{"id":1370,"date":"2023-04-04T10:18:04","date_gmt":"2023-04-04T03:18:04","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1370"},"modified":"2023-04-04T10:28:49","modified_gmt":"2023-04-04T03:28:49","slug":"csharp-custom-exceptions","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-custom-exceptions\/","title":{"rendered":"C# Custom Exceptions"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about C# custom exceptions and how to create and use a custom exception in your program.<\/p>\n\n\n\n

Introduction to the C# custom exceptions<\/h2>\n\n\n\n

C# provides you with many built-in exception classes. Sometimes, these built-in exception classes are not sufficient to describe the error in your application. In this case, you can define custom exception classes.<\/p>\n\n\n\n

By definition, a custom exception is an exception that you create to represent a specific error in your application.<\/p>\n\n\n\n

To create a custom exception, you define a class that inherits from the System.Exception<\/code> class. By convention, an exception class ends with Exception<\/code> like MyCustomException<\/code>:<\/p>\n\n\n

class<\/span> MyCustomException<\/span>: Exception<\/span>\n{\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
A custom exception class should have three standard constructors:<\/p>\n\n\n
class<\/span> MyCustomException<\/span>: Exception<\/span>\n{\n    MyCustomException(): base<\/span>() { }\n    MyCustomException(string<\/span> message) : base<\/span>(message) { }\n    MyCustomException(string<\/span> message, Exception innerException) : base<\/span>(message, innerException) { }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example:<\/p>\n\n\n\n
    \n
  • The first constructor is a default constructor that takes no arguments. <\/li>\n\n\n\n
  • The second constructor takes a string message that describes the exception. <\/li>\n\n\n\n
  • The third constructor takes both a message and an inner exception, which you can use to chain exceptions together to describe the error in more detail.<\/li>\n<\/ul>\n\n\n\n
    A custom exception class may also have additional properties to provide more information about the error that occurs.<\/p>\n\n\n\n
    C# custom exception example<\/h2>\n\n\n\n
    Let’s take a look at an example of using a custom exception.<\/p>\n\n\n
    using<\/span> static<\/span> System.Console;\n\npublic<\/span> class<\/span> Account<\/span>\n{\n    private<\/span> decimal<\/span> balance;\n    public<\/span> decimal<\/span> Balance => balance;\n\n    public<\/span> Account<\/span>(decimal<\/span> initialBalance = 0<\/span><\/span>)<\/span>\n    {\n        if<\/span> (initialBalance < 0<\/span>)\n        {\n            throw<\/span> new<\/span> ArgumentOutOfRangeException($\"The {nameof<\/span>(initialBalance)}<\/span> must be zero or positive.\"<\/span>);\n        }\n        balance = initialBalance;\n    }\n\n    public<\/span> Account Withdraw<\/span>(decimal<\/span> amount<\/span>)<\/span>\n    {\n        if<\/span> (amount > Balance)\n        {\n            throw<\/span> new<\/span> ArgumentOutOfRangeException(\n                nameof<\/span>(amount),\n                $\"Could not withdraw an amount ({amount:C}<\/span>) that is more than balance ({Balance:C}<\/span>)\"<\/span>\n            );\n        }\n\n        balance -= amount;\n        return<\/span> this<\/span>;\n    }\n    public<\/span> Account Deposit<\/span>(decimal<\/span> amount<\/span>)<\/span>\n    {\n        if<\/span> (amount <= 0<\/span>)\n        {\n            throw<\/span> new<\/span> ArgumentOutOfRangeException(nameof<\/span>(amount));\n        }\n        balance += amount;\n        return<\/span> this<\/span>;\n    }\n}\n\npublic<\/span> class<\/span> Program<\/span>\n{\n    public<\/span> static<\/span> void<\/span> Main<\/span>(string<\/span>[] args<\/span>)<\/span>\n    {\n\n        var<\/span> account = new<\/span> Account(100<\/span>);\n        try<\/span>\n        {\n            account.Withdraw(200<\/span>);\n        }\n        catch<\/span> (ArgumentOutOfRangeException ex)\n        {\n            WriteLine(ex.Message);\n        }\n        catch<\/span> (Exception ex)\n        {\n            WriteLine(ex.Message);\n        }\n\n        ReadLine();\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Output:<\/p>\n\n\n
