[英]Safe Multi-thread access in C#
我正在尝试进行聊天。 我在这里取了一个代码
发送邮件时出现错误:
控件“ ListMessage”的名称是从不是在其上创建线程的线程访问的。
其中ListMessage是随Visual Studio添加的ListView。
private void buttonSend_Click(object sender, EventArgs e)
{
//convert string message to byte[]
ASCIIEncoding aEncoding = new ASCIIEncoding();
byte[] sendingMessage = new byte[1500];
sendingMessage = aEncoding.GetBytes(textMessage.Text);
//sending the encoded message
sck.Send(sendingMessage);
//adding to the list box
listMessage.Items.Add("Me:" + textMessage.Text);
textMessage.Text = "";
}
private void MessageCallBack(IAsyncResult aResult)
{
try
{
byte[] receivedData = new byte[1500];
receivedData = (byte[])aResult.AsyncState;
//converting byte[] to string
ASCIIEncoding aEncoding = new ASCIIEncoding();
string receivedMessage = aEncoding.GetString(receivedData);
//Adding this message into list box
///// error is given in the following line/////
listMessage.Items.Add("Friend:" + receivedMessage);
buffer = new byte[1500];
sck.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref epRemote, new AsyncCallback(MessageCallBack), buffer);
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
我尝试按照此处所述使用Invoke,但出现错误
private void MessageCallBack(IAsyncResult aResult)
{
try
{
byte[] receivedData = new byte[1500];
receivedData = (byte[])aResult.AsyncState;
//converting byte[] to string
ASCIIEncoding aEncoding = new ASCIIEncoding();
string receivedMessage = aEncoding.GetString(receivedData);
//Adding this message into list box
//listMessage.Items.Add("Friend:" + receivedMessage);
listMessage.AddItemSafe("Friend:" + receivedMessage);
buffer = new byte[1500];
sck.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref epRemote, new AsyncCallback(MessageCallBack), buffer);
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
private void AddItemSafe(string text)
{
if (this.InvokeRequired)
{
AddItemSafeCallback a = new AddItemSafeCallback(AddItemSafe);
this.Invoke(a, new object[] { text });
}
else
{
this.Items.Add(text);
}
}
delegate void AddItemSafeCallback(string text);
错误是:
我的问题:
是的,这种方法是正确的,但是您在实现中确实错过了一些事情。
该AddItemSafe
方法只是你的形式派生类中的方法,而不是一种方法listMessage
(任何类型而定)。 因此,当您调用它时,只需指定方法名称和参数,而无需在另一个对象实例上调用它。
...
ASCIIEncoding aEncoding = new ASCIIEncoding();
string receivedMessage = aEncoding.GetString(receivedData);
//Adding this message into list box
//listMessage.Items.Add("Friend:" + receivedMessage);
// !!!!Note difference here:
AddItemSafe("Friend:" + receivedMessage);
...
然后,在AddItemSafe方法内部,您可以完全执行在单线程环境中的操作,即添加到listMessage
的项中。 如果需要invoke,则将整个内容包装到一个委托中。
private void AddItemSafe(string text)
{
if (this.InvokeRequired)
{
AddItemSafeCallback a = new AddItemSafeCallback(AddItemSafe);
this.Invoke(a, new object[] { text });
}
else
{
// !!!!Note difference here:
listmessage.Items.Add(text);
}
}
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