在 WPF 应用程序中缓存应用程序数据

参考学习链接：https://docs.microsoft.com/zh-cn/dotnet/framework/wpf/advanced/walkthrough-caching-application-data-in-a-wpf-application?redirectedfrom=MSDN

• 创建缓存类的实例，即，将实例化新的 MemoryCache 对象。

• 指定缓存使用 HostFileChangeMonitor 对象来监视文本文件中的更改。

• 读取文本文件并将其内容缓存为缓存条目。

• 显示缓存的文本文件的内容

创建WPFDemo 程序WpfApp2如下，验证使用 MemoryCache 缓存数据及缓存过期情况。

<Window x:Class="WpfApp2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp2"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Button Width="100" Height="60" Content="Cache" Click="Button_Click"></Button>
        <Button Content="Button" HorizontalAlignment="Left" Margin="117,145,0,0" VerticalAlignment="Top" Width="124" Height="74" Click="Button_Click_1"/>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.IO;
using System.Runtime.Caching;
using System.Threading;
using System.Windows;

namespace WpfApp2
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            ObjectCache cache = MemoryCache.Default;
            string fileContents = cache["filecontents"] as string;

            if (fileContents == null)
            {
                CacheItemPolicy policy = new CacheItemPolicy();
                policy.AbsoluteExpiration =
                    DateTimeOffset.Now.AddSeconds(1000.0);

                List<string> filePaths = new List<string>();
                filePaths.Add(@"C:\Users\wr\Desktop\cacheText.txt");

                policy.ChangeMonitors.Add(new
                    HostFileChangeMonitor(filePaths));

                // Fetch the file contents.
                fileContents = File.ReadAllText(@"C:\Users\wr\Desktop\cacheText.txt") + "\n" + DateTime.Now.ToString();

                cache.Set("filecontents", fileContents, policy);
            }
            MessageBox.Show(fileContents);
        }

        private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            ObjectCache cache = MemoryCache.Default;
            string fileContents = cache["filecontents"] as string;
            cache.Set(cache.GetCacheItem("filecontents"), new CacheItemPolicy() { AbsoluteExpiration = DateTimeOffset.Now.AddSeconds(5.0) });
            MessageBox.Show(cache["filecontents"].ToString());
            Thread.Sleep(5000);
            MessageBox.Show(cache["filecontents"] == null ? "缓存已清空" :cache["filecontents"].ToString());
        }
    }
}