Java applet: JavaScript call - JSObject.getWindow (this) returns always null
My Java applet
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.JApplet;
import javax.swing.JButton;
import netscape.javascript.JSObject;
@SuppressWarnings("serial")
public class LocalFileSystem extends JApplet {
private JSObject js;
private final JButton button;
public LocalFileSystem() {
setLayout(null);
button = new JButton("getDrives()");
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
button.setText( getDrives() );
}
});
button.setBounds(25, 72, 89, 23);
add(button);
}
public void init() {
js = JSObject.getWindow(this);
}
public String getDrives() {
if (js != null) return "NULL";
for (File f: File.listRoots())
js.call("addDrive", new String[] { f.getAbsolutePath() });
return "NOT NULL";
}
}
My HTML code:
<!-- language: lang-html --><html>
<head>
<script type="text/javascript"
src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js"></script>
</head>
<body>
<script type="text/javascript">
function addDrive(s) {
alert(s);
}
</script>
<object type="application/x-java-applet;version=1.4.1" width="180"
height="180" name="jsap" id="applet">
<param name="archive" value="http://localhost/LocalFileSystemApplet/bin/applet.jar?v=<?php print mt_rand().time(); ?>">
<param name="code" value="LocalFileSystem.class">
<param name="mayscript" value="yes">
<param name="scriptable" value="true">
<param name="name" value="jsapplet">
</object>
</body>
</html>
The applet is loaded and when I click the button, I always get NULL returned by getDrives (). Why?
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2 answers
From undefined memory, calls to set JSObject
will be out of order when the method is called init()
.
So this is ..
public void init() {
js = JSObject.getWindow(this);
}
.. probably should be ..
public void start() {
js = JSObject.getWindow(this);
}
Since the method start()
can be called many times (for example, restoring the browser from the bare minimum), it can pay to check:
public void start() {
if (js==null) {
js = JSObject.getWindow(this);
}
}
Update
I saw this in Reading / Writing HTML Field Values from JAVA . The "little stamp" at the bottom of the page notes:
For best results, never use JSbject LiveConnect in the init () method of Applet.
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