如何过滤通用对象列表

Question

I have find the code to implement a SortableBindingList that extends of BindingList and it theoretically let sort and filter a list of generic objects. It works perfectly sorting the list but I can not get filtering.

The filter code is as follows

       Protected Sub UpdateFilter()
        _isSorted = False 'remove sort.
        Try
            'We filter on the entire collection
            Dim filtered = _originalData.AsQueryable()

            If Not String.IsNullOrEmpty(_filter) Then filtered = filtered.Where(_filter)

            Dim filteredResult = filtered.ToList()
            Items.Clear()

            If filteredResult IsNot Nothing AndAlso filteredResult.Count > 0 Then
                For Each tItem As T In filtered
                    Items.Add(tItem)
                Next
            End If
        Catch
            'Reset the list
            Items.Clear()
            For Each tItem As T In _originalData
                Items.Add(tItem)
            Next

            'Rethrow the error
            Throw
        Finally
            OnListChanged(New ListChangedEventArgs(ListChangedType.Reset, -1))
        End Try
    End Sub

The problem is that the following example receive like a filter a string in the clause where but the compile trhow an error since it wait a function I don't know how to resolve this

Sorry if you do not understand well. I do not speak English well

Answer 1

You need to pass a predicate. I hope this example will guide you.

Private Function AddFilter(list As List(Of String), filter As Func(Of String, Integer, Boolean)) As List(Of String)
    Dim l As IEnumerable(Of String) = Nothing
    If Not IsNothing(filter) Then
        l = list.Where(filter)
    End If
    Return l.ToList
End Function

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim A As New List(Of String) From {"Mathew", "Mark", "Luke", "John"}
    Dim predicate As Func(Of String, Integer, Boolean) = Function(str, index) str.StartsWith("M")
    Dim FilteredList = AddFilter(A, predicate)
    For Each s As String In FilteredList
        Debug.Print(s)
    Next
End Sub

Answer 2

There is an answer in some post that recommend this.

You can use Dynamic Linq:

Dim filter As String = "property1>10 and property2 like 'anystring' or property3<=25".

Dim results = Elements.Where(filter).

But I don't know how to use dinamic linq