added 2nd input element

[*] second hidden input element
[*] added a js function to call the click on the hidden input element - this can be done by any custom button

BlazorInputFile/InputFile.razor

@@ -1,14 +1,25 @@
 @implements IDisposable
 @inject IJSRuntime JSRuntime
 
-<input type="file" @ref="inputFileElement" @attributes="UnmatchedParameters" />
+@if (IsElementHidden)
+{
+    <input id="@ElementId" type="file" @ref="inputFileElement" @attributes="UnmatchedParameters" style="display:none;"/>
+}
+else
+{
+    <input type="file" @ref="inputFileElement" @attributes="UnmatchedParameters" />
+}
 
 @code {
     [Parameter(CaptureUnmatchedValues = true)] public Dictionary<string, object> UnmatchedParameters { get; set; }
     [Parameter] public EventCallback<IFileListEntry[]> OnChange { get; set; }
     [Parameter] public int MaxMessageSize { get; set; } = 20 * 1024; // TODO: Use SignalR default
     [Parameter] public int MaxBufferSize { get; set; } = 1024 * 1024;
 
+
+    [Parameter] public string ElementId { get; set; } // this id is used by the js function 'wrapInput' which calls click()
+    [Parameter] public bool IsElementHidden { get; set; } = false;
+
     ElementReference inputFileElement;
     IDisposable thisReference;
 

BlazorInputFile/wwwroot/inputfile.js

@@ -63,6 +63,10 @@
             destinationUint8Array.set(sourceUint8Array, destinationOffset);
 
             return bytesToRead;
+        },
+
+        wrapInput: function wrapInput(elementId) {
+            document.getElementById(elementId).click();
         }
     };