Is there a faster way to loop through large amounts of Rows in a DataGridView?

I am looping though about 100,000 records and checking a DataGridViewCheckBox Column, but it is taking way too long. Is there a faster way of doing this? Here is how I am currently doing it:

Code:

---

For Each R0w As DataGridViewRow In DataGridView1.Rows
            Dim TST As String = DataGridView1.Item(3, R0w.Index).Value.ToString
            If TST = "loc_132" Then
                DataGridView1.CurrentRow.DefaultCellStyle.ForeColor = Color.Red
                DataGridView1(0, R0w.Index).Value = True
            End If
        Next

---

Here are a few optimization tips:

1. For/Next is faster than For/Each
2. Declare your TST outside of the loop so you only create it once
3. Declare the value that you're searching outside the loop so you only create it once

Code:

---

Dim TST AS String
Dim loc_123 As String = "loc_123"
For counter As Integer = 0 To DataGridView1.Rows.Count - 1
    TST = DataGridView1.Item(3, counter).Value.ToString()
    If TST = loc_123 Then
        DataGridView1.CurrentRow.DefaultCellStyle.ForeColor = Color.Red           
        DataGridView1(0, counter).Value = True
    End If
Next

---

However, if you're looping through that many rows you'll likely need to do this in a separate thread.

What do you mean by "However, if you're looping through that many rows you'll likely need to do this in a separate thread. "

Multithreading is a concept where you do a task on a separate thread other than the user interface thread. The reason why you would do this is because if you have a long running task then it will take up too much resources to where your UI will appear to freeze.

Here is an MSDN article on how to multithread within Visual Basic .NET: https://msdn.microsoft.com/en-us/lib...(v=vs.71).aspx

Here is a sample(free-typed) code for your scenario:

Code:

---

Private thread_UpdateDGVCheckBox As Threading.Thread
Private Sub ThreadedDGVCheckBoxUpdate()
    Dim TST AS String
    Dim loc_123 As String = "loc_123"
    For counter As Integer = 0 To DataGridView1.Rows.Count - 1
        TST = DataGridView1.Item(3, counter).Value.ToString()
        If TST = loc_123 Then
            Me.Invoke(Sub()
                          DataGridView1.CurrentRow.DefaultCellStyle.ForeColor = Color.Red
                          DataGridView1(0, counter).Value = True
                      End Sub
        End If
    Next
End Sub

---

Then when to use the code, you'd call:

Code:

---

thread_UpdateDGVCheckBox = New Threading.Thread(AddressOf ThreadedDGVCheckBoxUpdate)
thread_UpdateDGVCheckBox.Start()

---

Thank you for the helpful information!!! I will let you know how it goes once I give it a shot, because yeah after I made the changes of your initial suggestions it was still pretty slow. So, I will trying the multithreading!

No problem. Keep me updated on how you are doing.

Before I tip my hat for a while I wanted to make a point about this chunk of code:

Code:

---

Me.Invoke(Sub()
    DataGridView1.CurrentRow.DefaultCellStyle.ForeColor = Color.Red
    DataGridView1(0, counter).Value = True
End Sub

---

Using a Sub without a name like this is call an anonymous delegate. This will only work if you are using Visual Studios 2010 or higher; if you're using an older version like 2008 then you will need to use an old school delegate.

Here is a MSDN article on older style delegates just in case you need it: https://msdn.microsoft.com/en-us/lib...(v=vs.90).aspx

Whelp Im stepping through the code and its just immediately skipping this part of the code:

Code:

---

  TST = DataGridView1.Item(3, DataGridView1.Rows(counter).Index).Value.ToString()
            If TST = "loc_132" Then
                Me.Invoke(Sub()
                            DataGridView1.CurrentRow.DefaultCellStyle.ForeColor = Color.Red
                              DataGridView1(0, DataGridView1.Rows(counter).Index).Value = True
                          End Sub)
            End If

---

When you setup the breakpoint on your For/Next loop, what is the value of DataGridView1.Rows.Count - 1?

"0" from what I can tell...

just did some more digging it might be "-1"

Then that is why it is skipping the code, if there are no rows to loop through then there is no need to execute the code.

Edit - We cross-posted. If you pull up the watch window and type in:

Code:

---

DataGridView1.Rows.Count

---

It will tell you the amount.

Just to clarify I am accessing a datagridview on another form, not sure if this would have an affect on doing this? So, I've altered your code to look like this: (this MsgBox returns the value "-1" btw)

Code:

---

Dim StringCnt As Integer
        StringCnt = MyFormName.DataGridView1.RowCount - 1
        MsgBox(StringCnt)

---

The only way that it would affect the code is if the Form was never launched and so the data was never populated in the DataGridView.

That's weird its not seeing any rows, because the DataGridView is definitely populated...

Getting this from the watch window "Reference to a non-shared member requires an object reference" when I enter in:

Code:

---

DataGridView1.Rows.Count

---

If it's not even going into the For Loop then that not what making your app run slow. Where is this code located? What other code is relevant to what your doing.

@wes4dbt Its not getting a proper row count because of that error...

Code:

---

Private thread_UpdateDGVCheckBox As Threading.Thread
    Private Sub ThreadedDGVCheckBoxUpdate()

        Dim TST As String
        Dim StringCnt As Integer
        StringCnt = DataGridView1.RowCount - 1
        MsgBox(StringCnt)

        For counter As Int32 = 0 To DataGridView1.RowCount - 1
            TST = DataGridView1.Item(3, DataGridView1.Rows(counter).Index).Value.ToString()
            If TST = "loc_132" Then
                Invoke(Sub()
                                        DataGridView1.CurrentRow.DefaultCellStyle.ForeColor = Color.Red
                                      DataGridView1(0, DataGridView1.Rows(counter).Index).Value = True
                                    End Sub)
            End If
        Next
    End Sub

---

Ok, where uis this "Private Sub ThreadedDGVCheckBoxUpdate()" called from?

And WHAT error? You haven't mentioned getting an error when you run your code.

It's being called from a button on a separate form.

Not an error but the output in the watch window reads "Reference to a non-shared member requires an object reference" when I input this code:

Code:

---

DataGridView1.Rows.Count

---

There's no way your call "Private Sub ThreadedDGVCheckBoxUpdate()" from a button on a seperate form. You have declared the Sub as Private, it would not be visible from another form. I think there is some information you have not provided that making solving this issue a lot harder than is should be. Always provide a complete explanation and all relevant code.

My bad, it is being called from a button on the same form using this:

Code:

---

thread_UpdateDGVCheckBox = New Threading.Thread(AddressOf ThreadedDGVCheckBoxUpdate)
        thread_UpdateDGVCheckBox.Start()

---

Note: It's the DataGridView that is on another form, I have just excluded this from the code. So, its really:

Code:

---

MyFormName.DataGridView1.Rows.Count

---

Quote:

---

thread_UpdateDGVCheckBox = New Threading.Thread(AddressOf ThreadedDGVCheckBoxUpdate)
thread_UpdateDGVCheckBox.Start()

---

Just providing this little snippet isn't enough, we have no idea where this is located.

The fact that the dgv is located on a different form is extremely important. Like I said before, please provide a complete explanation. Maybe someone else can help you. I'm done for now.

This snippet is on the same form in a Button_Click event

This issue is still unresolved if anyone else has anymore insight...