WPF Learning Notes

Like WinForm, WPF also needs a application to govern some global behavior and operations, and only one application instance exists in each Domain. Unlike WinForm, the WPF application default consists of two parts: App.xaml and App.xaml.cs, which is somewhat similar to the Delphi Form, separating the definition from the behavior code. Of course, WebForm also used a similar approach. XAML is strictly not a pure XML format file, it is more like a DSL, all its definitions are mapped directly to some code, but the specific translation work is done by the compiler.

Here's a simple App definition.

public partial class App : Application
{
}

When you see paritial in the auto-generated Project code, you should subconsciously look for "This code is generated by a tool." This time, however, the automatically generated code is more erratic and--obj\debug\app.g.cs.

public partial class App : System.Windows.Application
{
　[DebuggerNonUserCode]
　public void InitializeComponent()
　{
　　this.StartupUri = new System.Uri("Window1.xaml", System.UriKind.Relative);
　}
　[STAThread]
　[DebuggerNonUserCode]
　public static void Main()
　{
　　App app = new App();
　　app.InitializeComponent();
　　app.Run();
　}
}

App.startupuri is used to set the Mainwindow,app.run () Start message loop. Of course, there's the stathread, which means that WPF still uses a UI Thread to process the UI message.

We can simply discard the auto-generated code and write an App by hand.

public class App : Application
{
　[STAThread]
　private static void Main()
　{
　　var app = new App();
　　var window = new Window { Title = "WPF" };
　　app.Run(window);
　}
}

Application provides a number of useful properties and methods.

Current: Gets the default application instance in Domain.

MainWindow: Gets the main window instance.

Windows: Gets all instances of the Window that are instantiated.

Shutdownmode: Specifies the Application.shutdown mode, including the main form closes, the last window closes, and the Shutdown () is called manually.

Properties: A thread-safe global dictionary that can be used to store a public information.

Shutdown: This method terminates the application Process and can return an exit code to the operating system.

We can still use mutexes to prevent multiple instances from running.

private void Application_Startup(object sender, StartupEventArgs e)
{
　var createdNew = false;
　var name = Assembly.GetEntryAssembly().FullName;
　new Mutex(true, name, out createdNew);
　
　if (!createdNew)
　{
　　MessageBox.Show("There is already an instance running, Exit!");
　　Application.Current.Shutdown();
　}
}

Of course, you can also use Windows properties to determine if a form already exists.

private void button1_Click(object sender, RoutedEventArgs e)
{
　var window2 = Application.Current.Windows.OfType<Window>().FirstOrDefault(w => w is Window2);
　if (window2 == null) window2 = new Window2();
　window2.Show();
　window2.Activate();
}