c# - Threading Basics -

using system; using system.collections.generic; using system.componentmodel; using system.data; using system.drawing; using system.linq; using system.text; using system.windows.forms; using system.threading;   namespace testthreads {     public partial class form1 : form     {         public form1()         {             initializecomponent();          }          private void form1_load(object sender, eventargs e)         {          }          public void counttolots()         {             (int = 0; < 10000000; i++)             {                 textbox1.text = "counting 10000000, value " + + environment.newline;             }         }          public void counttozero()         {             (int = 10000000; > 0; i--)             {                 textbox2.text = "counting 0, value " + + environment.newline;             }         }          private void button1_click(object sender, eventargs e)         {             thread countup = new thread(new threadstart(counttolots));             thread countdown = new thread(new threadstart(counttozero));             countup.start();             countdown.start();         }          private void button2_click(object sender, eventargs e)         {             textbox3.text = "bobby bob bob " + environment.newline;         }     } } 

i need try , hang of - dont understand theory behind why error message. me out please?

cross-thread operation not valid: control 'textbox1' accessed thread other thread created on.

ui controls have "thread affinity"; do not want touched except ui thread; includes reading , writing properties. assignment .text should done ui thread, either using invoke, or backgroundworker.

for example:

public void counttolots() {     (int = 0; < 10000000; i++)     {         // running on bg thread         textbox1.invoke((methodinvoker) delegate {             // running on ui thread             textbox1.text = "counting 10000000, value "                       + + environment.newline;         });         // running on bg thread again     } } 

but note type of thread switching has overhead. should not call every iteration - should (for example) update ui every [n] iterations - in above, every 10000 example.