本机活动和“无法加载本机库”

Question

I am attempting to build an Android-10 NDK native activity based on the "native-activity" sample project from the Android NDK folder. However, my native activity crashes with the following runtime exception when I open Eclipse and select "Run As -> Android Application" for my project:

02-09 03:02:12.599: E/AndroidRuntime(881): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.native_activity/android.app.NativeActivity}: java.lang.IllegalArgumentException: Unable to load native library: /data/app-lib/com.example.native_activity-1/[library name].so

However, I have confirmed that the file "lib[library name].so" already exists in the "libs/armeabi" (etc.) paths. My native activity eventually needs to load three ".so" files, but this error persists whether I am attempting to load one ".so" file or all three ".so" files. My "AndroidManifest.xml" file is as follows:

<?xml version="1.0" encoding="utf-8"?>
<!-- BEGIN_INCLUDE(manifest) -->
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.native_activity"
    android:versionCode="1"
    android:versionName="1.0">

<!-- This is the platform API where NativeActivity was introduced. -->
<uses-sdk android:minSdkVersion="9" />

<!-- This .apk has no Java code itself, so set hasCode to false. -->
<application android:label="@string/app_name" android:hasCode="false">

    <!-- Our activity is the built-in NativeActivity framework class.
         This will take care of integrating with our NDK code. -->
    <activity android:name="android.app.NativeActivity"
            android:label="@string/app_name"
            android:configChanges="orientation|keyboardHidden">
        <!-- Tell NativeActivity the name of or .so -->
        <meta-data android:name="android.app.lib_name"
            android:value="[library name]" />
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest> 
<!-- END_INCLUDE(manifest) -->

What needs to be done to fix this runtime exception?

Answer 1

A useful way to find more information about the load failure is to make a basic Android application and use System.loadLibrary to load the native libraries in the onCreate method, bypassing the NativeActivity altogether.

eg

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    System.loadLibrary("foo");
    System.loadLibrary("bar");
    System.loadLibrary("depends-on-foo-and-bar");
}

Then, instead of getting the not so useful "Unable to load native library" message NativeActivity provides, you will get a more useful message such as

java.lang.UnsatisfiedLinkError: dlopen failed: could not load library "lib42.so" needed by "libdepends-on-foo-and-bar.so"; caused by library "lib42.so" not found

Answer 2

In your JNI folder what is the "" set to ? "[library name]" name should be set as the name the package you are building.

Answer 3

The problem seems to be that the system is looking for a library with a -1 appended to its name

(from your error message) /data/app-lib/com.example.native_activity-1

Ive seen that andoird does this when a library previosuly exists then adds -1, -2 etc to the name. Not sure why but pretty sure its a versioning thing that you might solve with an uninstall or fresh install.

Answer 4

This happens due to missing dependencies (or even implementations). You may be getting the "unable to load library: libFoo.so" but the real dependency missing may be libBar.so that is depended by libFoo.so. Or you may simply have declared functions and called them but have no implementation for them.

The problem is due to the way building an so file works. When you build a shared object using gcc, the linking step doesn't truly happen. For example within libFoo.so, you may declare a myFunc() prototype and call it. And you can skip the implementation of myFunc(){}. The gcc will happily build you a .so file. And it will happily end up in the apk. However when it's time to load library, this will break with the "unable to load library" message.

There are two ways to deal with this: You either do what AndrewJC tells you in his answer. Or you start commenting code out until you are able to load again. Thus locating the function implementation missing.

IMPORTANT: the -1 -2 suffixes that are added to the so files ARE NOT the problem. That comment misled me to spend a few days only to find that those numeric suffixes are actually the expected behavior by the android package manager.