Goal:
Defining Knockout-style input controls can be tedious
and also may be something that you may find obtrusive, mixing your HTML with data bind syntax as well as binding your aspx, ascx files to Knockout.
The goal
is to make specifying Knockout specific HTML tags easy, seamless really, as well as being able to remove references to Knockout easily.
Environment considerations:
ASP.Net MVC2 or later
Knockoutjs.js
How to:
public static class HtmlExtensions
{
public static
string DataBoundCheckBox(this HtmlHelper helper,
string name, bool isChecked, object htmlAttributes)
{
var builder = new TagBuilder("input");
var dic = new RouteValueDictionary(htmlAttributes) { { "data-bind",
String.Format("checked: {0}", name) } };
builder.MergeAttributes(dic);
builder.MergeAttribute("type", @"checkbox");
builder.MergeAttribute("name", name);
builder.MergeAttribute("value", @"true");
if (isChecked)
{
builder.MergeAttribute("checked", @"checked");
}
return builder.ToString(TagRenderMode.SelfClosing);
}
public static MvcHtmlString DataBoundSelectList(this HtmlHelper helper,
string name, IEnumerable<SelectListItem> selectList,
String optionLabel)
{
var attrProperties = new StringBuilder();
attrProperties.Append(String.Format("optionsText: '{0}'", name));
if (!String.IsNullOrEmpty(optionLabel)) attrProperties.Append(String.Format(", optionsCaption: '{0}'", optionLabel));
attrProperties.Append(String.Format(", value: {0}", name));
var dic = new RouteValueDictionary { { "data-bind", attrProperties.ToString() } };
return helper.DropDownList(name, selectList, optionLabel, dic);
}
public static MvcHtmlString DataBoundSelectList(this HtmlHelper helper,
string name, IEnumerable<SelectListItem> selectList,
String optionLabel, object htmlAttributes)
{
var attrProperties = new StringBuilder();
attrProperties.Append(String.Format("optionsText: '{0}'", name));
if (!String.IsNullOrEmpty(optionLabel)) attrProperties.Append(String.Format(", optionsCaption: '{0}'", optionLabel));
attrProperties.Append(String.Format(", value: {0}", name));
var dic = new RouteValueDictionary(htmlAttributes) {{"data-bind", attrProperties}};
return helper.DropDownList(name, selectList, optionLabel, dic);
}
public static
String DataBoundSelectList(this HtmlHelper helper,
String options,
String optionsText,
String value)
{
return
String.Format("<select data-bind=\"options: {0},optionsText: '{1}',value: {2}\"></select>", options, optionsText, value);
}
public static MvcHtmlString DataBoundTextBox(this HtmlHelper helper,
string name, object value, object htmlAttributes)
{
var dic = new RouteValueDictionary(htmlAttributes);
dic.Add("data-bind",
String.Format("value: {0}", name));
return helper.TextBox(name, value, dic);
}
public static MvcHtmlString DataBoundTextBox(this HtmlHelper helper,
string name,
string observable, object value, object htmlAttributes)
{
var dic = new RouteValueDictionary(htmlAttributes);
dic.Add("data-bind",
String.Format("value: {0}", observable));
return helper.TextBox(name, value, dic);
}
public static MvcHtmlString DataBoundTextArea(this HtmlHelper helper,
string name,
string value, int rows, int columns, object htmlAttributes)
{
var dic = new RouteValueDictionary(htmlAttributes);
dic.Add("data-bind",
String.Format("value: {0}", name));
return helper.TextArea(name, value, rows, columns, dic);
}
public static MvcHtmlString DataBoundTextArea(this HtmlHelper helper,
string name,
string observable,
string value, int rows, int columns, object htmlAttributes)
{
var dic = new RouteValueDictionary(htmlAttributes);
dic.Add("data-bind",
String.Format("value: {0}", observable));
return helper.TextArea(name, value, rows, columns, dic);
}
public static
string BuildUrlFromExpression<T>(this HtmlHelper helper, Expression<Action<T>> action)
{
var values = CreateRouteValuesFromExpression(action);
var virtualPath = helper.RouteCollection.GetVirtualPath(helper.ViewContext.RequestContext, values);
if (virtualPath != null)
{
return virtualPath.VirtualPath;
}
return null;
}
public static
string ActionLink<T>(this HtmlHelper helper, Expression<Action<T>> action,
string linkText)
{
return helper.ActionLink(action, linkText, null);
}
public static
string ActionLink<T>(this HtmlHelper helper, Expression<Action<T>> action,
string linkText, object htmlAttributes)
{
var values = CreateRouteValuesFromExpression(action);
var controllerName = (string)values["controller"];
var actionName = (string)values["action"];
values.Remove("controller");
values.Remove("action");
return helper.ActionLink(linkText, actionName, controllerName, values, new RouteValueDictionary(htmlAttributes)).ToHtmlString();
}
public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action)
{
return helper.Form(action, FormMethod.Post);
}
public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action, FormMethod method)
{
var values = CreateRouteValuesFromExpression(action);
