资源的插件化

--摘自《android插件化开发指南》

1.android资源文件分为两类：

第一类是res目录下存放的可编译资源文件，编译时，系统会自动在R.java中生成资源文件的十六进制值

Resources resources = getResources();
String appName = resources.getString(R.string.app_name);　　　　　　　　　　　　   

第二类是assets目录下存放的原始资源文件，apk在编译时不会编译assets下的资源文件

Resources resources = getResources();
AssetManager am = getResources().getAssets();
InputStream is = getResources().getAssets().open("filename");

2.Resources内部各种方法其实都是间接调用AssetManager的内部方法。AssetManager的addAssetPath方法会在app启动的时候把当前apk的路径传进去，就能访问apk的所有资源了。在这里可以把插件apk的资源塞进去

3.apk打包时会生成一个resource.arsc文件，它就是一个Hash表，存放着每个十六进制值和资源的对应关系

***资源的插件化解决方案***

public class Dynamic implements IDynamic {

    @Override
    public String getStringForResId(Context context) {
        return context.getResources().getString(R.string.myplugin1_hello_world);
    }
}

<resources>
    <string name="app_name">Plugin1</string>
    <string name="myplugin1_hello_world">myplugin1_hello_world</string>
</resources>

public class BaseActivity extends Activity {

    private AssetManager mAssetManager;
    private Resources mResources;
    private Resources.Theme mTheme;
    private String dexpath = null;    //apk文件地址
    private File fileRelease = null;  //释放目录

    protected DexClassLoader classLoader = null;

    private String pluginName = "plugin1.apk";

    TextView tv;

    @Override
    protected void attachBaseContext(Context newBase) {
        super.attachBaseContext(newBase);

        Utils.extractAssets(newBase, pluginName);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //第三步：加载外部的插件，生成插件对应的ClassLoader
        File extractFile = this.getFileStreamPath(pluginName);
        dexpath = extractFile.getPath();

        fileRelease = getDir("dex", 0);

        classLoader = new DexClassLoader(dexpath, fileRelease.getAbsolutePath(), null, getClassLoader());
    }

    /**
     * 第一步：通过反射，创建AssetManager对象，调用addAssetPath方法，把插件Plugin的路径添加到这个AssetManager对象中
     **/
    protected void loadResources() {
        try {
            AssetManager assetManager = AssetManager.class.newInstance();
            Method addAssetPath = assetManager.getClass().getMethod("addAssetPath", String.class);
            addAssetPath.invoke(assetManager, dexpath);
            mAssetManager = assetManager;
        } catch (Exception e) {
            e.printStackTrace();
        }
        Resources superRes = super.getResources();
        superRes.getDisplayMetrics();
        superRes.getConfiguration();
        mResources = new Resources(mAssetManager, superRes.getDisplayMetrics(), superRes.getConfiguration());
        mTheme = mResources.newTheme();
        mTheme.setTo(super.getTheme());
    }

    /**
     * 第二步：重写Acitivity的getAsset，getResources和getTheme方法
     **/
    @Override
    public AssetManager getAssets() {
        return mAssetManager == null ? super.getAssets() : mAssetManager;
    }

    @Override
    public Resources getResources() {
        return mResources == null ? super.getResources() : mResources;
    }

    @Override
    public Resources.Theme getTheme() {
        return mTheme == null ? super.getTheme() : mTheme;
    }
}

public class MainActivity extends BaseActivity {
    TextView tv;

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

        Button btn_6 = (Button) findViewById(R.id.btn_6);

        tv = (TextView)findViewById(R.id.tv);

        //带资源文件的调用
        btn_6.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                loadResources();
                Class mLoadClassDynamic = null;
                try {
                    //第四步：通过反射，获取插件中的类，构造出插件类的对象dynamicObject，然后就可以让插件中的类读取插件中的资源了
                    mLoadClassDynamic = classLoader.loadClass("jianqiang.com.plugin1.Dynamic");
                    Object dynamicObject = mLoadClassDynamic.newInstance();

                    IDynamic dynamic = (IDynamic) dynamicObject;
                    String content = dynamic.getStringForResId(MainActivity.this);
                    tv.setText(content);
                    Toast.makeText(getApplicationContext(), content + "", Toast.LENGTH_LONG).show();
                } catch (Exception e) {
                    Log.e("DEMO", "msg:" + e.getMessage());
                }
            }
        });
    }
}

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