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POUtility and good practice of the Dispatcher
 

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    <p>To keep my question simple lets says that I use a thread to update on the fly a replacement in a string. In my real code I need a thread. I know I can avoid it in this simple example.</p> <p>So, my software has two fields. The user select a file, write a (sort of) regex and see the result of the modification at the same time he types his sentence. I start the thread when the user select a file (see listViewFiles_SelectionChanged method). The work of my thread is in DoWork method.</p> <pre><code>public void DoWork() { while (true) { FileData fileData = _selectedFile; if (fileData != null) { string name = fileData.FileName; string searchRegEx = GenerateRegex(_searchTextBox.Text); string replacement = _replaceTextBox.Text; name = Regex.Replace(name, searchRegEx, replacement); /* foreach (var action in _actionCollection) { name = action.Rename(name); }*/ _searchSample.Content = fileData.FileName; _replaceSample.Content = name; } Thread.Sleep(1000); } } private void listViewFiles_SelectionChanged(object sender, SelectionChangedEventArgs e) { _selectedFile = listViewFiles.SelectedItem as FileData; _thread.Start(); } </code></pre> <p>When my thread do his work I get an exception on the line string searchRegEx = GenerateRegex(_searchTextBox.Text); : The calling thread cannot access this object because a different thread owns it. I read a lot about this exception but I don't understand it.</p> <p>To fix it I surround my code with a Dispatcher. I don't understand the mecanism but it works. I have no idea if it is correct or performant but it works.</p> <pre><code> public void DoWork() { while (true) { FileData fileData = _selectedFile; if (fileData != null) { //use Window.Dispatcher this.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Normal, new Action(delegate() { string name = fileData.FileName; string searchRegEx = GenerateRegex(_searchTextBox.Text); string replacement = _replaceTextBox.Text; name = Regex.Replace(name, searchRegEx, replacement); /* foreach (var action in _actionCollection) { name = action.Rename(name); }*/ _searchSample.Content = fileData.FileName; _replaceSample.Content = name; })); } Thread.Sleep(1000); } } private void listViewFiles_SelectionChanged(object sender, SelectionChangedEventArgs e) { _selectedFile = listViewFiles.SelectedItem as FileData; _thread.Start(); } </code></pre> <p>I would like to know if this code is correct and prfomant. You see the foreach instruction in comment. My code should do a lot of work and I don't know if doing this in a delagate is the best way do do this. Utility and good practice of the Dispatcher ?</p>
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    1. USBastien Vandamme
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    1. COWhy you don't use mvvm at all ? Dispatcher.Invoke just invokes delegate synchronously in UI thread, so this code can cause ui freezes. You got error because trying to access _searchTextBox element in different thread, so you just need to separate ui updating & work in code.
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      1. UStrimeyko
    2. CO@trimeyko Because I am not comfortable with MVVM. But you're right, I should use it.
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      1. USBastien Vandamme
    3. CODid you consider to use a BlockingQueue as quick fix? From UI you push _replaceTextBox.Text and in the other thread you perform the work.
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      1. USAdriano Repetti
 

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