A More Real-World Example in Visual C#.NET

Creator Code39 in Visual C#.NET A More Real-World Example

adjust the button s size to your liking In this simple example, you re putting all code in the form class (The form is your window; its class here, named Form1 is responsible for all things graphical) Generally, you should put all business code the code that does your calculations, data access, and other important work in other classes Reserve the form class for code that s intimately involved with displaying elements on the form and responding to its controls I break that rule here but the delegate works no matter where its callback method is Now, still in design mode, add a handler method for each button:

This action generates a method in the code behind the form (or, simply, the code-behind ) the code that makes the form work It looks like this you add the boldfaced code:

private void button2_Click(object sender, EventArgs e) { thisClose(); // this refers to the Form1 class }

method, which looks like the following in the code-behind:

private void button1_Click(object sender, EventArgs e) { UpdateProgressCallback callback = UpdateProgressCallback(this DoUpdate); // Do something that needs periodic progress reports // This passes a delegate instance that knows how to update the bar DoSomethingLengthy(callback); // Clear the bar so that it can be used again progressBar1Value = 0; }

3 Add the following callback method to the form class:

private void DoUpdate() { progressBar1PerformStep(); // Tells progress bar to update itself }

I walk you through the remaining code, all of it on the form class, in the next section Later in the chapter, I show you other variations on the delegate that s passed

The remaining bits of code tucked into the Form1 class consist of the parts of the delegate life cycle, covered earlier in this chapter I show you the class and then show you where the parts are The boldfaced lines are new code that you add beyond the items you added in the previous section:

using System; using SystemWindowsForms; namespace SimpleProgress { public partial class Form1 : Form { // Declare the delegate This one is void delegate void UpdateProgressCallback(); public Form1() { InitializeComponent(); } // DoSomethingLengthy -- My workhorse method takes a delegate private void DoSomethingLengthy(UpdateProgressCallback updateProgress) { int duration = 2000; int updateInterval = duration / 10; for (int i = 0; i < duration; i++) { ConsoleWriteLine( Something or other ); // Update every tenth of the duration if ((i % updateInterval) == 0 && updateProgress != null) { updateProgress(); // Invoke the delegate } } } // DoUpdate -- The callback method private void DoUpdate() { progressBar1PerformStep(); } private void button1_Click(object sender, EventArgs e) { // Instantiate the delegate, telling it what method to call UpdateProgressCallback callback = new UpdateProgressCallback(this DoUpdate); // Do something that needs periodic progress reports // This passes a delegate instance that knows how to update the bar DoSomethingLengthy(callback); // Clear the bar so that it can be used again progressBar1Value = 0; } private void button2_Click(object sender, EventArgs e) { thisClose(); } } }

The class declaration is interesting as an aside:

The partial keyword indicates that this line is only part of the full class The rest can be found in the Form1Designercs file listed in Solution Explorer (Take a look at it) Later in this chapter, I revisit that file to show you a couple of things about events Partial classes, which were introduced in C# 20, let you split a class between two or more files The compiler generates the Form1Designercs file, so don t modify its code directly You can modify it indirectly, however, by changing elements on the form Form1cs is your part