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POcannot make multiple thread safe calls to windows forms control
 

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  1. POcannot make multiple thread safe calls to windows forms control
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    <p>I am enhancing a c# win forms application that interacts with SalesForce CRM via webservices.</p> <p>I have the below code to make a 'thread safe' update to a label on my form:</p> <pre><code> delegate void SetTextCallback(string text); private void SetText(string text) { // InvokeRequired required compares the thread ID of the // calling thread to the thread ID of the creating thread. // If these threads are different, it returns true. if (this.lblAccessStatus.InvokeRequired) { SetTextCallback d = new SetTextCallback(SetText); this.Invoke(d, new object[] { text }); } else { this.lblAccessStatus.Text = text; this.lblAccessStatus.Refresh(); } } </code></pre> <p>My form (called <code>SFDetachifier.cs</code>) has a button execute which takes the dates of two calendar controls then calls:</p> <pre><code>lblAccessStatus.Visible = true; picProgress.Visible = true; string fromDate = dtManualFromDate.Value.ToString("yyyy-MM-dd") + fromTime; string toDate = dtManualToDate.Value.ToString("yyyy-MM-dd") + toTime; string[] arg = new string[] { "S1", fromDate, toDate }; SFCtrl._SessionLog.Append("Manual detach requested on " + SFOrgName + "\n"); SFCtrl._SessionLog.Append("Date range requested: " + fromDate + " to " + toDate + "\n"); bgProcessing_Production.RunWorkerAsync(arg); </code></pre> <p><code>bgProcessing_Production</code> has the below code for the Background worker which includes a call to <code>setText</code></p> <pre><code>private void bgProcessing_Production_DoWork(object sender, DoWorkEventArgs e) { String[] args = (String[])e.Argument; e.Result = args[0]; // clear the datagrid view gvTaskCases.DataSource = null; //gvTaskCases.Rows.Clear(); //if (gvTaskCases.Rows.Count != 0) // { // gvTaskCases.Rows.Clear(); // .Update(); // } SetText("login to SalesForce (on " + SFOrgName + ") ...please wait"); </code></pre> <p>Now, when I run my application I set some dates, then execute the above code by clicking the execute button, it does it's work (calling SalesForce XML web services) and puts the results in a grid.</p> <p>that all works fine, the problem occurrs when I try to run the procedure again (for example with different dates)</p> <p>Then I get an error <strong>'Cross-thread operation not valid: Control '' accessed from a thread other than the thread it was created on.'</strong></p> <p>I don't understand, I have a delegate setup?</p> <p>What am I doing wrong - I'm guessing that when the backround worker is run again it runs on a new thread, thus being thread unsafe.</p> <p>How can I fix this error please?</p>
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    1. USOur Man in Bananas
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    1. COJust checking - could the `gvTaskCases.DataSource = null;` be causing the exception?
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      1. POcannot make multiple thread safe calls to windows forms control
      1. USC.Evenhuis
    2. COInteresting that the control name in the error message is ''
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      1. POcannot make multiple thread safe calls to windows forms control
      1. USLuc Morin
    3. COboth good points above, however, ` gvTaskCases.DataSource = null;` is not the problem (although I did get some thread safety issues with that control in the commented code above the call to `setText`
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      1. POcannot make multiple thread safe calls to windows forms control
      1. USOur Man in Bananas
 

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