Creating an array of datarows

  • Thread starter Thread starter creator_bob
  • Start date Start date
C

creator_bob

How do I create an array of datarows from a sorted list?

I put a bunch of datarows into a sorted list to sort them. Then I got
an array of the sorted elements. However, I cannot typecast them. I
get an invalid cast error. I notice that in the debugger, that arrays
of datarows are listed as {Length=xx}, but my arrays are listed as
{system.array} and refuse to typecast.

Public Class mySortedList
Inherits SortedList

Public ReadOnly Property array() As Object
Get
Dim Result() As Object, X As Integer
ReDim Result(Me.Count - 1)
For X = 0 To Me.Count - 1
Result(X) = Me.GetByIndex(X)
Next
Return Result
End Get
End Property
End Class


Dim O As Object, TestRows() As DataRow
O = EndRingsList.array ' OK to here
TestRows = DirectCast(O, PressData.End_RingsRow()) ' Fails here

O is listed in the debugger as {system.array} instead of {Length=xx}
 
It sounds like I need to understand arrays better.

getchildrows(...) returns DataRow() and I can typecast it to a specific
type of row array, but if I create my own function that returns
DataRow(), I can't type cast it.

Example:

Dim Test1 as DataRow(), Test2 as pressdata.end_ringsRow()

Test1=xx.GetChildRows("Relation")
Test2=directcast(Test1, pressdata.end_ringsRow()) ' This works.

Test1=myfunction() ' MyFunction returns type DataRow()
Test2=directcast(Test1, Pressdata.end_ringsRow()) ' Gives an invalid
cast error.

I can get around this by creating a casting function for each type I
need. I simply dimensions an array according to the number of elements
in the source array and copies them all over and returns the result.

How does the dataset class return DataRow() arrays that can be
typecasted and my own functions can't?
 
I would think that the DataSet (or DataTable) has schema information whereas
the Arraylist of datarows does not. Why are you not work with DataTables if
you want to work with DataRows. You can sort datatables easier.
 
Dennis said:
I would think that the DataSet (or DataTable) has schema information whereas
the Arraylist of datarows does not. Why are you not work with DataTables if
you want to work with DataRows. You can sort datatables easier.
Click to expand...

My situation is I needed a sorted list of grandchildren, and my
grandchild table, even if it was sorted, wouldn't be sorted after
getting all child rows; then with each of those child rows, getting its
child row.

I found the solution was to use the arraylist object. Then, when I am
ready to return, I use ToArray(Element0.GetType). This returns an
object that can be typecast.

Working with arrays of datarows is quite customary, since a datarow can
only belong to one datatable.
 
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