C# Discussion Boards - CodeProject

Eddy Vluggen12-Oct-12 5:28

12-Oct-12 5:28

UCLAdam wrote:
Am I approaching this right with an abstract base class or should I be taking a different approach?

Nope, sounds about right.

UCLAdam wrote:
But I also just want to be able to call _profiles.CurrentProfile.Rename(...).

As long as the object implements the member with the name "Rename", that should work. Your main application would still be working with that base-class, calling methods on it. You could use a strategy-pattern to decide which derived class gets instantiated;

namespace bla 
{
    abstract class DuckBase
    {
        abstract public void Rename();
    }
    class RubberDuck: DuckBase
    {
        // implementation 1
        override public void Rename()
        {
            Console.WriteLine("Squeek");
        }
    }
    class MallardDuck : DuckBase
    {
        // implementation 2
        public override void Rename()
        {
            Console.WriteLine("Quack");
        }
    }

    class Program
    {
        // These are the type of ducks we support. You could also use a string or 
        //  an int to identify them, just choose an enum for this example
        enum KindaDuck { RubberDuck, MallardDuck };

        // this is what's called a factory-method; it returns an actual implementation 
        //  of a "DuckBase"-object
        DuckBase DuckFactory(KindaDuck DuckType)
        {
            switch (DuckType)
            {
                case KindaDuck.MallardDuck: return new MallardDuck();
                case KindaDuck.RubberDuck: return new RubberDuck();
            }
            throw new IndexOutOfRangeException(DuckType.ToString() + " is not a known duck.");
        }

        static void Main(string[] args)
        {
            DuckBase ducky = new RubberDuck();
            ducky.Rename();
            Console.ReadKey(); 
        } 
    }
}

The only rule is that the Rename method must have the same signature everywhere. If that becomes a problem, call back again, as there's a simple solution Smile | :)

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

Adam_Dev14-Oct-12 22:13

Adam_Dev

14-Oct-12 22:13

Thanks Eddy, your reply really helped.

I thought it would probably have to be a strategy-pattern to decide which derived class gets instantiated.

I know it must be intentional, but just checking that in your example the DuckFactory isn't actually being used?

Thanks again.

Eddy Vluggen15-Oct-12 0:40

15-Oct-12 0:40

UCLAdam wrote:
Thanks Eddy, your reply really helped.

My pleasure Smile | :)

UCLAdam wrote:
I thought it would probably have to be a strategy-pattern to decide which derived class gets instantiated.

I know it must be intentional, but just checking that in your example the DuckFactory isn't actually being used?

Whehe, most important part of the entire pattern, and I simply forgot it WTF | :WTF:

static void Main(string[] args)
{
    // here the enum determines which object is created; you could program the same
    //  with a string. (Say, DuckFactory("MallardDuck"))
    DuckBase ducky = DuckFactory(KindaDuck.MallardDuck);
    ducky.Rename();
    Console.ReadKey();
}

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

How to implement a resumable HTTP download?

n.podbielski12-Oct-12 5:35

n.podbielski

12-Oct-12 5:35

Do you suspect many more of those renames to be requested?
I think that you trying to do simple think even simpler. And you complicating thinks to much in the same time. I know this. We all know (developers) this trap. Frown | :(

Basically what I mean that if you are making single exe, every change must be change in code. You must open code, change it, add something. So writing complex OOP class structure will be time consuming. And not worthit since end user will not use configuration or parametrized arguments.

I would write something simple like RegExp for matching/extracting files names and string.format for creating new names. New profile, new reg pattern and new format string.

You never know what will come to mind of customer so i think any clever solution will restrict you to much, to that point you wil have to rewrite whole thing every time. Will it be wort it? I think no. Better spend this time doing more interesting things.

It is my experience, but you wil what you decide.

No more Mister Nice Guy... >: |

Jun Du12-Oct-12 3:48

Jun Du

12-Oct-12 3:48

We have an app that needs to download some 20MB file via a GSM connection. Due to the size of file and nature of the GSM connection, we want the download can pick up and continue from where it dropped off. Any info or suggestions? Thanks!

Best,
Jun

Re: How to implement a resumable HTTP download?

Eddy Vluggen12-Oct-12 5:07

How to change color (combo,Text etc) when enable=false

12-Oct-12 5:07

Jun Du wrote:
Any info or suggestions?

Yes, a thing called "research". Start here[^], and use a HttpRequest to fetch the desired byte-range. There might be an article on the subject, but I was to lazy to check Smile | :)

--edit
Another downvote for the collection. Was it that really that annoying that I did not check? Here's[^] your article - you're welcome Suspicious | :suss:

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

modified 12-Oct-12 19:43pm.

himmubhai12-Oct-12 3:09

himmubhai

12-Oct-12 3:09

i want to change color.
If Groupbox enable fasle mode,.. then all text box, combo etc color change.
if Groupb box box enbale true,.. then no problem.

give me solution...

Re: How to change color (combo,Text etc) when enable=false

Marco Bertschi12-Oct-12 4:53

Marco Bertschi

12-Oct-12 4:53

Hi,

Can you please clarify if the textboxes and comboboxes are located within the group box?

Cheers
Marco

Re: How to change color (combo,Text etc) when enable=false

himmubhai12-Oct-12 6:13

himmubhai

12-Oct-12 6:13

textbox or combo with inside group box...
if inside groupbox control or not,
if define textboz1.enable=false;

then user define color not apply...
only enable false property does not take colour effect why?.
as like fore color, back color, border etc color and design effct.

other wise enable true,
user define color also runing on........

