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Call-ANDROID-Native-NDK

How to Call Android Native NDK Code from Delphi (JNI + C + SQLite Demo)

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README

Call Android Native NDK from Delphi

A production-ready demonstration of calling Android NDK native C code from Delphi FireMonkey applications using JNI (Java Native Interface). This project showcases a complete architecture with native calculations, SQLite persistence, and history tracking. call NDK

📋 Overview

This project demonstrates the complete data flow: Delphi (Pascal) → Java Bridge → Native C Library, featuring:

✅ Native C Math Operations via JNI
✅ Clean Architecture with interfaces and dependency injection
✅ SQLite History Persistence using FireDAC
✅ Production-Quality Code with proper error handling
✅ Responsive UI for phones and tablets

https://github.com/user-attachments/assets/a6f6b7fa-7f63-4212-8e3a-baae19baa135

my youtube video All Steps here

🎯 What Makes This Project Valuable

Unlike simple "Hello World" JNI examples, this project demonstrates:

Real-world Architecture: Service layer, interfaces, models, and data persistence
Bidirectional Communication: Delphi calls native code AND stores results in SQLite
Complete NDK Integration: Shows the full build process for C libraries
Production Patterns: Proper memory management, error handling, and logging
Multi-Layer Design: UI → Service → JNI → Native C

🏗️ Architecture

pascal

?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
???                    Delphi FMX UI Layer                          ???
???                     (Main.View.pas)                             ???
???  ??? User inputs two numbers                                      ???
???  ??? Clicks operation button (Add/Sub/Mul/Div)                   ???
???  ??? Displays result and history                                  ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
                         ???
                         ??? Uses iCalculatorService interface
                         ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
???                   Service Layer (Pascal)                        ???
???              (API.Calculator.Service.pas)                       ???
???  ??? TCalculatorService implements iCalculatorService             ???
???  ??? Calls Java bridge for calculations                           ???
???  ??? Logs results to SQLite via FireDAC                          ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
                         ???
                         ??? Calls FJavaBridge (JNI wrapper)
                         ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
???                   JNI Bridge Layer (Pascal)                     ???
???                (API.JNI.Calculator.pas)                         ???
???  ??? TJCalculatorBridge wraps Java class                          ???
???  ??? Exposes: nativeAdd, nativeSub, nativeMul, nativeDiv         ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
                         ???
                         ??? JNI call to Java
                         ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
???                    Java Bridge Class                            ???
???            (CalculatorBridge.java)                              ???
???  ??? Loads native library: System.loadLibrary("NativeCalcLIB")   ???
???  ??? Declares native methods matching C signatures                ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
                         ???
                         ??? JNI native call
                         ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
???                 Native C Implementation                         ???
???                  (NativeCalc.c)                                 ???
???  ??? JNIEXPORT jdouble JNICALL                                    ???
???    Java_com_MBenDelphi_CalculatorDemo_CalculatorBridge_XXX     ???
???  ??? Pure C math operations                                       ???
???  ??? Android logging for debugging                                ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
                         ???
                         ??? Result returns through same layers
                         ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
???                  SQLite Database (FireDAC)                      ???
???                 (Model.Connection.pas)                          ???
???  ??? History table: Operation, ValueA, ValueB, Result, Timestamp ???
???  ??? Stores calculation history                                   ???
???  ??? Retrieved and displayed in UI                                ???
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

