Jas*_*n94 7 c# caching portable-class-library windows-phone-8
我正在构建一个需要某种缓存的应用程序,而且由于我的模型和视图模型都存在于可移植类库中,我想在那里进行某种缓存......但是PCL是有限的,我似乎无法找到任何缓存.
我想使用System.Runtime.Caching但不包含在PCL中 - 还有其他选择吗？
我自己在找这样的选择; 我将很快推出自己的实现,并将发布它.在此之前,您可能希望尝试一些想法.
Runtime.Cache如果我没记错的话可以根据绝对时间,滑动时间和监控密钥/文件使缓存无效.
首先弄清楚你需要实现哪一个(我需要绝对和滑动,但我相信滑动会更昂贵)
看看这个链接. 替代到concurrentdictionary换便携式类库
我的想法是,为了在每个缓存项目的添加/删除上扩展该类,我们在字典对象中存储/删除缓存密钥以及到期时间(对于滑动项目,我们将在读取时更新此到期时间)
然后我们有一个主计时器,它经常检查这个字典并根据时间到期.
如果您还想要,可以使用另一个字典跟踪密钥依赖关系,因此在密钥到期时,您可以根据此过期使任何其他缓存过期.
希望这在某种程度上有所帮助.
---更新
我设法绕过去写自己的实现......在这里你去..
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reactive.Linq;
using System.Threading;
namespace RanaInside.CacheProvider
{
internal class CacheProvider : ICacheProvider
{
private IDictionary<object, CacheItem> _cache = new Dictionary<object, CacheItem>();
private IDictionary<object, SliderDetails> _slidingTime = new Dictionary<object, SliderDetails>();
private const int _monitorWaitDefault = 1000;
private const int _monitorWaitToUpdateSliding = 500;
/// <summary>
/// The sync object to make accessing the dictionary is thread safe.
/// </summary>
private readonly object _sync = new object();
#region Implementation of Interface
public event EventHandler KeyRemoved;
/// <summary>
/// Add a value to the cache with a relative expiry time, e.g 10 minutes.
/// </summary>
/// <typeparam name="TKey">The type of the key.</typeparam>
/// <typeparam name="TValue">The type of the value.</typeparam>
/// <param name="key">The key.</param>
/// <param name="value">The value.</param>
/// <param name="slidingExpiry">The sliding time when the key value pair should expire and be purged from the cache.</param>
/// <param name="priority">Normal priority will be purged on low memory warning.</param>
public void Add<TKey, TValue>(TKey key, TValue value, TimeSpan slidingExpiry, CacheItemPriority priority = CacheItemPriority.Normal) where TValue : class
{
Add(key, value, slidingExpiry, priority, true);
}
/// <summary>
/// Add a value to the cache with an absolute time, e.g. 01/01/2020.
/// </summary>
/// <typeparam name="TKey">The type of the key.</typeparam>
/// <typeparam name="TValue">The type of the value.</typeparam>
/// <param name="key">The key.</param>
/// <param name="value">The value.</param>
/// <param name="absoluteExpiry">The absolute date time when the cache should expire and be purged the value.</param>
/// <param name="priority">Normal priority will be purged on low memory warning.</param>
public void Add<TKey, TValue>(TKey key, TValue value, DateTime absoluteExpiry, CacheItemPriority priority = CacheItemPriority.Normal) where TValue : class
{
if (absoluteExpiry < DateTime.Now)
{
return;
}
var diff = absoluteExpiry - DateTime.Now;
Add(key, value, diff, priority, false);
}
/// <summary>
/// Gets a value from the cache for specified key.
/// </summary>
/// <typeparam name="TKey">The type of the key.</typeparam>
/// <typeparam name="TValue">The type of the value.</typeparam>
/// <param name="key">The key.</param>
/// <returns>
/// If the key exists in the cache then the value is returned, if the key does not exist then null is returned.
/// </returns>
public TValue Get<TKey, TValue>(TKey key) where TValue : class
{
try
{
var cacheItem = _cache[key];
if (cacheItem.RelativeExpiry.HasValue)
{
if (Monitor.TryEnter(_sync, _monitorWaitToUpdateSliding))
{
try
{
_slidingTime[key].Viewed();
}
finally
{
Monitor.Exit(_sync);
}
}
}
return (TValue)cacheItem.Value;
}
catch (Exception)
{
return null;
}
}
/// <summary>
/// Remove a value from the cache for specified key.
/// </summary>
/// <typeparam name="TKey">The type of the key.</typeparam>
/// <param name="key">The key.</param>
public void Remove<TKey>(TKey key)
{
if (!Equals(key, null))
{
_cache.Remove(key);
_slidingTime.Remove(key);
if (KeyRemoved != null)
{
KeyRemoved(key, new EventArgs());
}
}
}
/// <summary>
/// Clears the contents of the cache.
