参考文章:http://blog.csdn.net/lastinglate/article/details/5753113
如果您正在设计可取消的事件,请使用CancelEventArgs(而非是EventArgs)作为事件数据对象e的基类。
使用场景:订阅者可以通过e.Cancle来控制发布者引发事件的方法是否被执行!类似窗体的Form_Closing事件机制。
顺便有关静态事件链的实现,可以参考:https://cloud.tencent.com/developer/article/1341529
/1.自定义EventArgs类,封装事件参数信息
public class ActionCancelEventArgs:System.ComponentModel.CancelEventArgs
{
private string message;
public ActionCancelEventArgs() : this(false) { }
public ActionCancelEventArgs(bool cancel) : this(false, String.Empty) { }
public ActionCancelEventArgs(bool cancel, string message) : base(cancel) {
this.message = message;
}
public string Message { get; set; }
}
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//2.定义委托
public delegate void ActionEventHandler(object sender, ActionCancelEventArgs ev);
//3.声明事件(用到委托类型)
public static event ActionEventHandler Action;
//4.定义事件处理函数
protected void OnAction(object sender, ActionCancelEventArgs ev)
{
if (Action != null)
{
Action(sender, ev);
}
}
//注册事件处理程序
public class BusEntity
{
string time = String.Empty;
public BusEntity() {
//将事件处理程序添加到事件
Form1.Action += new Form1.ActionEventHandler(Form1_Action);
}
private void Form1_Action(object sender, ActionCancelEventArgs e) {
e.Cancel = !DoActions();
if (e.Cancel)
{
e.Message = "wasn't the right time.";
}
}
private bool DoActions() {
bool retVal = false;
DateTime tm = DateTime.Now;
if (tm.Second<30)
{
time = "The time is "+DateTime.Now.ToLongTimeString();
retVal = true;
}
else
{
time = "";
}
return retVal;
}
public string TimeString {
get { return time; }
}
}
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private void btnRaise_Click(object sender, EventArgs e)
{
ActionCancelEventArgs cancelEvent = new ActionCancelEventArgs();
OnAction(this, cancelEvent);
//抛出事件后,将根据询问订阅者是否取消事件的接受e.Cancle=False/True,来执行后续的代码。
if (cancelEvent.Cancel)
{
lblInfo.Text = cancelEvent.Message;
}
else
{
lblInfo.Text = busEntity.TimeString;
}
}