源码级分析app是如何被启动的_appdeathrecipient-程序员宅基地
技术标签： 项目经验总结
前言
- 一个app的程序是怎么启动的？入口在哪里？
- 听说ActivityManagerServices很屌，Why？
- Activity生命周期到底是谁调用的？
- Application又是在哪里初始化的？onCreate又是如何被调用的？
- 面试官常常会问：为什么主线程使用looper.loop不会卡死界面?
- 等等..
是不是一直有这样的疑问？很懵逼对不对 - - ，那我们就站在巨人的丁丁上来解决一下这些问题，如果文中出现一些错误，还望指正，互相学习
主要流程
大家都知道 Android是基于Linux系统的，而在Linux中，所有的进程都是由init进程直接或者是间接fork出来的，当我开机的时候init进程就会fork出一个Android的第一个新的进程
Zygote,中文翻译过来要”受精卵”，一个很有意识的名字。为什么这么说呢，当我们Zygote进程跑起来后，Android为了实现实现资源共用和更快的启动速度，通过Zygote进程直接去fork出一些子进程，这就是为什么要”受精卵”的原因，也就是我们的app全部都是基于Zygote上的 ，没有Zygote就没有我们，当Zygote初始化完成之后，首先会fork它的第一个子进程SystemServer,这个类非常的重要，为什么这么说呢？因为系统里面重要的服务都是在这个进程里面开启的，比如ActivityManagerService、PackageManagerService、WindowManagerService等等，有木有觉得似曾相识
当SystemServer跑起来后，这些重要的服务也会随之创建,系统初始化完成之后我们就会进到系统桌面->Launcher，其实Launcher也是一个app，它继承自Activity，当我们点击桌面上的app后，系统就会为我们的app创建一个进程，然后启动我们App的第一个类ActivityThread,其实说到底我们的app就是一个main函数,也就是启动了ActivityThread.main()。我们重点来看下这个类
App的程序入口
都说主线程更新ui，主线程不能有耗时操作，主线程是在哪里创建的呢？我们来看下ActivityThread.main()。
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public static void main(String[] args) {
....
final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
TrustedCertificateStore.setDefaultUserDirectory(configDir);
Process.setArgV0(
"<pre-initialized>");
//创建主线程Looper
Looper.prepareMainLooper();
ActivityThread thread =
new ActivityThread();
thread.attach(
false);
if (sMainThreadHandler ==
null) {
sMainThreadHandler = thread.getHandler();
}
if (
false) {
Looper.myLooper().setMessageLogging(
new
LogPrinter(Log.DEBUG,
"ActivityThread"));
}
// End of event ActivityThreadMain.
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
//主线程消息循环
Looper.
loop();
throw
new RuntimeException(
"Main thread loop unexpectedly exited");
}
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为什么主线程使用Looper.loop()不会卡死界面
首先我们要明白一点，主线程也是一个线程，也是有他的生命周期的，当我们new Thread()后执行完里面的代码也就意味着这个线程的结束，刚说了主线程也是线程，如果我们的代码一下就执行完了，那么我们这个app的功能还能执行吗？ 我还没开始呢，你咋就结束了？这样多不持久，Android为了解决这个问题，使用的Looper循环,了解Handler的机制的童鞋，会知道在处理消息的时候使用了Looper.loop()方法，并且在该方法中进入了一个死循环
同时Looper.loop()方法是在主线程中调用的，那么为什么没有卡死界面呢？
线程的生命周期
首先我们要明白线程它也是有生命周期的，它的生命周期在于这个线程里面所要执行的代码执行完成，这个线程的使命也就完成了
主线程如何与子线程通信
其次我们要明白我们主线程是如何跟子线程通信（发消息）的
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public
class MainActivity extends AppCompatActivity {
Handler mHandler;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Thread(
new Runnable() {
public void run() {
//初始化Looper对象 一个线程对应一个looper
Looper.prepare();
mHandler =
new
Handler() {
public void handleMessage(Message msg)
{
super
.handleMessage(msg);
Log.i(
"test"
,
"do somethings"
);
}
};
//开启消息循环
Looper.loop();
}
}).start();
findViewById(R.id.btn).setOnClickListener(
new
View.OnClickListener() {
public void onClick(View v)
{
mHandler.sendEmptyMessage(
1
);
}
});
}
}
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我们主线程跟子线程就是这样通信的，可是为什么要 先Looper.prepare(),然后执行处理逻辑，最后Looper.loop();
我们先来看看Looper.prepare()
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public static void prepare() {
prepare(
true);
}
private static void prepare(boolean quitAllowed) {
if (sThreadLocal.
get() !=
null) {
throw
new RuntimeException(
"Only one Looper may be created per thread");
}
sThreadLocal.
set(
new Looper(quitAllowed));
}
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sThreadLocal你可以理解成一个hashmap键值对，key就是我们当前的Thread线程，value就是new Lopper出来的对象，sThreadLocal.get()如果不等于空的话 表示直接调用了prepare已经set进去了，就会抛出一个异常。也就是说一个线程只能对应一个looper，人家可是很专一的~，在来看看
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/**
* Run the message queue in this thread. Be sure to call
* {
@link
#quit()} to end the loop.
