I am trying to run through all the controls in a panel and find which properties the user has changed for each control.
So I have this code:
Private Sub WriteProperties(ByVal cntrl As Control)
Try
Dim oType As Type = cntrl.GetType
'Create a new control the same type as cntrl to use it as the default control
Dim newCnt As New Control
newCnt = Activator.CreateInstance(oType)
For Each prop As PropertyInfo In newCnt.GetType().GetProperties
Dim val = cntrl.GetType().GetProperty(prop.Name).GetValue(cntrl, Nothing)
Dim defVal = newCnt.GetType().GetProperty(prop.Name).GetValue(newCnt, Nothing)
If val.Equals(defVal) = False Then
'So if something is different....
End If
Next
Catch ex As Exception
MsgBox("WriteProperties : " & ex.Message)
End Try
End Sub
Now I face three problems:
When the property refers to image (BackGround Image) I have an error :
ImageObject reference not set to an instance of an object.
The second problem is that the code:
If val.Equals(defVal) = False Then
'So if something is different....
End If
is executes sometimes when the val and defVal are the same.
This is happening in cases that the property is a "parentProperty" like FlatAppearance (which has more child properties)
My loop doesn't look into basic properties like Size, or Location which I want
Re: Not set to an instance of an object, do something like ...
If val IsNot Nothing AndAlso defVal IsNot Nothing AndAlso Not val.Equals(defVal) Then
Which will only do the comparison if neither value is Nothing (aka Null).
Unfortunately, #2 is a fundamental problem - .Equals by default checks if the 2 object references point at the same object in memory - eg if You did
Dim A As New SomeClass
Dim B As New SomeClass
If A.Equals(B) Then
...
End If
Would return False unless SomeClass has an overridden equality comparer, which many classes do not.
You could check if the value in question is a type you know you can compare (Integer, String, Double, etc). If not, you could iterate through its properties and perform the same check again. This would allow you to compare the public properties of any type for equality but wouldn't guarantee the internal state of the classes is the same.
Something Like (Untested/Pseudo)...
Function Compare (PropA, PropB) As Boolean
Dim Match = True
If PropA.Value Is Nothing Or PropB.Value Is Nothing
Match = False
Else
If PropA.Value.GetType.IsAssignableFrom(GetType(String)) Or
PropA.Value.GetType.IsAssignableFrom(GetType(Integer)) Or ... Then
Match = PropB.Value.Equals(PropB.Value)
Else
For Each Prop In PropA.Value.GetType.GetProperties()
Match = Compare(Prop, PropB.Value.GetType.GetProperty(Prop.Name))
If Not Match Then Exit For
Next
End If
End If
Return Match
End Function
This is still not ideal as the internal states of the values may differ.
Related
I am getting Runtime Error 13 when trying to update an object stored in a collection. Here is a minimal example.
The class (Class2) of the objects to be stored in the collection.
Option Explicit
Private pHasA As Boolean
Private pHasB As Boolean
Private pSomeRandomID As String
Property Get HasA() As Boolean
HasA = pHasA
End Property
Property Get HasB() As Boolean
HasB = pHasB
End Property
Property Let HasA(propValue As Boolean)
pHasA = propValue
End Property
Property Let HasB(propValue As Boolean)
pHasB = propValue
End Property
Property Let RandomID(propValue As String)
pSomeRandomID = propValue
End Property
Sub SetHasValues(key As String)
Select Case key
Case "A"
pHasA = True
Case "B"
pHasB = True
End Select
End Sub
Minimal code that reproduces the error:
Option Explicit
Private Sub TestCollectionError()
Dim classArray As Variant
Dim classCollection As Collection
Dim singleClass2Item As Class2
Dim iterator As Long
classArray = Array("A", "B", "C")
Set classCollection = New Collection
For iterator = LBound(classArray) To UBound(classArray)
Set singleClass2Item = New Class2
singleClass2Item.RandomID = classArray(iterator)
classCollection.Add singleClass2Item, classArray(iterator)
Next iterator
Debug.Print "Count: " & classCollection.Count
singleClass2Item.SetHasValues "A" ' <-- This code works fine.
Debug.Print "New Truth values: " & singleClass2Item.HasA, singleClass2Item.HasB
For iterator = LBound(classArray) To UBound(classArray)
classCollection(classArray(iterator)).RandomID = classArray(iterator)
classCollection(classArray(iterator)).SetHasValues classArray(iterator) '<-- Type mismatch on this line.
Next iterator
'***** outputs
'''Count: 3
'''New Truth values: True False
' Error dialog as noted in the comment above
End Sub
While the code above appears a little contrived, it is based on some real code that I am using to automate Excel.
