如何显式引发异常

可使用 C# throw 或 Visual Basic Throw 语句显式引发异常。 可使用 throw 语句再次引发捕获的异常。 在编码方面，建议向再次引发的异常添加信息以在调试时提供详细信息。

下方代码示例使用 try/catch 块来捕获可能的 FileNotFoundException。 以下 try 块为可捕获 FileNotFoundException 并在未找到数据文件时将消息写入控制台的 catch 块。 下一语句为 throw 语句，可引发新的 FileNotFoundException 并向异常添加文本信息。

var fs = default(FileStream);
try
{
    // Opens a text tile.
    fs = new FileStream(@"C:\temp\data.txt", FileMode.Open);
    var sr = new StreamReader(fs);

    // A value is read from the file and output to the console.
    string? line = sr.ReadLine();
    Console.WriteLine(line);
}
catch (FileNotFoundException e)
{
    Console.WriteLine($"[Data File Missing] {e}");
    throw new FileNotFoundException(@"[data.txt not in c:\temp directory]", e);
}
finally
{
    if (fs != null)
        fs.Close();
}

Option Strict On

Imports System.IO

Public Class ProcessFile

    Public Shared Sub Main()
        Dim fs As FileStream = Nothing
        Try
            ' Opens a text file.
            fs = New FileStream("c:\temp\data.txt", FileMode.Open)
            Dim sr As New StreamReader(fs)

            ' A value is read from the file and output to the console.
            Dim line As String = sr.ReadLine()
            Console.WriteLine(line)
        Catch e As FileNotFoundException
            Console.WriteLine($"[Data File Missing] {e}")
            Throw New FileNotFoundException("[data.txt not in c:\temp directory]", e)
        Finally
            If fs IsNot Nothing Then fs.Close()
        End Try
    End Sub
End Class

请参阅

• 异常