The scenario
I'm creating a simple cafe order form in visual studio.
I have one form to take orders and another as a summery page.
On the orders form i have a button "Save/ New order" when this button is pressed the order gets added to a listbox. I also want to create and accumulator to count the number of orders taken. I decided to create a global variable because i will only use this number in the summary form.
This is what ive done so far.
Public Class GlobalValues
Private Shared pItemIterator As Integer
Public Shared Property orderCounter As Integer
Get
Return pItemIterator
End Get
Set(value As Integer)
pItemIterator = value
End Set
End Property
End Class
And for the button
GlobalValues.orderCounter+= 1
The Problem
I currently stuck on how to minus -1 from this value. On the order form I have a button to remove the last order.
You cannot access pItemIterator as you made it private. You need to use the public Property you made for it:
GlobalValues.orderCounter -= 1
Is it okay for you to make a public sub for it that will deal with pItemIterator?
Public Class GlobalValues
Private Shared pItemIterator As Integer
Public Shared Property orderCounter As Integer
Get
orderCounter = pItemIterator
End Get
Set(value As Integer)
pItemIterator = value
End Set
End Property
Public Shared Sub subtractOneFromOrderCounter()
pItemIterator = pItemIterator - 1
End Sub
End Class
Then you would set subtractOneFromOrderCounter() to be called when your button is clicked.
Related
When creating a object based on a class. There are certain properties that I prefer to not be value 0 or nothing. So I would like to set the initial value to 1.
Is this best done via the constructor?
Class Product
Public Property Price As Decimal
Public Sub New()
Price = 1
End Sub
End Class
Or can you also write it as following? Does this second version make the value fixed at 1 or can you also alter the value if It's written like this?
Class Product
Public Property Price As Decimal = 1
End Class
Either way you do it, it'll function the same, however do defer to how your team normally does it to maintain consistency.
However, if you do have instances where you may open up the constructor to allow setting of those properties on initialization based on some argument given to the constructor, I would opt to always setting it in the constructor for consistency. If the property always has a default value of X on initialization then inline it at the top so it stands out.
Basic Example:
Class Product
Public Property Price As Decimal = 1
Public Property Quantity As Integer
Public Sub New()
Quantity = 0
End Sub
Public Sub New(quantity As Integer)
Quantity = quantity
End Sub
End Class
At the end its the same, in both cases you can change the values.
No difference, you can alter the value unless it's const or readonly. If you do the second, the compiler will sort of convert it like your first version. Here's a little program that'll show you. This will display 0 and then 1.
Module Module1
Sub Main()
Dim o As New B
Console.ReadLine()
End Sub
End Module
MustInherit Class A
Public Sub New()
Show()
End Sub
Public MustOverride Sub Show()
End Class
Class B
Inherits A
Private test As Integer = 1
Public Sub New()
MyBase.New()
' Value for test is being set here
Show()
End Sub
Public Overrides Sub Show()
Console.WriteLine(test)
End Sub
End Class
I'm trying to link my ListBox to an ObservableCollection.
Here's my class for defining mods:
Public Class TroveMod
Private m_FileName As String
Private m_Enabled As Boolean
Public Property FileName() As String
Get
Return m_FileName
End Get
Set(value As String)
m_FileName = value
End Set
End Property
Public Property Enabled() As Boolean
Get
Return m_Enabled
End Get
Set(value As Boolean)
m_Enabled = value
End Set
End Property
Public ReadOnly Property ModName()
Get
Return Path.GetFileNameWithoutExtension(FileName)
End Get
End Property
End Class
And this is the actual Property ModList:
Public Property ModList() As ObservableCollection(Of TroveMod)
Get
Return m_ModList
End Get
Set(value As ObservableCollection(Of TroveMod))
m_ModList = value
End Set
End Property
I add items using:
Private Sub AddMod(file__1 As String, enabled As Boolean)
If File.Exists(file__1) Then
ModList.Add(New TroveMod() With { _
.FileName = file__1, _
.Enabled = enabled _
})
End If
End Sub
Everytime I want to add something to this Collection using AddMod, it won't show off in my listbox :/ I added an ModListBindingSource to the ListBox and set the DisplayMember and ValueMember to ModName but it still won't work. I also got a status label, which says, that it successful added the mods to the collection but it simply won't show them in the ListBox. Did I miss something?
