Including static html file from ~/Content into ASP.NET MVC view - html

I've got master page in my project, which contains some information about site copyright and some contact info in it. I'd like to take it out of master page and place it in a static files (for some reason, these files must be placed in ~/Content folder). Is there a way that I can tell in my view something like
<% Html.Include("~/Content/snippet.html") %> // not a real code
?

You are better off using a partial view (even if it only contains static text) and include it with the Html.Partial helper. But if you insist:
<%= File.ReadAllText(Server.MapPath("~/Content/snippet.html")) %>

If you are in .Net MVC 5 and want to include a HTML file a partial file without having Razor that render it:
#Html.Raw(File.ReadAllText(Server.MapPath("~/Views/Shared/ICanHaz.html")))

Use your own view engine
using
#Html.Partial("_CommonHtmlHead")
as
/Views/Shared/_CommonHtmlHead.html
or
/Views/MyArea/Shared/_CommonHtmlHead.htm
is the best for me.
Creating your own view engine for this by using the System.Web.Mvc.VirtualPathProviderViewEngine ascending class seems to be relatively easy:
/// <summary>
/// Simple render engine to load static HTML files, supposing that view files has the html/htm extension, supporting replacing tilda paths (~/MyRelativePath) in the content
/// </summary>
public class HtmlStaticViewEngine : VirtualPathProviderViewEngine
{
private static readonly ILog _log = LogManager.GetLogger(typeof (HtmlStaticViewEngine));
protected readonly DateTime? AbsoluteTimeout;
protected readonly TimeSpan? SlidingTimeout;
protected readonly CacheItemPriority? Priority;
private readonly bool _useCache;
public HtmlStaticViewEngine(TimeSpan? slidingTimeout = null, DateTime? absoluteTimeout = null, CacheItemPriority? priority = null)
{
_useCache = absoluteTimeout.HasValue || slidingTimeout.HasValue || priority.HasValue;
SlidingTimeout = slidingTimeout;
AbsoluteTimeout = absoluteTimeout;
Priority = priority;
AreaViewLocationFormats = new[]
{
"~/Areas/{2}/Views/{1}/{0}.html",
"~/Areas/{2}/Views/{1}/{0}.htm",
"~/Areas/{2}/Views/Shared/{0}.html",
"~/Areas/{2}/Views/Shared/{0}.htm"
};
AreaMasterLocationFormats = new[]
{
"~/Areas/{2}/Views/{1}/{0}.html",
"~/Areas/{2}/Views/{1}/{0}.htm",
"~/Areas/{2}/Views/Shared/{0}.html",
"~/Areas/{2}/Views/Shared/{0}.htm"
};
AreaPartialViewLocationFormats = new[]
{
"~/Areas/{2}/Views/{1}/{0}.html",
"~/Areas/{2}/Views/{1}/{0}.htm",
"~/Areas/{2}/Views/Shared/{0}.html",
"~/Areas/{2}/Views/Shared/{0}.htm"
};
ViewLocationFormats = new[]
{
"~/Views/{1}/{0}.html",
"~/Views/{1}/{0}.htm",
"~/Views/Shared/{0}.html",
"~/Views/Shared/{0}.htm"
};
MasterLocationFormats = new[]
{
"~/Views/{1}/{0}.html",
"~/Views/{1}/{0}.htm",
"~/Views/Shared/{0}.html",
"~/Views/Shared/{0}.htm"
};
PartialViewLocationFormats = new[]
{
"~/Views/{1}/{0}.html",
"~/Views/{1}/{0}.htm",
"~/Views/Shared/{0}.html",
"~/Views/Shared/{0}.htm"
};
FileExtensions = new[]
{
"html",
"htm",
};
}
protected virtual string GetContent(string viewFilePath)
{
string result = null;
if (!string.IsNullOrWhiteSpace(viewFilePath))
{
if (_useCache)
{
result = TryCache(viewFilePath);
}
if (result == null)
{
using (StreamReader streamReader = File.OpenText(viewFilePath))
{
result = streamReader.ReadToEnd();
}
result = ParseContent(result);
if (_useCache)
{
CacheIt(viewFilePath, result);
}
}
}
return result;
}
static readonly Regex TildaRegularExpression = new Regex(#"~/", RegexOptions.Compiled);
/// <summary>
/// Finds all tilda paths in the content and replace it for current path
/// </summary>
/// <param name="content"></param>
/// <returns></returns>
protected virtual string ParseContent(string content)
{
if (String.IsNullOrWhiteSpace(content))
{
return content;
}
string absolutePath = VirtualPathUtility.ToAbsolute("~/");
string result = TildaRegularExpression.Replace(content, absolutePath);
return result;
}
protected override IView CreatePartialView(ControllerContext controllerContext, string partialPath)
{
HttpContextBase httpContextBase = controllerContext.RequestContext.HttpContext;
string filePath = httpContextBase.Server.MapPath(partialPath);
string content = GetContent(filePath);
return new StaticView(content);
}
protected override IView CreateView(ControllerContext controllerContext, string viewPath, string masterPath)
{
HttpContextBase httpContextBase = controllerContext.RequestContext.HttpContext;
string result = null;
if (!string.IsNullOrWhiteSpace(masterPath))
{
string filePath = httpContextBase.Server.MapPath(masterPath);
result = GetContent(filePath);
}
string physicalViewPath = httpContextBase.Server.MapPath(viewPath);
result += GetContent(physicalViewPath);
return new StaticView(result);
}
protected virtual string TryCache(string filePath)
{
HttpContext httpContext = HttpContext.Current;
if (httpContext != null && httpContext.Cache != null)
{
string cacheKey = CacheKey(filePath);
return (string)httpContext.Cache[cacheKey];
}
return null;
}
protected virtual bool CacheIt(string filePath, string content)
{
HttpContext httpContext = HttpContext.Current;
if (httpContext != null && httpContext.Cache != null)
{
string cacheKey = CacheKey(filePath);
httpContext.Cache.Add(cacheKey, content, new CacheDependency(filePath), AbsoluteTimeout.GetValueOrDefault(Cache.NoAbsoluteExpiration), SlidingTimeout.GetValueOrDefault(Cache.NoSlidingExpiration), Priority.GetValueOrDefault(CacheItemPriority.AboveNormal), CacheItemRemovedCallback);
return true;
}
return false;
}
protected virtual string CacheKey(string serverPath)
{
return serverPath;
}
protected virtual void CacheItemRemovedCallback(string key, object value, CacheItemRemovedReason reason)
{
_log.InfoFormat("CacheItemRemovedCallback(string key='{0}', object value = ..., {1} reason={2})", key, reason.GetType().Name, reason);
}
}
public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
ViewEngines.Engines.Add(new HtmlStaticViewEngine(new TimeSpan(12,0,0,0)));
}
}
public class StaticView : IView
{
private readonly string _text;
public StaticView(string text)
{
_text = text;
}
public void Render(ViewContext viewContext, TextWriter writer)
{
if (! string.IsNullOrEmpty(_text))
{
writer.Write(_text);
}
}
}
NOTE:
This code is tested only with simple usage for rendering
partial views