*/
public static void loop() {
//获取当前线程对应的Looper对象
final
Looper me = myLooper();
if
(me ==
null
) {
//没有调用Looper.prepare()
throw
new
RuntimeException(
"No Looper; Looper.prepare() wasn't called on this thread."
);
}
final
MessageQueue queue = me.mQueue;
// Make sure the identity of this thread is that of the local process,
// and keep track of what that identity token actually is.
Binder.clearCallingIdentity();
final
long
ident = Binder.clearCallingIdentity();
//死循环，不断从消息队列取消息，有消息就直接处理消息
for
(;;) {
//取出下一个消息
Message msg = queue.next();
// might block
if
(msg ==
null
) {
// No message indicates that the message queue is quitting.
//当前没有消息，直接返回
return
;
}
// This must be in a local variable, in case a UI event sets the logger
final
Printer logging = me.mLogging;
if
(logging !=
null
) {
logging.println(
">>>>> Dispatching to "
+ msg.target +
" "
+
msg.callback +
": "
+ msg.what);
}
final
long
traceTag = me.mTraceTag;
if
(traceTag !=
0
) {
Trace.traceBegin(traceTag, msg.target.getTraceName(msg));
}
try
{
//能走到这里，表示msg不为空，有消息要处理
//调用handler.dispatchMessage()处理消息
msg.target.dispatchMessage(msg);
}
finally
{
if
(traceTag !=
0
) {
Trace.traceEnd(traceTag);
}
}
if
(logging !=
null
) {
logging.println(
"<<<<< Finished to "
+ msg.target +
" "
+ msg.callback);
}
// Make sure that during the course of dispatching the
// identity of the thread wasn't corrupted.
final
long
newIdent = Binder.clearCallingIdentity();
if
(ident != newIdent) {
Log.wtf(TAG,
"Thread identity changed from 0x"
+ Long.toHexString(ident) +
" to 0x"
+ Long.toHexString(newIdent) +
" while dispatching to "
+ msg.target.getClass().getName() +
" "
+ msg.callback +
" what="
+ msg.what);
}
msg.recycleUnchecked();
}
}
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代码上注释也写的比较清楚了，我们刚说了线程也是有生命周期的，我们在线程里面创建了looper对象之后，new Handler()然后去处理消息，假如我们Looper.loop()没有这个死循环，这个线程任务就执行完成了，那Handler里面还能收到消息吗？所以我就需要调用Looper.loop()一个死循环，不断去消息队列去取,然后我们主线程发了消息后，Looper取到了消息，子线程里面的Handler也就自然能够处理消息这就是这个调用Looper.loop()的作用
主线程创建Handler的时候为什么不用调用Looper.prepare(),Loop.loop()?
我们在来看看AcivityThread源码
ActivityThread.java
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public static void main(String[] args) {
...
Looper.prepareMainLooper();
ActivityThread thread =
new ActivityThread();
thread.attach(
false);
if (sMainThreadHandler ==
null) {
sMainThreadHandler = thread.getHandler();
}
if (
false) {
Looper.myLooper().setMessageLogging(
new
LogPrinter(Log.DEBUG,
"ActivityThread"));
}
// End of event ActivityThreadMain.
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
Looper.loop();
...
}
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看到木有，在我们app启动的时候,ActivityThread已经帮我们做好了Looper消息循环，所以我们在主线程new Handler()的时候就不用创建Looper，反而你再次调用Looper.prepare()还会报错，因为主线程已经创建了Looper对象了。
为什么主线程不会卡死界面
理解了上面几个问题我们就比较好理解了，首先，主线程也是线程，只不过这个线程是被系统创建的（就好比我们自己创建了子线程一样），其次 Looper是不断的去消息队列里面取，取到消息就去处理消息，只要处理消息的操作不是耗时操作，就不会引起卡顿,其实Android的交互都是基于消息机制的分发，handler 可以发送消息，然后loop 里就分发消息然后就发给handler, 然后就执行到 H（Handler ）里的对应代码。所以这些代码就不会卡死～,也就说循环消息并不会使起卡死，而真正会卡死的是我们的处理消息，这也就是我们主线程为什么不能执行耗时操作的原因。
举个栗子
讲到这里你可能还不是很能理解，那我们就来举一个栗子~
我们去做地铁或者做火车的时候都要去过安检，这个安检的机器就好比我们的Looper对象，机器内部检测违禁品就好比是Handler，因为我们要依次排队去放到机器上去检查，我们一个人的行李物品就比作一个Message,多个人所以就组成了一个MessageQueue, 好，有了这些东西我们就可以脑补整个运行过程了，首先如果要运行机器首先你的插插头吧？不然怎么通电->（Looper.prepare）,通完点后你得按开关吧？（Looper.loop），因为运行很早，这个时候还没有人来安检，此时消息队列（MessageQueue）是空的，这个时候我过来安检，因为我是出去玩，所以带的东西比较少，这个时候我把我的包包（Message）放到了安检机器的韧带（MessageQueue）上面了，此时MessageQueue消息队列里面就有我的包包了，机器此时正在运转，
然后机器自动检测我的是否有违禁品（Handler.handleMessage）,这个时候来了位大叔，带着很大一包东西（Message），放到了MessageQueue里，这个安检机器还在循环（Looper）,当循环到这个大叔的大件后，大叔在另一头等待了好久发现怎么都不出来，因为太大，检测需要时间（假设机器比较low），而这个等待的时间就是我们所说的做了耗时操作导致ui卡顿。如果等了很久会导致很多乘客不满（ANR）。这个比喻可能不是很形象，但是话粗理不粗，这个只是我的个人理解
如果大家还是不能理解的话，可以参考Android事件机制详细解读里面有更深入的解读
ActivityThread.attach()
回归上一个话题，执行main函数的时候new ActivityThread(),执行了它的attach方法，我们来看下attach方法
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private void attach(boolean system) {
sCurrentActivityThread =
this;
mSystemThread = system;
if (!system) {
...