📁 Project Structure

pascal

Call-ANDROID-Native-NDK/
???
????????? API/                           # API & Interface Layer
???   ????????? API.Calculator.Interfaces.pas   # iCalculatorService & iCalculationHistory
???   ????????? API.Calculator.Service.pas      # TCalculatorService implementation
???   ????????? API.JNI.Calculator.pas          # JNI bridge to Java (TJCalculatorBridge)
???
????????? Model/                         # Data Layer
???   ????????? Model.Connection.pas            # FireDAC SQLite connection & schema
???   ????????? Model.History.pas               # TCalculationHistory model
???
????????? Java/                          # Java Bridge Layer
???   ????????? CalculatorBridge.java           # JNI bridge class
???
????????? Native/                        # C Native Library
???   ????????? NativeCalc.c                    # C implementation of math operations
???   ????????? Android.mk                      # NDK build configuration
???   ????????? Application.mk                  # ABI and platform settings
???
????????? Res/                           # Android Resources
???   ????????? drawable/
???   ???   ????????? splash_image_def.xml        # Splash screen (API 21+)
???   ???   ????????? splash_vector_def.xml       # Vector splash (API 21+)
???   ????????? values/
???
????????? Main.View.pas                  # Main FMX form (UI logic)
????????? Main.View.fmx                  # FMX UI design (base)
????????? Main.View.LgXhdpiPh.fmx       # Large XHDPI Phone layout
????????? Main.View.LgXhdpiTb.fmx       # Large XHDPI Tablet layout
????????? Main.View.XLgXhdpiTb.fmx      # Extra Large XHDPI Tablet layout
???
????????? CalculatorDemo.dpr             # Main Delphi project
????????? CalculatorDemo.dproj           # Project configuration
????????? AndroidManifest.template.xml   # Android manifest template
???
????????? LICENSE                        # MIT License

🚀 Getting Started

Prerequisites

Delphi RAD Studio 12 Athens or later (with Android SDK support)
Android NDK r21e or compatible (configured in Delphi SDK Manager)
Android SDK API Level 21+ (minimum) / API Level 23+ (recommended)
Java Development Kit JDK 8 or 11

Step 1: Clone the Repository

bash

git clone https://github.com/mben-dz/Call-ANDROID-Native-NDK.git
cd Call-ANDROID-Native-NDK

Step 2: Build the Native Library

Navigate to the Native/ directory and build the C library:

bash

cd Native
"%ANDROID_NDK_ROOT%\ndk-build.cmd" clean
"%ANDROID_NDK_ROOT%\ndk-build.cmd"

This generates:

libs/armeabi-v7a/libc++_shared.so
libs/armeabi-v7a/libNativeCalcLIB.so
libs/arm64-v8a/libc++_shared.so
libs/arm64-v8a/libNativeCalcLIB.so

Important: The library name NativeCalcLIB must match the System.loadLibrary("NativeCalcLIB") call in CalculatorBridge.java.

Step 3: Configure Delphi Project

Open CalculatorDemo.dproj in RAD Studio
Verify Android SDK/NDK paths:
- Tools → Options → Deployment → SDK Manager
- Ensure Android SDK and NDK paths are correct
- good Steps here
Add native libraries to deployment:
- Project → Deployment
- Ensure libc++_shared.so & libNativeCalcLIB.so is included for both architectures

Step 4: Add Java Bridge to Project

The Java file CalculatorBridge.java must be included in the project:

In Project Manager, right-click the Android target
open this tool and Add → Java Source and the latest android.Jar path in your SDK Folder
compile and then open this command: java2op -jar NativeCalcLib.jar -unit API.JNI.Calculator

java2op will automatically generate this into the Delphi JNI WRAPER Unit (to add it to your project).

Step 5: Build and Deploy

Select Android 32-bit or Android 64-bit target
Connect Android device or start emulator
Press F9 (Run) or Shift+Ctrl+F9 (Run Without Debugging)

The app will:

Compile Delphi code
Compile Java bridge
Package native .so libraries
Build and install APK
Launch on device

🔧 How It Works

Complete Call Flow Example: Adding Two Numbers

1. User Interaction (UI Layer)

pascal

// Main.View.pas - User clicks "Add" button
procedure TMainView.btnAddClick(Sender: TObject);
begin
  PerformCalculation(0);  // 0 = Add operation
end;

2. Service Layer Processes Request

pascal

// API.Calculator.Service.pas
function TCalculatorService.Add(const a, b: Double): Double;
begin
  // Call Java bridge which calls native C
  Result := FJavaBridge.nativeAdd(a, b);
  
  // Log to SQLite database
  LogHistory('ADD', a, b, Result);
end;

3. JNI Bridge to Java

pascal

// API.JNI.Calculator.pas - Delphi JNI wrapper
JCalculatorBridge = interface(JObject)
  function nativeAdd(d: Double; d1: Double): Double; cdecl;
end;

