I am new to vb6 so might be obvious for some of you.I have a collection problem, trying to put items in a collection to then evaluate if the item exists and setting a button to be enabled or not.
The Code:
For Each vBookmark In lstAssign.SelBookmarks
'---------------------------------------
'filtering with agency code and crew code.
sAssignmentValue = lstAssign.columns("AgencyCode").Value & lstAssign.columns("CrewCode").Value
'Show/hide value depending on crew existance.
If Not ExistsStartLocation(colParameters, sValue) Then
bEnableMyButton = True
colParameters.Add (sValue)
Else
bEnableMyButton = False
End If
'----------------------------------------
Next
sAssignmentValue = ""
tbrMain.TbrButtonEnabled "XXX", bEnableMyButton
tbrMain.TbrButtonEnabled "YYY", bEnable
Set colStartLocationParameters = Nothing
Exit Sub
Private Function ExistsStartLocation(col As collection, index As Variant) As Boolean
On Error GoTo ErrHandler
Dim v As Variant
v = col(index)
ExistsStartLocation = True
Exit Function
ErrHandler:
ExistsStartLocation = False
End Function
The problem is at this moment is that I only have colParameters(index) accessible, so I can't access my collection with a value "123-ABC" directly. I do not want to add an integer index, I want to keep simply accessing by item value, but my exists method will always return false. therefore always disabling my button.
How does this works?
At first glance, you should have to do something like this:
Private Function ExistsStartLocation(col As collection, val As String) As Boolean
Dim blnFoundItem As Boolean = False
For index As Integer = 1 To col.Count
If col(index) = val Then
blnFoundItem = True
End If
Next
ExistsStartLocation = blnFoundItem
End Function
Looping the collection works but is not efficient. If you assign the optional Key value in the Add method you can also use that as the Index to the Item method. In your example it appears you are assigning a string to the collection so the Add method would look something like ...
colParameters.Add sValue, sValue
Be aware though that if you are adding duplicate values this won't work. The keys need to be unique.
With the the collection item's key populated you can use a function that leverages the err object. If you try to get a collection item by the key and it exists no error is thrown. If it does not exists err.number 5 is thrown. The new function would be something like this.
Public Function ItemExists(ByVal vCollection As Collection, ByVal vKey As String) As Boolean
Dim varItem As Variant
On Error Resume Next
varItem = vCollection.Item(vKey)
ItemExists = (Err.Number = 0)
End Function
Related
I want to check collection variable contains the key or not in visual basic 6.0
Below is the collection variable I am having
pcolFields As Collection
and I want to check whether it contains the field Event_Code. I am doing this as below but it not worked for me.
If IsMissing(pcolFields("Event_Code")) = False Then
'Do Something
End If
Here is an example solution with try-catch:
Private Function IsMissing(col As Collection, field As String)
On Error GoTo IsMissingError
Dim val As Variant
val = col(field)
IsMissing = False
Exit Function
IsMissingError:
IsMissing = True
End Function
Use it like this:
Private Sub Form_Load()
Dim x As New Collection
x.Add "val1", "key1"
Dim testkey As String
testkey = "key2"
If IsMissing(x, testkey) Then
Debug.Print "Key is Missing"
Else
Debug.Print "Val is " + x(testkey)
End If
Exit Sub
End Sub
You could also try a to Implement or Subclass the Collection and add a "has" Function
Collections are not useful if you need to check for existence, but they're useful for iteration. However, collections are sets of Variants and so are inherently slower than typed variables.
In nearly every case it's more useful (and more optimal) to use a typed array. If you need to have a keyed collection you should use the Dictionary object.
Some examples of general ways of using typed arrays:
Dim my_array() As Long ' Or whichever type you need
Dim my_array_size As Long
Dim index As Long
Dim position As Long
' Add new item (push)
ReDim Preserve my_array(my_array_size)
my_array(my_array_size) = 123456 ' something to add
my_array_size = my_array_size + 1
' Remove item (pop)
my_array_size = my_array_size - 1
If my_array_size > 0 Then
ReDim Preserve my_array(my_array_size - 1)
Else
Erase my_array
End If
' Remove item (any position)
position = 3 'item to remove
For index = position To my_array_size - 2
my_array(index) = my_array(index + 1)
Next
my_array_size = my_array_size - 1
ReDim Preserve my_array(my_array_size - 1)
' Insert item (any position)
ReDim Preserve my_array(my_array_size)
my_array_size = my_array_size + 1
For index = my_array_size - 1 To position + 1 Step -1
my_array(index) = my_array(index - 1)
Next
my_array(position) = 123456 ' something to insert
' Find item
For index = 0 To my_array_size - 1
If my_array(index) = 123456 Then
Exit For
End If
Next
If index < my_array_size Then
'found, position is in index
Else
'not found
End If
Whilst it may seem like a lot code. It is way faster. Intellisense will also work, which is a bonus. The only caveat is if you have very large data sets, then redim starts to get slow and you have to use slightly different techniques.
