Android NDK Download 21: How to Install and Use the Latest Version
If you are an Android developer who wants to improve the performance, security, and compatibility of your app, you might want to consider using the Android Native Development Kit (NDK). The Android NDK is a toolset that lets you implement parts of your app in native code, using languages such as C and C++. In this article, we will show you how to download and install the latest version of the Android NDK, which is 21, and how to use it in your Android app. We will also cover some common issues that you might encounter when using the Android NDK and how to fix them.
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What is Android NDK and why do you need it?
The Android NDK is a set of tools that allows you to access native code libraries from your Java or Kotlin code. Native code libraries are compiled for a specific processor architecture, such as ARM or x86, and can run faster and more efficiently than Java or Kotlin code. Native code libraries can also provide features that are not available in the Android framework, such as low-level access to hardware, graphics, audio, and network.
The benefits of using native code in your Android app
Using native code in your Android app can have several advantages, such as:
Performance: Native code can run faster and use less memory than Java or Kotlin code, especially for computationally intensive tasks such as image processing, encryption, or machine learning.
Security: Native code can be harder to reverse engineer or tamper with than Java or Kotlin code, which can protect your app from hackers or pirates.
Compatibility: Native code can help you support older devices or devices with different architectures than the ones supported by the Android framework.
The challenges of using native code in your Android app
Using native code in your Android app can also have some drawbacks, such as:
Complexity: Native code can be more difficult to write, debug, and maintain than Java or Kotlin code, especially if you are not familiar with the native languages or tools.
Portability: Native code can be less portable than Java or Kotlin code, which means that you might have to write different versions of your native library for different architectures or platforms.
Stability: Native code can cause crashes or memory leaks if it is not written correctly or if it interacts poorly with the Java or Kotlin code.
How to download and install Android NDK 21
To use the Android NDK in your app, you need to download and install it on your development machine. There are two ways to do this: using Android Studio or manually.
The prerequisites for installing Android NDK 21
Before you install the Android NDK 21, you need to make sure that you have the following prerequisites:
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An IDE: You need an integrated development environment (IDE) that supports native development, such as , which is the official IDE for Android development.
A JDK : You need a Java Development Kit (JDK) that matches the minimum version required by Android Studio, which is JDK 11. You can download it from or use the one bundled with Android Studio.
A CMake: You need a CMake tool that can generate native build scripts for your native library project. You can download it from or use the one bundled with Android Studio.
An NDK: You need an Android NDK that matches the minimum version required by your app, which is NDK 21. You can download it from or use the one bundled with Android Studio.
The steps for installing Android NDK 21 using Android Studio
The easiest way to install the Android NDK 21 is to use Android Studio, which can automatically download and configure the NDK for you. Here are the steps to follow:
Open Android Studio and create a new project or open an existing one.
Go to File > Project Structure > SDK Location.
Under Android NDK Location, click Download.
Select NDK (Side by side) and choose 21.4.7075529, which is the latest stable version of NDK 21.
Click OK and wait for the download to finish.
Click Apply and OK.
Congratulations, you have successfully installed the Android NDK 21 using Android Studio!
The steps for installing Android NDK 21 manually
If you prefer to install the Android NDK 21 manually, you can follow these steps:
Go to and download the NDK package for your operating system.
Extract the NDK package to a location of your choice, such as C:\Android\ndk\21.4.7075529.
Add the NDK location to your system environment variables, such as ANDROID_NDK_HOME=C:\Android\ndk\21.4.7075529.
Add the NDK location to your project local.properties file, such as ndk.dir=C\:\\Android\\ndk\\21.4.7075529.
Congratulations, you have successfully installed the Android NDK 21 manually!
How to use Android NDK 21 in your Android app
To use the Android NDK 21 in your app, you need to create a native library project, link it to your app module, and call native methods from your Java or Kotlin code.
How to create a native library project using CMake
A native library project is a folder that contains your native source files, such as C or C++ files, and a CMakeLists.txt file that defines how to build your native library. Here are the steps to create a native library project using CMake:
Create a folder named jniLibs under your app module's src/main folder.
Create a subfolder named cpp under the jniLibs folder.
