Android Allowing Main Thread I/O

An important aspect of Android App design is to never block the main UI thread with long running tasks. Doing so can result in an Application Not Responding (ANR) condition that can cause your App to be stopped. To prevent ANR conditions, always perform long running tasks such as I/O in background threads.

If you need to test I/O access from the main UI thread, you'll need to change the Thread Policy as shown below. Only do this for testing. In your production App, make sure you perform I/O operation in a background thread.

StrictMode.ThreadPolicy policy = 
    new  StrictMode.ThreadPolicy.Builder().permitAll().build(); 
StrictMode.setThreadPolicy(policy);

B-tree and Binary Search Tree Data Structures

B-tree and Binary Search Tree data structures are similar but different ways to store data. The advantage of using search trees is that the test for membership can be performed efficiently provided that the tree is reasonably balanced, that is, the leaves of the tree are at comparable depths.

B-tree Implementations

B-tree implementations are normally commercial. Languages don't typically provide direct B-tree support. To find B-tree implementations, search Google for B-tree software.

Binary Search Tree Implementations

Some languages do provide support for Binary Search Trees. In Java, see the TreeMap class, which implements a variant of the Binary Search Tree, the Red-Black Tree.

Binary Tree Data Structure Comparison

Both structures operate in the average in O(log n) time. Note that in the worst case, B-tree, at O(log n), is faster than Binary Search Tree at O(n).

P Versus NP Complexity Theory

The P Versus NP issue deals with whether every problem whose solution can be quickly verified by a computer can also be quickly solved by a computer. This is a major unsolved problem in computer science.

In common, practical terms, it deals with how to identify problems that are either extremely difficult or impossible to solve.  In order of difficulty from easy to hard, problems are classified as P, NP, NP-Complete and NP-Hard.

So why do we care? When approaching complex problems, it's useful to have at least some idea of whether the problem is precisely solvable, or if an approximation is the best that can be accomplished. 

Android/PHP/JQuery RESTful JSON MySQL Client-Server Overview

The title of this blog entry is quite a mouthful.  The purpose is to give a broad overview of the moving parts necessary to implement an application with client mobile and desktop devices that interact with a server database to alter and retrieve data.

I won't define all the classes, methods and acronyms on the graphic as they're easy to look up using an Internet search.  There are other choices that can be made for the details of the implementation, but this should provide a starting point for thinking through the necessary elements.

The communication vehicle for client-server interaction is typically the Internet Protocol Suite.

 

Android Development Using API Demos

Google provides API Demos apps for various releases of the Android system.  These apps contain hundreds of demos of Android capabilities.  They demonstrate the use of tens of thousands of lines of code and can be a big help to developers as they create their own apps.

However, the API Demos apps are not well documented and it can be difficult to find the code within them for a given function.  In authoring a recently released video tutorial course for Android Developers, I addressed this issue by creating an Excel worksheet that gives developers a tool to better understand the structure of the API Demos and to search the demos based on keywords to find the code they need.

A video explaining the use of API Demos is below...

Describes how to use Android API Demos. From the course Learning Android App Programming published by InfiniteSkills. More information is available at http://donkcowan.com/android-development-course/

Which is the Best Browser

An analysis of Internet browsers by Top Ten Reviews places Google Chrome at the head of the list. The analysis shows, however, that it's a real horse race between the top five: Chrome, Firefox, Internet Explorer, Opera and Safari. Here are some of my observations based on this analysis and personal tests and experience:

Change after new releases: All of the browser developers are working hard to improve their products. With each new browser version release, the competitive landscape can change. For example, Internet Explorer had recently lagged in speed due to the lack of graphics hardware acceleration. Based on my tests, they're now the fastest running HTML5 Canvas animations.

Graphics hardware acceleration: GPU (Graphics Processing Unit) hardware acceleration is an important factor in browser speed. A browser displaying video or animation with GPU acceleration will outperform a browser without it by a factor of 3-4. That's right, 300-400%. A computer using just the CPU to manipulate graphics displays simply can't keep up with one using the combination of CPU and GPU. Hardware acceleration is a fairly complex topic. Basically, the browser offloads calculations from the CPU to the GPU. If you're interesting in some of the details, take a look at this discussion of hardware acceleration from the Chromium Projects.

Mobile lags desktop: Especially in speed, the mobile browsers lag desktop versions. Mobile devices simply don't have the computing power to match desktop devices. 

Code Comments

What makes good code comments? Should they be terse or expansive? Should they be frequent or used sparingly? Opinions on these and other aspects of code commenting vary widely. My take is this ... to answer these questions, start with the objectives for code comments:

To assist in development: Comments aid in understand functionality being implemented in code. For example, they can be used as pseudo-code place holders for eventual real code.

To speed development and maintenance: Comments allow more rapid digestion of code sections. This is especially important when revisiting code not recently seen or code developed by others.

To clarify code: The function of a section of even well constructed code may not be evident. Comments can add that critical piece of missing information.

Given these objectives, here are some suggestions:

Comment appropriate groups of code: Sometimes a single line of code might need explanation. Or there might be a long section of code that repeats similar functionality and a single comment will suffice for the group. It's a judgment call.

Leave signposts for developers: Even if a section of code can be understood without a comment, how long will it take for you, or someone else, to understand it after time passes? Also, it's sometimes important to be able to understand the flow of a function or application without necessarily understanding all the details. Give yourself and others a break, make understanding as easy as possible. Most code is not a programming quiz.

Clean up comments: Keep them up to date and free of extraneous information. Remove temporary words used during development. Make them understandable. After all, that's their purpose in life.

Add comments while coding: It's tempting to think you can go back later and add a comment to some code that looks perfectly clear to you as you write it. Don't do it. Leverage the knowledge you have in that temporary cache in your brain.

Use a fairly uniform comment style: You don't have to be perfectly uniform, but it's a good idea to used some consistency within an application. It helps with understanding and looks more professional. 

Add value to the code being commented: Don't just repeat what the code obviously tells you. Make the comment compliment and add value to the code.

Transient

HTML5 Canvas Performance Test

Browser support for HTML5 Canvas is constantly improving. More features are being supported and performance is improving. Click here or on the image below to see how your browser performs. The app rotates a ten layer gradient and displays the Frame Rate.

HTML5 Canvas on a Smartphone

HTML5 Canvas is a highly anticipated feature that allows web developers to create sophisticated graphics on their website pages. Most desktop and laptop browsers now support the Canvas feature. Mobile browsers are catching up. To see if your browser supports Canvas, you can access www.html5test.com for an analysis and rating of your browser.  Also, give this Canvas app a try:

Eye Tracking and Heat Maps

Eye tracking has become a hot topic in the last few years. Eye tracking devices are used to create heat maps showing where attention is focused on display pages. A sample heat map of a Google search results is shown below:

A dominant pattern for search engine results is the "F" pattern showing the eye being drawn to the upper left and then moving down and across from there. There are, however, factors (such as the inclusion of images, graphics, and additional columns) that can significantly alter this pattern. This is shown in the sample YouTube pages below:

You can do a Google Images search of "eye tracking" to see sample heat maps. Having a basic understanding of how people focus their attention on internet sites is important for improving traffic and conversions. Heat maps of specific sites can help to further improve results.

Basic Usability Testing

Doing basic testing for website usability can often be simplified down to a series of sessions with users who spend an hour or so each being observed carrying out specific website tasks. Usability testing is often put off or ignored resulting in websites which are difficult to use and have low conversion rates. Sometimes simple fixes can have big results.

 Click here to see a video on a sample usability testing session.