1 Introduction into Android Development {#tutorial_android_dev_intro}
2 =====================================
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8 This guide was designed to help you in learning Android development basics and setting up your
9 working environment quickly. It was written with Windows 7 in mind, though it would work with Linux
10 (Ubuntu), Mac OS X and any other OS supported by Android SDK.
12 If you encounter any error after thoroughly following these steps, feel free to contact us via
13 [OpenCV4Android](https://groups.google.com/group/android-opencv/) discussion group or OpenCV [Q&A
14 forum](http://answers.opencv.org). We'll do our best to help you out.
19 Android is a Linux-based, open source mobile operating system developed by Open Handset Alliance led
20 by Google. See the [Android home site](http://www.android.com/about/) for general details.
22 Development for Android significantly differs from development for other platforms. So before
23 starting programming for Android we recommend you make sure that you are familiar with the following
26 -# [Java](http://en.wikipedia.org/wiki/Java_(programming_language)) programming language that is
27 the primary development technology for Android OS. Also, you can find [Oracle docs on
28 Java](http://docs.oracle.com/javase/) useful.
29 -# [Java Native Interface (JNI)](http://en.wikipedia.org/wiki/Java_Native_Interface) that is a
30 technology of running native code in Java virtual machine. Also, you can find [Oracle docs on
31 JNI](http://docs.oracle.com/javase/7/docs/technotes/guides/jni/) useful.
33 Activity](http://developer.android.com/training/basics/activity-lifecycle/starting.html) and its
34 lifecycle, that is an essential Android API class.
35 -# OpenCV development will certainly require some knowledge of the [Android
36 Camera](http://developer.android.com/guide/topics/media/camera.html) specifics.
38 Manual environment setup for Android development
39 ------------------------------------------------
41 ### Development in Java
43 You need the following software to be installed in order to develop for Android in Java:
45 -# **Sun JDK 6** (Sun JDK 7 is also possible)
47 Visit [Java SE Downloads page](http://www.oracle.com/technetwork/java/javase/downloads/) and
48 download an installer for your OS.
50 Here is a detailed JDK (Java Development Kit) [installation
51 guide](http://source.android.com/source/initializing.html#installing-the-jdk) for Ubuntu and Mac
52 OS (only JDK sections are applicable for OpenCV)
54 @note OpenJDK is not suitable for Android development, since Android SDK supports only Sun JDK. If you use Ubuntu, after installation of Sun JDK you should run the following command to set Sun java environment:
56 sudo update-java-alternatives --set java-6-sun
61 Get the latest Android SDK from <http://developer.android.com/sdk/index.html>
63 Here is Google's [install guide](http://developer.android.com/sdk/installing.html) for the SDK.
65 @note You can choose downloading **ADT Bundle package** that in addition to Android SDK Tools
66 includes Eclipse + ADT + NDK/CDT plugins, Android Platform-tools, the latest Android platform and
67 the latest Android system image for the emulator - this is the best choice for those who is setting
68 up Android development environment the first time!
70 @note If you are running x64 version of Ubuntu Linux, then you need ia32 shared libraries for use on amd64 and ia64 systems to be installed. You can install them with the following command:
72 sudo apt-get install ia32-libs
74 For Red Hat based systems the following command might be helpful:
76 sudo yum install libXtst.i386
79 -# **Android SDK components**
81 You need the following SDK components to be installed:
83 - *Android SDK Tools, revision 20* or newer.
85 Older revisions should also work, but they are not recommended.
87 - *SDK Platform Android 3.0* (API 11).
89 The minimal platform supported by OpenCV Java API is **Android 2.2** (API 8). This is also
90 the minimum API Level required for the provided samples to run. See the
91 \<uses-sdk android:minSdkVersion="8"/\> tag in their **AndroidManifest.xml** files. But for
92 successful compilation the **target** platform should be set to Android 3.0 (API 11) or
93 higher. It will not prevent them from running on Android 2.2.
