Wsrtjtyk

I'm trying to replicate the this tutorial for building and using Rust lib in Android app, I build the library successful, and uploaded the generated libs here

The function required to be called by Android using the Java_<Package>_Class_function theme is:

Java_com_mozilla_greetings_RustGreetings_greeting

My android app structure is as below:

I'm getting the below error at my JNI wrapper:

Cannot resolve corresponding JNI function
Java_com_mozilla_greetings_RustGreetings_greeting

The JNI wrapper is:

package com.mozilla.greetings;



public class RustGreetings {



    private static native String greeting(final String pattern);



    public String sayHello(String to) {

        return greeting(to);

    }

}

And the main class is:

package com.mozilla.greetings;



import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.TextView;



public class GreetingsActivity extends AppCompatActivity {



    static {

        System.loadLibrary("greetings");

    }



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_greetings);



        RustGreetings g = new RustGreetings();

        String r = g.sayHello("world");

        ((TextView) findViewById(R.id.greetingField)).setText(r);

    }

}

I solved it using JNA whcih I think is slower than JNI, I'll write my solution below using JNA hoping someone provide the required fix using JNI

My app structure is as below, using kotlin:

• I added the libjnidispatch.so to each library build folder, , this can be obtained by extracted the requiredandroid architecture from here, download the required jar, then extract it to get the libjnidispatch.so
  


• I created interbface for jna
  

JNA.kt

package com.mozilla.greetings



import com.sun.jna.Library



   interface JNA : Library {

      fun rust_greeting(pattern: String): String

   }

3. 
   

   I created wrapper for jna, RustGreetings.kt:

   
   
   

   package com.mozilla.greetings
   
   
   
   import com.sun.jna.Native
   
   
   
   class RustGreetings {
   
   
   
   fun sayHello(to: String): String =
   
           Native.loadLibrary<JNA>("greetings", JNA::class.java).rust_greeting(to)
   
   }
   
   

   
   


4. 
   

   Main activity, GreetingsActivity.kt:

   
   
   

   package com.mozilla.greetings
   
   
   
   import android.support.v7.app.AppCompatActivity
   
   import android.os.Bundle
   
   import kotlinx.android.synthetic.main.activity_greetings.*
   
   
   
   
   
   class GreetingsActivity : AppCompatActivity() {
   
   override fun onCreate(savedInstanceState: Bundle?) {
   
       super.onCreate(savedInstanceState)
   
       setContentView(R.layout.activity_greetings)
   
   
   
       val g = RustGreetings()
   
       val r = g.sayHello("Rust")
   
       greetingField.text = r
   
   }
   
   
   
   companion object {
   
       init {
   
           System.loadLibrary("greetings")
   
       }
   
   }
   
   }
   
   

   
   

Note:
In order to avoid using findViewById I used kotlin extension, as explained here and addeding the below to the build.gradle (module):

apply plugin: 'kotlin-android-extensions'

UPDATE

It looks it is an IDE issue nothing with the code, the app had been executed.
I re-wrote it using Kotlin, and it was executed smoothly as well, below my kotlin code:

GreetingsActivity.kt

package com.mozilla.greetings



import android.support.v7.app.AppCompatActivity

import android.os.Bundle

import kotlinx.android.synthetic.main.activity_greetings.*



class GreetingsActivity : AppCompatActivity() {



    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_greetings)



        val g = RustGreetings()

        val r = g.sayHello("My Rust")

        greetingField.text = r

    }



    companion object {



        init {

            System.loadLibrary("greetings")

        }

    }

}

RustGreetings.kt

package com.mozilla.greetings



class RustGreetings {



    private external fun greeting(pattern: String): String



    fun sayHello(to: String): String = greeting(to)

}

build.gradle

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android-extensions'



apply plugin: 'kotlin-android'



apply plugin: 'kotlin-android-extensions'



android {

    compileSdkVersion 28

    defaultConfig {

        applicationId "com.mozilla.greetings"

        minSdkVersion 28

        targetSdkVersion 28

        versionCode 1

        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    }

    buildTypes {

        release {

            minifyEnabled false

            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

        }

    }

}



dependencies {

    implementation fileTree(dir: 'libs', include: ['*.jar'])

    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"

    implementation 'com.android.support:appcompat-v7:28.0.0'

    implementation 'com.android.support.constraint:constraint-layout:1.1.3'

    testImplementation 'junit:junit:4.12'

    androidTestImplementation 'com.android.support.test:runner:1.0.2'

    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

}

activity_greetings.xml

<?xml version="1.0" encoding="utf-8"?>

<android.support.constraint.ConstraintLayout

        xmlns:android="http://schemas.android.com/apk/res/android"

        xmlns:tools="http://schemas.android.com/tools"

        xmlns:app="http://schemas.android.com/apk/res-auto"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        tools:context=".GreetingsActivity">



    <TextView

            android:layout_width="wrap_content"

            android:layout_height="wrap_content"

            android:text="Hello World!"

            app:layout_constraintBottom_toBottomOf="parent"

            app:layout_constraintLeft_toLeftOf="parent"

            app:layout_constraintRight_toRightOf="parent"

            app:layout_constraintTop_toTopOf="parent" android:id="@+id/greetingField"/>



</android.support.constraint.ConstraintLayout>

Below structure and execution, , the apk is here: