Upload Files In .NET Core By Drag And Drop Using Dropzone.JS

17. October 2016 21:41

.NET Core ASP.NET MVC Jquery Web  0 Comments

Mostly all web applications out there has some way or the other amazing ways to upload a single or multiple files. While surfing on Github I found this amazing library to upload the files to the server in a unique way with lot of configurations. It support parallel uploads along with cancellation of the files which are in the upload queue along with a good looking progress bar to show the progress of upload.

I get the drag and drop to work in just like 5 minutes. It is super easy and that with some powerful configurations. To install Dropzone you can use the Nuget command.

PM> Install-Package dropzone
Add reference of js and css files on your page. To get the UI ready use this HTML.
<div class="row">
    <div class="col-md-9">
        <div id="dropzone">
            <form action="/Home/Upload" class="dropzone needsclick dz-clickable" id="uploader">
                <div class="dz-message needsclick">
                    Drop files here or click to upload.<br>
                </div>
            </form>
        </div>
    </div>
</div>

The output of the above HTML looks like this.

There are few points to be noted here in the above HTML. Notice the action and class attributes for the form element. You will also be needing the id attribute as well. Here the action attribute points to the ActionResult which is responsible to handle the file upload. I have pointed it to the Upload ActionResult in my controller class which accepts a parameter of type IFormFile. In case of a MVC application, we would have used HttpPostedFileBase class. Here is the complete code which handles the file upload.

[HttpPost]
public async Task<IActionResult> Upload(IFormFile file)
{
    var uploads = Path.Combine(_environment.WebRootPath, "uploads");
    if (file.Length > 0)
    {
        using (var fileStream = new FileStream(Path.Combine(uploads, file.FileName), FileMode.Create))
        {
            await file.CopyToAsync(fileStream);
        }
    }
    return RedirectToAction("Index");
}

The _environment variable you see in the above code is the instance of IHostingEnvironment interface which I have injected in the controller. Always use IHostingEnvironment interface to resolve the paths. You can hard code the file path but it may not work on other platforms. The combine method returns the correct path based on the platform the code is executing. The WebRootPath property returns the path of wwwroot folder and the second parameter uploads is then appended correctly with the path.

Now it is time to make some adjustment in the Dropzone configuration. Recall the id attribute of the form element. I named it uploader. The Dropzone library has a unique way to set the configuration. Like this.

<script>
    $(document).ready(function () {
        Dropzone.options.uploader = {
            paramName: "file",
            maxFilesize: 2,
            accept: function (file, done) {
                if (file.name == "test.jpg") {
                    alert("Can't upload a test file.");
                }
                else {
                    //Show a confirm alert and display the image on the page.
              }
           }
        };
});
</script>
You have to be a bit careful when setting this configuration. In the configuration above the paramName states the name that will be used to transfer the file. This name should be the same as the IFormFile parameter of the Upload method in the controller. In this case I am using file and the same has to be there in the param of the Upload method. If the names mis-match the files will not be uploaded. The other parameter I am using is the maxFileSize and is very much self-explanatory. I have set the size to be 2 MB and because of this configuration, any file above this limit will not be uploaded. Here is an example of such kind of failure.
All the other files were uploaded successfully except one file which is 4.32 MB and is way beyond the limit I set in my Dropzone configuration. If you hover the file, you will see why it got failed.
This is the simplest approach through which you can have drag and drop upload support in your applications. The configuration I am using here is the simplest and minimalistic configuration that can get you started in no time. There are some more powerful configurations like parallelUploads and uploadMultiple that you should look into and use it.
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Get The Correct File Paths In .NET Core

3. October 2016 22:12

.NET Core ASP.NET MVC Ubuntu Web  0 Comments

I run a custom blog engine I wrote myself on MVC 4 and as you would have thought it is on Windows hosting. I am re-writing my blog engine in .NET Core so that I can get it running on a Linux hosting as well. I am using Windows machine and Visual Studio Community Edition to write it and using a Ubuntu VM box to test it. My current blog uses SQL Server as a back-end but Linux does not support SQL Server and therefore I have to move to MySQL or any other No-SQL database available for Linux distros. For now I will be saving everything on the disk in JSON format.

The problem comes when I switch from database to file system. Both Windows and Linux file systems are different, so when working I hard-coded the data folder which holds all the posts for my blog. I publish the solution and deploy it to Ubuntu VM. I started the server and it ended up showing me this error in the console.

Notice the path of the data folder in the above screenshot. The path I am referring in the code ends up with backward slash which is not a UNIX format. Also a thing to note here is that UNIX follows a strict naming convention unlike Windows. For example, in Windows Data and data are same, but in UNIX they are not. Because I have hard-coded the path in my application while developing, it will end up in an error on UNIX machine.

