DxUpload Class

An Upload component.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v22.1.dll

NuGet Package: DevExpress.Blazor

Declaration

public class DxUpload :
    DxComponentBase,
    IUploadViewOwner,
    IRequireSelfCascading

Remarks

The DevExpress Upload component for Blazor (<DxUpload>) allows users to upload files to the server. Users can select files in the open file dialog or drag and drop files to the drop zone.

Run Demo: Upload - Overview

Add an Upload to a Project

Follow the steps below to add the Upload component to an application:

1. Use a DevExpress Project Template to create a new Blazor Server or Blazor WebAssembly application. If you use a Microsoft project template or already have a Blazor project, configure your project to incorporate DevExpress Blazor components.
2. Add the <DxUpload>...</DxUpload> markup to your application.
3. Connect the Upload component to the server.
4. Create a controller on the server.
5. Specify other Upload options (see the sections below).

How File Upload Works

Once a user selects a file, the Upload control packs the file into an Ajax request and sends this request to the server (the upload controller).

The controller’s upload action processes this file and sends a response to the Upload control. The Upload control displays the response result (for instance, shows the Uploaded text if the file was uploaded successfully).

Users can click the cancel button to interrupt file upload and remove files from the list. To hide the cancel button, set the AllowCancel property to false.

The SelectedFilesChanged event occurs each time the file list is changed. You can also handle other events to respond to file upload. Set the ShowFileList property to false to hide the file list.

Connect the Upload Component to the Server

1. Specify the Upload component’s Name property. Its value is required to access uploaded files on the server.
2. Set the UploadUrl property to a path of a server-side controller’s action that processes upload requests.

<DxUpload Name="myFile" UploadUrl="https://localhost:10000/api/Upload/Upload/">
</DxUpload>

Create an Upload Controller on the Server

Follow the steps below to create an Upload controller:

1. Create a separate Web API application and add a controller to it.
2. Implement a controller action.
3. Create the wwwroot folder in the project.
4. Optional. Enable cross-origin requests (CORS). Do this for projects with a controller and an Upload component on different servers.

Implement a Controller Action

Create a controller action that accepts the uploaded file, checks it, and saves it to the target location on a server. Follow the steps below to do this:

1. Add the Controllers folder to your project.
2. Right-click on the Controllers folder and select Add Controller.
3. In the invoked window, select MVC Controller - Empty and click Add.
4. Rename the controller (for example, UploadController) and click Add.

Do one of the following to access the uploaded file:

• Create an action with a parameter whose name matches the Name property value.

  public ActionResult Upload(IFormFile myFile) {
      // ...
  }
  

• Use the Name property value to get the uploaded file from form variables.

  public ActionResult Upload() {
      // ...
      var myFile = Request.Form.Files["myFile"];
      // ...
  }
  

The following example demonstrates how to implement the upload controller:

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace BlazorDemo.AspNetCoreHost;
[Route("api/[controller]")]
[ApiController]
public class UploadController : ControllerBase {
    [HttpPost("[action]")]
    public ActionResult Upload(IFormFile myFile) {
        try {
            // Write code that saves the 'myFile' file.
            // Don't rely on or trust the FileName property without validation.
        } catch {
            return BadRequest();
        }
        return Ok();
    }
}

Enable CORS for a Web API Application

For security reasons, browsers do not allow web pages to send requests to different domains (the same-origin policy). The Upload component and the Web API applications cannot communicate if you use them on different servers due to different domains.

To enable cross-origin requests, configure the Web API application as explained below. You can omit this step if you publish projects with the controller and Upload component on the same server.

1. In the Program.cs file, specify the CORS policy name and call the AddCors method to apply this policy. Call the UseCors method to add the CORS middleware.

   Program.cs

   // ...
   var builder = WebApplication.CreateBuilder(args);
   string MyAllowSpecificOrigins = "_myAllowSpecificOrigins";
   // ...
   builder.Services.AddCors(options => {
       options.AddPolicy(MyAllowSpecificOrigins,
       builder => {
           builder.AllowAnyOrigin();
       });
   });
   
   var app = builder.Build();
   // ...
   app.UseCors(MyAllowSpecificOrigins);
   app.UseAuthorization();
   // ...
   

