C # calls controls across threads

In C # application development, we often separate the UI thread from the worker thread to prevent the interface from stopping responding. At the same time we need to update the controls on the UI interface in the worker thread,

Here are a few common methods

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1. Invalid inter-thread operation
2. The first approach: prohibit the compiler from checking cross-thread access
3. Second approach: Use delegate and invoke to invoke controls from other threads
4. Third approach: Use delegate and BeginInvoke to control controls from other threads
5. Fourth approach: using the BackgroundWorker component
6. Source code Download

Invalid inter-thread operation

There is a button and a label on the interface, and clicking the button initiates a thread to update the value of the label

 private  void  button1_click (object   sender, EventArgs e) {Thread thread1  = new  Thread (new              Parameterizedthreadstart (Updatelabel)); Thread1. Start (   update label   " );  private  void  Updatelabel (object   str) { this . Lab El1. Text = Str.        ToString (); }

After running, the program will error "Invalid cross-threading operation, access it from a thread that is not creating" Label1 "

This is because. NET prohibits invoking a control across threads, otherwise anyone can manipulate the control, which may eventually cause an error.

Here are a few ways to call controls across threads

The first approach: prohibit the compiler from checking cross-thread access

This is the simplest approach, which is equivalent to not checking for conflicts between threads, allowing threads to be arbitrarily messed up, and finally Lable1 what the value of the control is ( This method is not recommended )

         Public Form1 ()        {            InitializeComponent ();             // Join this line            false ;        }

Second approach: Use delegate and invoke to invoke controls from other threads

Invoking the control's Invoke method, you can control the control, for example

        Private voidButton2_Click (Objectsender, EventArgs e) {Thread Thread1=NewThread (NewParameterizedthreadstart (UpdateLabel2)); Thread1. Start ("Update Label"); }        Private voidUpdateLabel2 (Objectstr) {            if(Label2. invokerequired) {//when a control's InvokeRequired property value is true, it is stated that a thread other than the one that created it wants to access itaction<string> actiondelegate = (x) + = { This. Label2. Text =x.tostring ();}; //or//action<string> actiondelegate = delegate (string txt) {this.label2.Text = txt;};                 This. Label2.            Invoke (Actiondelegate, str); }            Else            {                 This. Label2. Text =Str.            ToString (); }        }

Third approach: Use delegate and BeginInvoke to control controls from other threads

Just put the above this.label2.Invoke (Actiondelegate, str); Change the BeginInvoke method to the

The difference between the Invoke method and the BeginInvoke method is

The Invoke method is synchronous, and it waits for the worker thread to finish,

The BeginInvoke method is asynchronous, and it will start another thread to complete the worker thread

Fourth approach: Using the BackgroundWorker component (this method is recommended)

BackgroundWorker is a control that is used in. NET to perform multi-threaded tasks, allowing programmers to perform some operations on a separate thread. Time-consuming operations, such as downloads and database transactions. Simple to use

        Private voidButton4_Click (Objectsender, EventArgs e) {            using(BackgroundWorker bw =NewBackgroundWorker ()) {bw. RunWorkerCompleted+=NewRunworkercompletedeventhandler (bw_runworkercompleted); Bw. DoWork+=NewDoworkeventhandler (bw_dowork); Bw. RunWorkerAsync ("Tank"); }                 }        voidBw_dowork (Objectsender, DoWorkEventArgs e) {                   //here is the background thread, which is done on the other thread//This is a working thread that really does things.//you can do some time-consuming, complex operations here .Thread.Sleep ( the); E.result= E.argument +"Worker Threads Complete"; }        voidBw_runworkercompleted (Objectsender, Runworkercompletedeventargs e) {            //The background thread is now complete and the main thread is returned, so you can use the UI control directly             This. label4. Text =e.result.tostring (); }

Source code Download

Please open "Download" with VS2010

C # calls controls across threads