Re: Crossing the UI sync context with a datasource - .NET (Core and Framework) Discussion Boards

please reply fast.....for this question

C#

public bool MyBool { get; set; }

VB.NET

Private _myBool As Boolean

Property MyBool() As Boolean
    Get
       Return _myBool
    End Get
    Set(ByVal Value As Boolean)
        _myBool = Value
    End Set
End Property

ankita.rose9 wrote:
please reply fast.....for this question

..and where did you find the right to hurry me? Am I being paid by your company?

If you need this information "quick", I suggest studying; a property is a very basic construction, and studying makes sure that you can remember how to use it once you need it. Seriously, Google it, you'll find that it's nigh impossible to miss the examples.

Now, you're probably facing some other issue, like initializing this property correctly and/or getting it nicely in the propertygrid. If that's the case, change your question to reflect the actual problem.

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

Hello -

In one hand, I have a form which contains a DataGridView. Clearly, the DGV is running on the UI thread.

In the other hand, I have an library object, which contains a DataTable. That datatable is updated by an internal System.Threading.Timer (not a form timer). A couple of times a second, a row is added to that table.

Once I set the DataSource of the DataGridView to be the DataTable of that library object, the DGV never redraws. The data is there, it just doesn't draw.

The problem is that the DataTable is being updated by a different thread than the UI thread (verified). Apparently, the "your data has changed" methods of the DGV are also being called on that other thread.

So: how do I avoid this? Since the update mechanisms are private to the DataSource/Binding mechanism, there is no clear place where I can use Invoke to sync the datatable with the UI thread, so I can cross the thread boundary safely.

I do own the library object. I am currently exposing the DataTable as a public object. Is there another way to get the data in the table to the DGV, in a way that crosses the thread boundary safely?

there may be a couple of options for you that i can think of straight away you can either Invoke the Add calls on the UI thread, or after everything has been added you can Invoke a mothod that triggers a refresh. I'm not very familiar with how this is done on winforms, but you can call invoke i believe on any control create on the UI thread.
so something like

C#

dgv.Invoke(new Action(() =>
    {
      var toAdd = dt.NewRow();
      dt.Rows.Add(toAdd);
    }));

This may not be the neatest way but hopefully it should be a start for you. If you need a more tailored answer to your problem pop up a code sample and i'll take a look.

JoeRip wrote:
So: how do I avoid this? Since the update mechanisms are private to the DataSource/Binding mechanism, there is no clear place where I can use Invoke to sync the datatable with the UI thread, so I can cross the thread boundary safely.

I do own the library object. I am currently exposing the DataTable as a public object. Is there another way to get the data in the table to the DGV, in a way that crosses the thread boundary safely?

MSDN has a how-to[^] on the subject. The annoying part is updating the grid if you have the new data, and this works best if the grid is in virtual mode[^].

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

Thanks, but those articles assume that the non-Form thread knows about the Form, and call Form methods.

In my case, this library object does NOT know about the Form, and therefore cannot use Invoke to call Form methods. This is by design - the DataTable in the library object has no idea who is connecting to its DataSource, nor should it.

So there is no clear place where Invoke can be used, that I can tell. On the DataGridView's side, the RowsAdded event is simply not firing, because it's on the wrong thread. So the DGV is not getting updated.

I think it comes down to this: should I redesign the library object so that it takes a delegate to call after Rows.Add (seriously ugly)? Or should I not expose the DataTable directly, and look to find another method of making the DataTable's content available?

JoeRip wrote:
I think it comes down to this: should I redesign the library object so that it takes a delegate to call after Rows.Add (seriously ugly)? Or should I not expose the DataTable directly, and look to find another method of making the DataTable's content available?

Nothing "ugly" about a CallBack method; that's the way to go if you don't want to be passing a pointer to your form to the thread.

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

Okay, here is a very simplified version of the problem. Note that the GrowingTable() class is normally in a separate assembly and namespace.

So - I can't just convert the Timer to a FormTimer, unless I pass the form itself to the GrowingTable class, which would be incredibly ugly.

And there's no clear place where I can Invoke, as there is no actual update function (that is hidden in the DataSource mechanism).