final IActivityManager mgr =ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
}
catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
// Watch for getting close to heap limit.
BinderInternal.addGcWatcher(
new Runnable() {
public void run() {
if (!mSomeActivitiesChanged) {
return;
}
Runtime runtime = Runtime.getRuntime();
long dalvikMax = runtime.maxMemory();
long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
if (dalvikUsed > ((
3*dalvikMax)
/
4
)) {
if
(DEBUG_MEMORY_TRIM) Slog.d(TAG,
"Dalvik max="
+ (dalvikMax/
1024
)
+
" total="
+ (runtime.totalMemory()/
1024
)
+
" used="
+ (dalvikUsed/
1024
));
mSomeActivitiesChanged =
false
;
try
{
mgr.releaseSomeActivities(mAppThread);
}
catch
(RemoteException e) {
throw
e.rethrowFromSystemServer();
}
}
}
});
}
else
{
// Don't set application object here -- if the system crashes,
// we can't display an alert, we just want to die die die.
android.ddm.DdmHandleAppName.setAppName(
"system_process",
UserHandle.myUserId());
try {
mInstrumentation =
new Instrumentation();
ContextImpl context = ContextImpl.createAppContext(
this, getSystemContext().mPackageInfo);
mInitialApplication = context.mPackageInfo.makeApplication(
true,
null);
mInitialApplication.onCreate();
}
catch (Exception e) {
throw
new RuntimeException(
"Unable to instantiate Application():" + e.toString(), e);
}
}
}
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首先attach方法有一个boolean的变量system,传过来的是false，聪明的你一看就是这个意思，是否是系统应用 ，当然我们不是，然后我们会走到if里面，里面有一行比较关键的代码
final IActivityManager mgr = ActivityManagerNative.getDefault();
我点进去看下getDefault()函数
ActivityManagerNative.java
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/**
* Retrieve the system's default/global activity manager.
*/
static public IActivityManager getDefault() {
return gDefault.
get();
}
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看注释说返回一个系统全局的ActivityManager，调用了gDefault.get(),我们来看下这个gDefault变量看看是在哪里初始化的
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private
static
final Singleton<IActivityManager> gDefault =
new Singleton<IActivityManager>() {
protected IActivityManager create() {
IBinder b = ServiceManager.getService(
"activity");
if (
false) {
Log.v(
"ActivityManager",
"default service binder = " + b);
}
IActivityManager am = asInterface(b);
if (
false) {
Log.v(
"ActivityManager",
"default service = " + am);
}
return am;
}
};
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ServiceManager.getService(“activity”)返回一个IBinder 这个Binder对象是谁呢？既然有getService，那么肯定有addService，并且这个key是“activity”，我们来看下是在哪个类添加的
ActivityManagerService.java
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public void setSystemProcess() {
try {
ServiceManager.addService(Context.ACTIVITY_SERVICE,
this,
true);
ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
ServiceManager.addService(
"meminfo",
new MemBinder(
this));
ServiceManager.addService(
"gfxinfo",
new GraphicsBinder(
this));
ServiceManager.addService(
"dbinfo",
new DbBinder(
this));
if (MONITOR_CPU_USAGE) {
ServiceManager.addService(
"cpuinfo",
new CpuBinder(
this));
}
ServiceManager.addService(
"permission",
new PermissionController(
this));
ServiceManager.addService(
"processinfo",
new ProcessInfoService(
this));
ApplicationInfo info = mContext.getPackageManager().getApplicationInfo(
"android", STOCK_PM_FLAGS | MATCH_SYSTEM_ONLY);
mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());
synchronized (
this) {
ProcessRecord app = newProcessRecordLocked(info, info.processName,
false,
0);
app.persistent =
true;
app.pid = MY_PID;
app.maxAdj = ProcessList.SYSTEM_ADJ;
app.makeActive(mSystemThread.getApplicationThread(), mProcessStats);
synchronized (mPidsSelfLocked) {
mPidsSelfLocked.put(app.pid, app);
}
updateLruProcessLocked(app,
false,
null);
updateOomAdjLocked();
}
}
catch (PackageManager.NameNotFoundException e) {
throw
new RuntimeException(
"Unable to find android system package", e);
}
}
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我们看这一行代码
ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true);
看下这个Context这个常量：
public static final String ACTIVITY_SERVICE = “activity”;
正好是刚才ServiceManager.getService()传过去的key, addService()的时候传过去一个this，也就是ActivityManagerService自己，那么getService()的时候返回的毫无疑问就是ActivityManagerService
我们在回来看下ActivityThread.attach()方法
ActivityThread.java
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final IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
}
catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
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我们搞清楚调用ActivityManagerNative.getDefault()返回了IActivityManager类型的mgr，也就是ActivityManagerService之后 ，它调用了attachApplication,并传入了一个mAppThread我们首先来看下这个变量是什么类型
final ApplicationThread mAppThread = new ApplicationThread();
是ApplicationThread，我们在来看看调用了ActivityManagerService.attachApplication做了什么事情
ActivityManagerService.java
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final void attachApplication(IApplicationThread thread) {
synchronized (
this) {
int callingPid = Binder.getCallingPid();
final
long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
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调用了attachApplicationLocked()，继续看下做了啥
这个方法比较长，我就只取关键的部分贴出来
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private final boolean attachApplicationLocked(IApplicationThread thread,
int
pid) {
....
