• Introduction into Android Development


    Introduction into Android Development

    This guide was designed to help you in learning Android development basics and seting up your working environment quickly. It was written with Windows 7 in mind, though it would work with Linux (Ubuntu), Mac OS X and any other OS supported by Android SDK.

    If you encounter any error after thoroughly following these steps, feel free to contact us via  OpenCV4Android  discussion group or OpenCV  Q&A forum . We’ll do our best to help you out.

    Android is a Linux-based, open source mobile operating system developed by Open Handset Alliance led by Google. See the  Android home site  for general details.

    Development for Android significantly differs from development for other platforms. So before starting programming for Android we recommend you make sure that you are familiar with the following key topis:

    1. Java  programming language that is the primary development technology for Android OS. Also, you can find  Oracle docs on Java  useful.
    2. Java Native Interface (JNI)  that is a technology of running native code in Java virtual machine. Also, you can find  Oracle docs on JNI useful.
    3. Android Activity  and its lifecycle, that is an essential Android API class.
    4. OpenCV development will certainly require some knowlege of the  Android Camera  specifics.

    Quick environment setup for Android development

    If you are making a clean environment install, then you can try  Tegra Android Development Pack  ( TADP ) released by  NVIDIA .

    Note

     

    Starting the  version 2.0  the TADP package includes  OpenCV for Tegra  SDK that is a regular  OpenCV4Android SDK  extended with Tegra-specific stuff.

    When unpacked, TADP will cover all of the environment setup automatically and you can skip the rest of the guide.

    If you are a beginner in Android development then we also recommend you to start with TADP.

    Note

     

    NVIDIA ‘s Tegra Android Development Pack includes some special features for  NVIDIA ’s Tegra platform  but its use is not limited to  Tegra devices only.

    • You need at least  1.6 Gb  free disk space for the install.

    • TADP will download Android SDK platforms and Android NDK from Google’s server, so Internet connection is required for the installation.

    • TADP may ask you to flash your development kit at the end of installation process. Just skip this step if you have no  Tegra Development Kit .

    • UNIX ) TADP will ask you for  root  in the middle of installation, so you need to be a member of  sudo  group.

    Manual environment setup for Android development

    Development in Java

    You need the following software to be installed in order to develop for Android in Java:

    1. Sun JDK 6  (Sun JDK 7 is also possible)

      Visit  Java SE Downloads page  and download an installer for your OS.

      Here is a detailed  JDK   installation guide  for Ubuntu and Mac OS (only JDK sections are applicable for OpenCV)

      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:

      sudo update-java-alternatives --set java-6-sun
    2. Android SDK

      Get the latest  Android   SDK  from http://developer.android.com/sdk/index.html

      Here is Google’s  install guide  for the SDK.

      Note

       

      You can choose downloading  ADT Bundle package  that in addition to Android SDK Tools includes Eclipse + ADT + NDK/CDT plugins, Android Platform-tools, the latest Android platform and the latest Android system image for the emulator - this is the best choice for those who is setting up Android development environment the first time!

      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:

      sudo apt-get install ia32-libs

      For Red Hat based systems the following command might be helpful:

      sudo yum install libXtst.i386
    3. Android SDK components

      You need the following SDK components to be installed:

      • Android SDK Tools, revision 20  or newer.

        Older revisions should also work, but they are not recommended.

      • SDK Platform Android 3.0  ( API   11 ).

        The minimal platform supported by OpenCV Java API is  Android 2.2  (API   8 ). This is also the minimum API Level required for the provided samples to run. See the  <uses-sdk  android:minSdkVersion="8"/>  tag in their  AndroidManifest.xml files. But for successful compilation the  target platform should be set to Android 3.0 (API 11) or higher. It will not prevent them from running on Android 2.2.

        Android SDK Manager

        See  Adding Platforms and Packages  for help with installing/updating SDK components.

    4. Eclipse IDE

      Check the  Android SDK System Requirements  document for a list of Eclipse versions that are compatible with the Android SDK. For OpenCV 2.4.x we recommend  Eclipse 3.7 (Indigo)  or  Eclipse 4.2 (Juno) . They work well for OpenCV under both Windows and Linux.

      If you have no Eclipse installed, you can get it from the  official site .

    5. ADT plugin for Eclipse

      These instructions are copied from  Android Developers site , check it out in case of any ADT-related problem.

