Create a Scenario for CrossThread Exception
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CrossThread means your are in a thread and trying to access any resource in side another Thread. In .net winform all controls you pasted will be rendred and finally created in a builtin assigned thread. Now you may have Therad programming in your code like you are invoking a method using a separate Thread. Inside this method, when you try to access any of your controls, you will get CrossThread exception. Below is a CrossThread exception sample .
My Form Load code to call a method named "Method1" in a seprate Thread.
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private void Form1_Load(object sender, EventArgs e)
{
Thread th = new Thread(new ThreadStart(Method1));
th.Start();
}
My "Method1" code, which is trying to access a ListBox control named, "listBox1"
private void Method1()
{
listBox1.Items.Add("Jaish Mathews");
}
You just run this code and you will get an error which saying
"Cross-thread operation not valid: Control 'listBox1' accessed from a thread other than the thread it was created on."
This is the whole discussed CrossThread exception. 'listBox1' is created in an assigned Thread and your are running "Method1" in a different Thread and trying to access 'listBox1' in side "Method1". This is a clear ThreadCrossing scenario. Now how you can handle it. Yes, we can do it using an asynchronous way.
Method to Handle CrossThread Execution
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Here basically we are using the "Invoke" method of the control to invoke a specific method inside that control rather than execute an inline direct method call. A property named "InvokeRequired" is available to determine whether we need CrossThread handling.
1. Use Custom Delegates- You will create a delegate with same prototype of the method needs to be invoked. Then we fire the delgate and through delgate our method also will be fired.Below is the code
//This should be a class level declaration
private delegate void myDelegate();
//Below is the modified Method1
private void Method1()
{
//We need to handle CrossThred
if (listBox1.InvokeRequired)
{
//Through delegate firing the method "Method1"
myDelegate md = new myDelegate(Method1);
//Calling Invoke method to invoke the delegate and consequenty invoke Method1
this.Invoke(md, null);
}
//No need to handle CrossThread
else
{
listBox1.Items.Add("Jaish Mathews");
}
}
2. Use Builtin MethodInvoker Delegate - Here we are skipping the delegate declration from our part and using a builtin delegate named MethodInvoke. Just look the below modified code for Method1 which is handling the CrossThread using builting delegate
//Below is the modified Method1
private void Method1()
{
//We need to handle CrossThred
if (listBox1.InvokeRequired)
{
this.Invoke(new MethodInvoker(Method1));
}
//No need to handle CrossThread
else
{
listBox1.Items.Add("oooo");
}
}
So remind these matters whenever getting an exception like
"Cross-thread operation not valid: Control 'listBox1' accessed from a thread other than the thread it was created on."