Sorry, that's the best subject I can come up with, if I understood the solution better, I could probably phrase a better subject line.
I am using a great grid control, Super List,l located here:
http://www.codeproject.com/KB/list/outlooklistcontrol.aspx?fid=449232&df=90&mpp=25&noise=3&sort=Position&view=Quick&fr=276
Before you read the problem, please note that you can download a very small VB.NET 2005 sample app which demos the problem:
http://dokmanovich.com/Documents/SuperListEvents.zip
Getting the answer to my question will, I hope, help me to understand dynamic events better in the context of what I am trying to accomplish.
The grid works like this: When you add a column to the grid, you specify the address of an event handler which will return the value at run time. In this case, the CC_ItemValueAccessor function. The latter function will be called with an input parameter which, in this case, is a "ToDo" object. Each ToDo object will be rendered as one row in the grid. The job of the CC_ItemValueAccessor function is to return the column value to be displayed by the grid for the row that corresponds to the passed-in ToDo object.
This works fine till I take it to the next step:
I want to dynamically create columns at run time. For example, I want to display the output of a datatable returned as a result of executing a user-specified SQL.
Using the earlier described static approach, I have one columnItemValueAccessor function responsible for returning the value of each column in the grid for the passed in row object. Now, since the columns are determined at run time based on the SQL returned results, I believe I need to write a generic handler that handles all columns, determines the name of the column that triggered this event and then returns the value for that column within the row object that is passed in as the sole parameter.
The problem is that the ItemValueAccessor function has a signature that only includes the row object and I do not know of a way to determine which column name is needed since all of the columns were hooked up to the same ItemValueAccessor function as the event handler.
I suspect that this is just a limitation of the control and that to overcome this problem I would have to enhance the underlying custom control, but that is likely beyond my current skills as it is an advanced control written in C# and I am a VB guy.
Here's the code:
Private Sub AddCcColumn()
Dim NewColumn As New BinaryComponents.SuperList.Column("CC", "CC", 110, AddressOf Cc_ItemValueAccessor)
_SuperList.Columns.Add(NewColumn)
End Sub
Private Function Cc_ItemValueAccessor(ByVal rowItem As Object) As Object
Dim ToDo As ToDo = CType(rowItem, SrToDoAndException).ToDo
Return ToDo.CCs.ToString
End Function
'---------------------------
And here are the signatures of the Column's instantiator method and the definition of the last parameter which is responsible for specifying the procedure that handles identifies the event handler responsible for returning the value of the column.
Public Sub New(ByVal name As String, ByVal caption As String, ByVal width As Integer, ByVal columnItemValueAccessor As BinaryComponents.SuperList.ColumnItemValueAccessor)
Member of BinaryComponents.SuperList.Column
Public Sub New(ByVal object As Object, ByVal method As System.IntPtr)
Member of BinaryComponents.SuperList.ColumnItemValueAccessor
Does anyone have any suggestions or am I stuck? I would really love to utilize the fantasic grouping capabilities of this control so I can display dynamic output that allows the user to group the dynamic output of a SQL by any column that they want.
I addressed the question to the author at the above site but it has gone unanswered. This is a desperate attempt to find a way to do this.
Thanks for bearing with me. I hope this question isn't rejected based on the fact that I refer to a third party control. My hope is that the answer lies in a better understanding of delegates, a more universal topic.
I used a lambda function, as Matthew suggested. Here is the code from the dynamic approach:
Private Sub btnDynamic_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDynamic.Click
ListControl1.Columns.Clear()
For Each DataCol As DataColumn In _ds.dtbPerson.Columns
' Get the column name in a loop variable - it needs to be in loop scope or this won\'t work properly'
Dim colName = DataCol.ColumnName
' Create the function that will be called by the grid'
Dim colLambda As ColumnItemValueAccessor = Function(rowItem As Object) General_ItemValueAccessor(rowItem, colName)
' Setup each column in the grid'
Dim NewColumn As New BinaryComponents.SuperList.Column(DataCol.ColumnName, DataCol.ColumnName, 220, colLambda)
ListControl1.Columns.Add(NewColumn)
Next
End Sub
Private Function General_ItemValueAccessor(ByVal rowItem As Object, ByVal colName As Object) As Object
Dim rowPerson As DataRow = CType(rowItem, DataRow)
Return rowPerson.Item(colName).ToString
End Function
Here's a quick primer on how it works:
Each time through the loop the lambda function is creating a new callback function for each column that looks something like this:
Class Func1
Dim colName1 As String = "PersonId"
Private Function General_ItemValueAccessor1(ByVal rowItem As Object) As Object
Dim rowPerson As DataRow = CType(rowItem, DataRow)
Return rowPerson.Item(Me.colName1).ToString
End Function
End Class
Class Func2
Dim colName2 As String = "LastName"
Private Function General_ItemValueAccessor2(ByVal rowItem As Object) As Object
Dim rowPerson As DataRow = CType(rowItem, DataRow)
Return rowPerson.Item(Me.colName2).ToString
End Function
End Class
... for however many columns you have - 3 in this case.