Is there a reason you are holding the content in an HTML file rather than a partial view?
If you create a file called snippet.ascx in your Views/Shared folder you can import the content of that snippet.ascx file into any view by using <% Html.RenderPartial("snippet"); %>

To include static html file into a MVC View goes like this:
<!-- #include virtual="~\Content\snippet.htm" -->

For ASP .NET Core 3.1 Razor page you can do it like this:
#Html.Raw(System.IO.File.ReadAllText("wwwroot/Content/snippet.html"));
See documentation regarding static files here:
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/static-files?view=aspnetcore-3.1

Related

My static variables in my Blazor Server app are keeping their values, even if I refresh the page or even I close the tab and login again. Why?

I have a Blazor server app. Some variables on a specific razor page (main.razor) are defined as static because I want that these variables keep their values when the client navigates to other pages in the same project and comes back again to main.razor. So far it is working good.
But when I refresh the complete page, or even close the tab and reopen my app (login again), I see that the static variables still keep their values. How can prevent this? Of course I want that the values return to their default values (like 0 or ""), when the client makes a login or refreshes the page with F5. How can I do that?
I have defined the related variables in the following way:
private static StringBuilder log = new StringBuilder();
public static string testvar1= "";
public static int testvar2= 0;
Statics exist for the lifetime of the application instance which explains the behaviour you see.
You need to be maintaining state. At one end of the spectrum you can implement a State Management system such as Fluxor. At the other just create a user class, set it up as a service and inject it as a Scoped Service. Or you can build a middle-of-the-road solution.
This is mine.
A generic UIStateService that maintains a Dictionary of (state)objects against a Guid.
public class UIStateService
{
private Dictionary<Guid, object> _stateItems = new Dictionary<Guid, object>();
public void AddStateData(Guid Id, object value)
{
if (_stateItems.ContainsKey(Id))
_stateItems[Id] = value;
else
_stateItems.Add(Id, value);
}
public void ClearStateData(Guid Id)
{
if (_stateItems.ContainsKey(Id))
_stateItems.Remove(Id);
}
public bool TryGetStateData<T>(Guid Id, out T? value)
{
value = default;
if (Id == Guid.Empty)
return false;
var isdata = _stateItems.ContainsKey(Id);
var val = isdata
? _stateItems[Id]
: default;
if (val is T)
{
value = (T)val;
return true;
}
return false;
}
}
Set it up as a service:
builder.Services.AddScoped<UIStateService>();
Next define a simple template ComponentBase page that contains the common page code:
using Blazr.UI;
using Microsoft.AspNetCore.Components;
namespace BlazorApp2.Pages
{
public class StatePage : ComponentBase
{
// this provides a guid for this specific page during the lifetime of the application runtime
// we use this as the reference to store the state data against
private static Guid RouteId = Guid.NewGuid();
[Inject] protected UIStateService UIStateService { get; set; } = default!;
protected void SaveState<T>(T state) where T : class, new()
{
if (RouteId != Guid.Empty)
this.UIStateService.AddStateData(RouteId, state);
}
protected bool GetState<T>( out T value) where T : class, new()
{
value = new T();
if (RouteId != Guid.Empty && this.UIStateService.TryGetStateData<T>(RouteId, out T? returnedState))
{
value = returnedState ?? new T();
return true;
}
else
return false;
}
}
}
And use it in a page:
#page "/"
#inherits StatePage
<PageTitle>Index</PageTitle>
<h1>Hello, world!</h1>
Welcome to your new app.
<SurveyPrompt Title="How is Blazor working for you?" />
<div class="p-2">
<button class="btn btn-primary" #onclick=SetData>Set Data</button>
</div>
<div class="p-3 text-primary">
State Time : #stateData.StateTime;
</div>
#code {
private MyStateData stateData = new MyStateData();
protected override void OnInitialized()
{
if (this.GetState<MyStateData>(out MyStateData value))
this.stateData = value;
else
this.SaveState<MyStateData>(this.stateData);
}
private void SetData()
{
this.stateData.StateTime = DateTime.Now.ToLongTimeString();
SaveState<MyStateData>(this.stateData);
}
public class MyStateData
{
public string StateTime { get; set; } = DateTime.Now.ToLongTimeString();
}
}
You can now navigate around the application and the state will be maintained for the page.
You can apply an observer/notification pattern to the state object to trigger automatic state updates if you wish.

