-
Notifications
You must be signed in to change notification settings - Fork 73
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
kb(fileselect|upload): Add KB for image preview (#2260)
* kb(fileselect|upload): Add KB for image preview * Add description * Update knowledge-base/upload-preview-image.md Co-authored-by: Iva Stefanova Koevska-Atanasova <[email protected]> * Update knowledge-base/upload-preview-image.md Co-authored-by: Iva Stefanova Koevska-Atanasova <[email protected]> * Update knowledge-base/upload-preview-image.md Co-authored-by: Iva Stefanova Koevska-Atanasova <[email protected]> * polishing --------- Co-authored-by: Iva Stefanova Koevska-Atanasova <[email protected]>
- Loading branch information
1 parent
9d1cc2b
commit 41deb7f
Showing
2 changed files
with
304 additions
and
1 deletion.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,303 @@ | ||
--- | ||
title: Preview Selected or Uploaded Image | ||
description: Learn how to display or preview the images that the user selected in the Telerik Blazor Upload or FileSelect component. | ||
type: how-to | ||
page_title: How to Preview Selected or Uploaded Image | ||
slug: upload-kb-preview-image | ||
position: | ||
tags: telerik, blazor, fileselect, upload | ||
ticketid: 1468224, 1476179, 1481266, 1567963, 1621741 | ||
res_type: kb | ||
--- | ||
|
||
## Environment | ||
|
||
<table> | ||
<tbody> | ||
<tr> | ||
<td>Product</td> | ||
<td>FileSelect for Blazor, <br /> Upload for Blazor</td> | ||
</tr> | ||
</tbody> | ||
</table> | ||
|
||
## Description | ||
|
||
This KB article answers the following questions: | ||
|
||
* How to immediately display the uploaded image files in the Blazor app? | ||
* How to render an image preview when using the Blazor FileSelect? | ||
* How to show the uploaded file as a preview when using the Upload control? I prefer to show a Base64 image without saving the file to the server. | ||
* How to preview the selected image in the Upload `OnSelect` event? | ||
* How to get the raw file content from the Upload component and add it to a memory stream? | ||
|
||
## Solution | ||
|
||
Users can preview images that are uploaded through the [Upload component]({%slug upload-overview%}) or selected through the [FileSelect component]({%slug fileselect-overview%}). | ||
|
||
In Blazor, [previewing images is easier when using the FileSelect](#using-the-fileselect), but based on your requirements you might [choose the Upload over the FileSelect]({%slug upload-overview%}#upload-vs-fileselect) or vice versa. | ||
|
||
### Using the Upload | ||
|
||
1. Set the [`Accept`, `AllowedExtensions`, and `MaxFileSize`]({%slug upload-overview%}#upload-parameters) parameters of the Upload. | ||
1. [Ensure the Blazor app can handle large uploaded files]({%slug upload-overview%}#large-file-uploads) with a size that matches or exceeds `MaxFileSize`. | ||
1. [Implement a controller action method to receive the uploaded files]({%slug upload-overview%}#implement-controller-methods). Also see the [example on the Upload Events page]({%slug upload-events%}#example). | ||
1. Read the uploaded image(s) in the controller and return an image URL or [Base64 data URI](https://en.wikipedia.org/wiki/Data_URI_scheme) for the `<img>` tag(s) to render. You can choose to provide the original image to the UI or a smaller version for greater efficiency. | ||
1. Subscribe to the [Upload `OnSuccess` event]({%slug upload-events%}#onsuccess) to detect completed file uploads and obtain the `<img>` tag's `src` value. You can also use `OnSuccess` to detect file removals in the Upload component and remove the respective `<img>` tags. | ||