C#

using System;
using System.Windows.Forms;

namespace dgv
{
    public partial class Form1 : Form
    {
        DataGridView dgvMain = new DataGridView();
        GrowingTable ra = new GrowingTable();
        
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

            Controls.Add(dgvMain);
            dgvMain.Dock = System.Windows.Forms.DockStyle.Fill;
            dgvMain.Location = new System.Drawing.Point(0, 45);
            dgvMain.DataSource = ra.itemTable;
            ra.Start();
        }

        // this class would normally appear in a separate assembly and namespace
        public class GrowingTable
        {
            public System.Data.DataTable itemTable; 
            private System.Threading.Timer myTimer = null;

            // constructor
            public GrowingTable()
            {
                itemTable = new System.Data.DataTable();
                myTimer = new System.Threading.Timer(this.AddRow, null, System.Threading.Timeout.Infinite, System.Threading.Timeout.Infinite); 
                for (int i = 0; i < 11; i++)
                {
                    itemTable.Columns.Add(new System.Data.DataColumn(i.ToString(), typeof(System.DateTime)));
                }
            }

            public void Start()
            {
                myTimer.Change(0, 500);
            }

            private void AddRow(object state)
            {
                if (itemTable.Rows.Count < 50)
                {
                    System.Data.DataRow dr = this.itemTable.NewRow();
                    for (int i = 0; i < 11; i++) { dr[i.ToString()] = DateTime.Now; }
                    this.itemTable.Rows.Add(dr);
                }
                else
                {
                    myTimer.Dispose();
                    myTimer = null;
                }
            }
        }
    }
}

add this to Growing Table

C#

public Action<Action> InvokeOnUI{get;set;}

in the AddRow method replace

C#

this.itemTable.Rows.Add(dr);

with

C#

if (InvokeOnUI!=null)
    InvokeOnUI(()=>this.itemTable.Rows.Add(dr));
else
    this.itemTable.Rows.Add(dr);

and don't forget to set it up using:

C#

ra.InvokeOnUI = action => Invoke(action);

the sample i made is as follows if it helps

C#

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }
    Updater ud = new Updater();
    private void Form1_Load(object sender, EventArgs e)
    {
        this.dataGridView1.DataSource = ud.Data; 

        ud.InvokeOnIU = action => Invoke(action);
    }

    private void button1_Click(object sender, EventArgs e)
    {
        Thread run = new Thread(ud.AddInBackGround);
        run.Start();
    }
}

public class Updater
{
    public Updater()
    {
        Data = new DataTable();
        Data.Columns.Add("Column 1");
        Data.Columns.Add("Column 2");
        Data.Columns.Add("Column 3");
    }
    public Action<Action> InvokeOnIU { get; set; }

    public DataTable Data { get; set; }

    public void AddInBackGround()
    {
        if (InvokeOnIU!=null)
        {
            var toAdd = Data.NewRow();
            InvokeOnIU(()=>Data.Rows.Add(toAdd));
        }
    }

}

+5 for moving the dependency to a separate class, decoupling the form from the thread Thumbs Up | :thumbsup:

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

Thanks! Very nice.

This is very similar to what I eventually settled on. Since GrowingTable() is actually in another (library) assembly completely, it can't have intimate knowledge of the UI's Form methods. And in fact, it may not be called from a Form at all.

So, I simply added an optional callBack delegate parameter to GrowingTables constructor, and I let the caller pass in a callBack function, to be called on each AddRow. That way, the caller can check NeedsInvoke on his side, and invoke the callBack over to the UI thread if necessary.

It's still ugly, but it's doable. I think the real solution is to not expose a DataTable directly, and handle the binding directly.

Actually, looking closer at what you've done here... this might be cleaner. Will play with it tomorrow.

Thanks!

I think this is not general enough for what I need. GrowingTable updates its table at arbitrary times. The caller (form) can't know when to call InvokeOnIU. If I understand the code above correctly, the form is only calling InvokeOnIU when it wants to.

How about this: GrowingTable will have a property, method and event:

C#

bool fCallerNeedsUpdateOnItsOwnContext

C#

void UpdateGTDataSource(GTUpdates updates)

C#

event UpdateDataAgainstYourOwnContext

When GrowingTable needs to update its data, it will create a queue of updates (typically, rows to add, rows to replace other rows by id, or id's of rows to be deleted). If fCallerNeedsUpdateOnItsOwnContext is true, it will raise the UpdateDataAgainstYourOwnContext event, passing the queue of updates. Then the subscriber can call or Invoke GT.UpdateGTDataSource(updates) as it needs, to insure thread context safety.

If fCallerNeedsUpdateOnItsOwnContext is false, GrowingTable will simply execute the queue of updates itself.

