Question: Mono.Android performance: C# -> JNI wrapper -> native lib vs. C# -> Managed wrapper -> native?

I have currently ported a Java app to Mono.Android. The Java app uses a native library.

The full walk through can be read here: WebRTC app - C# / Xamarin - (C# - JNI - C/C++) - Summary and GitHub repository

Basically I have some Java code that looks like this

public native int GetVideoEngine();

Initially in my C# equivalent app I tried to use DllImport

[DllImport("libwebrtc-video-demo-jni.so")]
public static extern int Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_GetVideoEngine();

(which did not work), then I ended up wrapping the jars as Java Binding Libraries which in turn JNI'ed the needed classes, so I instead could call the generated JNI wrappers

static Delegate cb_GetVideoEngine;
#pragma warning disable 0169
static Delegate GetGetVideoEngineHandler ()
{
    if (cb_GetVideoEngine == null)
        cb_GetVideoEngine = JNINativeWrapper.CreateDelegate ((Func<IntPtr, IntPtr, int>) n_GetVideoEngine);
    return cb_GetVideoEngine;
}

static int n_GetVideoEngine (IntPtr jnienv, IntPtr native__this)
{
    global::Org.Webrtc.Videoengineapp.ViEAndroidJavaAPI __this = global::Java.Lang.Object.GetObject<global::Org.Webrtc.Videoengineapp.ViEAndroidJavaAPI> (jnienv, native__this, JniHandleOwnership.DoNotTransfer);
    return __this.VideoEngine;
}
#pragma warning restore 0169

static IntPtr id_GetVideoEngine;
public virtual int VideoEngine {
    // Metadata.xml XPath method reference: path="/api/package[@name='org.webrtc.videoengineapp']/class[@name='ViEAndroidJavaAPI']/method[@name='GetVideoEngine' and count(parameter)=0]"
    [Register ("GetVideoEngine", "()I", "GetGetVideoEngineHandler")]
    get {
        if (id_GetVideoEngine == IntPtr.Zero)
            id_GetVideoEngine = JNIEnv.GetMethodID (class_ref, "GetVideoEngine", "()I");

        if (GetType () == ThresholdType)
            return JNIEnv.CallIntMethod  (Handle, id_GetVideoEngine);
        else
            return JNIEnv.CallNonvirtualIntMethod  (Handle, ThresholdClass, id_GetVideoEngine);
    }
}

My question is related to performance:

How much slower is the C# -> JavaBindingLibrary (JAVA/JNI) -> C/C++ JNI Wrapper -> C native library than if I did unwrapped the C/C++ JNI Wrapper and rewrapped it with something like mono / cxxi or similar direct managed or manually wrote a direct callable wrapper?

WebRTC app - C# / Xamarin - Part #2 - Attempt #2 - success using a JNI .so file from C# / Mono

This is a post in a series of postings

1. WebRTC app - C# / Xamarin - Part #1 - Building platform native webrtc library
2. WebRTC app - C# / Xamarin - Part #2 - Attempt #1 - failure to using a JNI .so file directly from C# / Mono
3. WebRTC app - C# / Xamarin - Part #2 - Attempt #2 - success using a JNI .so file from C# / Mono
4. WebRTC app - C# / Xamarin - (C# - JNI - C/C++) - Summary and GitHub repository

And finally the associated GitHub repository https://github.com/kenneththorman/webrtc-app-mono

In my previous posting WebRTC app - C# / Xamarin - Part #2 - Attempt #1 - failure to using a JNI .so file directly from C# / Mono I wrote

This is pushing me in a direction that I initially hoped I could avoid (mainly due to my limited knowledge in the area), JNI.

There were a few reasons that I did not prefer to use a Java Binding Library in the solution. 

• I would have an even more mixed source code base (C# calling jar/Java which is wrapping C/C++), I would have preferred to keep it at C# wrapping C/C++.
• The upstream build process is packaging some of the compiled java classes that I need into jar files, but not all of them so now I manually need to add a build step to the build process.
• I am not familiar with JNI

If we look at the files that are generated during the build process explained in this posting WebRTC app - C# / Xamarin - Part #1 - Building platform native webrtc library we will see that the jars that we need to build the test android app supplied with the project are located in

~/WebRTCDemo/trunk/webrtc/video_engine/test/android/libs/

namely

audio_device_module_java.jar
video_capture_module_java.jar
video_render_module_java.jar

For each of these jars we need to create a Java Bindings Library that is using the relevant  jar as an input jar (actually 2 of the jars can go into the same Java Binding Library - video_capture_module_java.jar and video_render_module_java.jar since they share the same Java package/namespace). 

