Mi è piaciuta la soluzione pubblicata da @ john-w-harding, quindi l'ho combinata con la risposta di @ darin-dimitrov per creare la seguente soluzione probabilmente troppo complicata che ti consente di ritardare il rendering di qualsiasi html (anche script) all'interno di un blocco using.
USO
In una visualizzazione parziale ripetuta, includere il blocco solo una volta:
@using (Html.Delayed(isOnlyOne: "MYPARTIAL_scripts")) {
<script>
someInlineScript();
</script>
}
In una vista parziale (ripetuta?), Includere il blocco ogni volta che viene utilizzato il parziale:
@using (Html.Delayed()) {
<b>show me multiple times, @Model.Whatever</b>
}
In una vista parziale (ripetuta?), Includere il blocco una volta e successivamente renderlo specificatamente per nome one-time:
@using (Html.Delayed("one-time", isOnlyOne: "one-time")) {
<b>show me once by name</b>
<span>@Model.First().Value</span>
}
Per eseguire il rendering:
@Html.RenderDelayed(); // the "default" unidentified blocks
@Html.RenderDelayed("one-time", false); // render the specified block by name, and allow us to render it again in a second call
@Html.RenderDelayed("one-time"); // render the specified block by name
@Html.RenderDelayed("one-time"); // since it was "popped" in the last call, won't render anything
CODICE
public static class HtmlRenderExtensions {
/// <summary>
/// Delegate script/resource/etc injection until the end of the page
/// <para>@via https://stackoverflow.com/a/14127332/1037948 and http://jadnb.wordpress.com/2011/02/16/rendering-scripts-from-partial-views-at-the-end-in-mvc/ </para>
/// </summary>
private class DelayedInjectionBlock : IDisposable {
/// <summary>
/// Unique internal storage key
/// </summary>
private const string CACHE_KEY = "DCCF8C78-2E36-4567-B0CF-FE052ACCE309"; // "DelayedInjectionBlocks";
/// <summary>
/// Internal storage identifier for remembering unique/isOnlyOne items
/// </summary>
private const string UNIQUE_IDENTIFIER_KEY = CACHE_KEY;
/// <summary>
/// What to use as internal storage identifier if no identifier provided (since we can't use null as key)
/// </summary>
private const string EMPTY_IDENTIFIER = "";
/// <summary>
/// Retrieve a context-aware list of cached output delegates from the given helper; uses the helper's context rather than singleton HttpContext.Current.Items
/// </summary>
/// <param name="helper">the helper from which we use the context</param>
/// <param name="identifier">optional unique sub-identifier for a given injection block</param>
/// <returns>list of delayed-execution callbacks to render internal content</returns>
public static Queue<string> GetQueue(HtmlHelper helper, string identifier = null) {
return _GetOrSet(helper, new Queue<string>(), identifier ?? EMPTY_IDENTIFIER);
}
/// <summary>
/// Retrieve a context-aware list of cached output delegates from the given helper; uses the helper's context rather than singleton HttpContext.Current.Items
/// </summary>
/// <param name="helper">the helper from which we use the context</param>
/// <param name="defaultValue">the default value to return if the cached item isn't found or isn't the expected type; can also be used to set with an arbitrary value</param>
/// <param name="identifier">optional unique sub-identifier for a given injection block</param>
/// <returns>list of delayed-execution callbacks to render internal content</returns>
private static T _GetOrSet<T>(HtmlHelper helper, T defaultValue, string identifier = EMPTY_IDENTIFIER) where T : class {
var storage = GetStorage(helper);
// return the stored item, or set it if it does not exist
return (T) (storage.ContainsKey(identifier) ? storage[identifier] : (storage[identifier] = defaultValue));
}
/// <summary>
/// Get the storage, but if it doesn't exist or isn't the expected type, then create a new "bucket"
/// </summary>
/// <param name="helper"></param>
/// <returns></returns>
public static Dictionary<string, object> GetStorage(HtmlHelper helper) {
var storage = helper.ViewContext.HttpContext.Items[CACHE_KEY] as Dictionary<string, object>;
if (storage == null) helper.ViewContext.HttpContext.Items[CACHE_KEY] = (storage = new Dictionary<string, object>());
return storage;
}
private readonly HtmlHelper helper;
private readonly string identifier;
private readonly string isOnlyOne;
/// <summary>
/// Create a new using block from the given helper (used for trapping appropriate context)
/// </summary>
/// <param name="helper">the helper from which we use the context</param>
/// <param name="identifier">optional unique identifier to specify one or many injection blocks</param>
/// <param name="isOnlyOne">extra identifier used to ensure that this item is only added once; if provided, content should only appear once in the page (i.e. only the first block called for this identifier is used)</param>
public DelayedInjectionBlock(HtmlHelper helper, string identifier = null, string isOnlyOne = null) {