2. Apply the EnableCors attribute to the Upload controller with the policy name specified above.

   [ApiController]
   [EnableCors("_myAllowSpecificOrigins")]
   [Route("api/[controller]")]
   public class UploadController : ControllerBase {
       // ...
   }
   

If you deploy your application on an IIS web server, enable CORS in the server’s web.config file:

<system.webServer>  
<cors enabled="true" failUnlistedOrigins="true">  
    <add origin="\*" />  
</cors>
</system.webServer>

Upload Files

Common Information

Users can select files to be uploaded in the open file dialog or drag and drop files to the drop zone.

To upload/reload files in code, use the methods below:

• UploadFile/ReloadFile - Uploads/reloads a specific file.
• UploadFiles/ReloadFiles - Uploads/reloads multiple files.
• UploadAllFiles/ReloadAllFiles - Uploads/reloads all files displayed in the Upload component except for canceled files.

Chunk Upload for Large Files

The Upload can split large files into small packets and send them to the server in multiple requests (one by one). To enable chunk upload, set the ChunkSize property to a positive value that specifies the packet size in bytes.

<DxUpload Name="myFile" UploadUrl="https://localhost:10000/api/UploadChunks/Upload/"
          ChunkSize="1000000">
</DxUpload>

You should configure your Upload controller to process file chunks. To access the uploaded file, use the Upload component’s Name property value. To get information about the file chunk, use chunk metadata serialized to a JSON object (see the ChunkMetadata class in the example below).

Use one of the following ways to access file and chunk metadata:

• Create an action with two parameters. The first parameter’s name should match the Name property value. The second parameter should be a string that defines chunk metadata serialized to JSON.

  using System.Text.Json;
  
  public ActionResult Upload(IFormFile myFile, string chunkMetadata) {
      // ...
      var metaDataObject = JsonConvert.DeserializeObject<ChunkMetadata>(chunkMetadata);
      // ...
  }
  

• Get the uploaded file and chunk metadata from form variables.

  using System.Text.Json;
  
  public ActionResult Upload() {
      // ...
      var myFile = Request.Form.Files["myFile"];
      var chunkMetadata = Request.Form["chunkMetadata"];
      var metaDataObject = JsonConvert.DeserializeObject<ChunkMetadata>(chunkMetadata);
      // ...
  }
  

In the upload action, merge chunks and save the resulting file to the target location.

UploadController

using System;
using System.IO;
using System.Linq;
using System.Text.Json;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

// Declare a class that stores chunk details.
public class ChunkMetadata {
    public int Index { get; set; }
    public int TotalCount { get; set; }
    public int FileSize { get; set; }
    public string FileName { get; set; }
    public string FileType { get; set; }
    public string FileGuid { get; set; }
}

[Route("api/[controller]")]
[ApiController]
public class UploadChunksController : ControllerBase {
    [HttpPost("[action]")]
    public ActionResult Upload(IFormFile myFile) {
        string chunkMetadata = Request.Form["chunkMetadata"];
        try {
            if(!string.IsNullOrEmpty(chunkMetadata)) {
                var metaDataObject = JsonSerializer.Deserialize<ChunkMetadata>(chunkMetadata);
                // Write code that appends the 'myFile' file chunk to the temporary file.
                // You can use the $"{metaDataObject.FileGuid}.tmp" name for the temporary file.
                // Don't rely on or trust the FileName property without validation.
                if(metaDataObject.Index == metaDataObject.TotalCount - 1) {
                    // Write code that saves the 'myFile' file.
                    // Don't rely on or trust the FileName property without validation.
                }
            }
        } catch {
            return BadRequest();
        }
        return Ok();
    }
}

Run Demo: Upload - Chunk Upload

In this mode, users can pause file upload in the UI. To hide the pause button, set the AllowPause property to false.

Multiple File Upload

Set the AllowMultiFileUpload property to true to enable users to upload multiple files at once (asynchronously).

<DxUpload Name="myFile" UploadUrl="https://localhost:10000/api/Upload/Upload/"
          AllowMultiFileUpload="true">
</DxUpload>

Run Demo: Upload - Multiple File Selection

Upload Modes

The Upload component uploads files after a user selects or drops them (UploadMode.Instant). Set the UploadMode property to UploadMode.OnButtonClick to upload files after the user clicks the upload button.