    Could not withdraw an amount<\/span> ($200.00<\/span><\/span>) that exceeds the balance<\/span> ($100.00<\/span><\/span>) (Parameter 'amount'<\/span><\/span>)<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    How it works.<\/p>\n\n\n\n
    First, define an Account<\/code> class that represents a bank account with a balance. The Account<\/code> class has two methods for depositing and withdrawing money. These methods use a built-in exception class ArgumentOutOfRangeException<\/code> to prevent invalid operations.<\/p>\n\n\n\n
    Second, create a new Account<\/code> object in the Main()<\/code> method of the Program<\/code> class with an initial balance of 100. Then, attempt to withdraw 200 from the account using the Withdraw()<\/code> method. <\/p>\n\n\n\n
    Because the balance is insufficient, the Withdraw()<\/code> method throws an ArgumentOutOfRangeException<\/code>. <\/p>\n\n\n\n
    The catch block handles the ArgumentOutOfRangeException<\/code> exception by displaying the error message on the console.<\/p>\n\n\n\n
    The program works fine except that the ArgumentOutOfRangeException<\/code> is not very expressive and the error message doesn’t show the deficit.<\/p>\n\n\n\n
    To improve this, we can create a new custom exception as follows:<\/p>\n\n\n
    using<\/span> static<\/span> System.Console;\n\npublic<\/span> class<\/span> InsufficientFundException<\/span> : Exception<\/span>\n{\n    public<\/span> decimal<\/span> Deficit\n    {\n        get<\/span>;\n        set<\/span>;\n    }\n    public<\/span> InsufficientFundException<\/span>(<\/span>)\n        : base<\/span>(<\/span>)<\/span>\n    {\n    }\n\n    public<\/span> InsufficientFundException<\/span>(\n        string<\/span> message\n    <\/span>)\n        : base<\/span>(message<\/span>)<\/span>\n    {\n    }\n\n    public<\/span> InsufficientFundException<\/span>(\n      string<\/span> message,\n      Exception innerException\n  <\/span>) : base<\/span>(message, innerException<\/span>)<\/span>\n    {\n\n    }\n\n    public<\/span> InsufficientFundException<\/span>(decimal<\/span> deficit<\/span>)<\/span>\n    {\n        Deficit = deficit;\n    }\n\n\n    public<\/span> override<\/span> string<\/span> Message =>\n         $\"{base<\/span>.Message}<\/span> Could not withdraw due to a deficit of {Deficit:C}<\/span>\"<\/span>;\n\n\n}\npublic<\/span> class<\/span> Account<\/span>\n{\n\n    private<\/span> decimal<\/span> balance;\n    public<\/span> decimal<\/span> Balance => balance;\n\n    public<\/span> Account<\/span>(decimal<\/span> initialBalance = 0<\/span><\/span>)<\/span>\n    {\n        if<\/span> (initialBalance < 0<\/span>)\n        {\n            throw<\/span> new<\/span> ArgumentOutOfRangeException($\"The {nameof<\/span>(initialBalance)}<\/span> must be zero or positive.\"<\/span>);\n        }\n        balance = initialBalance;\n    }\n\n    public<\/span> Account Withdraw<\/span>(decimal<\/span> amount<\/span>)<\/span>\n    {\n        if<\/span> (amount > Balance)\n        {\n            var<\/span> deficit = amount - Balance;\n            throw<\/span> new<\/span> InsufficientFundException(deficit);\n\n        }\n\n        balance -= amount;\n        return<\/span> this<\/span>;\n    }\n    public<\/span> Account Deposit<\/span>(decimal<\/span> amount<\/span>)<\/span>\n    {\n        if<\/span> (amount <= 0<\/span>)\n        {\n            throw<\/span> new<\/span> ArgumentOutOfRangeException(nameof<\/span>(amount));\n        }\n        balance += amount;\n        return<\/span> this<\/span>;\n    }\n}\n\npublic<\/span> class<\/span> Program<\/span>\n{\n    public<\/span> static<\/span> void<\/span> Main<\/span>(string<\/span>[] args<\/span>)<\/span>\n    {\n\n        var<\/span> account = new<\/span> Account(100<\/span>);\n        try<\/span>\n        {\n            account.Withdraw(200<\/span>);\n        }\n        catch<\/span> (InsufficientFundException ex)\n        {\n            WriteLine(ex.Message);\n        }\n        catch<\/span> (Exception ex)\n        {\n            WriteLine(ex.Message);\n        }\n\n        ReadLine();\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Output:<\/p>\n\n\n
