无涯教程-C# - 异常处理异常提供了一种将控制从程序的一个部分转移到另一个部分的方法，C#异常处理基于四个关键字:t

异常提供了一种将控制从程序的一个部分转移到另一个部分的方法，C#异常处理基于四个关键字:try、catch、finally和throw。

try - TRY为其激活特定异常的代码块，后面跟着一个或多个catch块。
catch - catch关键字指示捕获异常。
finally - Finally块用于执行给定的一组语句，无论是否引发异常。例如，如果打开一个文件，则无论是否引发异常，都必须关闭该文件。
throw - 通过使用抛出throw关键字向上抛出异常。

假设块引发异常，则方法使用try和catch关键字的组合捕获异常。try/catch块放置在可能生成异常的代码周围。

try {
   //statements causing exception
} catch( ExceptionName e1 ) {
   //error handling code
} catch( ExceptionName e2 ) {
   //error handling code
} catch( ExceptionName eN ) {
   //error handling code
} finally {
   //statements to be executed
}

可以列出多个catch语句以捕获不同类型的异常，以防try块在不同的情况下引发多个异常。

异常类

C#中的异常类主要直接或间接从System.Exception类派生。System.Exception类派生异常类是System.ApplicationException和System.SystemException。

System.ApplicationException - 支持应用程序生成的异常，因此，程序员定义的异常应该派生自此类。

System.SystemException - 是所有预定义系统异常的基类。

下表提供了从Sytem.SystemException类-派生的一些预定义异常类

Sr.No.	Exception Class & 描述
1	System.IO.IOException 处理I/O错误。
2	System.IndexOutOfRangeException 数组索引超出范围时生成的错误。
3	System.ArrayTypeMismatchException 处理类型与数组类型不匹配时生成的错误。
4	System.NullReferenceException 处理引用空对象产生的错误。
5	System.DivideByZeroException 处理因被除数为零而产生的错误。
6	System.InvalidCastException 处理类型转换期间生成的错误。
7	System.OutOfMemoryException 处理由于可用内存不足而产生的错误。
8	System.StackOverflowException 处理堆栈溢出生成的错误。

处理异常

C#以try和catch块的形式提供了异常处理的解决方案，使用这些块，核心程序语句与错误处理语句分开，以下是在被零除条件发生-时引发异常的示例

using System;
namespace ErrorHandlingApplication {
class DivNumbers {
int result;
  </span><span class="typ">DivNumbers</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     result </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
  </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> division</span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> num1</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">int</span><span class="pln"> num2</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     </span><span class="kwd">try</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
        result </span><span class="pun">=</span><span class="pln"> num1</span><span class="pun">/</span><span class="pln">num2</span><span class="pun">;</span><span class="pln">
     </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">DivideByZeroException</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
        </span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="str">"Exception caught: {0}"</span><span class="pun">,</span><span class="pln"> e</span><span class="pun">);</span><span class="pln">
     </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">finally</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
        </span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="str">"Result: {0}"</span><span class="pun">,</span><span class="pln"> result</span><span class="pun">);</span><span class="pln">
     </span><span class="pun">}</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
  </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="typ">Main</span><span class="pun">(</span><span class="kwd">string</span><span class="pun">[]</span><span class="pln"> args</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     </span><span class="typ">DivNumbers</span><span class="pln"> d </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">DivNumbers</span><span class="pun">();</span><span class="pln">
     d</span><span class="pun">.</span><span class="pln">division</span><span class="pun">(</span><span class="lit">25</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">);</span><span class="pln">
     </span><span class="typ">Console</span><span class="pun">.</span><span class="typ">ReadKey</span><span class="pun">();</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">

}
}

编译并执行上述代码时，将生成以下输出-

Exception caught: System.DivideByZeroException: Attempted to divide by zero. 
at ...
Result: 0

自定义异常

您还可以定义自己的异常，用户定义的异常类派生自Exception类。以下示例演示了此-

using System;
namespace UserDefinedException {
class TestTemperature {
static void Main(string[] args) {
Temperature temp = new Temperature();
try {
temp.showTemp();
} catch(TempIsZeroException e) {
Console.WriteLine("TempIsZeroException: {0}", e.Message);
}
Console.ReadKey();
}
}
}
public class TempIsZeroException: Exception {
public TempIsZeroException(string message): base(message) {
}
}
public class Temperature {
int temperature = 0;
public void showTemp() {
  </span><span class="kwd">if</span><span class="pun">(</span><span class="pln">temperature </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     </span><span class="kwd">throw</span><span class="pln"> </span><span class="pun">(</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">TempIsZeroException</span><span class="pun">(</span><span class="str">"Zero Temperature found"</span><span class="pun">));</span><span class="pln">
  </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">else</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     </span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="str">"Temperature: {0}"</span><span class="pun">,</span><span class="pln"> temperature</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">

}
}

编译并执行上述代码时，将生成以下输出-

TempIsZeroException: Zero Temperature found

抛出异常

如果对象是直接或间接从System.Exception类派生的，则可以引发该对象，可以在catch块中使用throw语句将当前异常向外抛出。

Catch(Exception e) {
   ...
   Throw e
}

无涯教程-C# - 异常处理

异常类

处理异常

自定义异常

抛出异常

参考链接