Thanks for the reply Willy,
If you should never call DoEvents() then I have to ask why was it included? I believe it is similar to including GC.Collect in that it is exposed to the public for use in extreme circumstances.
I can understand that while a message is being processed that no other message can be processed hence the name synchronous message processing.
I can give an example taken straight from the support site of the product I am using, you can probably guess the product involved in the code. I am well aware that any code published on any site is not always the correct way to solve a problem. The code in question uses the primary interop assembly that was generated by the vendor.
If you are using (primary) COM interop library are you required to initialise COM ? - as far as I am aware you do not have too.
Here is the complete winforms example, check out the method 'Display_Instrument_Information'
Cheers
Ollie Riches
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
namespace PriceUpdate
{
/// <summary>
/// Summary description for Form1.
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.Label label1;
private System.Windows.Forms.Label label2;
private System.Windows.Forms.Label label3;
private System.Windows.Forms.Label label4;
private System.Windows.Forms.Label label5;
private System.Windows.Forms.Label lblContract;
private System.Windows.Forms.Label lblProdTape;
private System.Windows.Forms.Label lblProduct;
private System.Windows.Forms.Label lblExchange;
private System.Windows.Forms.Label label6;
private System.Windows.Forms.Label label7;
private System.Windows.Forms.Label label8;
private System.Windows.Forms.Label label9;
private System.Windows.Forms.Label label14;
private System.Windows.Forms.Label label15;
private System.Windows.Forms.Label lblAskQty;
private System.Windows.Forms.Label lblAskPrice;
private System.Windows.Forms.Label lblBidQty;
private System.Windows.Forms.Label lblBidPrice;
private System.Windows.Forms.Label lblLastQty;
private System.Windows.Forms.Label lblLastPrice;
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.Container components = null;
// using XTAPI objects
// this sample will need the drag and drop handler class,
// the Instrument object to temporary hold the selected instrument,
// and the instrument notification class for price updates
private XTAPI.TTDropHandlerClass m_DropHandler = null;
private XTAPI.TTInstrObj m_LiveInstr = null;
private XTAPI.TTInstrNotifyClass m_InstrNotify = null;
public Form1()
{
//
// Required for Windows Form Designer support
//
InitializeComponent();
}
/// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.label1 = new System.Windows.Forms.Label();
this.label2 = new System.Windows.Forms.Label();
this.label3 = new System.Windows.Forms.Label();
this.label4 = new System.Windows.Forms.Label();
this.label5 = new System.Windows.Forms.Label();
this.lblContract = new System.Windows.Forms.Label();
this.lblProdTape = new System.Windows.Forms.Label();
this.lblProduct = new System.Windows.Forms.Label();
this.lblExchange = new System.Windows.Forms.Label();
this.label6 = new System.Windows.Forms.Label();
this.label7 = new System.Windows.Forms.Label();
this.label8 = new System.Windows.Forms.Label();
this.label9 = new System.Windows.Forms.Label();
this.lblAskQty = new System.Windows.Forms.Label();
this.lblAskPrice = new System.Windows.Forms.Label();
this.lblBidQty = new System.Windows.Forms.Label();
this.lblBidPrice = new System.Windows.Forms.Label();
this.label14 = new System.Windows.Forms.Label();
this.label15 = new System.Windows.Forms.Label();
this.lblLastQty = new System.Windows.Forms.Label();
this.lblLastPrice = new System.Windows.Forms.Label();
this.SuspendLayout();
//
// label1
//
this.label1.Location = new System.Drawing.Point(16, 123);
this.label1.Name = "label1";
this.label1.Size = new System.Drawing.Size(96, 16);
this.label1.TabIndex = 17;
this.label1.Text = "CONTRACT:";
//
// label2
//
this.label2.Location = new System.Drawing.Point(16, 88);
this.label2.Name = "label2";
this.label2.Size = new System.Drawing.Size(96, 16);
this.label2.TabIndex = 16;
this.label2.Text = "PRODUCT TYPE:";
//
// label3
//
this.label3.Location = new System.Drawing.Point(16, 56);
this.label3.Name = "label3";
this.label3.Size = new System.Drawing.Size(96, 16);
this.label3.TabIndex = 15;
this.label3.Text = "PRODUCT:";
//
// label4
//
this.label4.Location = new System.Drawing.Point(16, 19);
this.label4.Name = "label4";
this.label4.Size = new System.Drawing.Size(96, 16);
this.label4.TabIndex = 14;
this.label4.Text = "EXCHANGE:";
//
// label5
//
this.label5.Location = new System.Drawing.Point(144, 256);