|
||
You cannot preview the image in the Upload `OnSelect` event, because this event handler has no access to the file contents. | ||
|
||
>caption Preview uploaded images when using the Upload component | ||
<div class="skip-repl"></div> | ||
|
||
````Razor | ||
@inject NavigationManager NavigationManager | ||
<h2>Upload</h2> | ||
<TelerikUpload Accept="@string.Join(",", ImageFileExtensions)" | ||
AllowedExtensions="@ImageFileExtensions" | ||
MaxFileSize="@MaxImageSize" | ||
SaveUrl="@ToAbsoluteUrl("api/upload/saveimage")" | ||
RemoveUrl="@ToAbsoluteUrl("api/upload/removeimage")" | ||
OnSuccess="@OnUploadSuccess"> | ||
</TelerikUpload> | ||
<div class="image-preview"> | ||
@foreach (var image in UploadImages) | ||
{ | ||
<img src="@image.ImageSource" class="k-border-2 k-border-solid k-border-primary" /> | ||
} | ||
</div> | ||
<style> | ||
.image-preview { | ||
display: flex; | ||
gap: 2em; | ||
flex-wrap: wrap; | ||
align-items: center; | ||
} | ||
.image-preview img { | ||
max-width: 200px; | ||
max-height: 200px; | ||
} | ||
</style> | ||
@code { | ||
private List<string> ImageFileExtensions { get; set; } = new List<string>() { ".jpg", ".jpeg", ".png", ".gif" }; | ||
private int? MaxImageSize { get; set; } = 8 * 1024 * 1024; | ||
private List<ImageModel> UploadImages { get; set; } = new(); | ||
private void OnUploadSuccess(UploadSuccessEventArgs args) | ||
{ | ||
var fileInfo = args.Files.First(); | ||
if (args.Operation == UploadOperationType.Upload) | ||
{ | ||
UploadImages.Add(new ImageModel() | ||
{ | ||
ImageId = fileInfo.Id, | ||
ImageSource = args.Request.ResponseText | ||
}); | ||
} | ||
else | ||
{ | ||
UploadImages.RemoveAll(x => x.ImageId == fileInfo.Id); | ||
} | ||
} | ||
private string ToAbsoluteUrl(string url) | ||
{ | ||
return $"{NavigationManager.BaseUri}{url}"; | ||
} | ||
public class ImageModel | ||
{ | ||
public string ImageId { get; set; } = string.Empty; | ||
public string ImageSource { get; set; } = string.Empty; | ||
} | ||
} | ||
```` | ||
````Controller | ||
using System; | ||
using System.IO; | ||
using System.Threading.Tasks; | ||
using Microsoft.AspNetCore.Hosting; | ||
using Microsoft.AspNetCore.Http; | ||
using Microsoft.AspNetCore.Mvc; | ||
namespace TelerikBlazorUpload.Controllers | ||
{ | ||
[Route("api/[controller]/[action]")] | ||
public class UploadController : ControllerBase | ||
{ | ||
public IWebHostEnvironment HostingEnvironment { get; set; } | ||
public UploadController(IWebHostEnvironment hostingEnvironment) | ||
{ | ||
HostingEnvironment = hostingEnvironment; | ||
} | ||
[HttpPost] | ||
public async Task<string> SaveImage(IFormFile files) | ||
{ | ||
string response = ""; | ||
if (files != null) | ||
{ | ||
try | ||
{ | ||
// OPTION 1. Return a Base64 string and display the image source as a data URI. | ||
// Not efficient for large files. | ||
//var imageBytes = new byte[files.Length]; | ||
//await files.OpenReadStream().ReadAsync(imageBytes); | ||
//response = $"data:image/{Path.GetExtension(files.FileName)};base64,{Convert.ToBase64String(imageBytes.ToArray())}"; | ||
// =============== | ||
// OPTION 2. Save the image as a file and return the image URL. | ||
// May not be efficient for large files. You can save another smaller version of the file. | ||
var imageSaveLocation = Path.Combine(HostingEnvironment.WebRootPath, files.FileName); | ||
using var imageStream = new FileStream(imageSaveLocation, FileMode.Create); | ||
await files.CopyToAsync(imageStream); | ||
response = files.FileName; | ||
} | ||
catch (Exception e) | ||
{ | ||
Response.StatusCode = 500; | ||