What say you, coders?

the code sample i gave you puts the class in charge of refreshing the data in total control, the one call made in the UI is just letting the GrowingTable class know how to perform tasks in sync with the UI thread. after that stage has been performed the UI has no more involvement.
I'm glad you have found a solutino but the assumptin that the form is callint InvokeOnUI is not quite right.

Well, it works. Not sure about design quality, but it was better than the hacks I was using before. Thanks for all the help! Let me know if it sucks. Here's a sample which demonstrates the pattern; first the caller/form:

using System;
using System.Windows.Forms;
using GrowingDataTable;

namespace dgv
{
    public partial class Form1 : Form
    {
        public DataGridView dgvMain;
        public delegate void delEventHandler(object sender,
               GrowingDataTable.UpdateDataTableOnYourThreadContextEventArgs e);
        public GrowingDataTable gt;
        
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            // add a datagridview to the form
            dgvMain = new DataGridView();
            Controls.Add(dgvMain);
            dgvMain.Dock = System.Windows.Forms.DockStyle.Fill;

            // create the GrowingTable object
            gt = new GrowingDataTable();

            // subscribe to the GrowingTable event
            gt.RaiseUpdateTableAgainstYourThreadContextEvent += new 
           EventHandler<GrowingDataTable.UpdateDataTableOnYourThreadContextEventArgs>
          (gt_RaiseUpdateTableAgainstYourThreadContextEvent);

            // tell gt that we want to be updated
            gt.UpdateDataTableOnCallerThreadContext = true;

            // assign the DataTable as DataSource for our datagridview
            dgvMain.DataSource = gt.itemTable;
            
            // tell the GrowingTable to start growing; 
            // delay start for 3 seconds, add row every 1 second
            gt.Start(3000, 1000);
        }

        void gt_RaiseUpdateTableAgainstYourThreadContextEvent(object sender,
                GrowingDataTable.UpdateDataTableOnYourThreadContextEventArgs e)
        {
            if (InvokeRequired) {
                Invoke(new
                delEventHandler(gt_RaiseUpdateTableAgainstYourThreadContextEvent),
                new object[] { sender, e}); }
            else
            {
                if ((e.Updates != null) || (e.Updates.Count > 0))
                {
                    gt.UpdateTableOnMyThreadContext(e.Updates);
                }
            }
        }
    }
}

Then the library class GrowingDataTable:

using System;
using System.Collections.Concurrent;

namespace GrowingDataTable
{
    public class GrowingDataTable
    {
        public System.Data.DataTable itemTable;
        public System.Threading.Timer myTimer = null;
        private ConcurrentQueue<System.Data.DataRow> qUpdates = new
                ConcurrentQueue<System.Data.DataRow>();

        // constructor
        public GrowingDataTable()
        {
            // table and timer
            itemTable = new System.Data.DataTable();
            myTimer = new System.Threading.Timer(this.AddRows, null, 
                  System.Threading.Timeout.Infinite, System.Threading.Timeout.Infinite);

            // add some columns to table
            for (int i = 0; i < 10; i++) {
                itemTable.Columns.Add(new System.Data.DataColumn
                       (i.ToString(), typeof(System.DateTime))); }
        }

        // Property which specifies that the caller needs table updates
        // to occur on their own thread context.
        public bool UpdateDataTableOnCallerThreadContext { get; set; }

        // Class which describes the custom event arguments raised
        public class UpdateDataTableOnYourThreadContextEventArgs : EventArgs
        {
            private ConcurrentQueue<System.Data.DataRow> qu;

            public UpdateDataTableOnYourThreadContextEventArgs
                       (ConcurrentQueue<System.Data.DataRow> Qu)
            {
                qu = Qu;
            }

            public ConcurrentQueue<System.Data.DataRow> Updates
            {
                get { return qu; }
            }
        }

        // Event raised when we need to update our data, and customer has specified
        // they need the update to occur on their own thread context (eg, UX thread).
        public event EventHandler<UpdateDataTableOnYourThreadContextEventArgs>
                                      RaiseUpdateTableAgainstYourThreadContextEvent;

        public void UpdateTableOnMyThreadContext(
                         ConcurrentQueue<System.Data.DataRow> Q)
        {
            System.Data.DataRow dr = null;
            while (Q.TryDequeue(out dr))
            {
                if (dr != null)
                {
                    itemTable.Rows.Add(dr);
                }
            }
        }

        public void Start(int delay, int interval)
        {
            myTimer.Change(delay, interval);
        }

        private void AddRows(object state)
        {
            if (itemTable.Rows.Count < 10)
            {
                System.Data.DataRow dr = this.itemTable.NewRow();

