Asp.net mvc Json.Net:Html帮助程序方法未重新生成_Asp.net Mvc_Angularjs_Json.net

Asp.net mvc Json.Net:Html帮助程序方法未重新生成

asp.net-mvc angularjs

Asp.net mvc Json.Net:Html帮助程序方法未重新生成,asp.net-mvc,angularjs,json.net,Asp.net Mvc,Angularjs,Json.net,我遇到了一个问题，我创建的ASP.NET MVC html帮助程序方法在每次调用时都没有“重新生成” helper方法的目的是创建要在angularjs框架中使用的Javascript对象。例如，这里有一个使用helper方法的代码段（从html页面的脚本标记中调用）： Model是一个具有多种属性的类的实例，但我只希望FirstName、LastName、ID和Role被序列化为一个javascript对象 ToJavascript（）助手方法在statis类中定义如下： public

我遇到了一个问题，我创建的ASP.NET MVC html帮助程序方法在每次调用时都没有“重新生成”

helper方法的目的是创建要在angularjs框架中使用的Javascript对象。例如，这里有一个使用helper方法的代码段（从html页面的脚本标记中调用）：

Model是一个具有多种属性的类的实例，但我只希望FirstName、LastName、ID和Role被序列化为一个javascript对象

ToJavascript（）助手方法在statis类中定义如下：

   public static HtmlString ToJavascript( this HtmlHelper helper, object toConvert, string[] includedFields = null, Formatting formatting = Formatting.Indented, ReferenceLoopHandling loopHandling = ReferenceLoopHandling.Ignore )
    {
        using( var stringWriter = new StringWriter() )
        using( var jsonWriter = new JsonTextWriter( stringWriter ) )
        {
            var serializer = new JsonSerializer()
            {
                // Let's use camelCasing as is common practice in JavaScript
                ContractResolver = new SpecificFieldsResolver( includedFields ),
                Formatting = formatting,
                ReferenceLoopHandling = loopHandling,
            };

            // We don't want quotes around object names
            jsonWriter.QuoteName = false;
            serializer.Serialize( jsonWriter, toConvert );

            return new HtmlString( stringWriter.ToString() );
        }
    }

public class SpecificFieldsResolver : CamelCasePropertyNamesContractResolver
{
    private string[] _included;

    public SpecificFieldsResolver( string[] included )
    {
        _included = included;
    }

    protected override JsonProperty CreateProperty( MemberInfo member, MemberSerialization memberSerialization )
    {
        JsonProperty prop = base.CreateProperty( member, memberSerialization );

        bool inclField = ( _included == null )
            || _included.Contains( member.Name, StringComparer.CurrentCultureIgnoreCase );

        prop.ShouldSerialize = obj => inclField;

        return prop;
    }
}

这将利用Json.NET进行实际的序列化

Json.NET的许多很酷的特性之一是，它允许您动态地定义哪些字段被序列化。这就是SpecificFieldsResolver所做的。我将其定义如下：

   public static HtmlString ToJavascript( this HtmlHelper helper, object toConvert, string[] includedFields = null, Formatting formatting = Formatting.Indented, ReferenceLoopHandling loopHandling = ReferenceLoopHandling.Ignore )
    {
        using( var stringWriter = new StringWriter() )
        using( var jsonWriter = new JsonTextWriter( stringWriter ) )
        {
            var serializer = new JsonSerializer()
            {
                // Let's use camelCasing as is common practice in JavaScript
                ContractResolver = new SpecificFieldsResolver( includedFields ),
                Formatting = formatting,
                ReferenceLoopHandling = loopHandling,
            };

            // We don't want quotes around object names
            jsonWriter.QuoteName = false;
            serializer.Serialize( jsonWriter, toConvert );

            return new HtmlString( stringWriter.ToString() );
        }
    }

public class SpecificFieldsResolver : CamelCasePropertyNamesContractResolver
{
    private string[] _included;

    public SpecificFieldsResolver( string[] included )
    {
        _included = included;
    }

    protected override JsonProperty CreateProperty( MemberInfo member, MemberSerialization memberSerialization )
    {
        JsonProperty prop = base.CreateProperty( member, memberSerialization );

        bool inclField = ( _included == null )
            || _included.Contains( member.Name, StringComparer.CurrentCultureIgnoreCase );

        prop.ShouldSerialize = obj => inclField;

        return prop;
    }
}

让我困惑的是调用CreateProperty（）的方式。具体地说，对于被序列化的每种类型的对象，它似乎只被调用一次

这是一个问题，因为在另一个cshtml文件中，我有另一个对ToJavascript（）的调用，该调用试图序列化相同类型的对象，但要从序列化中输出不同的字段：

var app = angular.module( "app2Name", ["ui.bootstrap"] );

app.controller( 'app2Ctrl', function( $scope ) {
    $scope.model = @Html.ToJavascript( Model, new string[] { "FirstName", "LastName", "ID", "Role", "Category", "VoterID" } );
} );