An ObservableCollection is not quite what you want - this would allow your code to see changes to the collection via events. For instance, if there were several actors adding items to the collection and you wanted to know that. In this case, since 'local' code is adding items, it is not needed.
It is also not clear how the collection is mapped to the ListBox as the DataSource. Try this:
Public Class Form...
Private myList As New BindingList(Of TroveMod)
Sub Form_Load(....
theListBox.DataSource = myList
theListBox.DisplayMember = "ModName"
Now, as you add things to the BindingList they will appear in theListBox. If an item changes though (e.g. the Name), that change will not show up without a little more work, but as these are file names that seems unlikely.
The form property is not needed unless an external class also needs access to the collection/BindingList; in that case, you probably do not want need a setter.
I have a class that inherits from CollectionBase. I tried to use the contains method to detect whether the Key already exists before inserting a new one. Here is what I have tried.
<Serializable()> Public Class validationList
Inherits CollectionBase
Public Function Add(ByVal Item As validationItem) As Integer
Return Me.List.Add(Item)
End Function
Default Public ReadOnly Property Item(ByVal index As Integer) As validationItem
Get
Return CType(List.Item(index), validationItem)
End Get
End Property
Public Sub Remove(ByVal index As Integer)
Me.List.RemoveAt(index)
End Sub
Protected Overrides Sub OnInsert(ByVal index As Integer, ByVal value As Object)
If Me.List.Contains(value) Then MsgBox("Already exist")
MyBase.OnInsert(index, value)
End Sub
Public Function IndexOf(ByVal key As validationItem)
Return List.IndexOf(key)
End Function
Public Sub AddRange(ByVal item() As validationItem)
For counter As Integer = 0 To item.GetLength(0) - 1
List.Add(item(counter))
Next
End Sub
End Class
<Serializable()> Public Class validationItem
Implements IEquatable(Of validationItem)
Private _key As validationTypes
Private _value As String
Public Sub New()
' Empty constructor is needed for serialization
End Sub
Public Sub New(ByVal k As validationTypes, ByVal v As String)
_key = k
_value = v
End Sub
Public Enum validationTypes
Madatory = 0
[Integer] = 1
Numeric = 2
[Decimal] = 3
MaxValue = 4
MinValue = 5
MinLength = 6
Email = 7
End Enum
Public Property Value As String
Get
Return _value
End Get
Set(ByVal Value As String)
_value = Value
End Set
End Property
Public Property Key As validationTypes
Get
Return _key
End Get
Set(ByVal value As validationTypes)
_key = value
End Set
End Property
Protected Overloads Function Equals(ByVal eqItem As validationItem) As Boolean Implements IEquatable(Of Testing_Project.validationItem).Equals
If eqItem Is Nothing Then Return False
Return Me._key = eqItem.Key
End Function
Public Overrides Function Equals(ByVal eqItem As Object) As Boolean
If eqItem Is Nothing Then Return False
Dim eqItemObj As validationItem = TryCast(eqItem, validationItem)
If eqItemObj Is Nothing Then Return False
Return Equals(eqItemObj)
End Function
Public Overrides Function GetHashCode() As Integer
Return Me._key.GetHashCode()
End Function
End Class
The validationList will be exposed from a usercontrol as a property, so that items could be added from the designer. When adding items I need to detect whether they already exist. I tried overriding the OnInsert but this sometime return that duplicates exists even when their aren't and doesn't report that duplicate exist when I try to add existing keys.
