插件化开发，主要解决三个问题
1.动态加载未安装的apk，dex，jar等文件
2.activity生命周期的问题，还有service
3.Android的资源调用的问题
简单说一下怎样解决这三个问题，让插件化开发成为可能
1.解决未安装的apk比较简单，用DexClassLoader就可以解决（原始的jar要用dx转换一下，不能直接加载）
2.activity在未安装的apk中只是一个普通的类，生命周期不会被系统管理。解决这个问题就是在宿主apk注册代理activity，
这个activity只是一个壳，什么也没干。就是用来调用一下未安装apk的activity的生命周期。这里或许不能一下看懂，下面会详细讲解
3.android的资源都是单例的，java中获取资源都是通过Resources，而Resources又是通过AssetManager创建的。所以通过反射拿到AssetManager，
然后创建一个未加载apk的Resources，就能解决这个问题。
接下来看一下DLPluginManager。这是个管理类。先看一下怎样加载未安装的插件。
public DLPluginPackage loadApk(final String dexPath, boolean hasSoLib) {
mFrom = DLConstants.FROM_EXTERNAL;
PackageInfo packageInfo = mContext.getPackageManager().getPackageArchiveInfo(dexPath,
PackageManager.GET_ACTIVITIES | PackageManager.GET_SERVICES);
if (packageInfo == null) {
return null;
}
DLPluginPackage pluginPackage = preparePluginEnv(packageInfo, dexPath);
if (hasSoLib) {
copySoLib(dexPath);
}
return pluginPackage;
}
loadApk这个方文件法有两个参数，一个就是要加载dex的路径，另一个是否有so库。然后跟踪到preparePluginEnv这个方法。
如果有so库，就拷贝到mContext.getDir("pluginlib", Context.MODE_PRIVATE).getAbsolutePath();这个目录/data/data/包名/pluginlib这个目录
private DLPluginPackage preparePluginEnv(PackageInfo packageInfo, String dexPath) {
DLPluginPackage pluginPackage = mPackagesHolder.get(packageInfo.packageName);
if (pluginPackage != null) {
return pluginPackage;
}
DexClassLoader dexClassLoader = createDexClassLoader(dexPath);
AssetManager assetManager = createAssetManager(dexPath);
Resources resources = createResources(assetManager);
// create pluginPackage
pluginPackage = new DLPluginPackage(dexClassLoader, resources, packageInfo);
mPackagesHolder.put(packageInfo.packageName, pluginPackage);
return pluginPackage;
}
mPackagesHolder是缓存，先从缓存换取，缓存没有就调用createDexClassLoader加载dex，同时把Resources也获取了，这点之后再说。动态加载的结果都保存到
DLPluginPackage这个类。
private DexClassLoader createDexClassLoader(String dexPath) {
File dexOutputDir = mContext.getDir("dex", Context.MODE_PRIVATE);
dexOutputPath = dexOutputDir.getAbsolutePath();
DexClassLoader loader = new DexClassLoader(dexPath, dexOutputPath, mNativeLibDir, mContext.getClassLoader());
return loader;
}
这里说明一下DexClassLoader四个参数
dexPath dex所在的路径
dexOutputPath 优化dex的存放路径
mNativeLibDir 表示dex要调用so库的路径，上面说了，有so库就copy到该路径。
mContext.getClassLoader() 加载自己的DexClassLoader。这里用到宿主context的DexClassLoader。
我们再看一下上面说到的创建AssetManager和createResources
private AssetManager createAssetManager(String dexPath) {
try {
AssetManager assetManager = AssetManager.class.newInstance();
Method addAssetPath = assetManager.getClass().getMethod("addAssetPath", String.class);
addAssetPath.invoke(assetManager, dexPath);
return assetManager;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
private Resources createResources(AssetManager assetManager) {
Resources superRes = mContext.getResources();
Resources resources = new Resources(assetManager, superRes.getDisplayMetrics(), superRes.getConfiguration());
return resources;
}
先通过反射获取AssetManager，然后再创建一个新的Resources。因为宿主的Resources不等于动态加载的dex文件的Resources。
接下来看一下DLProxyActivity这个类，这个类要在宿主apk上注册。用来控制未安装的apk的activity的生命周期等的各种回调函数。
回调的函数都在DLPlugin这个接口
public interface DLPlugin {
public void onCreate(Bundle savedInstanceState);
public void onStart();
public void onRestart();
public void onActivityResult(int requestCode, int resultCode, Intent data);
public void onResume();
public void onPause();
public void onStop();
public void onDestroy();
public void attach(Activity proxyActivity, DLPluginPackage pluginPackage);
public void onSaveInstanceState(Bundle outState);
public void onNewIntent(Intent intent);
public void onRestoreInstanceState(Bundle savedInstanceState);
public boolean onTouchEvent(MotionEvent event);
public boolean onKeyUp(int keyCode, KeyEvent event);
public void onWindowAttributesChanged(LayoutParams params);
public void onWindowFocusChanged(boolean hasFocus);
public void onBackPressed();
public boolean onCreateOptionsMenu(Menu menu);
public boolean onOptionsItemSelected(MenuItem item);
}
public class DLProxyActivity extends Activity implements DLAttachable {
protected DLPlugin mRemoteActivity;
private DLProxyImpl impl = new DLProxyImpl(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
impl.onCreate(getIntent());
}
@Override
public void attach(DLPlugin remoteActivity, DLPluginManager pluginManager) {
mRemoteActivity = remoteActivity;
}
@Override
public AssetManager getAssets() {
return impl.getAssets() == null ? super.getAssets() : impl.getAssets();
}
@Override
public Resources getResources() {
