How to use GLOBAL Dataset Between WinForms?

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Hi all,
I have a MainForm, a MyClass and different DialogForms. I want to use a dataset for storing my combobox tables as long as my application runs, because every time opening a dilaog form I do not want to make any query to fill comboboxes. The combobox defined on MyClass and filled when MainForm. So, what is the best method for my situation? Using static parameter, or some smart suggetsions, etc. Thanks in advance...:confused:

Posted 3-Mar-11 1:21am

H.Johnson

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3 solutions

Solution 3

Create a static Globals class that holds app-wide data members.

C#

public static class Globals
{
    public static DataSet MyData { get; set; }

    static Globals()
    {
        // initialize MyData property in the constructor with static methods
    }
}

This is the way I do it. I know - global data is "evil", but this is a handy solution to the "I want to get to it from anywhere" requirement.

Posted 3-Mar-11 1:50am

#realJSOP

v2

Comments

H.Johnson 3-Mar-11 7:54am

Thanks for reply. You are right global data is evil. But, my actual aim is simply to hold a dataset on MyClass and access it when opening my DialogForm. So, how can I do this in a smart way?

#realJSOP 3-Mar-11 11:55am

There's absolutely nothing wrong with doing it this way. It's static so that there's only one copy of it. You can put initiziation code into the Globals class that will take care of populating the dataset, and if you call that code from the Globals constructor, it will be available when your form is initially displayed. Just because someone else thinks a particular methodology is "evil" doesn't mean it ain't damn convenient. Besides considering globals to be "evil" is merely a guideline - kinda like the Bucaneer code.

Sergey Alexandrovich Kryukov 3-Mar-11 11:42am

Simple and will work, but does not have to be static, see my comment to Griff's answer.
However, why not static? A 5 anyway.
--SA

Solution 1

If the data it going to be the same for all parts of your application, then it does make some sense to hold it as a static property, probably in your MainForm, since that is the first thing loaded: it can set the values in it's Load event for everything else to use.

Posted 3-Mar-11 1:32am

OriginalGriff

Comments

H.Johnson 3-Mar-11 7:54am

Yes, the data is not changed everyday. The data is City names. So, I think to keep it on MyClass when MainForm is loaded. And whenever a DialogForm opens, I want to call this kept dataset to fill the comboboxes on my Dailog form. Any smart and intelligent method will be very appreciated.

Sergey Alexandrovich Kryukov 3-Mar-11 11:39am

Griff, if your offer to put a property in a main form, it does not have to be static, because it is created first, you can pass its reference to other forms (but better interface reference).
--SA

#realJSOP 3-Mar-11 11:56am

If you put the object into a global static class, it's even more convenient because it's available everywhere.

Sergey Alexandrovich Kryukov 3-Mar-11 14:21pm

As I say, nothing wrong with that, especially of it is accessed from one thread, thread synchronization is not needed.
--SA

OriginalGriff 3-Mar-11 14:15pm

You can pass the reference to other forms, but it gets messy: you have to be sure you have passed it all the way to all relevant forms/classes.
In practice, I would go with JSOP and create a static Globals class (I often do).
Dunno why I suggested putting it in the main form: I plead stupidity!

Sergey Alexandrovich Kryukov 3-Mar-11 14:25pm

This is what I say: you either make a singleton not related to any of the form, which is suggested by John and is the easiest, or you make if harder but potentially more flexible with passing all those references and not using static. Something in between does not add value to either.
--SA

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Dylan Morley · Accepted Answer · 2011-03-03T01:58:00

Solution 4

What you really want to do here is caching.

When you application launches, it's going to need to get some data from a database or whatever storage you are using to populate your cache.

The logic I use here is like this...

Cache Logic Diagram[^]

So, the first time you call a method, it will invoke the database operation and cache the data. Next time you call the method, the data is retrieved from the Cache.

You can implement this using a CacheManager class, source as follows

NB: this using the HttpRuntime caching mechanism, so you'd need a reference to System.Web in your project

PasteBin source code for CacheManager[^]

You can then call like follows...

C#

/// <summary>
/// Execution delegate that returns some data
/// </summary>
/// <typeparam name="TValue">value</typeparam>
/// <returns>Business set</returns>
public delegate TValue DataRetrievalDelegate<TValue>();

public System.Data.DataTable GetCityData()
{
    return CacheManager.RetrieveFromCacheOrInvoke<System.Data.DataTable>("Cache:CityData",
       new DataRetrievalDelegate<System.Data.DataTable>(delegate()
       {
           // Your code here for retrieving data from some source!
           return new System.Data.DataTable();
       }));
}

I've put together a little demo project if you're struggling with this.

Retrieve From Cache Or Invoke Demo[^]

Have a look in the Program.cs file. Put a breakpoint on the first line...run the project through line by line.

Notice how the first time it will call the delegate method, the second time it will retrieve from the cache

:thumbsup:

Posted 3-Mar-11 1:58am

Dylan Morley

Updated 3-Mar-11 5:15am

v2

Comments

H.Johnson 3-Mar-11 10:24am

Thanks, but there is a problem for some of the lines like Caching and Http. On the other hand, I have a WINFORM, not an Web Page. Caching is very nice, but if it is not suitable for WINFORM, could you suggest another intelligent solution please? On the other hand, when searching on the web, I have found this. What about it?Is it useless?

01.using System;
02.using System.Collections.Generic;
03.using System.Linq;
04.using System.Text;
05.using System.Threading;
06.
07.public class CacheManager
08.{
09. static System.Collections.Hashtable ht = new System.Collections.Hashtable();
10.
11. public static void AddItem(string key, object value, uint timeToCache)
12. {
13. if (timeToCache > 3600)
14. throw new ArgumentOutOfRangeException("Cache time cannot be more than 1 hour.");
15.
16. System.Threading.Timer t = new System.Threading.Timer(new TimerCallback(TimerProc));
17. t.Change(timeToCache * 1000, System.Threading.Timeout.Infinite);
18. ht.Add(t, key);
19. AppDomain.CurrentDomain.SetData(key, value);
20. }
21.
22. public static object GetItem(string key)
23. {
24. return AppDomain.CurrentDomain.GetData(key);
25. }
26.
27. private static void TimerProc(object state)
28. {
29. System.Threading.Timer t = state as System.Threading.Timer;
30.
31. if (t != null)
32. {
33. object key = ht[t];
34. ht.Remove(t);
35. t.Dispose();
36.
37. if (key != null)
38. AppDomain.CurrentDomain.SetData(key.ToString(), null);
39. }
40. }
41.}

Calling :
CacheManager.AddItem(cacheKey, myDataTable, 300);

Kindest regards...

Dylan Morley 3-Mar-11 11:16am

Please see my updated answer: Demo project is available at the bottom now

Sergey Alexandrovich Kryukov 3-Mar-11 11:43am

Very good in-depth stuff, my 5.
--SA

Dylan Morley 3-Mar-11 10:25am

Did you see the line I wrote??

NB: this using the HttpRuntime caching mechanism, so you'd need a reference to System.Web in your project

Add the reference to System.Web in your project that will do the caching & it will work.

H.Johnson 3-Mar-11 18:20pm

Dear Dylan,
thank you very much for your good explanations and wonderful method + sample source. That's really how a brief explanation could be. My 5. I just would like to ask some question regarding to positioning these logic to my project. Could you confirm the points below;

1) In my project there is MainForm, DialogForm and MyClass. I will add my project CacheManager and CachedData classes, is it true? Or is there anythink I should add to my project?

2) Shall I move CachedData class to MyClass? Or, should I use it seperately?

3) I think I call CachedData from MainForm. CachedData class going to Database and returns datatable (or I can change to return DatSet). The cached data is stored
on CachedData class? Is it true?

4) CacheManager class's task sets all the caching setup. Is it true?

5) Under this conditions, I think to build my logic like that; when MainForm load, I call CachedData. At this point, do I have to fill the returned datatable (or dataset) to a new variable on MainForm?
Because, I do not use this variable on MainForm. Actually I do not want to create a variable on MyClass to keep the cached data. Instead of this, I would like to
call CachedData.GetData() method to retrieve data directly without creating any variable. I mean;

//On CachedData class
DataSet ds = new DataSet();
ds = GetData();
myCombobox.DataSource = ds.Tables["Student"];

//Instead of this, should I use like below without creating a DataSet variable?;
myCombobox.DataSource = GetData().Tables["Student"];

I would be very appreciated if you suggest me the most suitable way according to my logic. Thanks in advance...

Dylan Morley 4-Mar-11 4:33am

1) Yes, just add the 'CacheManager' and a class that will expose your methods that require data caching. In the example project I created 'CachedData' class, but this can be anything you want...it's just a class that allow you to call a method and rerieve data from either the database or the cache.

2) See 1). You can do, you only need 1 class to manage the data acces \ caching. Again, see demo project for an example

3) Yes, you call the CachedData class...it will go to the database the *first* time you call the method. The *second* time it will get from the Cache. Data isn't actually stored in the CachedData class, it's stored in the Cache (by CacheManager). CachedData class just provides the methods that say 'Get this type of data from either a method or the Cache'

4) Yes, it's completely self contained & sets everything up. You don't need to touch any of the code in the class.

5) It doesn't matter if you use a variable on the MainForm, as long as it's locally scoped. e.g

private void LoadComboBox()
{
// Here, GetStudentData is a method that returns a 'DataTable' of student information from either the database or the cache
DataTable myData = CachedData.GetStudentData()

myCombobox.DataSource = myData;
}

In the above, the datatable we've created is locally scoped, it goes out of scope as soon as the method exits. Data is only managed it one place - the CacheManager.

Use the demo project a few times until you're confident exactly what's going on. Once you are, it's quite a simple and efficient way of storing data.

H.Johnson 4-Mar-11 19:11pm

Dear Dylan Morley,
you have completed your perfect example with a one-by-one answers. On the 5th answer is also very important point for me to decide whether to create a variable. As you mentioned, there is no need to worry about it as long as creating and using it a local method. Thank you very much for this professional solution and helps. On the other hand, thanks to the other friends for sharing their useful suggestions on this topic.
With kindest regards...