/// <summary>
/// Retrieves item represented by Uri from the in-memory cache if it exists and is not out of date. If item is not found or is out of date, default instance of the generic type is returned.
/// </summary>
/// <param name="uri">Uri of the item.</param>
/// <returns>an instance of Generic type</returns>
public T GetFromMemoryCache(Uri uri)
{
T instance = default(T);
string fileName = GetCacheFileName(uri);
if (_inMemoryFileStorage.MaxItemCount > 0)
{
var msi = _inMemoryFileStorage.GetItem(fileName, CacheDuration);
if (msi != null)
{
instance = msi.Item;
}
}
return(instance);
}
private async Task <T> GetFromCacheOrDownloadAsync(Uri uri, string fileName, bool preCacheOnly)
{
StorageFile baseFile = null;
T instance = default(T);
DateTime expirationDate = DateTime.Now.Subtract(CacheDuration);
if (_inMemoryFileStorage.MaxItemCount > 0)
{
var msi = _inMemoryFileStorage.GetItem(fileName, CacheDuration);
if (msi != null)
{
instance = msi.Item;
}
}
if (instance != null)
{
return(instance);
}
var folder = await GetCacheFolderAsync();
baseFile = await folder.TryGetItemAsync(fileName) as StorageFile;
if (await IsFileOutOfDate(baseFile, expirationDate))
{
baseFile = await folder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);
try
{
instance = await DownloadFileAsync(uri, baseFile, preCacheOnly);
}
catch (Exception)
{
await baseFile.DeleteAsync().AsTask().ConfigureAwait(false);
throw; // rethrowing the exception changes the stack trace. just throw
}
}
if (EqualityComparer <T> .Default.Equals(instance, default(T)) && !preCacheOnly)
{
using (var fileStream = await baseFile.OpenAsync(FileAccessMode.Read))
{
instance = await InitializeTypeAsync(fileStream);
}
if (_inMemoryFileStorage.MaxItemCount > 0)
{
var properties = await baseFile.GetBasicPropertiesAsync().AsTask().ConfigureAwait(false);
var msi = new InMemoryStorageItem <T>(fileName, properties.DateModified.DateTime, instance);
_inMemoryFileStorage.SetItem(msi);
}
}
return(instance);
}