I have searched for answers here (including the following posts), but they do not address the simple and non-ambiguous example that I have here. The answers that I have found have addressed true type mismatches, wrong use of indexing or similar clear answers.
Retrieve items in collection (Excel, VBA)
Can't access object from collection
Nested collections, access elements type mismatch
This is caused by the fact, that the parameter of your procedure SetHasValues is implicitely defined ByRef.
Defining it ByVal will fix your problem.
#ADJ That's annoying, but perhaps the example below will allow you to start making a case for allowing RubberDuck.
I've upgraded your code using ideas and concepts I've gained from the rubberduck blogs. The code now compiles cleanly and is (imho) is less cluttered due to fewer lookups.
Key points to note are
Not relying on implicit type conversions
Assigning objects retrieved from collections to a variable of the type you are retrieving to get access to intellisense for the object
VBA objects with true constructors (the Create and Self functions in class2)
Encapsulation of the backing variables for class properties to give consistent (and simple) naming coupled with intellisense.
The code below does contain Rubberduck Annotations (comments starting '#)
Updated Class 2
Option Explicit
'#Folder("StackOverflowExamples")
'#PredeclaredId
Private Type Properties
HasA As Boolean
HasB As Boolean
SomeRandomID As String
End Type
Private p As Properties
Property Get HasA() As Boolean
HasA = p.HasA
End Property
Property Get HasB() As Boolean
HasB = p.HasB
End Property
Property Let HasA(propValue As Boolean)
p.HasA = propValue
End Property
Property Let HasB(propValue As Boolean)
p.HasB = propValue
End Property
Property Let RandomID(propValue As String)
p.SomeRandomID = propValue
End Property
Sub SetHasValues(key As String)
Select Case key
Case "A"
p.HasA = True
Case "B"
p.HasB = True
End Select
End Sub
Public Function Create(ByVal arg As String) As Class2
With New Class2
Set Create = .Self(arg)
End With
End Function
Public Function Self(ByVal arg As String) As Class2
p.SomeRandomID = arg
Set Self = Me
End Function
Updated test code
Private Sub TestCollectionError()
Dim classArray As Variant
Dim classCollection As Collection
Dim singleClass2Item As Class2
Dim my_item As Variant
Dim my_retrieved_item As Class2
classArray = Array("A", "B", "C")
Set classCollection = New Collection
For Each my_item In classArray
classCollection.Add Item:=Class2.Create(my_item), key:=my_item
Next
Debug.Print "Count: " & classCollection.Count
Set singleClass2Item = classCollection.Item(classCollection.Count)
Debug.Print "Initial Truth values: " & singleClass2Item.HasA, singleClass2Item.HasB
singleClass2Item.SetHasValues "A" ' <-- This code works fine.
Debug.Print "New Truth values: " & singleClass2Item.HasA, singleClass2Item.HasB
For Each my_item In classArray
Set my_retrieved_item = classCollection.Item(my_item)
my_retrieved_item.RandomID = CStr(my_item)
my_retrieved_item.SetHasValues CStr(my_item)
Next
End Sub
The 'Private Type Properties' idea comes from a Rubberduck article encapsulating class variable in a 'This' type. My take on this idea is to use two type variable p and s (Properties and State) where p holds the backing variables to properties and s hold variables which represent the internal state of the class. Its not been necessary to use the 'Private Type State' definition in the code above.
VBA classes with constructors relies on the PredeclaredID attribute being set to True. You can do this manually by removing and saving the code, using a text editor to set the attributer to 'True' and then reimporting. The RUbberDuck attribute '#PredeclaredId' allows this to be done automatically by the RubberDuck addin. IN my own code the initialiser for class2 would detect report an error as New should not be used when Classes are their own factories.
BY assigning and intermediate variable when retrieving an object from a class (or even a variant) you give Option Explicit the best change for letting you n=know of any errors.
An finally the Rubberduck Code Inspection shows there are still some issues which need attention
I need to do some refactoring (actually it's A LOT, but this small step will be very helpful for the whole process). So, let's say I've got this code snippet:
If xmlDoc.SelectSingleNode("/dang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/dang")
Type = "dang"
ElseIf xmlDoc.SelectSingleNode("/nang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/nang")
Type = "nang"
ElseIf xmlDoc.SelectSingleNode("/lang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/lang")
Type = "lang"
ElseIf xmlDoc.SelectSingleNode("/tang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/tang")
Type = "tang"
ElseIf xmlDoc.SelectSingleNode("/xtang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/xtang")
Type = "xtang"
End If
It's in the body of a big function and I want to take it out to a separate function. So, what I was wondering is whether it will be better to pass both universalNode and Type by value and just assign to them the values, without the need of returning anything? Is that going to work well or it is risky?
