Android DexClassLoader 错误，“优化数据目录..不属于当前用户”

我正在尝试生成一个简单的 Android 应用程序，可以在运行时从 SD 卡加载 DEX 文件。

该应用程序有两个活动。第一个活动是一个带有按钮的简单屏幕。当按下按钮时，将启动第二个活动，从而调用 loadDex() 方法。 loadDex() 方法尝试在 SD 卡上找到 jar 文件并将其加载到当前应用程序中。

这是我的第一个活动的代码：

package poc.example.del.customclass;

import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;


public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public void launchLoadClass(View view) {
        Intent intent = new Intent(MainActivity.this, LoadClass.class);
        startActivity(intent);
    }
}

这是我的第二个活动的代码（加载 DEX 文件的活动）：

package poc.example.del.customclass;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Toast;

import java.io.File;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import dalvik.system.DexClassLoader;


public class LoadClass extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_load_class);
        loadDex();
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_load_class, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public void loadDex() {
        String dexFile = "/sdcard/output.jar";
        File jarFile = new File(dexFile);
        if (jarFile.exists()) {
            // Toast.makeText(getApplicationContext(), "It Worked!", Toast.LENGTH_LONG).show();
            DexClassLoader cl = new DexClassLoader (jarFile.toString (), "/data/test", null, ClassLoader.getSystemClassLoader());

        }
    }
}

调用 DexClassLoader 构造函数时会出现问题。在日志中可以发现如下错误：

03-25 10:15:48.441    1934-1934/poc.example.del.customclass E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{poc.example.del.customclass/poc.example.del.customclass.LoadClass}: java.lang.IllegalArgumentException: Optimized data directory /data/test is not owned by the current user. Shared storage cannot protect your application from code injection attacks.
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5039)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.IllegalArgumentException: Optimized data directory /data/test is not owned by the current user. Shared storage cannot protect your application from code injection attacks.
            at dalvik.system.DexFile.<init>(DexFile.java:100)
            at dalvik.system.DexFile.loadDex(DexFile.java:149)
            at dalvik.system.DexPathList.loadDexFile(DexPathList.java:261)
            at dalvik.system.DexPathList.makeDexElements(DexPathList.java:229)
            at dalvik.system.DexPathList.<init>(DexPathList.java:96)
            at dalvik.system.BaseDexClassLoader.<init>(BaseDexClassLoader.java:56)
            at dalvik.system.DexClassLoader.<init>(DexClassLoader.java:57)
            at poc.example.del.customclass.LoadClass.loadDex(LoadClass.java:54)
            at poc.example.del.customclass.LoadClass.onCreate(LoadClass.java:23)
            at android.app.Activity.performCreate(Activity.java:5104)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5039)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)

这是日志中我认为代表问题的行：

java.lang.IllegalArgumentException: Optimized data directory /data/test is not owned by the current user. Shared storage cannot protect your application from code injection attacks.

任何帮助将不胜感激，因为我在网上找到的有关该问题的信息很少。我正在开发适用于 Android 4.2、Api 17 的应用程序。

提前致谢。

经过几天的学习各种教程后，我找到了答案。我想我会在这里发布解决方案，以防其他人遇到类似的问题。

出于安全原因，Android 不允许应用程序将文件加载到任何随机文件夹。相反，它应该加载到应用程序环境中。这是修改后的代码，使我能够继续该项目。显示的代码适用于“loadDex()”方法：

public void loadDex() {
    // Toast the show the method has been invoked correctly
    // Toast.makeText(getApplicationContext(), "loadDex() Method invoked", Toast.LENGTH_LONG).show();

    // name of the DEX file
    String dexFile = "/output.jar";

    // Get the path to the SD card
    File f = new File(Environment.getExternalStorageDirectory().toString() + dexFile);

    // optimized directory, the applciation and package directory
    final File optimizedDexOutputPath = getDir("outdex", 0);

    // DexClassLoader to get the file and write it to the optimised directory
    DexClassLoader classLoader = new DexClassLoader(f.getAbsolutePath(),
    optimizedDexOutputPath.getAbsolutePath(),null, getClassLoader());

    // The classpath is created for the new class
    String completeClassName = "poc.example.del.mylibrary.name";
    String methodToInvoke = "display";

    try {
        Class<?> myClass = classLoader.loadClass(completeClassName);
        Object obj = (Object)myClass.newInstance();
        Method m = myClass.getMethod(methodToInvoke);
        String s = ""+m.invoke(obj);
        makeToast(s);
    }
    catch (Exception e) {
        e.printStackTrace();
        makeToast("Something went wrong!");
    }


}

解决问题的具体代码行是：

// DexClassLoader to get the file and write it to the optimized directory
DexClassLoader classLoader = new DexClassLoader(f.getAbsolutePath(),
optimizedDexOutputPath.getAbsolutePath(),null, getClassLoader());

如您所见，optimizedDexOutputPath,getAbsolutePath() 方法返回应用程序可用于写入文件的目录。

希望这可以帮助其他遇到类似问题的人！