Cannot Create The Object Of Abstract Class
Apr 22, 2010We all know that, we cannot create the object of Abstract class.
But why it is so?
I mean, can anyone explain it with real time example?
We all know that, we cannot create the object of Abstract class.
But why it is so?
I mean, can anyone explain it with real time example?
Why do we use the reference of abstract class (or base class) to create object of it's sub-class. eg: TextWriter is the abstract class for StreamWriter & StreamWriter.
TextWriter writer = new StreamWriter();
why can't we simply use :
StreamWriter writer = new StreamWriter();
I am trying to compile the following code and i am getting the error:
Cannot create instance of abstract class .
m_objExcel = new Excel.Application();
m_objBooks = (Excel.Workbooks)m_objExcel.Workbooks;
m_objBook = (Excel._Workbook)(m_objBooks.Add(m_objOpt));
m_objSheets = (Excel.Sheets)m_objBook.Worksheets;
m_objSheet = (Excel._Worksheet)(m_objSheets.get_Item(1));
// Create an array for the headers and add it to cells A1:C1.
object[] objHeaders = {"Order ID", "Amount", "Tax"};
m_objRange = m_objSheet.get_Range("A1", "C1");
m_objRange.Value = objHeaders;
m_objFont = m_objRange.Font;
m_objFont.Bold=true;
// Create an array with 3 columns and 100 rows and add it to
// the worksheet starting at cell A2.
object[,] objData = new Object[100,3];
Random rdm = new Random((int)DateTime.Now.Ticks);
double nOrderAmt, nTax;
for(int r=0;r<100;r++)
{
objData[r,0] = "ORD" + r.ToString("0000");
nOrderAmt = rdm.Next(1000);
objData[r,1] = nOrderAmt.ToString("c");
nTax = nOrderAmt*0.07;
objData[r,2] = nTax.ToString("c");
}
m_objRange = m_objSheet.get_Range("A2", m_objOpt);
m_objRange = m_objRange.get_Resize(100,3);
m_objRange.Value = objData;
// Save the Workbook and quit Excel.
m_objBook.SaveAs(m_strSampleFolder + "Book2.xls", m_objOpt, m_objOpt,
m_objOpt, m_objOpt, m_objOpt, Excel.XlSaveAsAccessMode.xlNoChange,
m_objOpt, m_objOpt, m_objOpt, m_objOpt);
m_objBook.Close(false, m_objOpt, m_objOpt);
m_objExcel.Quit();
Error 1279 Cannot create an instance of the abstract class or interface 'System.Web.Mvc.FileResult'
[Code]....
I am using MVC 2. The same code works in my onather application. I have no idea about this error.
Configuration Error Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately. Parser Error Message: Cannot create an abstract class.
Source Error:
Line 150: <providers>
Line 151: <clear/>
Line 152: <add name="NDMSMembershipProvider"
type="CSW.Web.Security.NDMSMemberProvider"/>
Line 153: </providers>
Line 154: </membership>
Source File: C:DevCSW2srcCSW.Webweb.config Line: 152
When to use Abstract class and when to use Interface class.
View 10 RepliesFrom the following URL i got some doubts about the Recommendations for using Abstract class vs interfaces
[URL]
1. If you anticipate creating multiple versions of your component, create an abstract class. Abstract classes provide a simple and easy way to version your components. By updating the base class, all inheriting classes are automatically updated with the change. Interfaces, on the other hand, cannot be changed once created. If a new version of an interface is required, you must create a whole new interface. { Is there any example for this t ounderstand throughly ?} If you are designing small, concise bits of functionality, use interfaces. If you are designing large functional units, use an abstract class. If you want to provide common, implemented functionality among all implementations of your component, use an abstract class. Abstract classes allow you to partially implement your class, whereas interfaces contain no implementation for any members. { Is there any example for this t ounderstand throughly?
I just want to know that how can I utilize the concept of Abstract class, virtual class etc. in my shopping cart website. I have read the tutorial out there on internet and I saw some examples too, but those examples are so general that they dosen't fit into real world scenerio like I am searching for a shopping website. Same questions again and again comes to my mind that why to made a class only to give the declaration of methods and property.
View 4 Replieswhat is the function of abstract class, why design pattern need to build BLL and DAL
anyone give an example for my reference as I am getting strat to build my web-based project
I know what Singleton Pattern means and Abstract class means.What I wanted to know was how would this apply to real world.Could anyone give me any good example or simple explanation.Say I have a simple website, why would I use any of the above if any.Why would it simplify my architechture.
View 3 RepliesWhat is the use of abstract class design in real time projects
and how to use abstract clases and interfaces
and inheritense concepts
like big shoping portals or content managment,blogs etc
how to create object of HttpResponse class
HttpResponse response=new
HttpResponse (TextWriter
tx);
how to inplement this wrong code to right one & how to implement TextWriter.
I am developing a couple of small ASP.NET application and would like to know what pattern. approach do you use in your projects.
My projects involve databases, using Data access and Business logic layers.
The data-access approach that I was using so far is the following(I read in some book and liked it):
For DAL layer:
Creating an abstract class that will define all database manipulation methods to implement.
The abstract class will contain a static "Instance" property, that will load (if instance == null) an instance (Activator.CreateInstance) of the needed type (a class that implements it).
