C＃Func的目的是什么 <object> getObject？

Question

I have found the following code snippet and was wondering what the purpose is of the Func<object> getObject property:

public void InsertCacheItem(string key, Func<object> getObject, TimeSpan duration)
{
    try
    {
        var value = getObject();
        if (value == null)
            return;

        key = GetCacheKey(key);

        _cache.Insert(
            key,
            value,
            null,
            System.Web.Caching.Cache.NoAbsoluteExpiration,
            duration,
            System.Web.Caching.CacheItemPriority.Normal,
            null);
    }
    catch { }
}

How do you call this particular function by passing the Func property?

Answer 1

You would call this with something like:

InsertCacheItem("bob", () => "valuetocache", TimeSpan.FromHours(1));

But why do it this way? Why not just pass in "valuetocache"? Well, mainly due to the try..catch . The code as written means that even if the Func fails to execute then the calling code isn't impacted.

So:

InsertCacheItem("bob", () => MethodThatThrowsException(), TimeSpan.FromHours(1));

will still work, for example. It won't cache anything, but it won't bubble up exceptions to the calling code.

Answer 2

In the case of your code above, it's actually almost pointless other than to catch the exception. You would more usually see this in a function to retrieve something from a cache. For example:

public object GetCacheItem(string key, Func<object> getObject, TimeSpan duration)
{
    var value = GetItemFromCache(key);

    if (value == null)
    {
        value = getObject();

        _cache.Insert(
            key,
            value,
            null,
            System.Web.Caching.Cache.NoAbsoluteExpiration,
            duration,
            System.Web.Caching.CacheItemPriority.Normal,
            null);
    }

    return value;
}

Now we retrieve from the cache if we can, otherwise we call the potentially expensive operation to create the value again. For example:

var listOfZombies = GetCacheItem(
    "zombies", 
    () => GetZombiesFromDatabaseWhichWillTakeALongTime(), 
    TimeSpan.FromMinutes(10));