插件化技術也就是說用戶只需安裝宿主apk,其它業務模塊打包成獨立的插件apk動態下發,然後通過宿主app加載運行。其天然的就解決了部分包體積大小的問題,畢竟只需將核心業務模塊打包到宿主app,隨之附帶的還有插件apk的熱更新能力,通過網絡可以隨時下載更新插件apk,避免宿主APP的頻繁發版。
市面上的框架原理都差不多,構建插件apk路徑的DexClassLoader,後續通過DexClassLoader加載插件類即可。普通類相對來說容易解決,加載即用。像四大組件比如Acitvity這種具有生命週期的組件則需要通過站樁方案轉發生命週期,當然還有插件apk資源加載的問題。
插件化是一個聽起來很厲害、很高大上的技術,但只要瞭解其中原理之後,自己擼一下也是很容易實現的,不過簡單的實現和穩定在線上運行又是兩碼事了。看的再多不如手寫一個,寫個demo踩趟坑基本就懂了,下面以加載插件Activity爲例。
首先需要構建一個DexClassLoader,加載插件apk dex文件中的class。
創建HostActivity
作爲宿主,爲了方便將插件apk拷貝到應用私有目錄的cache文件夾中,在宿主HostActivity.onCreate()中初始化DexClassLoader。
private var pluginClassLoader: PluginClassLoader? = null
private var pluginActivity: PluginActivity? = null
private var apkPath: String? = null
private fun initCurrentActivity() {
apkPath = "${cacheDir.absolutePath}${File.separator}plugin-debug.apk"
pluginClassLoader = PluginClassLoader(
dexPath = apkPath ?: "",
optimizedDirectory = cacheDir.absolutePath,
librarySearchPath = null,
classLoader
)
val activityName = intent.getStringExtra("ActivityName") ?: ""
pluginActivity = pluginClassLoader?.loadActivity(activityName, this)
}
跳轉插件Activity統一修改爲跳轉到HostActivity,如此便沒有校驗manifest的問題,在intent中傳入插件activity全類名,通過DexClassLoader加載插件activity並實例化。
class PluginClassLoader(
dexPath: String,
optimizedDirectory: String,
librarySearchPath: String?,
parent: ClassLoader
) : DexClassLoader(dexPath, optimizedDirectory, librarySearchPath, parent) {
fun loadActivity(activityName: String, host: HostActivity): PluginActivity? {
try {
return (loadClass(activityName)?.newInstance() as PluginActivity?).apply {
this?.bindHost(host)
}
} catch (e: Exception) {
e.printStackTrace()
}
return null
}
}
插件基類PluginActivity
實現接口PluginLifecycle
同步HostActivity生命週期。
PluginActivity
open class PluginActivity : PluginLifecycle {
private var host: HostActivity? = null
fun bindHost(host: HostActivity) {
this.host = host
}
override fun onCreate(savedInstanceState: Bundle?) {
}
override fun onStart() {
}
override fun onResume() {
}
override fun onRestart() {
}
override fun onPause() {
}
override fun onStop() {
}
override fun onDestroy() {
}
override fun onSaveInstanceState(outState: Bundle) {
}
override fun onRestoreInstanceState(savedInstanceState: Bundle) {
}
}
PluginLifecycle
interface PluginLifecycle {
fun onCreate(savedInstanceState: Bundle?)
