Application Like A Shopping Cart - Global Variable?
Dec 27, 2011
My project is to create a shopping cart application. I have my main form and from there the user can go to two different forms to add books to their cart, the cart being the main form. This all works. What I can't figure out, is how to use global variables for the prices, shipping, tax and updating the total. I have places for this information to show up on the main form, and I've created a module for the calculations and prices, but I don't know how to code it to get the prices to show up in the specified areas.
I am working on a class project and I am trying to create a shopping cart application. I need to transfer info from listboxes on 2 forms to the main form and calculate the charges for "the books." I am having a hard time writing the code to properly transfer the items and I really have no idea where to start with the calculating the charges for subtotals of the selected books.
I am in the middle of building a very simple shopping cart in asp.net with a VB backend but I am running into problems with my code. When I run my application and try to add a product to the cart I get an error message.
Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error:
Line 27: Dim blnMatch As Boolean = False Line 28: Line 29: For Each Me.objDR In objDT.Rows Line 30: If objDR("StockItemName") = Product Then Line 31: objDR("Quantity") += txtQuantity.Text
I am not sure why it is doing this and was hoping that perhaps someone could take a look and offer up some advice? I have checked over my code and I cannot find anything wrong however I would take any guidence that you may have on it.
I am trying to create a shopping cart in Visual Basic. I have most of it figured out. However, when I click the Add Cart button, the item will add; however, when I add a new item, it will not go to the next line to display it. It instead replaces the first item I added. For example if the user chooses 1111 for the part number and qty is 2 then clicks the Add to Cart button, the following will show in a group box below: 1111 Alarm Clock 2 $19.95 $39.90
If the person wants to add part number 2222 and qty is 2, that relating info should show up below the first entry of the Alarm clock. In my code, it's not doing that, it's just replacing the first line (alarm clock entry). However, it is keeping track of the total amount added to the cart.
Here is my code that I have done for the Add Cart button:
Private Sub xAddButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles xAddButton.Click Dim searchFor As String
The selecting products screen will look like a gridview which will display.
name price quantity Text Text Input box
So i.e. lets say I have 10 products per page so i.e. 10 quantity input boxes per gridview. And then I have 2 Buttons below my gridview i.e. Update and Checkout. Just even worrying about Update for now. How could that work i.e. would I have to check every input box in gridview for which a value was entered ?
I.e. is there any example how I can loop through gridview row check for a value which is greater than 0 or null for example and if there is a value then perform a function like [Code]
I've created a program that pulls item prices from a database. The problem I'm having right now is that I'd like to display a running total, as the program currently only displays the list of items and their prices.
Private Sub btnGoToCart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGoCart.Click Me.Hide()
How can I get the items in my code from my listbox which is called "selectListBox" to a shopping cart called "cartlistbox", when the add button is clicked?
Public Class MainForm Private Sub MainForm_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Using following method to create Shopping Cart Session [URL]Now running locally on my machine where sessionstate mode is inProc by default, all seems to perform fine.I'm writing an application which I've just placed up on hosting provider (shared hosting environment etc). Their default sessionstate is stateserver so I had to serialise the classes to fit in with this. It's using cookies.The basket (adding,removing etc) works fine but I'm seeing some odd things happen regarding the persistency of the session.
On my local machine, if I access the site in 2 separate browsers, if I add items in IE, I can see them in Firefox when I refresh. This doesn't make any sense to me since cookies are per browser.Plus I thought that when a session was generated, its id would be unique so there is no way that one user should be able to see anothers session data (unless tabbed in same browser perhaps)Even worse, if I start adding/removing items in IE and doing likewise in Firefox, both of them show very random cart results every time you refresh the browser.
Note: This code actually codes from a tutorial book I'm reading at the moment, so you can imagine this is frustrating me greatly! I'm building a basic shopping cart, using VB.NET 4, Visual Studio 2010 and MS SQL Server R2 2008. The code below is supposed to remove items from the cart, by reading a session variable, editing it to remove the appropriate ProductID and return the amending string to the session variable. It is then supposed to rebind the data to the gridview (gvCart) to refresh the data...but it seems here there is an error.
Every time I build the site in Visual Studio, it validates fine. But every time I run the site, and attempt to use the remove button it gives me the error:Incorrect syntax near ')'.ith the IDE pointing me toward the final parenthesis
Protected Sub gvCart_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles gvCart.SelectedIndexChanged 'This method is hooked to the Remove button & is removing items from the cart
And it actually seems to work on first instance (altho im not sure the above is a good way to do it, but the problem is when use the pagination on the gridview I get the error
Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index
On the line Dim productId As String = productListTable.DataKeys(i).Value
why I am getting this error and also is there a better way to do it ?
i havent had problems in visual basic all the ay up to this point. I have been given a shopping cart program that I must use: a MainForm, MP3From, AlbumForm, and a module
I finally got my program to send data from the listbox on my MP3Form to the listbox on my MainForm but something isnt right still. I need to be able to click an an item from the lstMP3(listbox on MP3Form) to lstShoppingCart(listbox on MainForm) multiple times without having to close the MP3Form everytime to add the items to lstShoppingCart. Here is what I got so far on my MainForm: [code...]
This assignment makes me mad cause we have not even covered half the stuff I am having to use in this form at all this semester. If i can get a little explanation on instantiate, inheritance, and declaring and object variable and how its used to transfer data from one to the other.