                // fill row with pseudo data
                for (int i = 0; i < 11; i++) { dr[i.ToString()] = DateTime.Now; }

                // If caller has specified, notify them so they can update the
                // data on their own thread context.
                if (UpdateDataTableOnCallerThreadContext)
                {
                    // add row to qUpdates, raise the event
                    qUpdates.Enqueue(dr);
                    OnRaiseUpdateDataTableAgainstYourThreadContextEvent(new
                             UpdateDataTableOnYourThreadContextEventArgs(qUpdates));
                }
                else
                {
                    this.itemTable.Rows.Add(dr);
                }
            }
            else
            {
                myTimer.Dispose();
                myTimer = null;
            }
        }

        protected virtual void OnRaiseUpdateDataTableAgainstYourThreadContextEvent(
                                     UpdateDataTableOnYourThreadContextEventArgs q)
        {
            // protect against race conditions:
            EventHandler<UpdateDataTableOnYourThreadContextEventArgs> handler =
                                     RaiseUpdateTableAgainstYourThreadContextEvent;

            // Event will be null if there are no subscribers
            if (handler != null)
            {
                handler(this, q);
            }
        }
    }

}

Hello Friends,,

well this is the situation im trying to simulate Keys but only when a proccess is actually running

this is what i have

VB

Private Sub letter_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles letter.Tick
       Dim rprocess() As System.Diagnostics.Process = Process.GetProcessesByName("Test.exe")

       If System.IO.File.Exists("C:\test\Listener.txt") Then
           'Do Nothing
       Else
           System.IO.File.Create("C:\Test\Listener.txt")
       End If

       If rprocess.Length = 1 Then

       ElseIf (GetAsyncKeyState(Keys.A)) Then
           Dim ReadIt As String = System.IO.File.ReadAllText("C:\Test\Listener.txt")
           System.IO.File.WriteAllText("C:\Test\Listener.txt", ReadIt & "A")
           'A
       End If
End Sub/pre>

but is stil reading the "A" even if the proccess is off or not present .. HELP !!

SORRY WORLD .. found the problem =)

if anyone tries then is

if rprocess.length = 1 then
getasynckeystate(keys.a)

remove elseif and the "()"

Hi Everyone,

I did a search on capturing screen shots in vb.net and I was wondering if there is a straight forward way to capture the active window? Or do I need to first get the handle of the active window, get the position and size and then capture it? I do not want to use any type of sendkeys method or use the clipboard. I want to save it to jpg format.

Thanks!

Done so far but its capturing the entire window is

Module patternAload

Private Declare Function CreateDC Lib "gdi32" Alias "CreateDCA" (ByVal lpDriverName As String, ByVal lpDeviceName As String, ByVal lpOutput As String, ByVal lpInitData As String) As Integer

Private Declare Function CreateCompatibleDC Lib "GDI32" (ByVal hDC As Integer) As Integer

Private Declare Function CreateCompatibleBitmap Lib "GDI32" (ByVal hDC As Integer, ByVal nWidth As Integer, ByVal nHeight As Integer) As Integer

Private Declare Function GetDeviceCaps Lib "gdi32" Alias "GetDeviceCaps" (ByVal hdc As Integer, ByVal nIndex As Integer) As Integer

Private Declare Function SelectObject Lib "GDI32" (ByVal hDC As Integer, ByVal hObject As Integer) As Integer

Private Declare Function BitBlt Lib "GDI32" (ByVal srchDC As Integer, ByVal srcX As Integer, ByVal srcY As Integer, ByVal srcW As Integer, ByVal srcH As Integer, ByVal desthDC As Integer, ByVal destX As Integer, ByVal destY As Integer, ByVal op As Integer) As Integer

Private Declare Function DeleteDC Lib "GDI32" (ByVal hDC As Integer) As Integer

Private Declare Function DeleteObject Lib "GDI32" (ByVal hObj As Integer) As Integer

Declare Function GetForegroundWindow Lib "user32" Alias "GetForegroundWindow" () As Integer

Const SRCCOPY As Integer = &HCC0020

Private oBackground As Bitmap
Private FW, FH As Integer

Public Sub CaptureScreen()

Dim hSDC, hMDC As Integer
Dim hBMP, hBMPOld As Integer
Dim r As Integer

Dim fgw As Long = GetForegroundWindow()

hSDC = CreateDC("DISPLAY", "", "", "")
hMDC = CreateCompatibleDC(hSDC)