// In service:
FJavaBridge := TJCalculatorBridge.JavaClass.init;
Result := FJavaBridge.nativeAdd(a, b);  // Calls Java method

4. Java Calls Native C

java

// Java/CalculatorBridge.java
public class CalculatorBridge {
    static {
        System.loadLibrary("NativeCalcLIB");  // Load .so library
    }
    
    public native double nativeAdd(double a, double b);  // JNI declaration
}

5. Native C Implementation

// Native/NativeCalc.c
JNIEXPORT jdouble JNICALL
Java_com_MBenDelphi_CalculatorDemo_CalculatorBridge_nativeAdd(
    JNIEnv *env, jobject thiz, jdouble a, jdouble b) {
    
    __android_log_print(ANDROID_LOG_DEBUG, "CALC_JNI", "nativeAdd called");
    return a + b;  // Pure C calculation
}

6. Result Returns & Persists

pascal

// Result flows back: C → Java → JNI → Service → UI
lblResult.Text := Format('Result: %.2f', [LRes]);

// Saved to SQLite via FireDAC
FDConnection.ExecSQL(
  'INSERT INTO History (Operation, ValueA, ValueB, Result) VALUES (?, ?, ?, ?)',
  ['ADD', a, b, Result]);

💾 Database Schema

SQLite database created automatically at app launch:

sql

CREATE TABLE IF NOT EXISTS History (
    ID INTEGER PRIMARY KEY AUTOINCREMENT,
    Operation TEXT,           -- 'ADD', 'SUB', 'MUL', 'DIV'
    ValueA REAL,             -- First operand
    ValueB REAL,             -- Second operand
    Result REAL,             -- Calculation result
    Timestamp DATETIME DEFAULT CURRENT_TIMESTAMP
);

Location:

Android: /data/data/com.MBenDelphi.CalculatorDemo/files/calculator.db
Desktop (testing): <EXE_PATH>/calculator.db

🔍 Key Components Explained

JNI Method Naming Convention

The C function names must follow this exact pattern:

JNIEXPORT <return_type> JNICALL
Java_<package_name>_<class_name>_<method_name>(JNIEnv *env, jobject thiz, <parameters>)

Example:

Java_com_MBenDelphi_CalculatorDemo_CalculatorBridge_nativeAdd
     └──────────────┬─────────────┘ └─────┬──────┘ └───┬───┘
              Package name          Class name    Method name

Java Package Declaration

Must match the package in CalculatorBridge.java:

java

package com.MBenDelphi.CalculatorDemo;

Library Loading

The native library is loaded once when the Java class initializes:

java

static {
    System.loadLibrary("NativeCalcLIB");  // Loads libNativeCalcLIB.so
}

Interface-Based Design

The project uses dependency injection with interfaces:

pascal

// Interface definition
iCalculatorService = interface
  function Add(const a, b: Double): Double;
  function GetHistory: TList<iCalculationHistory>;
end;

// Concrete implementation
TCalculatorService = class(TInterfacedObject, iCalculatorService)
  // Implementation details
end;

// Usage
FService: iCalculatorService;
FService := TCalculatorService.Create;

This allows for easy testing and future implementations (e.g., pure Pascal calculator for testing).

🛠️ Building Native Libraries

Android.mk Configuration

makefile

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

# Library name (produces libNativeCalcLIB.so)
LOCAL_MODULE := NativeCalcLIB

# Source files
LOCAL_SRC_FILES := NativeCalc.c

# Link Android log library for __android_log_print
LOCAL_LDLIBS := -llog

# Compiler flags
LOCAL_CFLAGS := -Wall -Wextra -O2 -DDEBUG

include $(BUILD_SHARED_LIBRARY)

