CODEWITHSUNDEEP
c#javascriptarraysforms
user2058002
user2058002

Reputation:

Passing variables from Javascript to C# via forms?

I have an array which I am storing inside an <input type="hidden">. Here is my code.

Javascript:

var trees;

// called when the body loads
function BodyOnLoad()
{
  trees = document.getElementById("trees");
  trees.value = new Array();
}

// this is what isn't working
function AddTree()
{
  var i = trees.value.length;

  trees.value[i] = new Array();
  /***/
  trees.value[i]["branches"] = 5;
  trees.value[i]["trunk"]    = 0;
}

HTML: <input type="hidden" name="trees" id="trees" />

In C#, Request.Form["trees"] is not an array. What am I doing wrong?

Upvotes: 3

Views: 2096

Answers (4)

AVH
AVH

Reputation: 1765

The HTML form post won't preserve a javascript object (in this case an Array). You should look at converting your Array to JSON and passing that in the form if you need to preserve the array object.

Include this script (JSON2) in your page: JSON2

var treesArray;

// called when the body loads
function BodyOnLoad()
{
  treesArray = new Array();
}

function AddTree()
{
  var tree = new Array();

  //branches      
  tree[0] = "5";

  //trunk      
  tree[1] = "0";

  //name
  tree[2] = "Elm";

  treesArray[treesArray.length] = tree;
  document.getElementById("trees").value = JSON.stringify(treesArray);
}

Then on the server side you will need to convert the JSON to a C# Array using something like this:

Add reference to JavaScriptSerializer from System.Web.Extensions.dll (.NET 3.5 SP1)

JavaScriptSerializer serializer = new JavaScriptSerializer();
string[][] trees = serializer.Deserialize<string[][]>(Request.Form["trees"]);

for(int i = 0; i < trees.Length; i++)
{
    Console.WriteLine("Branches:" + trees[i][0]);
    Console.WriteLine("Trunk:" + trees[i][1]);
    Console.WriteLine("Name:" + trees[i][2]);
}

Upvotes: 3

Adilson de Almeida Jr
Adilson de Almeida Jr

Reputation: 2755

You can read the value from the input, eval it, and when you will post the form, stringify your variable and write it into the input (JSON.stringify and eval functions).

Upvotes: 0

Miguel Angelo
Miguel Angelo

Reputation: 24212

You cannot set the value of an input element to an array in javascript.

You can only set strings as value of input elements.

If you want to send multiple values to the server, you must concatenate mutiple strings, and use a separator, like a pipe '|' or comma ','... and then on the server you need to split the string, by using that separator.

Upvotes: 1

Ashley_Ingram
Ashley_Ingram

Reputation: 62

You need to name the hidden form element with [] (for example, trees[]). Then, when you wish to add a new value to the array, append another DOM element to the form, a hidden input type with the same name (and the new value).

When posted, I believe you'll be able to access them in C# as a string of comma-delimited values.

Upvotes: 0

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