How to get data by json on xamarin android

public async override void OnActivityCreated (Bundle savedInstanceState)
{
base.OnActivityCreated (savedInstanceState);
lst = View.FindViewById<ListView> (Resource.Id.lstHome);
var result = await json.GetStringbyJson ("https://api-v2.soundcloud.com/explore/Popular+Music?tag=out-of-experiment&limit=20&linked_partitioning=1");
if (result != null)
{
var items = Newtonsoft.Json.JsonConvert.DeserializeObject<TrackModel.RootObject> (result);
lst.Adapter = new TrackAdapter(Activity, items.tracks);
}
}
public class TrackAdapter:BaseAdapter
{
LayoutInflater _inflater;
List<TrackModel.Track> _tracks;
public TrackAdapter(Context context, List<TrackModel.Track> tracks)
{
_inflater=LayoutInflater.FromContext(context);
_tracks=tracks;
}
public override TrackModel.Track this[int index]
{
get{ return _tracks [index]; }
}
public override int Count{
get{ return _tracks.Count; }
}
public override long GetItemId(int position)
{
return position;
}
public override View GetView(int position, View convertView,ViewGroup parent)
{
View view = convertView ?? _inflater.Inflate (Resource.Layout.ExploreFragment, parent, false);
var track = _tracks [position];
var viewHolder = view.Tag as TrackViewHolder;
if (viewHolder == null) {
viewHolder.Title = view.FindViewById<TextView> (Resource.Id.textviewItems);
viewHolder.SubTitle = view.FindViewById<TextView> (Resource.Id.textviewSubItem);
viewHolder.Image = view.FindViewById<ImageView> (Resource.Id.image);
view.Tag = viewHolder;
}
viewHolder.Title.Text = track.title;
viewHolder.SubTitle.Text = track.track_type;
Android.Net.Uri uri = Android.Net.Uri.Parse (track.artwork_url);
viewHolder.Image.SetImageURI(uri);
return view;
}
}
public class TrackViewHolder:Java.Lang.Object
{
public TextView Title{ get; set;}
public TextView SubTitle{get;set;}
public ImageView Image{ get; set;}
}
public override TrackModel.Track this[int index]. It get a error is makred as an overdie but no suitable indexer found to overide.
I want to take data from json up listview on xamarin android.
If it is unviersal app then it easy to use.
The way you want to set the adapter for your listview will not work that way.
Setting the adapter property of the listview inside the foreach loop is totally wrong. The same applies to your textviews.
You need to implement a custom adapter that loads a layout for each of your track list item. Your custom adapter could look like the following example I've written out of my mind with out further testing. But it implements the required methods a custom adapter needs to implement.
The important part is the GetView method that returns your track layout every time the listview ask for a new item to represent. To keep the app memory down it uses the ViewHolder pattern, which isn't required if you want to use the RecycleView.
public class TrackAdapter : BaseAdapter<Tracks>
{
LayoutInflater _inflater;
List<Tracks> _tracks;
public TrackAdapter(Context context, List<Tracks) tracks)
{
_inflater = LayoutInflater.FromContext(context);
_tracks = tracks;
}
public override Tracks this [int index]
{
get { return _tracks[index]; }
}
public override int Count
{
get { return _tracks.Count; }
}
public override long GetItemId(int position)
{
return position;
}
public override View GetView(int position, View convertView, ViewGroup parent)
{
View view = convertView ?? _inflater.Inflate(Resource.Layout.TrackListItem, parent, false);
var track = _tracks[position];
var viewHolder = view.Tag as TrackViewHolder;
if (viewHolder == null)
{
viewHolder = new TrackViewHolder();
viewHolder.Title = view.FindViewById<TextView>(Resource.Id.textviewItems);
viewHolder.Subtitle = view.FindViewById<TextView>(Resource.Id.textviewSubItems);
viewHolder.Image = view.FindViewById<ImageView>(Resource.Id.image);
view.Tag = viewHolder;
}
viewHolder.Title.Text = track.title;
viewHolder.SubTitle.Text = track.track_type;
viewHolder.Image.SetImageURI(Uri(track.artwork_url));
return view;
}
class TrackViewHolder : Java.Lang.Object
{
public TextView Title { get; set; }
public TextView SubTitle { get; set; }
public ImageView Image { get; set; }
}
}
The layout will contain your title, subtitle and image and could easily build with a normal layout file.
In your fragment you then create a new instance for TrackAdapter pass the context and the list of tracks you want to be shown in the listview.
public override void OnActivityCreated (Bundle savedInstanceState)
{
base.OnActivityCreated (savedInstanceState);
lst = View.FindViewById<ListView> (Resource.Id.lstHome);
var result = json.GetStringbyJson ("https://api-v2.soundcloud.com/explore/Popular+Music?tag=out-of-experiment&limit=20&linked_partitioning=1");
if (result != null)
{
var items = JsonConvert.DeserializeObject<TrackModel.RootObject> (result);
lst.Adapter = new TrackAdapter(Activity, items.tracks);
}
}

