I have an object called Statistics. Inside this object there are 6 more objects. Each contains properties with values.
So for example, Statistics(0) contains an 'age' field, a 'sex' field, 'vehicle' etc...
same goes for Statistics(1), Statistics(2) etc...
What I want to do is compare Statistics(0) all the way to Statistics(6) and find out if any one of them is identical to another.
If all of the fields contained within Statistics(0) have the same values as the fields in Statistics(1), I want to do something.
How can I compare these objects to one-another?
what I have tried
For Each Stat As ExportStatistics In Statistics
Insert_VehicleStats(Stat) 'Insert values into main Vehicle table
If Statistics.Length > 1 Then
Dim i = 0
Dim y = 0
Dim previousObject As ExportStatistics
For Each Stat2 In Statistics
If Stat2.Equals(previousObject) Then
Dim sadXml = "do something"
End If
previousObject = Stat2
Next
End if
You can either override the Equals function in your class or overload it then create your own comparison code. Here's an example (it assumes your object is of type VehicleStatisticsItem):
Public Class VehicleStatisticsItem
Public Overrides Function Equals(obj As Object) As Boolean
'Test for type and define tests or just pass to base function
Return MyBase.Equals(obj)
End Function
Public Overloads Function Equals(item As VehicleStatisticsItem) As Boolean
'Define your tests here
End Function
End Class
The 2 objects you are comparing will not equal each other even if their properties do. You need to specify that you are comparing their properties.
Change
If vehicleStatistic.Equals(previousObject) Then
Dim sadXml = "do something"
End If
To
If vehicleStatistic.GetType().GetProperties.Equals(previousObject.GetType().GetProperties) Then
Dim sadXml = "do something"
End If
This way you are comparing their properties.
Related
First of all, what I want to achieve:
I want to extend a value datatype by providing additional properties, especially to validate ranges provided at declaration time. I want the new datatype to be a value type as well.
Compare with Ada:
subtype Day_Number is Integer range 1 .. 31;
Ideal, but obviously not implementable, would be:
Dim DayNumber As Int64 Range 1 To 31
However, I would be happy with:
Dim DayNumber As RangeInt64(1, 31)
It is of no concern, if initialization takes its time. Once ranges are provided, they are considered to be immutable. The datatype from then on is only used to set/get values like with ordinary value types, only that they are subject of being validated against the initially provided range.
My attempt:
Since I cannot inherit from structures in order to expand on them, I tried to incorporate a structure into a structure as a member.
In a module, I have this structure:
Friend Structure SRangeValueType(Of T)
Private lMinimum As T
Private lMaximum As T
Friend Property Minimum As T
Get
Return lMinimum
End Get
Set(tValue As T)
lMinimum = tValue
End Set
End Property
Friend Property Maximum As T
Get
Return lMaximum
End Get
Set(tValue As T)
lMaximum = tValue
End Set
End Property
Friend Sub New(Minimum As T, Maximum As T)
lMinimum = Minimum
lMaximum = Maximum
End Sub
End Structure
I attempt to use this generic structure as a member of another structure (of concrete type Int64):
Public Structure RangeInt64
Private Range As SRangeValueType(Of Int64)
End Structure
However, this is not using the constructor with the two arguments.
Say I want to initialize Range (the only member of the structure RangeInt64) with the values 100 and 200 for Minimum and Maximum, resp.
I am not allowed to use something like:
Private Range As SRangeValueType(Of Int64)(100,200)
What is the correct syntax to provide my values to the generic constructor?
Normally, if you add a constructor to a structure, you can call it using the New keyword:
Dim x As SRangeValueType(Of Int64) ' Calls the default, infered, parameter-less constructor
Dim y As New SRangeValueType(Of Int64)(100, 200) ' Calls the explicitly defined constructor
However, that's not really the problem. The problem is that you are trying to set the default value of a non-shared field in a structure. That is something which is never allowed. All non-shared fields in structures must default to their default value (i.e. Nothing). For instance:
Public Structure RangeInt64
Private x As Integer = 5 ' Error: Initializers on structure members are valid only for 'Shared' members and constants
Private y As New StringBuilder() ' Error: Non-shared members in a structure cannot be declared 'New'
End Structure
And, as you may already know, you cannot override the default, inferred, parameter-less constructor on a structure either:
Public Structure RangeInt64
Public Sub New() ' Error: Structures cannot declare a non-shared 'Sub New' with no parameters
x = 5
y = New StringBuilder()
End Sub
Private x As Integer
Private y As StringBuilder
End Structure
As such, you are stuck. By design, when the default constructor is used, all fields in the structure must always default to Nothing. However, if you really, really need it to be a structure, and you can't just convert it to a class, and you really need to change it's default value, you could theoretically fake it into working by using a property to wrap the field:
Public Structure RangeInt64
Private _Range As SRangeValueType(Of Int64)
Private _RangeInitialized As Boolean
Private Property Range As SRangeValueType(Of Int64)
Get
If Not _RangeInitialized Then
_Range = New SRangeValueType(Of Int64)(100, 200)
_RangeInitialized = True
End If
Return _Range
End Get
Set(value As SRangeValueType(Of Int64))
_Range = value
End Set
End Property
End Structure
It should go without saying, though, that it's pretty gross and should be avoided if possible.