You can also use a Dictionary, be sure to include the Microsoft Scripting Runtime reference in your project:
Dim dict As New Dictionary
Dim value As Long
dict.Add "somekey", 123456
dict.Remove "somekey"
value = dict.Item("somekey")
If dict.Exists("somekey") Then
' found!
Else
' not found
End If
Dictionaries like collections just hold a bunch of Variants, so can hold objects etc.
We can check following code into vb.net code
If Collection.ContainsKey(KeyString) Then
'write code
End if
Collection is variable of Dictionary and KeyString is a key string which we need to find into collection
The method from efkah will fail if the Collection contains objects rather than primitive types. Here is a small adjustment:
'Test if a key is available in a collection
Public Function HasKey(coll As Collection, strKey As String) As Boolean
On Error GoTo IsMissingError
Dim val As Variant
' val = coll(strKey)
HasKey = IsObject(coll(strKey))
HasKey = True
On Error GoTo 0
Exit Function
IsMissingError:
HasKey = False
On Error GoTo 0
End Function
I'm trying to pre-view if a field of the recordset is empty/null or not.
If IsNull(rs.Fields("fieldname")) = True Then ...
If IsNull(rs.Fields("fieldname")).Value = True Then ...
if IsNull(rs.Fields("fieldName").Value) Then...
All of these methods fires up an error... Why? How may I check if the recordset is null before I assign it's value to a variable.
If I understand correctly, you want to ensure that a field exists in the recordset. If that is correct, you need to either iterate the fields looking for the field you are searching for, or try to directly access the field and trap any errors. Here is a method that iterates the field collection and returns True if the field exists.
Public Function FieldExists(ByVal rsRecSet As ADODB.Recordset, ByVal FieldName As String) As Boolean
Dim fld As ADODB.Field
Dim Rtn As Boolean
If Not rsRecSet Is Nothing Then
For Each fld In rsRecSet.Fields
If StrComp(fld.Name, FieldName, vbTextCompare) = 0 Then
Rtn = True
Exit For
End If
Next fld
End If
FieldExists = Rtn
End Function
Here is a way to print out the columns of a table.
Dim cat
Set cat = CreateObject("ADOX.Catalog")
Set cat.ActiveConnection = db 'db is the adodb.connection object
Dim tbl
Dim clm
For Each tbl In cat.Tables
For Each clm In tbl.Columns
Debug.Print (clm) ' Prints the column name from the table
Next
Next
Try using IsDbNull() instead. DbNull is different than Null.
Edit, just loop through the field names and have a boolean if it found it, otherwise use a try catch structure.
For Each field in rs.Fields
if field.Name = "someFieldName" then
foundField = true
exit for
else
foundField = false
end if
next
I'm using AtValue and AtField helpers like this
Option Explicit
Private Sub Form_Load()
Dim rs As Recordset
If IsEmpty(AtValue(rs, "Test")) Then
Debug.Print "Field is Empty or non-existant"
End If
If LenB(C2Str(AtValue(rs, "Test"))) = 0 Then
Debug.Print "Field is Null, Empty, empty string or non-existant"
End If
'-- this will never fail, even if field does not exist
AtField(rs, "Test").Value = 42
End Sub
Public Function AtValue(rs As Recordset, Field As String) As Variant
On Error GoTo QH
AtValue = rs.Fields(Field).Value
Exit Function
QH:
' Debug.Print "Field not found: " & Field
End Function
Public Function AtField(rs As Recordset, Field As String) As ADODB.Field
Static rsDummy As Recordset
On Error GoTo QH
Set AtField = rs.Fields(Field)
Exit Function
QH:
' Debug.Print "Field not found: " & Field
Set rsDummy = New Recordset
rsDummy.Fields.Append Field, adVariant
rsDummy.Open
rsDummy.AddNew
Set AtField = rsDummy.Fields(Field)
End Function
Public Function C2Str(Value As Variant) As String
On Error GoTo QH
C2Str = CStr(Value)
QH:
End Function
My type-casting helpers are actually using VariatChangeType API (so to work with Break on all errors setting) like this
Public Function C_Str(Value As Variant) As String
Dim vDest As Variant
If VarType(Value) = vbString Then
C_Str = Value
ElseIf VariantChangeType(vDest, Value, VARIANT_ALPHABOOL, VT_BSTR) = 0 Then
C_Str = vDest
End If
End Function
rs.EOF flag will tell whether RecordSet is Empty or not
If Not rs.EOF Then
..Your desired logic..