I am working on a project for a class, and am having trouble getting my program to automatically calculate the subtotal every time an item is added to the shopping cart list. I've tried sub procedures and functions, but I can't seem to get it to work.
I have a variable whose scope needs to be global, because it needs to be called in a function as well as in a button press. So I declared the variable in a Module so it would be global.The problem is that the value of this variable needs to be equal to the value of the text property of a textbox in the form.You enter a string into the textbox, in this case I entered "Hello". Then you click the button and it displays what you wrote.You click OK in that message box and change the value in the textbox. In this case I changed it to "Goodbye". Then I hit the button again, but the variable did not change values and the messagebox displays "Hello" again.
[code]....
Here is the entire source code:
Module Module1 Public strDataValue = frmTest.txtDataValue.Text End Module
[code]....
Note: This is just a demonstration of a problem I'm having in a much larger program so the variable does have to be global.
VB2008: I would like to set a #Const value in a module and use it throughout my project. Is this possible? It appears that the #Const scope is limited to the function it's in.
How Can I create a Global Varibale for my vb.net project. When I LongIn I want to keep the user Id in a varible and I will Use it in deferent Forms. And The User name will be saver in the varible untill I close the Software.
I'm focusing on Networking programming and I had found something that was very interesting to me in Remoting, which is the ability to have some how a "shared global variable accross applications" ... Here's a quick example of what I'm saying (which is stripped and modified from one found example on internet):
In the Remoting class:
Code:Namespace remoteclass Public Class xx Inherits MarshalByRefObject Public Shared_Var As String 'This is our share variable End ClassEnd Namespace
[Code]....
I found that I can eaisly use this red-marked variable (Shared_Var) acrross all application clients without any extra line of code to update its value ... without using even what is called "singlecall" and "sigletron".
But I have concerns:
1) This is only applicable for simple types of variables (e.g. string and integer) but an array or DataTable for example are not updated! and I don't know why!!
2) Would that load the communication network (I mean the content of these shared variables (few KBs to 1MB) will always be communicated across machines all the time without any management) ... Actually I don't how this works from inside, Does it update on change or cyclic ...
3) And finally, can I found something like this in WCF?
I'm wanting to declare a variable as below for use in several pages on my site. I assume rather than declaring it once per page I can do it globally? I've tried it in a class (app_code folder) and in the global.asax page but my code can't seem to find it. I may be going abo9ut it all wrong though? Code as below...
Dim myUser As MembershipUser = Membership.GetUser()
So basically as it stands my pages can't find the 'myUser' variable.
I'm writing a subneting calculator in VB.NET.I'm using the IDE SharpDevelop.Well my problem is I'm using a function to do some calculations and then to figure out the class of the IP addresses.Well I pass a variable from the subroutine, that is accessed when a button is clicked, to the function then the variable is passed back to the subroutine and then the variable is passed again to another function but when it reaches this second function it doesn't retain the value it was given in the first function.I'm not sure if I'm just passing the variable wrong or if this is how it works.I know I can make this work probably by using global variables but I'm not sure if this is proper. So my ultimate question is what is the difference between local and global variables besides just scope and should I try and use one more than the other.
I have no idea as to how I can define a variable as "GLOBAL" in VB Express 2008. I used VB V 3.0 and if I remember correctly the statement "Global varName as Integer" allowed me to use the variable across different forms. I've tried the statement "Public varName as Integer = 0" on Form1 but Form2 tells me the variable is not declared.
The statement (in Form1) "Form2.Label1.Text = CStr(varName)" displays the value on Form2 in Label1 but I cannot then use the value again in Form2, e.g. "Label2.Text = Label1.Text". How I can transfer a variable value from one form to another and manipulate that variable in the second form?
I have a problem to load a value into a global variable, I am using VB Net (2005) in Windows Forms, this is a multi-Forms program. Here is my problem, as I start my program, it check if my form "Setup Option" has been loaded ounce, if it did it, it does skip it. When "Setup Option" is loaded the first time I have written 2 values into 2 textboxes using My. Settings and on form Closing it does work, if I re-open "Setup Option" form I can see the 2 values in the textboxes E.g.: txtGst.text=5, txtPst.text=6.5, so good so far. Now what I would like is to be able to use the contains of them 2 textboxes and place them into global variables, I already have a Module "modGlobals.vb".
Private Sub NoteTabToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NoteTabToolStripMenuItem.Click Dim NewTab As New TabPage
I have set a global variable in a module, which I then set the value in form1.I then wish to use this in form 2 in a Select Command for a dataadapter, it however says the variable is not declared although if I call it in a MsgBox on loading form2 it tells me the variable.
My code for the select is: Me.OleDbSelectCommand1.CommandText = "SELECT Amount, [Record Number] FROM [" & _ "Test] WHERE ([Record Number] = ?)"
I'm working on my final for VB.NET, and maybe it's just late...but here's how it goes. I need to make a variable named intMoney and it will be used to keep track of how much money you have and the value will be displayed in a label. Since this 'game' will have a lot of things going on, it needs to be available in a lot of places, not just one click event.
But I need to set intMoney to a starting value of 200 and then assign intMoney to a label called lblMoney. I can't assign intMoney to lblMoney in global. I get build errors. Where should I put the lblMoney.Text = intMoney?
I need regarding declarations of global variable.. I created a module here is the script.
[Code]...
and then I set the value of that variable in my Login form and then my PROBLEM is when accessing it on the my Main form and I want to display the data of that variable in a textbox, the variable does'nt hold the value that I already set. I'm waiting for replies!
