我知道在C#中,有几个内置事件会传递一个参数 ("Cancel") ,如果设置为true,则会停止引发事件的对象的进一步执行。
您如何实现一个事件,使得引发事件的对象能够跟踪 EventArgs 中的属性呢?
以下是一个 WinForms 示例,展示了我要实现的功能:
http://msdn.microsoft.com/en-us/library/system.componentmodel.canceleventargs.cancel.aspx
谢谢。
我知道在C#中,有几个内置事件会传递一个参数 ("Cancel") ,如果设置为true,则会停止引发事件的对象的进一步执行。
您如何实现一个事件,使得引发事件的对象能够跟踪 EventArgs 中的属性呢?
以下是一个 WinForms 示例,展示了我要实现的功能:
http://msdn.microsoft.com/en-us/library/system.componentmodel.canceleventargs.cancel.aspx
谢谢。
非常简单。
private event _myEvent;
// ...
// Create the event args
CancelEventArgs args = new CancelEventArgs();
// Fire the event
_myEvent.DynamicInvoke(new object[] { this, args });
// Check the result when the event handler returns
if (args.Cancel)
{
// ...
}
以下是我避免在一个订阅者取消后继续调用其他订阅者的方法:
var tmp = AutoBalanceTriggered;
if (tmp != null)
{
var args = new CancelEventArgs();
foreach (EventHandler<CancelEventArgs> t in tmp.GetInvocationList())
{
t(this, args);
if (args.Cancel) // a client cancelled the operation
{
break;
}
}
}
public class Program
{
private static List<EventHandler<CancelEventArgs>> SubscribersList = new List<EventHandler<CancelEventArgs>>();
public static event EventHandler<CancelEventArgs> TheEvent
{
add {
if (!SubscribersList.Contains(value))
{
SubscribersList.Add(value);
}
}
remove
{
if (SubscribersList.Contains(value))
{
SubscribersList.Remove(value);
}
}
}
public static void RaiseTheEvent(object sender, CancelEventArgs cancelArgs)
{
foreach (EventHandler<CancelEventArgs> sub in SubscribersList)
{
sub(sender, cancelArgs);
// Stop the Execution after a subscriber cancels the event
if (cancelArgs.Cancel)
{
break;
}
}
}
static void Main(string[] args)
{
new Subscriber1();
new Subscriber2();
Console.WriteLine("Program: Raising the event");
CancelEventArgs cancelArgs = new CancelEventArgs();
RaiseTheEvent(null, cancelArgs);
if (cancelArgs.Cancel)
{
Console.WriteLine("Program: The Event was Canceled");
}
else
{
Console.WriteLine("Program: The Event was NOT Canceled");
}
Console.ReadLine();
}
}
public class Subscriber1
{
public Subscriber1()
{
Program.TheEvent += new EventHandler<CancelEventArgs>(program_TheEvent);
}
void program_TheEvent(object sender, CancelEventArgs e)
{
Console.WriteLine("Subscriber1: in program_TheEvent");
Console.WriteLine("Subscriber1: Canceling the event");
e.Cancel = true;
}
}
public class Subscriber2
{
public Subscriber2()
{
Program.TheEvent += new EventHandler<CancelEventArgs>(program_TheEvent);
}
void program_TheEvent(object sender, CancelEventArgs e)
{
Console.WriteLine("Subscriber2: in program_TheEvent");
}
}
简单易懂:
您需要代码示例吗?
你需要等待调用引发事件并在你的EventArgs(特别是CancelEventArgs)中检查标志。
args.Cancel
设为 true,第二个将args.Cancel
设为 false,那么结果是args.Cancel==false
吗? - thersch