(It might be possible to add them all in one Java Binding Library but I encountered problems due to Visual Studios project setting of Default Namespace, which basically was affecting the namespace of the Java classes that I needed to invoke from C#. Since each of the jars contained classes from a different Java package, the easy work around was to add a Java Binding Library for each of the jars and make sure that the Visual Studio Default namespace matched the Java package name.)

Looking at the existing Java WebRTC demo app available in the folder

~/WebRTCDemo/trunk/webrtc/video_engine/test/android/src/org/webrtc/videoengineapp

you will find

IViEAndroidCallback.java
ViEAndroidJavaAPI.java
WebRTCDemo.java

The main file is called WebRTCDemo.java and contains code like the following

...
import org.webrtc.videoengine.ViERenderer;

import java.io.File;
import java.io.IOException;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.util.Enumeration;

public class WebRTCDemo extends TabActivity implements IViEAndroidCallback,
                                                       View.OnClickListener,
                                                       OnItemSelectedListener {
    private ViEAndroidJavaAPI vieAndroidAPI = null;

    // remote renderer
    private SurfaceView remoteSurfaceView = null;

    // local renderer and camera
    private SurfaceView svLocal = null;

    // channel number
    private int channel = -1;
    private int cameraId;
    private int voiceChannel = -1;
...

By looking at the code I could see there would be some problems, since the main activity is referencing 2 classes that are defined and located side by side with the main activity IViEAndroidCallback.java and ViEAndroidJavaAPI.java. In other words these are not available in a jar and especially the ViEAndroidJavaAPI.java ois the wrapper for the JNI native library so we cannot do this directly from C# according to Native library integration (posting #2).

In the beginning of this posting I outlined 3 reasons I preferred to avoid using JNI and Java Binding Libraries, one of them was

•  The upstream build process is packaging some of the compiled java classes that I need into jar files, but not all of them so now I manually need to add a build step to the build process.

Anyhow this was fairly easy to remedy by manually creating a new jar containing the 2 files that was needed and then adding this new jar to a new Java Binding Library.
 

XXX@ubuntu:~/WebRTCDemo/trunk/webrtc/video_engine/test/android/bin/classes$
jar cvf ViEAndroidJavaAPI.jar
org/webrtc/videoengineapp/IViEAndroidCallback.class
org/webrtc/videoengineapp/ViEAndroidJavaAPI.class
added manifest
adding: org/webrtc/videoengineapp/IViEAndroidCallback.class(in = 218)
(out= 173)(deflated 20%)
adding: org/webrtc/videoengineapp/ViEAndroidJavaAPI.class(in = 2845)
(out= 1303)(deflated 54%)

Now I was able to use the native library without any exceptions occurring.

WebRTC app - C# / Xamarin - Part #2 - Attempt #1 - failure to using a JNI .so file directly from C# / Mono

This is a post in a series of postings

1. WebRTC app - C# / Xamarin - Part #1 - Building platform native webrtc library
2. WebRTC app - C# / Xamarin - Part #2 - Attempt #1 - failure to using a JNI .so file directly from C# / Mono
3. WebRTC app - C# / Xamarin - Part #2 - Attempt #2 - success using a JNI .so file from C# / Mono
4. WebRTC app - C# / Xamarin - (C# - JNI - C/C++) - Summary and GitHub repository

And finally the associated GitHub repository https://github.com/kenneththorman/webrtc-app-mono

In my previous posting WebRTC app - C# / Xamarin - Part #1 - Building platform native webrtc library I have showed how to build a native library that we need to use to build a WebRTC app on Xamarin / Mono.Droid.

In this posting I will take you through my struggles, subsequent failure and the next posting finally success on how to actually use this JNI native library from Mono.Android.

I started a new solution in Visual Studio 2013 and added new Android Application project. Then according to Xamarin: Using Native Libraries.
I needed to add my .so file to the location  
<project>\lib\armeabi-v7a\libwebrtc-video-demo-jni.so.

