WebCast听课录(10)

课程名：Windows应用程序开发入门到精通七：优化.NET异常处理

 

1.多个catch块的情况时会过滤异常，先截获具体的异常，再截获一般的异常，并且这是从编译器的层次就支持的。

2.应该从系统异常(System.ApplicationException)派生自己的具体异常，从而为特定的应用程序提供更好的支持。

3.异常处理技术：1）记录异常：在文件中记录异常；在数据库中记录；在Eventlog中记录。2）发email等信息来通知异常。总之，要以用户友好的方式通知异常的发生。

4.使用Application对象中的ThreadException属性来设置一个delegate来捕获所有未处理的主线程中出现的异常，但并不能处理你自己创建的工作进程中出现的异常。

public static void Main(string[] args)
        {
            Application.ThreadException += new 
                ThreadExceptionEventHandler(
                MainUIThreadExceptionHandler);
        
            
            Demo6();

            System.Windows.Forms.Application.Run(
                new NorthwindMDIMain());
        }

        public static void MainUIThreadExceptionHandler(
            Exception e)
        {
            MainUIThreadExceptionHandler(null, new System.Threading.
                ThreadExceptionEventArgs(e));
        }

        public static void MainUIThreadExceptionHandler(object
            sender, ThreadExceptionEventArgs t)
        {

            ExceptionManager.Publish(t.Exception);

            //Tell the user a boo-boo occurred
            MessageBox.Show(
                "Northwind Orders has encountered the following "
                + " problem:" + (char)13
                + (char)13 + t.Exception.Message
                + (char)13 + (char)13 
                + "Please contact your administrator or the "
                + "Northwind Help desk at "
                + (char)13 + (char)13 +"1-855-555-5555."
                + (char)13 + (char)13 
                + "We apologize for the inconvenience."
                , "Northwind Orders Encountered a Problem"
                , MessageBoxButtons.OK
                , MessageBoxIcon.Error
                , MessageBoxDefaultButton.Button1 
                , MessageBoxOptions.ServiceNotification);        
        }

5，必须考虑在工作线程中出现的异常，在线程的入口使用try-catch,并且使用delegate等方式将异常通知给主线程，此外，线程之间要访问对方的界面成员时，应该通过BeginInvoke（）方法来进行。

        public delegate void DoneDelegate(bool Stopped);
        public delegate void
            WorkerThreadExceptionHandlerDelegate(Exception e);
        void WorkerThreadExceptionHandler(Exception e)
        {
            UpdateProgress();
            SetStatusText("Problem Encountered");
            this.Text = "Customers";
            btnSave.Text = "Save";
            btnClose.Enabled = true;
            
            //Call the global exception handler
            MainClass.MainUIThreadExceptionHandler(
                this, new System.Threading.
                ThreadExceptionEventArgs(e));
        }
        private void btnSave_Click(object sender, System.EventArgs e)
        {
            try
            {
                if(true==btnSave.Enabled)
                {
                    this.Text = "Customers (Saving)";
                    btnSave.Enabled=false;
                    btnClose.Enabled=false;
                    System.Threading.Thread t = 
                        new System.Threading.Thread( 
                        new System.Threading.ThreadStart(
                        SaveCustomer));
                    t.Start();
                }
                else
                {
                    isCanceled = true;
                    btnSave.Enabled = true;
                }        
            }
            catch(NotSupportedException exception)
            {
                MessageBox.Show("Code not done yet "
                    + exception.Message 
                    );
            }
            catch(Exception exception)
            {
                //Tell the user a boo-boo occurred
                MainClass.MainUIThreadExceptionHandler(this
                    ,new System.Threading.
                    ThreadExceptionEventArgs(exception));
                MessageBox.Show(
                    "Northwind Orders has encountered a problem.  "
                    + "Please contact your administrator or the "
                    + "Northwind Help desk at "
                    + (char)13 + (char)13 +"1-855-555-5555."
                    + (char)13 + (char)13 
                    + "We apologize for the inconvenience."
                    , "Northwind Orders Encountered a Problem"
                    , MessageBoxButtons.OK
                    , MessageBoxIcon.Error);
            }
            finally
            {
                this.Cursor=Cursors.Default;
            }
        }
        private void SaveCustomer()
        {
            try
            {
                SetStatusText(
                    "Saving record on a background thread");

                //TODO:  Add code to save the customer record
                this.BindingContext[dsCustomers,"Customers"].
                    EndCurrentEdit();
                dsCustomers objDataSetChanges = ((dsCustomers)
                    (dsCustomers.GetChanges()));
                if(null!=objDataSetChanges)
                    new NorthwindDataAccess().UpdateCustomers(
                        objDataSetChanges);

                isCanceled = false;
                DoneDelegate delDone = new DoneDelegate(Done);
                delDone.BeginInvoke(isCanceled, null, null);

            }
            catch(Exception e)
            {
                new WorkerThreadExceptionHandlerDelegate(
                    WorkerThreadExceptionHandler).BeginInvoke(e
                    ,null
                    ,null);
            }
        }
    private void Done (bool Stopped)
        {

            UpdateProgress();
            this.Text = "Customers";
            btnSave.Enabled=true;
            btnClose.Enabled=true;
            if(Stopped)
            {
                MessageBox.Show("Save Stopped"
                    , "Stopped"
                    , MessageBoxButtons.OK
                    , MessageBoxIcon.Warning);
                SetStatusText("Save Stopped");
            }
            else
            {
                MessageBox.Show("Save Done"
                    , "Done" 
                    , MessageBoxButtons.OK 
                    , MessageBoxIcon.Information);
                SetStatusText("Save Done");
            }
        }

6，在构造函数中不要加try-catch，因为这会把异常再抛给外部方法，还不如不处理，直接抛给外部好了。

7，异常处理程序块采用的是publisher/subscriber设计模式，在工程中添加对它的引用，并引入名称空间Microsoft.ApplicationBlocks.ExceptionManagement就可以使用ExceptionManager.Publish()来进行异常的发布。在app.config中可以对异常管理进行启/停，还可以添加自己的异常处理模块。

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
        <section name="exceptionManagement" 
                type="Microsoft.ApplicationBlocks.ExceptionManagement.ExceptionManagerSectionHandler,Microsoft.ApplicationBlocks.ExceptionManagement" />
    </configSections>

    <exceptionManagement mode="on">        
        <publisher mode="on" assembly="Microsoft.ApplicationBlocks.ExceptionManagement" 
          type="Microsoft.ApplicationBlocks.ExceptionManagement.DefaultPublisher" 
          logname="Northwind Exceptions Log" 
          applicationname="Northwind Traders Orders" />
    </exceptionManagement>

</configuration>

    public static void MainUIThreadExceptionHandler(object
            sender, ThreadExceptionEventArgs t)
        {

            ExceptionManager.Publish(t.Exception);

            //Tell the user a boo-boo occurred
            MessageBox.Show(
                "Northwind Orders has encountered the following "
                + " problem:" + (char)13
                + (char)13 + t.Exception.Message
                + (char)13 + (char)13 
                + "Please contact your administrator or the "
                + "Northwind Help desk at "
                + (char)13 + (char)13 +"1-855-555-5555."
                + (char)13 + (char)13 
                + "We apologize for the inconvenience."
                , "Northwind Orders Encountered a Problem"
                , MessageBoxButtons.OK
                , MessageBoxIcon.Error
                , MessageBoxDefaultButton.Button1 
                , MessageBoxOptions.ServiceNotification);        
        }

可以在“事件查看器”中看到异常已经发布进来了：