Question

C#中异步回调的问题（回调函数返回值调用）。??如何将tag_mreade的str传递给 carlist？？(代码如下)

private void btn_rtag_Click(object sender, EventArgs e)
{//利用异步回调获取标签
string carlist;
bool b_tag=true;
Tag_reader tr;
tr = new Tag_reader(tag_mreade);
IAsyncResult tg = tr.BeginInvoke(b_tag, TagReadCompleted,tr);
do
{
textBox1.Text = textBox1.Text + ".";
}
while (!tg.IsCompleted);
//??如何将tag_mreade的str传递给 carlist？？
textBox1.AppendText( carlist);
}

private delegate string Tag_reader(bool bl_cmdd);
private string tag_mreade(bool bl_cmd)
{
string str;
try
{
if (bl_cmd)
{
str = card.TagList;//
}
else { str = "查看tag_reade的布尔值，未进行读取"; }
return str;
}
catch (Exception e1) { return e1.Message.ToString(); }
}
private void TagReadCompleted(IAsyncResult asyncResult)
{//回调函数
string str_tags;
if (asyncResult == null) {str_tags= ""; }
str_tags = (asyncResult.AsyncState as Tag_reader).EndInvoke(asyncResult);
}

Answer 1

你这写法根本都不对，EndInvoke怎么写到回调函数里去了
判断执行完不需要while循环判断，直接执行EndInvoke最自动阻塞，EndInvoke的参数里就有返回值可以解决你这问题

仔细看看：
http://msdn.microsoft.com/zh-cn/library/2e08f6yc.aspx