The next step that I tried was to start using DllImport statements.

using System;
using System.Runtime.InteropServices;
using Android.Content;
using Android.Util;
using Encoding = System.Text.Encoding;

namespace WebRtc
{
        public class ViEAndroidJavaAPI
        {

...
                // API Native

                [DllImport("libwebrtc-video-demo-jni.so")]
                private static extern bool NativeInit(Context context);

                // Video Engine API
                // Initialization and Termination functions
                [DllImport("libwebrtc-video-demo-jni.so")]
                public static extern int GetVideoEngine();

                [DllImport("libwebrtc-video-demo-jni.so")]
                public static extern int Init(bool enableTrace);

                [DllImport("libwebrtc-video-demo-jni.so")]
                public static extern int Terminate();
...

Trying to run my project yielded some EntryPointNotFoundException in the error log. After a bit of Google-ing I found that the method names as seen from Mono are not as you expect instead they contain the full package/class path.

Using the following command on the Ubuntu build machine

~/WebRTCDemo/trunk/webrtc/video_engine/test/android/libs/armeabi-v7a$ arm-linux-androideabi-nm -D libwebrtc-video-demo-jni.so

yielded the following output

00015358 T JNI_OnLoad
00015be4 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_AddRemoteRenderer
00016e3c T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_CreateChannel
00015f14 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_EnableNACK
00015f58 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_EnablePLI
00015e04 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_GetCameraOrientation
00015acc T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_GetCodecs
000153d4 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_GetVideoEngine
000154cc T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_Init
000153d0 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_NativeInit
00015c30 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_RemoveRemoteRenderer
00015fb0 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_SetCallback
00015ea8 T Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_SetExternalMediaCodecDecoderRenderer
...

So changing my code to the following made the EntryPointNotFoundException go away

using System;
using System.Runtime.InteropServices;
using Android.Content;
using Android.Util;
using Encoding = System.Text.Encoding;

namespace WebRtc
{
        public class ViEAndroidJavaAPI
        {

...
                // API Native

                [DllImport("libwebrtc-video-demo-jni.so")]
                private static extern bool Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_NativeInit(Context context);

                // Video Engine API
                // Initialization and Termination functions
                [DllImport("libwebrtc-video-demo-jni.so")]
                public static extern int Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_GetVideoEngine();

                [DllImport("libwebrtc-video-demo-jni.so")]
                public static extern int Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_Init(bool enableTrace);

                [DllImport("libwebrtc-video-demo-jni.so")]
                public static extern int Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_Terminate();

...

Now I was faced with another exception which seemed much nastier.
UNHANDLED EXCEPTION: System.Runtime.InteropServices.MarshalDirectiveException: Type Java.Lang.Object which is passed to unmanaged code must have a StructLayout attribute.

12-21 19:29:04.298 I/MonoDroid(15226): UNHANDLED EXCEPTION: System.Runtime.InteropServices.MarshalDirectiveException: Type Java.Lang.Object which is passed to unmanaged code must have a StructLayout attribute.
12-21 19:29:04.298 I/MonoDroid(15226): at (wrapper managed-to-native) WebRtc.ViEAndroidJavaAPI.Java_org_webrtc_videoengineapp_ViEAndroidJavaAPI_NativeInit (Android.Content.Context) 
12-21 19:29:04.298 I/MonoDroid(15226): at WebRtc.ViEAndroidJavaAPI..ctor (Android.Content.Context) [0x00033] in XXX\WebRtc.Mono.Droid\ViEAndroidJavaAPI.cs:30
12-21 19:29:04.298 I/MonoDroid(15226): at WebRtc.Mono.Droid.WebRTCDemo.startMain () [0x0004b] in XXX\WebRtc.Mono.Droid\WebRTCDemo.cs:533
12-21 19:29:04.298 I/MonoDroid(15226): at WebRtc.Mono.Droid.WebRTCDemo.OnCreate (Android.OS.Bundle) [0x0028e] in XXX\WebRtc.Mono.Droid\WebRTCDemo.cs:313
12-21 19:29:04.298 I/MonoDroid(15226): at Android.App.Activity.n_OnCreate_Landroid_os_Bundle_ (intptr,intptr,intptr) [0x00011] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.10.1-branch/d23a19bf/source/monodroid/src/Mono.Android/platforms/android-17/src/generated/Android.App.Activity.cs:2119
12-21 19:29:04.298 I/MonoDroid(15226): at (wrapper dynamic-method) object.705dc6ba-9c58-4bcd-a8a2-f12584a9175f (intptr,intptr,intptr)

Finally after digging I found this posting Native library integration which basically state

you cannot sanely use P/Invoke to invoke the native method. You must instead use JNI to invoke the Java-side native method.