try {
...
ProfilerInfo profilerInfo = profileFile ==
null ?
null
:
new ProfilerInfo(profileFile, profileFd, samplingInterval, profileAutoStop);
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked());
updateLruProcessLocked(app,
false,
null);
app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
}
catch (Exception e) {
// todo: Yikes! What should we do? For now we will try to
// start another process, but that could easily get us in
// an infinite loop of restarting processes...
Slog.wtf(TAG,
"Exception thrown during bind of "
+ app, e);
app.resetPackageList(mProcessStats);
app.unlinkDeathRecipient();
startProcessLocked(app,
"bind fail"
, processName);
return
false
;
}
....
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Application是在什么时候创建的？onCreate()什么时候调用的？
执行完判断和赋值的操作后最后调用了thread.bindApplication(),刚才看到是ApplicationThread,所以我来看看ApplicationThread.bindApplication
ActivityThread.java
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private
class ApplicationThread extends ApplicationThreadNative {
private
static
final String DB_INFO_FORMAT =
" %8s %8s %14s %14s %s";
private
int mLastProcessState = -
1;
...
public final void bindApplication(String processName, ApplicationInfo appInfo,
List<ProviderInfo> providers, ComponentName instrumentationName,
ProfilerInfo profilerInfo, Bundle instrumentationArgs,
IInstrumentationWatcher instrumentationWatcher,
IUiAutomationConnection instrumentationUiConnection,
int
debugMode,
boolean
enableBinderTracking,
boolean
trackAllocation,
boolean
isRestrictedBackupMode,
boolean
persistent, Configuration config,
CompatibilityInfo compatInfo, Map<String, IBinder> services, Bundle coreSettings) {
if (services !=
null) {
// Setup the service cache in the ServiceManager
ServiceManager.initServiceCache(services);
}
setCoreSettings(coreSettings);
AppBindData data =
new
AppBindData();
data.processName = processName;
data.appInfo = appInfo;
data.providers = providers;
data.instrumentationName = instrumentationName;
data.instrumentationArgs = instrumentationArgs;
data.instrumentationWatcher = instrumentationWatcher;
data.instrumentationUiAutomationConnection = instrumentationUiConnection;
data.debugMode = debugMode;
data.enableBinderTracking = enableBinderTracking;
data.trackAllocation = trackAllocation;
data.restrictedBackupMode = isRestrictedBackupMode;
data.persistent = persistent;
data.config = config;
data.compatInfo = compatInfo;
data.initProfilerInfo = profilerInfo;
sendMessage(H.BIND_APPLICATION, data);
...
}
|
可以看到是ActivityThread的内部类，我去！你在玩我呢？绕了这么半天又绕回来了。
客官别急，我们继续向下看，执行bindApplication的时候发了一个消息
sendMessage(H.BIND_APPLICATION, data);
这个H就是我们前面说的Handler，我们来看下handler做了哪些处理
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private
class H extends Handler {
.....
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG,
">>> handling: " + codeToString(msg.what));
switch (msg.what) {
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER,
"bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
}
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看到它调用了handleBindApplication()，其主要作用是绑定我的的自定义的application，做一些初始化操作，我们继续看
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private void handleBindApplication(AppBindData data) {
...