You need the colName variable within the loop and not use just DataCol.ColumnName directly in the lambda. Otherwise, when the grid gets around to calling the callback functions, that DataCol variable would be equal to the last value from the collection (or Nothing) for all the callback functions.
Basically, it would do this and you wouldn't get what you expected:
Class Func
Dim DataCol1 = DataCol
Private Function General_ItemValueAccessor1(ByVal rowItem As Object) As Object
Dim rowPerson As DataRow = CType(rowItem, DataRow)
Return rowPerson.Item(Me.DataCol1.ColumnName).ToString
End Function
Private Function General_ItemValueAccessor2(ByVal rowItem As Object) As Object
Dim rowPerson As DataRow = CType(rowItem, DataRow)
Return rowPerson.Item(Me.DataCol1.ColumnName).ToString
End Function
...
End Class
Hope that helps. Good luck.
The problem is that the ItemValueAccessor function has a signature that only includes the row object and I do not know of a way to determine which column name is needed since all of the columns were hooked up to the same ItemValueAccessor function as the event handler.
Okay, I haven't used that control in the past, and I'm really a C# person. But I think you may be able to accomplish this by creating a new lambda function for each column. Something like:
Private Sub AddCcColumn(ByVal sender As System.Object As System.String)
colLambda = (Function(rowItem As Object) Cc_InternalItemValueAccessor(columnName, rowItem))
Dim NewColumn As New BinaryComponents.SuperList.Column("CC", "CC", 110, colLambda)
_SuperList.Columns.Add(NewColumn)
End Sub
Then, colLambda will fit the signature, while your internal Cc_InternalItemValueAccessor gets the info it needs. Totally untested, but I think the basic idea works.
Related
So I am trying to make a code where the user inputs an ID number and receives the line of text that the ID corresponds to. I am having trouble with the code as I am unable to display the result (or correct result) in a label box.
For example:
If I type in ID 1, it displays the data that corresponds to ID 2, ID 2 corresponds to ID 3 and ID 3 ends the loop (there are only 3 records in the data currently).
I have included my code below
Private Sub btnSearch_Click(sender As Object, e As EventArgs) Handles btnSearch.Click
Filename = "NamesAndAges.txt"
FileOpen(1, Filename, OpenMode.Input,,,)
Dim ID As Integer
ID = txtSearch.Text
Dim Found As Boolean
Found = False
Do While Not EOF(1) And Found = False
If LineInput(1).Contains(ID) Then
lblDisplaySearch.Text = LineInput(1)
Found = True
Else MsgBox("Not Found")
End If
Loop
FileClose(1)
End Sub
Thanks in advance, would also really appreciate if anyone could explain the code they use as I am still a visual basic beginner.
Every time you call LineInput(1), it reads a line, so you're reading a line and checking if it contains ID then reading another line and setting lblDisplaySearch.Text to that value.
Try something like this:
Dim line As String
Do While Not EOF(1) And Found = False
line = LineInput(1)
If line.Contains(ID) Then
lblDisplaySearch.Text = line
Found = True
Else MsgBox("Not Found")
End If
Loop
I would strongly suggest simplifying this code, by using File.ReadLines:
Private Sub btnSearch_Click(sender As Object, e As EventArgs) Handles btnSearch.Click
Filename = "NamesAndAges.txt"
Dim line = File.ReadLines(Filename).FirstOrDefault(Function(x) x.Contains(txtSearch.Text))
If line Is Nothing Then
MsgBox("Not Found")
Exit Sub
End If
lblDisplaySearch.Text = line
End Sub
The primary advantage is that you don't need to manage the Do While loop. Instead, you are passing the match condition (Function(x) x.Contains(txtSearch.Text)) to the FirstOrDefault method, which internally will find the first line matching the condition and return it, or return Nothing if it's not found.
For Each and IEnumerable
VB.NET allows you to loop over a set of items without knowing or caring about the index within the set. For example:
For Each x As String In File.ReadLines(Filename)
'do something with the line, which is now in x
Next
In order to use For Each with an object, that object has to implement a specific interface — the IEnumerable interface.
