Question

我有一个Windows窗体，其中包含一个列表框（Listbox1），一个标签（label1）和一个按钮（button1）。我已将点击事件分配给button1，代码如下：

public void button1_Click(object sender, EventArgs e)
{                  
    label1.Text = "Parsing entries && initializing comms ...";

    apples = new Task(Apple);
    apples.Start();
    Task.WaitAll(apples);

    label1.Text = "No. of items: " + Listbox1.Items.Count.ToString();

    if (Listbox1.Items.Count >= 2)
    {
        Listbox1.SetSelected(1, true);
    }
}

public void Apple() {    
//Send 1st command - 90000
command = "90000";
CommPort com = CommPort.Instance;

if (command.Length > 0)
{
command = ConvertEscapeSequences(command);
com.Send(command);
}
Thread.Sleep(100); //allow 100ms delay for receiving response from serial port

//Send 2nd command - 90001
command = "90001";

if (command.Length > 0)
{
command = ConvertEscapeSequences(command);
com.Send(command);
}
Thread.Sleep(100); //allow 100ms delay for receiving response from serial port

//Send 3rd command - 90002
command = "90002";

if (command.Length > 0)
{
command = ConvertEscapeSequences(command);
com.Send(command);
}
Thread.Sleep(100); //allow 100ms delay for receiving response from serial port

//Send 4th command - 90003
command = "90003";

if (command.Length > 0)
{
command = ConvertEscapeSequences(command);
com.Send(command);
}
Thread.Sleep(100); //allow 100ms delay for receiving response from serial port

//Send 5th command - 90004
command = "90004";

if (command.Length > 0)
{
command = ConvertEscapeSequences(command);
com.Send(command);
}
Thread.Sleep(100); //allow 100ms delay for receiving response from serial port

//Send 6th command - 90005
command = "90005";

if (command.Length > 0)
{
command = ConvertEscapeSequences(command);
com.Send(command);
}
Thread.Sleep(100); //allow 100ms delay for receiving response from serial port
//Listbox1 eventually contains some (~6) entries
}

但是，当我点击button1时，label1会显示文字No. of items: 0，但Listbox1确实包含6个项目。当Listbox1.Items.Count.ToString()中实际有6个项目时，为什么代码Listbox1会返回0？

Answer 1

你不应该在诸如WaitAll的UI线程上使用阻塞调用，因为这会导致死锁，更好的选择是使用async-await。

有一篇关于async-await here的最佳做法的好文章。

您只能在await mehtod中使用async，因此您需要button1_Click async然后await拨打{{1} }}。

您Apple需要返回await或Task所以Task<T>的返回值所需的方法需要更改为其中之一。您可以使用Apple向线程池发送任何同步阻塞调用，但是必须在将在线程池上运行的Task.Run委托之外的主线程上访问任何GUI元素。

Task.Run

如果您的串口通信api支持public async void button1_Click(object sender, EventArgs e) { label1.Text = "Parsing entries && initializing comms ..."; await Apple(); label1.Text = "No. of items: " + ((Listbox1.Items.Count).ToString()); if (Listbox1.Items.Count >= 2) { Listbox1.SetSelected(1, true); } } public async Task Apple() { await Task.Run(()=> { // serial comms work ... } // add items to list here ... }，即async，您只需SendAsync await次来电，并使用SendAsync进行异步睡眠，不需要await Task.Delay(100)。

如何计算C＃中更新列表框中的条目？

1 个答案: