當執行緒發生例外時會去觸發ErrorEvent事件
若再catch中直接呼叫 this.ErrorEvent(this, new EventArgs()); 則會發生(InvalidOperationException)例外
(呼叫執行緒無法存取此物件，因為此物件屬於另一個執行緒)
因為Label1在主執行緒中被建立，所以不能被子執行緒直接呼叫。
因此我們可以透過Dispatcher物件來處理這個問題
class MainForm : Form
{
private A _a = new A();
void Main()
{
_a.ErrorEvent += new EventHandler(Alert);
A.Start();
}
privaet void Alert(object sender, EventArgs e)
{
Label1.Text = "發生例外了!!";
}
}
class A
{
private Thread _thread = null;
private Dispatcher dispatcher = Dispatcher.CurrentDispatcher;
public event EventHandler ErrorEvent;
public void Start()
{
if (_thread == null)
{
_thread = new Thread(new ThreadStart(ThreadMethod));
_thread.Start();
}
}
private void ThreadMethod()
{
try
{
// do something;
}
catch (Exception ex)
{
//if (this.ErrorEvent != null) this.ErrorEvent(this, new EventArgs()); <= 錯誤
if (this.ErrorEvent != null) dispatcher.BeginInvoke(this.ErrorEvent, this, new EventArgs()); <= 正確
}
}
}
