Random Thoughts of a Programmer

Recently, I was working on a project in Java and needed to have a combo box, but with certain items in the list disabled (e.g. gray and non-selectable). At first, I simply set a custom renderer for the combo box which checked if the item was disabled. That, however, did not prevent the items from being selected. Thus, I set about to find a viable solution. There are plenty of solutions out there, but none seemed to work exactly the way I wanted. In the end, I ended up subclassing JComboBox to provide the functionality of disabling individual items. Here is my result, in under 100 lines: import java.awt.Component; import java.util.ArrayList; import javax.swing.JComboBox; import javax.swing.JList; import javax.swing.plaf.basic.BasicComboBoxRenderer; public class PartialDisableComboBox extends JComboBox { private static final long serialVersionUID = -1690671707274328126L; private ArrayList<boolean> itemsState = new ArrayList<boolean>(); public PartialDisableComboBox...

Recently, I came across an issue I had with full-screen (more specifically, full-viewport) canvas drawing. It all worked fine, except that the canvas dimensions must be specified in pixels, as opposed to percentages. This means you can't just set the canvas' width and height to "100%" and be done with it... The dimensions were automatically set when the page loaded, but if the user resized the browser window after that, the canvas would stay the same size, and would be either too big or too small. Thus, the canvas must be resized every time the browser window is resized. Prototype makes all of this easy. All that's necessary is to attach a listener to the onresize event of the window object, and then use document.viewport.getDimensions() to determine the new width and height. Here's some sample code: Event.observe(window, "resize", function() { var width = document.viewport.getWidth(); var height = document.viewport.getHeight(); ...

Many times, there are various interactions that take place in a web app based on mouse movement, clicking, dragging, etc. With a mouse, this is fairly simple, as there is a single point, and events like mousedown, mouseup, and mousemove can be used to discover the state of the mouse at any given time. On mobile browsers, however, it's a different story. Most phones support at least some kind of multi-touch, and the mousedown and mouseup events are not fired (there is, after all, no button). In addition, mousemove will only be applicable when dragging. Instead, mobile browsers dispatch touchstart, touchmove, and touchend events. Moreover, these events keep track of all touch points, not just the first or last one, and as such make handling them a bit more difficult. For the purposes of an application that only requires tracking clicks and drags, it is more convenient to translate these touch events into mouse events without having code duplication. This can be accomplished quick...

The canvas element in HTML is great, but has one strange shortcoming: it cannot draw dashed lines (natively). However, dashed lines seem like a pretty common thing to draw, which only highlights the problem. Looking around, I've noticed several solutions to this problem. Some use trig, and others use their own libraries that must be imported. So in the end, I decided to create my own method. This code will add the function to all canvas elements, both those already on the page, and any that are dynamically added later. Here is the code: CanvasRenderingContext2D.prototype.dashedLine = function(x1, y1, x2, y2, dashLen) { if (dashLen == undefined) dashLen = 2; this.beginPath(); this.moveTo(x1, y1); var dX = x2 - x1; var dY = y2 - y1; var dashes = Math.floor(Math.sqrt(dX * dX + dY * dY) / dashLen); var dashX = dX / dashes; var dashY = dY / dashes; var q = 0; while (q++ < dashes) { x1 += dashX; y1 += dashY; ...

I've been watching Android since it was first released, and got myself a Nexus One about half a year ago. The potential this platform has is very nice, and not just for smartphones. I would really like to see the tablets that will come with Android. But this isn't about me discussing Android itself. It's about the vendors who sell Android handsets and tablets, and their relationship with Google. Android is great for its customizability. Unfortunately, vendors have taken this too far and made a perversion of the platform with forced apps, home screens, missing features, etc. Forced Apps If I don't use/want an app on my phone, I should be able to remove it at will, unless it is a system app (e.g. removing the Dialer app would be plain stupid). But carriers and manufacturers insist on putting apps on the users' phones that cannot be removed unless the user roots their phone (which will void the warranty). Why? If the app really is good, I will keep it, use it, an...

I have read many, many articles about the whole tab vs. space indentation thing. Personally, I don't necessarily agree with most of them. They will require the coder to use a specific indentation size and stick with it, even forcing that on other coders. First off, let me outline my method for indenting code. Then I will explain the reasons and advantages/disadvantages. When I indent code, I will use tabs, but only at the beginning of a line. To align something in the rest of the line, I will use spaces. If a line spills to the next line(s), I will indent that line two tabs further. Rationale: Tabs Why tabs? First off, they're compact in the file (1 byte each). This is really insignificant with current disk sizes, but still. If you indent in spaces, then your file will be larger (unless you indent with one space). Another advantage of tabs is that a tab is a tab. It doesn't specify by how many spaces the code is indented, but rather by how many tabs it is indente...

There are several different PDF generation libraries available for Rails apps. Some of these are PDF::Writer, Prawn, Ruport, RGhost, and FlyingSaucer (for JRuby). First off, Ruport is basically a higher-level API for PDF::Writer. FlyingSaucer is only for JRuby (because JRuby allows for loading of Java classes). Not having any experience with RGhost, I can't exactly write a guide for using it. So now it's basically between Prawn and PDF::Writer, unless there's another library I haven't hear of. However, to my dismay, there is not UTF-8 support in PDF::Writer. So Prawn ends up being the PDF generation library of choice. One thing to keep in mind is that Prawn and Prawnto are beta-stage (sometimes even alpha) libraries, so some code hacking is going to be necessary. Also note the Prawnto is not maintained or tested by the Prawn developers, so there's no guarantee that it'll work with future versions (especially since Prawnto's developer has been "below t...