Fixed file upload field markup

flask_admin/form/upload.py

@@ -39,6 +39,7 @@ class FileUploadInput(object):
         look and feel.
     """
     empty_template = ('<input %(file)s>')
+    input_type = 'file'
 
     data_template = ('<div>'
                      ' <input %(text)s>'
@@ -80,6 +81,7 @@ class ImageUploadInput(object):
         look and feel.
     """
     empty_template = ('<input %(file)s>')
+    input_type = 'file'
 
     data_template = ('<div class="image-thumbnail">'
                      ' <img %(image)s>'

flask_admin/templates/bootstrap4/admin/lib.html

@@ -137,6 +137,8 @@
     {% endif %}
       {% if field.widget.input_type == 'checkbox' %}
         {% set _class = kwargs.setdefault('class', 'form-control-lg') %}
+      {% elif field.widget.input_type == 'file' %}
+        {% set _class = kwargs.setdefault('class', 'form-control-file') %}
       {% else %}
         {% set _class = kwargs.setdefault('class', 'form-control') %}
       {% endif %}