C# 对象引用未设置为对象请求的实例。浏览器设置为null NullReferenceException

有人能告诉我们这段代码有什么问题吗（下面的代码发生在同一个名为EntityNameBusinessLayer的类中，我们使用的是C#ASP.NET MVC 5）：

公共类请求 { 私有HttpRequest请求

    public Request(HttpRequest request)
    {
        if(request.Browser == null)
        {

        }
        else
        {

        }
    }
}

public HttpBrowserCapabilities Browser { get; set; }

public  class ShogunTypeBusinessLayer
{

public string RetrieveUserBrowserDetails()
{               
    string browserSignature;
    HttpBrowserCapabilities browserCapabilities = Request.Browser;
    string typeBrowser = "Type : " + browserCapabilities.Type + " ";
    string nameBrowser = "Name = " + browserCapabilities.Browser + " ";
    string versionBrowser = "Version = " + browserCapabilities.Version + " ";
    string majorVersionBrowser = "Major Version = " + browserCapabilities.MajorVersion + " ";
    string minorVersionBrowser = "Minor Version = " + browserCapabilities.MinorVersion + " ";
    string browserCapabilitiesBrowser = "Platform = " + browserCapabilities.Platform + " ";
    string betaBrowser = "Is Beta = " + browserCapabilities.Beta + " ";
    string isCrawlerBrowser = "Is Crawler = " + browserCapabilities.Crawler +  " ";
    string isAOLBrowser = "Is AOL = " + browserCapabilities.AOL +  " ";
    string isWin16Browser = "Is Win16 = " + browserCapabilities.Win16 +  " ";
    string isWin32Browser = "Is Win32 = " + browserCapabilities.Win32 +  " ";
    string supportFramesBrowserStatus ="Supports Frames = " + browserCapabilities.Frames + " ";
    string supportTableBrowserStatus = "Supports Tables = " + browserCapabilities.Tables + " ";
    string supportCookiesBrowserStatus = "Supports Cookies = " + browserCapabilities.Cookies + " ";
    string supportVBScriptBrowserStatus = "Supports VB Script = " + browserCapabilities.VBScript + " ";
    string supportJavaScriptBrowserStatus = "Supports JavaScript = " + browserCapabilities.JavaScript + " ";
    string supportJavaAppletsBrowserStatus = "Supports Java Applets = " + browserCapabilities.JavaApplets + " ";
    string supportActiveXControlsBrowserStatus ="Supports ActiveX Controls = " + browserCapabilities.ActiveXControls + " ";
    string supportChannelDefinitionFormatBrowserStatus = "CDF = " + browserCapabilities.CDF + " ";

    browserSignature = typeBrowser + 
                       nameBrowser + 
                       versionBrowser + 
                       majorVersionBrowser + 
                       minorVersionBrowser + 
                       browserCapabilitiesBrowser + 
                       betaBrowser +
                       isCrawlerBrowser +
                       isAOLBrowser + 
                       isWin16Browser + 
                       isWin32Browser + 
                       supportFramesBrowserStatus + 
                       supportTableBrowserStatus +  
                       supportCookiesBrowserStatus + 
                       supportVBScriptBrowserStatus + 
                       supportJavaScriptBrowserStatus +  
                       supportJavaAppletsBrowserStatus + 
                       supportActiveXControlsBrowserStatus + 
                       supportChannelDefinitionFormatBrowserStatus;

    return browserSignature;
}

执行后，我们得到以下异常。我们正在尝试将附加的字符串保存到数据库中，以便能够确定浏览器执行了插入操作

描述标题：对象引用未设置为对象的实例

描述：在执行当前web请求期间发生未经处理的异常。请查看堆栈跟踪，以了解有关错误及其在代码中起源的详细信息

异常详细信息：System.NullReferenceException:对象引用未设置为对象的实例

源错误：

第791行：字符串浏览器签名； 第792行： 第793行：HttpBrowserCapabilities browserCapabilities=Request.Browser； 第794行： 第795行：字符串typeBrowser=“Type:+browserCapabilities.Type+”

源文件：

c:\Users\25025\Documents\Visual Studio 2012\Projects\censys_cross\censys\BusinessLayer\ShogunTypeBusinessLayer.cs    Line:  793 