If it was just the Type that I'm working on, i.e., then I would just return it, but it's more than 1 variable that is being changed, and both are local variables for the big function, from which I am taking out this code snippet.
Any other suggestions maybe?
You can pass the variables by reference (not by value) to the function, it's not a bad practice and should work:
Public Sub MyFunc(ByRef node As MyNode, ByRef typ As String)
node = ...
typ = ...
End Sub
Or you can return some complex data holder:
Public Class MyParams
Public node As MyNode
Public typ As String
End Class
Public MyParams MyFunc()
Dim result As New MyParams()
result.node = ...
result.typ = ...
Return result
End Sub
I am a relative VB.Net noob, and I'm learning by doing. I'm sure what I'm about to ask has been asked 10^19 times before, but whatever code word it's under, I can't figure out how to Google it. Here goes...
We have an object model with one or more Project objects that consists of several Tables, which contain Rows which have Fields. This leads to code all over our apps that looks something like this...
Dim theColor As String = Projects(1).Tables(5).Rows(22).Fields(3)
In our application, if any of the objects in this "call chain" does not exist, the correct value for theColor should be Nothing*. This is just like Excel - the value of an empty cell in an empty row is vbnull, not "Excel has crashed".
This is not how VB.Net works, however. If, for instance, Rows(22) does not exist, the Fields(3) is called on Nothing and an exception is thrown. My question is how to best deal with this...
1) I could check each value to see it it's not Nothing, but that leads to horrible amounts of code...
If Projects(1) IsNot Nothing AndAlso Projects(1).Tables(5) AndAlso...
We have thousands of these, the amount of code this would require would be enormous.
2) I could wrap all accessors in try/catch, but that's really just a different sort of (1)
3) I could have a special instance of each object that has empty values. So, for instance, Tables(5) returns NullTable and Row(22) returns NullRow. But this means I have to always use accessor methods, I can't just look in the underlying arrays. You're probably saying good, but sadly a lot of our older code does just that (yes, duh).
4) Something else entirely? Am I missing some magic that everyone other than me knows?
You could have a function called GetField
Instead of
Dim theColor As String = Projects(1).Tables(5).Rows(22).Fields(3)
You would have
Dim theColor As String = GetField(1, 5, 22, 3)
Function GetField(ByVal projectIndex As Integer, ByVal tableIndex As Integer, ByVal rowIndex As Integer, byVal fieldIndex As Integer) As Object
If Projects(projectIndex) Is Nothing Then
Return Nothing
End If
If Projects(projectIndex).Tables(tableIndex) Is Nothing Then
Return Nothing
End If
If Projects(projectIndex).Tables(tableIndex).Rows(rowIndex) Is Nothing Then
Return Nothing
End If
If Projects(projectIndex).Tables(tableIndex).Rows(rowIndex).fields(fieldIndex) Is Nothing Then
Return Nothing
End If
Return Projects(projectIndex).Tables(tableIndex).Rows(rowIndex).fields(fieldIndex)
End Function
But I got to say... what you are doing looks sloppy. You should think of using classes with properties.
You could concoct a "project manager" of sorts. It is hard to know how viable this is from the post, but something like:
Class ProjectManager
Public Property CurrentProject As ProjectThing
Public Property CurrentTable As Integer
Get
Return tblIndex
End Get
Set
If CurrentProject IsNot Nothing Then
If CurrentProject.Tables(value) Is Nothing Then
Throw exception
Else
tblIndex = value
End If
End If
End Set
End Property
' etc
Then use it to store the current reference to the project and/or table. All the Is Not Nothings can be embedded there.
Private myPrj As New ProjectManager
...
myPrj.CurrentProject = Project(1)
myPrj.CurrentTable = 5
With the "manager" doing all the checking for everyone, you dont have to (much):
Dim theColor As String = myPrj.Rows(22).Fields(3)
or
Dim theColor As String = myPrj.GetRowValue(22, 3)
What it would really be doing is storing a validated object references for you, and testing those not worth storing. It could go as deep as you needed. Even if all it really did was encapsulate those Is Nothing/Is Not Nothing tests, it might add some value.
Public Function GetRowValue(r As Integer, f as Integer) As Something
If r < CurrentProject.Tables(tblIndex).Rows.Count AndAlso
f < CurrentProject.Tables(tblIndex).Rows(r).Fields.Count Then
Return ...