if (ii !=
null) {
final ApplicationInfo instrApp =
new ApplicationInfo();
ii.copyTo(instrApp);
instrApp.initForUser(UserHandle.myUserId());
final LoadedApk pi = getPackageInfo(instrApp, data.compatInfo,
appContext.getClassLoader(),
false,
true,
false);
final ContextImpl instrContext = ContextImpl.createAppContext(
this, pi);
try {
final ClassLoader cl = instrContext.getClassLoader();
mInstrumentation = (Instrumentation)
cl.loadClass(data.instrumentationName.getClassName()).newInstance();
}
catch (Exception e) {
throw
new RuntimeException(
"Unable to instantiate instrumentation "
+ data.instrumentationName +
": " + e.toString(), e);
}
final ComponentName component =
new ComponentName(ii.packageName, ii.name);
mInstrumentation.init(
this, instrContext, appContext, component,
data.instrumentationWatcher, data.instrumentationUiAutomationConnection);
if (mProfiler.profileFile !=
null && !ii.handleProfiling
&& mProfiler.profileFd ==
null) {
mProfiler.handlingProfiling =
true;
final File file =
new File(mProfiler.profileFile);
file.getParentFile().mkdirs();
Debug.startMethodTracing(file.toString(),
8 *
1024 *
1024);
}
}
else {
mInstrumentation =
new Instrumentation();
}
....
try {
// If the app is being launched for full backup or restore, bring it up in
// a restricted environment with the base application class.
Application app = data.info.makeApplication(data.restrictedBackupMode,
null
);
mInitialApplication = app;
// don't bring up providers in restricted mode; they may depend on the
// app's custom Application class
if
(!data.restrictedBackupMode) {
if
(!ArrayUtils.isEmpty(data.providers)) {
installContentProviders(app, data.providers);
// For process that contains content providers, we want to
// ensure that the JIT is enabled "at some point".
mH.sendEmptyMessageDelayed(H.ENABLE_JIT,
10
*
1000
);
}
}
// Do this after providers, since instrumentation tests generally start their
// test thread at this point, and we don't want that racing.
try
{
mInstrumentation.onCreate(data.instrumentationArgs);
}
catch
(Exception e) {
throw
new
RuntimeException(
"Exception thrown in onCreate() of "
+ data.instrumentationName +
": "
+ e.toString(), e);
}
try
{
mInstrumentation.callApplicationOnCreate(app);
}
catch
(Exception e) {
if
(!mInstrumentation.onException(app, e)) {
throw
new
RuntimeException(
"Unable to create application "
+ app.getClass().getName()
+
": "
+ e.toString(), e);
}
}
}
finally
{
StrictMode.setThreadPolicy(savedPolicy);
}
}
|
这里有个比较重要的类，mInstrumentation 为什么说它特别重要呢，我们先来看看它怎么初始化的
final ClassLoader cl = instrContext.getClassLoader();
mInstrumentation=(Instrumentation)cl.loadClass(data.instrumentationName.getClassName()).newInstance();
通过反射创建mInstrumentation 然后给进行一系列初始化操作,然后执行了
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
data.info是一个LoadeApk对象。
LoadeApk.java
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public Application makeApplication(boolean forceDefaultAppClass,
Instrumentation instrumentation) {
if (mApplication !=
null) {
return mApplication;
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER,
"makeApplication");
Application app =
null;
String appClass = mApplicationInfo.className;
if (forceDefaultAppClass || (appClass ==
null)) {
appClass =
"android.app.Application";
}
try {
java.lang.ClassLoader cl = getClassLoader();
if (!mPackageName.equals(
"android")) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER,
"initializeJavaContextClassLoader");
initializeJavaContextClassLoader();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread,
this);
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
}
catch (Exception e) {
if (!mActivityThread.mInstrumentation.onException(app, e)) {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
throw
new RuntimeException(
"Unable to instantiate application " + appClass
+
": " + e.toString(), e);
}
}
mActivityThread.mAllApplications.add(app);
mApplication = app;
if (instrumentation !=
null) {
try {
//这里不会执行，以为传过来的是null，onCreate在上一层执行的
instrumentation.callApplicationOnCreate(app);
}
catch (Exception e) {
if (!instrumentation.onException(app, e)) {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
throw
new RuntimeException(
"Unable to create application " + app.getClass().getName()
+
": " + e.toString(), e);
}
}
}
}
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执行了
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
Instrumentation.java
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static public Application newApplication(Class<?> clazz, Context context)
throws
InstantiationException, IllegalAccessException,
ClassNotFoundException {
Application app = (Application)clazz.newInstance();
app.attach(context);
return app;
}
|
同样通过反射出一个application并且 调用其attach(),也就是说我的自定义application的时候attach就是在这里调用的
接着上面ActivityThread.handleBindApplication()中,首先反射出mInstrumentation
和Application然后执行了下面一句代码
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try {
mInstrumentation.callApplicationOnCreate(app);
}
catch (
Exception e) {
if (!mInstrumentation.onException(app, e)) {
throw
new RuntimeException(
"Unable to create application " + app.getClass().getName()
+
": " + e.toString(), e);
}
}
|
调用了mInstrumentation.callApplicationOnCreate()，我们的Application.oncreate()就是在这里调用的，现在明白为什么Instrumentation为什么那么重要了吧，它就像个管家婆一样，负责家里的大事小事，但是一般不抛头露面，听一家之主ActivityThread的安排。
好，搞清楚Application后我们在来看看activity在哪里被初始化以及调用oncreate()方法的
Activity是怎样启动的
前面说了ActivityThread.attach()调用了ActivityManagerService.attachApplication(),在代码中看到通过调用ApplicationThread.bindApplication()绑定了application,我们在看看bindApplication()之后在干了什么
ActivityManagerService.java
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private final boolean attachApplicationLocked(IApplicationThread thread,
int
pid) {
...
try {
...
