Monday, October 14, 2013

Android Programming with Lazarus through Custom Drawn Interface

OK, so you've read that it's possible to write Android applications with Lazarus and Free Pascal. You go straight to the wiki, follow the bunch of steps there and FAIL! And then you start grumbling and doubting whether it's really possible or just a joke.

Listen up, dude. The Android support in FPC is still in development, and a pure arm-android target has just been added a couple of months ago. This target is available for those experienced enough with FPC (bootstrapping the compiler, set options for building, etc.) and not lazy to do the whole setup. Most problems come from those who don't read and do the steps thoroughly, possibly skipping important part. So if you're one of them, either change your behavior or wait until the support is available in the stable release.

I will try to explain step by step setting up FPC trunk with arm-android target support, followed by setting up Lazarus to support building Android application. Note that it's all done on Linux (Kubuntu 13.04) 32-bit, but it should work for any supported host platforms.

First thing first, latest stable FPC

FPC is a bootstrapping compiler, and it's guaranteed that latest stable version will be able to build trunk and next stable version. No guarantee for older version or between revisions of trunk, and things can be broken anytime on trunk. At this time of writing, latest stable FPC is of version 2.6.2. So grab that one if yours is not.

Next, Android NDK

For arm-android target, FPC makes use of external assembler and linker provided by Android NDK. Mine is still version r8e, but looking at the changelog version 9 should work just fine. Extract it anywhere you want, we will refer to this location as {ndk.dir}. To be sure, right under {ndk.dir} there should be README.TXT and RELEASE.TXT.

Let's identify the tools we need:
  • {ndk.dir}/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-as (assembler)
  • {ndk.dir}/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-ld (linker)
If you want, you can change the part after /toolchains/ in case you want to use androideabi 4.6 or 4.7. Look at the corresponding directory you have in your {ndk.dir}.

Open up your fpc.cfg file, by default it should contain the line:


This line tells the compiler to prepend any external tools called with $FPCTARGET- (note the dash), so when the compiler wants to call "as", for arm-android target, it will call "arm-android-as" instead. As you can see, the name is then inconsistent with the NDK tools name. The solution is to create symbolic links for the tools with names expected by the compiler. For hosts that don't support symbolic links (e.g. Windows), you can create a small exe wrapper for the tools, or simply rename the tool. Put the symbolic links / wrappers somewhere in PATH (I put it in /usr/bin/).

Ensure you do it correctly by verifying the output of ls -l `which arm-android-<toolname>` (*nix only). It looks like this on my system (real directory replaced with {ndk.dir}):

$ ls -l `which arm-android-as`
lrwxrwxrwx 1 root root 120 Mar  8  2013 /usr/bin/arm-android-as -> {ndk.dir}/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-as
$ ls -l `which arm-android-ld`

lrwxrwxrwx 1 root root 120 Mar  8  2013 /usr/bin/arm-android-ld -> {ndk.dir}/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-ld

Try executing arm-android-as and arm-android-ld in terminal or command prompt to ensure it works.

Next, FPC trunk

Get FPC trunk either from svn (I won't teach how to use svn, go find tutorial somewhere) or Free Pascal's FTP. In case of svn, here's the address:

Build FPC for arm-android target

Using your terminal, go to FPC trunk directory and execute the following:

make crossall OS_TARGET=android CPU_TARGET=arm CROSSOPT='-Cp<ARM Arch> -Cf<ARM VFP>'

<ARM Arch> defines the ARM architecture you want to compile for, my device is ARMv6, so I use -CpARMv6.
<ARM VFP> defines the Vector Floating Point unit you want to use for floating point calculation, for at least ARMv6, VFPv2 and VFPv3 are available. The default is to use soft-float, which is very slow as the calculation is performed by software. Since I seldom use floating point, soft-float is fine for me, so I don't pass any -Cf option.

If everything goes well, it's time to install. Execute the following (still in the same FPC trunk folder):

make crossinstall OS_TARGET=android CPU_TARGET=arm INSTALL_PREFIX=<directory of your choice>

Feel free to choose any directory you want, but ensure it fulfills the standard requirement (no space in the file path). I suggest installing to the same host FPC directory so you can easily share fpc.cfg. FPC directory structure is made such that it's possible to install cross compiler (and the respective units) in the same tree as the host compiler. The fpc driver can then be used to query which ppc[ross]XXX to call.