Interfaces
Interfaces guarantee that a given object has, or implements, specific members. In this case, if an object implements the IEnumerable interface, that means it has a GetEnumerator method, which the For Each uses under the hood.
IEnumerable(Of T)
The object returned from File.ReadLines implements another more advanced generic interface called IEnumerable(Of T). With this interface, the compiler can figure out automatically that each step of the For Each will be parsing a string, and we don't need to specify it as a string:
For Each x In File.ReadLines(Filename)
'x is known to be a String here
Next
Lambda expressions
The condition "the line which contains the search text" is written as a lambda expression, which (in this case) is made into a method without an explicit name or definition. This is convenient, because we don't have to write this:
Function ContainsCondition(line As String, toFind As String) As Boolean
Return line.Contains(toFind)
End Function`
every time we want to express a condition this way.
Type of x in the condition
Because File.ReadLines returns an IEnumerable(Of T), in this case an IEnumerable(Of String), the compiler can figure out that the condition is working on strings, so we don't have to specify that x is a string within the condition.
I have a custom class with approximately 30 properties. (I.E. headername, headersize...)
I would like to be able to update a property by the name of the property as a string.
I am looking at using reflection (not 100% sure if this is the best method) instead of a large case statement that would continuously need to be updated if I add to the main object.
Through things I have found I have created the following Sub. I have put this in another location than the class of the object.
Public Sub UpdateValue(ByRef MainData As FilesMainData, ByVal SearchForObjectPartName As String, ByVal NewValue As Object)
Dim ObjectPartTypes() As System.Reflection.PropertyInfo = MainData.GetType().GetProperties()
Dim ObjectPartNames() As System.Reflection.FieldInfo = MainData.GetType().GetFields()
For I As Integer = 0 To ObjectPartNames.Count - 1
If ObjectPartTypes(I).Name.Equals(SearchForObjectPartName) Then
ObjectPartTypes(I).SetValue(ObjectPartTypes(I).GetType, NewValue,CType(I, Object) )
End If
Next
End Sub
1) I am getting some errors and know the code isn't right, but am unsure how to fix
2) I am unsure it's in the correct location.
Any help would be appreciated, thank you.
There are a few problems with the code:
You want to update the properties, but when iterating through the loop you are using the wrong count
Also you are using SetValue incorrectly, the first parameter must be the instance of the object containing the property
Here's the update method:
Public Sub UpdateValue(ByRef MainData As FilesMainData, ByVal SearchForObjectPartName As String, ByVal NewValue As Object)
Dim ObjectPartTypes() As System.Reflection.PropertyInfo = MainData.GetType().GetProperties()
For I As Integer = 0 To ObjectPartTypes.Count - 1
If ObjectPartTypes(I).Name.Equals(SearchForObjectPartName) Then
ObjectPartTypes(I).SetValue(MainData, NewValue)
End If
Next
End Sub
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.
Rather than giving the very specific case (which I did earlier), let me give a general example. Let's say that I have a function, called callingFunction. It has one parameter, called parameter. Parameter is of an unknown type. Let us then say that I wish to copy this parameter, and return it as a new object. For example, in pseudo code, something along the lines of...
Function callingFunction(ByVal parameter As Object) As Object
Dim newObj As New Object
'newObj has the same value as parameter, but is a distinctly different object
'with a different reference
newObj = parameter
return newObj
End Function
EDIT: Additional Information
The first time I posted this question, I received only one response - I felt that perhaps I made the question too specific. I guess I will explain more, perhaps that will help. I have an ASP page with 10 tables on it. I am trying, using the VB code behind, to come up with a single solution to add new rows to any table. When the user clicks a button, a generic "add row" function should be called.
The difficulty lies in the fact that I have no guarantee of the contents of any table. A new row will have the same contents as the row above it, but given that there are 10 tables, 1 row could contain any number of objects - text boxes, check boxes, etc. So I want to create a generic object, make it of the same type as the row above it, then add it to a new cell, then to a new row, then to the table.
I've tested it thoroughly, and the only part my code is failing on lies in this dynamic generation of an object type. Hence why I asked about copying objects. Neither of the solutions posted so far work correctly, by the way. Thank you for your help so far, perhaps this additional information will make it easier to provide advice?
