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如何：自訂以時間為基礎的快取原則

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在建立以時間為基礎的快取原則時，您可以藉由指定最長使用期限、最短有效期限、最長過時或快取同步處理日期的值來自訂快取行為。 HttpRequestCachePolicy 物件所提供的建構函式可讓您指定這些值的有效組合。

建立使用快取同步處理日期之以時間為基礎的快取原則

藉由將 DateTime 物件傳遞給 HttpRequestCachePolicy 建構函式，建立使用快取同步處理日期之以時間為基礎的快取原則：

public static HttpRequestCachePolicy CreateLastSyncPolicy(DateTime when)
{
    var policy = new HttpRequestCachePolicy(when);
    Console.WriteLine("When: {0}", when);
    Console.WriteLine(policy.ToString());
    return policy;
}

Public Shared Function CreateLastSyncPolicy([when] As DateTime) As HttpRequestCachePolicy
    Dim policy As New HttpRequestCachePolicy([when])
    Console.WriteLine("When: {0}", [when])
    Console.WriteLine(policy.ToString())
    Return policy
End Function

輸出結果看起來與下列相似：

When: 1/14/2004 8:07:30 AM
Level:Default CacheSyncDate:1/14/2004 8:07:30 AM

建立依據最短有效期限之以時間為基礎的快取原則

藉由將 MinFresh 指定為 cacheAgeControl 參數值並將 TimeSpan 物件傳遞給 HttpRequestCachePolicy 建構函式，建立依據最短有效期限之以時間為基礎的快取原則：

public static HttpRequestCachePolicy CreateMinFreshPolicy(TimeSpan span)
{
    var policy = new HttpRequestCachePolicy(HttpCacheAgeControl.MinFresh, span);
    Console.WriteLine(policy.ToString());
    return policy;
}

Public Shared Function CreateMinFreshPolicy(span As TimeSpan) As HttpRequestCachePolicy
    Dim policy As New HttpRequestCachePolicy(HttpCacheAgeControl.MinFresh, span)
    Console.WriteLine(policy.ToString())
    Return policy
End Function

對於下列引動過程：

CreateMinFreshPolicy(new TimeSpan(1,0,0));

輸出如下：

Level:Default MinFresh:3600

建立依據最短有效期限和最長使用期限之以時間為基礎的快取原則

藉由將 MaxAgeAndMinFresh 指定為 cacheAgeControl 參數值並將兩個 TimeSpan 物件傳遞給 HttpRequestCachePolicy 建構函式 ( 一個用來指定資源的最長使用期限，另一個用來指定從快取傳回的物件所允許的最短有效期限)，建立依據最短有效期限和最長使用期限之以時間為基礎的快取原則：

public static HttpRequestCachePolicy CreateFreshAndAgePolicy(TimeSpan freshMinimum, TimeSpan ageMaximum)
{
    var policy = new HttpRequestCachePolicy(HttpCacheAgeControl.MaxAgeAndMinFresh, ageMaximum, freshMinimum);
    Console.WriteLine(policy.ToString());
    return policy;
}

Public Shared Function CreateFreshAndAgePolicy(freshMinimum As TimeSpan, ageMaximum As TimeSpan) As HttpRequestCachePolicy
    Dim policy As New HttpRequestCachePolicy(HttpCacheAgeControl.MaxAgeAndMinFresh, ageMaximum, freshMinimum)
    Console.WriteLine(policy.ToString())
    Return policy
End Function

對於下列引動過程：

CreateFreshAndAgePolicy(new TimeSpan(5,0,0), new TimeSpan(10,0,0));

輸出如下：

Level:Default MaxAge:36000 MinFresh:18000

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