FW = GetDeviceCaps(hSDC, 8)
FH = GetDeviceCaps(hSDC, 10)
hBMP = CreateCompatibleBitmap(hSDC, FW, FH)

hBMPOld = SelectObject(hMDC, hBMP)
r = BitBlt(hMDC, 40, 40, FW, FH, hSDC, 0, 0, SRCCOPY)

hBMP = SelectObject(hMDC, hBMPOld)

r = DeleteDC(hSDC)
r = DeleteDC(hMDC)

oBackground = Image.FromHbitmap(New IntPtr(hBMP))

DeleteObject(hBMP)

End Sub

I suspect that the following code should help:

VB

<DllImport("user32.dll")> _
Public Shared Function GetForegroundWindow() As IntPtr
End Function
<DllImport("user32.dll")> _
Private Shared Function GetWindowRect(hWnd As IntPtr, ByRef lpRect As RECT) As <MarshalAs(UnmanagedType.Bool)> Boolean
End Function
<DllImport("user32.dll", ExactSpelling := True, CharSet := CharSet.Auto)> _
Private Shared Function SetForegroundWindow(hWnd As IntPtr) As <MarshalAs(UnmanagedType.Bool)> Boolean
End Function
<StructLayout(LayoutKind.Sequential)> _
Public Structure RECT
	Public Left As Integer
	Public Top As Integer
	Public Right As Integer
	Public Bottom As Integer
End Structure

Public Shared Sub CaptureWindow(fileName As String, format As ImageFormat)
	Dim hWnd As IntPtr = GetForegroundWindow()
	If hWnd = IntPtr.Zero Then
		Return
	End If
	Dim srcRect As RECT
	If Not GetWindowRect(hWnd, srcRect) Then
		Return
	End If
	Dim width As Integer = srcRect.Right - srcRect.Left
	Dim height As Integer = srcRect.Bottom - srcRect.Top
	Using bmp As New Bitmap(width, height)
		Using g As Graphics = Graphics.FromImage(bmp)
			g.CopyFromScreen(srcRect.Left, srcRect.Top, 0, 0, New Size(width, height), CopyPixelOperation.SourceCopy)
			bmp.Save(fileName, format)
		End Using
	End Using
End Sub

If you want to do it in C#, the same code would look like this:

C#

[DllImport("user32.dll")]
public static extern IntPtr GetForegroundWindow();
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);
[DllImport("user32.dll", ExactSpelling = true, CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool SetForegroundWindow(IntPtr hWnd);
[StructLayout(LayoutKind.Sequential)]
public struct RECT
{
  public int Left;
  public int Top;
  public int Right;
  public int Bottom;
}
public static void CaptureWindow(string fileName, ImageFormat format)
{
  IntPtr hWnd = GetForegroundWindow();
  if (hWnd == IntPtr.Zero) return;
  RECT srcRect;
  if (!GetWindowRect(hWnd, out srcRect)) return;
  int width = srcRect.Right - srcRect.Left;
  int height = srcRect.Bottom - srcRect.Top;
  using (Bitmap bmp = new Bitmap(width, height))
  {
    using (Graphics g = Graphics.FromImage(bmp))
    {
      g.CopyFromScreen(srcRect.Left, srcRect.Top, 0, 0,
        new Size(width, height), CopyPixelOperation.SourceCopy);
      bmp.Save(fileName, format);
    }
  }
}

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

OK i will retry with this code lets see what happens ..

Thanks

No problem. Good luck.

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

i got confused sorry ... so the public sub to save the file will be ???

i try Private Sub Form1_load()
CaptureWindow(fileName:="C:\test.jpg", format:="")
bmp.Save("C:\test.jpg")

End Sub

and its not working

hey my bad im sorry =)

i got it

bmp.Save("test.bmp", jpeg)

i did change it and it wasnt working i had to put
bmp.save("c:\test.bmp", system.drawing.imaging.ImageFormat.Jpeg)

and on the click

CaptureWindow("C:\test.bmp", Jpeg)

that was it
Thanks

Sweet. Not too bad when you consider I just knocked that up in Notepad. Big Grin | :-D

I'm glad it's working for you.

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

hehe Thanks a lot man

i have another question its killing me lol ima post the new topic =) is different lol .. thanks a gain man

I have an application that uses Comparer class to compare the objects. In 4.0 framework, the function public int Compare(object a, object b) took much time than 2.0. Please help me to resolve this issue!!!

modified 8-Aug-12 8:32am.