To make the paths consistent in your application, I have to make use of the System.IO namespace Path class's Combine method. Combine method is an overloaded method. If you are hearing this method for the first time then make sure you read the documentation. This method renders the correct path based on the platform my code is executing. So instead of doing something like this.

var _posts = Directory.EnumerateFiles("Data\\Posts");
I have done something like this.
string posts = Path.Combine("Data", "Posts");
_files = Directory.EnumerateFiles(posts);
In short, if you are developing a .NET Core application targeting Windows along with UNIX and OSX, then make sure that you follow this approach to get the correct paths or else you will end up with an exception and your website inaccessible.
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Building Angular 2 App With Web API And .NET Core

21. May 2016 18:45

.NET Core ASP.NET MVC  0 Comments

Setting up the new Angular 2 app with Web API and .NET core is easy but can be a bit tricky. The older beta releases of Angular 2 works fine as there are not many files to refer and to work with. When I started using Angular 2 it was in RC1 and the way the files are being referenced in the app is bit different than the older versions of Angular 2. I don't want to repeat these steps again and again so I put up a Github repo for this seed project. You clone it and hit F5 and you will have your Angular 2 app with Web API.

At the time of writing this post I am using .NET Core version 1.0.0-preview1-002702. The complete seed project is available on GitHub.
Here is how I did it. Select ASP.NET Core Web Application (.NET Core). I have installed the new .NET Core RC2. Name the project as you like.
Select the Web API project template.
After the project creation is successfull. The first thing is to create a Views folder. The folder structure is like the same like it is for MVC application. This is how the folder structure looks like.
Because its a a Web API project, by default it will not render the views and therefore we have to add some dependencies in project.json file.
"Microsoft.AspNetCore.StaticFiles": "1.0.0-rc2-final",
"Microsoft.AspNetCore.Mvc.TagHelpers": "1.0.0-rc2-final",
"Microsoft.AspNetCore.Mvc.WebApiCompatShim": "1.0.0-rc2-final"
The project.json file is different than that of the older version of the .NET Core. You will see the difference when you see it.
Next we set the routes for the views we have in the Startup.cs file.
app.UseMvc(routes =>
{
    routes.MapRoute("default",
                    "{controller=Home}/{action=Index}/{id?}");

    routes.MapWebApiRoute("defaultApi",
                          "api/{controller}/{id?}");
});
The routes are now set and you can run the application and check if you can see the view or not. Once that is set, let start adding the support for Angular. Here is the list of the files which we need to add.
tsconfig.json file

Add the below code to the file and save it.
{
  "compilerOptions": {
    "target": "es5",
    "module": "system",
    "moduleResolution": "node",
    "sourceMap": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "removeComments": false,
    "noImplicitAny": false,
    "rootDir": "wwwroot",
    "outDir": "wwwroot",
    "listFiles": true,
    "noLib": false,
    "diagnostics": true
  },
  "exclude": [
    "node_modules"
  ]
}
typings.json file

Add a blank .json file and name it typings.json

Add below lines to the typings.json file.
{
  "ambientDependencies": {
    "es6-shim": "registry:dt/es6-shim#0.31.2+20160317120654",
    "jasmine": "registry:dt/jasmine#2.2.0+20160412134438"
  }
}
As per the official Angular documentation, we will stick with NPM to fulfill the client-side dependencies. Start with adding new npm Configuration File. The content of the NPM file is almost the same, but I made few changes as per my requirement. Here is the complete configuration file.
{
  "name": "Angular2WebAPI-Seed",
  "version": "1.0.0",
  "scripts": {
    "postinstall": "typings install"
  },
  "license": "ISC",
  "dependencies": {
    "@angular/common": "2.0.0-rc.1",
    "@angular/compiler": "2.0.0-rc.1",
    "@angular/core": "2.0.0-rc.1",
    "@angular/http": "2.0.0-rc.1",
    "@angular/platform-browser": "2.0.0-rc.1",
    "@angular/platform-browser-dynamic": "2.0.0-rc.1",
    "@angular/router": "2.0.0-rc.1",
    "@angular/router-deprecated": "2.0.0-rc.1",
    "@angular/upgrade": "2.0.0-rc.1",