<DxUpload Name="myFile" UploadUrl="https://localhost:10000/api/Upload/Upload/" 
          UploadMode="UploadMode.OnButtonClick">
</DxUpload>

Run Demo: Upload - Upload Modes

Respond to File Upload

Handle the following events to respond to actions during the file upload process:

Event	Description
FileUploadStart	Fires when file upload is about to start.
FileUploadStarted	Fires when file upload starts.
FileUploaded	Fires when a file is uploaded successfully.
FileUploadAborted	Fires when file upload is aborted.
FileUploadPaused	Fires when file upload is paused.
FileUploadError	Fires when an error occurs during file upload.
FileReloaded	Fires when a file is reloaded.
FileUploadProgressChanged	Fires when the upload progress changes.

Cancel File Upload

Users can cancel file upload in the UI. To hide the cancel button, set the AllowCancel property to false.

Users can then reload or remove the file whose upload was canceled.

To cancel file upload or remove files from the upload queue in code, use the methods below:

• CancelFileUpload/RemoveFile - Cancels a specific file’s upload or removes a specific file from the upload queue.
• CancelFilesUpload/RemoveFiles - Cancels upload of multiple files or removes multiple files from the upload queue.
• CancelAllFilesUpload/RemoveAllFiles - Cancels upload of all files or removes all files from the upload queue.

Drag and Drop

To enable drag and drop in the Upload, implement an external zone where users can drop a file to upload. Use the following properties to define the drop zone UI:

• ExternalDropZoneCssSelector - Specifies the CSS selector of a container or HTML element where to drop the files.
• ExternalDropZoneDragOverCssClass - Specifies the CSS class of the drop zone when users drag files over it.

Razor

<div id="overviewDemoDropZone" class="card custom-drop-zone jumbotron w-100 m-0">
    <svg version="1.1" id="_x31_" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" viewBox="0 0 42 42" style="enable-background:new 0 0 42 42;" xml:space="preserve">
        <style type="text/css">
            .st0{fill-rule:evenodd;clip-rule:evenodd;}
        </style>
        <g id="_x32_">
            <path id="_x33_" class="st0" d="M34,42H8c-2.2,0-4-1.8-4-4V4c0-2.2,1.8-4,4-4h19l11,11v27C38,40.2,36.2,42,34,42z M27,4v7h7L27,4z
            M34,14H24V4H8v34h26V14z" />
        </g>
        <g id="_x31_2"><path id="_x33__1_" class="st0" d="M28,26h-5v8h-2h-2v-8h-5l7-7L28,26z" /></g>
    </svg>
    <span>Drag and Drop File Here</span>
</div>
<DxUpload Name="myFile" 
          UploadUrl="https://localhost:10000/api/Upload/Upload/"
          ExternalDropZoneCssSelector="#overviewDemoDropZone"
          ExternalDropZoneDragOverCssClass="bg-light border-secondary text-dark" >
</DxUpload>

CSS

.custom-drop-zone {
    padding: 0 !important;
    border-style: dashed !important;
    border-width: 2px !important;
    height: 230px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}
.custom-drop-zone.custom-drag-over {
    background-color: #868A8D;
}

Run Demo: Upload - Overview

Validation

Client-Side Validation

Use the following Upload properties to validate uploaded files on the client:

• MaxFileSize/MinFileSize - Specifies the maximum/minimum allowed file size in bytes.
• AcceptedFileTypes - Lists allowed MIME file types.
• AllowedFileExtensions - Lists allowed file extensions.

<DxUpload Name="myFile" UploadUrl="https://localhost:10000/api/Upload/Upload/"
          AllowedFileExtensions="@(new List<string> { ".jpg", ".jpeg", ".gif", ".png" })" 
          MaxFileSize="4000000">
</DxUpload>

If validation fails, the Upload component displays an error message.

Run Demo: Upload - Validation

Server-Side Validation

To introduce secure file upload operations to your application, we recommend that you add different validation types to upload controller code, for example:

• Validate the file name: Use Path.GetFileName against the file name to obtain the actual file name.

• Limit file name length and restrict allowed characters.

• If using a real file system, check whether the file is within the expected root directory. Use Path.GetFullPath to resolve path information.

  var rootDirectory = new Directorylnfo("."); 
  var resolvedPath = Path.GetFullPath(Path.Combine(rootDirectory.FullName, userProvidedPath) ) ; 
  
  if (!resolvedPath.StartsWith(rootDirectory.FullName + Path.DirectorySeparatorChar)) { 
      throw new Exception(); 
  }
  

• Limit file size.