/// </summary>
public void Clear()
{
if (!Monitor.TryEnter(_sync, _monitorWaitDefault))
{
return;
}
try
{
_cache.Clear();
_slidingTime.Clear();
}
finally
{
Monitor.Exit(_sync);
}
}
/// <summary>
/// Gets an enumerator for keys of a specific type.
/// </summary>
/// <typeparam name="TKey">The type of the key.</typeparam>
/// <returns>
/// Returns an enumerator for keys of a specific type.
/// </returns>
public IEnumerable<TKey> Keys<TKey>()
{
if (!Monitor.TryEnter(_sync, _monitorWaitDefault))
{
return Enumerable.Empty<TKey>();
}
try
{
return _cache.Keys.Where(k => k.GetType() == typeof(TKey)).Cast<TKey>().ToList();
}
finally
{
Monitor.Exit(_sync);
}
}
/// <summary>
/// Gets an enumerator for all the keys
/// </summary>
/// <returns>
/// Returns an enumerator for all the keys.
/// </returns>
public IEnumerable<object> Keys()
{
if (!Monitor.TryEnter(_sync, _monitorWaitDefault))
{
return Enumerable.Empty<object>();
}
try
{
return _cache.Keys.ToList();
}
finally
{
Monitor.Exit(_sync);
}
}
/// <summary>
/// Gets the total count of items in cache
/// </summary>
/// <returns>
/// -1 if failed
/// </returns>
public int TotalItems()
{
if (!Monitor.TryEnter(_sync, _monitorWaitDefault))
{
return -1;
}
try
{
return _cache.Keys.Count;
}
finally
{
Monitor.Exit(_sync);
}
}
/// <summary>
/// Purges all cache item with normal priorities.
/// </summary>
/// <returns>
/// Number of items removed (-1 if failed)
/// </returns>
public int PurgeNormalPriorities()
{
if (Monitor.TryEnter(_sync, _monitorWaitDefault))
{
try
{
var keysToRemove = (from cacheItem in _cache where cacheItem.Value.Priority == CacheItemPriority.Normal select cacheItem.Key).ToList();
return keysToRemove.Count(key => _cache.Remove(key));
}
finally
{
Monitor.Exit(_sync);
}
}
return -1;
}
#endregion
#region Private class helper
private void Add<TKey, TValue>(TKey key, TValue value, TimeSpan timeSpan, CacheItemPriority priority, bool isSliding) where TValue : class
{
if (!Monitor.TryEnter(_sync, _monitorWaitDefault))
{
return;
}
try
{
// add to cache
_cache.Add(key, new CacheItem(value, priority, ((isSliding) ? timeSpan : (TimeSpan?)null)));
// keep sliding track
if (isSliding)
{
_slidingTime.Add(key, new SliderDetails(timeSpan));
}
StartObserving(key, timeSpan);
}
finally
{
Monitor.Exit(_sync);
}
}
private void StartObserving<TKey>(TKey key, TimeSpan timeSpan)
{
Observable.Timer(timeSpan)
.Finally(() =>
{
// on finished
GC.Collect();
GC.WaitForPendingFinalizers();
})
// on next
.Subscribe(x => TryPurgeItem(key),
exception =>
{
// on error: Purge Failed with exception.Message
});
}
private void TryPurgeItem<TKey>(TKey key)
{
if (_slidingTime.ContainsKey(key))
{
TimeSpan tryAfter;
if (!_slidingTime[key].CanExpire(out tryAfter))
{
// restart observing
StartObserving(key, tryAfter);
return;
}
}
Remove(key);
}
private class CacheItem
{
public CacheItem() { }
public CacheItem(object value, CacheItemPriority priority, TimeSpan? relativeExpiry = null)
{
Value = value;
Priority = priority;
RelativeExpiry = relativeExpiry;
}
public object Value { get; set; }
public CacheItemPriority Priority { get; set; }
public TimeSpan? RelativeExpiry { get; set; }
}
private class SliderDetails
{
public SliderDetails(TimeSpan relativeExpiry)
{
RelativeExpiry = relativeExpiry;
Viewed();
}
private TimeSpan RelativeExpiry { get; set; }
private DateTime ExpireAt { get; set; }
public bool CanExpire(out TimeSpan tryAfter)
{
tryAfter = (ExpireAt - DateTime.Now);
return (0 > tryAfter.Ticks);
}
public void Viewed()
{
ExpireAt = DateTime.Now.Add(RelativeExpiry);
var z = ExpireAt;
}
}
#endregion
}
}
有关最新更新,请访问我的博客
http://ranahossain.blogspot.co.uk/2014/01/cache-provider-for-portable-class.html