对象引用未设置为实例。 [英] Object reference is not set to instance .

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问题描述

程序运行时出现上述错误。它在SendKeys.SendWait方法中给出错误。

它获得了正确的输入,但没有奏效。实际上,在我的场景中,我想将接收的数据发送到激活的窗口(即word,excel,notepad或在该实例中激活的任何应用程序文本框)。

请帮帮我,谢谢



这里是代码,



< pre lang =c#> void sendkeytest( string input)
{
// static extern int SetForegroundWindow(IntPtr point);
Process p = Process.GetCurrentProcess( );

IntPtr h = p.Handle;
SetForegroundWindow(h);
if (p.Responding)
{
foreach (< span class =code-keyword> char c in input)
{
SendKeys.SendWait(c.ToString() );
}
}
}

if (res.StartsWith( *))
{
sendkeytest(res);

}





在上面的代码中,res是从套接字收到的字符串,我想要将此字符串发送到激活窗口,即在运行时打开文本编辑器。

解决方案

我们无法分辨 - 因为我们无法运行您的应用程序。

所以从调试器开始,看看收到错误时到底发生了什么。

SendKeys.SendWait 是静态的方法 - 所以它不能自己生成 null 引用错误。所以 res 必须这样做。

由于 res 字符串(或 StartsWith 方法调用无法编译)我们可以忽略 ToString 调用,因为它已经是字符串并且这个电话是多余的。

所以它必须是 res.StartsWith 本身导致问题 - 这意味着 res 本身是 null



现在你必须找出原因:我们不能为你做到这一点!

一旦你确认 res null ,在方法的顶部放置一个断点,然后逐步查找原因。


如果您的观察结果正确, res 为null,在if语句中抛出异常。是不是很明显?



你没有真正显示确切的行,其中引发了异常,并带有对象引用未设置为对象实例的消息。



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。但是如果下一个记录功能的条件对象引用未设置为对象的实例则会出错。



有时候,你不能这样做在调试器下,由一个或另一个原因。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



祝你好运,

-SA


I got above error when my program runs. It gives error at SendKeys.SendWait method.
It gets proper input but didn't work. Actually in my scenario I want to send received data to activated window (i.e word , excel , notepad , or any application text box which is activated at that instance).
Help me please, Thanks

here is code,

void sendkeytest(string input)
      {
           //static extern int SetForegroundWindow(IntPtr point);
          Process p = Process.GetCurrentProcess();

          IntPtr h = p.Handle;
          SetForegroundWindow(h);
          if (p.Responding)
          {
              foreach (char c in input)
              {
                  SendKeys.SendWait(c.ToString());
              }
          }
      }

if (res.StartsWith("*"))
{
   sendkeytest(res);

}



In above code "res" is string received from socket and i want to send this string to activated window i.e text editor opened at runtime.

解决方案

We can't tell - because we can't run your app.
So start with the debugger, and look at exactly what is happening when you get the error.
SendKeys.SendWait is a static method - so it can't generate a null reference error on it's own. So res must be doing it.
Since res is a string (or the StartsWith method call would not compile) we can ignore the ToString call as it's already a string and the call is redundant.
So it must be the res.StartsWith itself that causes the problem - which means that res itself is null.

Now you have to find out why: and we can't do that for you!
Once you have confirmed that res is null, put a breakpoint at the top of the method, and step through to find out why.


If your observations are correct, res is null, which throws exception in "if" statement. Isn't it obvious?

You did not really show exact line 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".

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,
—SA


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