This indirectly answers the question after dealing with the issue which emerged in comments about Collection(Of T):
Add a reference to System.Collections.ObjectModel if needed, then
Imports System.Collections.ObjectModel
' a ValidationItem collection class
Public Class ValidationItems
Inherits Collection(Of ValidationItem)
Public Shadows Sub Add(NewItem As ValidationItem)
' test for existence
' do not add if it is not unique
Dim dupe As Boolean = False
For n As Int32 = 0 To Items.Count - 1
If Items(n).Key = NewItem.Key Then
dupe = True
Exit For
End If
Next
If dupe = False then
items.Add(newitem)
End if
' I would actually use an IndexOfKey function which might
' be useful elsewhere and only add if the return is -1
If IndexOfKey(NewItem.Key) <> -1 Then
Items.Add(newItem)
End If
End Sub
Some NET collection types implement Add as a function and return the item added. This sounds weird since you pass it the item to add. But returning Nothing if the item cannot be added is a neat semaphore for "I cant/wont do that". I cant recall if the std NET Collection Editor recognizes that or not.
One problem with using Contains is that it will test if item passed as param is the same object as one in the list. They never will be the same object, even if they have the same values. Testing the key in a loop is simpler than calling a method which implements an interface. (That previous answer was totally valid in the context presented, but the context has changed).
Even if you stay with CollectionBase, you want to handle it in the Add. If you try to remove it in OnInsert, VS will have problems deserializing the collection.
Also, your validationitem needs a Name property or the Collection Editor will display "Myassembly+MyType" as the Name (or a ToString override).
Other issues:
I am not sure your IndexOf will work. The list contains ValidationItems (objects), but you check it for _key (string). This will not matter if you change to Collection(Of T) which implements it for you.
The simple ctor is needed by the Collection Editor, not serialization. But the important thing is that it is there.
As for the comment about all Zeroes coming back - that is because your ValidationItem is not yet decorated for designer serialization. Maybe not the Collection Property either, that isnt shown.
I have a Datagridview that changes its content according to a selection the user makes in a listBox.
The DGV consits of 2 comboboxes (Country, Product) and 1 textbox (Quantity).
I've created a class combined of 3 integers.
This class is used as a type of list, which is the datasource for the DGV.
There is also another list containing the prior list, so I have a list of datasources.
The DGV's datasource is a BindingSource that changes whenever the SelectedIndex of the listBox is fired.
My problem occurs whenever a new row is added to the DGV:
I use the BindingSource.AddNew which calls the constructor of the class, but it must assign values to each item in the class. That way, whenever I click any cell in the DGV I don't get a blank row.
Moreover, when the BS changes and then returned, another row is added.
What I want to get is a blank row - empty comboboxes and textbox.
Thanks for your help!
The class:
Public Class PoList
Private _CountryID As Integer
Private _ProductID As Integer
Private _Quantity As Integer
Public Sub New(ByVal CountryID As Integer, ByVal ProductID As Integer, ByVal Quantity As Integer)
_CountryID = CountryID
_ProductID = ProductID
_Quantity = Quantity
End Sub
Private Sub New()
_CountryID = 1
_ProductID = 2
_Quantity = Nothing
End Sub
Public Property CountryID() As Integer
Get
Return _CountryID
End Get
Set(ByVal value As Integer)
_CountryID = value
End Set
End Property
Public Property ProductID() As Integer
Get
Return _ProductID
End Get
Set(ByVal value As Integer)
_ProductID = value
End Set
End Property
Public Property Quantity() As Integer
Get
Return _Quantity
End Get
Set(ByVal value As Integer)
_Quantity = value
End Set
End Property
Public Shared Function CreateNewPoList() As PoList
Return New PoList
End Function
End Class
Private Sub List_AddRow(ByVal sender As Object, ByVal e As AddingNewEventArgs) Handles AllListBindingSource.AddingNew
e.NewObject = PoList.CreateNewPoList
End Sub
Creating a new inner list:
AllList.Add(New List(Of PoList))
AllListBindingSource.AddNew()
AllListBindingSource.DataSource = AllList(TableCounter)
AddPoDetails.DataSource = AllListBindingSource
SelectedIndexChanged event:
AllListBindingSource.DataSource = AllList(AddPoList.SelectedIndex)
AddPoDetails.DataSource = Nothing
AddPoDetails.DataSource = AllListBindingSource
Right, lets see if I can help you.
As I interpret it you have a list filled with lists. These lists don't know their own identity and is based on the current index in the list.
First of I wouldn't use Bindingsource.AddNew I would add the new object straight to the list instead.
