base.OnStartup(e) 有什么作用？

Question

我看到很多人像这样在 App.xaml.cs 中使用“base.OnStartup(e)”：

protected override void OnStartup(StartupEventArgs e)
{
    base.OnStartup(e);

    MainWindow app = new MainWindow();
    app.Show();
}

有需要吗？这样做的目的是什么？

Answer 1

它允许任何基类逻辑运行；就像base 的任何其他用法一样。

它可能严格没有必要；但是在覆盖 virtual 方法时调用基类的实现被认为是最佳实践（除非您积极地想要抑制基类行为）。

Answer 2

.NET Framework 代码可以在https://referencesource.microsoft.com找到

Application.OnStartup() 不包含太多功能：

/// <summary>
///     OnStartup is called to raise the Startup event. The developer will typically override this method
///     if they want to take action at startup time ( or they may choose to attach an event).
///     This method will be called once when the application begins, once that application's Run() method
///     has been called.
/// </summary>
/// <param name="e">The event args that will be passed to the Startup event</param>
protected virtual void OnStartup(StartupEventArgs e)
{
    // Verifies that the calling thread has access to this object.
    VerifyAccess();

    StartupEventHandler handler = (StartupEventHandler)Events[EVENT_STARTUP];
    if (handler != null)
    {
        handler(this, e);
    }
}

我们可以向 Startup 事件添加一个处理程序，而不是覆盖 OnStartup()：

<Application x:Class="WpfApp.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             Startup="LaunchWpfApp"> 

private void LaunchWpfApp(object sender, StartupEventArgs e)
{
    MaiWindow app = new MainWindow();
    app.Show();
}