Application.mk Configuration

makefile

# Target architectures (32-bit and 64-bit ARM)
APP_ABI := armeabi-v7a arm64-v8a

# Minimum Android API level
APP_PLATFORM := android-21

# C++ standard library
APP_STL := c++_shared

# C++ version
APP_CPPFLAGS := -std=c++11

Build Commands

bash

# Clean previous builds
ndk-build clean

# Build for all ABIs defined in Application.mk
ndk-build

# Build for specific ABI
ndk-build APP_ABI=arm64-v8a

# Verbose build output
ndk-build V=1

📱 Android Splash Screen Fix

For Android 5.0+ (API 21+), the splash screen requires android:scaleType="centerInside" to display correctly:

Res/drawable/splash_image_def.xml:

xml

<bitmap
    android:src="@drawable/splash_image"
    android:gravity="center"
    android:scaleType="centerInside"  <!-- Required for API 21+ -->
    android:tileMode="disabled"/>

Res/drawable/splash_vector_def.xml:

xml

<item
    android:gravity="center"
    android:scaleType="centerInside"  <!-- Required for API 21+ -->
    android:drawable="@drawable/splash_vector">
</item>

This ensures the app icon displays properly in the splash screen on modern Android versions.

🐛 Troubleshooting

Issue: "UnsatisfiedLinkError: dlopen failed"

Cause: Native library not found or wrong architecture

Solutions:

Verify libNativeCalcLIB.so exists in libs/armeabi-v7a/ or libs/arm64-v8a/
Check deployment configuration includes .so files
Ensure library name matches: System.loadLibrary("NativeCalcLIB")
Rebuild with ndk-build clean && ndk-build

Issue: "NoSuchMethodError" when calling native method

Cause: JNI method signature mismatch

Solutions:

Verify C function name matches Java package/class/method exactly
Check parameter types match (jdouble vs double, etc.)
Regenerate JNI headers: javah -classpath . com.MBenDelphi.CalculatorDemo.CalculatorBridge

Issue: App crashes when calling native method

Cause: JNI reference handling or null pointer

Solutions:

Check C code for null parameter validation
Verify (void)env; (void)thiz; to avoid unused parameter warnings
Enable NDK debugging: Add android:debuggable="true" to manifest
Check Android logcat for native crash logs: adb logcat | grep CALC_JNI

Issue: SQLite database errors

Cause: File permissions or path issues

Solutions:

Verify app has storage permissions in AndroidManifest.xml
Check database path: TPath.GetDocumentsPath on Android
Ensure table creation SQL executes on first run
Test with a simple query before complex operations

Issue: JNI bridge not found in Delphi

Cause: Java file not included in project

Solutions:

the jar file not found you should compile and deploy
Verify package name matches: com.MBenDelphi.CalculatorDemo
Clean and rebuild project

📊 Performance Considerations

Why Use Native Code?

This example uses simple math operations for demonstration, but native code is beneficial for:

Heavy Computations: Image processing, cryptography, physics simulations
Existing C Libraries: FFmpeg, OpenCV, TensorFlow Lite
Performance-Critical Code: Game engines, real-time audio processing
Hardware Access: Camera HAL, sensors, custom drivers

Overhead

JNI calls have overhead (~100-200ns per call). For best performance:

Batch operations: Pass arrays instead of single values
Minimize JNI boundary crossings: Do more work per call
Use native threads: For long-running computations

Example:

// Less efficient: 1000 JNI calls
for (int i = 0; i < 1000; i++) {
    result[i] = nativeAdd(a[i], b[i]);
}

// More efficient: 1 JNI call
JNIEXPORT jdoubleArray JNICALL
Java_..._nativeAddArray(JNIEnv *env, jobject thiz, jdoubleArray a, jdoubleArray b) {
    // Process entire array in C
}

🧪 Testing

Unit Testing (Recommended Approach)

Create a pure Pascal implementation of iCalculatorService for testing:

pascal

type
  TCalculatorServiceMock = class(TInterfacedObject, iCalculatorService)
  public
    function Add(const a, b: Double): Double;
    // ... simple Pascal implementations for testing
  end;

// In tests:
FService := TCalculatorServiceMock.Create;  // No JNI, fast testing

Integration Testing

Test the full JNI stack on a real device:

pascal

procedure TestNativeAdd;
var
  LService: iCalculatorService;
  LResult: Double;
begin
  LService := TCalculatorService.Create;
  LResult := LService.Add(2.5, 3.7);
  Assert(Abs(LResult - 6.2) < 0.001);  // Float comparison
end;