95 ![](images/android_sdk_and_avd_manager.png)
97 See [Adding Platforms and
98 Packages](http://developer.android.com/sdk/installing/adding-packages.html) for help with
99 installing/updating SDK components.
103 Check the [Android SDK System Requirements](http://developer.android.com/sdk/requirements.html)
104 document for a list of Eclipse versions that are compatible with the Android SDK. For OpenCV
105 2.4.x we recommend **Eclipse 3.7 (Indigo)** or **Eclipse 4.2 (Juno)**. They work well for OpenCV
106 under both Windows and Linux.
108 If you have no Eclipse installed, you can get it from the [official
109 site](http://www.eclipse.org/downloads/).
111 -# **ADT plugin for Eclipse**
113 These instructions are copied from [Android Developers
114 site](http://developer.android.com/sdk/installing/installing-adt.html), check it out in case of
115 any ADT-related problem.
117 Assuming that you have Eclipse IDE installed, as described above, follow these steps to download
118 and install the ADT plugin:
120 -# Start Eclipse, then select Help --\> Install New Software...
121 -# Click Add (in the top-right corner).
122 -# In the Add Repository dialog that appears, enter "ADT Plugin" for the Name and the following
123 URL for the Location: <https://dl-ssl.google.com/android/eclipse/>
127 @note If you have trouble acquiring the plugin, try using "http" in the Location URL, instead of "https" (https is preferred for security reasons).
129 -# In the Available Software dialog, select the checkbox next to Developer Tools and click Next.
131 -# In the next window, you'll see a list of the tools to be downloaded. Click Next.
133 @note If you also plan to develop native C++ code with Android NDK don't forget to enable NDK Plugins installations as well.
135 ![](images/eclipse_inst_adt.png)
137 -# Read and accept the license agreements, then click Finish.
139 @note If you get a security warning saying that the authenticity or validity of the software can't be established, click OK.
141 -# When the installation completes, restart Eclipse.
143 ### Native development in C++
145 You need the following software to be installed in order to develop for Android in C++:
149 To compile C++ code for Android platform you need Android Native Development Kit (*NDK*).
151 You can get the latest version of NDK from the [download
152 page](http://developer.android.com/tools/sdk/ndk/index.html). To install Android NDK just
153 extract the archive to some folder on your computer. Here are [installation
154 instructions](http://developer.android.com/tools/sdk/ndk/index.html#Installing).
156 @note Before start you can read official Android NDK documentation which is in the Android NDK
157 archive, in the folder `docs/`. The main article about using Android NDK build system is in the
158 `ANDROID-MK.html` file. Some additional information you can find in the `APPLICATION-MK.html`,
159 `NDK-BUILD.html` files, and `CPU-ARM-NEON.html`, `CPLUSPLUS-SUPPORT.html`, `PREBUILTS.html`.
161 -# **CDT plugin for Eclipse**
163 If you selected for installation the NDK plugins component of Eclipse ADT plugin (see the picture
164 above) your Eclipse IDE should already have CDT plugin (that means C/C++ Development Tooling).
165 There are several possible ways to integrate compilation of C++ code by Android NDK into Eclipse
166 compilation process. We recommend the approach based on Eclipse CDT(C/C++ Development Tooling)
169 Android application structure
170 -----------------------------
172 Usually source code of an Android application has the following structure:
174 - `root folder of the project/`
179 - `AndroidManifest.xml`
180 - `project.properties`
181 - `... other files ...`
185 - the `src` folder contains Java code of the application,
186 - the `res` folder contains resources of the application (images, xml files describing UI layout,
188 - the `libs` folder will contain native libraries after a successful build,
189 - and the `jni` folder contains C/C++ application source code and NDK's build scripts `Android.mk`
190 and `Application.mk` producing the native libraries,
191 - `AndroidManifest.xml` file presents essential information about application to the Android
192 system (name of the Application, name of main application's package, components of the
193 application, required permissions, etc).