this.label5.Name = "label5";
this.label5.Size = new System.Drawing.Size(232, 56);
this.label5.TabIndex = 13;
this.label5.Text = "Drag an instrument from X_Trader Market Grid and drop it anywhere on this form.";
//
// lblContract
//
this.lblContract.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblContract.Location = new System.Drawing.Point(128, 120);
this.lblContract.Name = "lblContract";
this.lblContract.TabIndex = 12;
//
// lblProdTape
//
this.lblProdTape.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblProdTape.Location = new System.Drawing.Point(128, 88);
this.lblProdTape.Name = "lblProdTape";
this.lblProdTape.TabIndex = 18;
//
// lblProduct
//
this.lblProduct.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblProduct.Location = new System.Drawing.Point(128, 56);
this.lblProduct.Name = "lblProduct";
this.lblProduct.TabIndex = 19;
//
// lblExchange
//
this.lblExchange.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblExchange.Location = new System.Drawing.Point(128, 16);
this.lblExchange.Name = "lblExchange";
this.lblExchange.TabIndex = 20;
//
// label6
//
this.label6.Location = new System.Drawing.Point(264, 120);
this.label6.Name = "label6";
this.label6.Size = new System.Drawing.Size(96, 16);
this.label6.TabIndex = 25;
this.label6.Text = "ASK QTY:";
//
// label7
//
this.label7.Location = new System.Drawing.Point(264, 88);
this.label7.Name = "label7";
this.label7.Size = new System.Drawing.Size(96, 16);
this.label7.TabIndex = 24;
this.label7.Text = "ASK PRICE:";
//
// label8
//
this.label8.Location = new System.Drawing.Point(264, 56);
this.label8.Name = "label8";
this.label8.Size = new System.Drawing.Size(96, 16);
this.label8.TabIndex = 23;
this.label8.Text = "BID QTY:";
//
// label9
//
this.label9.Location = new System.Drawing.Point(264, 19);
this.label9.Name = "label9";
this.label9.Size = new System.Drawing.Size(96, 16);
this.label9.TabIndex = 22;
this.label9.Text = "BID PRICE:";
//
// lblAskQty
//
this.lblAskQty.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblAskQty.Location = new System.Drawing.Point(376, 120);
this.lblAskQty.Name = "lblAskQty";
this.lblAskQty.TabIndex = 21;
//
// lblAskPrice
//
this.lblAskPrice.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblAskPrice.Location = new System.Drawing.Point(376, 88);
this.lblAskPrice.Name = "lblAskPrice";
this.lblAskPrice.TabIndex = 26;
//
// lblBidQty
//
this.lblBidQty.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblBidQty.Location = new System.Drawing.Point(376, 56);
this.lblBidQty.Name = "lblBidQty";
this.lblBidQty.TabIndex = 27;
//
// lblBidPrice
//
this.lblBidPrice.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblBidPrice.Location = new System.Drawing.Point(376, 16);
this.lblBidPrice.Name = "lblBidPrice";
this.lblBidPrice.TabIndex = 28;
//
// label14
//
this.label14.Location = new System.Drawing.Point(264, 184);
this.label14.Name = "label14";
this.label14.Size = new System.Drawing.Size(96, 16);
this.label14.TabIndex = 31;
this.label14.Text = "LAST QTY:";
//
// label15
//
this.label15.Location = new System.Drawing.Point(264, 152);
this.label15.Name = "label15";
this.label15.Size = new System.Drawing.Size(96, 16);
this.label15.TabIndex = 30;
this.label15.Text = "LAST PRICE:";
//
// lblLastQty
//
this.lblLastQty.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblLastQty.Location = new System.Drawing.Point(376, 184);
this.lblLastQty.Name = "lblLastQty";
this.lblLastQty.TabIndex = 29;
//
// lblLastPrice
//
this.lblLastPrice.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblLastPrice.Location = new System.Drawing.Point(376, 152);
this.lblLastPrice.Name = "lblLastPrice";
this.lblLastPrice.TabIndex = 32;
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(496, 341);
this.Controls.Add(this.label14);
this.Controls.Add(this.label15);
this.Controls.Add(this.lblLastQty);
this.Controls.Add(this.lblLastPrice);
this.Controls.Add(this.label6);
this.Controls.Add(this.label7);
this.Controls.Add(this.label8);
this.Controls.Add(this.label9);
this.Controls.Add(this.lblAskQty);
this.Controls.Add(this.lblAskPrice);
this.Controls.Add(this.lblBidQty);
this.Controls.Add(this.lblBidPrice);
this.Controls.Add(this.label1);
this.Controls.Add(this.label2);
this.Controls.Add(this.label3);
this.Controls.Add(this.label4);
this.Controls.Add(this.label5);
this.Controls.Add(this.lblContract);
this.Controls.Add(this.lblProdTape);
this.Controls.Add(this.lblProduct);
this.Controls.Add(this.lblExchange);
this.Name = "Form1";
this.Text = " Price Update From";
this.Load += new System.EventHandler(this.Form1_Load);
this.ResumeLayout(false);
}
#endregion
/// <summary>
/// The main entry point for the application.