'or
Public Function GetRowValue(Of T)(r As Integer, f as Integer) As T
Once a project is specified, it could expose helpful properties like TableCount. It is possible that the data represented by some of the most used, most important Const definitions, could be exposed as properties:
' swap a property interface for "3"
Dim theColor As String = myPrj.FooColor(22)
You can handle the exception:
Dim theColor As String = Nothing
Try
theColor = Projects(1).Tables(5).Rows(22).Fields(3)
Catch
End Try
If you want to do it 'properly' you should specify the exceptions you are guarding against:
Dim theColor As String = Nothing
Try
theColor = Projects(1).Tables(5).Rows(22).Fields(3)
Catch ex As IndexOutOfRangeException
Catch ex As NullReferenceException
End Try
How do i loop through this class once I add items via this method. Just I am quite new to generic lists so was wonding if someone could point me in right direction in datatables im used to doing the following:
For Each thisentry In dt.rows
Next
What do I use in collections
Calling Code
Calling this in my delciarations of main class
Dim infoNoProductAvail As List(Of infoProductsNotFound) = New List(Of infoProductsNotFound)()
this is how i am adding the files but I have checked in the routine and the count for the list is at 2 products
If medProductInfo.SKU.SKUID = 0 Then
infoNoProductAvail.Add(New infoProductsNotFound(thisenty2.Item("EAN13").ToString(), True))
End If
this is the class itselfs
Public Class infoProductsNotFound
Public Sub New(tbcode As String, notfound As Boolean)
Me.tagbarcode = tbcode
Me.notfound = notfound
End Sub
Private tagbarcode As String = String.Empty
Private notfound As Boolean
Public Property tbcode() As String
Get
Return tagbarcode
End Get
Set(ByVal value As String)
tagbarcode = value
End Set
End Property
Public Property isNotFound() As Boolean
Get
Return notfound
End Get
Set(ByVal value As Boolean)
notfound = value
End Set
End Property
End Class
Tried
I tried using the following
Function BuildExceptionsForEmail()
Dim retval As String = ""
Dim cnt As Int32 = 0
retval = "The following products are not avialable" & vbCrLf
For Each info As infoProductsNotFound In infoNoProductAvail
retval &= info.tbcode
cnt &= 1
Next
Return retval
but for some reason at this point my info noproductAvail is blank even though in the routine above its sitting at count of 2 what gives?
First I'd shrink that declaration a bit:
Dim infoNoProductAvail As New List(Of infoProductsNotFound)
Next, to iterate there are several options. First (and what you're likely most used to):
For Each info as infoProductsNotFound in infoNoProductAvail
If info.tbCode = "xyz" Then
DoSomething(info)
End If
Next
Or you might want to use lambda expressions (if you're using .Net 3.5 and above I think - might be .Net 4):
infoNoProductAvail.ForEach (Function(item) DoSomething(item))
Remember that generics are strongly typed (unlike the old VB collections) so no need to cast whatever comes out: you can access properties and methods directly.
If infoNoProductAvail(3).isNotFound Then
'Do something
End If
(Not that that is a great example, but you get the idea).
The For Each syntax is the same. It works the same way for all IEnumerable objects. The only "trick" to it is to make sure that your iterator variable is of the correct type, and also to make sure that you are iterating through the correct object.
In the case of the DataTable, you are iterating over it's Rows property. That property is an IEnumerable object containing a list of DataRow objects. Therefore, to iterate through it with For Each, you must use an iterator variable of type DataRow (or one of its base classes, such as Object).
To iterate through a generic List(Of T), the IEnumerable object is the List object itself. You don't need to go to one of it's properties. The type of the iterator needs to match the type of the items in the list:
For Each i As infoProductsNotFound In infoNoProductAvail
' ...
Next
Or:
Dim i As infoProductsNotFound
For Each i In infoNoProductAvail
' ...
Next
Or:
For Each i As Object In infoNoProductAvail
' ...
Next
Etc.
I am coding in vb.net.
At times the data is empty/null this is due to user's input into the db.
i will like to bypass it, however i get no luck.
here is snippet of my code:
If hct.mydbvalue.name IsNot Nothing Then
dr("mydbvalue") = hct.mydbvalue.name
End If
I still get an error:
System.NullReferenceException: Object reference not set to an instance of an object.
is there a way if it is a null value to not do anything?