Basically because this is Java native C/C++ interface we are to invoke, you cannot do this like normal non JNI wrapped C/C++ methods.


This is pushing me in a direction that I initially hoped I could avoid (mainly due to my limited knowledge in the area), JNI.


Later: I did some (quite a bit) reading, namely I found these links useful:

Interop with Native Libraries
Java Integration Overview
Working With JNI

In the next posting in this series I manage to invoke the native methods.

WebRTC app - C# / Xamarin - Part #1 - Building platform native webrtc library

This is a post in a series of postings

1. WebRTC app - C# / Xamarin - Part #1 - Building platform native webrtc library
2. WebRTC app - C# / Xamarin - Part #2 - Attempt #1 - failure to using a JNI .so file directly from C# / Mono
3. WebRTC app - C# / Xamarin - Part #2 - Attempt #2 - success using a JNI .so file from C# / Mono
4. WebRTC app - C# / Xamarin - (C# - JNI - C/C++) - Summary and GitHub repository

And finally the associated GitHub repository https://github.com/kenneththorman/webrtc-app-mono

I wish to build a cross platform app that supports WebRTC (real time communication - wikipedia article here). I would like to use Xamarin to achieve some level of code reuse between iOS and Android. There are several areas of the application that can use common code like the:

• webrtc signaling
• UI (ViewModel) logic if we utilize Stuart Lodge's MVVMCross.

This series of blog postings will document my attempt at implementing the Android initial app (Mono.Android) and then I will attempt to move this to iOS (monotouch). Unlike some of my other postings this is a documentation project during the attempt to reach that goal.

Lets get started. 
Now building webrtc and all the associated libraries is not for the faint of heart, but luckily there are some pretty nice build tools available that does the job nicely. For both the Android and later the iOS edition we will need a C/C++ native compiled library that does all the heavy lifting with regards to audio/video rendering, decoding and encoding. So my first goal was to build a Android compatible library that I could include in my solution.

Here are some good links that got me started
http://www.webrtc.org/reference/getting-started

and then I found this little gem at Ryazantsev's blog which basically walks you through the process step by step. I already had a Ubuntu 12.04 LTS virtual machine installed and configured so the below is the console commands run on my machine. I use some slightly modified commands compared to Ryazantsev's blog. Thanks to Ryazantsev for posting this great post.

##Installing JAVA (first install default JAVA)
sudo apt-get install python-software-properties
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update && sudo apt-get install oracle-jdk7-installer
chmod a+x jdk-6u45-linux-x64.bin
./jdk-6u45-linux-x64.bin
mkdir /usr/lib/jvm
mv jdk1.6.0_45 /usr/lib/jvm/jdk1.6.0_45

##Update alternatives of java tools
jdir=jdk1.6.0_45
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/$jdir/bin/javac 1
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/$jdir/bin/java 1
sudo update-alternatives --install /usr/bin/javaws javaws /usr/lib/jvm/$jdir/bin/javaws 1
sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/$jdir/bin/jar 1

##Check alternatives and java version
sudo update-alternatives --config javac
sudo update-alternatives --config java
sudo update-alternatives --config javaws
sudo update-alternatives --config jar
ls -la /etc/alternatives/{java,javac,javaws,jar}
java -version

echo 'export JAVA_HOME=/usr/lib/jvm/jdk1.6.0_45' >> ~/.bashrc
echo 'PATH="$PATH":`pwd`/depot_tools' >> ~/.bashrc
source ~/.bashrc
printenv | grep depot_tools
 
sudo apt-get install git subversion libpulse-dev g++ pkg-config gtk+-2.0 libnss3-dev
git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git

###Building WebRTC Trunk
cd ~
mkdir WebRTCDemo
cd WebRTCDemo/

gclient config https://webrtc.googlecode.com/svn/trunk
gclient sync
echo target_os = [\'android\', \'unix\'] >> .gclient
./trunk/build/install-build-deps.sh  --no-chromeos-fonts
./trunk/build/install-build-deps-android.sh
check  'sudo update-alternatives --config java ' for correct path
gclient sync
cd trunk
source ./build/android/envsetup.sh
gclient runhooks
GYP_GENERATORS=ninja ./build/gyp_chromium --depth=. all.gyp 
ninja -C out/Debug -j10 All

After downloading all the files and building the project it takes up about 4.6GB on my disk in the virtual machine. Most source files in the project will show to be a good reference when we need to start using this in a Xamarin project. The really relevant parts through is the java sources for the Java version of the app (written by the WebRTC authors) as well as the Android compatible .so file.