If everything goes well, test the compiler. Execute the following:

fpc -Parm -Tandroid

It should output something like:

Free Pascal Compiler version 2.7.1 [2013/09/21] for arm
Copyright (c) 1993-2013 by Florian Klaempfl and others
Fatal: No source file name in command line
Fatal: Compilation aborted

Error: /usr/bin/ppcrossarm returned an error exitcode

Next, Android SDK

Grab Android SDK if you haven't, r22 should be fine. We just need the SDK tools, so no need to waste time and bandwidth downloading the ADT bundle. I will refer to the SDK installation directory as {sdk.dir}. To be sure, right under {ndk.dir} there should be SDK README.TXT.

Test AndroidLCL example, yay!

Go to your Lazarus installation directory (I will refer it as {lazarus.dir} from now on) and open examples/androidlcl/androidlcltest.lpi. Now open Project->Project Options, ensure in Target Platform OS is set to android and CPU is set to arm (or just pick the respective build mode). If upon FPC trunk building you use -Cf option, specify the same option in Other. You might need to also set it in Tools->Configure Build Lazarus dialog. Now press the Run->Build menu. If you get:

Trying to use a unit which was compiled with a different FPU mode

Then you don't put the -Cf option correctly. Remember you will need to put it for both your project (through Project Options dialog) and LCL (and its dependencies, through Configure Build Lazarus).

If everything goes well, you will get android/libs/armeabi/ in the project folder.

Get Ant

Android SDK uses ant build tool for building apk, so you'll need to install it as well.

Build the APK

Go to android folder under androidlcl project folder, and open the build.xml. Inside, you will see 2 loadproperties and 1 property tags. These points to files you will need to edit to match your SDK installation. Mine is below:

<loadproperties srcFile="" />
<property file="" />
<loadproperties srcFile="" /> contains the sdk.dir which you should fill with {sdk.dir} (actual value where you install it, of course). contains the target android API level. The complete list can be seen here. Note that you have to install the respective SDK platform through Android SDK manager. contains and key.alias which is required for release version of your apk. For debug version, it's not required and the apk builder utility will assign a debug key on its own.

If all set, execute:

ant debug

in android folder. The resulting .apk will be in android/bin folder named LCLExample-debug.apk. Install that and enjoy.

From this point forward, you can make use of androidlcl structure as a template. General Java package structure and Android build system knowledge will be required to change the package name.


Friday, January 18, 2013

Top Down Agile Program Development

This time I would like to post something out of coding world, but rather something about software engineering.

Traditional agile program development commonly uses bottom up approach, where one builds the lowest level functionality first then goes up further. API changes is not an uncommon things to happen during agile development, which could lead to code rewriting problems at higher level(s). For example, consider the following function:

function Init(var R: TSomeRecord): Boolean;

which somehow in the middle of development gets changed to:

procedure Init(var R: TSomeRecord);

with purpose of raising an exception instead of returning boolean value to indicate successfulness of the operation.

If this change happens in far future, then all codes using this routine must be rewritten. The problem could arise because we usually don't think how we are going to use an API, or a combination/series of them, when we design. We only think of the API as itself, standalone, away from how it will be used. Therefore, to cover the problem, we could use alternative development method, that is the top down approach.

This method requires you to build program from its highest level first (usually user interface), then goes down further. The idea of this method is largely based on test driven development, when you write test cases first prior to implementing the test unit. The difference lies in the fact that test driven development is still bottom up in the large, yet it's top down for the unit to be implemented. This method ASSUMES the lower level API already exists, regardless of its existence. So, when you code you're thinking of using the API, possibly with other API, together to do some tasks. Because of this, the changes in the future would be minimal or even none. When something goes wrong when you test, the chance is that source of error is at lower level, which means less code to change (one place instead of several).

However, this method is not magical (in fact, none is), as with other methods it has disadvantages as well. You can't see immediate result of your program until the lowest level is implemented, though you can simply put "not implemented yet" output for some functionalities. Functions with deep dependencies (e.g.: requires function X which in turn requires function Y which in turn requires function Z and so on) will be the least ones visible. This method also doesn't play well with incremental approach, which is designed to be bottom up.

Final words: Choose your weapon wisely ;)