.Net 读取配置文件 xml

直接解析XML文件

1、System.Xml.Linq命名空间下提供可以使用linq查询的类，使用linq to xml读取也很方便。

2、还可以使用System.Xml.Serialization类的DeSerialize方法直接实例化。

https://docs.microsoft.com/zh-cn/dotnet/api/system.xml.serialization.xmlserializer.deserialize?view=netcore-2.2

在直接读取文件的时候由于手动getAttribute很麻烦，而且容易出错，attribute可以参考log4net的方式，全部做成宏定义：

使用.Net提供的的方式（ConfigurationManager类，支持.Net Core 2）

特别说明：

using System.Configuration 之后可能还要手动勾选，如下图：

使用.Net提供的方法读取有时候会很方便，可以直接将配置信息填写在app.config文件中例如下面的配置文件

<?xml version="1.0" encoding="utf-8" ?>
<configuration>

  <startup>
      <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
  </startup>

  <appSettings>
    <add key="name" value="kun"/>
    <add key="name2" value="kun"/>
  </appSettings>

  <connectionStrings>
    <add name="WingtipToys" connectionString="Data Source=(LocalDB)\v11.0;Initial Catalog=WingtipToys;Integrated Security=True;Pooling=False" />
  </connectionStrings>

</configuration>

读取的时候：

static void ReadAllSettings()
        {
            try
            {
                var appSettings = ConfigurationManager.AppSettings;

                if (appSettings.Count == 0)
                {
                    Console.WriteLine("AppSettings is empty.");
                }
                else
                {
                    foreach (var key in appSettings.AllKeys.Where((key) =>  key == "name"))
                    {
                        Console.WriteLine("Key: {0} Value: {1}", key, appSettings[key]);
                    }
                }
            }
            catch (ConfigurationErrorsException)
            {
                Console.WriteLine("Error reading app settings");
            }
        }

        static void ReadSetting(string key)
        {
            try
            {
                var appSettings = ConfigurationManager.AppSettings;
                string result = appSettings[key] ?? "Not Found";
                Console.WriteLine(result);
            }
            catch (ConfigurationErrorsException)
            {
                Console.WriteLine("Error reading app settings");
            }
        }

读取数据库连接信息也可以只用一句代码：

var connectionString = ConfigurationManager.ConnectionStrings["WingtipToys"].ConnectionString;

对于这种简单key/Value方式的配置，使用ConfigurationManager类还是很方便的。

自定义配置

配置比较复杂呢？当然App.config文件也支持自定义，就是用起来比较复杂，需要手动写一个有各种限制的类。

<?xml version="1.0" encoding="utf-8" ?>
<configuration>

  <configSections>
    <section name="sampleSection" type="System.Configuration.SingleTagSectionHandler" />
  </configSections>

  <startup>
      <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
  </startup>

  <appSettings>
    <add key="name" value="kun"/>
    <add key="name2" value="kun"/>
  </appSettings>

  <connectionStrings>
    <add name="WingtipToys" connectionString="Data Source=(LocalDB)\v11.0;Initial Catalog=WingtipToys;Integrated Security=True;Pooling=False" />
  </connectionStrings>

  <sampleSection setting1="Value1"
                 setting2="value two"
                 setting3="third value">
  </sampleSection>

</configuration>

上面sampleSection 就是自定义的配置，使用起来的话需要手动实现下面这个类(微软官方的示例)：

// Define a custom section.
// The CustomSection type allows to define a custom section
// programmatically.
public sealed class CustomSection :
    ConfigurationSection
{
    // The collection (property bag) that contains
    // the section properties.
    private static ConfigurationPropertyCollection _Properties;

    // Internal flag to disable
    // property setting.
    private static bool _ReadOnly;

    // The FileName property.
    private static readonly ConfigurationProperty _FileName =
        new ConfigurationProperty("fileName",
        typeof(string),"default.txt",
        ConfigurationPropertyOptions.IsRequired);

    // The MaxUsers property.
    private static readonly ConfigurationProperty _MaxUsers =
        new ConfigurationProperty("maxUsers",
        typeof(long), (long)1000,
        ConfigurationPropertyOptions.None);

    // The MaxIdleTime property.
    private static readonly ConfigurationProperty _MaxIdleTime =
        new ConfigurationProperty("maxIdleTime",
        typeof(TimeSpan), TimeSpan.FromMinutes(5),
        ConfigurationPropertyOptions.IsRequired);

    // CustomSection constructor.
    public CustomSection()
    {
        // Property initialization
        _Properties =
            new ConfigurationPropertyCollection();

        _Properties.Add(_FileName);
        _Properties.Add(_MaxUsers);
        _Properties.Add(_MaxIdleTime);
   }

    // This is a key customization.
    // It returns the initialized property bag.
    protected override ConfigurationPropertyCollection Properties
    {
        get
        {
            return _Properties;
        }
    }

    private new bool IsReadOnly
    {
        get
        {
            return _ReadOnly;
        }
    }

    // Use this to disable property setting.
    private void ThrowIfReadOnly(string propertyName)
    {
        if (IsReadOnly)
            throw new ConfigurationErrorsException(
                "The property " + propertyName + " is read only.");
    }

    // Customizes the use of CustomSection
    // by setting _ReadOnly to false.
    // Remember you must use it along with ThrowIfReadOnly.
    protected override object GetRuntimeObject()
    {
        // To enable property setting just assign true to
        // the following flag.
        _ReadOnly = true;
        return base.GetRuntimeObject();
    }

    [StringValidator(InvalidCharacters = " ~!@#$%^&*()[]{}/;'\"|\\",
        MinLength = 1, MaxLength = 60)]
    public string FileName
    {
        get
        {
            return (string)this["fileName"];
        }
        set
        {
            // With this you disable the setting.
            // Remember that the _ReadOnly flag must
            // be set to true in the GetRuntimeObject.
            ThrowIfReadOnly("FileName");
            this["fileName"] = value;
        }
    }

    [LongValidator(MinValue = 1, MaxValue = 1000000,
        ExcludeRange = false)]
    public long MaxUsers
    {
        get
        {
            return (long)this["maxUsers"];
        }
        set
        {
            this["maxUsers"] = value;
        }
    }

    [TimeSpanValidator(MinValueString = "0:0:30",
        MaxValueString = "5:00:0",
        ExcludeRange = false)]
    public TimeSpan MaxIdleTime
    {
        get
        {
            return  (TimeSpan)this["maxIdleTime"];
        }
        set
        {
            this["maxIdleTime"] = value;
        }
    }

}

参考：

https://docs.microsoft.com/zh-cn/dotnet/api/system.configuration.configurationmanager?view=netframework-4.7.2

https://docs.microsoft.com/zh-cn/dotnet/api/system.configuration.configurationsection?view=netframework-4.7.2

https://blog.csdn.net/aojiancc2/article/details/21618299