting,
therefore it should not be included in the TVCard ("separation of concerns").

So I would stick with the simple Station propery and let the app do timing and GUI stuff.

Smile | :)

Luc Pattyn

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pusch3-Jul-07 6:04

3-Jul-07 6:04

-So I would stick with the simple Station propery and let the app do timing and GUI stuff-

I think its a clean solution!
Thank you very much

Poke tongue | ;-P

pusch

Jimmanuel3-Jul-07 5:47

Jimmanuel

3-Jul-07 5:47

The System.Timers.Timer has a SynchronizingObject[^] property. This can be used to make sure that the timer callback function is called on a specific thread.

Maybe this will help . . .

pusch3-Jul-07 6:15

Text Disappear From MessageBox

3-Jul-07 6:15

this is what I was looking for!

May be it is not the best solution for my posted question, but its exactly what I had in mind.

Thanks a lot.

regards

pusch

Himanshu_ITDevloper3-Jul-07 2:37

Himanshu_ITDevloper

3-Jul-07 2:37

Hi,

I have written simple code in click event of button as below

MessageBox.Show("HI");

When I run the application, I got the blank messagebox means it doesn't have the message text "HI" and also doesn't display OK messagebox button. Anybody have any idea. Please guide. Any type of help is appreciated.

Himanshu Batavia

Re: Text Disappear From MessageBox

Dave Sexton3-Jul-07 2:58

Dave Sexton

3-Jul-07 2:58

You only need to post your question once. Someone will answer eventually.

Your code should look something like this

private void button1_Click(object sender, EventArgs e)
       {
           MessageBox.Show("Hello");
       }

I would seriously suggest buying a book and working through it to get started in programming before looking for help online. Learn the basics first.

I think I'm going to call my next project "Chuck Norris". It's a sure way to guarantee it's unbreakable.

• • •

But fortunately we have the nanny-state politicians who can step in to protect us poor stupid consumers, most of whom would not know a JVM from a frozen chicken. Bruce Pierson

Re: Text Disappear From MessageBox

mfmaneef3-Jul-07 9:45

mfmaneef

3-Jul-07 9:45

read this

http://www.thescripts.com/forum/thread409766.html

aneef

Disappear Text From MessageBox

shah_pranav13-Jul-07 2:20

shah_pranav1

3-Jul-07 2:20

Hello

I have written simple code like this :

MessageBox.Show("Hello");

in click event of Button1. But when I run the program and click on Button1, I get the messagebox but having no output means I don't get "Hello" text and also don't get OK messagebox button. Why it is so? Any type of help is appreciated

Himanshu Batavia

Re: Disappear Text From MessageBox

Judah Gabriel Himango3-Jul-07 4:34

Judah Gabriel Himango

3-Jul-07 4:34

Sounds like your code isn't working right. Are you certain the button1.Click event is setup to be handled by your handler function? You should show us the appropriate code.

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Judah Himango

fetch jpeg image dimension without load it

small_programmer3-Jul-07 2:18

3-Jul-07 2:18

I want to know image dimension but I can't use Image.FromFile method to load image file because it is very slow and I want get image dimention quickly.
my image file format is JPEG
i will thank every one help me
(excuse me i can't speak english correctly)

Pete O'Hanlon3-Jul-07 2:26

Pete O'Hanlon

3-Jul-07 2:26

You will need to read the header information from the file then. This link[^] takes you to the specification. Be aware though that there are *many* different versions of JPEG, so you will need to test this thoroughly.

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Deja View - the feeling that you've seen this post before.

small_programmer3-Jul-07 2:39

3-Jul-07 2:39

thank you a lot.
but this site does not offer any C# code and I can't find image dimension obviously in it's jpeg header format.
thank you again.
if any one have more simple answer please send it. thank you again.

Re: fetch jpeg image dimension without load it [modified]

Luc Pattyn3-Jul-07 2:45

Luc Pattyn

3-Jul-07 2:45

I answered this question a couple of days ago right here.[^]

Smile | :)

Luc Pattyn

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small_programmer3-Jul-07 2:57

3-Jul-07 2:57

thank you very much Rose | [Rose]

.
can i trust it completely that it work correctly in any jpeg file?
thank you again.

Dave Kreskowiak3-Jul-07 6:51

Dave Kreskowiak

3-Jul-07 6:51

Only if you test it to death.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

small_programmer10-Jul-07 2:55

10-Jul-07 2:55

i dont understand what you say?

Dave Kreskowiak10-Jul-07 12:26

Dave Kreskowiak

10-Jul-07 12:26

What's not to understand??!! The only way YOU can "trust" any code you use is if YOU exhaustively test it!

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007