return impl.getResources() == null ? super.getResources() : impl.getResources();
}
····省略代码
····
@Override
public boolean onTouchEvent(MotionEvent event) {
super.onTouchEvent(event);
return mRemoteActivity.onTouchEvent(event);
}
@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
super.onKeyUp(keyCode, event);
return mRemoteActivity.onKeyUp(keyCode, event);
}
@Override
public void onWindowAttributesChanged(LayoutParams params) {
mRemoteActivity.onWindowAttributesChanged(params);
super.onWindowAttributesChanged(params);
}
@Override
public void onWindowFocusChanged(boolean hasFocus) {
mRemoteActivity.onWindowFocusChanged(hasFocus);
super.onWindowFocusChanged(hasFocus);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
mRemoteActivity.onCreateOptionsMenu(menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
mRemoteActivity.onOptionsItemSelected(item);
return super.onOptionsItemSelected(item);
}
@Override
public ComponentName startService(Intent service) {
return super.startService(service);
}
}
这里有mRemoteActivity和DLProxyImpl。mRemoteActivity一般都是未安装apk的activity。DLProxyImpl就是一个代理处理未加载activity的类。
这个类负责解析插件apk的资源、ClassLoader、通过反射加载插件Activity，DLProxyImpl加载了插件Activity之后又会调用Proxy Activity的
attach方法将插件Activity实例传递给Proxy Activity，也就是mRemoteActivity。
这里看一下DLProxyImpl这个类
public void onCreate(Intent intent) {
// set the extra‘s class loader
intent.setExtrasClassLoader(DLConfigs.sPluginClassloader);
mPackageName = intent.getStringExtra(DLConstants.EXTRA_PACKAGE);
mClass = intent.getStringExtra(DLConstants.EXTRA_CLASS);
Log.d(TAG, "mClass=" + mClass + " mPackageName=" + mPackageName);
mPluginManager = DLPluginManager.getInstance(mProxyActivity);
mPluginPackage = mPluginManager.getPackage(mPackageName);
mAssetManager = mPluginPackage.assetManager;
mResources = mPluginPackage.resources;
initializeActivityInfo();
handleActivityInfo();
launchTargetActivity();
}
先是给intent set一个加载器。这个加载器放在DLConfigs这个类中，其实首先重写了intent为DLintent这个类，这个类putExtra的时候就会
把classloader存放到DLConfigs中，然后接收的activity就能从DLConfigs获取到classloader.然后就可以获取各种需要的信息。接下来看一下
initializeActivityInfo()， handleActivityInfo(); launchTargetActivity();这三个方法
private void initializeActivityInfo() {
PackageInfo packageInfo = mPluginPackage.packageInfo;
if ((packageInfo.activities != null) && (packageInfo.activities.length > 0)) {
if (mClass == null) {
mClass = packageInfo.activities[0].name;
}
//Finals 修复主题BUG
int defaultTheme = packageInfo.applicationInfo.theme;
for (ActivityInfo a : packageInfo.activities) {
if (a.name.equals(mClass)) {
mActivityInfo = a;
// Finals ADD 修复主题没有配置的时候插件异常
if (mActivityInfo.theme == 0) {
if (defaultTheme != 0) {
mActivityInfo.theme = defaultTheme;
} else {
if (Build.VERSION.SDK_INT >= 14) {
mActivityInfo.theme = android.R.style.Theme_DeviceDefault;
} else {
mActivityInfo.theme = android.R.style.Theme;
}
}
}
}
}
}
}
这里获取ActivityInfo和修正theme。
private void handleActivityInfo() {
Log.d(TAG, "handleActivityInfo, theme=" + mActivityInfo.theme);
if (mActivityInfo.theme > 0) {
mProxyActivity.setTheme(mActivityInfo.theme);
}
Theme superTheme = mProxyActivity.getTheme();
mTheme = mResources.newTheme();
mTheme.setTo(superTheme);
// Finals适配三星以及部分加载XML出现异常BUG
try {
mTheme.applyStyle(mActivityInfo.theme, true);
} catch (Exception e) {
e.printStackTrace();
}
// TODO: handle mActivityInfo.launchMode here in the future.
}
这里设置mProxyActivity的主题
protected void launchTargetActivity() {
try {
Class<?> localClass = getClassLoader().loadClass(mClass);
Constructor<?> localConstructor = localClass.getConstructor(new Class[] {});
Object instance = localConstructor.newInstance(new Object[] {});
mPluginActivity = (DLPlugin) instance;
((DLAttachable) mProxyActivity).attach(mPluginActivity, mPluginManager);
Log.d(TAG, "instance = " + instance);
// attach the proxy activity and plugin package to the mPluginActivity
mPluginActivity.attach(mProxyActivity, mPluginPackage);
Bundle bundle = new Bundle();
bundle.putInt(DLConstants.FROM, DLConstants.FROM_EXTERNAL);
mPluginActivity.onCreate(bundle);
} catch (Exception e) {
e.printStackTrace();
}
}
这里获取mPluginActivity插件的activity，attach方法调用了两次，一次把插件activity给代理activity。另一次把代理activity给插件activity
然后创建一个bundle，调用插件activity的onCreate方法。这样插件activity就启动起来了。
PluginActivity里面创造了that语法。是插件就使用that，that是指代理activity，this代表自己。自己不是插件，就用this。
最后：
1.service和activity原理差不多，但是没有使用that语法。PluginFragmentActivity也不说了。
2.使用dl开发，插件中会依赖dl.jar包，但不能打包到apk。否则会发生内链接错误。内存中有多个相同的类是不允许的。
demo中放到external-jar目录下，然后再.classpath加上<classpathentry kind="lib" path="external-jars/dl-lib.jar"/>
3.有哪里说得不对，请指出。