Can someone explain this...

DanielSheets12-Oct-12 2:34

12-Oct-12 2:34

private void ReadDaqThreadProc()
        {
            dThreadCallback tcb = new dThreadCallback(ReadDaq);
            while (flags.daqEnabled)
            {
                try
                {
                    this.Invoke(tcb, new Object[] { });                }
                catch (Exception e)
                {
                }
                Thread.Sleep(50);
            }
        }

This snippet is part of a multithreaded app. "tcb" is a delegate, ReadDaq is a function in the MainForm code, and ReadDaqThreadProc is in its own thread. I know what the code does but I dont know how. I'd like to understand how this works. The line in question is the invoke line. Is 'new Object[] {}' an argument list for ReadDaq?

Eddy Vluggen12-Oct-12 2:38

12-Oct-12 2:38

Yes, it's passing an empty object array (the default container for invoke-params) and calling "tcb", the ReadDaq method - a method without parameters. And it seems to swallow any exceptions, which isn't such a great thing.

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

DanielSheets12-Oct-12 2:40

12-Oct-12 2:40

It should be in a try block?

Eddy Vluggen12-Oct-12 2:51

12-Oct-12 2:51

Member 8461599 wrote:
It should be in a try block?

Why? Which exceptions does the Invoke method throw? It's only there to ensure that any exceptions from the implementation of the method do not kill the application; and those exceptions should be handled there - locally; not here. Also, it's wise to "log" all exceptions, as a "swallow all and be silent" is a known point of failure. Sometimes an exception is thrown away that you did not expect, causing weird program-behaviour.

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

DanielSheets12-Oct-12 2:55

12-Oct-12 2:55

If you'll forgive my ignorance... I guess I dont know what you mean by "swallow any exceptions, which isn't such a great thing".

My knowledge of C# isnt very deep, as you can see.

OriginalGriff12-Oct-12 3:52

OriginalGriff

12-Oct-12 3:52

This code:

try
 {
     ...
 }
 catch (Exception e)
 {
 }

is called "swallowing an exception", because whatever error occurs in the try block will be caught by the catch block and discarded without any attempt to handle it, log it, or in any other way acknowledge that there is a problem that should be fixed, or at least investigated.

This is considered a poor programming practice, as it just masks problems that may become serious later. There can (occasionally) be a good reasons for ignoring specific exceptions, but these should be restricted to specific exception classes (such as ArgumentNullException, or FileLoadException) rather than a blanket "Exception" and commented thoroughly.

Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water

DanielSheets19-Oct-12 1:31

19-Oct-12 1:31

Ahh... Gotcha.

There actually is code there. I took it out when I posted it here.

OriginalGriff19-Oct-12 1:35

OriginalGriff

19-Oct-12 1:35

Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water

Bernhard Hiller12-Oct-12 3:14

Bernhard Hiller

12-Oct-12 3:14

The exceptions which could arise in the ReadDaq function will arise in a different thread - the thread of the GUI. You are not able to catch them here, hence you can omit the try-catch-block here. But ReadDaq ought to have its own try-catch.

Alan N12-Oct-12 7:04

Alan N

12-Oct-12 7:04

Bernhard Hiller wrote:
You are not able to catch them here,

No, not quite true (at all). The Invoke mechanism catches an unhandled exception within the target method and rethrows it in the calling thread. In doing this the stack trace containing the site of the original exception is lost. Whether or not something bad happens when the exception is rethrown depends on the caller. For example I've noticed that the thread used by a System.Timers.Timer to call the Elapsed event handler carries on obliviously with no hint of discomfort!

See the remarks section in Control.Invoke[^]

Alan.

How to Check Printer Status using SNMP and c#

V.12-Oct-12 3:22

12-Oct-12 3:22

not 100% sure, but you could pass null instead of new Object[]{}. The signature of the Invoke method requires an object array. This is actually used to box/unbox parameters for the threading function. If null is allowed (I think so) this is for me preferable, because it indicates we're passing it to fulfill the method requirement. passing a new Object[]{} not only initializes memory, but also might indicate we "forgot" to do something.

Hope this helps.

V.

(MQOTD Rules )

batuhan karaduman11-Oct-12 22:14

batuhan karaduman

11-Oct-12 22:14

XML

String snmpAgent = "ipAddressOfPrinter";
String snmpCommunity = "public";
SimpleSnmp snmp = new SimpleSnmp(snmpAgent, snmpCommunity);
Dictionary<SnmpSharpNet.Oid, AsnType> result = snmp.Get(SnmpSharpNet.SnmpVersion.Ver1, new string[] { "OidOfPrinter" });
if (result == null)
{
    MessageBox.Show("Request Failed", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
else
{

    foreach (KeyValuePair<SnmpSharpNet.Oid, AsnType> entry in result)
    {
        textBox1.Text = entry.Key.ToString() + " = " + SnmpConstants.GetTypeName(entry.Value.Type) + " (SysDesc.): " + entry.Value.ToString() + "->

here is the connection to the printer. I can get the name, properties, software etc. of the printer, but i cant get the status of the printer(if it is online, offline, toner level, paper status, etc.) can you help me to code this?

Thanks a lot for your ideas and helps.

Re: How to Check Printer Status using SNMP and c#

OriginalGriff12-Oct-12 1:52

OriginalGriff

12-Oct-12 1:52

Please do not repost the same question, particularly only two hours later!
It's rude, unnecessary, and unlikely to win you friends or get a better answer.

Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water

Re: How to Check Printer Status using SNMP and c#

Eddy Vluggen12-Oct-12 1:54