End If
I'm working on an application in vb6 that draws information from a database. I've come across many problems that come from null values in the database as vb6 functions and subroutines don't like nulls. The string problem is easily solved by concatenating an empty string to the value. But what do I do for a null value where a boolean should be?
Thanks for your help!
This assumes you are using the ADO objects for data access.
Dim boolField As Boolean
If Not IsNull(fields("FieldName").value) Then
boolField = CBool(fields("FieldName").value)
End If
I'm using most of these function to handle nulls
'--- type-casting without errors'
Public Function C2Str(Value As Variant) As String
On Error Resume Next
C2Str = CStr(Value)
On Error GoTo 0
End Function
Public Function C2Lng(Value As Variant) As Long
On Error Resume Next
C2Lng = CLng(Value)
On Error GoTo 0
End Function
Public Function C2Cur(Value As Variant) As Currency
On Error Resume Next
C2Cur = CCur(Value)
On Error GoTo 0
End Function
Public Function C2Dbl(Value As Variant) As Double
On Error Resume Next
C2Dbl = CDbl(Value)
On Error GoTo 0
End Function
Public Function C2Date(Value As Variant) As Date
On Error Resume Next
C2Date = CDate(Value)
On Error GoTo 0
End Function
Public Function C2Bool(Value As Variant) As Boolean
On Error Resume Next
C2Bool = CBool(Value)
On Error GoTo 0
End Function
You can use C2Bool in your case :-))
This is an old problem with VB6 and ASP. I use Trim(l_BankAccount.Recordset.Fields("BANKCODE").value & " ") which gets rid of many problems including the dbNull.
For a whole number field CLng("0" & Trim(l_BankAccount.Recordset.Fields("BANKCODE").value & " "))
works.
Try using isnull and specifying the .value of the field, as otherwise the isnull() checks the field object (and not the value):
If (IsNull(l_BankAccount.Recordset.Fields("BANKCODE").value) = True) Or _
Is there a way to ask for a control property in a loop??
I need somethig like this:
For each p in control.properties
if p = "Value" then
msgbox "I Have Value Property"
elseif p = "Caption" then
msgbox "I Have Caption Property"
end if
next
It could be done somehow?
Found this code on Experts Exchange. Add a reference to TypeLib Information.
Public Enum EPType
ReadableProperties = 2
WriteableProperties = 4
End Enum
Public Function EnumerateProperties(pObject As Object, pType As EPType) As Variant
Dim rArray() As String
Dim iVal As Long
Dim TypeLib As TLI.InterfaceInfo
Dim Prop As TLI.MemberInfo
On Error Resume Next
ReDim rArray(0) As String
Set TypeLib = TLI.InterfaceInfoFromObject(pObject)
For Each Prop In TypeLib.Members
If Prop.InvokeKind = pType Then
iVal = UBound(rArray)
rArray(iVal) = UCase$(Prop.Name)
ReDim Preserve rArray(iVal + 1) As String
End If
Next
ReDim Preserve rArray(UBound(rArray) - 1) As String
EnumerateProperties = rArray
End Function
You can ask for a list of the readable, or writeable properties.
Bonus, ask if a specific property exists.
Public Function DoesPropertyExist(pObject As Object, ByVal _
PropertyName As String, pType As EPType) As Boolean
Dim Item As Variant
PropertyName = UCase$(PropertyName)
For Each Item In EnumerateProperties(pObject, pType)
If Item = PropertyName Then
DoesPropertyExist = True
Exit For
End If
Next
End Function
Beaner has given an excellent direct answer to the question you have asked.
I'm guessing what you might be trying to do. Perhaps you're trying to get the "text" from a control but you don't know the type of the control at runtime. You could consider something like this, which tries a number of hard-coded property names in turn until something works.