Create a file named CMakeLists.txt under the jniLibs/cpp folder.
Edit the CMakeLists.txt file and add the following content:
# Set the minimum version of CMake required cmake_minimum_required(VERSION 3.10.2) # Set the name of your native library project project("my-native-lib") # Add your native source files add_library(my-native-lib SHARED my-native-lib.cpp) # Find and link the log library find_library(log-lib log) target_link_libraries(my-native-lib $log-lib)
Create a file named my-native-lib.cpp under the jniLibs/cpp folder.
Edit the my-native-lib.cpp file and add the following content:
# # Include the JNI header file #include
# Include the Android log header file #include
# Define a macro for logging #define LOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "my-native-lib", __VA_ARGS__)) # Define a native method that returns a string extern "C" JNIEXPORT jstring JNICALL Java_com_example_mynativelib_MainActivity_stringFromJNI( JNIEnv* env, jobject /* this */) LOGI("Hello from native code"); std::string hello = "Hello from C++"; return env->NewStringUTF(hello.c_str());
Congratulations, you have successfully created a native library project using CMake!
How to link your native library to your app module
To link your native library to your app module, you need to edit your app module's build.gradle file and add the following content:
android ... # Enable CMake support externalNativeBuild cmake path "src/main/jniLibs/cpp/CMakeLists.txt" version "3.10.2" # Specify the ABIs that you want to support defaultConfig ... externalNativeBuild cmake abiFilters "armeabi-v7a", "arm64-v8a", "x86", "x86_64"
After editing the build.gradle file, sync your project with Gradle files and wait for the native library to be built.
How to call native methods from your Java or Kotlin code
To call native methods from your Java or Kotlin code, you need to do the following:
Declare the native methods in your Java or Kotlin class using the native keyword and the @JvmStatic annotation (for Kotlin only).
Load your native library using the System.loadLibrary() method in a static block or an init block (for Kotlin only).
Call your native methods from your Java or Kotlin code as you would call any other methods.
For example, if you want to call the stringFromJNI() method from your MainActivity class, you can write something like this:
// For Java public class MainActivity extends AppCompatActivity // Declare the native method public static native String stringFromJNI(); // Load the native library static System.loadLibrary("my-native-lib"); @Override protected void onCreate(Bundle savedInstanceState) super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // Call the native method and display the result TextView tv = findViewById(R.id.sample_text); tv.setText(stringFromJNI()); // For Kotlin class MainActivity : AppCompatActivity() // Declare the native method companion object @JvmStatic external fun stringFromJNI(): String // Load the native library init System.loadLibrary("my-native-lib") override fun onCreate(savedInstanceState: Bundle?) super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // Call the native method and display the result sample_text.text = stringFromJNI()
Congratulations, you have successfully called native methods from your Java or Kotlin code!
How to troubleshoot common issues with Android NDK 21
Sometimes, you might encounter some issues when using the Android NDK 21 in your app, such as errors during compilation, linking, or runtime. Here are some common issues and how to fix them:
How to fix incompatible ABIs errors
If you see an error message like this:
Error: The following ABIs are incompatible with the target device: armeabi-v7a. Please either remove these ABIs from build.gradle or use a compatible device.
It means that you are trying to run your app on a device that does not support the ABIs that you specified in your build.gradle file. To fix this, you can either:
Remove the incompatible ABIs from your build.gradle file: For example, if your device only supports arm64-v8a, you can remove armeabi-v7a, x86, and x86_64 from your abiFilters.
Use a compatible device or emulator: For example, if you want to test your app on all ABIs, you can use a device or emulator that supports all ABIs, such as a Pixel 4 XL or a Nexus 5X.
How to fix undefined reference errors
If you see an error message like this:
Error: undefined reference to 'some_function'
It means that you are trying to use a function that is not defined in your native library or in any of the libraries that you linked to. To fix this, you can either:
Define the function in your native library: For example, if you are calling a function named some_function from your native code, you need to make sure that you have defined it in your native source file or header file.
Link to the library that contains the function: For example, if you are using a function from another native library, such as libpng, you need to make sure that you have added it to your target_link_libraries command in your CMakeLists.txt file.
