How to serialize a function to json (using razor @)

Question

How can I serialize a client function to a json object? (similar to how kendo controls work)

This is what I have so far...

View:

@Html.TestCo         


        

Answer 1

You are confusing a function on the server with a function on the client. You're actually executing onSubmit on the server and the result of that is being put into your object which you serialize into json.

Instead:

Make your 2nd parameter to TestControl a string. Also, don't serialize an object. Instead, create your json manually.

public static HtmlString TestControl<TModel>(this HtmlHelper<TModel> helper, string onSubmit)
{
  string jsonObj = String.Format("{{ \"onSubmit\": {0} }}", onSubmit);
  return new HtmlString(string.Format("<script>var obj = {0};</script>", jsonObj));
}

Then you can use:

@Html.TestControl("function(){ alert('test'); }")

Your jsonObj will be:

{ "onSubmit": function(){ alert('test'); } }

and finally, your TestControl() method will return

<script>var obj = { "onSubmit": function(){ alert("test"); } };</script>

Answer 2

Based on @ryan's answer, I upgrade a little bit to more like kendoUI.

public class TextBox : BaseControl
{
    [JsonProperty("onChange", NullValueHandling = NullValueHandling.Ignore)]
    [JsonConverter(typeof(JsFunctionConverter))]
    public Func<object, object> OnChange { get; set; }

    public override MvcHtmlString Render()
    {
        // Create html
        // <input />
        _tagBuilder = new TagBuilder("input");

        // Add script
        StringBuilder builder = new StringBuilder(base.Render().ToString());
        string script = @"<script>var {0} = {{name: '{0}', scope : angular.element($('#{0}')).scope(), options: {1}}}; textBox({0});</script>";

        BuildOptions();
        builder.AppendFormat(script, Name, JsonConvert.SerializeObject(this));
        return MvcHtmlString.Create(builder.ToString());
    }

Here is JsFunctionConverter:

public class JsFunctionConverter : JsonConverter
{
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException("Unnecessary because CanRead is false. The type will skip the converter.");
    }

    public override bool CanRead
    {
        get { return false; }
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof (string) || objectType == typeof (Func<object,object>);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        JRaw jRawData;

        if (value.GetType() == typeof(Func<object, object>))
        {
            jRawData = new JRaw(((Func<object,object>)value).Invoke(null));
        }
        else
        {
            jRawData = new JRaw(value);
        }

        jRawData.WriteTo(writer);
    }
}

And you can do it like KendoUI

var textBox = new TextBox
{
    OnChange = @<text>
                    function(e){

                            return e;
                    }
                </text>
};

Answer 3

Just make this onSubmit argument being a string and use its value as is. You will no longer need the text tags when calling the helper.

Answer 4

I spent more time searching around and found similar posts but didn't see a solution:

Serializing a function as a parameter in json using C#

JSON serializing an object with function parameter

Finally got it to work using the Json.net library. Using the JRaw class will generate a json object with the onSubmit property defined as a function.

Json.net documentation: http://james.newtonking.com/projects/json/help/html/SerializeRawJson.htm

Updated Control Helper:

public static HtmlString TestControl<TModel>(this HtmlHelper<TModel> helper, Func<object, object> onSubmit)
{
    var obj = new { onSubmit = new JRaw(onSubmit.Invoke(null).ToString()) };
    var jsonObj = JsonConvert.SerializeObject(obj);
    return new HtmlString(string.Format("<script>var obj = {0};</script>", jsonObj));
}

Output:

<script>var obj = {"onSubmit":function(){alert("test");}};</script>

Now I can call obj.onSubmit() on the client to call the function.