{"id":21930,"date":"2015-06-29T10:36:43","date_gmt":"2015-06-29T05:06:43","guid":{"rendered":"https:\/\/tothenewco.pro\/blog\/?p=21930"},"modified":"2015-07-09T15:08:05","modified_gmt":"2015-07-09T09:38:05","slug":"android-application-using-ndk","status":"publish","type":"post","link":"https:\/\/tothenewco.pro\/blog\/android-application-using-ndk\/","title":{"rendered":"Building Android Application using NDK"},"content":{"rendered":"

The Native Development Kit (NDK)<\/strong> is a toolset enables us to implement parts of our app using native-code languages like C and C++. Typically, good use cases for the NDK are CPU-intensive applications such as signal processing, game engines, and physics simulation.<\/p>\n

[java]
\npublic class MyActivity extends Activity {
\n \/**
\n * Native method implemented in C\/C++
\n *\/
\n public native void invokeNativeFunction();
\n}
\n[\/java]<\/p>\n

The use of native code in Android apps<\/a> are particularly useful to developers who wish<\/a> to do one of the following:
\n1.<\/strong> Port their apps between platforms.
\n2.<\/strong> Reuse existing libraries, or provide their own libraries for reuse.
\n3.<\/strong> Increase performance in certain cases, particularly computationally intensive ones like games.<\/p>\n

Installing the Android NDK:<\/strong><\/span>
\n1.<\/strong> Download the ndk package from the link:
\n http:\/\/developer.android.com\/tools\/sdk\/ndk\/index.html<\/a><\/strong>
\n2.<\/strong> Open a terminal window.
\n3.<\/strong> Go to the directory to which you downloaded the package.
\n4.<\/strong> Run chmod a+x<\/strong> on the downloaded package.
\n5.<\/strong> Execute the package. For example:<\/p>\n

[java]
\n\tndk$ chmod a+x android-ndk-r10c-darwin-x86_64.bin
\n\tndk$ .\/android-ndk-r10c-darwin-x86_64.bin
\n [\/java]<\/p>\n

The folder containing the NDK extracts itself.<\/p>\n

Making a Basic NDK App:<\/strong><\/span>
\nStep 1.<\/strong> In the Android project, Make a folder called jni<\/strong> in the root of project (right-click the project node, New \u2013 Folder).
\nStep 2.<\/strong> Create a file called Android.mk<\/strong> within jni folder with the following contents:<\/p>\n

[java]
\nLOCAL_PATH:=$(call my-dir)
\ninclude $(CLEAR_VARS)
\nHere we give our module name and source file(s)
\nLOCAL_MODULE := ndk_test
\nLOCAL_SRC_FILES := ndk_test.c
\ninclude $(BUILD_SHARED_LIBRARY)
\n[\/java]<\/p>\n

The Android.mk<\/strong> file is important for the NDK build process to recognize your NDK modules. In our case we named our module ndk_test and told the build tool that it consists of one source file named ndk_test.c.<\/p>\n

Step 3.<\/strong> Create file ndk_test.c<\/strong> in jni folder<\/p>\n

[java]
\n#include <string.h>
\n#include <jni.h><\/p>\n

jstring Java_com_example_ndktest_NdkTestActivity_invokeNativeFunction(JNIEnv* env, jobject javaThis) {
\n return (*env)->NewStringUTF(env, "Hello from native code!");
\n}
\n [\/java]<\/p>\n

Step 4.<\/strong> In NdkTestActivity<\/strong> class to use the NDK code:<\/p>\n

[java]
\npublic class NdkTestActivity extends Activity {<\/p>\n

\/\/ load the library – name matches jni\/Android.mk
\n static {
\n System.loadLibrary("ndk_test");
\n }<\/p>\n

\/\/ declare the native code function – must match ndkfoo.c
\n private native String invokeNativeFunction();<\/p>\n

@Override
\n public void onCreate(Bundle savedInstanceState) {
\n super.onCreate(savedInstanceState);
\n setContentView(R.layout.main);<\/p>\n

\/\/ this is where we call the native code
\n String hello = invokeNativeFunction();<\/p>\n

new AlertDialog.Builder(this).setMessage(hello).show();
\n }
\n}
\n [\/java]<\/p>\n

This code will invoke the NDK method that will return the string, that will be displayed as an alert on the screen. Here\u2019s the result of running the ndk_test app<\/p>\n

A successful run of ndk-build tool. Create an .so<\/strong> file in a new folder called libs
\nThe .so file is the binary library that will be included into the application .apk package and will be available for the Java code of the app to link to.<\/p>\n

Hope this was useful to the readers.<\/p>\n

Happy NDK\u2019ing.<\/strong> \ud83d\ude42<\/p>\n","protected":false},"excerpt":{"rendered":"

The Native Development Kit (NDK) is a toolset enables us to implement parts of our app using native-code languages like C and C++. Typically, good use cases for the NDK are CPU-intensive applications such as signal processing, game engines, and physics simulation. [java] public class MyActivity extends Activity { \/** * Native method implemented in […]<\/p>\n","protected":false},"author":167,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"iawp_total_views":25,"footnotes":""},"categories":[518],"tags":[1928,1927],"class_list":["post-21930","post","type-post","status-publish","format-standard","hentry","category-android","tag-android-ndk","tag-ndk"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t