如何比較圖像（緩存圖像）？

Question

我正在都市風格的應用程序中進行簡單的圖像緩存。 這是我已經完成的工作：

    private async void GetImage()
    {
        bool isFolderExisting = true;
        bool isFileExisting = true;
        StorageFolder storageFolder = null;
        StorageFile storageFile = null;

        // get screenshots folder    
        try
        {
            storageFolder = await ApplicationData.Current.TemporaryFolder.GetFolderAsync("screenshots");
        }
        catch (System.IO.FileNotFoundException ex)
        {
            isFolderExisting = false;
        }
        // if folder doesn't exist, create new one
        if (isFolderExisting == false)
            storageFolder = await ApplicationData.Current.TemporaryFolder.CreateFolderAsync("screenshots");

        // get screenshot
        try
        {
            storageFile = await storageFolder.GetFileAsync(this.LinkId);
            //IAsyncAction threadPoolWorkItem = ThreadPool.RunAsync((source) => { updateImage(storageFile); });
        }
        catch (System.IO.FileNotFoundException ex)
        {
            isFileExisting = false;
        }

        // if file doesn't exists, download and save new one
        if (isFileExisting == false)
        {
            var uri = new Uri(WebServiceAddress + "/screenshot/" + this.LinkId, UriKind.Absolute);
            var thumbnail = Windows.Storage.Streams.RandomAccessStreamReference.CreateFromUri(uri);
            storageFile = await StorageFile.CreateStreamedFileFromUriAsync(this.LinkId, uri, thumbnail);
            await storageFile.CopyAsync(storageFolder, storageFile.Name, NameCollisionOption.ReplaceExisting);
        }

        //this.ImageSource = new Windows.UI.Xaml.Media.Imaging.BitmapImage(new Uri("ms-appdata:///temp/screenshots/" + this.LinkId)); 
        this.Image = "ms-appdata:///temp/screenshots/" + this.LinkId;
    }

現在，我必須照顧比較圖像的最后一部分。 我正在檢查臨時文件夾中是否存在圖像。 如果不存在，那么我只是下載新的，但是如果存在，則需要檢查它是否與服務器上的相同。 我該如何實現？

Answer 1

在StorageFile類上使用GetBasicPropertiesAsync方法。 BasicProperties對象包含一個DateModified屬性，可用於在客戶端和服務器之間進行比較。