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POC# - Can't access a global variable from an event handler
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copied!<p>I have a Windows Forms Application with a global variable - a string called <code>testPath</code>.</p> <p>This string is used to save a path - by default it is <code>C:\temp\</code>. When the user clicks a button, this directory is created (if it does not exist already).</p> <p>There is also a textbox control, in case the user wants to change the value of the path.</p> <p>At the button's event handler, I try to access <code>testPath</code> and I get a null reference.</p> <p>I am not changing the value of <code>testPath</code> anywhere, except when I pass it to and from the textbox Control.</p> <p>What am I doing wrong? How does the global variable have something inside at one second, and then right afterwards it points to a null reference?</p> <p>Here is the complete code:</p> <pre><code>public string testPath = @"C:\temp\"; public MainForm() { //Windows Designer call InitializeComponent(); //Show the testPath in the textBox (using Invokes) this.textBox1.Invoke(new MethodInvoker(delegate { this.textBox1.Text = testPath; } )); //here, testPath contains 'C:\temp\' } //Button "Click" handler private void Button1Click(object sender, EventArgs e) { //here, testPath contains a null reference! //If the user changed testPath in the textBox, we need to save it again this.textBox1.Invoke(new MethodInvoker(delegate { testPath = this.textBox1.Text; } )); //Create the path if(!Directory.Exists(testPath)) //If it does not exist already { Directory.CreateDirectory(testPath); } //...Do something else } </code></pre>

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