How to fix missing header files errors
If you see an error message like this:
Error: fatal error: 'some_header.h' file not found
It means that you are trying to include a header file that is not found in your native library or in any of the directories that you specified. To fix this, you can either:
Add the header file to your native library: For example, if you are including a header file named some_header.h from your native code, you need to make sure that you have added it to your native library project folder or subfolder.
Add the directory that contains the header file to your CMakeLists.txt file: For example, if you are using a header file from another native library, such as libpng, you need to make sure that you have added its directory to your include_directories command in your CMakeLists.txt file.
Conclusion
In this article, we have learned how to download and install the Android NDK 21, how to use it in our Android app, and how to troubleshoot some common issues with it. We have seen that the Android NDK can help us improve the performance, security, and compatibility of our app by using native code libraries. However, we have also seen that using native code can introduce some complexity, portability, and stability challenges. Therefore, we should use the Android NDK wisely and only when necessary.
We hope that this article has been helpful and informative for you. If you have any questions or feedback, please feel free to leave a comment below. Thank you for reading!
Frequently Asked Questions
Here are some frequently asked questions about the Android NDK 21 and their answers:
What is the difference between Android NDK and Android SDK?
The Android SDK (Software Development Kit) is a set of tools that allows you to develop Android apps using Java or Kotlin code. The Android SDK provides access to the Android framework, which is a collection of libraries and APIs that provide common functionality for Android apps, such as user interface, networking, media, location, etc.
The Android NDK (Native Development Kit) is a set of tools that allows you to develop parts of your app using native code, such as C or C++. The Android NDK provides access to native code libraries, which are compiled for a specific processor architecture and can run faster and more efficiently than Java or Kotlin code. Native code libraries can also provide features that are not available in the Android framework, such as low-level access to hardware, graphics, audio, and network.
When should I use the Android NDK?
You should use the Android NDK only when you need to:
Improve the performance of your app: If your app has some computationally intensive tasks that require high speed or low memory usage, such as image processing, encryption, or machine learning, you might want to use native code to optimize them.
Improve the security of your app: If your app has some sensitive data or logic that you want to protect from reverse engineering or tampering, you might want to use native code to obfuscate them.
Improve the compatibility of your app: If your app needs to support older devices or devices with different architectures than the ones supported by the Android framework, such as low-end or custom devices, you might want to use native code to support them.
However, you should not use the Android NDK if you don't need to, because it can introduce some complexity, portability, and stability challenges. For most Android apps, the Android SDK is sufficient and recommended.
How can I update the Android NDK?
To update the Android NDK, you can either use Android Studio or manually download and install the latest version of the NDK. Here are the steps to follow:
Using Android Studio:
Open Android Studio and go to Tools > SDK Manager.
Select SDK Tools and check NDK (Side by side).
Select the latest version of the NDK that you want to install, such as 23.0.7599858.
Click OK and wait for the download and installation to finish.
Go to File > Project Structure > SDK Location.
Under Android NDK Location, select the latest version of the NDK that you installed.
Click Apply and OK.
Manually:
Go to and download the latest version of the NDK package for your operating system.
Delete or rename your old NDK folder, such as C:\Android\ndk\21.4.7075529.
Extract the new NDK package to the same location as your old NDK folder, such as C:\Android\ndk\23.0.7599858.
Add the new NDK location to your system environment variables, such as ANDROID_NDK_HOME=C:\Android\ndk\23.0.7599858.
Add the new NDK location to your project local.properties file, such as ndk.dir=C\:\\Android\\ndk\\23.0.7599858.
How can I learn more about the Android NDK?
If you want to learn more about the Android NDK, you can check out the following resources:
: This is the official documentation for the Android NDK, where you can find guides, tutorials, reference materials, and samples for using the NDK in your app.
: This is a series of codelabs that teach you how to build Android apps using Java or Kotlin code and native code libraries.
: This is a free online course that teaches you how to build Android apps using Kotlin code and native code libraries.
: This is a tutorial that teaches you how to use CMake to create and build native library projects for your Android app.
I hope you enjoyed reading this article and learned something new. If you have any questions or feedback, please feel free to leave a comment below. Thank you for reading! 44f88ac181