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked());
...
}
catch (Exception e) {
...
}
...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething =
true;
}
}
catch (Exception e) {
Slog.wtf(TAG,
"Exception thrown launching activities in " + app, e);
badApp =
true;
}
}
|
调用了mStackSupervisor.attachApplicationLocked(app)，mStackSupervisor是ActivityStackSupervisor类型,这个类也是非常重要的，它决定着我们app是否能启动成功,我们看看做了什么
ActivityStackSupervisor.java
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boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
final String processName = app.processName;
boolean didSomething =
false;
for (
int displayNdx = mActivityDisplays.size() -
1; displayNdx >=
0; --displayNdx) {
//当前应用的整个activity堆信息
ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (
int stackNdx = stacks.size() -
1; stackNdx >=
0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (!isFocusedStack(stack)) {
continue;
}
ActivityRecord hr = stack.topRunningActivityLocked();
if (hr !=
null) {
if (hr.app ==
null && app.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
//启动Activity
if (realStartActivityLocked(hr, app,
true,
true)) {
didSomething =
true;
}
}
catch (RemoteException e) {
Slog.w(TAG,
"Exception in new application when starting activity "
+ hr.intent.getComponent().flattenToShortString(), e);
throw e;
}
}
}
}
}
if (!didSomething) {
ensureActivitiesVisibleLocked(
null,
0, !PRESERVE_WINDOWS);
}
return didSomething;
}
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看到调用了realStartActivityLocked(hr, app, true, true))，继续看
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final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean
andResume,
boolean
checkConfig)
throws
RemoteException {
...
if (andResume) {
app.hasShownUi =
true;
app.pendingUiClean =
true;
}
app.forceProcessStateUpTo(mService.mTopProcessState);
app.thread.scheduleLaunchActivity(
new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info,
new Configuration(mService.mConfiguration),
new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage,
task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);
...
}
|
看到了调用了app.thread.scheduleLaunchActivity()，这个app是上一层传过来的ActivityRecord，它代表的就是要开启的Activity对象里面分装了很多信息，比如所在的ActivityTask等，如果这是首次打开应用，那么这个Activity会被放到ActivityTask的栈顶，那么这个thread就是我们的ApplicationThread,我们回到ActivityThread
看下ApplicationThread.scheduleLaunchActivity()做了什么
ActivityThread.java
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private
class ApplicationThread extends ApplicationThreadNative {
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,
int
procState, Bundle state, PersistableBundle persistentState,
List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,
boolean
notResumed,
boolean
isForward, ProfilerInfo profilerInfo) {
...
updatePendingConfiguration(curConfig);
sendMessage(H.LAUNCH_ACTIVITY, r);
}
}
|
又用hanlder发了个消息，我们来看看hanlder怎么处理的
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public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG,
">>> handling: " + codeToString(msg.what));
switch (msg.what) {
case LAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER,
"activityStart");
final ActivityClientRecord r = (ActivityClientRecord) msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo, r.compatInfo);
handleLaunchActivity(r,
null,
"LAUNCH_ACTIVITY");
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
break;
}
|
Word天，几经周折又回到ActivityThread自己,心好累。。我们继续~
ActivityThread.java
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private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged =
true
;
if
(r.profilerInfo !=
null
) {
mProfiler.setProfiler(r.profilerInfo);
mProfiler.startProfiling();
}
// Make sure we are running with the most recent config.
handleConfigurationChanged(
null
,
null
);
if
(localLOGV) Slog.v(
TAG,
"Handling launch of "
+ r);
// Initialize before creating the activity
WindowManagerGlobal.initialize();
//反射创建一个Activity
Activity a = performLaunchActivity(r, customIntent);
if
(a !=
null
) {
r.createdConfig =
new
Configuration(mConfiguration);
reportSizeConfigurations(r);
Bundle oldState = r.state;
//调用Activity.onResume
handleResumeActivity(r.token,
false
, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
if
(!r.activity.mFinished && r.startsNotResumed) {
// The activity manager actually wants this one to start out paused, because it
// needs to be visible but isn't in the foreground. We accomplish this by going
// through the normal startup (because activities expect to go through onResume()
// the first time they run, before their window is displayed), and then pausing it.
// However, in this case we do -not- need to do the full pause cycle (of freezing
// and such) because the activity manager assumes it can just retain the current
// state it has.
performPauseActivityIfNeeded(r, reason);
// We need to keep around the original state, in case we need to be created again.
