File Upload control OnChange Event JQuery

问题

I am trying to build the page to upload the file by using AJAX, JQUERY and .Net HTTPHandler as in http://dotnet.dzone.com/news/async-file-upload-jquery-and

It works only for the first time I chose a file and uploaded it. But it doesn't work when I select the file next time and doesn't show any error.

If I change the javascript event binding to the old school way like the following, it works perfectly. But I want to use the JQuery Binding. Is there anything I did wrongly? Thanks.

<input id="fileToUpload" type="file" size="45" name="fileToUpload" class="input" onchange="return ajaxFileUpload();">

HTML Code:

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" CellPadding="4" ForeColor="#333333" GridLines="None">
            <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
            <Columns>
                <asp:BoundField DataField="StudentID" HeaderText="ID" />
                <asp:BoundField DataField="name" HeaderText="Name" />
                <asp:TemplateField>
                    <ItemTemplate>                           
                        <input id="fileToUpload" type="file" size="45" name="fileToUpload" class="fileToUpload" >
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>

JQuery Binding Code:

<script>

    $().ready(function () {
        $(".fileToUpload").change(function() {
            $.ajaxFileUpload
                (
                    {
                        url: 'AJaxUploadHandler.ashx',
                        secureuri: false,
                        fileElementId: 'fileToUpload',
                        dataType: 'json',
                        data: { name: 'logan', id: 'id' },
                        success: function (data, status) {
                            if (typeof (data.error) != 'undefined') {
                                if (data.error != '') {
                                    console.log(data.error);
                                } else {
                                    console.log(data.msg);
                                }
                            }
                        },
                        error: function (data, status, e) {
                            alert(e);
                        }
                    }
                )

                return false;

        });
    });

</script>

回答1:

Use .on method as shown below and try again

  $(".fileToUpload").on('change', function() {
         ///// Your code
});

回答2:

This has worked for me.

$(document).on("change", "#inputId", function(){
     //Do something
});

For performance it is better to avoiding using $(document) and call the on() method on a wrapper div like this.

<div id="wrapper">
   <input id="#inputId" type="file"/>
</div>

$("#wrapper").on("change", "#inputId", function(){
     //Do something
});

It has to do with Direct and delegated events: http://api.jquery.com/on/

回答3:

I had a similar issue. If I tried to upload the exact same file name at the exact same location. Then the change event would basically say no change. I ended up using a click even, checked for $(this).val() and call the the change event inside the click event handler.

$("input[type='file']").on('click', function () {
    if(!$(this).val()){
        //Initial Case when no document has been uploaded
        $("input[type='file']").change(function(){
            upload_file_setup(this);
        });
    }else{
        //Subsequent cases when the exact same document will be uploaded several times
        $(this).val('');
        $("input[type='file']").unbind('change');
        $("input[type='file']").change(function(){
            upload_file_setup(this);
        });
    }
});

The unbind may not be necessary but it works for me.

来源：https://stackoverflow.com/questions/23424417/file-upload-control-onchange-event-jquery

标签

jquery

jquery-file-upload