上一篇我們介紹了載入已安裝apk，本篇將介紹載入未安裝apk。

未安裝apk由於系統毫不知情，因此無法通過系統api獲取其上下文，自然也就無法獲取其資源。接下來，我們將另闢蹊徑來解決這個問題。

步驟如下：
一、採用上一篇中的Android Host工程，仍然匯出外掛介面類
二、新建Android外掛工程，匯入外掛介面類，編譯成apk，並push到手機
三、執行Android Host，載入外掛

Android Host工程如下

public class MainActivity extends Activity {

    private Button mBtn;

    @Override
 

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

        mBtn = (Button) findViewById(R.id.btn);
        mBtn.setOnClickListener(new View.OnClickListener() {

            @Override
            public
 
 void onClick(View v) {
                // TODO Auto-generated method stub
                loadPlugin();
            }
        });

    }

    private void loadPlugin() {
        File jarFile = new File(getExternalCacheDir(), "AndroidPlugin.apk");
        File outputDir = getDir("plugin", 0);

        FileUtils.deleteDirectory(outputDir);

        DexClassLoader loader = new
 
 DexClassLoader(jarFile.getAbsolutePath(),
                outputDir.getAbsolutePath(), null, getClass().getClassLoader());

        try {
            Class<?> clazz = loader.loadClass("com.example.androidplugin.MainActivity");
            IPlugin plugin = (IPlugin) clazz.newInstance();

            String text = String.format("getInt: %d, getString: %s", plugin.getInt(),
                    plugin.getString());
            Toast.makeText(this, text, Toast.LENGTH_SHORT).show();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InstantiationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

Android外掛工程

public class MainActivity extends Activity implements IPlugin {

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

    @Override
    public int getInt() {
        // TODO Auto-generated method stub
        return 100;
    }

    @Override
    public String getString() {
        // TODO Auto-generated method stub
        return "Hello, This is Plugin!";
    }
}

有一點需要注意：外掛工程中不能直接匯入外掛介面jar，如下

不能選擇Add JARs，而是應該選擇Add External JARs，否則會報執行時錯誤如下

我們注意到外掛工程中外掛的介面jar放在libs_ex目錄中，而不是libs目錄中，就是為避免eclipse自動將libs中的jar直接新增到工程中了。

執行Host工程，可以成功地載入外掛apk中的MainActivity，並呼叫其外掛介面getString返回了字串，然而這裡MainActivity只是被當做了一個普通java類被調起而已，並不是真正意義上的Android元件，我們可以嘗試著在getString時返回Android字串資源。如下：

public class MainActivity extends Activity implements IPlugin {

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

    @Override
    public int getInt() {
        // TODO Auto-generated method stub
        return 100;
    }

    @Override
    public String getString() {
        // TODO Auto-generated method stub
        return getString(R.string.hello_world);
    }
}

執行Host調起外掛，結果會崩潰，日誌如下：

可見外掛中的Activity只是一個普通的Java類，無法獲取其系統資源，要獲取系統資源必須獲取外掛的Resources，Host中修改如下：

public class MainActivity extends Activity {

    private Button mBtn;

    private Resources mPluginResources;

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

        mBtn = (Button) findViewById(R.id.btn);
        mBtn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                loadPlugin();
            }
        });

    }

    private void loadPlugin() {
        File jarFile = new File(getExternalCacheDir(), "AndroidPlugin.apk");
        File outputDir = getDir("plugin", 0);

        FileUtils.deleteDirectory(outputDir);

        DexClassLoader loader = new DexClassLoader(jarFile.getAbsolutePath(),
                outputDir.getAbsolutePath(), null, getClass().getClassLoader());

        try {
            Class<?> clazz = loader.loadClass("com.example.androidplugin.MainActivity");
            IPlugin plugin = (IPlugin) clazz.newInstance();

            loadResources(jarFile.getAbsolutePath());

            int resId = mPluginResources.getIdentifier("hello_world", "string",
                    "com.example.androidplugin");
            String text = mPluginResources.getString(resId);

            Toast.makeText(this, plugin.getInt() + text, Toast.LENGTH_SHORT).show();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InstantiationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    private void loadResources(String dexPath) {
        AssetManager assetManager = null;

        try {
            assetManager = AssetManager.class.newInstance();
            Method addAssetPath = assetManager.getClass().getMethod("addAssetPath", String.class);
            addAssetPath.invoke(assetManager, dexPath);
        } catch (InstantiationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        Resources resources = getResources();
        mPluginResources = new Resources(assetManager, resources.getDisplayMetrics(),
                resources.getConfiguration());
        mPluginResources.newTheme().setTo(getTheme());
    }
}