MVC6 alternative to #Html.DisplayFor

MVC6 introduces Tag Helpers which is a better way compared to using #Html.EditorFor, etc. However I have not found any Tag Helper that would be an alternative to #Html.DisplayFor.
Of course I can use a variable directly on a Razor page, such as #Model.BookingCode. But this does not allow to control formatting.
With MVC6, what's conceptually correct way for displaying a value of a model property?
#Html.DisplayFor still exists and can still be used.
The difference between HtmlHelpers and TagHelpers is that HtmlHelpers choose which html elements to render for you whereas TagHelpers work with html tags that you add yourself so you have more full control over what html element is used. You do have some control over the markup using templates with HtmlHelpers but you have more control with TagHelpers.
So you should think in terms of what html markup do I want to wrap this model property in and add that markup around the property itself using #Model.Property with some markup around it or continue using DisplayFor if you prefer to let the helper decide.
You can create your own tag helper
namespace MyDemo.TagHelpers
{
[HtmlTargetElement("p", Attributes = ForAttributeName)]
public class DisplayForTagHelper : TagHelper
{
private const string ForAttributeName = "asp-for";
[HtmlAttributeName(ForAttributeName)]
public ModelExpression For { get; set; }
public override void Process(TagHelperContext context, TagHelperOutput output)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (output == null)
{
throw new ArgumentNullException(nameof(output));
}
var text = For.ModelExplorer.GetSimpleDisplayText();
output.Content.SetContent(text);
}
}
}
Add use it in view:
<p asp-for="MyProperty" class="form-control-static"></p>
I have been using this as a display tag helper.
[HtmlTargetElement("*", Attributes = ForAttributeName)]
public class DisplayForTagHelper : TagHelper
{
private const string ForAttributeName = "asp-display-for";
private readonly IHtmlHelper _html;
public DisplayForTagHelper(IHtmlHelper html)
{
_html = html;
}
[HtmlAttributeName(ForAttributeName)]
public ModelExpression Expression { get; set; }
public IHtmlHelper Html
{
get
{
(_html as IViewContextAware)?.Contextualize(ViewContext);
return _html;
}
}
[HtmlAttributeNotBound]
[ViewContext]
public ViewContext ViewContext { get; set; }
public override void Process(TagHelperContext context, TagHelperOutput output)
{
if (context == null)
throw new ArgumentNullException(nameof(context));
if (output == null)
throw new ArgumentNullException(nameof(output));
var type = Expression.Metadata.UnderlyingOrModelType;
if (type.IsPrimitive)
{
output.Content.SetContent(Expression.ModelExplorer.GetSimpleDisplayText());
}
// Special Case for Personal Use
else if (typeof(Dictionary<string, string>).IsAssignableFrom(type))
{
output.Content.SetHtmlContent(Html?.Partial("Dictionary", Expression.ModelExplorer.Model));
}
else
{
var htmlContent = Html.GetHtmlContent(Expression);
output.Content.SetHtmlContent(htmlContent);
}
}
}
public static class ModelExpressionExtensions
{
public static IHtmlContent GetHtmlContent(this IHtmlHelper html, ModelExpression expression)
{
var ViewEngine = html.ViewContext.HttpContext.RequestServices.GetService(typeof(ICompositeViewEngine)) as ICompositeViewEngine;
var BufferScope = html.GetFieldValue<IViewBufferScope>();
var htmlContent = new TemplateBuilder(ViewEngine, BufferScope, html.ViewContext, html.ViewContext.ViewData, expression.ModelExplorer, expression.Name, null, true, null).Build();
return htmlContent;
}
public static TValue GetFieldValue<TValue>(this object instance)
{
var type = instance.GetType();
var field = type.GetFields(BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance).FirstOrDefault(e => typeof(TValue).IsAssignableFrom(e.FieldType));
return (TValue)field?.GetValue(instance);
}
}
try below code
public class movie
{
public int ID { get; set; }
[DisplayName("Movie Title")]
public string Title { get; set; }
}
///////////////////////////////////////////////////
#model IEnumerable<MvcMovie.Models.Movie>
<h1>Show List Movies</h1>
<label asp-for="ToList()[0].Title">< /label>
#foreach (var movie in Model)
{
#movie.Title
}