      Assuming that you have Eclipse IDE installed, as described above, follow these steps to download and install the ADT plugin:

      1. Start Eclipse, then select  Help ‣ Install New Software...

      2. Click  Add  (in the top-right corner).

      3. In the  Add Repository  dialog that appears, enter “ADT Plugin” for the Name and the following URL for the Location:

        https://dl-ssl.google.com/android/eclipse/

      4. Click  OK

        Note

         

        If you have trouble acquiring the plugin, try using “http” in the Location URL, instead of “https” (https is preferred for security reasons).

      5. In the  Available Software  dialog, select the checkbox next to Developer Tools  and click  Next .

      6. In the next window, you’ll see a list of the tools to be downloaded. Click  Next .

        Note

         

        If you also plan to develop native C++ code with Android NDK don’t forget to enable  NDK Plugins  installations as well.

        ADT installation
      7. Read and accept the license agreements, then click  Finish .

        Note

         

        If you get a security warning saying that the authenticity or validity of the software can’t be established, click  OK .

      8. When the installation completes, restart Eclipse.

    Native development in C++

    You need the following software to be installed in order to develop for Android in C++:

    1. Android NDK

      To compile C++ code for Android platform you need  Android   Native  Development   Kit  ( NDK ).

      You can get the latest version of NDK from the  download page . To install Android NDK just extract the archive to some folder on your computer. Here are installation instructions .

      Note

       

      Before start you can read official Android NDK documentation which is in the Android NDK archive, in the folder  docs/ . The main article about using Android NDK build system is in the  ANDROID-MK.html  file. Some additional information you can find in the  APPLICATION-MK.html NDK-BUILD.html  files, and  CPU-ARM-NEON.html ,  CPLUSPLUS-SUPPORT.html,  PREBUILTS.html .

    2. CDT plugin for Eclipse

      If you selected for installation the  NDK   plugins  component of Eclipse ADT plugin (see the picture above) your Eclipse IDE should already have  CDT plugin  (that means  C/C++   Development   Tooling ). There are several possible ways to integrate compilation of C++ code by Android NDK into Eclipse compilation process. We recommend the approach based on Eclipse  CDT  Builder.

    Android application structure

    Usually source code of an Android application has the following structure:

    • root   folder   of   the   project/
      • jni/
      • libs/
      • res/
      • src/
      • AndroidManifest.xml
      • project.properties
      • ...   other   files   ...

    Where:

    • the  src  folder contains Java code of the application,

    • the  res  folder contains resources of the application (images, xml files describing UI layout, etc),

    • the  libs  folder will contain native libraries after a successful build,

    • and the  jni  folder contains C/C++ application source code and NDK’s build scripts  Android.mk  and  Application.mk  producing the native libraries,

    • AndroidManifest.xml  file presents essential information about application to the Android system (name of the Application, name of main application’s package, components of the application, required permissions, etc).

      It can be created using Eclipse wizard or  android  tool from Android SDK.

    • project.properties  is a text file containing information about target Android platform and other build details. This file is generated by Eclipse or can be created with  android  tool included in Android SDK.

    Note

     

    Both  AndroidManifest.xml  and  project.properties  files are required to compile the C++ part of the application, since Android NDK build system relies on them. If any of these files does not exist, compile the Java part of the project before the C++ part.

    Android.mk  and  Application.mk  scripts

    The script  Android.mk  usually has the following structure:

    1
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    LOCAL_PATH := $(call my-dir)
    
    include $(CLEAR_VARS)
    LOCAL_MODULE    := <module_name>
    LOCAL_SRC_FILES := <list of .c and .cpp project files>
    <some variable name> := <some variable value>
    ...
    <some variable name> := <some variable value>
    
    include $(BUILD_SHARED_LIBRARY)

    This is the minimal file  Android.mk , which builds C++ source code of an Android application. Note that the first two lines and the last line are mandatory for any Android.mk .

    Usually the file  Application.mk  is optional, but in case of project using OpenCV, when STL and exceptions are used in C++, it also should be created. Example of the file  Application.mk :

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    APP_STL := gnustl_static
    APP_CPPFLAGS := -frtti -fexceptions
    APP_ABI := all

    Note

     

    We recommend setting  APP_ABI   :=   all  for all targets. If you want to specify the target explicitly, use  armeabi  for ARMv5/ARMv6,  armeabi-v7afor ARMv7,  x86  for Intel Atom or  mips  for MIPS.