/// </summary>
///
[STAThread]
static void Main()
{
Application.Run(new Form1());
}
private void Form1_Load(object sender, System.EventArgs e)
{
// initilize XTAPI needed classes and/or objects
// Instantiate the drag and drop handler class
m_DropHandler = new XTAPI.TTDropHandlerClass();
// register the active window to enable drag and drop
m_DropHandler.RegisterDropWindow((int) this.Handle);
// associate drop and drag events with the handler
m_DropHandler.OnNotifyDrop += new XTAPI._ITTDropHandlerEvents_OnNotifyDropEventHandl er(this.m_DropHandler_OnNotifyDrop);
// instantiate the instrument notification class
m_InstrNotify = new XTAPI.TTInstrNotifyClass();
// associate instrument notification events with the instrument notification class
// setup the instrument notification call back function
m_InstrNotify.OnNotifyFound += new XTAPI._ITTInstrNotifyEvents_OnNotifyFoundEventHand ler(this.m_InstrNotify_OnNotifyFound);
// setup the instrument update call back function
m_InstrNotify.OnNotifyUpdate += new XTAPI._ITTInstrNotifyEvents_OnNotifyUpdateEventHan dler(this.m_InstrNotify_OnNotifyUpdate);
}
// XTAPI specific used functions
private void m_DropHandler_OnNotifyDrop()
{ // drag and drop call back function
try
{
// get live instrument from the call back - Index starts at 1
// cast the call back instrument as an instrument object
m_LiveInstr = (XTAPI.TTInstrObj) m_DropHandler[1]; // 1 for a single instrument
// **** 88888888888888 *************
// must attach instrument to the notification object
m_InstrNotify.AttachInstrument(m_LiveInstr);
// **** 88888888888888 *************
// open / access selected instrument
m_LiveInstr.Open(0); // turn off depth
// clear drop handler list
m_DropHandler.Reset();
}
catch (Exception e)
{
MessageBox.Show(e.Message,"Exception");
}
}
private void m_InstrNotify_OnNotifyFound(XTAPI.TTInstrNotify pNotify, XTAPI.TTInstrObj pInstr)
{
// retrieve and display instrument information
Display_Instrument_Information(pInstr);
// retrieve and display pricing information
Get_Live_Data(pInstr);
// turn on price updates
m_InstrNotify.EnablePriceUpdates = 1; // 1 for true
}
private void m_InstrNotify_OnNotifyUpdate(XTAPI.TTInstrNotify pNotify, XTAPI.TTInstrObj pInstr)
{
// retrieve live instrument prices
Get_Live_Data(pInstr);
}
private void Display_Instrument_Information(XTAPI.TTInstrObj pInstr)
{
// display instrument fields onto labels
this.lblExchange.Text = pInstr.Exchange;
this.lblProduct.Text = pInstr.Product;
this.lblProdTape.Text = pInstr.ProdType;
this.lblContract.Text = pInstr.Contract;
Application.DoEvents(); // force update in case it does not
}
private void Get_Live_Data(XTAPI.TTInstrObj pInstr)
{
// display instrument pricing information onto labels
this.lblBidQty.Text = (string) pInstr.get_Get("BidQty$");
this.lblBidPrice.Text = (string) pInstr.get_Get("Bid$");
this.lblAskPrice.Text = (string) pInstr.get_Get("Ask$");
this.lblAskQty.Text= (string) pInstr.get_Get("AskQty$");
this.lblLastPrice.Text = (string) pInstr.get_Get("Last$");
this.lblLastQty.Text = (string) pInstr.get_Get("LastQty$");
Application.DoEvents(); // force update in case it does not
}
}
}
"Willy Denoyette [MVP]" <wi*************@telenet.be> wrote in message news:eg**************@TK2MSFTNGP10.phx.gbl...
DoEvents() should never be called nor in a COM interop scenario and not on
the UI thread. All you have to do is make sure you don't block the message
pumping/dispatching by calling functions or running code that take a long
time before yielding (~300msec. might be too long for a decent user
experience). The same thing goes for a COM callback that runs on the UI
thread, messages aren't dispatched as long as the callback code runs.
Now it's hard to tell what happens in your code without some more context
(apartment requirements of COM object) and seeing any code; What's not clear
is where you call DoEvents() on a UI thread that is not pumping, so it looks
like your code blocks the message while running in a tight loop and you call
DoEvents in the loop.
Willy.
"Ollie Riches" <ol**********@phoneanalyser.net> wrote in message
news:en**************@tk2msftngp13.phx.gbl...I understand the use of Application.DoEvents() to process all outstanding
messages on the message queue in a winforms application if you have long
running process on the UI thread. But can anyone explain to me why I need
to call DoEvents when I am using a COM component that calls back to into
the .Net application? - If I don't call DoEvents after receiving a callback
then sometimes no more messages are pumped, it appears that the message
pump is suspended until the call is made.
I suspect that when a callback occurs from COM into the .Net process that
it will not be guaranteed to be executed on the UI thread is this true?
( Note: I do know about updating the UI thread from a worker thread so
people pleased don't try and tell me about the 'Invoke' method on the
Control class)
Cheers
Ollie Riches