Update
Now that you've provided more details about what you are trying to accomplish, I think I may have a better solution for you. You're right that structures do not support inheritance, but what they do support is interfaces. So, if all you need is a bunch of range types, one per value-type, all having the same minimum and maximum properties, but all returning different predetermined values, then you could do something like this:
Private Interface IRangeValueType(Of T)
ReadOnly Property Minimum As T
ReadOnly Property Maximum As T
End Interface
Private Structure RangeInt64
Implements IRangeValueType(Of Int64)
Public ReadOnly Property Minimum As Long Implements IRangeValueType(Of Int64).Minimum
Get
Return 100
End Get
End Property
Public ReadOnly Property Maximum As Long Implements IRangeValueType(Of Int64).Maximum
Get
Return 200
End Get
End Property
End Structure
One of the main problems in VBA are custom data structures and lists.
I have a loop which generates with each iteration multiple values.
So as an example:
Each loop iteration generates a string "name" an integer "price" and an integer "value".
In C# for example I'd create a class which can hold these three values and with each loop iteration I add the class object to a list.
How can I do the same thing in VBA if I want to store multiple sets of data when not knowing how many iterations the loop will have (I cant create an array with a fixed size)
Any ideas?
The approach I use very frequently is to use a class and a collection. I also tend to use an interface model to make things more flexible. An example would look something like this:
Class Module IFoo
Option Explicit
Public Sub Create(ByVal Name as String, ByVal ID as String)
End Property
Public Property Get Name() as String
End Property
Public Property Get ID() as String
End Property
This enforces the pattern I want for my Foo class.
Class Module Foo
Option Explicit
Private Type TFoo
Name as String
ID as String
End Type
Private this as TFoo
Implements IFoo
Private Sub IFoo_Create(ByVal Name as String, ByVal ID as String)
this.Name = Name
this.ID = Name
End Sub
Private Property Get IFoo_Name() as String
IFoo_Name = this.Name
End Property
Private Property Get IFoo_ID() as String
IFoo_ID = this.ID
End Property
We get intellisense from the Private Type TFoo : Private this as TFoo where the former defines the properties of our container, the latter exposes them privately. The Implements IFoo allows us to selectively expose properties. This also allows you to iterate a Collection using an IFoo instead of a Foo. Sounds pointless until you have an Employee and a Manager where IFoo_BaseRate changes depending on employee type.
Then in practice, we have something like this:
Code Module Bar
Public Sub CollectFoo()
Dim AllTheFoos as Collection
Set AllTheFoos = New Collection
While SomeCondition
Dim Foo as IFoo
Set Foo = New Foo
Foo.Create(Name, ID)
AllTheFoos.Add Foo
Loop
For each Foo in AllTheFoos
Debug.Print Foo.Name, Foo.ID
Next
End Sub
While the pattern is super simple once you learn it, you'll find that it is incredibly powerful and scalable if implemented properly. It also can dramatically reduce the amount of copypasta that exists within your code (and thus reduce debug time).
You can use classes in VBA as well as in C#: Class Module Step by Step or A Quick Guide to the VBA Class Module
And to to the problem with the array: you can create an array with dynamic size like this
'Method 1 : Using Dim
Dim arr1() 'Without Size
'somewhere later -> increase a size to 1
redim arr1(UBound(arr1) + 1)
You could create a class - but if all you want to do is hold three bits of data together, I would define a Type structure. It needs to be defines at the top of an ordinary module, after option explicit and before any subs
Type MyType
Name As String
Price As Integer
Value As Integer
End Type
And then to use it
Sub test()
Dim t As MyType
t.Name = "fred"
t.Price = 12
t.Value = 3
End Sub
I have to check a piece of user input against a list of items; if the input is in the list of items, then direct the flow one way. If not, direct the flow to another.
This list is NOT visible on the worksheet itself; it has to be obfuscated under code.
I have thought of two strategies to do this:
Declare as an enum and check if input is part of this enum, although I'm not sure on the syntax for this - do I need to initialise the enum every time I want to use it?
