2
我有一個帶有兩個按鈕的窗體（開始,停止）。在C中取消任務＃
當我按下開始按鈕任務被初始化，一個函數被調用的是繼續工作，直到停止按鈕被按下。
但是當我按停止按鈕表單凍結。爲什麼？ 我已經從StackOverflow複製片段，但它仍凍結窗體。 那麼告訴我如何正確取消任務？從MSDN
public partial class Form1 : Form
{
private readonly CancellationTokenSource _cts = new CancellationTokenSource();
private Task _task;
public Form1()
{
InitializeComponent();
}
//Funtion that runs when Task is initialized.
private void EventLoop(CancellationToken token)
{
//Code here..
while (!token.IsCancellationRequested)
{
//Code here..
}
if (token.IsCancellationRequested)
{
MessageBox.Show("Operation Complete..!!");
}
}
//Function for Start Button.
private void Start_Click(object sender, EventArgs e)
{
_task = Task.Factory.StartNew(() => EventLoop(_cts.Token), _cts.Token);
}
//Function for Stop button.
private void Stop_Click(object sender, EventArgs e)
{
_cts.Cancel();
}
}
類似的實施例：按鈕被按下停止
var compute = Task.Factory.StartNew(() =>
{
return SumRootN(j);
}, tokenSource.Token);`
窗體後。 token.IsCancellationRequested是true。
完全EventLoop()功能。
private void EventLoop(CancellationToken token)
{
SerialPort sp = new SerialPort();
string text, batch, part, courseName;
text = batch = part = courseName = "";
int courseId = 0;
this.Invoke((MethodInvoker)delegate()
{
text = portCB.SelectedItem.ToString();
batch = comboBox2.SelectedItem.ToString();
part = comboBox3.SelectedItem.ToString();
courseName = comboBox1.SelectedItem.ToString();
progressBar1.Value = 20;
using (Model1 db = new Model1())
{
courseId = db.Courses.Where(c => c.Course_name.ToUpper() == courseName.ToUpper()).Select(c => c.Course_Id).Single();
}
});
sp.PortName = text;
sp.BaudRate = 9600;
sp.Open();
while (!token.IsCancellationRequested)
{
text = sp.ReadLine();
if (text.Contains("Found ID #"))
{
this.Invoke((MethodInvoker)delegate()
{
textBox2.Clear();
textBox2.Text = "Getting Registation ID.\n";
progressBar1.Value = 60;
});
string splitText = text.Split('#')[1];
int end = splitText.IndexOf(' ');
int id = int.Parse(splitText.Substring(0, end));
using (Model1 db = new Model1())
{
var result = db.Students.Where(s => s.Reg_Id == id && s.Batch == batch && s.Class == part).Select(s => s).SingleOrDefault();
if (result != null)
{
Attendance a = new Attendance();
a.Course_Id = courseId;
a.Student_Id = id;
a.Status = "P";
a.Date = DateTime.Today.Date;
a.Batch = batch;
a.Part = part;
db.Attendances.Add(a);
string message = "";
if (db.SaveChanges() != 0)
{
message = "Attendance Uploaded..!!\n";
}
else
{
message = "Attendance Not Uploaded ..!!\n";
}
this.Invoke((MethodInvoker)delegate()
{
progressBar1.Value = 100;
textBox2.AppendText(message);
});
}
else
{
this.BeginInvoke((MethodInvoker)delegate()
{
textBox2.AppendText("Student Does not belong to Specified Batch Or Part..\n");
});
}
}
}
else
{
this.Invoke((MethodInvoker)delegate()
{
textBox2.AppendText("No Match Found..!! \n");
});
}
this.Invoke((MethodInvoker)delegate()
{
textBox1.AppendText(text + "\n");
});
}
sp.Close();
// This exception will be handled by the Task
// and will not cause the program to crash
if (token.IsCancellationRequested)
{
//MessageBox.Show("Operation Comptele..!!");
}
}
這顯然是非常，非常邋遢使用異步調用，但我沒有看到任何會導致僵局的事情。當然你沒有在'CancellationToken'上註冊取消回調或者在任何地方調用'_task.Wait' /'_task.Result'？ –
沒有我沒有做任何事情，除了啓用和禁用CheckBoxes在**開始**和**停止**按鈕Codding ..我可以告訴你，但然後大家會downvote我的問題.. –
截圖中的窗體很清楚禁用，但我沒有看到窗體的'Enabled'屬性被設置在代碼中的任何地方，所以我傾向於認爲問題發生在未發佈的代碼部分。 –