堆栈跟踪：

[NullReferenceException: Object reference not set to an instance of an object.]
   censys.BusinessLayer.ShogunTypeBusinessLayer.RetrieveUserBrowserDetails() in c:\Users\25025\Documents\Visual Studio 2012\Projects\censys_cross\censys\BusinessLayer\ShogunTypeBusinessLayer.cs:793
   censys.BusinessLayer.ShogunTypeBusinessLayer.AddShogunType(SHOGUN_TYPEda shogunType) in c:\Users\25025\Documents\Visual Studio 2012\Projects\censys_cross\censys\BusinessLayer\ShogunTypeBusinessLayer.cs:1124
   censys.Controllers.ShogunTypeController.Create_Post() in c:\Users\25025\Documents\Visual Studio 2012\Projects\censys_cross\censys\Controllers\ShogunTypeController.cs:33
   lambda_method(Closure , ControllerBase , Object[] ) +101
   System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +14
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +208
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +27
   System.Web.Mvc.Async.<>c__DisplayClass42.<BeginInvokeSynchronousActionMethod>b__41() +28
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +10
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +57
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +48
   System.Web.Mvc.Async.<>c__DisplayClass39.<BeginInvokeActionMethodWithFilters>b__33() +57
   System.Web.Mvc.Async.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49() +223
   System.Web.Mvc.Async.<>c__DisplayClass37.<BeginInvokeActionMethodWithFilters>b__36(IAsyncResult asyncResult) +10
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +57
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) +48
   System.Web.Mvc.Async.<>c__DisplayClass2a.<BeginInvokeAction>b__20() +24
   System.Web.Mvc.Async.<>c__DisplayClass25.<BeginInvokeAction>b__22(IAsyncResult asyncResult) +102
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +57
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +43
   System.Web.Mvc.<>c__DisplayClass1d.<BeginExecuteCore>b__18(IAsyncResult asyncResult) +14
   System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +23
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +62
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +57
   System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +23
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +62
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +47
   System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute(IAsyncResult asyncResult) +10
   System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__3(IAsyncResult asyncResult) +25
   System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +23
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +62
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +47
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +9651532
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

[NullReferenceException:对象引用未设置为对象的实例。]
c:\Users\25025\Documents\Visual Studio 2012\Projects\censys\u cross\censys\BusinessLayer\ShogunTypeBusinessLayer.RetrieveUserBrowserDetails（）中的censys.BusinessLayer.ShogunTypeBusinessLayer.RetrieveUserBrowserDetails（）
c:\Users\25025\Documents\visualstudio 2012\Projects\censys\u cross\censys\BusinessLayer\ShogunTypeBusinessLayer.AddShogunType（SHOGUN\u TYPEda shogunType）中的censys.BusinessLayer.AddShogunType（SHOGUN\u TYPEda shogunType）cs:1124
在c:\Users\25025\Documents\Visual Studio 2012\Projects\censys\u cross\censys\Controllers\ShogunTypeController.Create_Post（）中创建
lambda_方法（闭包、控制器库、对象[]）+101
System.Web.Mvc.ActionMethodDispatcher.Execute（ControllerBase控制器，对象[]参数）+14
System.Web.Mvc.ReflectedActionDescriptor.Execute（ControllerContext ControllerContext，IDictionary`2参数）+208
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod（ControllerContext ControllerContext，ActionDescriptor ActionDescriptor，IDictionary`2参数）+27
System.Web.Mvc.Async.c__显示类42.b__41（）+28
System.Web.Mvc.Async.c_uuuudisplayClass8`1.b_uuuu7（IAsyncResult）+10
System.Web.Mvc.Async.WrappedAsyncResult`1.End（）+57
System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod（IAsyncResult asyncResult）+48
System.Web.Mvc.Async.c__显示类39.b__33（）+57
System.Web.Mvc.Async.c__DisplayClass4f.b__49（）+223
System.Web.Mvc.Async.c__显示类37.b__36（IAsyncResult asyncResult）+10
System.Web.Mvc.Async.WrappedAsyncResult`1.End（）+57
System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters（IAsyncResult asyncResult）+48
System.Web.Mvc.Async.c__DisplayClass2a.b__20（）+24
System.Web.Mvc.Async.c__显示类25.b__22（IAsyncResult asyncResult）+102
System.Web.Mvc.Async.WrappedAsyncResult`1.End（）+57
System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction（IAsyncResult asyncResult）+43
System.Web.Mvc.c__;u displayClassId.b__u18（IAsyncResult asyncResult）+14
System.Web.Mvc.Async.c__显示类4.b__3（IAsyncResult ar）+23
System.Web.Mvc.Async.WrappedAsyncResult`1.End（）+62
System.Web.Mvc.Controller.EndExecuteCore（IAsyncResult asyncResult）+57
System.Web.Mvc.Async.c__显示类4.b__3（IAsyncResult ar）+23
System.Web.Mvc.Async.WrappedAsyncResult`1.End（）+62
System.Web.Mvc.Controller.EndExecute（IAsyncResult asyncResult）+47
System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute（IAsyncResult asyncResult）+10
System.Web.Mvc.c__;u DisplayClass8.b__;u 3（IAsyncResult asyncResult）+25
System.Web.Mvc.Async.c__显示类4.b__3（IAsyncResult ar）+23
System.Web.Mvc.Async.WrappedAsyncResult`1.End（）+62
System.Web.Mvc.MvcHandler.EndProcessRequest（IAsyncResult asyncResult）+47
System.Web.Mvc.MvcHandler.System.Web.IHTTPassynchandler.EndProcessRequest（IAsyncResult结果）+9
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute（）+9651532
System.Web.HttpApplication.ExecuteStep（IExecutionStep步骤，布尔值&同步完成）+155

