上一篇介紹到CreateActionResult方法會產生一個ActionResult物件利用MethodInfo資訊.
最後透過InvokeActionResult來呼叫ExecuteResult方法來執行ActionResult的ExecuteResult方法,基本上MVC找到且執行Action方法後面就沒再做甚麼特別的事情了(後面做資源釋放...)
protected virtual void InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
{
actionResult.ExecuteResult(controllerContext);
}
本篇來介紹常用的ActionResult其內部運作程式碼
下面這六個類別是直接繼承於ActionResult的類別(其中有標註Base class代表這是抽象類別另外有類別繼承它)
ContentResult:回傳一組字串,利用response.Write方法EmptyResult:什麼都不動作(當Action回傳void使用)FileResult(Base class):把檔案當作回傳HttpStatusCodeResult:回傳HTTP狀態碼RedirectResult & RedirectToRouteResult:使用Response.Redirect轉導到其他頁面ViewResultBase(Base class):會找尋相對應View檔案(cshtml會編譯成一個DLL)來執行
ViewResultBase會在另一篇介紹(因為機制比較複雜)
在ContentResult有三個屬性
Content:響應內容.ContentType:設置Http Header攔位ContentType
ContentEncoding:設置Encoding方式public class ContentResult : ActionResult
{
public string Content { get; set; }
public Encoding ContentEncoding { get; set; }
public string ContentType { get; set; }
public override void ExecuteResult(ControllerContext context)
{
if (context == null)
{
throw new ArgumentNullException("context");
}
HttpResponseBase response = context.HttpContext.Response;
if (!String.IsNullOrEmpty(ContentType))
{
response.ContentType = ContentType;
}
if (ContentEncoding != null)
{
response.ContentEncoding = ContentEncoding;
}
if (Content != null)
{
response.Write(Content);
}
}
}
ContentResult操作很簡單透過response.Write把內容Print出來
RedirectResult這個ActionResult如其名就是導轉頁面.
Permanent:屬性判斷是否需要Permanently導轉頁面(Http-Code:RedirectPermanent=301,Redirect=302)Url:轉導的URL透過UrlHelper.GenerateContentUrl產生URL.(在GenerateContentUrl會判斷第一個字元是否是~波浪號,如果是代表站內導轉.)最後利用Permanent布林判斷使用RedirectPermanent還是Redirect方法.
public class RedirectResult : ActionResult
{
public bool Permanent { get; private set; }
public string Url { get; private set; }
public override void ExecuteResult(ControllerContext context)
{
if (context == null)
{
throw new ArgumentNullException("context");
}
if (context.IsChildAction)
{
throw new InvalidOperationException(MvcResources.RedirectAction_CannotRedirectInChildAction);
}
string destinationUrl = UrlHelper.GenerateContentUrl(Url, context.HttpContext);
context.Controller.TempData.Keep();
if (Permanent)
{
context.HttpContext.Response.RedirectPermanent(destinationUrl, endResponse: false);
}
else
{
context.HttpContext.Response.Redirect(destinationUrl, endResponse: false);
}
}
}
RedirectToRouteResult基本流程跟上面一樣只是透過UrlHelper.GenerateUrl產生要導轉URL
EmptyResult這個類別很有趣,只有override ExecuteResult方法但沒有實做,上篇小結有提到這裡使用一個設計模式null object pattern.
public class EmptyResult : ActionResult
{
private static readonly EmptyResult _singleton = new EmptyResult();
internal static EmptyResult Instance
{
get { return _singleton; }
}
public override void ExecuteResult(ControllerContext context)
{
}
}
FileResult是一個抽象類別,提供一個抽象方法給abstract void WriteFile(HttpResponseBase response)子類提供覆寫.
有兩個類別繼承於FileResult抽象類別
FilePathResult
FileContentResult
FileResult抽象類別在ExecuteResult設置傳輸檔案需要的前置作業(設置Content-Type...),最後的資料傳輸透過各個子類別去實現.
其中
headerValue實做Http回應擋頭對於RFC規範.
// From RFC 2183, Sec. 2.3:
// The sender may want to suggest a filename to be used if the entity is
// detached and stored in a separate file. If the receiving MUA writes
// the entity to a file, the suggested filename should be used as a
// basis for the actual filename, where possible.
string headerValue = ContentDispositionUtil.GetHeaderValue(FileDownloadName);
public abstract class FileResult : ActionResult
{
private string _fileDownloadName;
protected FileResult(string contentType)
{
if (String.IsNullOrEmpty(contentType))
{
throw new ArgumentException(MvcResources.Common_NullOrEmpty, "contentType");
}
ContentType = contentType;
}
public string ContentType { get; private set; }
public string FileDownloadName
{
get { return _fileDownloadName ?? String.Empty; }
set { _fileDownloadName = value; }
}
public override void ExecuteResult(ControllerContext context)
{
if (context == null)
{
throw new ArgumentNullException("context");
}
HttpResponseBase response = context.HttpContext.Response;
response.ContentType = ContentType;
if (!String.IsNullOrEmpty(FileDownloadName))
{
string headerValue = ContentDispositionUtil.GetHeaderValue(FileDownloadName);
context.HttpContext.Response.AddHeader("Content-Disposition", headerValue);
}
WriteFile(response);
}
protected abstract void WriteFile(HttpResponseBase response);
}
}
FileContentResult將檔案已位元組方式轉存給Client端.
透過HttpResponseBase.OutputStream.Write方法.
public class FileContentResult : FileResult
{
public FileContentResult(byte[] fileContents, string contentType)
: base(contentType)
{
if (fileContents == null)
{
throw new ArgumentNullException("fileContents");
}
FileContents = fileContents;
}
public byte[] FileContents { get; private set; }
protected override void WriteFile(HttpResponseBase response)
{
response.OutputStream.Write(FileContents, 0, FileContents.Length);
}
}
FilePathResult透過檔案名稱FileName將檔案提供給Client
藉由HttpResponseBase.TransmitFile方法.
public class FilePathResult : FileResult
{
public FilePathResult(string fileName, string contentType)
: base(contentType)
{
if (String.IsNullOrEmpty(fileName))
{
throw new ArgumentException(MvcResources.Common_NullOrEmpty, "fileName");
}
FileName = fileName;
}
public string FileName { get; private set; }
protected override void WriteFile(HttpResponseBase response)
{
response.TransmitFile(FileName);
}
}
本篇介紹了幾個實現ActionResult類別,跟其內部程式碼,這裡能了解到MVC返回結果機於ActionResult方法.(這個概念我運用在Web Api服務,建立ResponseBase共同簽章,因為在做服務串接每個服務都有自己的加解密,回傳格式攔位.我可以統一透過一個ResponseBase類別裝載資料再藉由過濾器來幫忙組成相對應的資料回傳....)
下篇會來介紹繼承ActionResult最複雜的ViewResultBase相關程式碼.
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