C＃| Convert.FromBase64String(String)方法

此方法用于将指定的字符串转换为等效的8位无符号整数数组，该字符串将二进制数据编码为以64位为基数。

句法：

public static byte[] FromBase64String (string s);

在这里， s是要转换的字符串。

返回值：该方法返回一个与s等效的8位无符号整数数组。

例外情况

• ArgumentNullException ：如果s为null。
• FormatException ：如果s的长度(不包括空格字符)不为零或4的倍数，或者s的格式无效。 s包含非基本-64字符，两个以上的填充字符，或填充字符之间的非空白字符。

下面的程序说明了Convert.FromBase64String(String)方法的用法：

范例1：

// C# program to demonstrate the
// Convert.FromBase64String(String) Method
using System;
  
class GFG {
  
    // Main Method
    public static void Main()
    {
        try {
  
            // defining and initializing
            // byte1 and byte2
            byte[] byte1 = {2, 4, 6, 8, 10, 
                       12, 14, 16, 18, 20};
  
            byte[] byte2 = {10, 20, 30, 
                                40, 50};
            
            // calling get() Method
            get(byte1, "byte1");
  
            Console.WriteLine("");
            get(byte2, "byte2");
        }
  
        catch (ArgumentNullException e) {
  
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
  
        catch (FormatException e) {
  
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), 
                                  e.Message);
        }
    }
  
    // Defining get() method
    public static void get(byte[] bytes, string str)
    {
  
        Console.WriteLine("For {0}", str);
  
        // converting byte to base 64 string
        string s = Convert.ToBase64String(bytes);
  
        Console.WriteLine("The base 64 string: '{0}'", s);
        Console.WriteLine("The base 64 string: '{0}'", s);
  
        // converting base 64 string to byte array
        byte[] val = Convert.FromBase64String(s);
        Console.WriteLine("Converted byte value: {0}", 
                          BitConverter.ToString(val));
    }
}

输出：

For byte1
The base 64 string: 'AgQGCAoMDhASFA=='
The base 64 string: 'AgQGCAoMDhASFA=='
Converted byte value: 02-04-06-08-0A-0C-0E-10-12-14

For byte2
The base 64 string: 'ChQeKDI='
The base 64 string: 'ChQeKDI='
Converted byte value: 0A-14-1E-28-32

示例2：对于ArgumentNullException

// C# program to demonstrate the
// Convert.FromBase64String(String) Method
using System;
  
class GFG {
  
    // Main Method
    public static void Main()
    {
        try {
  
            // defining and initializing
            // byte1 and byte2
            byte[] byte1 = {2, 4, 6, 8, 10, 12,
                               14, 16, 18, 20};
  
            // calling get() Method
            get(byte1, "byte1");
            Console.WriteLine("");
  
            // converting base 64 string to byte array
            Console.WriteLine("s is null");
  
            byte[] val = Convert.FromBase64String(null);
            Console.WriteLine("Converted byte value: {0}",
                              BitConverter.ToString(val));
        }
        catch (ArgumentNullException e) {
  
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
        catch (FormatException e) {
  
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
    }
  
    // Defining get() method
    public static void get(byte[] bytes, string str)
    {
  
        Console.WriteLine("For {0}", str);
  
        // converting byte to base 64 string
        string s = Convert.ToBase64String(bytes);
        Console.WriteLine("The base 64 string: '{0}'", s);
  
        // converting base 64 string to byte array
        byte[] val = Convert.FromBase64String(s);
        Console.WriteLine("Converted byte value: {0}", 
                          BitConverter.ToString(val));
    }
}

输出：

For byte1
The base 64 string: 'AgQGCAoMDhASFA=='
Converted byte value: 02-04-06-08-0A-0C-0E-10-12-14

s is null
Exception Thrown: System.ArgumentNullException

示例3：对于FormatException

// C# program to demonstrate the
// Convert.FromBase64String(String) Method
using System;
  
class GFG {
  
    // Main Method
    public static void Main()
    {
  
        try {
  
            // defining and initializing 
            // byte1 and byte2
            byte[] byte1 = {2, 4, 6, 8, 10, 
                       12, 14, 16, 18, 20};
  
            // calling get() Method
            get(byte1, "byte1");
            Console.WriteLine("");
  
            // converting base 64 
            // string to byte array
            Console.WriteLine("s contains a non-base-64 character");
  
            byte[] val = Convert.FromBase64String("sun");
            Console.WriteLine("Converted byte value: {0}", 
                              BitConverter.ToString(val));
        }
        catch (ArgumentNullException e) {
  
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
        catch (FormatException e) {
  
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
    }
  
    // Defining get() method
    public static void get(byte[] bytes, string str)
    {
  
        Console.WriteLine("For {0}", str);
  
        // converting byte to base 64 string
        string s = Convert.ToBase64String(bytes);
        Console.WriteLine("The base 64 string: '{0}'", s);
  
        // converting base 64 string to byte array
        byte[] val = Convert.FromBase64String(s);
        Console.WriteLine("Converted byte value: {0}",
                           BitConverter.ToString(val));
    }
}

输出：

For byte1
The base 64 string: 'AgQGCAoMDhASFA=='
Converted byte value: 02-04-06-08-0A-0C-0E-10-12-14

s contains a non-base-64 character
Exception Thrown: System.FormatException

参考：

• https://docs.microsoft.com/zh-cn/dotnet/api/system.convert.frombase64string?view=netframework-4.7.2