Category和VoterID也是有效的类字段。但是ToJavascript（）并没有将它们序列化。相反，它只序列化在对ToJavascript（）的第一次调用中定义的字段……即使该调用发生在不同的cshtml文件中。这就好像SpecificFieldsResolver记住了它创建的JsonProperty对象一样

想法

更新

Thanx感谢dbc准确诊断错误并提出解决方案。我稍微修改了一下，因为我在几个解析器中依赖Json.NET的驼峰大小写名称解析：

public class CamelCaseNameMapper : CamelCasePropertyNamesContractResolver
{
    public string ToCamelCase( string propertyName )
    {
        return ResolvePropertyName( propertyName );
    }
}

public class MaoDefaultContractResolver : DefaultContractResolver
{
    private CamelCaseNameMapper _mapper = new CamelCaseNameMapper();

    protected override string ResolvePropertyName( string propertyName )
    {
        return _mapper.ToCamelCase( propertyName );
    }

}

现在，每个解析器，例如my SpecificFieldsResolver，它派生自MaoDefaultContractResolver，自动继承camel大小写，但避免了dbc识别的缓存问题。

这似乎是一个错误。它的基类有两个构造函数：a和一个版本（刚刚在Json.NET 7.0中过时）。此参数具有以下含义：

共享缓存

类型：System.Boolean
如果设置为true，则
```
DefaultContractResolver
```
将使用与相同类型的其他解析程序共享的缓存。共享缓存将显著提高多个解析器实例的性能，因为昂贵的反射只会发生一次。如果假定解析器的不同实例产生不同的结果，则此设置可能会导致意外行为。当设置为false时，强烈建议将
```
DefaultContractResolver
```
实例与
```
JsonSerializer
```
一起重用

默认值为

false

不幸的是，for

CamelCasePropertyNamesContractResolver

将该值设置为true
：

public class CamelCasePropertyNamesContractResolver : DefaultContractResolver
{
    public CamelCasePropertyNamesContractResolver()
#pragma warning disable 612,618
        : base(true)
#pragma warning restore 612,618
    {
        NamingStrategy = new CamelCaseNamingStrategy
        {
            ProcessDictionaryKeys = true,
            OverrideSpecifiedNames = true
        };
    }
}

此外，没有第二个构造函数具有

shareCache

选项。这会中断您的

SpecificFieldsResolver

作为一种解决方法，您可以从

DefaultContractResolver

派生解析器，并使用它进行名称映射：

public class IndependentCamelCasePropertyNamesContractResolver : DefaultContractResolver
{
    public IndependentCamelCasePropertyNamesContractResolver()
        : base()
    {
        NamingStrategy = new CamelCaseNamingStrategy
        {
            ProcessDictionaryKeys = true,
            OverrideSpecifiedNames = true
        };
    }    
}

public class SpecificFieldsResolver : IndependentCamelCasePropertyNamesContractResolver
{
    // Remainder unchanged
}

请注意，如果您使用的是9.0之前的Json.NET版本，

CamelCaseNamingStrategy

不存在。相反，可以使用嵌套的kludge

CamelCasePropertyNamesContractResolver

映射名称：

public class IndependentCamelCasePropertyNamesContractResolver : DefaultContractResolver
{
    class CamelCaseNameMapper : CamelCasePropertyNamesContractResolver
    {
        // Purely to make the protected method public.
        public string ToCamelCase(string propertyName)
        {
            return ResolvePropertyName(propertyName);
        }
    }
    readonly CamelCaseNameMapper nameMapper = new CamelCaseNameMapper();

    protected override string ResolvePropertyName(string propertyName)
    {
        return nameMapper.ToCamelCase(propertyName);
    }
}