1、xaml页面<Window x:Class="EssentialWPF.MainWindow"        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"        Title="MainWindow" Height="350" Width="525">    <Grid>        <Button            Name="_button1"            HorizontalAlignment="Center"            VerticalAlignment="Center"            FontSize="9pt">            Hello World        </Button>    </Grid></Window>2、后台using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows;using System.Windows.Controls;using System.Windows.Data;using System.Windows.Documents;using System.Windows.Input;using System.Windows.Media;using System.Windows.Media.Imaging;using System.Windows.Navigation;using System.Windows.Shapes;using System.Windows.Threading;namespace EssentialWPF{    /// <summary>    /// MainWindow.xaml 的交互逻辑    /// </summary>    public partial class MainWindow : Window    {        long _start;        public MainWindow()        {            InitializeComponent();            DispatcherTimer timer = new DispatcherTimer();            timer.Interval = TimeSpan.FromMilliseconds(50);            _start = Environment.TickCount;            timer.Tick += timer_Tick;            timer.IsEnabled = true;        }        void timer_Tick(object sender, EventArgs e)        {            long elapsed = Environment.TickCount - _start;            if (elapsed >= 5000)            {                _button1.FontSize = 18.0;                ((DispatcherTimer)sender).IsEnabled = false;                return;            }            _button1.FontSize = 9.0 + (9.0 / (5000.0 / elapsed));        }    }}