如何修复“未设置为对象实例的对象引用”请给我一个溶胶。

本文介绍了如何修复“未设置为对象实例的对象引用”请给我一个溶胶。的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 使用系统; 使用 System.Collections.Generic; 使用 System.Linq; 使用 System.Web; 使用 System.Web.UI; 使用 System.Web.UI.WebControls; 使用 System.Data; 使用 System.Data.SqlClient; public partial class _Default：System.Web.UI.Page { private SqlConnection con = new SqlConnection（ user id = sa; password = 123; database = TESTDB; server = 127.0.0.1 ）; 受保护 void Page_Load（ object sender，EventArgs e） { if （！IsPostBack） { BindGrid（）; } } 受保护 void BindGrid（ ） { con.Open（）; SqlCommand cmd = new SqlCommand（ select *来自EmployeeDetails，con）; SqlDataAdapter da = new SqlDataAdapter（cmd）; DataSet ds = new DataSet（）; da.Fill（ds）; con.Close（）; gvDetails.DataSource = ds; gvDetails.DataBind（）; } protected void gvDetails_RowEdit（ object sender，GridViewEditEventArgs e） { gvDetails.EditIndex = e.NewEditIndex; BindGrid（）; } 受保护 void gvDetails_RowUpdate（ object sender，GridViewUpdateEventArgs e） { int UserId = Convert.ToInt32（gvDetails.DataKeys [e.RowIndex]。值[ UserId]。ToString（））; TextBox txtUsrName =（TextBox）gvDetails.Rows [e.RowIndex] .FindControl（ txtUsrName）; TextBox txtCity =（TextBox）gvDetails.Rows [e.RowIndex] .FindControl（ txtCity）; TextBox txtDesg =（TextBox）gvDetails.Rows [e.RowIndex] .FindControl（ txtdesg）; con.Open（）; SqlCommand cmd = new SqlCommand（ update EmployeeDetails设置UserName =' + txtUsrName.Text + '，City =' + txtCity.Text + '，' + txtDesg.Text + '其中UserId = + UserId，con）; cmd.ExecuteNonQuery（）; con.Close（）; gvDetails.EditIndex = -1; BindGrid（）; } 受保护 void gvDetails_CancelEdit（ object sender，GridViewCancelEditEventArgs e） { gvDetails.EditIndex = -1; BindGrid（）; } 受保护 void gvDetails_RowDelete（ object sender，GridViewDeleteEventArgs e） { int UserId = Convert.ToInt32（gvDetails.DataKeys [e .RowIndex] .Values [ UserId]。ToString（））; con.Open（）; SqlCommand cmd = new SqlCommand（ delete来自EmployeeDetails，其中UserId = + UserId，con）; cmd.ExecuteNonQuery（）; con.Close（）; BindGrid（）; } protected void gvDetails_Command（ object sender，GridViewCommandEventArgs e） { if （e.CommandName.Equals（ AddNew）） { TextBox txtUsrName =（TextBox）gvDetails.FooterRow.FindControl（ txtUsrName）; TextBox txtCity =（TextBox）gvDetails.FooterRow.FindControl（ txtCity）; TextBox txtDesg =（TextBox）gvDetails.FooterRow.FindControl（ txtDesg）; con.Open（）; SqlCommand cmd = new SqlCommand（ 插入EmployeeDetails（UserName，City，Designation）值（' + txtUsrName.Text + '，' + txtCity.Text + '，' + txtDesg.Text + '），con）; 这里我收到错误消息： 对象引用未设置为对象的实例 cmd.ExecuteNonQuery（）; con.Close（）; BindGrid（）; } } 解决方案 在线上设置断点并调试应用程序，将鼠标移到该行，看看哪个部分 null 。 首先，由于未找到控件，请检查您的标识符。要进行健全性检查，请删除有问题的行并运行该页面，然后从客户端角度查看该页面：在浏览器中，使用查看页面源（或类似的内容，具体取决于浏览器）。 /> 在更一般的情况下，请参阅我的解决空例外的建议： 这是其中一个最容易检测和修复的案例。它只是意味着某些引用类型的某个成员/变量通过使用和它的实例（非静态）成员解除引用，这要求此成员/变量为非null，但实际上它似乎为null。只需在调试器下执行它，它将停止抛出异常的执行。在该行上设置一个断点，重新启动应用程序并再次到达这一点。评估下一行中涉及的所有引用，并查看哪一个为null，而不需要为null。解决这个问题之后，修复代码：要么确保将成员/变量正确初始化为非空引用，要么将其检查为null，如果为null，则执行其他操作。 另请参阅：想要在按钮点击时显示下一条记录。但是如果下一条记录功能的条件对象引用没有设置为对象的实例 [ ^ ]。 有时候，你不能在调试器下，由于一个或另一个原因做到这一点。一个非常讨厌的情况是，只有在调试信息不​​可用时构建软件时才会出现问题。在这种情况下，你必须使用更难的方式。首先，你需要确保你永远不会通过静默处理异常来阻止异常的传播（这是开发人员对自己的犯罪，但很常见）。您需要在每个线程的最顶层堆栈帧上捕获绝对所有异常。如果处理类型 System.Exception 的异常，则可以执行此操作。在处理程序中，您需要记录所有异常信息，尤其是 System.Exception.StackTrace ： http://msdn.microsoft.com/en-us/library/system.exception.aspx [ ^ ]， http://msdn.microsoft.com/en-us/library/system.exception。 stacktrace.aspx [ ^ ]。 堆栈跟踪只是一个字符串，显示从throw语句到处理程序的异常传播的完整路径。通过阅读，您总能找到目的。对于日志记录，使用类 System.Diagnostics.EventLog ： http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx [ ^ ]。 -SA 我希望你能解决你的null问题很快，因为这个问题是最简单的问题之一。但是你有一个更深层次的问题：你进行查询的方式使你的代码对于一个名为 SQK injection 的众所周知的漏洞开放。您永远不应该通过连接UI控件中的数据来获取查询文本。它们可以包含任何内容，包括......一些SQL片段。为了获得和想法，请参阅： http://xkcd.com/327 [ ^ ]。 怎么办？首先阅读问题和基本解决方案：使用参数化语句： http://en.wikipedia.org/wiki/SQL_injection [ ^ ]。 另请参阅我过去的答案，并按照我提供的链接： EROR IN com.ExecuteNonQuery（）; [ ^ ]， http：// msdn .microsoft.com / zh-cn / library / ff648339.aspx [ ^ ]， 你的名字没有显示名字？ [ ^ ]。 -SA using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;using System.Data;using System.Data.SqlClient;public partial class _Default : System.Web.UI.Page{ private SqlConnection con = new SqlConnection("user id=sa;password=123;database=TESTDB;server=127.0.0.1"); protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { BindGrid(); } } protected void BindGrid() { con.Open(); SqlCommand cmd = new SqlCommand("select * from EmployeeDetails", con); SqlDataAdapter da = new SqlDataAdapter(cmd); DataSet ds = new DataSet(); da.Fill(ds); con.Close(); gvDetails.DataSource = ds; gvDetails.DataBind(); } protected void gvDetails_RowEdit(object sender, GridViewEditEventArgs e) { gvDetails.EditIndex = e.NewEditIndex; BindGrid(); } protected void gvDetails_RowUpdate(object sender, GridViewUpdateEventArgs e) { int UserId=Convert.ToInt32(gvDetails.DataKeys[e.RowIndex].Values["UserId"].ToString()); TextBox txtUsrName = (TextBox)gvDetails.Rows[e.RowIndex].FindControl("txtUsrName"); TextBox txtCity = (TextBox)gvDetails.Rows[e.RowIndex].FindControl("txtCity"); TextBox txtDesg = (TextBox)gvDetails.Rows[e.RowIndex].FindControl("txtdesg"); con.Open(); SqlCommand cmd = new SqlCommand("update EmployeeDetails set UserName='"+txtUsrName.Text+"',City='"+txtCity.Text+"','"+txtDesg.Text+"' where UserId="+UserId,con); cmd.ExecuteNonQuery(); con.Close(); gvDetails.EditIndex = -1; BindGrid(); } protected void gvDetails_CancelEdit(object sender, GridViewCancelEditEventArgs e) { gvDetails.EditIndex = -1; BindGrid(); } protected void gvDetails_RowDelete(object sender, GridViewDeleteEventArgs e) { int UserId = Convert.ToInt32(gvDetails.DataKeys[e.RowIndex].Values["UserId"].ToString()); con.Open(); SqlCommand cmd = new SqlCommand("delete from EmployeeDetails where UserId=" + UserId, con); cmd.ExecuteNonQuery(); con.Close(); BindGrid(); } protected void gvDetails_Command(object sender, GridViewCommandEventArgs e) { if (e.CommandName.Equals("AddNew")) { TextBox txtUsrName = (TextBox)gvDetails.FooterRow.FindControl("txtUsrName"); TextBox txtCity = (TextBox)gvDetails.FooterRow.FindControl("txtCity"); TextBox txtDesg = (TextBox)gvDetails.FooterRow.FindControl("txtDesg"); con.Open(); SqlCommand cmd = new SqlCommand( "insert into EmployeeDetails(UserName,City,Designation) values('"+txtUsrName.Text+"','"+txtCity.Text+"','"+txtDesg.Text+"')",con);here i got an error msg:"object reference not set to an instance of an object" cmd.ExecuteNonQuery(); con.Close(); BindGrid(); } } 解决方案 Put a break point on the line and debug you application, move your mouse over the line and see what part is null.First of all, as controls are not found checkup your identifiers. For a sanity check, remove offending line(s) and run the page, and then look at the page from the client standpoint: in a browser, use "View page source" (or something similar, depending on the browser).In more general case, please see my recommendation for resolving null exceptions:This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"[^].Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:http://msdn.microsoft.com/en-us/library/system.exception.aspx[^],http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx[^].The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx[^].Good luck,—SAI hope you will resolve your null problem soon, as this problem is one of the simplest. But you have one deeper problem: the way you do queries makes your code wide open for a well-known exploit called SQK injection. You should never obtain a text of query by concatenating the data from UI controls. They can contain anything, including… some SQL fragments. To get and idea, please see:http://xkcd.com/327[^].What to do? First read on the problem and the basic solution: using parametrized statements: http://en.wikipedia.org/wiki/SQL_injection[^].See also my past answers and follow the links I provided:EROR IN UPATE in com.ExecuteNonQuery();[^],http://msdn.microsoft.com/en-us/library/ff648339.aspx[^],hi name is not displaying in name?[^].—SA 这篇关于如何修复“未设置为对象实例的对象引用”请给我一个溶胶。的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！