You can't do this in general. And it won't be a good idea, for example, if parameter is of a type which implements the singleton pattern. If parameter is of a type which supports copying, it should implement the ICloneable interface. So, your function could look like this:
Function MyFunc(ByVal parameter As Object) As Object
Dim cloneableObject As ICloneable = TryCast(parameter, ICloneable)
If Not cloneableObject Is Nothing Then
Return cloneableObject.Clone()
Else
Return Nothing
End If
End Function
You could implement something like this:
Dim p1 As Person = New Person("Tim")
Dim p2 As Object = CloneObject(p1)
Dim sameRef As Boolean = p2 Is p1 'false'
Private Function CloneObject(ByVal o As Object) As Object
Dim retObject As Object
Try
Dim objType As Type = o.GetType
Dim properties() As Reflection.PropertyInfo = objType.GetProperties
retObject = objType.InvokeMember("", System.Reflection.BindingFlags.CreateInstance, Nothing, o, Nothing)
For Each propertyInfo As PropertyInfo In properties
If (propertyInfo.CanWrite) Then
propertyInfo.SetValue(retObject, propertyInfo.GetValue(o, Nothing), Nothing)
End If
Next
Catch ex As Exception
retObject = o
End Try
Return retObject
End Function
Class Person
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Public Sub New()
End Sub
Public Sub New(ByVal name As String)
Me.Name = name
End Sub
End Class
Here's a simple class that will work for most objects (assumes at least .Net 2.0):
Public Class ObjectCloner
Public Shared Function Clone(Of T)(ByVal obj As T) As T
Using buffer As MemoryStream = New MemoryStream
Dim formatter As New BinaryFormatter
formatter.Serialize(buffer, obj)
buffer.Position = 0
Return DirectCast(formatter.Deserialize(buffer), T)
End Using
End Function
End Class
I'm currently working in .NET 2.0 Visual Basic. The current project is an Active Directory Wrapper class library within which I have a Searcher(Of T) generic class that I wish to use to search the underlying directory for objects.
In this Searcher(Of T) class I have the following methods:
Private Function GetResults() As CustomSet(Of T)
Public Function ToList() As CustomSet(Of T)
Public Function Find(ByVal ParamArray filter() As Object) As CustomSet(Of T)
// And some other functions here...
The one that interests me the most is the Find() method to which I can pass property and values and would like to parse my LDAP query from this filter() ParamArray parameter. Actually, all I can figure out is this:
Public Sub SomeSub()
Dim groupSearcher As Searcher(Of Group) = New Searcher(Of Group)()
Dim groupsSet as CustomSet(Of Group) = groupSearcher.Find("Name=someName", "Description=someDescription")
// Working with the result here...
End Sub
But what I want to be able to offer to my users is this:
Public Sub SomeSub()
Dim groupSearcher As Searcher(Of Group) = New Searcher(Of Group)()
Dim groupsSet As CustomSet(Of Groupe) = groupSearcher.Find(Name = "someName", Guid = someGuid, Description = "someDescription")
// And work with the result here...
End Sub
In short, I want to offer some kind of Expression feature to my users, unless it is too much work, as this project is not the most important one and I don't have like 2 years to develop it. I think that the better thing I should do is to write something like CustomExpression that could be passed in parameters to some functions or subs.
Thanks for any suggestions that might bring me to my goal!
Interesting question. This is a language dependent feature, so I don't see this happening without some clever trickery of the IDE/compiler.
You could however have optional overloads on your Find method (vb.net is good for this), then make the search string manually to obtain the result.
Finally you could make use of lambda functions, but only in .net 3.5 and above. Even still, it would require your searcher to expose a preliminary set of data so you can recover the expression tree and build up the find string.
UPDATE
I've just been playing around with Reflection to see if I can retrieve the parameters passed, and build up a string dynamically depending on if they exist. This doesn't appear to be possible, due to the fact that compiled code doesn't reference the names.
This code just used was:
'-- Get all the "parameters"
Dim m As MethodInfo = GetType(Finder).GetMethod("Find")
Dim params() As ParameterInfo = m.GetParameters()
'-- We now have a reference to the parameter names, like Name and Description
Hmm. http://channel9.msdn.com/forums/TechOff/259443-Using-SystemReflection-to-obtain-parameter-values-dynamically/
Annoyingly it's not (easily) possible to recover the values sent, so we'll have to stick with building up the string in a non-dynamic fashion.
A simple optional method would look like:
Public Sub Find( _
Optional ByVal Name As String = "", _
Optional ByVal Description As String = "")
Dim query As String = String.Empty
If Not String.IsNullOrEmpty(Name) Then
query &= "Name=" & Name
'-- ..... more go here with your string seperater.
End If
End Sub