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Dot Net (C #): Invoke () method for multi-threaded applications with windows forms

a Control on a windows forms from another thread from, the Invoke () method of the form or controls are used. A Control can only be changed by the thread from which it was created!

following minimal example (incomplete ) shows a use case in which a thread reports its status to a form: The class

MathClass generated Thread objects whose method CalcBackground () should ausgefürt in a thread wird.Aus this method out the GUI on the current thread state be informed:

  1:  

  2:   public   class  MathClass 

  3: { 

  4:  

  5:    private MainForm myForm; 

  6:   private int   iNumber ; 

  7:  

  8:   public    Thread Initialize(MainForm myform,   int   number) 

      9:            { 

     10:                  this  .myForm = myform; 

     11:                  this  .iNumber = number; 

     12:                  return     new   Thread(  new   ThreadStart(  this  .CalcBackground)); 

     13:            } 

     14:      

     15:              delegate     void   UpdateUI(  int   number,    int   state); 

     16:              delegate     void   Finish(  int   number); 

     17:      

     18:              public     void   CalcBackground() 

     19:            { 

     20:                UpdateUI updateUI =   new   UpdateUI(  this  .myForm.updateUIProc); 

     21:                Finish finish =   new   Finish(  this  .myForm.FinishThread); 

     22:      

      23:                  try   

     24:                { 

     25:                      // do something   

     26:                      // ...   

     27:                      // report status to form:   

     28:                      object  [] param =   new     object  [2] {   this  .iNumber, i }; 

     29:                    myForm.Invoke(updateUI, param);   // call myForm.updateUIProc(iNumber, i)   

      30:                } 

     31:                  catch   (ThreadAbortException) 

     32:                { 

     33:                      // clean up   

     34:                } 

     35:                  catch   (Exception) 

     36:                { 

     37:                      // catch any other exception   

     38:                } 

     39:                  finally   

      40:                { 

     41:                      try   

     42:                    { 

     43:                          // call myForm.FinishThread(iNumber)   

     44:                        myForm.Invoke(finish,   new     object  [] {   this  .iNumber });  

     45:                    } 

     46:                      catch   (ObjectDisposedException e) 

     47:                    { 

     48:                    } 

  49:    catch (Exception ee) 

  50: { 

  51:  

 } 52:}  

  53:}  

  54:  

  55:}  

created the Main form in the method StartThreads () two new threads. The methods updateUIProc () finish and thread () be started by Invoke () method of thread from the thread and run myself the Main Form :

      1:          public     partial     class   MainForm : Form 

      2:        { 

      3:      

      4:              public   MainForm() 

      5:            { 

      6:                InitializeComponent(); 

      7:            } 

      8:      

      9:              private     void   Form1_FormClosing(  object   sender, FormClosingEventArgs e) 

      10:            { 

     11:                  // kill threads before form closes   

     12:                  if   (anyThreadAlive) 

     13:                { 

     14:                    killThreads(); 

     15:                } 

     16:            } 

     17:      

     18:              public     void   updateUIProc(  int   number,   int   val) 

     19:            {  

     20:                  this  .textBox1.AppendText( 

     21:                      string  .Format(  "thread {0} has done {1} % of its job"  , number, val)); 

     22:            } 

     23:      

     24:              public     void   FinishThread(  int   number) 

     25:            { 

     26:                  this  .textBox1.AppendText( 

     27:                      string  .Format(   "thread {0} has finished"  , number)); 

     28:            } 

     29:      

     30:              private     void   startThreads() 

     31:            { 

     32:                Thread th1 =   new   MathClass().Initialize(  this  , 0); 

     33:                Thread th2 =   new   MathClass().Initialize(  this  , 1); 

     34:                th1.Start(); 

     35:          th2.Start (); 

  36:  

 } 37:}  

It is not allowed to change the Control Mainform.textBox1 directly from the thread. A Control can only be changed by the thread from which it was created. order to still change a control from a thread out, use the method Invoke () and passes this one delegate (function pointer) and a parameter array. The actual method (eg updateUIProc () or finish thread ()) is then (in this case) in the thread of the main form. This has also means that neither of the two functions can be executed in parallel several times.