// But we only do this for pre-Honeycomb apps, which always save their state when
// pausing, so we can not have them save their state when restarting from a paused
// state. For HC and later, we want to (and can) let the state be saved as the
// normal part of stopping the activity.
if
(r.isPreHoneycomb()) {
r.state = oldState;
}
}
}
else
{
// If there was an error, for any reason, tell the activity manager to stop us.
try
{
ActivityManagerNative.getDefault()
.finishActivity(r.token, Activity.RESULT_CANCELED,
null
,
Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
}
catch
(RemoteException ex) {
throw
ex.rethrowFromSystemServer();
}
}
}
|
看到开头 ，关键代码调用了Activity a = performLaunchActivity(r, customIntent);
返回一个Activity，我们看看performLaunchActivity()
ActivityThread.java
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private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")");
ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo ==
null) {
r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
Context.CONTEXT_INCLUDE_CODE);
}
ComponentName component = r.intent.getComponent();
if (component ==
null) {
component = r.intent.resolveActivity(
mInitialApplication.getPackageManager());
r.intent.setComponent(component);
}
if (r.activityInfo.targetActivity !=
null) {
component =
new ComponentName(r.activityInfo.packageName,
r.activityInfo.targetActivity);
}
Activity activity =
null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
//通过反射创建activity实例
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state !=
null) {
r.state.setClassLoader(cl);
}
}
catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw
new RuntimeException(
"Unable to instantiate activity " + component
+
": " + e.toString(), e);
}
}
try {
Application app = r.packageInfo.makeApplication(
false, mInstrumentation);
if (localLOGV) Slog.v(TAG,
"Performing launch of " + r);
if (localLOGV) Slog.v(
TAG, r +
": app=" + app
+
", appName=" + app.getPackageName()
+
", pkg=" + r.packageInfo.getPackageName()
+
", comp=" + r.intent.getComponent().toShortString()
+
", dir=" + r.packageInfo.getAppDir());
if (activity !=
null) {
//创建BaseContext
Context appContext = createBaseContextForActivity(r, activity);
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config =
new Configuration(mCompatConfiguration);
if (r.overrideConfig !=
null) {
config.updateFrom(r.overrideConfig);
}
if (DEBUG_CONFIGURATION) Slog.v(TAG,
"Launching activity "
+ r.activityInfo.name +
" with config " + config);
Window
window =
null;
if (r.mPendingRemoveWindow !=
null && r.mPreserveWindow) {
window = r.mPendingRemoveWindow;
r.mPendingRemoveWindow =
null;
r.mPendingRemoveWindowManager =
null;
}
//我们的activity.attach就在这里被调用的
activity.attach(appContext,
this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor,
window);
if (customIntent !=
null) {
activity.mIntent = customIntent;
}
r.lastNonConfigurationInstances =
null;
activity.mStartedActivity =
false;
int theme = r.activityInfo.getThemeResource();
if (theme !=
0) {
activity.setTheme(theme);
}
activity.mCalled =
false;
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
}
else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
if (!activity.mCalled) {
throw
new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onCreate()");
}
r.activity = activity;
r.stopped =
true;
if (!r.activity.mFinished) {
activity.performStart();
r.stopped =
false;
}
if (!r.activity.mFinished) {
if (r.isPersistable()) {
if (r.state !=
null || r.persistentState !=
null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
r.persistentState);
}
}
else
if (r.state !=
null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
}
}
if (!r.activity.mFinished) {
activity.mCalled =
false;
if (r.isPersistable()) {
mInstrumentation.callActivityOnPostCreate(activity, r.state,
r.persistentState);
}
else {
mInstrumentation.callActivityOnPostCreate(activity, r.state);
}
if (!activity.mCalled) {
throw
new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onPostCreate()");
}
}
}
r.paused =
true;
mActivities.put(r.token, r);
}
catch (SuperNotCalledException e) {
throw e;
}
catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw
new RuntimeException(
"Unable to start activity " + component
+
": " + e.toString(), e);
}
}
return activity;
}
|
我们看到通过调用mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);返回一个Activity，哇~这个管家婆真是厉害！看看做了啥？肯定是反射创建一个Activity嘛。。不信？
Instrumentation.java
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public Activity newActivity(ClassLoader cl, String className,
Intent intent)
throws
InstantiationException, IllegalAccessException,
ClassNotFoundException {
return (Activity)cl.loadClass(className).newInstance();
}
|
不得不说Instrumentation真是任劳任怨啊。。
好，接着上面创建Activity之后,判断activity是否不等于空，走进if里面调用了
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activity
.attach(
appContext,
this,
getInstrumentation(),
r
.token,
r
.ident,
app,
r
.intent,
r
.activityInfo,
title,
r
.parent,
r
.embeddedID,
r
.lastNonConfigurationInstances,
config,
r
.referrer,
r
.voiceInteractor,
window);
|
原来我们Activity的attach在这里调用的啊。。。接着下面走
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if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
}
else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
|
看到没！看到没！熟悉不，我的application.onCreate也是这样调用的,管家婆666666
Instrumentation.java
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5
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public void callActivityOnCreate(Activity activity, Bundle icicle) {
prePerformCreate(activity);
activity.performCreate(icicle);
postPerformCreate(activity);
}
|
调用了activity.performCreate(icicle);看到这么名字就应该很清楚了吧~，又不信？
Activity.java
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final void performCreate(Bundle icicle) {
restoreHasCurrentPermissionRequest(icicle);
onCreate(icicle);
mActivityTransitionState.readState(icicle);
performCreateCommon();
}
|
看到木有~~~回到上面，当执行handleLaunchActivity的时候，调用performLaunchActivity(r, customIntent);返回了Activity之后
我们接着向下看
ActivityThread.java
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Activity a = performLaunchActivity(r, customIntent);
if (a !=
null) {
r.createdConfig =
new Configuration(mConfiguration);
reportSizeConfigurations(r);
Bundle oldState = r.state;
handleResumeActivity(r.token,
false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
}
|
调用了handleResumeActivity，不用说 我敢肯定是用mInstrumentation来调用Activity.onResume的,我们来验证一下
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final void handleResumeActivity(IBinder token,
boolean
clearHide,
boolean
isForward,
boolean
reallyResume,
int
seq, String reason) {
ActivityClientRecord r = mActivities.get(token);
....