Function sGetSomeText(ctl As Object) As String
On Error Resume Next
sGetSomeText = ctl.Text
If Err = 0 Then Exit Function
sGetSomeText = ctl.Caption
If Err = 0 Then Exit Function
sGetSomeText = ctl.Value
If Err = 0 Then Exit Function
sGetSomeText = "" 'Nothing worked '
End Function
Another approach would be to check the type of the control at runtime. You can use
If TypeName(ctl) = "whatever" or
If TypeOf ctl Is whatever.
Then you could switch to code for specific control types that definitely have the Text property, etc.
I'm not sure what you're hoping to accomplish, but I'm pretty sure VB6 does not support what you're talking about. You could try something like this:
If control.Value Is Not Nothing Then
msgbox "I Have Value Property"
Else If control.Caption Is Not Nothing Then
msgbox "I Have Caption Property"
See if that accomplishes what you're looking to do.
I've inherited a large VB6 app at my current workplace. I'm kinda learning VB6 on the job and there are a number of problems I'm having. The major issue at the moment is I can't figure out how to check if a key exists in a Collection object. Can anyone help?
My standard function is very simple. This will work regardless of the element type, since it doesn't bother doing any assignment, it merely executes the collection property get.
Public Function Exists(ByVal oCol As Collection, ByVal vKey As Variant) As Boolean
On Error Resume Next
oCol.Item vKey
Exists = (Err.Number = 0)
Err.Clear
End Function
#Mark Biek Your keyExists closely matches my standard Exists() function. To make the class more useful for COM-exposed collections and checking for numeric indexes, I'd recommend changing sKey and myCollection to not be typed. If the function is going to be used with a collection of objects, 'set' is required (on the line where val is set).
EDIT: It was bugging me that I've never noticed different requirements for an object-based and value-based Exists() function. I very rarely use collections for non-objects, but this seemed such a perfect bottleneck for a bug that would be so hard to track down when I needed to check for existence. Because error handling will fail if an error handler is already active, two functions are required to get a new error scope. Only the Exists() function need ever be called:
Public Function Exists(col, index) As Boolean
On Error GoTo ExistsTryNonObject
Dim o As Object
Set o = col(index)
Exists = True
Exit Function
ExistsTryNonObject:
Exists = ExistsNonObject(col, index)
End Function
Private Function ExistsNonObject(col, index) As Boolean
On Error GoTo ExistsNonObjectErrorHandler
Dim v As Variant
v = col(index)
ExistsNonObject = True
Exit Function
ExistsNonObjectErrorHandler:
ExistsNonObject = False
End Function
And to verify the functionality:
Public Sub TestExists()
Dim c As New Collection
Dim b As New Class1
c.Add "a string", "a"
c.Add b, "b"
Debug.Print "a", Exists(c, "a") ' True '
Debug.Print "b", Exists(c, "b") ' True '
Debug.Print "c", Exists(c, "c") ' False '
Debug.Print 1, Exists(c, 1) ' True '
Debug.Print 2, Exists(c, 2) ' True '
Debug.Print 3, Exists(c, 3) ' False '
End Sub
I've always done it with a function like this:
public function keyExists(myCollection as collection, sKey as string) as Boolean
on error goto handleerror:
dim val as variant
val = myCollection(sKey)
keyExists = true
exit sub
handleerror:
keyExists = false
end function
As pointed out by Thomas, you need to Set an object instead of Let. Here's a general function from my library that works for value and object types:
Public Function Exists(ByVal key As Variant, ByRef col As Collection) As Boolean
'Returns True if item with key exists in collection
On Error Resume Next
Const ERR_OBJECT_TYPE As Long = 438
Dim item As Variant
'Try reach item by key
item = col.item(key)
'If no error occurred, key exists
If Err.Number = 0 Then
Exists = True
'In cases where error 438 is thrown, it is likely that
'the item does exist, but is an object that cannot be Let
ElseIf Err.Number = ERR_OBJECT_TYPE Then
'Try reach object by key
Set item = col.item(key)
'If an object was found, the key exists
If Not item Is Nothing Then
Exists = True
End If
End If
Err.Clear
End Function
As also advised by Thomas, you can change the Collection type to Object to generalize this. The .Item(key) syntax is shared by most collection classes, so that might actually be useful.
