向文本块WPF添加倒计时计时器

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Threading;

namespace WpfApp
{
    public partial class MainWindow : Window
    {
        private DispatcherTimer countdownTimer;
        private int countdownSeconds = 60;

        public MainWindow()
        {
            InitializeComponent();
            countdownTimer = new DispatcherTimer();
            countdownTimer.Interval = TimeSpan.FromSeconds(1);
            countdownTimer.Tick += CountdownTimer_Tick;
        }

        private void CountdownTimer_Tick(object sender, EventArgs e)
        {
            countdownSeconds--;
            if (countdownSeconds >= 0)
            {
                textBlock.Text = TimeSpan.FromSeconds(countdownSeconds).ToString(@"mm\:ss");
            }
            else
            {
                countdownTimer.Stop();
                MessageBox.Show("倒计时结束！");
            }
        }

        private void StartButton_Click(object sender, RoutedEventArgs e)
        {
            countdownTimer.Start();
        }
    }
}