195 It can be created using Eclipse wizard or android tool from Android SDK.
197 - `project.properties` is a text file containing information about target Android platform and
198 other build details. This file is generated by Eclipse or can be created with android tool
199 included in Android SDK.
201 @note Both `AndroidManifest.xml` and `project.properties` files are required to compile the C++ part
202 of the application, since Android NDK build system relies on them. If any of these files does not
203 exist, compile the Java part of the project before the C++ part.
205 `Android.mk` and `Application.mk` scripts
206 -----------------------------------------
208 The script `Android.mk` usually has the following structure:
210 LOCAL_PATH := \f$(call my-dir)
212 include \f$(CLEAR_VARS)
213 LOCAL_MODULE := <module_name>
214 LOCAL_SRC_FILES := <list of .c and .cpp project files>
215 <some variable name> := <some variable value>
217 <some variable name> := <some variable value>
219 include \f$(BUILD_SHARED_LIBRARY)
221 This is the minimal file `Android.mk`, which builds C++ source code of an Android application. Note
222 that the first two lines and the last line are mandatory for any `Android.mk`.
224 Usually the file `Application.mk` is optional, but in case of project using OpenCV, when STL and
225 exceptions are used in C++, it also should be created. Example of the file `Application.mk`:
227 APP_STL := gnustl_static
228 APP_CPPFLAGS := -frtti -fexceptions
232 @note We recommend setting APP_ABI := all for all targets. If you want to specify the target
233 explicitly, use armeabi for ARMv5/ARMv6, armeabi-v7a for ARMv7, x86 for Intel Atom or mips for MIPS.
235 @anchor tutorial_android_dev_intro_ndk
236 Building application native part from command line
237 --------------------------------------------------
239 Here is the standard way to compile C++ part of an Android application:
243 We strongly recommend using cmd.exe (standard Windows console) instead of Cygwin on
244 **Windows**. Use the latter if only you're absolutely sure about, what you're doing. Cygwin is
245 not really supported and we are unlikely to help you in case you encounter some problems with
246 it. So, use it only if you're capable of handling the consequences yourself.
248 -# Open console and go to the root folder of an Android application
250 cd <root folder of the project>/
252 -# Run the following command
254 <path_where_NDK_is_placed>/ndk-build
256 @note On Windows we recommend to use ndk-build.cmd in standard Windows console (cmd.exe) rather than the similar bash script in Cygwin shell.
257 ![](images/ndk_build.png)
259 -# After executing this command the C++ part of the source code is compiled.
261 After that the Java part of the application can be (re)compiled (using either *Eclipse* or *Ant*
264 @note Some parameters can be set for the ndk-build:
265 **Example 1**: Verbose compilation
267 <path_where_NDK_is_placed>/ndk-build V=1
269 **Example 2**: Rebuild all
271 <path_where_NDK_is_placed>/ndk-build -B
274 @anchor tutorial_android_dev_intro_eclipse
275 Building application native part from *Eclipse* (CDT Builder)
276 -------------------------------------------------------------
278 There are several possible ways to integrate compilation of native C++ code by Android NDK into
279 Eclipse build process. We recommend the approach based on Eclipse CDT(C/C++ Development Tooling)
284 OpenCV for Android package since version 2.4.2 contains sample projects
285 pre-configured CDT Builders. For your own projects follow the steps below.
287 -# Define the NDKROOT environment variable containing the path to Android NDK in your system (e.g.
288 "X:\\Apps\\android-ndk-r8" or "/opt/android-ndk-r8").
290 **On Windows** an environment variable can be set via
291 My Computer -\> Properties -\> Advanced -\> Environment variables. On Windows 7 it's also
292 possible to use [setx](http://ss64.com/nt/setx.html) command in a console session.