How to perform partial object serialization providing "paths" using Newtonsoft JSON.NET

I have a situation in which I have a very large C# object, however, I only need to return a handful of properties (which can be on nested objects), allow for client-side JavaScript to modify those properties and then send the resulting object back to the server in order to perform in-place partial de-serialization.
The idea is to re-use some very large existing business objects, but be intelligent about only serializing and sending only those properties back to the client application for modification (to keep the amount of data transferred at a minimum).
I basically have an XML file where I pre-define all of the bindings using a "path syntax" which would indicate only those properties I need to serialize. So, I could use something like "WorkOrder.UserField1" or "WorkOrder.Client.Name".
I have tried using a custom contract resolver to determine whether or not a property should be serialized; however, it doesn't seem that I have information as to the "path" (in other words, other properties in the object model up the chain) in order to determine if the property should or should not be serialized.
I have also tried using a custom JsonTextWriter, but it doesn't seem that I can override the methods necessary to keep track of the path, even though there is a Path property available. Is there something perhaps simple that I am overlooking in order to be able to view the path hierarchy of a property being serialized and determine if it should be serialized by looking up the path in a table and making the decision?
The basic difficulty here is that Json.NET is a contract-based serializer which creates a contract for each type to be serialized, then (de)serializes according to the contract. If a type appears in multiple locations in the object hierarchy, the same contract applies. But you want to selectively include properties for a given type depending on its location in the hierarchy, which conflicts with the basic "one type one contract" design.
One quick way to work around this is to serialize to a JObject, then use JToken.SelectTokens() to select only the JSON data you want to return, removing everything else. Since SelectTokens has full support for JSONPath query syntax, you can selectively include using array and property wildcards or other filters, for instance:
"$.FirstLevel[*].Bar"
includes all properties named "Bar" in all array members of a property named "FirstLevel" of the root object.
This should reduce your network usage as desired, but won't save any processing time on the server.
Removal can be accomplished with the following extension methods:
public static partial class JsonExtensions
{
public static TJToken RemoveAllExcept<TJToken>(this TJToken obj, IEnumerable<string> paths) where TJToken : JToken
{
if (obj == null || paths == null)
throw new NullReferenceException();
var keepers = new HashSet<JToken>(paths.SelectMany(path => obj.SelectTokens(path)), ObjectReferenceEqualityComparer<JToken>.Default);
var keepersAndParents = new HashSet<JToken>(keepers.SelectMany(t => t.AncestorsAndSelf()), ObjectReferenceEqualityComparer<JToken>.Default);
// Keep any token that is a keeper, or a child of a keeper, or a parent of a keeper
// I.e. if you have a path ""$.A.B" and it turns out that B is an object, then everything
// under B should be kept.
foreach (var token in obj.DescendantsAndSelfReversed().Where(t => !keepersAndParents.Contains(t) && !t.AncestorsAndSelf().Any(p => keepers.Contains(p))))
token.RemoveFromLowestPossibleParent();
// Return the object itself for fluent style programming.
return obj;
}
public static string SerializeAndSelectTokens<T>(T root, string[] paths, Formatting formatting = Formatting.None, JsonSerializerSettings settings = null)
{
var obj = JObject.FromObject(root, JsonSerializer.CreateDefault(settings));
obj.RemoveAllExcept(paths);
var json = obj.ToString(formatting);
return json;
}
public static TJToken RemoveFromLowestPossibleParent<TJToken>(this TJToken node) where TJToken : JToken
{
if (node == null)
return null;
JToken toRemove;
var property = node.Parent as JProperty;
if (property != null)
{
// Also detach the node from its immediate containing property -- Remove() does not do this even though it seems like it should
toRemove = property;
property.Value = null;
}
else
{
toRemove = node;
}
if (toRemove.Parent != null)
toRemove.Remove();
return node;
}
public static IEnumerable<JToken> DescendantsAndSelfReversed(this JToken node)
{
if (node == null)
throw new ArgumentNullException();
return RecursiveEnumerableExtensions.Traverse(node, t => ListReversed(t as JContainer));
}
// Iterate backwards through a list without throwing an exception if the list is modified.
static IEnumerable<T> ListReversed<T>(this IList<T> list)
{
if (list == null)
yield break;
for (int i = list.Count - 1; i >= 0; i--)
yield return list[i];