Both #FishBasketGordo and #Yuck are correct, you need to check the full object path for nullability:
If (hct IsNot Nothing) AndAlso (hct.mydbvalue IsNot Nothing) AndAlso (hct.mydbvalue.name IsNot Nothing) Then
dr("mydbvalue") = hct.mydbvalue.name
End If
You won't get a NullReferenceException from data in the database that's null when using ADO.NET; ADO.NET uses DBNull.Value to represent null, so your null reference is coming from somewhere else. In the code above, your exception could occur if any of the following were null:
hct
hct.mydbvalue
dr
Make sure that the whole chain is not null. If hct or mydbvalue is null, you'll get the exception.
To me this looks like hct.mydbvalue is null, and therefore you can't call "name" on it.
Private Function NullCheck(ByVal inObject As Object, Optional ByVal defaultValue As Object = "") As Object
Dim out As Object
If Not IsDBNull(inObject) Then
out = inObject ' This returns the value that was passed in when it is not null
Else
out = defaultValue ' This ensures that out is something and defaults to ""
End If
Return out
End Function
You should be checking whether hct is Nothing, as well as mydbvalue. If you look at the exception message property, it will tell you which is causing the error.
I'm also solving this problem, but in C#.
On my project we've complex object paths like "RootObject.childObject.LitleObject.TinyObject.StringName"
when any of these objects in the path is null, you'll get a null reference when you try something easy like
if(RootObject.childObject.LitleObject.TinyObject.StringName == "a")
I would be okay if it just works as whole rest of the path will be null.
eg. when childObject = null, then I want also RootObject.childObject.LitleObject.TinyObject.StringName to be null, not null reference exception.
However I've found no solution yet, but there is one new operator which can slightly help you in some null tasks.
a = object.object ?? defaultValue;
operator ?? is something like ISNULL in SQL server. If object on left is null, it returns the object from right.
It also replaces whole function NullCheck posted by Michael above.
Hope this will help a bit.
more info on operators
http://msdn.microsoft.com/en-us/library/ms173224(v=vs.80).aspx
http://msdn.microsoft.com/en-us/library/6a71f45d(v=vs.80).aspx
you're talking about diferent things.
It doesn't matter if you use ISDBNull(x.y), String.IsNullOrEmpty(x.y) or (x.y=null)
The problem is far sooner than your selected function is called.
when X is null, it cannot have a property Y. so when you call
AnyOfYourPrefferedFunctions(x.y);
the error raises during evaluation of x.y (null. doesn't exist), so it stops before the machine actually knows what is the function you want to call.
Probably only way to check this, would be using reflection. But you would need to send string with path and reference to root. so something like:
var v = GetValueThroughReflection(rootObject, "rootObject.path.to.the.last.object");
Then you'll be able to write a function which will go through the object path and find which one is null and handle it accordingly. e.g. returns null.
But when you'll heavy use that function, it can make your application run slower. as you'll use reflection for such simple task as is getting value out of variable.
from VS14+ you can use
If hct?.mydbvalue?.name IsNot Nothing Then
dr("mydbvalue") = hct.mydbvalue.name
End If
Try inserting a IF NOT isdbnull(hct.mydbvalue.name)
The following code checks all values.
If hct IsNot Nothing AndAlso
hct.mydbvalue IsNot Nothing AndAlso
Not String.IsNullOrWhitespace(hct.mydbvalue.name) Then
dr("mydbvalue") = hct.mydbvalue.name
End If
Note that the last test used String.IsNullOrWhitespace(). I'm assuming name is a string and you don't want to save empty strings.
Update 1
The following code is a simple console application to prove that using IsDbNull() or Micheal's NullCheck() will throw NullReferenceException when hct.mydbvalue is Nothing.
Module Module1
Sub Main()
Dim hct = New hct
Dim dr = New Dictionary(Of String, String)
Dim errorCount = 0
Try
Dim thisCallWillFail = IsDBNull(hct.mydbvalue.name)
Catch ex As NullReferenceException
Console.WriteLine(
"Using IsDBNull() threw NullReferenceException as expected."
)
errorCount += 1
End Try
Try
Dim thisCallWillFail = NullCheck(hct.mydbvalue.name)
Catch ex As NullReferenceException
Console.WriteLine(
"Using NullCheck() threw NullReferenceException as expected."
)
errorCount += 1
End Try
Console.WriteLine("errorCount = 2? {0}", errorCount = 2)
End Sub
Private Function NullCheck(ByVal inObject As Object,
Optional ByVal defaultValue As Object = "") As Object
Dim out As Object
If Not IsDBNull(inObject) Then
' This returns the value that was passed in when it is not null
out = inObject
Else
' This ensures that out is something and defaults to ""
out = defaultValue
End If
Return out
End Function
End Module
Public Class hct
Property mydbvalue As mydbvalue
End Class
Public Class mydbvalue
Property name As String
End Class