Re: Hashtable with Structure or Class Object - C# Discussion Boards

16-Dec-09 0:37

I am trying to use a hashtable (or equivalent) to store and recover a number of small structures or classes.

The hashtable record will need to have a UInst32 key and an associated data structure or class that looks some thing like this:

bool bRecUsedFlag;
UInt32 uiPGN;
UInt32 uiRecCtr;
byte[] bPGNData;

I can see odd references that indicate that this is possible but every attempt I have to code it is failing.

Can anyone give me a small example of how to create this table, add records to it and get records from it please?

Many thanks, Bruce Smile | :)

Richard MacCutchan16-Dec-09 0:50

Richard MacCutchan

16-Dec-09 0:50

First thing to do is design the class you want to contain your data, and its hash key. Then you just need to use the Hashtable[^] class to store and retrieve your individual objects.

[edit]spelling[/edit]

Bruce Coward16-Dec-09 1:06

16-Dec-09 1:06

That is what I thought was possible but I must be missing a trick because everyway I come at this I hit problems that I haven't solved yet.

Can anyone point this comparative newbie in the right direction with a simple example based on the data in my first email please?

Many thanks, Bruce

Richard MacCutchan16-Dec-09 1:20

Richard MacCutchan

16-Dec-09 1:20

Bruce Coward wrote:
Can anyone point this comparative newbie in the right direction with a simple example based on the data in my first email please?

I just did so; did you look at the examples in that link?

Bruce Coward16-Dec-09 1:26

16-Dec-09 1:26

I looked at those examples but all I could see were bog standard string keys and single string data. This I have working. My problem is lifting the data up into a structure or class...

Cheers Bruce

Richard MacCutchan16-Dec-09 1:46

Richard MacCutchan

16-Dec-09 1:46

Bruce Coward wrote:
My problem is lifting the data up into a structure or class

It's just the same, instead of String you use your own class. Here[^] is the top link Google offers, you can work through this tutorial to get an understanding of Hashtable basics, and then use the same code with your custom class as the content. Remember that a string is just a class in C#.

Bruce Coward16-Dec-09 2:08

16-Dec-09 2:08

Hi Richard,

Thank you for your continuing patience...

I have spent quite a time with that link yesterday and am happy with it's basic message. I appreciate that string is only a class but my problem comes when I try to build my small class and store it in the Hashtable. I can do that and by single stepping I can see my two data records be added to the hashtable. I notice that the hashtable seems to add both records but put the second records data over the first hash position as well as the second hash posotion but I haven't chased that problem yet.

My real problem comes when I try to recover the records when I am not getting the data back. Here is my code:

namespace ConsoleApplication7
{
    class Program
    {
        class csFPRec
        {
            public UInt32 uiPGN;
            public UInt32 uiFrameCtr;
        }
        
        static void Main(string[] args)
        {
            // Instantiate Class
            csFPRec FPRec = new csFPRec();
            Hashtable HT = new Hashtable();
 
            Console.WriteLine("Writing Initial Records");
            
            Console.WriteLine("Writing 0x1234");
            FPRec.uiPGN = 0x1234;
            FPRec.uiFrameCtr = 0x01;
            HT.Add(FPRec.uiPGN, FPRec);
            
            Console.WriteLine("Writing 0x5678");
            FPRec.uiPGN = 0x5678;
            FPRec.uiFrameCtr = 0x02;
            HT.Add(FPRec.uiPGN, FPRec);
            
            Console.WriteLine();
            Console.WriteLine("Reading Records");

            // Get record back from Hashtable
            object pgnobj = new object();
            pgnobj = HT[0x1234];


            Console.ReadLine();
        }
    }
}

As you can tell I am a newbie with C# having been writing embedded C for more than 20 years.

Best regards

Estys16-Dec-09 2:28

Estys

16-Dec-09 2:28

Try this :

....
FPRec = new csFPRec();
FPRec.uiPGN = 0x5678;
FPRec.uiFrameCtr = 0x02;
...

You added the same instance FPRec twice

Bruce Coward16-Dec-09 2:37

16-Dec-09 2:37

Thanks Richard - that has fixed the records being the same on the hashtable.

Can you see what I am doing wrong in getting the records off the hashtable?

Many thanks, Bruce Thumbs Up | :thumbsup:

Bruce Coward16-Dec-09 3:02

Re: Hashtable with Structure or Class Object [modified]

16-Dec-09 3:02

Woops! - Wrong thanks. Thanks Estys.

Chers Bruce Thumbs Up | :thumbsup:

Estys16-Dec-09 3:10

Estys

16-Dec-09 3:10

...
pgnobj = HT[(UInt32)0x1234];
...

The basic Comparer is Object.Equals()
Your key value was converted (cast) to System.Int32 which does NOT equal UInt32 (I suspect)

modified on Wednesday, December 16, 2009 9:21 AM

Bruce Coward16-Dec-09 3:25

Silverlight Control interactions with WinForms

16-Dec-09 3:25

Got It!

Many thanks Estys. Solved it. Really appreciate your help.

Cheers Bruce Smile | :)

softwarejaeger16-Dec-09 0:31

softwarejaeger

16-Dec-09 0:31

Hello,

how is it possible to communicate with a Silverlight-App in a WebBrowser-Control in WinForms?
Is there also a possibility to use the same Classes (of course both need to have the same Interfaces)?