// TODO Push resumeArgs into the activity for consideration
r = performResumeActivity(token, clearHide, reason);
....
}
|
继续看performResumeActivity()
|
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public final ActivityClientRecord performResumeActivity(IBinder token,
boolean
clearHide, String reason) {
ActivityClientRecord r = mActivities.get(token);
if (localLOGV) Slog.v(TAG,
"Performing resume of " + r
+
" finished=" + r.activity.mFinished);
if (r !=
null && !r.activity.mFinished) {
if (clearHide) {
r.hideForNow =
false;
r.activity.mStartedActivity =
false;
}
try {
r.activity.onStateNotSaved();
r.activity.mFragments.noteStateNotSaved();
if (r.pendingIntents !=
null) {
deliverNewIntents(r, r.pendingIntents);
r.pendingIntents =
null;
}
if (r.pendingResults !=
null) {
deliverResults(r, r.pendingResults);
r.pendingResults =
null;
}
r.activity.performResume();
...
}
catch (Exception e) {
if (!mInstrumentation.onException(r.activity, e)) {
throw
new RuntimeException(
"Unable to resume activity "
+ r.intent.getComponent().toShortString()
+
": " + e.toString(), e);
}
}
}
|
看到了调用r.activity.performResume()，我们在继续看看Activity.performResume()
Activity.java
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final void performResume() {
performRestart();
mFragments.execPendingActions();
mLastNonConfigurationInstances =
null;
mCalled =
false;
// mResumed is set by the instrumentation
mInstrumentation.callActivityOnResume(
this);
if (!mCalled) {
throw
new SuperNotCalledException(
"Activity " + mComponent.toShortString() +
" did not call through to super.onResume()");
}
// invisible activities must be finished before onResume() completes
if (!mVisibleFromClient && !mFinished) {
Log.w(TAG,
"An activity without a UI must call finish() before onResume() completes");
if (getApplicationInfo().targetSdkVersion
> android.os.Build.VERSION_CODES.LOLLIPOP_MR1) {
throw
new IllegalStateException(
"Activity " + mComponent.toShortString() +
" did not call finish() prior to onResume() completing");
}
}
// Now really resume, and install the current status bar and menu.
mCalled =
false;
mFragments.dispatchResume();
mFragments.execPendingActions();
onPostResume();
if (!mCalled) {
throw
new SuperNotCalledException(
"Activity " + mComponent.toShortString() +
" did not call through to super.onPostResume()");
}
}
|
调用了mInstrumentation.callActivityOnResume(this);看来我们的验证是没错的
结语
至此，Activity整个的启动流程也讲完了，大家也看到，调用过程极其复杂
源码中各种条件判断让人眼花缭乱，所以说如果你没记住也没关系，你只要记住这个流程，理解了Android在控制Activity生命周期时是如何操作，以及是通过哪几个关键的类进行操作的就可以了，以后遇到相关的问题之道从哪块下手即可，这些过程我虽然也是撸了一遍，但还是记不清。
时序图
为了大家方便，我整理了下整个的调用过程
以上是本文讲的整个流程图,写的比较水，希望对大家学习有所帮助。。。
Android Studio查看源码的小技巧
不知道大家遇到过没，我们平时做项目的时候,想要查看哪些类使用了这个变量的，或者调用过这个类的方法的时候，都会去按住Ctrl加上鼠标点击那个变量或者方法,但是你只能查看自己的项目使用过
比如你想查看这个方法在哪里使用过你可以按住ctrl再点击这个方法查看它的引用
可是我们查看源码的时候，比如我们查看ActivityThread的源码 想看一下handleResumeActivity在哪里调用了，可是你会发现你按住ctrl在点击会找不到引用。为什么呢？因为默认是搜索你的项目，也就是说只要你的项目调用了这个方法，你才可以搜到，可是这是系统调用的，我想查看到底是谁调用的，怎么办捏？
右键单击这个方法弹出菜单，点击Find Usages，快捷是Ctrl+g
默认是搜索我们的Project引用，我们修改成
然后点击Find
就找了调用的地方，然后我们双击就到了调用的那行代码,下次你在按住ctrl单击那个方法的时候就会弹出来引用的地方
这对于我们查看源码有很大的帮助~
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