    "lodash": "4.12.0",
    "systemjs": "0.19.27",
    "es6-shim": "^0.35.0",
    "reflect-metadata": "^0.1.3",
    "rxjs": "5.0.0-beta.6",
    "zone.js": "^0.6.12",
    "angular2-in-memory-web-api": "0.0.7",
    "bootstrap": "^3.3.6"
  },
  "devDependencies": {
    "gulp": "3.9.1",
    "concurrently": "^2.0.0",
    "typescript": "^1.8.10",
    "typings": "^0.8.1"
  }
}
Notice the postinstall section in the npm configuration file. In this section we are installing the types required by our Angular 2 application. Now we can start setting up the Angular stuff in the wwwroot folder. Create an app and js folder inside this folder. Inside app folder create a new .ts file (TypeScript file). Here is the folder structure looks like in the wwwroot folder.
You can see a system.config.js file is the same as you can see the Angular quickstart guide. I just have map the paths for the dependencies so that can be loaded without any problem. The main.ts file will be the main bootstrapper and app.component.ts file is the component file which will render the content on the page. At this point running the application will fail and it will give you several warnings and errors. To resolve that we need to add the references and we can do this easily by using a gulp file. The gulp file will automate the copying of dependencies in the wwwroot folder and ease our task. 
The content of the gulp file in this case looks like this.
/// <binding BeforeBuild='default' />

var _ = require('lodash');
var gulp = require('gulp');

var js = [
    'node_modules/zone.js/dist/zone.min.js',
    'node_modules/systemjs/dist/system.js',
    'node_modules/reflect-metadata/Reflect.js',
    'node_modules/es6-shim/es6-shim.min.js'
];

var map = [
    'node_modules/es6-shim/es6-shim.map',
    'node_modules/reflect-metadata/reflect.js.map',
    'node_modules/systemjs/dist/system.js.map'
];

var folders = [
    'node_modules/@angular/**/*.*',
    'node_modules/rxjs/**/*.*'
];

gulp.task('copy-js', function () {
    _.forEach(js, function (file, _) {
        gulp.src(file)
       .pipe(gulp.dest('./wwwroot/js'))
    });
});

gulp.task('copy-map', function () {
    _.forEach(map, function (file, _) {
        gulp.src(file)
        .pipe(gulp.dest('./wwwroot/js'))
    });
});

gulp.task('copy-folders', function () {
    _.forEach(folders, function (folder) {
        gulp.src(folder, { base: 'node_modules' })
            .pipe(gulp.dest('./wwwroot/js'))
    });
})

gulp.task('default', ['copy-js', 'copy-map', 'copy-folders']);
Notice the very first line in the file above. We want to execute the task on every time before the build is triggered. The gulp file will only be copying the required files to the js folder and other unnecessary files will not be required. After the task is executed here is the how the final directiry structure will look like under wwwroot.
Depending on the selector you have in your component, you need to add the selector to your view. In my case the selector is app, hence add <app></app> in your Index.cshtml file.

After you set up the index page, there is one more thing that you have to do is to set the launch URL.

The URL may change and differ as per your API endpoint. Press F5 to run the application.

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Parsing Markdown Using Custom TagHelper In ASP.NET MVC 6

30. November 2015 21:01

.NET Core ASP.NET MVC  0 Comments

Previous versions of MVC allows us to write HtmlHelpers which does a pretty good job then and they are doing it now as well. But in MVC 6, the ASP.NET team has introduced TagHelpers.

Parsing Mardown in .NET is way too simple than one can imagine. Thanks to Stackoverflow's MardownSharp and Karlis Gangis's CommonMark.NET. I use CommonMark.NET as it provides a much faster parsing than other libraries. The blogging platform I use is a custom blogging engine I wrote in MVC4. The post content is saved in HTML which makes my raw HTML way to messy when compared to simple markdown syntax. I have no plans to change the way it is right now, but for the other simple application which is quite similar to notes taking or blogging apps, I would like to save the content in markdown.

I will start with a simple implementation of this custom TagHelper and then then we can look into the other ways to enhance it. Here is how easy it is to create your custom TagHelper.

Create a new class file MarkdownTagHelper.cs. Inside the file, rename the class name to match the file name or you can change the name way you like. In my case I am keeping the class name as same as the file name.

Pay attention to the name of the custom TagHelper. By design, compiler will remove the word TagHelper from the class name and the rest of the name will become your custom TagHelper name.

The next step is to inherit our class with TagHelpers class. Every custom TagHelper will inherit this class. Just like the UserControl class when creating a custom user control. The TagHelper provide us two virtual methods, Process and a ProcessAsync method which we will be going to override to implement our custom logic for our custom markdown TagHelper. The first parameter is the TagHelperContext which holds the information about the current tag and the second parameter is TagHelperOutput object represents the output being generated by the TagHelper. As we need to parse the markdown in our razor view pages, we need to add reference of CommonMark.Net library. Use the below Nuget command to add it to your current project.

Install-Package CommonMark.Net

Till here this is how the code will look like.

So now we have our custom TagHelper that will let us parse the markdown. But to use it in our views we need to opt-in for this TagHelper in the _ViewImports.cshtml file. To enable your custom TagHelper just type in like this:

@addTagHelper "*, WebApplication1"

Your custom tag helper would have been turned purple in color on the view page. It is similar to the line above it where @addTagHelper is importing all the TagHelpers from the given namespace. If you are not interested in opting-in for all the TagHelpers in the given namespace then make use of the @removeTagHelper to disable the TagHelpers you don’t need. For this I want all the tag helpers I have created to be a part of the application and hence the * symbol.