this.helper = helper;
// start a new writing context
((WebViewPage)this.helper.ViewDataContainer).OutputStack.Push(new StringWriter());
this.identifier = identifier ?? EMPTY_IDENTIFIER;
this.isOnlyOne = isOnlyOne;
}
/// <summary>
/// Append the internal content to the context's cached list of output delegates
/// </summary>
public void Dispose() {
// render the internal content of the injection block helper
// make sure to pop from the stack rather than just render from the Writer
// so it will remove it from regular rendering
var content = ((WebViewPage)this.helper.ViewDataContainer).OutputStack;
var renderedContent = content.Count == 0 ? string.Empty : content.Pop().ToString();
// if we only want one, remove the existing
var queue = GetQueue(this.helper, this.identifier);
// get the index of the existing item from the alternate storage
var existingIdentifiers = _GetOrSet(this.helper, new Dictionary<string, int>(), UNIQUE_IDENTIFIER_KEY);
// only save the result if this isn't meant to be unique, or
// if it's supposed to be unique and we haven't encountered this identifier before
if( null == this.isOnlyOne || !existingIdentifiers.ContainsKey(this.isOnlyOne) ) {
// remove the new writing context we created for this block
// and save the output to the queue for later
queue.Enqueue(renderedContent);
// only remember this if supposed to
if(null != this.isOnlyOne) existingIdentifiers[this.isOnlyOne] = queue.Count; // save the index, so we could remove it directly (if we want to use the last instance of the block rather than the first)
}
}
}
/// <summary>
/// <para>Start a delayed-execution block of output -- this will be rendered/printed on the next call to <see cref="RenderDelayed"/>.</para>
/// <para>
/// <example>
/// Print once in "default block" (usually rendered at end via <code>@Html.RenderDelayed()</code>). Code:
/// <code>
/// @using (Html.Delayed()) {
/// <b>show at later</b>
/// <span>@Model.Name</span>
/// etc
/// }
/// </code>
/// </example>
/// </para>
/// <para>
/// <example>
/// Print once (i.e. if within a looped partial), using identified block via <code>@Html.RenderDelayed("one-time")</code>. Code:
/// <code>
/// @using (Html.Delayed("one-time", isOnlyOne: "one-time")) {
/// <b>show me once</b>
/// <span>@Model.First().Value</span>
/// }
/// </code>
/// </example>
/// </para>
/// </summary>
/// <param name="helper">the helper from which we use the context</param>
/// <param name="injectionBlockId">optional unique identifier to specify one or many injection blocks</param>
/// <param name="isOnlyOne">extra identifier used to ensure that this item is only added once; if provided, content should only appear once in the page (i.e. only the first block called for this identifier is used)</param>
/// <returns>using block to wrap delayed output</returns>
public static IDisposable Delayed(this HtmlHelper helper, string injectionBlockId = null, string isOnlyOne = null) {
return new DelayedInjectionBlock(helper, injectionBlockId, isOnlyOne);
}
/// <summary>
/// Render all queued output blocks injected via <see cref="Delayed"/>.
/// <para>
/// <example>
/// Print all delayed blocks using default identifier (i.e. not provided)
/// <code>
/// @using (Html.Delayed()) {
/// <b>show me later</b>
/// <span>@Model.Name</span>
/// etc
/// }
/// </code>
/// -- then later --
/// <code>
/// @using (Html.Delayed()) {
/// <b>more for later</b>
/// etc
/// }
/// </code>
/// -- then later --
/// <code>
/// @Html.RenderDelayed() // will print both delayed blocks
/// </code>
/// </example>
/// </para>
/// <para>
/// <example>
/// Allow multiple repetitions of rendered blocks, using same <code>@Html.Delayed()...</code> as before. Code:
/// <code>
/// @Html.RenderDelayed(removeAfterRendering: false); /* will print */
/// @Html.RenderDelayed() /* will print again because not removed before */
/// </code>
/// </example>
/// </para>
/// </summary>
/// <param name="helper">the helper from which we use the context</param>
/// <param name="injectionBlockId">optional unique identifier to specify one or many injection blocks</param>
/// <param name="removeAfterRendering">only render this once</param>
/// <returns>rendered output content</returns>
public static MvcHtmlString RenderDelayed(this HtmlHelper helper, string injectionBlockId = null, bool removeAfterRendering = true) {
var stack = DelayedInjectionBlock.GetQueue(helper, injectionBlockId);
if( removeAfterRendering ) {
var sb = new StringBuilder(
#if DEBUG
string.Format("<!-- delayed-block: {0} -->", injectionBlockId)
#endif
);
// .count faster than .any
while (stack.Count > 0) {
sb.AppendLine(stack.Dequeue());
}
return MvcHtmlString.Create(sb.ToString());
}
return MvcHtmlString.Create(
#if DEBUG
string.Format("<!-- delayed-block: {0} -->", injectionBlockId) +
#endif
string.Join(Environment.NewLine, stack));
}
}