await Response.WriteAsync($"File processing failed: {e.Message}"); | ||
} | ||
} | ||
return response; | ||
} | ||
[HttpPost] | ||
public async Task<IActionResult> RemoveImage([FromForm] string files) | ||
{ | ||
if (files != null) | ||
{ | ||
try | ||
{ | ||
var imageLocation = Path.Combine(HostingEnvironment.WebRootPath, files); | ||
if (System.IO.File.Exists(imageLocation)) | ||
{ | ||
System.IO.File.Delete(imageLocation); | ||
} | ||
} | ||
catch | ||
{ | ||
Response.StatusCode = 500; | ||
await Response.WriteAsync("File deletion failed."); | ||
} | ||
} | ||
return new EmptyResult(); | ||
} | ||
} | ||
} | ||
```` | ||
|
||
### Using the FileSelect | ||
|
||
1. Set the [`Accept`, `AllowedExtensions`, and `MaxFileSize`]({%slug fileselect-overview%}#fileselect-parameters) parameters of the FileSelect. | ||
1. [Increase the SignalR message size]({%slug common-kb-increase-signalr-max-message-size%}) to match or exceed `MaxFileSize`. | ||
1. Subscribe to the [FileSelect `OnSelect` event]({%slug fileselect-events%}#onselect). | ||
1. Read the selected image(s) and create a [Base64 data URI](https://en.wikipedia.org/wiki/Data_URI_scheme) for the `<img>` tag(s) to render. | ||
1. (optional) Subscribe to the [FileSelect `OnRemove` event]({%slug fileselect-events%}#onremove) to remove the image preview. | ||
|
||
>caption Preview selected images when using the FileSelect component | ||
````CSHTML | ||
<h2>FileSelect</h2> | ||
<TelerikFileSelect Accept="@string.Join(",", ImageFileExtensions)" | ||
AllowedExtensions="@ImageFileExtensions" | ||
MaxFileSize="@MaxImageSize" | ||
OnSelect="@OnFileSelectSelect" | ||
OnRemove="@OnFileSelectRemove"> | ||
</TelerikFileSelect> | ||
@if (FileSelectImages.Any()) | ||
{ | ||
<h2>Image Preview</h2> | ||
<div class="image-preview"> | ||
@foreach (var image in FileSelectImages) | ||
{ | ||
<img src="@image.ImageSource" class="k-border-2 k-border-solid k-border-primary" /> | ||
} | ||
</div> | ||
} | ||
<style> | ||
.image-preview { | ||
display: flex; | ||
gap: 2em; | ||
flex-wrap: wrap; | ||
align-items: center; | ||
} | ||
.image-preview img { | ||
max-width: 200px; | ||
max-height: 200px; | ||
} | ||
</style> | ||
@code { | ||
private List<string> ImageFileExtensions { get; set; } = new List<string>() { ".jpg", ".jpeg", ".png", ".gif" }; | ||
private int? MaxImageSize { get; set; } = 8 * 1024 * 1024; | ||
private List<ImageModel> FileSelectImages { get; set; } = new(); | ||
private async Task OnFileSelectSelect(FileSelectEventArgs args) | ||
{ | ||
foreach (var file in args.Files) | ||
{ | ||
if (!file.InvalidExtension && !file.InvalidMaxFileSize) | ||
{ | ||
var imageBytes = new byte[file.Size]; | ||
await using MemoryStream ms = new MemoryStream(imageBytes); | ||
await file.Stream.CopyToAsync(ms); | ||
FileSelectImages.Add(new ImageModel() | ||
{ | ||
ImageId = file.Id, | ||
ImageSource = $"data:image/{file.Extension};base64,{Convert.ToBase64String(ms.ToArray())}" | ||
}); | ||
} | ||
} | ||
} | ||
private void OnFileSelectRemove(FileSelectEventArgs args) | ||
{ | ||
foreach (var file in args.Files) | ||
{ | ||
FileSelectImages.RemoveAll(x => x.ImageId == file.Id); | ||
} | ||
} | ||
public class ImageModel | ||
{ | ||
public string ImageId { get; set; } = string.Empty; | ||
public string ImageSource { get; set; } = string.Empty; | ||
} | ||
} | ||
```` | ||
|
||
## See Also | ||
|
||
* [Upload Overview]({%slug upload-overview%}) | ||
* [Handle Upload Events]({%slug upload-events%}) | ||
* [FileSelect Overview]({%slug fileselect-overview%}) | ||
* [Handle FileSelect Events]({%slug fileselect-events%}) |