插件系统实现
插件化启动Activity的过程
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在宿主里面的AndroidManifest.xml里面注册一个空的activity
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从开始执行execStartActivity到最终将Activity对象new出来这个过程，系统层会去校验需要启动的activity的合法性[就是是否有在某个应用的AndroidManifest.xml里面注册]以及按启动要求创建activity对象。清晰了这点我们就可以很好的绕过系统的约束，达到我们的目的：【插件中的组件拥有真正生命周期，完全交由系统管理、非反射代理】。 简单来说方案就两步： Step1、在开始startActivity的时候将需要启动的插件组件替换成宿主预先声明号的。
public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) { //如果启动的是插件的activity组件，这里面将会被替换成宿主预先声明的 PluginIntentResolver.resolveActivity(intent); return hackInstrumentation.execStartActivity(who, contextThread, token, target, intent, requestCode, ptions); }
Step2、在最终创建activity对象的时候改回成插件组件的。
@Override
public Activity newActivity(ClassLoader cl, String className, Intent intent) throws InstantiationException,
IllegalAccessException, ClassNotFoundException {
ClassLoader orignalCl = cl;
String orginalClassName = className;
String orignalIntent = intent.toString();
if (ProcessUtil.isPluginProcess()) {
// 将PluginStubActivity替换成插件中的activity
if (PluginManagerHelper.isStub(className)) {
String action = intent.getAction();
if (action != null && action.contains(PluginIntentResolver.CLASS_SEPARATOR)) {
String[] targetClassName = action.split(PluginIntentResolver.CLASS_SEPARATOR);
String pluginClassName = targetClassName[0];
final String pid = intent.getStringExtra(PluginIntentResolver.INTENT_EXTRA_PID).trim();
PluginDescriptor pluginDescriptor = TextUtils.isEmpty(pid) ? PluginManagerHelper.getPluginDescriptorByClassName(pluginClassName) : PluginManagerHelper.getPluginDescriptorByPluginId(pid);
Class<?> clazz = PluginLoader.loadPluginClassByName(pluginDescriptor, pluginClassName);
if (clazz != null) {
className = pluginClassName;
cl = clazz.getClassLoader();
intent.setExtrasClassLoader(cl);
if (targetClassName.length > 1) {
// 之前为了传递classNae，intent的action被修改过
// 这里再把Action还原到原始的Action
intent.setAction(targetClassName[1]);
} else {
intent.setAction(null);
}
// 添加一个标记符
intent.addCategory(RELAUNCH_FLAG + className);
} else {
throw new ClassNotFoundException("pluginClassName : " + pluginClassName, new Throwable());
}
} else if (PluginManagerHelper.isExact(className, PluginDescriptor.ACTIVITY)) {
// 这个逻辑是为了支持外部app唤起配置了stub_exact的插件Activity
PluginDescriptor pluginDescriptor = PluginManagerHelper.getPluginDescriptorByClassName(className);
if (pluginDescriptor != null) {
boolean isRunning = PluginLauncher.instance().isRunning(pluginDescriptor.getPackageName());
if (!isRunning) {
return waitForLoading(pluginDescriptor);
}
}
Class<?> clazz = PluginLoader.loadPluginClassByName(pluginDescriptor, className);
if (clazz != null) {
cl = clazz.getClassLoader();
} else {
throw new ClassNotFoundException("className : " + className, new Throwable());
}
} else {
// 进入这个分支可能是因为activity重启了，比如横竖屏切换，由于上面的分支已经把Action还原到原始到Action了
// 这里只能通过之前添加的标记符来查找className
boolean found = false;
Set<String> category = intent.getCategories();
if (category != null) {
Iterator<String> itr = category.iterator();
while (itr.hasNext()) {
String cate = itr.next();
if (cate.startsWith(RELAUNCH_FLAG)) {
className = cate.replace(RELAUNCH_FLAG, "");
PluginDescriptor pluginDescriptor = PluginManagerHelper.getPluginDescriptorByClassName(className);
if (pluginDescriptor != null) {
boolean isRunning = PluginLauncher.instance().isRunning(
pluginDescriptor.getPackageName());
if (!isRunning) {
return waitForLoading(pluginDescriptor);
}
}
Class<?> clazz = PluginLoader.loadPluginClassByName(pluginDescriptor, className);
cl = clazz.getClassLoader();
found = true;
break;
}
}
}
if (!found) {
throw new ClassNotFoundException(
"className : " + className + ", intent : " + intent.toString(), new Throwable());
}
}
} else {
if (cl instanceof PluginClassLoader) {
PluginIntentResolver.resolveActivity(intent);
} else {
// Do Nothing
}
}
}
try {
Activity activity = super.newActivity(cl, className, intent);
if (activity instanceof PluginContainer) {
((PluginContainer) activity).setPluginId(intent.getStringExtra(PluginContainer.FRAGMENT_PLUGIN_ID));
}
return activity;
} catch (ClassNotFoundException e) {
// 收集状态，便于异常分析
throw new ClassNotFoundException(" orignalCl : " + orignalCl.toString() + ", orginalClassName : "
+ orginalClassName + ", orignalIntent : " + orignalIntent + ", currentCl : " + cl.toString()
+ ", currentClassName : " + className + ", currentIntent : " + intent.toString() + ", process : "
+ ProcessUtil.isPluginProcess() + ", isStubActivity : "
+ PluginManagerHelper.isStub(orginalClassName) + ", isExact : "
+ PluginManagerHelper.isExact(orginalClassName, PluginDescriptor.ACTIVITY), e);
}
}
方案确实很简单，不过还有一些收尾工作，就是将创建好的[插件]组件进行一些必要的init操作，比如：在声明周期onCreate之前进行上下文替换等操作，这些都在插件框架提供的PluginInstrumentionWrapper里面进行完成的，看一下代码片段：
@Override
public void callActivityOnCreate(Activity activity, Bundle icicle) {
PluginInjector.injectActivityContext(activity);
Intent intent = activity.getIntent();
if (intent != null) {
intent.setExtrasClassLoader(activity.getClassLoader());
}
if (icicle != null) {
icicle.setClassLoader(activity.getClassLoader());
}
if (ProcessUtil.isPluginProcess()) {
installPluginViewFactory(activity);
if (activity instanceof WaitForLoadingPluginActivity) {
// NOTHING
} else {
}
if (activity.isChild()) {
// 修正TabActivity中的Activity的ContextImpl的packageName
Context base = activity.getBaseContext();
while (base instanceof ContextWrapper) {
base = ((ContextWrapper) base).getBaseContext();
}
if (HackContextImpl.instanceOf(base)) {
HackContextImpl impl = new HackContextImpl(base);
String packageName = PluginLoader.getApplication().getPackageName();
// String packageName1 = activity.getPackageName();
impl.setBasePackageName(packageName);
impl.setOpPackageName(packageName);
}
}
}
super.callActivityOnCreate(activity, icicle);
monitor.onActivityCreate(activity);
}
到这插件activity组件就被顺序的启动起来了，并且是系统在维护具备完整的生命周期。 组件service、Receiver也是一样的，只是这两个组件的拦截点在ActivityThread的Handler成员的回调Callback里面进行的。Application和provider在插件启动的时候进行加载。
资源冲突的解决方案
resources.arsc资源描述符详解
- packageId: 包名id
- 资源类型id：string,drawable,layout,color
- 偏移：某一种类型的偏移值
解决冲突的方案
由于每个插件的包名是不一致的，可以事先规定某个插件的packageId的值固定，然后修改aapt对其进行编译固定，就可以保证每个插件分配的值不一样了。