string controllerName = (string)values["controller"];
string actionName = (string)values["action"];
values.Remove("controller");
values.Remove("action");
return helper.BeginForm(actionName, controllerName, values, method);
}
public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action, FormMethod method, object htmlAttributes)
{
var values = CreateRouteValuesFromExpression(action);
string controllerName = (string)values["controller"];
string actionName = (string)values["action"];
values.Remove("controller");
values.Remove("action");
return helper.BeginForm(actionName, controllerName, values, method, new RouteValueDictionary(htmlAttributes));
}
public static
string VertCheckBox(this HtmlHelper helper,
string name, bool isChecked)
{
return helper.CustomCheckBox(name, isChecked, null);
}
public static
string CustomCheckBox(this HtmlHelper helper,
string name, bool isChecked, object htmlAttributes)
{
TagBuilder builder = new TagBuilder("input");
builder.MergeAttributes(new RouteValueDictionary(htmlAttributes));
builder.MergeAttribute("type", "checkbox");
builder.MergeAttribute("name", name);
builder.MergeAttribute("value", "true");
if (isChecked)
{
builder.MergeAttribute("checked", "checked");
}
return builder.ToString(TagRenderMode.SelfClosing);
}
public static
string Script(this HtmlHelper helper,
string script, object scriptAttributes)
{
var pathForCRMScripts = ScriptsController.GetPathForCRMScripts();
if (ScriptOptimizerConfig.EnableMinimizedFileLoad)
{
string newPathForCRM = pathForCRMScripts + "Min/";
ScriptsController.ServerPathMapper = new ServerPathMapper();
string fullPath = ScriptsController.ServerMapPath(newPathForCRM);
if (!File.Exists(fullPath + script))
return null;
if (!Directory.Exists(fullPath))
return null;
pathForCRMScripts = newPathForCRM;
}
var builder = new TagBuilder("script");
builder.MergeAttributes(new RouteValueDictionary(scriptAttributes));
builder.MergeAttribute("type", @"text/javascript");
builder.MergeAttribute("src",
String.Format("{0}{1}", pathForCRMScripts.Replace("~",
String.Empty), script));
return builder.ToString(TagRenderMode.SelfClosing);
}
private static RouteValueDictionary CreateRouteValuesFromExpression<T>(Expression<Action<T>> action)
{
if (action == null)
throw new InvalidOperationException("Action must be provided");
var body = action.Body as MethodCallExpression;
if (body == null)
{
throw new InvalidOperationException("Expression must be a method call");
}
if (body.Object != action.Parameters[0])
{
throw new InvalidOperationException("Method call must target lambda argument");
}
// This will build up a RouteValueDictionary containing
the controller name, action name,
and any
// parameters passed as part of
the "action" parameter.
string name = body.Method.Name;
string controllerName = typeof(T).Name;
if (controllerName.EndsWith("Controller", StringComparison.OrdinalIgnoreCase))
{
controllerName = controllerName.Remove(controllerName.Length - 10, 10);
}
var values = BuildParameterValuesFromExpression(body) ?? new RouteValueDictionary();
values.Add("controller", controllerName);
values.Add("action", name);
return values;
}
private static RouteValueDictionary BuildParameterValuesFromExpression(MethodCallExpression call)
{
// Build up a RouteValueDictionary containing parameter names as keys
and parameter values
// as values based on
the MethodCallExpression passed
in.
var values = new RouteValueDictionary();
ParameterInfo[] parameters = call.Method.GetParameters();
// If
the passed
in method has no parameters, just return an empty dictionary.
if (parameters.Length == 0)
{
return values;
}
for (int i = 0; i < parameters.Length; i++)
{
object parameterValue;
Expression expression = call.Arguments[i];
// If
the current parameter
is a constant, just use its value as
the parameter value.
var constant = expression as ConstantExpression;
if (constant != null)
{
parameterValue = constant.Value;
}
else
{
// Otherwise, compile
and execute
the expression
and use that as
the parameter value.
var function = Expression.Lambda<Func<object>>(Expression.Convert(expression, typeof(object)),
new ParameterExpression[0]);
try
{
parameterValue = function.Compile()();
}
catch
{
parameterValue = null;
}
}
values.Add(parameters[i].Name, parameterValue);
}
return values;
}
}
Some observations:
The first two DataBoundSelectList overloaded methods are specifically built to load
the data right into
the drop down box as part of
the HTML response stream rather than let Knockout's engine populate
the options client-side.
The third overloaded method does it client-side via
the viewmodel.
The first two overloads can be done when you have no requirement to add complex JSON objects to your lists. Furthermore, why render
and parse
the JSON object when you can have it all built
and rendered server-side like any other list control.