}
}
public static partial class RecursiveEnumerableExtensions
{
// Rewritten from the answer by Eric Lippert https://stackoverflow.com/users/88656/eric-lippert
// to "Efficient graph traversal with LINQ - eliminating recursion" http://stackoverflow.com/questions/10253161/efficient-graph-traversal-with-linq-eliminating-recursion
// to ensure items are returned in the order they are encountered.
public static IEnumerable<T> Traverse<T>(
T root,
Func<T, IEnumerable<T>> children)
{
yield return root;
var stack = new Stack<IEnumerator<T>>();
try
{
stack.Push((children(root) ?? Enumerable.Empty<T>()).GetEnumerator());
while (stack.Count != 0)
{
var enumerator = stack.Peek();
if (!enumerator.MoveNext())
{
stack.Pop();
enumerator.Dispose();
}
else
{
yield return enumerator.Current;
stack.Push((children(enumerator.Current) ?? Enumerable.Empty<T>()).GetEnumerator());
}
}
}
finally
{
foreach (var enumerator in stack)
enumerator.Dispose();
}
}
}
/// <summary>
/// A generic object comparerer that would only use object's reference,
/// ignoring any <see cref="IEquatable{T}"/> or <see cref="object.Equals(object)"/> overrides.
/// </summary>
public class ObjectReferenceEqualityComparer<T> : IEqualityComparer<T> where T : class
{
// Adapted from this answer https://stackoverflow.com/a/1890230
// to https://stackoverflow.com/questions/1890058/iequalitycomparert-that-uses-referenceequals
// By https://stackoverflow.com/users/177275/yurik
private static readonly IEqualityComparer<T> _defaultComparer;
static ObjectReferenceEqualityComparer() { _defaultComparer = new ObjectReferenceEqualityComparer<T>(); }
public static IEqualityComparer<T> Default { get { return _defaultComparer; } }
#region IEqualityComparer<T> Members
public bool Equals(T x, T y)
{
return ReferenceEquals(x, y);
}
public int GetHashCode(T obj)
{
return System.Runtime.CompilerServices.RuntimeHelpers.GetHashCode(obj);
}
#endregion
}
And then use them like:
public class TestClass
{
public static void Test()
{
var root = new RootObject
{
FirstLevel1 = new FirstLevel
{
SecondLevel1 = new List<SecondLevel> { new SecondLevel { A = "a11", B = "b11", Third1 = new ThirdLevel { Foo = "Foos11", Bar = "Bars11" }, Third2 = new List<ThirdLevel> { new ThirdLevel { Foo = "FooList11", Bar = "BarList11" } } } },
SecondLevel2 = new List<SecondLevel> { new SecondLevel { A = "a12", B = "b12", Third1 = new ThirdLevel { Foo = "Foos12", Bar = "Bars12" }, Third2 = new List<ThirdLevel> { new ThirdLevel { Foo = "FooList12", Bar = "BarList12" } } } },
},
FirstLevel2 = new FirstLevel
{
SecondLevel1 = new List<SecondLevel> { new SecondLevel { A = "a21", B = "b21", Third1 = new ThirdLevel { Foo = "Foos21", Bar = "Bars21" }, Third2 = new List<ThirdLevel> { new ThirdLevel { Foo = "FooList21", Bar = "BarList21" } } } },
SecondLevel2 = new List<SecondLevel> { new SecondLevel { A = "a22", B = "b22", Third1 = new ThirdLevel { Foo = "Foos22", Bar = "Bars22" }, Third2 = new List<ThirdLevel> { new ThirdLevel { Foo = "FooList22", Bar = "BarList22" } } } },
}
};
Assert.IsTrue(JObject.FromObject(root).DescendantsAndSelf().OfType<JValue>().Count() == 24); // No assert
var paths1 = new string[]
{
"$.FirstLevel2.SecondLevel1[*].A",
"$.FirstLevel1.SecondLevel2[*].Third2[*].Bar",
};
Test(root, paths1, 2);
var paths3 = new string[]
{
"$.FirstLevel1.SecondLevel2[*].Third2[*].Bar",
};
Test(root, paths3, 1);
var paths4 = new string[]
{
"$.*.SecondLevel2[*].Third2[*].Bar",
};
Test(root, paths4, 2);
}
static void Test<T>(T root, string [] paths, int expectedCount)
{
var json = JsonExtensions.SerializeAndSelectTokens(root, paths, Formatting.Indented);
Console.WriteLine("Result using paths: {0}", JsonConvert.SerializeObject(paths));
Console.WriteLine(json);
Assert.IsTrue(JObject.Parse(json).DescendantsAndSelf().OfType<JValue>().Count() == expectedCount); // No assert
}
}
public class ThirdLevel
{
public string Foo { get; set; }
public string Bar { get; set; }
}
public class SecondLevel
{
public ThirdLevel Third1 { get; set; }
public List<ThirdLevel> Third2 { get; set; }
public string A { get; set; }
public string B { get; set; }
}
public class FirstLevel
{
public List<SecondLevel> SecondLevel1 { get; set; }
public List<SecondLevel> SecondLevel2 { get; set; }
}
public class RootObject
{
public FirstLevel FirstLevel1 { get; set; }
public FirstLevel FirstLevel2 { get; set; }
}
Note that there is an enhancement request Feature request: ADD JsonProperty.ShouldSerialize(object target, string path) #1857 that would enable this sort of functionality more easily.
Demo fiddles here and here.
The much easier implementation (comparing to the accepted answer) is presented here:
public static class JsonExtensions
{
public static TJToken RemoveAllExcept<TJToken>(this TJToken token, IEnumerable<string> paths) where TJToken : JContainer
{
HashSet<JToken> nodesToRemove = new(ReferenceEqualityComparer.Instance);
HashSet<JToken> nodesToKeep = new(ReferenceEqualityComparer.Instance);
