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Generally, properties are used to represent the state of an object and have few if any side effects when set, and functions are used to get something that will require a lot of calculation. FxCop will also tell you that you should never return an array from a property, but I do not always agree (especially for databinding).
There are no hard and fast rules, but there are a few things I would consider when making the choice. (I'm sure a quick Google search would find plenty of other opinions)
1) Will you both get and set the value? (if yes, +1 for property)
2) Will you only get the value? (could go either way)
3) Will you only set the value? (if yes, I would always make this a function. Write-only properties do not make much sense to me)
4) Are you going to need to databind to this value? (if yes, you will probably be required to make this a property)
5) Would the Get/Set functions be simple? (if yes, +2 for property)
Simple is of course subjective, but generally it means something like this:
Get
Return _memberVar
End Get
Set (value as YourTypeHere)
If value = _memberVar Then Exit Property
_memberVar = value
OnPropertyNameChanged()
End Set
and the OnPropertyNameChanged would raise any events and perform any other state changes that come from setting the property (eg: when PropertyA to false, PropertyB must be 0).
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A few more points to consider, IMHO:
-1- When an attribute is written, is the value likely to remain set indefinitely absent user intervention (things like controls may be changed by the user--that's their purpose).
-2- Will writing the attribute with the value it already contains have any effect (if so, use a method)
-3- Will writing this attribute have side-effects on other writable properties that are not subsets or supersets? There's nothing wrong with an object having properties for, e.g., X, Y, and position; changing position will update both X and Y; changing X or Y will update position. On the other hand, the 'length' property for a StringBuilder is ugly, since reducing the length has the side-effect of clearing some (or all) of the contents.
-4- Will reading this attribute have any side-effects other than possibly caching, or will it require access to a resource guarded by a mutex or synclock? If so, use a method.
-5- IMHO, some attributes should use a method for writing and a property for reading. For example, if I were designing the timer object, I would have included a TimeLeft property (read-only) and a SetTimeLeft method (possibly an AddTime method as well). The time remaining on a timer is apt to change as soon as it's written, so I don't like the idea of using a writable property for that; nonetheless, since the remaining time represents the object's logical state, a read property seems appropriate.
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I use two criteria: Will it behave like a variable or like a function? If it will behave like a variable, do I need to do anything other that store/retrieve the data?
If all I need is some place to store data, I will write a private variable declaration; if I don't need to do the extra coding, I don't. If the value is static, I write a private constant declaration.
Private X As Integer
Private Const CaptionText As String = "Enter some data" If the value is dynamic and read-only, then I will write a private function.
Private Function FolderPath() As String
Return String.Format("{0}\{1}", PathTextbox.Text, FileTextbox.Text)
End Function
If I need to validate the data when it is retrieved or stored, do some other kind of processing or perform multiple operations with that value, that is when I will write a private property with at least a Get.
Private pStringList As List(Of String)
Private ReadOnly Property StringList() As List(Of String)
Get
If pStringList Is Nothing Then pStringList = New List(Of String)
Return pStringList
End Get
End Property
Private pMyHeight As Integer
Private Property MyHeight() As Integer
Get
Return pMyHeight
End Get
Set(ByVal value As Integer)
Dim H As Integer = MinHeight
If value > MaxHeight Then
H = MaxHeight
ElseIf value > MinHeight Then
H = value
End If
pMyHeight = H
ResizeMe()
End Set
End Property
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Hi experts,
I have a typed dataset in my VB.Net project, where I use to add tables at
design time. Bydefault there are only four properties for the tables
like.. CaseSensitive, DisplayExpression, Locale and Name.
Here, my requirement is, I need three more user defined properties for as
many tables as I added at design time and in the same manner I need three
more user defined properties for the columns in the tables.
I hope, that my requirement is clear and I am awaiting for your help
Thanks a lot in advance to all who helps me
Ravi Shanker .L
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Sounds like you want to derive a new class from the class that defines your tables now ?
Christian Graus
No longer a Microsoft MVP, but still happy to answer your questions.
