How Do I Access Interface Methods Here.

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I would like to implement the Interface concept in my application , So ijust tried some thing like below but its going something wrong

Interface

C#

interface Grid
{
    DataTable Gridbind(string FromDate, string ToDate);

}

Implementation Class

C#

public class GridImplementationClass : Admin_PerformanceIncentive, Grid
{
   
    public DataTable Gridbind(string FromDate,string ToDate)
    {
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["constring"].ConnectionString);

        using (SqlCommand cmd = new SqlCommand("Incentive_Sp", con))
        {
            con.Open();
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@FromDate", FromDate.ToString());
            cmd.Parameters.AddWithValue("@ToDate", FromDate.ToString());
            cmd.Parameters.AddWithValue("@type", 2);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataTable  dt= new DataTable();
            da.Fill(dt);

            con.Close();
            return dt;
           
        }
       
    }

}

Another Class

C#

public partial class Admin_PerformanceIncentive : System.Web.UI.Page
{
    GridImplementationClass obj = new GridImplementationClass();//Something wrong here.
 protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        { 
           
            DataTable dt = new DataTable();
         dt= obj.Gridbind(FromDate.ToShortDateString(), Todate.ToShortDateString());
        
        }
    }
}

GridImplementationClass obj = new GridImplementationClass()
In obj it shows NULL and it doesn't move to next line while debugging.
Its blink on the same line while i hit F10
How to fix it?

Posted 22-Mar-15 21:16pm

King Fisher

Updated 22-Mar-15 21:43pm

v2

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Comments

Sinisa Hajnal 23-Mar-15 3:25am

Move your instantiation into the postback. There is nothing wrong with the code, except obviously your "obj" is not created.

Set breakpoint on new GridImplenetationClass and into Page_Load and see what happens in what order :)

King Fisher 23-Mar-15 3:31am

I moved now it works.Can't we instantiate the obj Globally?

2 solutions

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Sergey Alexandrovich Kryukov · Accepted Answer · 2015-03-22T21:41:00

Solution 1

Better don't violate naming conventions: your interface should be named IGrid. It won't fix your problems but will make life easier. :-)

Also, don't use the word "class" in the name of the class. Isn't it obvious?

I agree with Sinisa Hajnal: you don't show the all the code helping to figure out why obj is null, but you can easily find it out under the debugger. Your problem is different: understanding. If you want to use interfaces, actually use them.

Consider this:

C#

public class GridImplementationClass : AdminPerformanceIncentive, IGrid
{
   // explicit interface implementation will help you
   // to hide implementation from the user of
   // the class reference, you will need to use only
   // the interface reference,
   // to improve discipline of your code:
   DataTable IGrid.Gridbind(string FromDate, string ToDate) { /* ... */ } 
   // ...
}

// ...

GridImplementationClass @object = new GridImplementationClass();
// it's very likely that you never need to use this object,
// it seems so because of the name of your class "...Implementation";

IGrid grid = @object; // works, according to general rules
                      // of assignment compatibility
                      // for derived types
// or, better, directly IGrid grid = new GridImplementationClass();

// ...

DataTable dataTable = grid.Gridbind(/* ... */);

Are you getting the point?

—SA

Posted 22-Mar-15 21:41pm

Sergey Alexandrovich Kryukov

Updated 22-Mar-15 21:42pm

v2

Comments

King Fisher 23-Mar-15 3:50am

I'm getting this error "Error 1 'IGrid.Gridbind': explicit interface declaration can only be declared in a class or struct
"

Sergey Alexandrovich Kryukov 23-Mar-15 3:57am

And I suggested to do it for the class, precisely. Probably, you screwed up something somewhere. Can you show some code sample manifesting that problem. It would be better if you could reduce it to the simplest and self-contained sample, not depending on your other declarations.
—SA

King Fisher 23-Mar-15 3:55am

Sorry I mention declared with in Interface, sorry. :)

Sergey Alexandrovich Kryukov 23-Mar-15 3:58am

No problem.
Will you accept my answer formally now?
In all cases, your follow-up questions will be welcome.
—SA

King Fisher 23-Mar-15 4:02am

Still I'm getting null while Instantiate globally .Can i show my Code?