The compiled .so file we need is available at 

~/WebRTCDemo/trunk/webrtc/video_engine/test/android/libs/armeabi-v7a/libwebrtc-video-demo-jni.so 

The next posting will be attempt #1 in converting a Java app to a c# equivalent

Droidulus - Reverse Calculator for Android Desire (very much beta)

I have over time slowly improved this reverse calculator for 2 reasons. 

1. My daughter likes to try my phone
2. As long as she find it fun I might as well try to get her used to the multiplication and math.

Here is a small video showing the application

For those interested you can find the app here Droidulus - Reverse Calculator.

There are many things that could be improved

• UI
• Saving and retrieving shared preferences
• Not hard coding strings in the code :) this should be language controlled
• Inversion of Control via Dependency Injection using Spring ME

I have posted the source code on Github more specifically located here kenneththorman's Droidulus at master - GitHub.

Adding a menu to your Android application

This posting attempts to explain in simple terms what is needed to add a menu to your Android application.

Assuming that you have installed needed Android development tools in Eclipse, the SDK and have a simple application running you need to do the following.

1. add a menu structure defined in xml (in this case menu/title_only.xml)
2. add some string resources for the titles to display in the menu (values/strings.xml)
3. inflate the xml structure to a menu object in your Android application

I am going to create the menu shown in the following screenshot

The 2 first files can be seen here in the project structure in Eclipse

title_only.xml is about as simple as they come without icons or submenus and it looks like this

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/menuoptions"
        android:title="@string/menuoptions" />

    <item android:id="@+id/menuabout"
        android:title="@string/menuabout" />
</menu>

And the strings.xml contains the labels/titles to be used for the menu

<?xml version="1.0" encoding="utf-8"?>
<resources>
...
 <string name="menuoptions">Options</string>
 <string name="menuabout">About</string>
...
</resources>

Now we need to display this menu when someone clicks the menu button on the phone. The menu button click is tied to the currently shown Activity (form or screen). In my case I want to show this menu on the main screen of my application which is the Droidulus class (Droidulus.java).

The class representing this Activity has a few methods that can be overridden that are relevant to menus.

boolean onCreateOptionsMenu(Menu menu)
boolean onOptionsItemSelected(MenuItem item)

In the following very simple implementations I am inflating the menu to actually generate the menu shown on the Android device

private Menu menu;

...

/** Called when clicking the menu button. */
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    this.menu = menu;
    
    // Inflate the currently selected menu XML resource.
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.title_only, menu);
    
    return true;
}

Now we need to react to the actual menu item clicks and this happens in the following method

/** Called when a menu item in the menu is clicked. */
@Override
public boolean onOptionsItemSelected(MenuItem item) {
 switch (item.getItemId()) {
  case R.id.menuabout:
   Toast.makeText(this, "Droidulus 1.0 by Kenneth Thorman", Toast.LENGTH_SHORT).show();
   return true;

  case R.id.menuoptions:
   Intent intent = new Intent(Droidulus.this, OptionsScreen.class);
   startActivityForResult(intent, OPTIONS_ACTIVITY_REQUEST_CODE);
   return true;
   
  // Generic catch all for all the other menu resources
  default:
   if (!item.hasSubMenu()) {
    return true;
   }
   break;
 }
 
 return false;
}

The menuabout menu item yields the following screenshot

with regards to the menuoptions menu item click that is the subject of another posting dealing with sub forms/activities and reacting to when those forms are closed it can be found here Child windows / activities in Android

Android: Fading images and forcing them to stay that way

In my attempts at making the world best reverse calculator (in tight competition with the 100's of other developers doing the same thing on Market - talk about reinventing the wheel) I was considering how to visually best show the math concept subtraction.

After contemplating a bit I wanted to implement a small Packman eating the images representing operand2.

This would look something like

5 - 2 =

***** (packman eats the last 2 dots) and the result is ***

My initial though was to use animated gifs, but my findings (here amongst other places www.anddev.org) were that this was a non trivial exercise and that I really wanted to use something that was built in to Android.