294 **On Linux** and **MacOS** an environment variable can be set via appending a
295 "export VAR_NAME=VAR_VALUE" line to the `"~/.bashrc"` file and logging off and then on.
297 @note It's also possible to define the NDKROOT environment variable within Eclipse IDE, but it
298 should be done for every new workspace you create. If you prefer this option better than setting
299 system environment variable, open Eclipse menu
300 Window -\> Preferences -\> C/C++ -\> Build -\> Environment, press the Add... button and set variable
301 name to NDKROOT and value to local Android NDK path. \#. After that you need to **restart Eclipse**
302 to apply the changes.
304 -# Open Eclipse and load the Android app project to configure.
306 -# Add C/C++ Nature to the project via Eclipse menu
307 New -\> Other -\> C/C++ -\> Convert to a C/C++ Project.
308 ![](images/eclipse_cdt_cfg1.png)
310 ![](images/eclipse_cdt_cfg2.png)
312 -# Select the project(s) to convert. Specify "Project type" = Makefile project, "Toolchains" =
314 ![](images/eclipse_cdt_cfg3.png)
316 -# Open Project Properties -\> C/C++ Build, uncheck Use default build command, replace "Build
317 command" text from "make" to
319 "${NDKROOT}/ndk-build.cmd" on Windows,
321 "${NDKROOT}/ndk-build" on Linux and MacOS.
323 ![](images/eclipse_cdt_cfg4.png)
325 -# Go to Behaviour tab and change "Workbench build type" section like shown below:
327 ![](images/eclipse_cdt_cfg5.png)
329 -# Press OK and make sure the ndk-build is successfully invoked when building the project.
331 ![](images/eclipse_cdt_cfg6.png)
333 -# If you open your C++ source file in Eclipse editor, you'll see syntax error notifications. They
334 are not real errors, but additional CDT configuring is required.
336 ![](images/eclipse_cdt_cfg7.png)
338 -# Open Project Properties -\> C/C++ General -\> Paths and Symbols and add the following
339 **Include** paths for **C++**:
341 # for NDK r8 and prior:
342 ${NDKROOT}/platforms/android-9/arch-arm/usr/include
343 ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/include
344 ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/libs/armeabi-v7a/include
345 ${ProjDirPath}/../../sdk/native/jni/include
347 # for NDK r8b and later:
348 ${NDKROOT}/platforms/android-9/arch-arm/usr/include
349 ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/4.6/include
350 ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/4.6/libs/armeabi-v7a/include
351 ${ProjDirPath}/../../sdk/native/jni/include
353 The last path should be changed to the correct absolute or relative path to OpenCV4Android SDK
356 This should clear the syntax error notifications in Eclipse C++ editor.
358 ![](images/eclipse_cdt_cfg8.png)
360 Debugging and Testing
361 ---------------------
363 In this section we will give you some easy-to-follow instructions on how to set up an emulator or
364 hardware device for testing and debugging an Android project.
368 AVD (*Android Virtual Device*) is not probably the most convenient way to test an OpenCV-dependent
369 application, but sure the most uncomplicated one to configure.
371 -# Assuming you already have *Android SDK* and *Eclipse IDE* installed, in Eclipse go
372 Window -\> AVD Manager.
373 -# Press the New button in AVD Manager window.
374 -# Create new Android Virtual Device window will let you select some properties for your new
375 device, like target API level, size of SD-card and other.
377 ![](images/AVD_create.png)
379 -# When you click the Create AVD button, your new AVD will be available in AVD Manager.
380 -# Press Start to launch the device. Be aware that any AVD (a.k.a. Emulator) is usually much slower
381 than a hardware Android device, so it may take up to several minutes to start.
382 -# Go Run -\> Run/Debug in Eclipse IDE to run your application in regular or debugging mode.
383 Device Chooser will let you choose among the running devices or to start a new one.
387 If you have an Android device, you can use it to test and debug your applications. This way is more
388 authentic, though a little bit harder to set up. You need to make some actions for Windows and Linux
389 operating systems to be able to work with Android devices. No extra actions are required for Mac OS.
