public event EventHandler<MyEventArgs> SampleEvent;

public void DemoEvent(string val)
{
// Copy to a temporary variable to be thread-safe.
    EventHandler<MyEventArgs> temp = SampleEvent;

是参考吗？
如果是这样,我不明白它的含义,因为当SampleEvent变为null时,temp也是如此

if (temp != null)
        temp(this,new MyEventArgs(val));
}