private async Task <T> GetFromCacheOrDownloadAsync(Uri uri, string fileName, bool preCacheOnly, CancellationToken cancellationToken, List <KeyValuePair <string, object> > initializerKeyValues)
{
StorageFile baseFile = null;
T instance = default(T);
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().ConfigureAwait(MaintainContext);
baseFile = await folder.TryGetItemAsync(fileName).AsTask().ConfigureAwait(MaintainContext) as StorageFile;
if (baseFile == null || await IsFileOutOfDateAsync(baseFile, CacheDuration).ConfigureAwait(MaintainContext))
{
baseFile = await folder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting).AsTask().ConfigureAwait(MaintainContext);
try
{
instance = await DownloadFileAsync(uri, baseFile, preCacheOnly, cancellationToken, initializerKeyValues).ConfigureAwait(false);
}
catch (Exception)
{
await baseFile.DeleteAsync().AsTask().ConfigureAwait(false);
throw; // re-throwing the exception changes the stack trace. just throw
}
}
if (EqualityComparer <T> .Default.Equals(instance, default(T)) && !preCacheOnly)
{
instance = await InitializeTypeAsync(baseFile, initializerKeyValues).ConfigureAwait(false);
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);
}
/// <summary>
/// Remove items based on provided keys
/// </summary>
/// <param name="keys">identified of the in-memory storage item</param>
public void Remove(IEnumerable <string> keys)
{
foreach (var key in keys)
{
if (string.IsNullOrWhiteSpace(key))
{
continue;
}
InMemoryStorageItem <T> tempItem = null;
_inMemoryStorage.TryRemove(key, out tempItem);
tempItem = null;
}
}
/// <summary>
/// Add new item to in-memory storage
/// </summary>
/// <param name="item">item to be stored</param>
public void SetItem(InMemoryStorageItem <T> item)
{
if (MaxItemCount == 0)
{
return;
}
_inMemoryStorage[item.Id] = item;
// ensure max limit is maintained. trim older entries first
if (_inMemoryStorage.Count > MaxItemCount)
{
var itemsToRemove = _inMemoryStorage.OrderBy(kvp => kvp.Value.Created).Take(_inMemoryStorage.Count - MaxItemCount).Select(kvp => kvp.Key);
Remove(itemsToRemove);
}
}
/// <summary>
/// Get item from in-memory storage as long as it has not ex
/// </summary>
/// <param name="id">id of the in-memory storage item</param>
/// <param name="duration">timespan denoting expiration</param>
/// <returns>Valid item if not out of date or return null if out of date or item does not exist</returns>
public InMemoryStorageItem <T> GetItem(string id, TimeSpan duration)
{
InMemoryStorageItem <T> tempItem = null;
if (!_inMemoryStorage.TryGetValue(id, out tempItem))
{
return(null);
}
DateTime expirationDate = DateTime.Now.Subtract(duration);
if (tempItem.LastUpdated > expirationDate)
{
return(tempItem);
}
_inMemoryStorage.TryRemove(id, out tempItem);
return(null);
}