AllList(TableCounter).Add(New Polist())
This way you know exactly how many objects has been created, by using events you aren't quite sure are you.
To refresh the list do this:
AllListBindingSource.ResetBindings(true)
Which will update your DGV with the new line.
Now you need to restructure your class since when you create a new Polist you set a value to nothing. This will crash your table. What you need to do is this:
Private _Quantity As String
Public Property Quantity() As String
Get
Return _Quantity
End Get
Set(ByVal value As String)
_Quantity = value
End Set
End Property
Using a string is the only way for you to get a blank textbox, I would recommend you to have 0 as default if you are using Quantity as an integer (which you should). Your constructor needs to be changed to this:
Private Sub New()
_CountryID = 0
_ProductID = 0
_Quantity = ""
End Sub
In your combobox columns you have to add a blank item in the top (I'm guessing your adding them manually), should be possible by having a blank row in the top of the items.
I've created a custom user control that has several properties. One specifies which database I want the control to access. I want to be able to present the user of the control a drop down from which he can select which database the control will interact with.
How do I get the dropdown to work? I can get default values, but have yet to figure out how to get the selectable list.
Any help is apprectiated.
Thanks.
Marshall
You just need to attach your own TypeConverter to your property. You will override the GetStandardValuesSupported and GetStandardValues methods (maybe GetStandardValuesExclusive too) to return the list of databases you want to show.
If you are new to the PropertyGrid and the TypeConverter, here is a document.
It turns out to be simpler than I thought.
I had an enumeration set up for the property, but was having trouble using it for the property type. Said it was unaccessable outside of the class.
Then I had a 'duh' moment and changed the enumeration from Friend to Public, and then I was able to use the enumeration as the property type. As a result the values from the enumeration are listed in a dropdown when I look at the values for that property of the controls.
Thanks to all that answered.
Marshall
I'm a little confused about your problem.
If your user control contains a DropDownList control, just inititalize somewhere in the user control.
The easiest way is in the Codebehind for the usercontrol, just do DropDownList.Items.Add() or whatever the syntax is for adding an item.
Here is the template I use to create a custom datasource for my comboboxes:
Private Class Listing
Private _List As New ArrayList
Public Sub Add(ByVal ItemNumber As Integer, ByVal ItemName As String)
_List.Add(New dataItem(ItemNumber, ItemName))
End Sub
Public ReadOnly Property List() As ArrayList
Get
Return _List
End Get
End Property
End Class
Private Class dataItem
Private _ItemNumber As Integer
Private _ItemName As String
Public Sub New(ByVal intItemNumber As Integer, ByVal strItemName As String)
Me._ItemNumber = intItemNumber
Me._ItemName = strItemName
End Sub
Public ReadOnly Property ItemName() As String
Get
Return _ItemName
End Get
End Property
Public ReadOnly Property ItemNumber() As Integer
Get
Return _ItemNumber
End Get
End Property
Public ReadOnly Property DisplayValue() As String
Get
Return CStr(Me._ItemNumber).Trim & " - " & _ItemName.Trim
End Get
End Property
Public Overrides Function ToString() As String
Return CStr(Me._ItemNumber).Trim & " - " & _ItemName.Trim
End Function
End Class
And this is how I load it:
ListBindSource = New Listing
Me.BindingSource.MoveFirst()
For Each Row As DataRowView In Me.BindingSource.List
Dim strName As String = String.Empty
Dim intPos As Integer = Me.BindingSource.Find("Number", Row("Number"))
If intPos > -1 Then
Me.BindingSource.Position = intPos
strName = Me.BindingSource.Current("Name")
End If
ListBindSource.Add(Row("Number"), strName)
Next
cboNumber.DataSource = ListBindSource.POList
cboNumber.DisplayMember = "DisplayValue"
cboNumber.ValueMember = "Number"
AddHandler cboNumber.SelectedIndexChanged, AddressOf _
cboNumber_SelectedIndexChanged
Hope this helps. One thing to keep in mind is that if cboNumber has a handler already assigned to the SelectedIndexchanged event, you will encounter problems. So don't create a default event.