    Building application native part from command line

    Here is the standard way to compile C++ part of an Android application:

    Warning

     

    We strongly reccomend using  cmd.exe  (standard Windows console) instead of Cygwin on  Windows . Use the latter if only you’re absolutely sure about, what you’re doing. Cygwin is not really supported and we are unlikely to help you in case you encounter some problems with it. So, use it only if you’re capable of handling the consequences yourself.

    1. Open console and go to the root folder of an Android application

      cd <root folder of the project>/
    2. Run the following command

      <path_where_NDK_is_placed>/ndk-build

      Note

       

      On Windows we recommend to use  ndk-build.cmd  in standard Windows console ( cmd.exe ) rather than the similar  bash  script in  Cygwinshell.

      NDK build
    3. After executing this command the C++ part of the source code is compiled.

    After that the Java part of the application can be (re)compiled (using either  Eclipse  or  Ant  build tool).

    Note

     

    Some parameters can be set for the  ndk-build :

    Example 1 : Verbose compilation

    <path_where_NDK_is_placed>/ndk-build V=1

    Example 2 : Rebuild all

    <path_where_NDK_is_placed>/ndk-build -B

    Building application native part from  Eclipse  (CDT Builder)

    There are several possible ways to integrate compilation of native C++ code by Android NDK into Eclipse build process. We recommend the approach based on Eclipse  CDT  Builder.

    Important

     

    OpenCV for Android package since version 2.4.2 contains sample projects pre-configured CDT Builders. For your own projects follow the steps below.

    1. Define the  NDKROOT  environment variable containing the path to Android NDK in your system (e.g.  "X:\Apps\android-ndk-r8"  or"/opt/android-ndk-r8" ).

      On Windows  an environment variable can be set via  My Computer -> Properties -> Advanced -> Environment variables . On Windows 7 it’s also possible to use  setx  command in a console session.

      On Linux  and  MacOS  an environment variable can be set via appending a  "export   VAR_NAME=VAR_VALUE"  line to the  "~/.bashrc" file and logging off and then on.

      Note

       

      It’s also possible to define the  NDKROOT  environment variable within Eclipse IDE, but it should be done for every new workspace you create. If you prefer this option better than setting system environment variable, open Eclipse menu  Window -> Preferences -> C/C++ -> Build -> Environment , press the  Add...  button and set variable name to NDKROOT  and value to local Android NDK path.

    2. After that you need to  restart Eclipse  to apply the changes.

    3. Open Eclipse and load the Android app project to configure.

    4. Add C/C++ Nature to the project via Eclipse menu  New -> Other -> C/C++ -> Convert to a C/C++ Project .

      Configure CDT

      And:

      Configure CDT
    5. Select the project(s) to convert. Specify “Project type” =  Makefile  project , “Toolchains” =  Other   Toolchain .

      Configure CDT
    6. Open  Project Properties -> C/C++ Build , uncheck  Use   default  build   command , replace “Build command” text from  "make"  to

      "${NDKROOT}/ndk-build.cmd"  on Windows,

      "${NDKROOT}/ndk-build"  on Linux and MacOS.

      Configure CDT
    7. Go to  Behaviour  tab and change “Workbench build type” section like shown below:

      Configure CDT
    8. Press  OK  and make sure the  ndk-build  is successfully invoked when building the project.

      Configure CDT
    9. If you open your C++ source file in Eclipse editor, you’ll see syntax error notifications. They are not real errors, but additional CDT configuring is required.

      Configure CDT
    10. Open  Project Properties -> C/C++ General -> Paths and Symbols  and add the following  Include  paths for  C++ :

      # for NDK r8 and prior:
      ${NDKROOT}/platforms/android-9/arch-arm/usr/include
      ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/include
      ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/libs/armeabi-v7a/include
      ${ProjDirPath}/../../sdk/native/jni/include
      # for NDK r8b and later:
      ${NDKROOT}/platforms/android-9/arch-arm/usr/include
      ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/4.6/include
      ${NDKROOT}/sources/cxx-stl/gnu-libstdc++/4.6/libs/armeabi-v7a/include
      ${ProjDirPath}/../../sdk/native/jni/include

      The last path should be changed to the correct absolute or relative path to OpenCV4Android SDK location.

