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  1. using System;
  2. using System.Collections.Generic;
  3. using System.Drawing;
  4. using System.IO;
  5. using System.Net;
  6. using System.Threading.Tasks;
  7. using System.Windows.Forms;
  8.  
  9. namespace WindowsFormsApplication1
  10. {
  11.     public partial class Form1 : Form
  12.     {
  13.         public Form1()
  14.         {
  15.             InitializeComponent();
  16.         }
  17.  
  18.         private static Dictionary<Uri, Image> cache = new Dictionary<Uri, Image>();
  19.  
  20.         private static Task<Image> DownloadImageAsync(Uri uri)
  21.         {
  22.             var tcs = new TaskCompletionSource<Image>();
  23.             Image cachedImage;
  24.             lock (cache)
  25.             {
  26.                 if (cache.TryGetValue(uri, out cachedImage))
  27.                 {
  28.                     tcs.SetResult(cachedImage);
  29.                     return tcs.Task;
  30.                 }
  31.             }
  32.  
  33.             var wc = new WebClient();
  34.             wc.DownloadDataCompleted += (s, e) =>
  35.             {
  36.                 if (e.Cancelled)
  37.                 {
  38.                     tcs.SetCanceled();
  39.                 }
  40.                 else if (e.Error != null)
  41.                 {
  42.                     tcs.SetException(e.Error);
  43.                 }
  44.                 else
  45.                 {
  46.                     Bitmap bmp;
  47.                     using (var stream = new MemoryStream(e.Result))
  48.                     {
  49.                         bmp = new Bitmap(stream);
  50.                     }
  51.  
  52.                     lock (cache)
  53.                     {
  54.                         if (!cache.ContainsKey(uri))
  55.                         {
  56.                             cache.Add(uri, bmp);
  57.                         }
  58.                     }
  59.                     tcs.SetResult(bmp);
  60.                 }
  61.             };
  62.  
  63.             wc.DownloadDataAsync(uri);
  64.             return tcs.Task;
  65.         }
  66.  
  67.         private void button1_Click(object sender, EventArgs e)
  68.         {
  69.             var uri = new Uri("http://hoge/sample.png");
  70.             DownloadImageAsync(uri).ContinueWith(t =>
  71.             {
  72.                 pictureBox1.Image = t.Result;
  73.             });
  74.         }
  75.     }
  76. }
  77.  
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https://ideone.com/D5XWf
language:
C# (gmcs 5.20.1)
created:
12 years ago
visibility:
public

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