In your view, where you want to use this just type in <markdown> and inside this tag you should have your markdown. To test it, you can view the any raw file in Github and copy the text. I am using README.md from CommonMark.NET and it rendered perfectly.

Caution: When copy-pasting the markdown code from anywhere to your view make sure that you do not have a whitespace in the front of the line. This is only applicable when you are working with the in-line markdown. Here is the screenshot with comparison.

Hit F5 and see the markdown tag helper in action. Below is the output I get.

This is the simplest of all. Now let’s add some prefix to our custom TagHelper. To add a custom tag prefix to the TagHelper, we just need to pay a visit to _ViewImports.cshtml file again and add a new line like so:

@tagHelperPrefix "blog-"

After adding the above line in the file, go to the view page where you have used your custom TagHelper and you can notice that the <markdown> tag isn’t purple anymore. This is because we now have to add a custom tag-prefix that we just defined in the _ViewImports.cshtml file. Change it from <markdown> to <blog-markdown> and it is purple again.

By design, the TagHelper will take <markdown> as a tag to be processed. But it can be easily ignored by using the HtmlTargetElement attribute at the top of the class and allow the use of another name rather than <markdown>. This does not mean that you cannot use <markdown> but instead you can also use the custom TagHelper with the name specify in this attribute.

Now let’s add some attributes to my markdown TagHelper. Let’s try to add a url attribute which will help user to render the markdown on the view from a remote site like Github. To add an attribute, simply add a new public property of type string and call it url. When you create a public property in the TagHelper class it is automatically assumed it is an attribute. To make use of this property, my view now simply say this:

<blog-markdown url="https://raw.githubusercontent.com/Knagis/CommonMark.NET/master/README.md">
</blog-markdown>

The url attribute value is being read by the TagHelper which in turn read the whole string of markdown from Github and render the HTML on the page. Let’s focus again on TargetElement attribute for a while. Consider a scenario where you don’t want your custom TagHelper to render or work if the attributes are not passed or missing. This is where HtmlTargetElement attribute comes into picture. If I don’t want my TagHelper to work if the url parameter is missing then you can simple write your HtmlTargetElement attribute like so:

[HtmlTargetElement("markdown", Attributes = "url")]

Notice the Attributes parameter. The Attributes parameter allows you to set the name of all the attributes which should be processed by your TagHelper or else the TagHelper will not work. For instance, if I just use the <markdown> TagHelper but did not pass the url attribute, the TagHelper will not execute and you will see the raw markdown code. My requirement is to have this TagHelper working with or without the use of url attribute. I can comment out or remove the HtmlTargetElemen attribute or just remove the Attributes parameter to get going.

Here is the complete MarkdownTagHelper.cs:

using Microsoft.AspNet.Razor.Runtime.TagHelpers;
using System;
using System.Net.Http;
using System.Threading.Tasks;

namespace WebApplication1.TagHelpers
{
    //[HtmlTargetElement("markdown", Attributes = "url")]
    public class MarkdownTagHelper : TagHelper
    {
        //Attribute for our custom markdown
        public string Url { get; set; }

        private string parse_content = string.Empty;

        //Stolen from: http://stackoverflow.com/questions/7578857/how-to-check-whether-a-string-is-a-valid-http-url
        private bool isValidURL(string URL)
        {
            Uri uriResult;
            return Uri.TryCreate(URL, UriKind.Absolute, out uriResult)
                && (uriResult.Scheme.ToLowerInvariant() == "http" || uriResult.Scheme.ToLowerInvariant() == "https");
        }

        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
        {
            if (context.AllAttributes["url"] != null)
            {
                string url = context.AllAttributes["url"].Value.ToString();
                string webContent = string.Empty;
                if (url.Trim().Length > 0)
                {
                    if (isValidURL(url))
                    {
                        using (HttpClient client = new HttpClient())
                        {
                            webContent = await client.GetStringAsync(new Uri(url));
                            parse_content = CommonMark.CommonMarkConverter.Convert(webContent);
                            output.Content.SetHtmlContent(parse_content);
                        }
                    }
                }
            }
            else
            {
                //Gets the content inside the markdown element
                var content = await output.GetChildContentAsync();

                //Read the content as a string and parse it.
                parse_content = CommonMark.CommonMarkConverter.Convert(content.GetContent());

                //Render the parsed markdown inside the tags.
                output.Content.SetHtmlContent(parse_content);
            }
        }
    }
}

I found the full TagHelper feature in MVC 6 a lot more convenient and powerful. I hope you like it as well.

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