Declare as an array and check if input is part of this array.
I was wondering for VBA which is better in terms of efficiency and readability?
You can run a simple array test as below where you add the words to a single list:
Sub Main1()
arrList = Array("cat", "dog", "dogfish", "mouse")
Debug.Print "dog", Test("dog") 'True
Debug.Print "horse", Test("horse") 'False
End Sub
Function Test(strIn As String) As Boolean
Test = Not (IsError(Application.Match(strIn, arrList, 0)))
End Function
Or if you wanted to do a more detailed search and return a list of sub-string matches for further work then use Filter. This code would return the following via vFilter if looking up dog
dog, dogfish
In this particular case the code then checks for an exact match for dog.
Sub Main2()
arrList = Array("cat", "dog", "dogfish", "mouse")
Debug.Print "dog", Test1("dog")
Debug.Print "horse", Test1("horse")
End Sub
Function Test1(strIn As String) As Boolean
Dim vFilter
Dim lngCnt As Long
vFilter = Filter(arrList, strIn, True)
For lngCnt = 0 To UBound(vFilter)
If vFilter(lngCnt) = strIn Then
Test1 = True
Exit For
End If
Next
End Function
Unlike in .NET languages VBA does not expose Enum as text. It strictly is a number and there is no .ToString() method that would expose the name of the Enum. It's possible to create your own ToString() method and return a String representation of an enum. It's also possible to enumerate an Enum type. Although all is achievable I wouldn't recommend doing it this way as things are overcomplicated for such a single task.
How about you create a Dictionary collection of the items and simply use Exist method and some sort of error handling (or simple if/else statements) to check whether whatever user inputs in the input box exists in your list.
For instance:
Sub Main()
Dim myList As Object
Set myList = CreateObject("Scripting.Dictionary")
myList.Add "item1", 1
myList.Add "item2", 2
myList.Add "item3", 3
Dim userInput As String
userInput = InputBox("Type something:")
If myList.Exists(userInput) Then
MsgBox userInput & " exists in the list"
Else
MsgBox userInput & " does not exist in the list"
End If
End Sub
Note: If you add references to Microsoft Scripting Runtime library you then will be able to use the intelli-sense with the myList object as it would have been early bound replacing
Dim myList As Object
Set myList = CreateObject("Scripting.Dictionary")
with
Dim myList as Dictionary
Set myList = new Dictionary
It's up to you which way you want to go about this and what is more convenient. Note that you don't need to add references if you go with the Late Binding while references are required if you want Early Binding with the intelli-sense.
Just for the sake of readers to be able to visualize the version using Enum let me demonstrate how this mechanism could possibly work
Enum EList
item1
item2
item3
[_Min] = item1
[_Max] = item3
End Enum
Function ToString(eItem As EList) As String
Select Case eItem
Case EList.item1
ToString = "item1"
Case EList.item2
ToString = "item2"
Case EList.item3
ToString = "item3"
End Select
End Function
Function Exists(userInput As String) As Boolean
Dim i As EList
For i = EList.[_Min] To EList.[_Max]
If userInput = ToString(i) Then
Exists = True
Exit Function
End If
Next
Exists = False
End Function
Sub Main()
Dim userInput As String
userInput = InputBox("type something:")
MsgBox Exists(userInput)
End Sub
First you declare your List as Enum. I have added only 3 items for the example to be as simple as possible. [_Min] and [_Max] indicate the minimum value and maximum value of enum (it's possible to tweak this but again, let's keep it simple for now). You declare them both to be able to iterate over your EList.
ToString() method returns a String representation of Enum. Any VBA developer realizes at some point that it's too bad VBA is missing this as a built in feature. Anyway, you've got your own implementation now.
Exists takes whatever userInput stores and while iterating over the Enum EList matches against a String representation of your Enum. It's an overkill because you need to call many methods and loop over the enum to be able to achieve what a simple Dictionary's Exists method does in one go. This is mainly why I wouldn't recommend using Enums for your specific problem.
Then in the end you have the Main sub which simply gathers the input from the user and calls the Exists method. It shows a Message Box with either true or false which indicates if the String exists as an Enum type.
Just use the Select Case with a list:
Select Case entry
Case item1,item2, ite3,item4 ' add up to limit for Case, add more Case if limit exceeded
do stuff for being in the list
Case Else
do stuff for not being in list
End Select
I am trying to assign a value to global variable, which has a Property of type Double. This Property is passed as Object and the assignment fails.