      This should clear the syntax error notifications in Eclipse C++ editor.

      Configure CDT

    Debugging and Testing

    In this section we will give you some easy-to-follow instructions on how to set up an emulator or hardware device for testing and debugging an Android project.

    AVD ( Android Virtual Device ) is not probably the most convenient way to test an OpenCV-dependent application, but sure the most uncomplicated one to configure.

    1. Assuming you already have  Android SDK  and  Eclipse IDE  installed, in Eclipse go  Window -> AVD Manager .

    2. Press the  New  button in  AVD Manager  window.

    3. Create new Android Virtual Device  window will let you select some properties for your new device, like target API level, size of SD-card and other.

      Configure builders
    4. When you click the  Create AVD  button, your new AVD will be availible in  AVD Manager .

    5. Press  Start  to launch the device. Be aware that any AVD (a.k.a. Emulator) is usually much slower than a hardware Android device, so it may take up to several minutes to start.

    6. Go  Run -> Run/Debug  in Eclipse IDE to run your application in regular or debugging mode.  Device Chooser  will let you choose among the running devices or to start a new one.

    If you have an Android device, you can use it to test and debug your applications. This way is more authentic, though a little bit harder to set up. You need to make some actions for Windows and Linux operating systems to be able to work with Android devices. No extra actions are required for Mac OS. See detailed information on configuring hardware devices in subsections below.

    You may also consult the official  Android Developers site instructions  for more information.

    Windows host computer

    1. Enable USB debugging on the Android device (via  Settings  menu).

    2. Attach the Android device to your PC with a USB cable.

    3. Go to  Start Menu  and  right-click  on  Computer . Select Manage  in the context menu. You may be asked for Administrative permissions.

    4. Select  Device Manager  in the left pane and find an unknown device in the list. You may try unplugging it and then plugging back in order to check whether it’s your exact equipment appears in the list.

      Unknown device
    5. Try your luck installing  Google USB drivers  without any modifications:  right-click  on the unknown device, select  Properties menu item –>  Details  tab –> Update Driver  button.

      Device properties
    6. Select  Browse computer for driver software .

      Browse for driver
    7. Specify the path to  <Android   SDK  folder>/extras/google/usb_driver/  folder.

      Browse for driver
    8. If you get the prompt to install unverified drivers and report about success - you’ve finished with USB driver installation.

      Install prompt
      ` `
      Installed OK
    9. Otherwise (getting the failure like shown below) follow the next steps.

      No driver
    10. Again  right-click  on the unknown device, select  Properties –> Details –> Hardware Ids  and copy the line like USBVID_XXXX&PID_XXXX&MI_XX .

      Device properties details
    11. Now open file  <Android   SDK  folder>/extras/google/usb_driver/android_winusb.inf . Select either Google.NTx86  or Google.NTamd64  section depending on your host system architecture.

    12. There should be a record like existing ones for your device and you need to add one manually.

    13. Save the  android_winusb.inf  file and try to install the USB driver again.

      Device properties

      ` `

      Browse for driver

      ` `

      Browse for driver
    14. This time installation should go successfully.

      Install prompt

      ` `

      Installed OK
    15. And an unknown device is now recognized as an Android phone.

    16. Successful device USB connection can be verified in console via  adb  devices  command.

    17. Now, in Eclipse go  Run -> Run/Debug  to run your application in regular or debugging mode.  Device Chooser  will let you choose among the devices.

    Linux host computer

    By default Linux doesn’t recognize Android devices, but it’s easy to fix this issue. On Ubuntu Linux you have to create a new /etc/udev/rules.d/51-android.rules configuration file that contains information about your Android device. You may find some Vendor ID’s  here or execute  lsusb  command to view VendorID of plugged Android device. Here is an example of such file for LG device:

    SUBSYSTEM=="usb", ATTR{idVendor}=="1004",  MODE="0666", GROUP="plugdev"

    Then restart your adb server (even better to restart the system), plug in your Android device and execute  adb devices  command. You will see the list of attached devices:

    List of attached devices

    Mac OS host computer

    No actions are required, just connect your device via USB and run  adb  devices  to check connection.

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  • 原文地址:https://www.cnblogs.com/Anzhongliu/p/6092017.html
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