Wizard API updated!
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Tip 80: Resize applets within browser frames

Break the rules with a little bit of JavaScript

By Francis Lu, JavaWorld.com, 10/05/99

When an applet is embedded within a Web browser, the browser becomes the applet's frame. However, when the user resizes the browser frame, the applet does not adjust its size to fit within the new dimensions. This is because applets have hard-coded dimensions in their <APPLET> tags. Therefore, despite the fact that your applet may be using layout managers, it won't adjust its components accordingly. A little JavaScript easily remedies this problem.

A complete example

This approach uses JavaScript to handle the browser's onResize and onLoad events and forward new dimensions to the applet. The applet overrides the setSize() method to revalidate its component layout, and thus let its layout manager adjust itself to the new size. The HTML looks like this: 
   <HTML>
   <HEAD>
   <TITLE>Resizable Applet Demo</TITLE>
   </HEAD>
   <BODY bgcolor=#C6C3C6 onResize="resize()" onLoad="resize()" 
   topmargin="0" leftmargin="0" marginwidth="0" marginheight="0">
   <SCRIPT LANGUAGE="JavaScript">
   function resize() {
    var w_newWidth,w_newHeight;
    var w_maxWidth=1600, w_maxHeight=1200;
    if (navigator.appName.indexOf("Microsoft") != -1)
    {
        w_newWidth=document.body.clientWidth;
        w_newHeight=document.body.clientHeight;
    }else{
        var netscapeScrollWidth=15;
        w_newWidth=window.innerWidth-netscapeScrollWidth;
        w_newHeight=window.innerHeight-netscapeScrollWidth;
    }
    if (w_newWidth>w_maxWidth)
        w_newWidth=w_maxWidth;
    if (w_newHeight>w_maxHeight)
        w_newHeight=w_maxHeight;
    document.myApplet.setSize(w_newWidth,w_newHeight);
    window.scroll(0,0);
        }
   window.onResize = resize;
   window.onLoad = resize;
   </SCRIPT>
   <APPLET NAME="myApplet" CODE="SizeApplet.class" WIDTH=1600 
           HEIGHT=1200>/APPLET>
   </BODY>
   </HTML>


Internet Explorer and Netscape Navigator implement JavaScript in slightly different ways. The onResize and onLoad parameters in the <BODY> tag specify the resize event handlers for Internet Explorer, while window.onResize = resize; and window.onLoad = resize; do so for Netscape Navigator. Both methods must be included in order to support the two major browsers. Whenever the browser frame is loaded or resized, the applet's resize() method is invoked.

Navigator and IE have different methods of accessing the browser window's dimensions. In Navigator, the window object is referenced; in IE, the document's body object is used. These objects also return slightly different values for the window dimensions. Thus, it is necessary to determine the browser in which the applet is running before sending the correct window dimensions. Netscape does not include the width of the scrollbars, and does not let you access this length, so 15 pixels is used as an offset in the netscapeScrollWidth variable.

The <APPLET> tag still specifies the applet's Width and Height parameters, but these dimensions now specify the applet's maximum bounds. The window's maximum width and height, w_maxWidth and w_maxHeight, are checked in the resize() method to ensure that the applet does not go beyond these bounds. The browser still takes up room for this dimension; thus, the scrollbars will not show all the information in the window. Signed JavaScript in Netscape has the ability to hide the scrollbars. The HTML page is also scrolled to the top left corner whenever it is resized to ensure that the applet is fully visible.

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