使用元组作为参数对象的C＃backgroundworker未找到？ [英] C# backgroundworker using tuple as argument object not found?

问题描述

我正在尝试向后台工作者发送一个参数，我希望这个参数是一个元组对象。



出于某种原因，我得到一个nullreferenceException我想从参数中提取列表，似乎无法找出原因。

 System.NullReferenceException： 对象引用未设置在对象的实例上。 

我尝试过：

 //全球var 
 public static List< informatie> LsLotto = new List< informatie>（）; 
 BackgroundWorker Worker; 
 
 
 form_load（）{
 //后台工作人员
工人=新的BackgroundWorker（）; 
 Worker.DoWork + =新的DoWorkEventHandler（worker_function）; 
 
 //这里我填写清单
 
} 

 function1（）{
元组< List< informatie>，int> tuple = new Tuple< List< informatie>，int>（LsLotto，2）; 
 Worker.RunWorkerAsync（tuple）; 
} 

 worker_function（对象发送者，DoWorkEventArgs e） {
 //提取列表
元组<列表< informatie>，int> tuple = e.Argument as Tuple< List< informatie>，int> ;; 
列表< informatie> gegevens =（List< informatie>）tuple.Item1; //<  - 错误行（上面看到的错误）
} 

解决方案

这是最常见的一种我们被问到的问题，也是我们最不能回答的问题，但你最有能力回答自己。



我来解释一下错误是什么意思：您尝试使用变量，属性或方法返回值，但它包含null - 这意味着变量中没有类的实例。

它有点像一个口袋：你的衬衫里有一个口袋，用来握笔。如果你进入口袋并发现那里没有笔，你就不能在一张纸上签名 - 如果你尝试的话，你会得到非常有趣的外观！空口袋给你一个空值（这里没有笔！）所以你不能做任何你检索笔通常做的事情。它为什么空？这就是问题 - 可能是你今天早上离开家时忘了拿起你的笔，或者你昨晚把它拿到昨天的衬衫口袋里时可能会把笔留下来。



我们无法分辨，因为我们不在那里，更重要的是，我们甚至看不到你的衬衫，更不用说口袋里的东西了！



回到计算机，你做了同样的事情，不知何故 - 我们看不到你的代码，更不用说运行它了，找不到包含null的东西。

但是你可以 - 而Visual Studio将在这里帮助你。在调试器中运行您的程序，当它失败时，VS将向您显示它发现问题的行。然后，您可以开始查看它的各个部分，以查看哪个值为null，并开始回顾代码以找出原因。因此，在包含错误行的方法的开头放置一个断点，然后从头再次运行程序。这一次，VS会在错误发生前停止，让你通过查看代码来查看你的价值来检查发生了什么。



但我们做不到那 - 我们没有您的代码，如果我们拥有它，我们不知道如何使用它，我们没有您的数据。所以尝试一下 - 看看你能找到多少信息！

引用：

我更新了代码，但是如果我放一个断点并查看e.argument，它会被设置为'null'。但是为什么因为我把Tuple作为一个参数，对吧？

好吧，当我尝试它时：

私人类信息{} 
列表与LT; informatie> LsLotto = new List< informatie>（）; 
 BackgroundWorker Worker; 
 private void worker_function（object sender，DoWorkEventArgs e）
 {
 //提取列表
元组< List< informatie>，int> tuple = e.Argument as Tuple< List< informatie>，int> ;; 
列表< informatie> gegevens =（List< informatie>）tuple.Item1; //<  - 错误行（上面看到的错误）
} 
 private void MyButton_Click（object sender，EventArgs ew）
 {
 Worker = new BackgroundWorker（）; 
 Worker.DoWork + =新的DoWorkEventHandler（worker_function）; 
元组< List< informatie>，int> tuple = new Tuple< List< informatie>，int>（LsLotto，2）; 
 Worker.RunWorkerAsync（tuple）; 
 

我在元组中得到一个元组，gegevens变成一个没有任何问题的空列表。



那么......究竟是什么......我这样做是不同的，因为我复制了你的主要代码？ ：笑：

即使我提供的是null而不是列表：

 Tuple< List< informatie>，int> tuple = new Tuple< List< informatie>，int>（null，3）; // LsLotto，2）; 

我没有得到异常，我只是在gegevens中得到一个null。

I am trying to send an argument to the background worker, I want this argument to be a tuple object.

for some reason, I get a nullreferenceException when i want to extract the list from the argument and can't seem to figure out why.

System.NullReferenceException: "The object reference is not set on an instance of an object."

What I have tried:

//global var
public static List<informatie> LsLotto = new List<informatie>();
BackgroundWorker Worker;


form_load(){
   //background worker
   Worker = new BackgroundWorker();
   Worker.DoWork += new DoWorkEventHandler(worker_function);
  
   // here I fill op the list

}

function1(){
    Tuple<List<informatie>, int> tuple = new Tuple<List<informatie>, int>(LsLotto, 2);
    Worker.RunWorkerAsync(tuple);   
}

worker_function(object sender, DoWorkEventArgs e){
    //extracting the list
  Tuple < List < informatie >, int> tuple = e.Argument as Tuple<List<informatie>, int>;
  List<informatie> gegevens = (List<informatie>)tuple.Item1 ; // <-- line of error (erorr seen above) 
}

解决方案

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

Quote:

I updated the code, but yea if I put a breakpoint and look at the e.argument, it is set to 'null'. But idk why because I did put the Tuple in as an argument, right?

Well, when I try it:

private class informatie { }
List<informatie> LsLotto = new List<informatie>();
BackgroundWorker Worker;
private void worker_function(object sender, DoWorkEventArgs e)
    {
    //extracting the list
    Tuple<List<informatie>, int> tuple = e.Argument as Tuple<List<informatie>, int>;
    List<informatie> gegevens = (List<informatie>)tuple.Item1; // <-- line of error (erorr seen above)
    }
private void MyButton_Click(object sender, EventArgs ew)
    {
    Worker = new BackgroundWorker();
    Worker.DoWork += new DoWorkEventHandler(worker_function);
    Tuple<List<informatie>, int> tuple = new Tuple<List<informatie>, int>(LsLotto, 2);
    Worker.RunWorkerAsync(tuple);

I get a Tuple in tuple, and gegevens becomes an empty List without any problems.

So what ... exactly ... am I doing that is different, given that I copied the main code from you? :laugh:
Even if I supply a null instead of the list:

Tuple<List<informatie>, int> tuple = new Tuple<List<informatie>, int>(null, 3);//LsLotto, 2);

I don't get an exception, I just get a null in gegevens.

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