foreach (var whitelistedToken in paths.SelectMany(token.SelectTokens))
TraverseTokenPath(whitelistedToken, nodesToRemove, nodesToKeep);
//In that case neither path from paths has returned any token
if (nodesToKeep.Count == 0)
{
token.RemoveAll();
return token;
}
nodesToRemove.ExceptWith(nodesToKeep);
foreach (var notWhitelistedNode in nodesToRemove)
notWhitelistedNode.Remove();
return token;
}
private static void TraverseTokenPath(JToken value, ISet<JToken> nodesToRemove, ISet<JToken> nodesToKeep)
{
JToken? immediateValue = value;
do
{
nodesToKeep.Add(immediateValue);
if (immediateValue.Parent is JObject or JArray)
{
foreach (var child in immediateValue.Parent.Children())
if (!ReferenceEqualityComparer.Instance.Equals(child, value))
nodesToRemove.Add(child);
}
immediateValue = immediateValue.Parent;
} while (immediateValue != null);
}
}
For most cases this can be achieved by a simple single line extension method
public static string ToJson<T>(this T self, string path) => $#"{{""{path}"":{JObject.FromObject(self)[path]?.ToString(Formatting.None)}}}";
This is only valid for extracting an object nested under the root object but is easily adapted with a separate parameter to specify the output path if needed
Thanks to #dbc answer as a good solution, but like he said, it doesn't affect the performance. Sometimes the data loaded from database has numerous references and only ignoring ReferenceLoopHandling is not enough for serialization; hence the serialized data becomes very large and takes a lot of ram in server, and this is caused by repetition of serializing a single object. In this situation, it's better to make a limited jobject from data straightly, rather than making a jobject and then exclude the unwanted paths from it. This can be done with a little customization of database pure data and a ContractResolver. Let's assume all the database entities inherit from a class or interface like DbModel (this is necessary in this solution). Then by a special ContractResolver, serialization of objects can be limited. A sample is like below:
class TypeName
{
public Type Type { get; set; }
public string Name { get; set; }
}
class MyContractResolver : DefaultContractResolver
{
private List<List<TypeName>> allTypeNames = new List<List<TypeName>>();
public MyContractResolver(Type parentType, string[] includePaths)
{
foreach (var includePath in includePaths)
{
List<TypeName> typeNames = new List<TypeName>() { new TypeName() { Type = parentType } };
var pathChilderen = includePath.Split('.');
for(int i = 0; i < pathChilderen.Length; i++)
{
var propType = typeNames[i].Type.GetProperties().FirstOrDefault(c => c.Name == pathChilderen[i]).PropertyType;
if (propType.GetInterface(nameof(IEnumerable)) != null && propType != typeof(String))
{
propType = propType.GetGenericArguments().Single();
}
typeNames.Add(new TypeName() { Name = pathChilderen[i], Type = propType });
}
allTypeNames.Add(typeNames);
}
}
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
IList<JsonProperty> properties = base.CreateProperties(type, memberSerialization);
// only serializer properties that are in include paths
List<JsonProperty> excludeProperties = new List<JsonProperty>();
foreach (var property in properties)
{
if (typeof(DbModel).IsAssignableFrom(property.PropertyType) || (property.PropertyType.GetInterface(nameof(IEnumerable)) != null && property.PropertyType != typeof(String)))
{
Console.WriteLine(property.PropertyType.ToString());
var exclude = true;
foreach (var typeNames in allTypeNames)
{
var index = typeNames.FindIndex(c => c.Name == property.PropertyName && c.Type == property.PropertyType);
if (index > 0)
{
if (typeNames[index - 1].Type == type)
{
exclude = false;
goto EndSearch;
}
}
}
EndSearch:
if (exclude)
excludeProperties.Add(property);
}
}
properties = properties.Where(c => excludeProperties.All(d => d.PropertyName != c.PropertyName)).ToList();
return properties;
}
}
This class can be used like this:
// return Ok(data);
var jObject = JObject.FromObject(data,
JsonSerializer.CreateDefault(new JsonSerializerSettings()
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
Converters = new List<JsonConverter>()
{
new ValidationProblemDetailsConverter(),
new ProblemDetailsConverter(),
new StringEnumConverter()
},
ContractResolver = new MyContractResolver(typeof(Foo), new[] { "bar", "baz.qux" })
}));
return Ok(jObject);
In this example Foo is the class of main object to return, and bar and baz are properties that are going to be serialized (they are loaded from database too). In addition qux is one of the baz properties that is loaded from database and has to be serialized. In this example all the other properties of each model that are not entities of database (so are not inherited from DbModel) are serialized and all the entities of database that exist in original data but not in the including paths, are ignored to be serialized.

