App.xaml.cs

using System;
using Windows.ApplicationModel;
using Windows.ApplicationModel.Activation;
using Windows.Foundation;
using Windows.UI.ViewManagement;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;

namespace CountDown_Day {
    /// <summary>
    /// 提供特定于应用程序的行为，以补充默认的应用程序类。
    /// </summary>
    sealed partial class App : Application {
        public static MainPage Main { get; private set; }

        /// <summary>
        /// 初始化单一实例应用程序对象。这是执行的创作代码的第一行，
        /// 已执行，逻辑上等同于 main() 或 WinMain()。
        /// </summary>
        public App() {
            this.InitializeComponent();
            this.Suspending += OnSuspending;
        }

        /// <summary>
        /// 在应用程序由最终用户正常启动时进行调用。
        /// 将在启动应用程序以打开特定文件等情况下使用。
        /// </summary>
        /// <param name="e">有关启动请求和过程的详细信息。</param>
        protected override void OnLaunched(LaunchActivatedEventArgs e) {
            Frame rootFrame = Window.Current.Content as Frame;

            // 不要在窗口已包含内容时重复应用程序初始化，
            // 只需确保窗口处于活动状态
            if (rootFrame == null) {
                // 创建要充当导航上下文的框架，并导航到第一页
                rootFrame = new Frame();

                rootFrame.NavigationFailed += OnNavigationFailed;

                if (e.PreviousExecutionState == ApplicationExecutionState.Terminated) {
                    //TODO: 从之前挂起的应用程序加载状态
                }

                // 将框架放在当前窗口中
                rootFrame.Content = new MainPage();
                Window.Current.Content = rootFrame;
                // Main = rootFrame.Content as MainPage;
                if (rootFrame.Content is MainPage) {
                    Main = rootFrame.Content as MainPage;
                }
            }

            if (e.PrelaunchActivated == false) {
                if (rootFrame.Content == null) {
                    // 当导航堆栈尚未还原时，导航到第一页，
                    // 并通过将所需信息作为导航参数传入来配置
                    // 参数
                    rootFrame.Navigate(typeof(MainPage), e.Arguments);
                }
                // 确保当前窗口处于活动状态
                Window.Current.Activate();
            }

            // set the smallest size of the uwp window
            // but it may not to be done...

            var minsize = new Size(644, 396);
            ApplicationView view = ApplicationView.GetForCurrentView();
            view.SetPreferredMinSize(minsize);
        }

        /// <summary>
        /// 导航到特定页失败时调用
        /// </summary>
        ///<param name="sender">导航失败的框架</param>
        ///<param name="e">有关导航失败的详细信息</param>
        void OnNavigationFailed(object sender, NavigationFailedEventArgs e) {
            throw new Exception("Failed to load Page " + e.SourcePageType.FullName);
        }

        /// <summary>
        /// 在将要挂起应用程序执行时调用。  在不知道应用程序
        /// 无需知道应用程序会被终止还是会恢复，
        /// 并让内存内容保持不变。
        /// </summary>
        /// <param name="sender">挂起的请求的源。</param>
        /// <param name="e">有关挂起请求的详细信息。</param>
        private void OnSuspending(object sender, SuspendingEventArgs e) {
            var deferral = e.SuspendingOperation.GetDeferral();
            //TODO: 保存应用程序状态并停止任何后台活动
            deferral.Complete();
        }

        //Hard implementation enforces window size.
        private readonly double minW = 644, minH = 396;
        protected override void OnWindowCreated(WindowCreatedEventArgs args) {
            SetWindowMinSize(new Size(args.Window.Bounds.Width, args.Window.Bounds.Height));
            args.Window.CoreWindow.SizeChanged += CoreWindow_SizeChanged;
            base.OnWindowCreated(args);
        }
        private void CoreWindow_SizeChanged(Windows.UI.Core.CoreWindow sender, Windows.UI.Core.WindowSizeChangedEventArgs args) {
            if (SetWindowMinSize(args.Size)) sender.ReleasePointerCapture();
        }
        private bool SetWindowMinSize(Size size) {
            if (size.Width < minW || size.Height < minH) {
                if (size.Width < minW) size.Width = minW;
                if (size.Height < minH) size.Height = minH;
                return ApplicationView.GetForCurrentView().TryResizeView(size);
            }
            return false;
        }
    }
}