Creating a new folder under the res folder in the Eclipse project named anim and placing a file named fadeout.xml with the following content

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
 <alpha android:fromAlpha="1.0" android:toAlpha="0.0" android:interpolator="@android:anim/accelerate_interpolator" android:duration="3000" android:repeatCount="0" />
</set>

allowed me to use the following code in my SubtractionProblem class

...
// Fade out all the imageviews that are representing operand2
for(View view : operand2Views){
 Animation myFadeOutAnimation = AnimationUtils.loadAnimation(view.getContext(), R.anim.fadeout);
 myFadeOutAnimation.setFillAfter(true);
 view.startAnimation(myFadeOutAnimation); //Set animation to your ImageView

 ...
}

This fades the operand2 images and the
myFadeOutAnimation.setFillAfter(true) code makes the images stay faded (otherwise Android will animate them and return the images to the original state)

Android - UI Sleep

I have lately (since I got my HTC Desire phone) been tinkering a little with developing a small application for Android. Since my daughter is learning the multiplication tables and since she finds my phone "cool" then making this little app would be a good starting point.


I am here of course ignoring the fact that there are more than a hundred apps similar available on the Market.


When developing the first version of this app I ran into an interesting point about UI responsiveness and how I could do a "sleep()" function.

The flow is:

1. The problem is presented
2. The user answers by clicking on of the available buttons
3. Mark the problem green for a second before continuing if the answer was correct
4. If the asnwer was incorrect mark the problem red until the correct answer is chosen

I ended up doing it as follows

private void verifyResult(final View view){
 answerAttempts++; // The user has tried to answer the problem increment answer attempts
 disableAnswerButtons(); // Disable further user input when the text is green/red otherwise the user can click many times on the buttons
 
 int result = Integer.parseInt(view.getTag().toString());
 if (correctResult == result)
 {
  problem.setTextColor(Color.GREEN);
  problem.setText(getProblemText(true)); // Show full problem + correct result
  points++;        
  
  // Wait 1 second before resetting the text color and showing a new problem text
  new Handler().postDelayed(new Runnable() { 
   public void run() { 
    problem.setTextColor(Color.WHITE); 
    generateProblem(); // Generate a new problem and update UI
    enableAnswerButtons();
   } 
  }, 1000);
 }
 else{
  problem.setTextColor(Color.RED); 
  enableAnswerButtons();     
 }
 score.setText(String.format("%s %d/%d", getString(R.string.score), points, answerAttempts));
}

Android development - unable to open ..apk! file

Today when continuing my escapades in Android development I ran into an error in Eclipse.
I just started Eclipse and I was going to build the package when the following error was displayed in the console window. 


[2010-09-02 20:15:11 - Droidulus] ERROR: unable to open 'D:\...\Programming\android\Droidulus\trunk\bin\resources.ap_' as Zip file for writing
[2010-09-02 20:15:11 - Droidulus] Error generating final archive: D:\...\Programming\android\Droidulus\trunk\bin\Droidulus.apk (The system cannot find the path specified)
[2010-09-02 21:32:20 - Droidulus] ------------------------------
[2010-09-02 21:32:20 - Droidulus] Android Launch!
[2010-09-02 21:32:20 - Droidulus] adb is running normally.
[2010-09-02 21:32:20 - Droidulus] Could not find Droidulus.apk!
[2010-09-02 21:33:25 - Droidulus] ------------------------------

After verifying that the path and the files were located where Eclipse and the ADT plug in expected them to be, and that no other compilation bugs was lurking I hit Google. Apparently there are quite a few mentions of this or similar error messages out there.

After nothing useful really showing in the results in 2 or 3 searches I grew impatient and started looking into the error myself.

The first thing I tried was to clean the project (Project Menu/Clean/Clean all).

This fixed the error message for me and I could go back to tinkering.

Android developement - first try

I recently purchased a HTC Desire which basically is my first foray into the new generation of smart phones.


I wanted to try some development so I downloaded the SDK and the other bits and piece described here http://developer.android.com/guide/developing/eclipse-adt.html.


The java development part was fairly straight forward, however the layout and how to get that right, that seems a bit harder. Probably something that I am missing.


Anyway my first application is a reverse calculator.

This visualizes the operands as small blue dots and then allows you to pick a choice for the answer.


I would like it to be centered in the screen like this

This has however had me running in circles until now, spending at least 5 hours trying to get this right. I have tried RelativeLayouts, LinearLayouts & TableLayouts. 


I have done a few applications for windows mobile and I must admit that I found layout easier to do in visual Studio.