How does Asp.net Core renders a view

How does MVC 6 renders a view. What's the actual method in Razor ViewEngine that generates the html output? Also if possible please explain the process of rendering a view.
May be you could point me to a file on mvc source on github. thanks!
Here is a complete solution of what you are looking for. I used dependency injection to get the HtmlHelper in the controller. You can inject your own helper if you want too.
using Microsoft.AspNet.Html.Abstractions;
using Microsoft.AspNet.Mvc;
using Microsoft.AspNet.Mvc.ModelBinding;
using Microsoft.AspNet.Mvc.Rendering;
using Microsoft.AspNet.Mvc.ViewEngines;
using Microsoft.AspNet.Mvc.ViewFeatures;
using Microsoft.AspNet.Mvc.ViewFeatures.Internal;
using Microsoft.Extensions.WebEncoders;
using System.ComponentModel.DataAnnotations;
using System;
public class MyController : Controller
{
private readonly IHtmlGenerator htmlGenerator;
ICompositeViewEngine viewEngine;
IModelMetadataProvider metadataProvider;
private readonly IHtmlHelper helper;
IHtmlEncoder htmlEncoder;
IUrlEncoder urlEncoder;
IJavaScriptStringEncoder javaScriptStringEncoder;
public MyController(IHtmlHelper helper, IHtmlGenerator htmlGenerator, ICompositeViewEngine viewEngine, IModelMetadataProvider metadataProvider, IHtmlEncoder htmlEncoder, IUrlEncoder urlEncoder, IJavaScriptStringEncoder javaScriptStringEncoder)
{
this.htmlGenerator = htmlGenerator;
this.viewEngine = viewEngine;
this.metadataProvider = metadataProvider;
this.htmlEncoder = htmlEncoder;
this.urlEncoder = urlEncoder;
this.javaScriptStringEncoder = javaScriptStringEncoder;
this.helper = helper;
}
[HttpGet]
public IActionResult MyHtmlGenerator()
{
MyViewModel temp = new MyViewModel();
var options = new HtmlHelperOptions();
options.ClientValidationEnabled = true;
ViewDataDictionary<MyViewModel> dic = new ViewDataDictionary<MyViewModel>(this.metadataProvider, new ModelStateDictionary());
ViewContext cc = new ViewContext(ActionContext, new FakeView(), dic, TempData, TextWriter.Null, options);
var type = typeof(MyViewModel);
var metadata = this.metadataProvider.GetMetadataForType(type);
ModelExplorer modelEx = new ModelExplorer(this.metadataProvider, metadata, temp);
ViewData["Description"] = "test desc";
ViewData["Id"] = 1;
this.ViewData = new ViewDataDictionary(this.metadataProvider, new ModelStateDictionary());
IHtmlHelper<MyViewModel> dd = new HtmlHelper<MyViewModel>(this.htmlGenerator, this.viewEngine, this.metadataProvider, this.htmlEncoder, this.urlEncoder, this.javaScriptStringEncoder);
((ICanHasViewContext)dd).Contextualize(cc);
dd.ViewContext.ViewData = this.ViewData;
var desc = GetString(dd.TextBoxFor(m => m.ID));
var ID = GetString(dd.TextBoxFor(m => m.Description));
// Do whatever you want with the ID and desc
return new ContentResult() { Content = ID + desc };
}
public static string GetString(IHtmlContent content)
{
var writer = new System.IO.StringWriter();
content.WriteTo(writer, new HtmlEncoder());
return writer.ToString();
}
}
public class MyViewModel : BaseAssetViewModel
{
// [RegularExpression(#"^-?\d{1,13}(\.\d{0,5})?$|^-?\.\d{1,5}$")]
[Required]
public int ID { get; set; }
[MinLength(2)]
public string Description { get; set; }
// Property with no validation
public string Other { get; set; }
}
public class FakeView : IView
{
string IView.Path
{
get
{
throw new NotImplementedException();
}
}
public Task RenderAsync(ViewContext viewContext)
{
throw new InvalidOperationException();
}
Task IView.RenderAsync(ViewContext context)
{
throw new NotImplementedException();
}
}
I don't know if this may be of help, may be you have to start to look at tag helpers:
https://github.com/DamianEdwards/TagHelperStarterWeb
they're working to a different way to create helpers that integrate in the page in a more natural way.