C# - 线程中止和 System.NullReferenceException

Question

我正在使用线程做一个练习 GUI Oven 程序，我不确定我是否应该这样做，因为我想在加热过程正在进行时与 GUI 交互。当我尝试通过单击 btnStop_Click 中止线程时，它会引发 NullReference 异常:

System.NullReferenceException:对象引用未设置为对象的实例。

请就如何优雅地停止线程提出建议。谢谢。

代码:

 public partial class Form1 : Form
        {
            private Thread t;

            public Form1()
            {
                InitializeComponent();
            }
            // button to begin heating
            private void btnStart_Click(object sender, EventArgs e)
            {   
                if ((txtMin.Text) == "" || (txtSec.Text) == "")
                {
                    MessageBox.Show("Please enter duration of heating");
                }
                else
                {
                    t = new Thread(heatIt);
                    btnHeat.Enabled = false;
                    t.Start();
                }
            }

           //stop heating
            private void btnStop_Click(object sender, EventArgs e)
            {
                Heating heat = new Heating();
                Form1 l = new Form1();
                l.Subscribe(heat);
                heat.stopHeat();
                btnHeat.Enabled = true;
            }

            private void heatIt()
            {
            // heat food Implementation that calls the 'Heating' class
            }

           public void Subscribe(Heating m)
           {
            m.heatComplete += SignalHeatCompleted;
            m.heatStop += SignalStop;
           }

           private void SignalHeatCompleted(Heating m, EventArgs e)
           {
            MessageBox.Show( "Done, please enjoy your food");
            return;
           }

           private void SignalStop(Heating m, EventArgs e)
           {
           t.Abort();
            MessageBox.Show("Heating Terminated");
            return;            
           }

public class Heating
        {
            public event HeatingCompleted heatComplete; // Heating Completed Event
            public event HeatingStop heatStop;          // Heating Stop Event
            public EventArgs e = null;
            public delegate void HeatingCompleted(Heating h, EventArgs e);
            public delegate void HeatingStop(Heating s, EventArgs e);

            public void startHeat(int temp, int min, int sec)
            {
                int totalSec;
                totalSec = ((min*60) + sec) * 1000;

                Thread.Sleep(totalSec);
                if (heatComplete != null)
                {
                    heatComplete(this, e);
                }
                else
                {
                    //Use default signal if there's no subscription to this event
                    MessageBox.Show("*TING*");

                }
                return;    
            }

            public void stopHeat()
            {
                if (heatStop != null)
                {
                    heatStop(this, e);
                }
            }
        }
    }

Answer 1

您正在停止单击事件中创建 Form1 的新实例，因此您正在与与开始单击中的 t 完全不同的 t 交谈。

您可能还希望拥有一个在 heatIt 中分配的 Heat 实例，然后在停止单击中使用该引用。

对于后台处理，您可能还想查看 BackgroundWorker class为您完成繁重的工作。