EDIT Seems like I was beaten to the punch somewhat by Thomas himself. However for easier reuse I personally prefer a single function with no private dependencies.
Using the error handler to catch cases when the key does not exists in the Collection can make debugging with "break on all errors" option quite annoying. To avoid unwanted errors I quite often create a class which has the stored objects in a Collection and all keys in a Dictionary. Dictionary has exists(key) -function so I can call that before trying to get an object from the collection. You can only store strings in a Dictionary, so a Collection is still needed if you need to store objects.
The statement "error handling will fail if an error handler is already active" is only partly right.
You can have multiple error handlers within your routine.
So, one could accommodate the same functionality in only one function.
Just rewrite your code like this:
Public Function Exists(col, index) As Boolean
Dim v As Variant
TryObject:
On Error GoTo ExistsTryObject
Set v = col(index)
Exists = True
Exit Function
TryNonObject:
On Error GoTo ExistsTryNonObject
v = col(index)
Exists = True
Exit Function
ExistsTryObject:
' This will reset your Err Handler
Resume TryNonObject
ExistsTryNonObject:
Exists = False
End Function
However, if you were to only incorporate the code in the TryNonObject section of the routine, this would yield the same information.
It will succeed for both Objects, and non-objects.
It will speed up your code for non-objects, however, since you would only have to perform one single statement to assert that the item exists within the collection.
Better solution would be to write a TryGet function. A lot of the time you are going to be checking exists, and then getting the item. Save time by doing it at the same time.
public Function TryGet(key as string, col as collection) as Variant
on error goto errhandler
Set TryGet= col(key)
exit function
errhandler:
Set TryGet = nothing
end function
see
http://www.visualbasic.happycodings.com/Other/code10.html
the implementation here has the advantage of also optionally returning the found element, and works with object/native types (according to the comments).
reproduced here since the link is no longer available:
Determine if an item exists in a collection
The following code shows you how to determine if an item exists within a collection.
Option Explicit
'Purpose : Determines if an item already exists in a collection
'Inputs : oCollection The collection to test for the existance of the item
' vIndex The index of the item.
' [vItem] See Outputs
'Outputs : Returns True if the item already exists in the collection.
' [vItem] The value of the item, if it exists, else returns "empty".
'Notes :
'Example :
Function CollectionItemExists(vIndex As Variant, oCollection As Collection, Optional vItem As Variant) As Boolean
On Error GoTo ErrNotExist
'Clear output result
If IsObject(vItem) Then
Set vItem = Nothing
Else
vItem = Empty
End If
If VarType(vIndex) = vbString Then
'Test if item exists
If VarType(oCollection.Item(CStr(vIndex))) = vbObject Then
'Return an object
Set vItem = oCollection.Item(CStr(vIndex))
Else
'Return an standard variable
vItem = oCollection.Item(CStr(vIndex))
End If
Else
'Test if item exists
If VarType(oCollection.Item(Int(vIndex))) = vbObject Then
'Return an object
Set vItem = oCollection.Item(Int(vIndex))
Else
'Return an standard variable
vItem = oCollection.Item(Int(vIndex))
End If
End If
'Return success
CollectionItemExists = True
Exit Function
ErrNotExist:
CollectionItemExists = False
On Error GoTo 0
End Function
'Demonstration routine
Sub Test()
Dim oColl As New Collection, oValue As Variant
oColl.Add "red1", "KEYA"
oColl.Add "red2", "KEYB"
'Return the two items in the collection
Debug.Print CollectionItemExists("KEYA", oColl, oValue)
Debug.Print "Returned: " & oValue
Debug.Print "-----------"
Debug.Print CollectionItemExists(2, oColl, oValue)
Debug.Print "Returned: " & oValue
'Should fail
Debug.Print CollectionItemExists("KEYC", oColl, oValue)
Debug.Print "Returned: " & oValue
Set oColl = Nothing
End Sub
See more at: https://web.archive.org/web/20140723190623/http://visualbasic.happycodings.com/other/code10.html#sthash.MlGE42VM.dpuf
While looking for a function like this i designed it as following.
This should work with objects and non-objects without assigning new variables.
Public Function Exists(ByRef Col As Collection, ByVal Key) As Boolean
On Error GoTo KeyError
If Not Col(Key) Is Nothing Then
Exists = True
Else
Exists = False
End If
Exit Function
KeyError:
Err.Clear
Exists = False
End Function