    Exception of type 'InsufficientFundException'<\/span> was thrown. Could not withdraw due to a deficit of $100.00<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    How it works.<\/p>\n\n\n\n
    First, define a new custom exception class named InsufficientFundException<\/code> that inherits from the Exception<\/code> class. <\/p>\n\n\n
    public<\/span> class<\/span> InsufficientFundException<\/span> : Exception<\/span>\n{\n    public<\/span> decimal<\/span> Deficit\n    {\n        get<\/span>;\n        set<\/span>;\n    }\n    public<\/span> InsufficientFundException<\/span>(<\/span>)\n        : base<\/span>(<\/span>)<\/span>\n    {\n    }\n\n    public<\/span> InsufficientFundException<\/span>(\n        string<\/span> message\n    <\/span>)\n        : base<\/span>(message<\/span>)<\/span>\n    {\n    }\n\n    public<\/span> InsufficientFundException<\/span>(\n      string<\/span> message,\n      Exception innerException\n  <\/span>) : base<\/span>(message, innerException<\/span>)<\/span>\n    {\n\n    }\n\n    public<\/span> InsufficientFundException<\/span>(decimal<\/span> deficit<\/span>)<\/span>\n    {\n        Deficit = deficit;\n    }\n\n\n    public<\/span> override<\/span> string<\/span> Message =>\n         $\"{base<\/span>.Message}<\/span> Could not withdraw due to a deficit of {Deficit:C}<\/span>\"<\/span>;\n\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    The InsufficientFundException<\/code> class implements three standard constructors. <\/p>\n\n\n\n
    The InsufficientFundException<\/code> class also has a fourth constructor that takes a decimal parameter called deficit<\/code>, which represents the deficit when attempting to withdraw an amount that exceeds the balance. This constructor sets the Deficit<\/code> property to the deficit parameter.<\/p>\n\n\n\n
    The InsufficientFundException<\/code> class extends the Message<\/code> property of the Exception<\/code> class. It concatenates the Message<\/code> of the base class with a custom message that includes the deficit<\/code>.<\/p>\n\n\n\n
    In the Withdraw()<\/code> method of the Account<\/code> class, instead of throwing the ArgumentOutOfRangeException<\/code>, it throws the InsufficientFundException<\/code> exception and pass the deficit<\/code> to its constructor.<\/p>\n\n\n
    public<\/span> Account Withdraw<\/span>(decimal<\/span> amount<\/span>)<\/span>\n{\n    if<\/span> (amount > Balance)\n    {\n        var<\/span> deficit = amount - Balance;\n        throw<\/span> new<\/span> InsufficientFundException(deficit);\n    }\n\n    balance -= amount;\n    return<\/span> this<\/span>;\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    In the Main<\/code> method of the Program<\/code> class, instead of catching the ArgumentOutOfRangeException<\/code><\/code> exception, we catch the ArgumentOutOfRangeException<\/code><\/code> and display the error message on the console:<\/p>\n\n\n
    public<\/span> class<\/span> Program<\/span>\n{\n    public<\/span> static<\/span> void<\/span> Main<\/span>(string<\/span>[] args<\/span>)<\/span>\n    {\n        var<\/span> account = new<\/span> Account(100<\/span>);\n        try<\/span>\n        {\n            account.Withdraw(200<\/span>);\n        }\n        catch<\/span> (ArgumentOutOfRangeException ex)\n        {\n            WriteLine(ex.Message);\n        }\n        catch<\/span> (Exception ex)\n        {\n            WriteLine(ex.Message);\n        }\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
    Summary<\/h2>\n\n\n\n
      \n
    • Only create a custom class exception class if it provides more meaningful and detailed information about the error in your application.<\/li>\n\n\n\n
    • Extend the built-in System.Exception<\/code> class to define a custom exception class.<\/li>\n\n\n\n
    • Throw a custom exception by using the throw<\/code> keyword followed by the custom exception object.<\/li>\n\n\n\n
    • Use the try...catch<\/code> block to catch a custom exception by specifying the custom exception type in the catch<\/code> block.<\/li>\n<\/ul>\n
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