Spawning isolates in Dart

Spawning new isolates in Dart is easy if you know how to do it:


[dart]import ‚dart:isolate‘;
import ‚dart:async‘;

void main() {
Future isolate1 = Isolate.spawnUri(Uri.parse(‚isolate.dart‘), [], null);
Future isolate2 = Isolate.spawnUri(Uri.parse(‚isolate.dart‘), [], null);

Future.wait only waits until the two isolates are spawned. If the main application stops running, the two spawned isolates will stop running as well. That’s why we need a while(true)-loop here.

The isolate itself looks like this:

[dart]library isolate;

void main() {

The two arguments after the URI are used for a list of arguments and an optional message. If you want to use this, just modify the main method of your isolate:

void main(args) {…}
void main(args, message) {…}[/dart]

Nested Polymer Elements and Data Binding in Google’s Dart

Nesting Polymer Elements in Dart can be difficult sometimes. I want to give you some ideas how to nest polymer elements in Dart and how to realize data binding between multiple nested elements. Let’s get started:

Nested Polymer Elements and Data Binding in Google’s Dart weiterlesen

MySQL: ORDER BY RAND() – a case study of alternatives

I finally had the time to translate my post from german to english – so here we go 🙂

Das Problem

Many of you reading this post might already stopped by this problem – you just want a few random rows from your database and most of the times you might have used „ORDER BY RAND()“ and not thought about, what’s happening there. Just add all the columns you want to select, add JOINS, WHERE, etc. and add ORDER BY RAND() and LIMIT.

For small applications this might even scale well, but what happens in large applications with hundreds, thousands or millions of rows in a table?

I want to look a little closer into this. While developing my deprecated rhCMS (a content management system), I asked myself the same question.

MySQL: ORDER BY RAND() – a case study of alternatives weiterlesen

[Dart+Polymer] Styling Elements

Styling custom elements is sometimes tricky. In general the website styles do NOT apply to the custom element. There is a special attribute called „apply-author-styles“ that can be set to „true“ to apply your website’s styles to your custom element.

In general each custom element should have its  styles separated from the website so it can be reused easily. Let’s have a look at a simple example:

[Dart+Polymer] Styling Elements weiterlesen

Animatr – GUI & Structure: Nesting Polymer Elements

The first step of rebuilding animatr was to remove all code and totally rebuild the GUI using a single custom element: <animatr-gui> using polymer. The GUI itself has three nested custom elements:

<animatr-titlebar> – Containins the windows‘ title, close button, …
<animatr-toolbars> – Wrapper for the toolbars
<animatr-panels> – A wrapper to create a GUI using pannels that can be dragged.

The HTML code of the root element looks like this:

[code language=“html“]
<link href="packages/animatr_gui/elements/animatr-ui.html" rel="import" />

The corresponding element HTML code is:

[code language=“html“]
<polymer-element name="animatr-ui">
<meta charset="utf-8"/>
<link rel="import" href="animatr-titlebar.html">
<link rel="import" href="animatr-toolbars.html">
<link rel="import" href="animatr-panels.html">
<link rel="import" href="animatr-panel-….html">
<animatr-titlebar id="animatr-titlebar"></animatr-titlebar>
<animatr-toolbars id="animatr-toolbars"></animatr-toolbars>
<animatr-panels id="animatr-panels"></animatr-panels>
<script type="application/dart" src="animatr-ui.dart"></script>

The Dart code for the custom element is:

import 'package:polymer/polymer.dart';

import 'dart:html';

import 'package:animatr_gui/elements/animatr-titlebar.dart';
import 'package:animatr_gui/elements/animatr-toolbars.dart';
import 'package:animatr_gui/elements/animatr-panels.dart';

import 'animatr-panel-....dart';

class AnimatrUiElement extends PolymerElement {
  bool get applyAuthorStyles => true;

  ...PanelElement panel_...;

  AnimatrUiElement.created() : super.created() {
    panel_... = document.createElement('animatr-panel-...');

  AnimatrTitlebarElement titlebar;

  AnimatrToolbarsElement toolbars;

  AnimatrPanelsElement panels;

  @observable Project currentProject;

  void enteredView() {

    titlebar = $['animatr-titlebar'];
    toolbars = $['animatr-toolbars'];
    panels = $['animatr-panels'];

    titlebar.ui = this;
    panels.ui = this;

    panels.addPanel(panel_..., 'north/east/south/west/center');

Nesting elements was complicated first. Assuming you have your project’s root file (mine is called animatr.html), you could import all elements in this file, at a central place. But this had some strange behaviour to me:
The outer elements get created first and thus, before all nested elements. Thus I wasn’t able to correctly query for the nested elements. Because the custom element wasn’t registered Google Dart had some type errors.

The solution was to import other elements within the custom element itself, right before the <template> tag.

I had another problem using special characters. It turned out that the charset settings (e.g. by using <meta charset=“utf-8″/>) is not propagated to custom elements. Thus make sure to include a <meta>-tag in your custom elements if you want to use custom elements.

Animatr – A first introduction

In this post I want to briefly introduce you to my most recent project called „animatr“. Animatr is a tool to create canvas animations. I will focus on advertisements but in theory you can create all types of animations and sizes. Even playing a video within the animation is possible.

The first version was developed about a year ago and was based on fabric.js But very soon I felt the framework limited me to their features. So I quickly decided to rewrite it as a web app on my own. Due to some specific webkit/chrome features I decided to finally rewrite the project using Google’s Dart and to make an app out of it using node-webkit.

The latest and third version is based on Google Dart, Node-Webkit and Polymer. While polymer is the replacement for web-ui.

I will write follow up blogs about concepts and code I use while developing animatr and give you examples. So far I can tell that detailed examples are rare. That’s why I felt to blog about it myself.