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GWT - easiest way to do a simple loading screen until file is loaded

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轻奢々
轻奢々 2021-02-04 06:30

When clicking a button, my GWT application returns a PDF file embedded in an HTML page which looks something like:
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  • 甜味超标
    2021-02-04 06:53

    Did you see this stackoverflow question Detect when browser receives file download? Basically the answer given is that you set a cookie in the return response and wait on the client side for this cookie to be set. This can be done easily with GWT as it has a Scheduler (for the repeated timer check) and easy access to Cookies. You still need to make some server changes, but you don't have to create a background process.

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  • 后悔当初
    2021-02-04 06:57

    I don't have the full answer, but the following code works for me in Safari, and maybe you can modify it, to make it work with other browsers, too (?):

    <html><head>
<script type="text/javascript">
  function showPdf() {
    document.getElementById("loading").style.visibility = "hidden";
    document.getElementById("pdf").style.visibility = "visible";
  }
</script>
</head>

<body marginwidth="0" marginheight="0" bgcolor="rgb(38,38,38)">
  <div id="loading"
    style="position: absolute; background-color: white;">Loading...</div>

  <iframe id="pdf" width="100%" height="100%" name="plugin"
    src="http://myserver/?cmd=getMyPdf" onload="javascript:showPdf();"
        style="visibility: hidden;"></iframe>
</body>
</html>

    This is pure JavaScript - but could certainly be done with GWT, too. Note, that I'm using an iframe instead of embed, because embed doesn't really support the onload method (and embed is not a standard HTML element, as far as I remember).

    The reason, why this may not be the full answer, is that Chrome fires the onload event as soon as the PDF starts downloading (but after the PDF generation on the server side has finished). I'm not sure, if this is what you want?

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