In the example code below, the value is never assigned to the actual object, but only locally:
Public Class Form1
Friend Home As New Building
Private Sub AssignValues() Handles Me.Load
'Objects of different types are added to a list
Dim listObjects As New List(Of Object)
listObjects.Add(Home.Surface)
'All the Objects in listObjects are assigned a value that
'is stored as String
For Each o As Object In listObjects
SetProperty(o, "45.6")
Debug.Print("Surface = " & Home.Surface.ToString)
Next
End Sub
Private Sub SetProperty(ByRef Variable As Object, ByVal Value As String)
Select Case Variable.GetType
Case GetType(Double)
Variable = CDbl(Value)
Case Else
'...
End Select
End Sub
End Class
Public Class Building
Dim _surface As Double = 0
Public Property Surface As Double
Get
Return _surface
End Get
Set(ByVal value As Double)
_surface = value
End Set
End Property
End Class
The program invariably outputs Surface = 0 instead of 45.6. What am I doing wrong?
I tried to pass the Variable as reference, as suggested here, but without success. I also read about using Reflection, but there ought to be something simpler than that...
When your adding home.surface to the list, your adding a copy of the double to the list and then adjusting that copy. Stick a watch on "o" and see how it changes whilst home.surface remains the same.
If you want to use reflection, try something along these lines.
Dim prop As Reflection.PropertyInfo = o.GetType().GetProperty("Surface")
prop.SetValue(o, 45.6)
With Variable.GetType you will get always Object, because this is the type of Variable. What you can do with an Object is converting/casting it into a different type (like Double).
The best way to determine the "original type" from where the Object comes would be including an additional variable telling it. Another option might be converting the given Object into the target Type and see if it is not nothing/does not trigger an error. But this second option is not too accurate, mainly when dealing with "equivalent types" like Doubles/Integers.
I have defined a variable with an own type, say
Dim point As DataPoint
Public Type DataPoint
list as Collection
name as String
number as Integer
End Type
and I want to delete all values of the variable point at once. If it was a class, I would just use Set point = New DataPoint, or set Set point = Nothing, but how can I proceed if it's a type?
You can benefit from the fact that functions in VB have an implicit variable that holds the result, and that contains the default type value by default.
public function GetBlankPoint() as DataPoint
end function
Usage:
point = GetBlankPoint()
The standard way is to reset each member to its default value individually. This is one limitation of user-defined types compared to objects.
At the risk of stating the obvious:
With point
Set .list = Nothing
.name = ""
.number = 0
End With
Alternatively, you can create a "blank" variable and assign it to your variable each time you want to "clear" it.
Dim point As DataPoint
Dim blank As DataPoint
With point
Set .list = New Collection
.list.Add "carrots"
.name = "joe"
.number = 12
End With
point = blank
' point members are now reset to default values
EDIT: Damn! Beaten by JFC :D
Here is an alternative to achieve that in 1 line ;)
Dim point As DataPoint
Dim emptyPoint As DataPoint
Public Type DataPoint
list As Collection
name As String
number As Integer
End Type
Sub Sample()
'~~> Fill the point
Debug.Print ">"; point.name
Debug.Print ">"; point.number
point.name = "a"
point.number = 25
Debug.Print ">>"; point.name
Debug.Print ">>"; point.number
'~~> Empty the point
point = emptyPoint
Debug.Print ">>>"; point.name
Debug.Print ">>>"; point.number
End Sub
SNAPSHOT
One-liner:
Function resetDataPoint() As DataPoint: End Function
Usage:
point = resetDataPoint()
Another option is to use the reserved word "Empty" such as:
.number= Empty
The only issue is that you will need to change the number from integer to variant.
Using classes in VBA is usually a good practice in case it is not a single purpose solution or the class do not contain too many private attributes because if you want to adhere on OOP rules and keep your class safe, you should declare all the Let and Get properties for all private attributes of class. This is too much coding in case you have more than 50 private attributes. Another negative side of using classes in excel is fact, that VBA do not fully support the OOP. There is no polymorfism, overloading, etc.) Even you want to use an inheritance, you have to declare all the attributes and methods from the original class in the inherited class.
So in this case I would prefer the solution suggested by Jean-François Corbett or GSeng, i.e. to assign an empty variable of the same UDT as the variable you want to clear or to use a function which to me seems little bit more elegant solution because it will not reserve permanent memory for the emtpy variable of your UDT type.
For that is better to use classes, you can declare a class module with the name of your type, then declare all of your members as public, then automatically you can set to nothing and new for create and delete instances.
syntax will be somthing like this after you create the class module and named like your type:
'
Public List as Collection
Public Name as String
Public Number as Long
Private Sub Class_Initialize()
'Here you can assign default values for the public members that you created if you want
End Sub