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Known Limitations

RadUpload has been replaced by RadAsyncUpload, Telerik’s next-generation ASP.NET upload component. If you are considering Telerik’s Upload control for new development, check out the documentation of RadAsyncUpload or the control’s product page. If you are already using RadUpload in your projects, you may be interested in reading how easy the transition to RadAsyncUpload is and how you can benefit from it in this blog post. The official support for RadUpload has been discontinued in June 2013 (Q2’13), although it is still be available in the suite. We deeply believe that RadAsyncUpload can better serve your upload needs and we kindly ask you to transition to it to make sure you take advantage of its support and the new features we constantly add to it.

The RadUpload control uses and extends the existing API of the browsers and the .NET framework. However, due to some known restrictions, the control has the limitations listed below:

  • RadUpload cannot upload files using AJAX calls. This is a limitation of the XmlHttpRequest component, which is used in the AJAX frameworks for asynchronous calls to the application. To upload a file you must perform a full page postback. In most cases, it is possible to disable AJAX for a given submit button, to allow file uploads. Fortunately this is possible in RadAsyncUpload- check the demo here.

  • RadUpload cannot check the size and the mime-type of its selected files before an upload starts. This is because of a security restriction of the JavaScript engine of popular browsers. You cannot access the client file system with JavaScript, hence the inability to get the file size, mime type or content. You can, however, check the file size when the upload first starts. Client-side validation is possible with RadAsyncUpload - check the demo here.

  • RadUpload cannot select multiple files in one file select box. This is a limitation of the standard <input type=file> elements that RadUpload uses for file selection. Currently, there are no plans for changing this restriction. You can check this code-library: How to upload multiple files using RadUpload (uploading .zip file and extract it on the server). In addition, this is possible in RadAsyncUpload - check the demo here.

  • RadUpload does not support initially selected files or allow file selections to persist across postbacks. This is a security limitation of the standard <input type=file> elements which it uses internally for file selection.

  • The file will not upload if you try to open the 'browse for file' window with javascript. Only the user can click on the Select button and select a file.

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