C#

Satish - Developer wrote:

But i getting the following error:
Cross-thread operation not valid: Control 'label1' accessed from a thread other than the thread it was created on.

bool listFocused()
{
    if(this.list.InvokeRequired)
    {
        ListFocusCallBack d = new ListFocusCallBack(listFocused);
        this.list.Invoke(d, new object[] {});
    }
    return this.list.Focused;
}

bool listFocused()
{
    // lets say this method is called from thread [T1], different from main application thread [T0] (thread that that listbox was created on)

    if(this.list.InvokeRequired) // if this condition is true, we are on [T1]
    {
        ListFocusCallBack d = new ListFocusCallBack(listFocused); // still [T1]
        this.list.Invoke(d, new object[] {}); // 'd' executes on [T0] !! [T1] is blocked until Invoke finishes

       // now we're back at [T1] !!
    }

    return this.list.Focused; // !!! again [T1] - if u invoke a delegate using control invoke, it doesn't mean
                              // that the rest of this method will be executed on that invoked thread. it
                              // remains on thread [T1], where it's not safe to get the Focused value.
}

bool listFocused()
{
    // [T1]

    if(this.list.InvokeRequired) // if on other than [T0]
    {
         ListFocusCallBack d = new ListFocusCallBack(listFocused);
         return (bool)this.list.Invoke(d, new object[] {}); // wait for Invoked method to finish and return result (again on [T1])       
    }
    
    else // [T0] now we are sure this is thread safe 
    {
        return this.list.Focused; 
    } 
}

Zilo(svk) wrote:

return this.list.Focused; // !!! again [T1] - if u invoke a delegate using control invoke, it doesn't mean // that the rest of this method will be executed on that invoked thread. it // remains on thread [T1], where it's not safe to get the Focused value.

<br />
if (this.list.InvokeRequired)<br />
{<br />
	ListFocusCallBack d = new ListFocusCallBack(listFocused);<br />
	Object obj = this.list.Invoke(d, new object[] {});<br />
				<br />
        if( obj.Equals(Boolean.TrueString ))<br />
	     return true;<br />
        return false;<br />
}<br />
else<br />
{<br />
	return this.list.Focused;<br />
}<br />

Pete O`Hanlon wrote:

f you can't cope with a task like this, with the advice you've already been given, then I would consider a career change to one where the only questions you need to ask is

"Do you want fries with that?"