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Thanks for the response
Its nothing like "derive a new class from the class that defines my
tables"
I just want to use the dataset designer to visually create and edit tables
and as well i need more properties at the same time. I can explain you a
bit clearly. Take a new VB.Net project, add new item to the project and
select 'Dataset'. There after, right click on the dataset area, select
Add -> DataTable from the popup menu, you are going to get a table with
no columns, right ?. Now, right click on the table and select properties
from the popup menu, a properties window is going to appear there are only
four properties bydefault right ?. But, i want some more properties there
Once again thanks for the response and I am awaiting for another response
Ravi Shanker .L
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I think you'll probably find that Christian's answer is correct - there's no way to make properties 'magically' appear in the property window. You have to have a way of putting them there, and deriving another class with further public properties from the datatable class could be one way to go. Mind you, you might want to consider your design in general...
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Thanks Paddy Body
I think I am a bit clear now, let me work on this as you both people
suggested me. Thanks once again for you both
Ravi Shanker .L
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Hi, All
iam stuck on that how i reterive the particular record from data table object
Actullay i passed query result into dataset and create data table onject and fill the table with sql data adopter but now i have to extract particular record form data table object
PLease help me iam stuck on this .
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The Rows property is a collection of all rows in the DataTable. You can use it to access any of the rows by index.
Despite everything, the person most likely to be fooling you next is yourself.
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thnks for response
kindly write few lines of code that how i do that actully i wants to extract particular record from data table object and loop through the each row .
thanks for response
Rameez
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Its just a simple for next loop, during which you look for the record you want.
Bob
Ashfield Consultants Ltd
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Free hand, but you get the point:
For each oRow as DataRow in dsSales.Tables(0).Rows
If convert.toint32(oRow("CustomerID")) = 1234 then
'Do work here......
End if
Next
Cheers
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You could use a DataView to filter your table and return the results.
Steve Jowett
-------------------------
It is offen dangerous to try and see someone else's point of view, without proper training. Douglas Adams (Mostly Harmless)
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Hello,
How do i include the ADODB component to vb6? I've searched the available components though I can't find Microsoft ActiveX Data Objects 2.5 Library or 2.6 for that matter. Is there anyway around this? Many thanks for the help
Aim small, miss small
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tatchung wrote: How do i include the ADODB component to vb6? I've searched the available components though I can't find Microsoft ActiveX Data Objects 2.5 Library or 2.6 for that matter. Is there anyway around this? Many thanks for the help
You need to install MS Data Access Components.
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How to Create utility page in VB.Net?Please help me out of this issue.
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The reason someone gave you a 1 is that your question makes no sense. It's ridiculous. What the hell is a utility page, and why are you asking a top level question that implies you have absolutely no idea what you're doing ? How are we to know how to answer it, in a way that you understand, if you can't even explain what you mean ?
Christian Graus
No longer a Microsoft MVP, but still happy to answer your questions.
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5 rating for that answer 
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A would suggest a 6 
Lloyd J. Atkinson
"Logic will get you from A to B, but imagination will take you everywhere" - ALbert Einstein
I look at Microsoft, and turn to my poster on the wall saying: "Bang head here in case of stress".
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I kept on asking myself what do you mean when you say "utility page". But atleast someone tought you a lesson, next time you will think befoer you post here.
Vuyiswa Maseko,
Sorrow is Better than Laughter, it may Sadden your Face, but It sharpens your Understanding
VB.NET/SQL7/2000/2005
http://vuyiswamb.007ihost.com
http://Ecadre.007ihost.com
vuyiswam@tshwane.gov.za
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Im communicating with a PLC which works on MODBUS RTU protocol. Need to continuously monitor the registers in it using serial communication. Iv used RS232 Class which i found from Codeproject. Im using a timer object to continuously send read/write command on the port. Iv Set Timeout period as 1000ms and Timer's Interval time as also 1000ms. After a few cycles communication fails and it prompts NULL Exception Argument.Can you Plz guide with it.
Jalpa
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There are also some articles about MODBUS here at CP [^].
See also these pages [^], [^].
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
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First of all thanx for replying. Iv tried all those links but none of them worked. Since in coding in VB.NET it does not provide me with any readymade class so iv included a class called as CRs232 which I found through the NET. I think the NULL EXCEPTION ARGUMENT that im getting is due to the incorrect CommTimeOuts that iv set. So if you could help me with a method for finding out the correct Time-Outs.
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jalpam wrote: Since in coding in VB.NET it does not provide me with any readymade class
Are you sure [^]?
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
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