docs(fileselect): Add KB for sync Stream exceptions

Author: dimodi

components/fileselect/events.md

@@ -33,8 +33,9 @@ Property | Type | Description
 `InvalidExtension` | `bool` | a boolean flag that shows if the file type is invalid
 `InvalidMinFileSize` | `bool` | a boolean flag that shows if file size is below the minimum
 `InvalidMaxFileSize` | `bool` | a boolean flag that shows if the file size exceeds the maximum
-`Stream`| `FileInfoStream` | a [System.IO.Stream](https://docs.microsoft.com/en-us/dotnet/api/system.io.stream) that can be used to load the file to memory, file system or other. Use it to asynchronously get the file contents as byte array.
+`Stream`| `FileInfoStream` | a [System.IO.Stream](https://docs.microsoft.com/en-us/dotnet/api/system.io.stream) that can be used to load the file to memory, file system or other. Use it to **asynchronously** get the file contents as byte array.
 
+> Due to Blazor framework limitations, `FileInfoStream` does not support **synchronous** operations such as `Read`, `Seek`, `Flush` and `Write`. The methods exist, but will [throw an exception]({%slug fileselect-kb-stream-exception%}). A possible workaround is to copy the `FileInfoStream` **asynchronously** to another `Stream` via `CopyToAsync`. The `OnSelect` event example below demonstrates this.
 
 ## OnSelect
 
@@ -73,10 +74,10 @@ The event handler receives a [`FileSelectEventArgs` object](#fileselectfileinfo)
         {
             if (!file.InvalidExtension)
             {
-	        // save to local file system
+                // save to local file system
                 await UploadFile(file);
-		// or read file in-memory
-		//await ReadFile(file);
+                // or read file in-memory
+                //await ReadFile(file);
             }
         }
     }
@@ -99,8 +100,6 @@ The event handler receives a [`FileSelectEventArgs` object](#fileselectfileinfo)
 }
 ````
 
-@[template](/_contentTemplates/common/general-info.md#event-callback-can-be-async)
-
 
 ## OnRemove
 

knowledge-base/common-null-value-parameter-format.md

@@ -30,13 +30,19 @@ I am getting an error when I am using a Telerik Blazor component in an applicati
 The exact error message can vary. Here are just a few examples:
 
 >warning Unhandled exception rendering component: Value cannot be null. (Parameter 'format')
+>
 System.ArgumentNullException: Value cannot be null. (Parameter 'format')
+>
 at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)
+>
 at System.String.Format(String format, Object arg0, Object arg1)
+>
 at Telerik.Blazor.Components.TelerikWizard.get_PagerMessage()
 
 >warning System.ArgumentNullException: Value cannot be null. (Parameter 'format')
+>
 at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)
+>
 at Telerik.Blazor.Components.Common.Filters.FilterMenu.TelerikFilterMenu.get_FilterMenuSettingsLabel() 
 
 

knowledge-base/fileselect-stream-exception.md

@@ -0,0 +1,80 @@
+---
+title: FileSelect Stream throws NotImplementedException
+description: FileSelect Stream (FileInfoStream) methods throw Not Implemented exceptions
+type: troubleshooting
+page_title: FileSelect Stream throws NotImplementedException
+slug: fileselect-kb-stream-exception
+position: 
+tags: fileselect, exception
+ticketid: 1551288, 1552410, 1560275, 1585580
+res_type: kb
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>FileSelect for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+
+## Description
+
+The `file.Stream` object in the [FileSelect `OnSelect` event handler]({%slug fileselect-events%}#onselect) throws a `NotImplementedException`.
+
+The FileSelect `Stream` (`FileInfoStream`) has exposed methods that are "not implemented".
+
+## Error Message
+
+>warning System.NotImplementedException: The method or operation is not implemented.
+>
+at Telerik.Blazor.Components.FileSelect.Stream.FileInfoStream.Read()
+
+The same exception will occur for the following methods and properties:
+
+* `Position`
+* `Flush()`
+* `Read()`
+* `Seek()`
+* `SetLength()`
+* `Write()`
+
+## Cause\Possible Cause(s)
+
+Due to Blazor framework limitations, [`FileInfoStream` does not support synchronous operations]({%slug fileselect-events%}#fileselectfileinfo) such as `Read`, `Seek`, `Flush` and `Write`. The methods exist, but throw an exception.
+
+## Solution
+
+Copy the `FileInfoStream` **asynchronously** to another `Stream` via `CopyToAsync()`. Apart from the example below, also check the [FileSelect `OnSelect` event documentation]({%slug fileselect-events%}#onselect).
+
+>caption Copy the FileSelect Stream to another one and use sync methods
+
+```CSHTML
+@using System.IO
+
+<TelerikFileSelect OnSelect="@ReadSelectedFiles" />
+
+@code {
+    private async Task ReadSelectedFiles(FileSelectEventArgs args)
+    {
+        foreach (var file in args.Files)
+        {
+            var ms = new MemoryStream();
+            await file.Stream.CopyToAsync(ms);
+
+            var byteArray = new byte[file.Size];
+
+            ms.Seek(0, SeekOrigin.Begin); // not supported by file.Stream
+            ms.Read(byteArray); // not supported by file.Stream
+        }
+    }
+}
+````
+
+## See Also
+
+* [FileSelect Overview]({%slug fileselect-overview%})