Obtaining in IE the length of a Java array passed from an applet to its Javascript wrapper

Question

I have the following method in my applet:

public File[] getFiles()

Which I call from Javascript as follows:

var files = applet.getFiles();

for (var i = 0; i < files.length; i++) {
    // Do something.
}

This works in Firefox but IE gives me

'length' is null or not an object

Any ideas anyone?

Answer 1

You can use Firebug Lite in IE to investigate what's going on with files

First, include Firebug Lite in your file

<script type='text/javascript' 
    src='http://getfirebug.com/releases/lite/1.2/firebug-lite-compressed.js'&gt;&lt;/script&gt;

Now log it in the console with

var files = applet.getFiles();
console.log(files);
for (var i = 0; i < files.length; i++) //...

Now you can investigate what object was actually being returned by getFiles()

I give this suggestion because IE said length is null not or not an object instead of files is null or not an object, so maybe files have other methods that you can use. Use Firebug to reflect those.

Answer 2

Not sure how widely supported passing a Java array to javascript is. A workaround is to return the array as a delimited string as shown in the following example

http://www.rgagnon.com/javadetails/java-0183.html

Answer 3

Work-around found. Instead of returning an array, return a list instead. Then iterate through it using the get and size methods. Works in both IE and Firefox.

So, the applet method should be:

public List<File> getFiles()

And to use it Javascript-side:

var files = applet.getFiles();
for (var i = 0; i < files.size(); i++) {
    // Do something with files.get(i).
}