System Monitor
Tutorial Series   JavaScript Plasmoids
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Further Reading   JavaScript Plasmoid API reference

This example assumes that you are familiar with previous examples such as NowPlaying (from which this example was adapted).

Following code illustrates how to connect to systemmonitor and how to receive updates from various data sources.

You should have a working plasmoid application from previous examples. Take a copy of the plasmoid and rename it. After this you can replace contents of the contents/code/main.js with following:

layout = new LinearLayout(plasmoid);

label = new Label();
label.text = "No connection";

// current values
var systemData = new Array();

function printData() {
    label.text = "";
    for (var name in systemData) {
	var data = systemData[name];
	label.text = label.text + name + ": ";
	for (var elt in data) {
	    label.text = label.text + " " + data[elt];
	label.text = label.text + "\n";

plasmoid.dataUpdated = function(name, data) {
    systemData[name] = data;

smDataEngine = dataEngine("systemmonitor");

smDataEngine.sourceRemoved.connect(function(name) {
	// unsubscribe
	smDataEngine.disconnectSource(name, plasmoid);

smDataEngine.sourceAdded.connect(function(name) {
	if (name.toString().match("^mem/physical")) {
	    // subscribe
	    smDataEngine.connectSource(name, plasmoid, 500);

In smDataEngine.sourceAdded.connect() we give a function to connect to signal. The signal connection function is called by the systemmonitor for each data source. In this example we only connect to physical memory data sources.

After this the plasmoid.dataUpdate() receives updates. Update values are stored into an array. The array is printed on every update.

Note that this example is bit inefficient since we call printData() on every update. One way to optimize is to update label text only when "mem/physical/free" data source is updated.

This page was last edited on 11 September 2014, at 23:27. Content is available under Creative Commons License SA 4.0 unless otherwise noted.