fun onStart()
fun onResume()
fun onRestart()
fun onPause()
fun onStop()
fun onDestroy()
fun onSaveInstanceState(outState: Bundle)
fun onRestoreInstanceState(savedInstanceState: Bundle)
}
HostActivity宿主在生命週期回調中調用插件PluginActivity
對應方法
class HostActivity : AppCompatActivity() {
private var pluginClassLoader: PluginClassLoader? = null
private var pluginActivity: PluginActivity? = null
private var apkPath: String? = null
override fun onCreate(savedInstanceState: Bundle?) {
initCurrentActivity()
super.onCreate(savedInstanceState)
pluginActivity?.onCreate(savedInstanceState)
}
private fun initCurrentActivity() {
apkPath = "${cacheDir.absolutePath}${File.separator}plugin-debug.apk"
pluginClassLoader = PluginClassLoader(
dexPath = apkPath ?: "",
optimizedDirectory = cacheDir.absolutePath,
librarySearchPath = null,
classLoader
)
val activityName = intent.getStringExtra("ActivityName") ?: ""
pluginActivity = pluginClassLoader?.loadActivity(activityName, this)
}
override fun onStart() {
super.onStart()
pluginActivity?.onStart()
}
override fun onResume() {
super.onResume()
pluginActivity?.onResume()
}
override fun onRestart() {
super.onRestart()
pluginActivity?.onRestart()
}
override fun onPause() {
super.onPause()
pluginActivity?.onPause()
}
override fun onStop() {
super.onStop()
pluginActivity?.onStop()
}
override fun onDestroy() {
super.onDestroy()
pluginActivity?.onDestroy()
}
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
pluginActivity?.onSaveInstanceState(outState)
}
override fun onRestoreInstanceState(savedInstanceState: Bundle) {
super.onRestoreInstanceState(savedInstanceState)
pluginActivity?.onRestoreInstanceState(savedInstanceState)
}
}
插件Activity編寫時繼承PluginActivity,此方案本質上運行在系統中的是HostActivity,只不過我們開發時編寫的代碼在插件Activity中。將HostActivity生命週期轉發給PluginActivity,讓插件類同步感知生命週期;插件使用到Activity方法時也需要將調用轉發給HostActivity進行真正的調用(雙向奔赴了屬於是),畢竟PluginActivity不是一個真正的Activity,比如設置佈局的setContentView()方法。
PluginActivity
fun setContentView(@LayoutRes layoutResID: Int) {
host?.setContentView(layoutResID)
}
這個host在DexClassLoader加載插件activity時進行了綁定,也就是宿主HostActivity,插件類需要使用Activity方法時都由host進行轉發。
基類差不多寫好了,都放到base module,然後新建plugin module,app和plugin都依賴base module,下面是目錄結構。
ActivityKtx粗略封裝一下跳轉插件Activity方法
fun Activity.jumpPluginActivity(activityName: String, pluginName: String? = "") {
startActivity(Intent(this, HostActivity::class.java).apply {
putExtra("ActivityName", activityName)
putExtra("PluginName", pluginName)
})
}
接下來在Plugin module中編寫插件Activity
LoginActivity
class LoginActivity : PluginActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_login)
}
}
代碼很簡單,在onCreate時調用setContentView設置佈局。然後run plugin,將生成的plugin-debug.apk複製到應用私有目錄,對應到之前初始化PluginClassLoader的路徑。可以用AS自帶的Devices File Explorer upload到data/user/0/package/cache目錄。
如此便算是模擬下載插件apk,下面回到宿主app。
MainActivity
點擊按鈕跳轉插件Activity,調用前面封裝的jumpPluginActivity()
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
findViewById<TextView>(R.id.tv).setOnClickListener {
jumpPluginActivity("com.chenxuan.plugin.LoginActivity")
}
}
}
不出意外跳轉會崩潰,因爲LoginActivity
設置佈局使用到的lauout資源文件在插件apk中,調用HostActivity.setContentView()時,HostActivity運行在宿主app中,資源無法引用到。
下面解決資源問題,HostActivity
中反射創建AssetManager,調用其addAssetPath()方法指定資源路徑,然後構造資源類Resources,重寫getResources()
方法返回插件資源。
HostActivity
private var pluginClassLoader: PluginClassLoader? = null
private var pluginActivity: PluginActivity? = null
private var apkPath: String? = null
private var pluginResources: Resources? = null
override fun onCreate(savedInstanceState: Bundle?) {
initCurrentActivity()
initActivityResource()
super.onCreate(savedInstanceState)
pluginActivity?.onCreate(savedInstanceState)
}
override fun getResources(): Resources {
return pluginResources ?: super.getResources()
}
private fun initActivityResource() {
try {
val pluginAssetManager = AssetManager::class.java.newInstance()
val addAssetPathMethod = pluginAssetManager.javaClass
.getMethod("addAssetPath", String::class.java)
addAssetPathMethod.invoke(pluginAssetManager, apkPath)
pluginResources = Resources(
pluginAssetManager,
super.getResources().displayMetrics,
super.getResources().configuration
)
} catch (e: Exception) {
e.printStackTrace()
}
}
run app,點擊按鈕跳轉。
沒啥問題,正常加載插件Activity。到這即使是作爲一個demo還是略顯粗糙的,Activity的方法還是有很多的,後續還需完善插件Activity的能力,搬磚式的將各種調用轉發給HostActivity。而且四大組件還有其它三個要處理,即使是Activity,其啓動模式不同也需要對應的站樁Activity。不過擼完原理肯定是拿捏了,加載資源包也是輕而易舉,畢竟很多皮膚包的實現原理也是這樣下發資源包apk動態加載的。