The SelectAll property is write only. The SelectAll on True, selects all items, while the SelectAll on False, unselects all items in the control's view. The SelectAll property has effect only if the control allows multiple selection. The ViewFloderFlags property is used to determine custom flags that are applied to the control determining its appearance. Use the ModifyFolderFlags method to add or remove flags on the current view, including enabling single or multiple selection. 

The following VB/NET sample shows how to enable multiple selection within the view:

Exshellview1.ViewFolderFlags = Exshellview1.ViewFolderFlags And Not exontrol.EXSHELLVIEWLib.FolderFlagsEnum.SingleSel

The following C# sample shows how to enable multiple selection within the view:

exshellview1.ViewFolderFlags = exshellview1.ViewFolderFlags & ~((int)exontrol.EXSHELLVIEWLib.FolderFlagsEnum.SingleSel);

The following VB.NET sample shows how to get the selected files/folder for /NET assembly version:

Dim i As Long = 0, s As String = ""
With Exshellview1
    .Objects.Get(exontrol.EXSHELLVIEWLib.ObjectTypeEnum.SelectedItems)
    With .Objects
        For i = 0 To .Count - 1
            Dim sel As exontrol.EXSHELLVIEWLib.exshellobject = .Item(i)
            ' * The sel indicates the shell object being selected *
            s = s + sel.Name + vbCrLf
        Next
    End With
End With
If s.Length > 0 Then
    MessageBox.Show(s, "Selection")
Else
    MessageBox.Show("Empty", "Selection")
End If

The following C# sample shows how to get the selected files/folder for /NET assembly version:

string s = "";
exshellview1.Objects.Get(exontrol.EXSHELLVIEWLib.ObjectTypeEnum.SelectedItems);
for ( int i = 0; i < exshellview1.Objects.Count; i++ )
{
    exontrol.EXSHELLVIEWLib.exshellobject sel = exshellview1.Objects[i];
    // * The sel indicates the shell object being selected *
    s = s + sel.Name + "\r\n";
}
if (s.Length > 0)
    MessageBox.Show(s, "Selection");
else
    MessageBox.Show("Empty", "Selection");