So can i return a class from the Silverlight-App into my WinForms-App? And that without JSON and JavaScript and blah? Smile | :)

Many thanks

Backup of the application data [modified] Solved

NarendraSinghJTV16-Dec-09 0:17

NarendraSinghJTV

16-Dec-09 0:17

Hi all,

There is a small problem with me, so thought to share it with all of you, thought i will find any idea, I have a window application created with C#, i want to create the functionality of taking backup and restoration of application data, i found some threads on google which r showing the process of taking backup from the database, my need is to create a backup file of application database n again restore it when needed

waiting for positive reply

thanks in advance for all your responses

Regards
Narendra Singh
(Jindal Tech Ventures)

modified on Friday, December 18, 2009 7:46 AM

Saksida Bojan16-Dec-09 2:42

16-Dec-09 2:42

So what's the problem?

If application uses local file, just copy to different folder

NarendraSinghJTV16-Dec-09 23:39

NarendraSinghJTV

16-Dec-09 23:39

thats the question,
HOW

Regards
Narendra Singh
(Jindal Tech Ventures)

Saksida Bojan17-Dec-09 4:02

17-Dec-09 4:02

System.IO.FileCopy()[^]

If you are using SQL database, read all data, then save as xml file

MS SQL backup and restore in C#[^]

Trying To Create A Data Access Layer

NarendraSinghJTV18-Dec-09 1:45

NarendraSinghJTV

18-Dec-09 1:45

Thanks saksida for ur helpful reply

Regards
Narendra Singh
(Jindal Tech Ventures)

Roger Wright15-Dec-09 19:17

Roger Wright

15-Dec-09 19:17

and I have little idea how to implement it...

I created a code folder, and a DeviceData class in it, with a constructor that (hopefully) constructs a local device of a variable type when it's instantiated. I don't actually know if it's possible to pass an object to a constructor and cast it to a specific object type based upon a Type parameter, but the compiler doesn't whine about it. I assume it's working. But I could be wrong...

My thinking is to add to the DeviceData class member functions that handle the Add, Edit, Delete, and View functions that encapsulate all the nasty database communication details so the rest of my program doesn't have to deal with them. I just want to pass an object of one of 5 types to this code block, specify what I want it to do with it, and forget it.

The devil is always in the details, though, and when I try to buld a function to add a new device to the database, the IDE snivels about an Identifier being required as the Add function parameter. I know that doesn't help much, so here's the constructor:

public DeviceData(int Type, object Device)
   {
       //Create a local device instance of the proper type

       switch (Type)
       {
           case 1:         //Recloser
               Recloser dev = new Recloser();
               dev = (Recloser)Device;
               break;
           case 2:
               //Regulator dev = new Regulator();
               //dev = (Regulator)Device;
               break;
           case 3:
               //Breaker dev = new Breaker();
               //dev = (Breaker)Device;
               break;
           case 4:
               //Transformer dev = new Transformer();
               //dev= (Transformer)Device;
               break;
           case 5:
               //LTC dev = new LTC();
               //dev = (LTC)Device;
               break;
           default:
               break;
       }

   }

I could be completely out to lunch, but I think that creates a member variable called dev of a type defined by the object type passed to it. At least, I hope so, and VS doesn't generate any nasty errors when I build the solution. Unfortunately, when I try to actually use the variable, things get ugly:

public int GetDevice(dev)
    {
        return 0;

    }

At this point, the compiler complains that I haven't provided an identifier, and I don't know why. My intent is to instantiate the DeviceData object by passing the constructor a specific object that has been populated using a Form in another part of the program. My thinking is that this should create an instance variable, called dev, that can be filled with the field data from the passed object. The next step would be to query the database to populate the fields, then return the object to the calling Form module. I haven't a clue at this point why I'm receiving this message, though, and would appreciate any input.

"A Journey of a Thousand Rest Stops Begins with a Single Movement"

Saksida Bojan15-Dec-09 20:37

15-Dec-09 20:37

public DeviceData(int Type, object Device)

Where is return Type? This is function and if you do not want to have return type, use void

Edit: To check object for type use:

if (device is Recloser)
    dev = (Recloser)Device;

This (int Type) shroud be avoided, you can make a mistake, and it the code can become unreadable

0x3c015-Dec-09 21:06

0x3c0

15-Dec-09 21:06

Saksida Bojan wrote:
Where is return Type? This is function and if you do not want to have return type, use void

It's probably a constructor.

OSDev

Roger Wright16-Dec-09 6:51

Roger Wright

16-Dec-09 6:51

Exactly.

"A Journey of a Thousand Rest Stops Begins with a Single Movement"

0x3c015-Dec-09 21:06

0x3c0

15-Dec-09 21:06

The IDE is supposed to snivel at the switch-block. I don't think you can put a declaration in the case-blocks, unless you enclose the entire case block in {}. So this:

case 5:
    LTC dev = new LTC();
    dev = (LTC)Device;
    break;

becomes this:

case 5:
{
    LTC dev = new LTC();
    dev = (LTC)Device;
    break;
}

Roger Wright wrote:
public int GetDevice(dev)

I don't know if this is a proof of concept, but I think you need to provide a type, or remove the parameter and use the local variable instead.

OSDev

Saksida Bojan15-Dec-09 22:44