当我的枚举与json属性中提供的字符串值不匹配时,如何让Json.net不要抛出？
当我基于当前文档创建枚举时,会发生这种情况,但第三方API稍后会添加更多枚举值.
我会很高兴将特殊值标记为未知或使用可空的枚举,而不匹配的值将返回null.
解决方法
您可以使用自定义JsonConverter解决此问题.这是一个我使用来自Json.Net的StringEnumConverter类中的几个集合.它应该给你灵活的处理事情,无论你决定什么.以下是它的工作原理：
>如果JSON中找到的值与枚举(作为字符串或整数)匹配,则使用该值. (如果值是整数,并且有多个可能的匹配,则使用第一个匹配项.)
>否则,如果枚举类型为空,则将该值设置为null.
>否则,如果枚举有一个名为“未知”的值,那么使用该值.
>否则使用枚举的第一个值.
如果你不喜欢规则的工作方式,或者想要简化它,那么请自由.以下是代码：
class TolerantEnumConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
Type type = IsNullableType(objectType) ? Nullable.GetUnderlyingType(objectType) : objectType;
return type.IsEnum;
}
public override object ReadJson(JsonReader reader,Type objectType,object existingValue,JsonSerializer serializer)
{
bool isNullable = IsNullableType(objectType);
Type enumType = isNullable ? Nullable.GetUnderlyingType(objectType) : objectType;
string[] names = Enum.GetNames(enumType);
if (reader.TokenType == JsonToken.String)
{
string enumText = reader.Value.ToString();
if (!string.IsNullOrEmpty(enumText))
{
string match = names
.Where(n => string.Equals(n,enumText,StringComparison.OrdinalIgnoreCase))
.FirstOrDefault();
if (match != null)
{
return Enum.Parse(enumType,match);
}
}
}
else if (reader.TokenType == JsonToken.Integer)
{
int enumVal = Convert.ToInt32(reader.Value);
int[] values = (int[])Enum.GetValues(enumType);
if (values.Contains(enumVal))
{
return Enum.Parse(enumType,enumVal.ToString());
}
}
if (!isNullable)
{
string defaultName = names
.Where(n => string.Equals(n,"Unknown",StringComparison.OrdinalIgnoreCase))
.FirstOrDefault();
if (defaultName == null)
{
defaultName = names.First();
}
return Enum.Parse(enumType,defaultName);
}
return null;
}
public override void WriteJson(JsonWriter writer,object value,JsonSerializer serializer)
{
writer.WriteValue(value.ToString());
}
private bool IsNullableType(Type t)
{
return (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>));
}
}
这是一个演示,它使转换器使用几个不同的枚举(一个有一个“未知”值,而另一个不)：
[JsonConverter(typeof(TolerantEnumConverter))]
enum Status
{
Ready = 1,Set = 2,Go = 3
}
[JsonConverter(typeof(TolerantEnumConverter))]
enum Color
{
Red = 1,Yellow = 2,Green = 3,Unknown = 99
}
class Foo
{
public Status NonNullableStatusWithValidStringValue { get; set; }
public Status NonNullableStatusWithValidIntValue { get; set; }
public Status NonNullableStatusWithInvalidStringValue { get; set; }
public Status NonNullableStatusWithInvalidIntValue { get; set; }
public Status NonNullableStatusWithNullValue { get; set; }
public Status? NullableStatusWithValidStringValue { get; set; }
public Status? NullableStatusWithValidIntValue { get; set; }
public Status? NullableStatusWithInvalidStringValue { get; set; }
public Status? NullableStatusWithInvalidIntValue { get; set; }
public Status? NullableStatusWithNullValue { get; set; }
public Color NonNullableColorWithValidStringValue { get; set; }
public Color NonNullableColorWithValidIntValue { get; set; }
public Color NonNullableColorWithInvalidStringValue { get; set; }
public Color NonNullableColorWithInvalidIntValue { get; set; }
public Color NonNullableColorWithNullValue { get; set; }
public Color? NullableColorWithValidStringValue { get; set; }
public Color? NullableColorWithValidIntValue { get; set; }
public Color? NullableColorWithInvalidStringValue { get; set; }
public Color? NullableColorWithInvalidIntValue { get; set; }
public Color? NullableColorWithNullValue { get; set; }
}
class Program
{
static void Main(string[] args)
{
string json = @"
{
""NonNullableStatusWithValidStringValue"" : ""Set"",""NonNullableStatusWithValidIntValue"" : 2,""NonNullableStatusWithInvalidStringValue"" : ""Blah"",""NonNullableStatusWithInvalidIntValue"" : 9,""NonNullableStatusWithNullValue"" : null,""NullableStatusWithValidStringValue"" : ""Go"",""NullableStatusWithValidIntValue"" : 3,""NullableStatusWithNullValue"" : null,""NullableStatusWithInvalidStringValue"" : ""Blah"",""NullableStatusWithInvalidIntValue"" : 9,""NonNullableColorWithValidStringValue"" : ""Green"",""NonNullableColorWithValidIntValue"" : 3,""NonNullableColorWithInvalidStringValue"" : ""Blah"",""NonNullableColorWithInvalidIntValue"" : 0,""NonNullableColorWithNullValue"" : null,""NullableColorWithValidStringValue"" : ""Yellow"",""NullableColorWithValidIntValue"" : 2,""NullableColorWithNullValue"" : null,""NullableColorWithInvalidStringValue"" : ""Blah"",""NullableColorWithInvalidIntValue"" : 0,}";
Foo foo = JsonConvert.DeserializeObject<Foo>(json);
foreach (PropertyInfo prop in typeof(Foo).GetProperties())
{
object val = prop.GetValue(foo,null);
Console.WriteLine(prop.Name + ": " +
(val == null ? "(null)" : val.ToString()));
}
}
}
输出：
NonNullableStatusWithValidStringValue: Set NonNullableStatusWithValidIntValue: Set NonNullableStatusWithInvalidStringValue: Ready NonNullableStatusWithInvalidIntValue: Ready NonNullableStatusWithNullValue: Ready NullableStatusWithValidStringValue: Go NullableStatusWithValidIntValue: Go NullableStatusWithInvalidStringValue: (null) NullableStatusWithInvalidIntValue: (null) NullableStatusWithNullValue: (null) NonNullableColorWithValidStringValue: Green NonNullableColorWithValidIntValue: Green NonNullableColorWithInvalidStringValue: Unknown NonNullableColorWithInvalidIntValue: Unknown NonNullableColorWithNullValue: Unknown NullableColorWithValidStringValue: Yellow NullableColorWithValidIntValue: Yellow NullableColorWithInvalidStringValue: (null) NullableColorWithInvalidIntValue: (null) NullableColorWithNullValue: (null)