---

由于某种原因，代码没有执行。

此代码将不会编译为c#将不允许您拥有未在类/类型中定义的方法和属性。实际上，您需要有一个类，该类应该有一个构造函数，该构造函数应该将一个

请求

实例作为参数，并执行一个空值lue检入构造函数。然后将请求属性设置为私有字段。这将确保：

调用方在运行时不会得到一些难以跟踪的NRE

代码很早就失败了

该类型的要求很明确，因为您无法创建状态不好的有效实例（请求的值为null）

或者，您可以让该方法接收一个请求实例，并让它检查参数是否为null

public class EntityNameBusinessLayer
{
    // private member, i left the naming the same but the usual convention for private members is camelcase and not pascal.
    private HttpRequest Request;

    // constructor
    public EntityNameBusinessLayer(HttpRequest request) {
        // check for null
        if(request == null)
            throw new ArgumentNullException("request");
        Request = request; // now the state of the instance is valid and it can be used by the caller
    }

    public string RetrieveUserBrowserDetails()
    { /*your code*/ }
}

在asp.net web窗体中调用代码

public class YourAspWebPage : System.Web.UI.Page {
    protected void Button_Click(object sender, EventArgs args) {
        var bl = new EntityNameBusinessLayer(this.Request);
        var result = bl.RetrieveUserBrowserDetails();
    }
}

在Asp.net Mvc控制器中调用代码。请注意，当您在Mvc中工作时，不鼓励直接使用类型

HttpRequest

。相反，使用类型

HttpRequestBase

，因为在单元测试中很容易模拟/伪造。另请参见CountZero的第二个答案（得票最多的一个）

---

Request

在这个类中是如何设置的？似乎是null/never set.@stephen.vakil这是类public HttpRequest Request{get；set；}顶部的代码行代码中似乎没有任何内容初始化

请求的值

——它正在声明但从未设置。此应用程序是否使用基于属性的依赖项注入和per

public class YourAspWebPage : System.Web.UI.Page {
    protected void Button_Click(object sender, EventArgs args) {
        var bl = new EntityNameBusinessLayer(this.Request);
        var result = bl.RetrieveUserBrowserDetails();
    }
}

public class YourController : System.Web.Mvc.Controller {
    public void SomeAction() {
        var bl = new EntityNameBusinessLayer(System.Web.HttpContext.Current.Request);
        var result = bl.RetrieveUserBrowserDetails();
    }
}