错误！未在对象实例上设置对象引用。 C＃ [英] Error! Object reference not set on instance of an object. c#
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问题描述
为什么我收到错误：错误！未在对象实例上设置对象引用。 c＃
Why i getting error : Error! Object reference not set on instance of an object. c#
private StringBuilder htmlMessageBody(DataGridView dg)
{
StringBuilder strB = new StringBuilder();
//create html & table
strB.AppendLine("<html><body><center><table border='1' cellpadding='0' cellspacing='0'>");
strB.AppendLine("<tr>");
//cteate table header
for (int i = 0; i < dg.Columns.Count; i++)
{
strB.AppendLine("<td align='center' valign='middle'>" + dg.Columns[i].HeaderText + "</td>");
}
//create table body
strB.AppendLine("<tr>");
for (int i = 0; i < dg.Rows.Count; i++)
{
strB.AppendLine("<tr>");
foreach (DataGridViewCell dgvc in dg.Rows[i].Cells)
{
strB.AppendLine("<td align='center' valign='middle'>" + dgvc.Value.ToString() + "</td>");
}
strB.AppendLine("</tr>");
}
//table footer & end of html file
strB.AppendLine("</table></center></body></html>");
return strB;
}
private void bMail_Click(object sender, EventArgs e)
{
MailMessage myMessage = new MailMessage();
try
{
myMessage.From = "test@test.com";
myMessage.To = "test@test.com";
myMessage.Cc = "test@test.com";
myMessage.BodyEncoding = Encoding.UTF8;
myMessage.BodyFormat = MailFormat.Html;
myMessage.Body = htmlMessageBody(dataGridView2).ToString();
myMessage.Subject = "Test";
myMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", "0");
myMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", "userName");
myMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", "password");
SmtpMail.SmtpServer = "mail.t-com.hr";
SmtpMail.Send(myMessage);
MessageBox.Show("Message sent!");
}
catch (Exception ex)
{
MessageBox.Show("Error! " + ex.Message);
}
推荐答案
对象引用未设置为对象的实例
当您尝试使用属性或调用null对象的方法时，会发生此错误。更多细节：此处 [ ^ ]
Visual Studio DEBUGGER的简单使用可以告诉你对象因为它正在发生。只需查看堆栈跟踪并将调试器放在该行上即可。检查该行的对象，看看是否有任何一个为null，并且您正在尝试使用该对象属性。处理相同的内容。
Object reference not set to an instance of an object
This error happens when you try to use a property or call a method of an object that is null. More details: here[^]
A simple use of Visual studio DEBUGGER can tell you the object because of which it is happening. Just look at the stack trace and put a debugger on that line. Check the objects of that line and see if any one is null and you are trying to use that objects property. Handle the same.
您没有显示带有对象引用未设置为对象实例消息的异常位置。
不用担心。这是检测和修复的最简单的案例之一。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 [ ^ ]。
祝你好运，
-SA
You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.
Not to worry. 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"[^].
Good luck,
—SA
上面的源码无法编译，但我确实注意到以下内容：
要发送邮件，您需要执行以下操作：
Can''t get the source above to compile but I did notice the following :
To send the mail, you need to do something like this :
SmtpClient client = new SmtpClient("mail.t-com.hr");
client.Send(myMessage);
我怀疑你的异常可能来自传递给htmlMessageBody方法的dataGridView2 。逐步执行代码并确保变量''dg''在进入该方法时不为null。
I suspect that your exception may be coming from the dataGridView2 passed into the htmlMessageBody method. Step through the code and make sure that the variable ''dg'' is not null when it enters that method.
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