Loading 3rd party shared libraries from an Android native activity

Question

I\'ve built the Assimp library as a shared library. I\'ve included it in my Android ndk project and it builds fine but when I load it I get the following error: Unable to lo

Answer 1

You want to start the NativeActivity with a java activity. This way you can load the shared libraries before NativeActivity.

AndroidManifest.xml:

<application android:label="@string/app_name" android:hasCode="true">
    <activity android:name="DummyActivity"
            android:label="@string/app_name"
            android:configChanges="orientation|keyboardHidden">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name="android.app.NativeActivity"
            android:label="@string/app_name"
            android:configChanges="orientation|keyboardHidden">
        <meta-data android:name="android.app.lib_name"
                android:value="native-activity" />
    </activity>
</application>

DummyActivity.java:

package com.example.native_activity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

public class DummyActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {       
        System.loadLibrary("some_shared_lib");
        System.loadLibrary("native-activity");

        super.onCreate(savedInstanceState);

        Intent intent = new Intent(DummyActivity.this, android.app.NativeActivity.class);
        DummyActivity.this.startActivity(intent);
    }
}

Answer 2

Using System.loadLibrary is the way to go.

Android won't automatically load dependent shared libraries for you. So you need to do something like this:

static {
    System.loadLibrary("assimp");  // dependency .so first
    System.loadLibrary("native-activity"); // dependent .so second
}

This code usually goes in the class which contains the native Java methods (i.e. methods defined with keyword native, which map through to native code). Because this code is executed in a static block it is executed when the Java classloader loads the class -- i.e. before any code in the class actually gets executed.

You shouldn't have to add any reference to assimp to LOCAL_LDLIBS because you're already referencing assimp via the LOCAL_SHARED_LIBRARIES declaration.

This question may be relevant.

Answer 3

1: U could not use dlopen, since System.loadLibrary is the only method u load a native library from Java layer. 2: Ur library path looks not right, the location should be something like /data/data/urapp/lib/

U need to zip ur library to ur apk file, and while installing, android will unzip it and put it to /data/data/urapp/lib/ automatically.

Hope above information is useful for u.

Answer 4

Subclassing android.app.NativeActivity is the simplest way to solve this problem.

package com.you;

public class MyNativeActivity extends android.app.NativeActivity {

    static {
       System.loadLibrary("assimp");
    }
 }

Then change your AndroidManifest.xml. Replace android.app.NativeActivity with MyNativeActivity and remove the tag hasCode="false".

As a side note, Android does search for dependencies when loading a shared library. But the scope of the search is limited to /system/lib.