Sergey Alexandrovich Kryukov 23-Mar-15 4:06am

You can try to show your code using "Improve question", but it should better be some self-contained code. What does it mean, "globally"?
—SA

King Fisher 23-Mar-15 4:05am

Can't we instantiate globally.If instantiate with in any methods it works well.Do i have to instantiate the GridImplementationClass in every methods?

Sergey Alexandrovich Kryukov 23-Mar-15 4:06am

Essentially, there is no such thing as "globally". It might be some misconception which is the root of all your problems. Please explain the two cases.

It you instantiate something twice, it would be two different objects. Isn't that obvious? Do you need one object used in many places? (It doesn't mean "global".)

—SA

King Fisher 23-Mar-15 5:03am

sorry for delay ,I was in lunch .Yes i need to use one object many places.

Sinisa Hajnal 23-Mar-15 4:39am

There is no "globally" in asp.net. Each request is separate, there is no persistent objects between postbacks that keeps your state. If you need that you have to use Session or some other persistance mechanism.

King Fisher 23-Mar-15 5:11am

How can i use single object in many places?

Sinisa Hajnal 23-Mar-15 5:19am

Session object. When you initially create your object put it in a session like this:
Session("your_label") = obj where your_label can be whatever unique string you want. When you need to take that same object you cast the object you stored and use it: CType(Session("your_label"), IGrid)

Sergey Alexandrovich Kryukov 23-Mar-15 8:24am

You are talking about Web applications. I don't think this is about the same object on different page...
—SA

King Fisher 23-Mar-15 8:27am

No i don't mean different page.for eg - I have more that 10 methods in my page.So if i Instantiate the object with in postback then how can i access the object to other methods.

Sinisa Hajnal 23-Mar-15 9:28am

There is ASP.NET tag...I'd say this is web application. Each time he comes to the page there will be new instance of the object...Unless some persistence is used.

King Fisher 23-Mar-15 9:29am

thank you I understand.

Sergey Alexandrovich Kryukov 23-Mar-15 9:30am

Yes, but I feel the question is unrelated to that. King Fisher confirmed that by his previous comment.
Unfortunately, it looks like the lack of understanding of reference types, and hence, .NET programming in general...
—SA

Sergey Alexandrovich Kryukov 23-Mar-15 8:27am

First thing to understand: this is a reference object.
Do you understand them? You have multiple references to the same object.
Do you know what happens here?
class myClass {}
myClass instance1 = new myClasss();
myClass instance2 = instance1.
How many objects are there?
—SA

F-ES Sitecore · Accepted Answer · 2015-03-22T22:57:00

Solution 2

You haven't said why you want to use an interface, and as already pointed out your code wasn't even using it. If you have no real need for an interface and you are looking for "global" code then my advice is to not use the interface at all and use a static method instead.

C#

public class GridImplementationClass : Admin_PerformanceIncentive
{
    public static DataTable Gridbind(string FromDate, string ToDate)
    {
        // your existing code
    }
}

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        DataTable dt = GridImplementationClass.Gridbind(FromDate.ToShortDateString(), Todate.ToShortDateString());
    }
}

No need to instantiate the GridImplementationClass class to use the Gridbind method.

Posted 22-Mar-15 22:57pm

F-ES Sitecore

Comments

King Fisher 23-Mar-15 5:14am

Actually I have attended 3-4 interviews, they asked me that have you used Interface? so i decided to implement interface in my Project ,that' it :)

Sinisa Hajnal 23-Mar-15 5:19am

This is terrible reason. If you don't need it, don't use it.

King Fisher 23-Mar-15 5:23am

How do i know whether its needed or not ? I think its applicable in this case. if not ,then which case can i use Interface? can u please explain where i use Interfaces? In many interviews its asked by Interviewer.

F-ES Sitecore 23-Mar-15 5:38am

They ask you that question because they are wanting to know if you have understanding of interfaces etc and if you have used them before. Trust me when I say that using interfaces because you think you should is as bad as not understanding them at all. Rather than trying to "trick" your way to a job by misrepresenting your understanding, read some articles on interfaces (there are many on the net if you google) and get to a stage where you genuinely understand them and their uses and when you use them and when you don't.

They're commonly used for dependency inject\inversion of control, unit testing, and general OOP practices where you're only interested in the methods an object exposes rather than the object's concrete class.