• Validate file extensions and manage allowed extensions. Use Path.GetExtension against a file name to obtain the actual file name extension.

  var extension = Path.GetExtension(myFile.FileName).ToUpperInvariant(); 
  var isValidExtenstion = imageExtensions.Contains(extension);  
  
  if(!isValidExtenstion) throw new InvalidOperationException();     
  

For more information and examples, refer to the following documents:

• Unrestricted File Upload
• Azure Validation
• Microsoft Security Considerations
• Validation

The following code implements a simple upload controller and validates file extensions/file paths on the server side. You can also add implement other validation methods to further secure your solution.

UploadController

using System;
using System.IO;
using System.Linq;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

[Route("api/[controller]")]
[ApiController]
public class UploadValidationController : ControllerBase {
    const long MaxFileSize = 4_000_000;
    readonly string[] imageExtensions = { ".JPG", ".JPEG", ".GIF", ".PNG" };
    [HttpPost("[action]")]
    public ActionResult Upload(IFormFile myFile) {
        try {
            var extension = Path.GetExtension(myFile.FileName).ToUpperInvariant();
            var isValidExtenstion = imageExtensions.Contains(extension);
            var isValidSize = myFile.Length <= MaxFileSize;
            if(!isValidExtenstion || !isValidSize)
                throw new InvalidOperationException();
            // Write code that saves the 'myFile' file.
            // Don't rely on or trust the FileName property without validation.
        } catch {
            return BadRequest();
        }
        return Ok();
    }
}

Run Demo: Upload - Validation

Select Button Customization

Use the SelectButtonText property to change the Select File button’s text.

<DxUpload Name="myFile" UploadUrl="https://localhost:10000/api/Upload/Upload/"
          SelectButtonText="Select My File">
</DxUpload>

To hide the select button, set the ShowSelectButton property to false.

You can also implement an external select button that invokes the open file dialog. Use the ExternalSelectButtonCssSelector to specify the CSS selector of a button or another HTML element.

The following example demonstrates how to implement the external Select File button and drop zone container. Handle the SelectedFilesChanged event and use the Visible property to hide the Upload when the file list is empty.

Razor

<div id="overviewDemoDropZone" class="card custom-drop-zone bg-light rounded-3 w-100 m-0">
    <svg version="1.1" id="_x31_" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" viewBox="0 0 42 42" style="enable-background:new 0 0 42 42;" xml:space="preserve">
        <style type="text/css">
            .st0{fill-rule:evenodd;clip-rule:evenodd;}
        </style>
        <g id="_x32_">
            <path id="_x33_" class="st0" d="M34,42H8c-2.2,0-4-1.8-4-4V4c0-2.2,1.8-4,4-4h19l11,11v27C38,40.2,36.2,42,34,42z M27,4v7h7L27,4z
            M34,14H24V4H8v34h26V14z" />
        </g>
        <g id="_x31_2"><path id="_x33__1_" class="st0" d="M28,26h-5v8h-2h-2v-8h-5l7-7L28,26z" /></g>
    </svg>
    <span>Drag and Drop File Here</span><span class="m-1">or</span>
    <button id="overviewDemoSelectButton" class="btn border-primary btn-primary m-1">Select File</button>
</div>
<DxUpload Name="myFile" UploadUrl="https://localhost:10000/api/Upload/Upload/" 
          Visible="@UploadVisible" 
          ExternalSelectButtonCssSelector="#overviewDemoSelectButton" 
          ExternalDropZoneCssSelector="#overviewDemoDropZone"
          ExternalDropZoneDragOverCssClass="custom-drag-over border-light text-white" 
          SelectedFilesChanged="@SelectedFilesChanged">
</DxUpload>

@code {
    bool UploadVisible { get; set; } = false;

    protected void SelectedFilesChanged(IEnumerable<UploadFileInfo> files) {
        UploadVisible = files.ToList().Count > 0;
        InvokeAsync(StateHasChanged);
    }
}

CSS

.custom-drop-zone {
    padding: 0 !important;
    border-style: dashed !important;
    border-width: 2px !important;
    height: 230px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}
.custom-drop-zone.custom-drag-over {
    background-color: #868A8D;
}

Run Demo: Upload - Overview

Troubleshooting

If a Blazor application throws unexpected exceptions, refer to the following help topic: Troubleshooting.

Implements

IHandleEvent

IHandleAfterRender

IAsyncDisposable

IComponent

Inheritance

Object

ComponentBase

DevExpress.Blazor.Base.DxAsyncDisposableComponent

DevExpress.Blazor.Base.DxDecoratedComponent

DxComponentBase

DxUpload