🎓 Learning Path

1. Understand the Basics

Review CalculatorBridge.java → Simple Java class with native methods
Review NativeCalc.c → Simple C functions with JNI macros
Review API.JNI.Calculator.pas → Delphi JNI wrapper

2. Modify the Example

Add a new operation (e.g., modulo, power)
Add it to C, Java, and Delphi layers
Rebuild and test

3. Extend with Real Libraries

Integrate an existing C library
Create proper JNI wrappers for complex structs
Handle memory management carefully

📚 Additional Resources

Official Documentation

Build Tools

Best Practices

🤝 Contributing

Contributions are welcome! Areas for improvement:

[ ] Add more complex C library integration (e.g., image processing)
[ ] Implement unit tests for all layers
[ ] Add CMake build option (alternative to Android.mk)
[ ] Create desktop version using C++ Builder RTL instead of JNI
[ ] Add async calculation support with callbacks
[ ] Improve error handling and validation

How to Contribute

Fork the repository
Create a feature branch: git checkout -b feature/YourFeature
Make your changes and test thoroughly
Commit with clear messages: git commit -m 'Add XYZ feature'
Push to your fork: git push origin feature/YourFeature
Open a Pull Request with detailed description

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

You are free to:

✅ Use commercially
✅ Modify
✅ Distribute
✅ Use privately

👤 Author

mben-dz

GitHub: @mben-dz
Repository: Call-ANDROID-Native-NDK

🙏 Acknowledgments

Embarcadero Technologies - Delphi and FireMonkey framework
Google Android Team - Android NDK and SDK
Community Contributors - Testing and feedback

💬 Support

Need help? Here's how to get support:

Check Issues: Existing Issues
Open New Issue: Describe your problem with:
- Delphi version
- Android API level
- Error messages or logs
- Steps to reproduce
Community: Ask in Delphi forums or Stack Overflow with tag delphi-android-ndk

📈 Version History

v1.0 (Current)
- Initial release
- Basic calculator with Add/Sub/Mul/Div
- SQLite history persistence
- Support for Android API 21+
- ARM 32-bit and 64-bit support

⭐ If this project helped you understand Delphi + Android NDK integration, please star the repository!

🔗 Share your projects built with this knowledge - We'd love to see what you create!

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Member rating

README

Call Android Native NDK from Delphi

📋 Overview

my youtube video All Steps here

🎯 What Makes This Project Valuable

🏗️ Architecture

📁 Project Structure

🚀 Getting Started

Prerequisites

Step 1: Clone the Repository

Step 2: Build the Native Library

Step 3: Configure Delphi Project

Step 4: Add Java Bridge to Project

Step 5: Build and Deploy

🔧 How It Works

Complete Call Flow Example: Adding Two Numbers

1. User Interaction (UI Layer)

2. Service Layer Processes Request

3. JNI Bridge to Java

4. Java Calls Native C

5. Native C Implementation

6. Result Returns & Persists

💾 Database Schema

🔍 Key Components Explained

JNI Method Naming Convention

Java Package Declaration

Library Loading

Interface-Based Design

🛠️ Building Native Libraries

Android.mk Configuration

Application.mk Configuration

Build Commands

📱 Android Splash Screen Fix

🐛 Troubleshooting

Issue: "UnsatisfiedLinkError: dlopen failed"

Issue: "NoSuchMethodError" when calling native method

Issue: App crashes when calling native method

Issue: SQLite database errors

Issue: JNI bridge not found in Delphi

📊 Performance Considerations

Why Use Native Code?

Overhead

🧪 Testing

Unit Testing (Recommended Approach)

Integration Testing

🎓 Learning Path

1. Understand the Basics

2. Modify the Example

3. Extend with Real Libraries

📚 Additional Resources

Official Documentation

Build Tools

Best Practices

🤝 Contributing

How to Contribute

📄 License

👤 Author

🙏 Acknowledgments

💬 Support

📈 Version History

Call-ANDROID-Native-NDK