Evolution of an Android Application: Day 3

Posted by Tim Freund Wed, 07 Jan 2009 04:32:00 GMT

Where we last left off, Rhymote worked, but it was painfully slow. All of the network communication takes place in the UI thread, and that's a big problem. An application has 5 seconds to respond to a UI event, and if the click handler isn't done in that amount of time, the user will be asked if they'd like to terminate the application. The exact error message will look something like this:

Sorry!  Activity Rhymote
(in application Rhymote)
is not responding.

Even though Rhymote is only making one HTTP request per button press, that can put us over the 5 second limit. The HTTP requests return quickly in the emulator, but the phone is a totally different world.

A partial solution to the problem is threading. We want to start a new thread of execution separate from the UI to handle time intensive work. These time intensive tasks can then update the UI if necessary once they are done. If you are at all experienced with Java threading, you will already know how to create a Runnable object and pass that Runnable to a Thread. If you are new here, follow this cheat sheet:

package com.example.androidapp;

public class WebRequestRunnable implements Runnable {
    public void run(){
        // do resource intensive stuff here...
        // create an http request and read the results
    }
}

and

package com.example.androidapp;

public class Application {
    ...
    private OnClickListener mButtonListener = new OnClickListener() {
        public void onClick(View v) {
            WebRequestRunnable wrr = new WebRequestRunnable();
            Thread t = new Thread(wrr);
            t.start();
        }
    }
}

More information about this basic pattern can be found at the following Android resource pages:

• Developing Responsive Applications
• Handling Expensive Operations in the UI Thread

Although the application no longer hangs when responding to a button press, there is still a latency problem. The HTTP request that was taking 5+ seconds to execute in the UI thread is now taking 5+ seconds to execute in a second thread. Two potential issues come to mind:

• The Apache Commons HttpClient code is really slow
• I'm doing something foolish in my code

I learned long ago to never blame another programmer or library without some very solid evidence. When in doubt, it is probably my own fault. Next time we will attempt to find the most efficient way to deal with the required network requests.

Posted in Android, Open Source

Evolution of an Android Application: Day 2

Posted by Tim Freund Fri, 19 Dec 2008 06:31:00 GMT

I'm still working on the Rhymote project.

I sat down with the intent of immediately putting the code on my phone, but it was just so ugly that I had to spend about 30 minutes cleaning things up. Let that be a lesson: late night programming can be fun, but it isn't always productive.

Configuring the G1 for Deployment

First I opened the Settings program and choose Applications.

I checked the box next to Unknown Sources

While I was still on the Applications screen of the Settings program, I selected Development and checked the box next to USB Debugging.

Posted in Android, Open Source

Evolution of an Android Application: Day 1

Posted by Tim Freund Wed, 17 Dec 2008 03:04:00 GMT

Programmers are supposed to be lazy right? Here is the scene for one of my lazy moments: my home office contains a desk and a futon in opposite corners. I often want to change music on my desktop PC while reading on the futon. Most people would just get up to change the music without much thought, but I'd much rather use my G1 as a remote control for Rhythmbox. This will be my first Android project, and it shouldn't be too much to handle for a newbie like myself.

I started the Rhymote project yesterday, and I am writing these posts to keep track of all the hurdles I encounter along the way. Although the project could end up doing all sorts of neat stuff, all I really want to do is a handful of operations:

• Play/Pause
• Next track
• Previous track
• Volume adjustments

I have a tendency to over-engineer solutions, so I'm going to explicitly avoid anything that smacks of over ambitious design. Quick and dirty is the name of the game. The code will grow up if it holds my interest for long enough.

Here's the gear I am working with:

• Ubuntu 8.10
• Rhythmbox 0.11.6
• Eclipse 3.4
• Android SDK + Eclipse Plug-in
• T-Mobile G1

All of the code that I write throughout the series can be found in this repository.

Start an Android Project

I write Java in Eclipse most of the day, so I felt pretty comfortable starting the Android portion of the Rhymote project. I followed along with the Hello Android tutorial, and it wasn't long before the string "Hello Android" was staring back at me from the emulator.

Create a User Interface

The first thing I needed was a UI, and building fat client user interfaces is foreign territory for me. Oh, what's that? Android uses XML to define screen layouts? Maybe this won't be so bad after all. Remember, I did say I am a Java developer by day.

Make no mistakes, my UI is ugly. Did I mention that I don't write much UI code at my day job?

Find the System Log

I spotted the commons-httpclient code in the API, and decided to code up a client in an OnClickListener for each of my buttons.

After deploying the code and watching the application crash, I was left scratching my head. Where can I see the logs? Fortunately the command adb logcat is the Android equivalent of tail -f, and I was able to pinpoint the problem with my HTTP client code.

Discover Permissions

The exception I found was a little strange:

E/AndroidRuntime( 6490): Caused by: java.net.SocketException: unknown error E/AndroidRuntime( 6490): at org.apache.harmony.luni.platform.OSNetworkSystem.createSocketImpl(Native Method) E/AndroidRuntime( 6490): at org.apache.harmony.luni.platform.OSNetworkSystem.createSocket(OSNetworkSystem.java:79) E/AndroidRuntime( 6490): at org.apache.harmony.luni.net.PlainSocketImpl2.create(PlainSocketImpl2.java:59) E/AndroidRuntime( 6490): at java.net.Socket.checkClosedAndCreate(Socket.java:763) E/AndroidRuntime( 6490): at java.net.Socket.connect(Socket.java:910) E/AndroidRuntime( 6490): at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:117) E/AndroidRuntime( 6490): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:129) E/AndroidRuntime( 6490): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164) E/AndroidRuntime( 6490): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119) E/AndroidRuntime( 6490): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:348) E/AndroidRuntime( 6490): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555) E/AndroidRuntime( 6490): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:509) E/AndroidRuntime( 6490): at us.achievewith.Rhymote.Rhymote$1.onClick(Rhymote.java:60) E/AndroidRuntime( 6490): ... 23 more

I was expecting something along the lines of Connection Refused or Unknown Host, but unknown error was a little vague to be of much use. It was already late, and I foolishly struggled with the error for a while before letting Google Search work its magic, and that's when I learned about permissions.

Android applications don't just get free reign over the system without first asking for permissions to do most anything that interacts with the system at large or other systems. The following line cleared up the exception once it was added to the AndroidManifest.xml file:

<uses-permission android:name="android.permission.INTERNET"/>

One more run through the emulator, and I was able to start and stop my music. At this point it was 3:00 AM, and I decided that putting the code on the phone could wait.

Posted in Android, Open Source