390 See detailed information on configuring hardware devices in subsections below.
392 You may also consult the official [Android Developers site
393 instructions](http://developer.android.com/tools/device.html) for more information.
395 #### Windows host computer
397 -# Enable USB debugging on the Android device (via Settings menu).
398 -# Attach the Android device to your PC with a USB cable.
399 -# Go to Start Menu and **right-click** on Computer. Select Manage in the context menu. You may be
400 asked for Administrative permissions.
401 -# Select Device Manager in the left pane and find an unknown device in the list. You may try
402 unplugging it and then plugging back in order to check whether it's your exact equipment appears
405 ![](images/usb_device_connect_01.png)
407 -# Try your luck installing Google USB drivers without any modifications: **right-click** on the
408 unknown device, select Properties menu item --\> Details tab --\> Update Driver button.
410 ![](images/usb_device_connect_05.png)
412 -# Select Browse computer for driver software.
414 ![](images/usb_device_connect_06.png)
416 -# Specify the path to `<Android SDK folder>/extras/google/usb_driver/` folder.
418 ![](images/usb_device_connect_07.png)
420 -# If you get the prompt to install unverified drivers and report about success - you've finished
421 with USB driver installation.
423 ![](images/usb_device_connect_08.png)
425 ![](images/usb_device_connect_09.png)
427 -# Otherwise (getting the failure like shown below) follow the next steps.
429 ![](images/usb_device_connect_12.png)
431 -# Again **right-click** on the unknown device, select Properties --\> Details --\> Hardware Ids
432 and copy the line like `USB\VID_XXXX&PID_XXXX&MI_XX`.
434 ![](images/usb_device_connect_02.png)
436 -# Now open file `<Android SDK folder>/extras/google/usb_driver/android_winusb.inf`. Select either
437 Google.NTx86 or Google.NTamd64 section depending on your host system architecture.
439 ![](images/usb_device_connect_03.png)
441 -# There should be a record like existing ones for your device and you need to add one manually.
443 ![](images/usb_device_connect_04.png)
445 -# Save the `android_winusb.inf` file and try to install the USB driver again.
447 ![](images/usb_device_connect_05.png)
449 ![](images/usb_device_connect_06.png)
451 ![](images/usb_device_connect_07.png)
453 -# This time installation should go successfully.
455 ![](images/usb_device_connect_08.png)
457 ![](images/usb_device_connect_09.png)
459 -# And an unknown device is now recognized as an Android phone.
461 ![](images/usb_device_connect_10.png)
463 -# Successful device USB connection can be verified in console via adb devices command.
465 ![](images/usb_device_connect_11.png)
467 -# Now, in Eclipse go Run -\> Run/Debug to run your application in regular or debugging mode.
468 Device Chooser will let you choose among the devices.
470 #### Linux host computer
472 By default Linux doesn't recognize Android devices, but it's easy to fix this issue. On Ubuntu Linux
473 you have to create a new **/etc/udev/rules.d/51-android.rules** configuration file that contains
474 information about your Android device. You may find some Vendor ID's
475 [here](http://developer.android.com/tools/device.html#VendorIds) or execute lsusb command to view
476 VendorID of plugged Android device. Here is an example of such file for LG device:
478 SUBSYSTEM=="usb", ATTR{idVendor}=="1004", MODE="0666", GROUP="plugdev"
480 Then restart your adb server (even better to restart the system), plug in your Android device and
481 execute adb devices command. You will see the list of attached devices:
483 ![](images/usb_device_connect_ubuntu.png)
485 #### Mac OS host computer
487 No actions are required, just connect your device via USB and run adb devices to check connection.
492 Now, when you have your development environment set up and configured, you may want to proceed to
493 installing OpenCV4Android SDK. You can learn how to do that in a separate @ref tutorial_O4A_SDK tutorial.