c# - 在用户看到之前在另一个线程中缓存图像

Question

最近在做一个WPF的电子书程序，书页都保存为.jpg格式。由于图片都是高质量的，程序在切换页面时会卡顿。

我试图在用户在另一个线程中看到的当前图像之后缓存一些图像。但它给了我一个错误。

An unhandled exception of type 'System.InvalidOperationException' occurred in WindowsBase.dll

Additional information: The calling thread cannot access this object because a different thread owns it.

我可以通过添加 Invoke 来修复错误，但是性能就像没有内存缓存一样。

但是如果没有Invoke，程序会显示上面的错误。而且我不知道如何修复它。

我尽量使代码尽可能简单。

感谢任何帮助。

完整代码:

using System;
using System.Collections.Specialized;
using System.IO;
using System.Runtime.Caching;
using System.Threading;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media.Imaging;

namespace ThreadedMemoryCache_Test
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        MemoryCache memcache;
        int num = 0;
        Image img;
        int BufferPages = 2;

        public MainWindow()
        {
            InitializeComponent();
            //Change Content
            img = new Image();
            Content = img;
            //Mouse Events
            MouseDown += (s, e) =>
            {
                int add = 0;
                if (e.LeftButton == MouseButtonState.Pressed)
                    add--;
                else if (e.RightButton == MouseButtonState.Pressed)
                    add++;
                else
                    return;
                num += add;
                img.Source = GetBitmap(num);  //Error here
                Buffer();
            };
        }
        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            //Initiallize MemoryCache
            NameValueCollection CacheSettings = new NameValueCollection(3);
            CacheSettings.Add("CacheMemoryLimitMegabytes", Convert.ToString(1));
            CacheSettings.Add("physicalMemoryLimitPercentage", Convert.ToString(10));
            CacheSettings.Add("pollingInterval", Convert.ToString("00:00:10"));
            memcache = new MemoryCache("BitmapCache", CacheSettings);
            //Get First Photo
            img.Source = GetBitmap(num);
            Buffer();
        }
        BitmapImage GetBitmap(int num)
        {
            String id = num.ToString();
            BitmapImage cachebmp = memcache[id] as BitmapImage;
            if (cachebmp == null)
            {
                CacheItemPolicy policy = new CacheItemPolicy();
                String name = num.ToString() + ".jpg";
                FileInfo file = new FileInfo(name);
                if(!file.Exists)
                {
                    num = 0;
                    return GetBitmap(num);
                }
                cachebmp = new BitmapImage(new Uri(file.FullName));
                memcache.Set(id, cachebmp, policy);
            }
            return cachebmp;
        }
        void Buffer()
        {
            //Start Thread
            Thread cachethread = new Thread(() =>
            {
                for (int i = 1; i <= BufferPages; i++)
                {
                    //Adding invoke fixes the error, but it seems to delay the main thread and cause lag.
                    //this.Dispatcher.Invoke((Action)(() =>
                    //{
                    GetBitmap(num + i);
                    //}));
                }
            });
            cachethread.IsBackground = true;
            cachethread.Start();
        }
    }
}

Answer 1

您必须卡住 BitmapImage 以使其可跨线程访问:

cachebmp = new BitmapImage(new Uri(file.FullName));
cachebmp.Freeze();
memcache.Set(id, cachebmp, policy);

---

也就是说，您的代码可以在很多方面进行改进。最好使用 ThreadPool线程或 BackgroundWorker 或 Task执行后台任务。

此外，如果图像文件不存在，您不应该使用 num = 0 递归调用 GetBitmap(num)。如果 0.jpg 也丢失了会怎样？