將其設置爲NoCache後更改Response.Cache._cacheability

看起來好像一旦將緩存性設置爲Response.Cache爲NoCache，則無法再次更改它。這是一個簡單但完整的問題說明：將其設置爲NoCache後更改Response.Cache._cacheability

protected void Page_Load(object sender, EventArgs e) 
{ 
    FieldInfo fi = typeof(HttpCachePolicy).GetField(
     "_cacheability", 
     BindingFlags.NonPublic | BindingFlags.Instance); 

    // Default value = 6 
    HttpCacheability first = (HttpCacheability)fi.GetValue(Response.Cache); 

    // Can change it to Public 
    Response.Cache.SetCacheability(HttpCacheability.Public); 
    HttpCacheability second = (HttpCacheability)fi.GetValue(Response.Cache); 

    // Can change it to Private 
    Response.Cache.SetCacheability(HttpCacheability.Private); 
    HttpCacheability third = (HttpCacheability)fi.GetValue(Response.Cache); 

    // Can change it to NoCache 
    Response.Cache.SetCacheability(HttpCacheability.NoCache); 
    HttpCacheability fourth = (HttpCacheability)fi.GetValue(Response.Cache); 

    // Can't go back to Private! Stuck on NoCache 
    Response.Cache.SetCacheability(HttpCacheability.Private); 
    HttpCacheability fifth = (HttpCacheability)fi.GetValue(Response.Cache); 
}

我錯過了什麼嗎？有沒有辦法做到這一點？

編輯：當然，它的工作原理，如果我與反思設置它，但我擔心，還有別的情況發生，當你設置爲HttpCacheability.NoCache如果我去幕後，我會想念..和希望無論如何都要以官方支持的方式來完成。

編輯2：同樣的事情似乎發生在Private;你只能限制更多嗎？

protected void Page_Load(object sender, EventArgs e) 
{ 
    FieldInfo fi = typeof(HttpCachePolicy).GetField(
     "_cacheability", 
     BindingFlags.NonPublic | BindingFlags.Instance); 

    // Default value = 6 
    HttpCacheability first = (HttpCacheability)fi.GetValue(Response.Cache); 

    // Can change it to Private 
    Response.Cache.SetCacheability(HttpCacheability.Private); 
    HttpCacheability second = (HttpCacheability)fi.GetValue(Response.Cache); 

    // Can't change to Public! Stuck on Private 
    Response.Cache.SetCacheability(HttpCacheability.Public); 
    HttpCacheability third = (HttpCacheability)fi.GetValue(Response.Cache); 

    // Can change to NoCache - Can only go more restrictive? 
    Response.Cache.SetCacheability(HttpCacheability.NoCache); 
    HttpCacheability fourth = (HttpCacheability)fi.GetValue(Response.Cache); 
}

來源

2012-09-13 zimdanen

裂了開來反射並看了看裏面HttpCachePolicy：

public void SetCacheability(HttpCacheability cacheability) 
{ 
    if ((cacheability < HttpCacheability.NoCache) || (HttpCacheability.ServerAndPrivate < cacheability)) 
    { 
     throw new ArgumentOutOfRangeException("cacheability"); 
    } 
    if (s_cacheabilityValues[(int) cacheability] < s_cacheabilityValues[(int) this._cacheability]) 
    { 
     this.Dirtied(); 
     this._cacheability = cacheability; 
    } 
}

s_cacheabilityValues靜態構造函數中設置：

s_cacheabilityValues = new int[] { -1, 0, 2, 1, 4, 3, 100 };

Dirtied()被調用，但它似乎只是設置一些標誌：

private void Dirtied() 
{ 
    this._isModified = true; 
    this._useCachedHeaders = false; 
}

它確實看起來有改變值的規則，但看起來沒有太大的影響。因此，使用反射來改變可能是安全的。

fi.SetValue(Response.Cache, HttpCacheability.Private);

來源

2012-09-13 21:20:42 zimdanen

現在回想起來這一點，可能要在設定'_useCachedHeaders'爲假同時，或者只是使用反射調用'Dirtied（）'。 – zimdanen

事實上，似乎反射是唯一安全的方式。展望代碼越深，則需要從響應的Cache屬性提取類型爲HttpCachePolicy的對象，你可以在下面看到它：

public class HttpCachePolicyWrapper : HttpCachePolicyBase 
{ 
    private HttpCachePolicy _httpCachePolicy; 
    .... 
}

要做到這一點，只需使用反射來設置的值正確的對象從Response.Cache對象像下面的代碼：

FieldInfo fi = typeof(HttpCachePolicy).GetField("_cacheability", BindingFlags.NonPublic | BindingFlags.Instance); 
var objectToChange = (HttpCachePolicy)context.Response.Cache.GetType().GetField("_httpCachePolicy", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(context.Response.Cache); 
fi.SetValue(objectToChange, HttpCacheability.Public);

這只是增加了更多的conrete步驟將zimdanen的回答

來源

2015-01-07 10:39:15

將其設置爲NoCache後更改Response.Cache._cacheability

回答

相關問題