EXCEPTION

◎ 常用的 EXCEPTION 的 Field / Function

• System.Exception.Message：錯誤原因
• System.Exception.StackTrace：印出追蹤的錯誤訊息
• System.Exception.GetType().Name：錯誤的類型，e.g：FileNotFoundException、SqlException、FormatException、OverflowException、DivideByZeroException

◎ EXCEPTION 的子類別(Exception的類型)

• System.FileNotFoundException
• System.SqlException
• System.FormatException
• System.OverflowException
• System.DivideByZeroException

◎ 範例程式碼

using OnLineGame;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.Serialization;
using System.Text;
using System.Threading.Tasks;

namespace ExceptionDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //Console.WriteLine("================最簡單的 Exception 範例================");
            //TryCatchSample1();
            //Console.WriteLine("================巢狀 TryCatch================");
            //NestedTryCatch();
            //Console.WriteLine("================自定義屬於自己的 Exception================");
            //NoVpnConnectionSample();

            Console.ReadLine();
        }

        #region 最簡單的 Exception 範例
        public static void TryCatchSample1()
        {
            StreamReader reader = null;
            StreamWriter writer = null;
            try
            {
                // Reader
                reader = new StreamReader(@"D:\0_DeleteMe\Data.txt");
                string readerInputStr = reader.ReadToEnd();
                Console.WriteLine(readerInputStr);
                // Writer.
                string filePath = @"D:\0_DeleteMe\Data2.txt";
                writer = new StreamWriter(filePath);
                writer.Write(readerInputStr);
                writer.Close();
                Console.WriteLine("StreamWriter Updated.");
            }
            catch (FileNotFoundException ex)
            {
                //if the fielPath doesn't exist, throw System.FileNotFoundException
                Console.WriteLine("{0} can not be found. Please create it.\n", ex.FileName);
                Console.WriteLine("Exception Message : {0} \n", ex.Message);
                Console.WriteLine("Stack Trace : {0} \n", ex.StackTrace);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                Console.WriteLine(ex.StackTrace);
            }
            finally
            {
                //if (reader != null)
                //{
                //    reader.Close();
                //}
                reader?.Close();
            }
        }
        #endregion

        #region 巢狀 TryCatch
        public static void NestedTryCatch()
        {
            try
            {
                try
                {
                    Console.WriteLine("請輸入被除數：");
                    int dividend = Convert.ToInt32(Console.ReadLine());
                    Console.WriteLine("請輸入除數：");
                    int divisor = Convert.ToInt32(Console.ReadLine());

                    int quotient = dividend / divisor;
                    Console.WriteLine("計算結果 = {0}", quotient);
                }
                catch (Exception ex)
                {
                    //「\n」代表換行 for Console
                    //ex.GetType().Name會回傳是什麼樣類型的錯誤，e.g：FormatException、OverflowException、DivideByZeroException
                    Console.WriteLine("Exception : {0} \nMessage : {1} \nStackTrace : {2} \n", ex.GetType().Name, ex.Message, ex.StackTrace);

                    #region 產生 log 檔案
                    string filePath = @"D:\0_DeleteMe\Log.txt";
                    if (File.Exists(filePath))
                    {
                        #region 若 Log 檔案存在，則繼續往下寫
                        StreamWriter writer = new StreamWriter(filePath);
                        //「\r\n」代表換行 for Console for file，「r」means return,n means new line.
                        writer.Write("Exception : {0} \r\nMessage : {1} \r\nStackTrace : {2} \r\n", ex.GetType().Name, ex.Message, ex.StackTrace);
                        writer.Close();
                        Console.WriteLine("Error Log 已更新!!!");
                        #endregion
                    }
                    else
                    {
                        //拋出一個 FileNotFoundException 類型的錯誤給 外面的 catch 接
                        throw new FileNotFoundException(filePath + " does not Exist, please create it. \n", ex);
                    }
                    #endregion
                }
            }
            catch (Exception ex)
            {
                //outer Try Catch Clause
                //ex.Message return the current exception message from outer Try Catch Clause.
                Console.WriteLine("Current Exception Message from outer Try Catch Clause : {0} \n", ex.Message);
                //if the writer filePath doesn't exist, here will catch System.FileNotFoundException
                //inner Try Catch Clause
                //ex.InnerException.Message return the exception message from inner Try Catch Clause.
                //if ex.InnerException is exist then print it.
                if (ex.InnerException != null)
                {
                    Console.WriteLine("Exception Message From Inner Try Catch Clause : {0} \n", ex.InnerException.Message);
                }
                // E.g.1.
                // Enter "A" will cause System.FormatException
                // E.g.2.
                // Enter "12345678901" will cause System.OverflowException
                // E.g.3.
                // Enter "0" in Divisor will cause System.DivideByZeroException
            }
        }
        #endregion

        #region 自定義屬於自己的 Exception 
        public static void NoVpnConnectionSample()
        {
            try
            {
                throw new NoVpnConnectionException("User is using vpn");
            }
            catch (NoVpnConnectionException ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
        #endregion
    }
}

#region 自定義自己的 Exception
// 3. -------------------------------------------------------------
// Custom Exceptions
//Sometimes there is no existing system exception can fit your situation.
//In this case, you might have to create your own Customize Exceptions.
namespace OnLineGame
{
    //The Customize Exceptions must extend the System.Exception class.
    //In addition the suffix should be "Exception" to fulfill the naming convention.
    [Serializable]
    public class NoVpnConnectionException : Exception
    {
        // The Customize Exceptions should always provide a public constructor
        //which take a string message parameter,
        //and then pass it to base class constructor.
        public NoVpnConnectionException(string message)
            : base(message)
        {
        }
        //The Customize Exceptions should always provide the capability to handle inner exception.
        public NoVpnConnectionException(string message, Exception innerException)
            : base(message, innerException)
        {
        }
        //The Customize Exceptions should always support Serializable, thus,
        //it can work across application domains.
        public NoVpnConnectionException(SerializationInfo info, StreamingContext context)
            : base(info, context)
        {
        }
    }
}
#endregion