Creating a classes that implement this abstract class, the implementation will be according to the databases (SQL, mySQL and etc) in use.
With this I can create different implementation according to database in use.
For BLL layer:
A class that encapsulates all all retrieved fields , and static methods that will call the DAL classes.
I am attempting to bind a Repeater (but it could be a GridView or ListView) to a list of objects. The List's type is an abstract type, which has two different classes derived from it, both with different properties. Because they have different properties, I cannot just have one ItemTemplate. If I bind a control to a property of one type of class and the other type doesn't have it, it throws an error.
Here's where I'm at:
I cannot use <% if (whatever) { %> some stuff <% } else { %> some other stuff <% } %> because I cannot access the databound item to make the choice based on its type. I cannot use the <%# %> syntax, which lets me use the databound information, because you cannot code logic like if...then...else. I cannot (rather not) call a function and return a string with the code because what I want to render is complex and contains further nested databound controls. Has anyone found an ingenious way of doing if it is this type of object, display these controls, else display these other controls?
I have a product class which contains 11 public fields.
ProductId
ShortTitle
LongTitle
Description
Price
Length
Width
Depth
Material
Img
Colors
Pattern
The number of fields may grow with attributes for more specific product tyes. The description may contain a large amount of data. I want to create a slim version of this product class that only contains the data needed. I'm only displaying 4 of the 12 fields when listing products on a category page. It seems like a waste to retrieve all of the data when most of it isn't being used. I created a parent class of ProductListing that contains the 4 fields I need for the category page
ProductId
ShortTitle
Price
Img
Then created a class of Product that inherits from ProductListing containing all product data. It seems backwards as "ProductListing" is not a kind of "Product" but I just started reading about inheritance a few months ago so it's stil a little new to me. Is there a better way to get a slim object so I'm not pulling data I don't need? Is the solution I have in place fine how it is?
i need to create a instant of class by string value which store in hiddenfield.value()
string str = "myclass1";
var x = new <str>();
or
var x = new <hiddenfields1.value.tostring()>();
How to create object of class file (asp.net) using javascript and call is methods.
View 1 RepliesFor some unknown reason I suddenly am unable to create an object variable for a Linq Data Class. If I create a new project and try the process again with the same database everything works as advertized.The code I am using is Dim db As New RoggDataContext which gives me an error on the object variable "db": Overload resolution failed because no accessibility 'NEW' accepts this number of arguments.I have looked inside every file in the Web Project like the web config to check the connection string, gobal, and designer.vb looking for any errors whit no JOY. I also tried to create a new form and code behind with a button and received the same error.This is mind blowing because as I already stated, I can create a new Web Site and the problem goes away.
View 3 RepliesAm looking for control like html editor in windows forms so i want to use ajaxtoolkit.dll for html editor.
Can i create object for toolkit and use htm editor.
for example while we composing mail we have options like bold italic for these options and also i want to change rich text to html code .
I have a Google spreadsheet that I am reading data from and I want to load the data into a list object so I can use but I am having some issues.
Google Spreadsheet
-Worksheet name: Charts
-Tab: Color_Summarized
-Column 1: ColorSummary
-Column 2: ChildID
-Column 3: ParentID
sample rows:
Aqua|29|28
Blue|49|23
Yellow|55|28
My results are
Yellow Color_Summarized FH 55 28
How do I need to set it up so it keeps all the data loaded instead of just the last instance? Is there a better way then putting in class?
My code:
Code:
Imports Microsoft.VisualBasic
Imports System.Data
Imports System.Collections.Generic
Imports Google.GData.Spreadsheets
[code]....
I am following the Nerd Dinner tutorial as I'm learning ASP.NET MVC, and I am currently on Step 3: Building the Model. One part of this section discusses how to integrate validation and business rule logic with the model classes. All this makes perfect sense. However, in the case of this source code, the author only validates one class: Dinner.
What I am wondering is, say I have multiple classes that need validation (Dinner, Guest, etc). It doesn't seem smart to me to repeatedly write these two methods in the partial class:
[code]....
This doesn't "feel" right, but I wanted to check with SO to get opinions of individuals smarter than me on this. I also tested it out, and it seems that the partial keyword on the OnValidate method is causing problems (understandably so). This doesn't seem possible to fix (but I could very well be wrong).
I've scenario where I want to insert data into database without post back. there are around 12 to 13 fields which i need to insert. I'm passing DTO from the client side which is actually Json object. Now the problem which i'm facing is how to convert that Json object which i got in webservice to the "class" (in my case class name is User) object.
[Code]....
In the above case AddNewUser method takes the object of User class. But i'm getting casting error. So how do I convert Json object to the "User" class object?
I have an existing class for an input, is it possible to add an additional class for the object in C#.net, instead of doing a if/else and not having a preset class on the object in the first place?
View 3 RepliesActually i want to cast the type from find control to div but i cant find the class with div or body or form name why so?
View 5 RepliesI used Object Test Bench to test my classes in VS 2008 professional edition . Right click on Class name and then selected create instance ,then its Constructor, there comes a dialog box, that just gives a message and a TextBox field is present there, i filled that field with any name and clicked OK.Then error message comes that "Create Instance Failed" and its error code is "0x80004005" . What's this ? How to instantiate object of my classes ?
View 4 Replies