Android Launcher3各启动场景源码分析

2024-01-19 20:36
文章标签 分析 android 源码 启动 场景 launcher3

本文主要是介绍Android Launcher3各启动场景源码分析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

文章目录

  • 一、概述
  • 二、开机启动Launcher
    • 2.1、开机启动Launcher流程图
    • 2.2、开机启动流程源码分析
  • 三、短压Home键启动Launcher
    • 3.1、短压Home键启动Launcher流程图
    • 3.2、短压Home键启动Launcher源码分析
  • 四、Launcher异常崩溃后的自启动
    • 4.1、Launcher异常崩溃后的自启动流程图
    • 4.2、Launcher异常崩溃后的自启动源码分析

  团队博客: 汽车电子社区

一、概述

  Launcher3是Android系统提供的默认桌面应用(Launcher)，它的源码路径在**“packages/apps/Launcher3/”**。Launcher3的启动场景主要包括：
    1、开机后启动：开机时，android ams服务拉起Launcher。
    2、按键启动：比如短压home键，android wms中的PhoneWindowManager拉起Launcher。
    3、异常崩溃后启动：Launcher异常崩溃后，android ams再次拉起Launcher。
  针对这三种情况，分析一下Aosp源码如何实现。

二、开机启动Launcher

2.1、开机启动Launcher流程图

在这里插入图片描述

2.2、开机启动流程源码分析

  Launcher的开机启动由Android的AMS服务完成。AMS在SystemReady阶段会调用startHomeOnAllDisplays函数。Android支持多Display（虚拟Display或者由硬件上报的实际Display），多Display情况下一般Launcher会针对不同Display做不同的效果。

// frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {traceLog.traceBegin("PhaseActivityManagerReady");synchronized(this) {if (mSystemReady) {// If we're done calling all the receivers, run the next "boot phase" passed in// by the SystemServerif (goingCallback != null) {goingCallback.run();}return;}mLocalDeviceIdleController= LocalServices.getService(DeviceIdleController.LocalService.class);mActivityTaskManager.onSystemReady();// Make sure we have the current profile info, since it is needed for security checks.mUserController.onSystemReady();mAppOpsService.systemReady();mSystemReady = true;}try {sTheRealBuildSerial = IDeviceIdentifiersPolicyService.Stub.asInterface(ServiceManager.getService(Context.DEVICE_IDENTIFIERS_SERVICE)).getSerial();} catch (RemoteException e) {}ArrayList<ProcessRecord> procsToKill = null;synchronized(mPidsSelfLocked) {for (int i=mPidsSelfLocked.size()-1; i>=0; i--) {ProcessRecord proc = mPidsSelfLocked.valueAt(i);if (!isAllowedWhileBooting(proc.info)){if (procsToKill == null) {procsToKill = new ArrayList<ProcessRecord>();}procsToKill.add(proc);}}}synchronized(this) {if (procsToKill != null) {for (int i=procsToKill.size()-1; i>=0; i--) {ProcessRecord proc = procsToKill.get(i);Slog.i(TAG, "Removing system update proc: " + proc);mProcessList.removeProcessLocked(proc, true, false, "system update done");}}// Now that we have cleaned up any update processes, we// are ready to start launching real processes and know that// we won't trample on them any more.mProcessesReady = true;}Slog.i(TAG, "System now ready");EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_AMS_READY, SystemClock.uptimeMillis());mAtmInternal.updateTopComponentForFactoryTest();mAtmInternal.getLaunchObserverRegistry().registerLaunchObserver(mActivityLaunchObserver);watchDeviceProvisioning(mContext);retrieveSettings();mUgmInternal.onSystemReady();final PowerManagerInternal pmi = LocalServices.getService(PowerManagerInternal.class);if (pmi != null) {pmi.registerLowPowerModeObserver(ServiceType.FORCE_BACKGROUND_CHECK,state -> updateForceBackgroundCheck(state.batterySaverEnabled));updateForceBackgroundCheck(pmi.getLowPowerState(ServiceType.FORCE_BACKGROUND_CHECK).batterySaverEnabled);} else {Slog.wtf(TAG, "PowerManagerInternal not found.");}if (goingCallback != null) goingCallback.run();// Check the current user here as a user can be started inside goingCallback.run() from// other system services.final int currentUserId = mUserController.getCurrentUserId();Slog.i(TAG, "Current user:" + currentUserId);if (currentUserId != UserHandle.USER_SYSTEM && !mUserController.isSystemUserStarted()) {// User other than system user has started. Make sure that system user is already// started before switching user.throw new RuntimeException("System user not started while current user is:"+ currentUserId);}traceLog.traceBegin("ActivityManagerStartApps");mBatteryStatsService.noteEvent(BatteryStats.HistoryItem.EVENT_USER_RUNNING_START,Integer.toString(currentUserId), currentUserId);mBatteryStatsService.noteEvent(BatteryStats.HistoryItem.EVENT_USER_FOREGROUND_START,Integer.toString(currentUserId), currentUserId);// On Automotive, at this point the system user has already been started and unlocked,// and some of the tasks we do here have already been done. So skip those in that case.// TODO(b/132262830): this workdound shouldn't be necessary once we move the// headless-user start logic to UserManager-landfinal boolean bootingSystemUser = currentUserId == UserHandle.USER_SYSTEM;if (bootingSystemUser) {mSystemServiceManager.startUser(currentUserId);}synchronized (this) {// Only start up encryption-aware persistent apps; once user is// unlocked we'll come back around and start unaware appsstartPersistentApps(PackageManager.MATCH_DIRECT_BOOT_AWARE);// Start up initial activity.mBooting = true;// Enable home activity for system user, so that the system can always boot. We don't// do this when the system user is not setup since the setup wizard should be the one// to handle home activity in this case.if (UserManager.isSplitSystemUser() &&Settings.Secure.getInt(mContext.getContentResolver(),Settings.Secure.USER_SETUP_COMPLETE, 0) != 0) {ComponentName cName = new ComponentName(mContext, SystemUserHomeActivity.class);try {AppGlobals.getPackageManager().setComponentEnabledSetting(cName,PackageManager.COMPONENT_ENABLED_STATE_ENABLED, 0,UserHandle.USER_SYSTEM);} catch (RemoteException e) {throw e.rethrowAsRuntimeException();}}if (bootingSystemUser) {// 启动Home，也就是LaunchermAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");}mAtmInternal.showSystemReadyErrorDialogsIfNeeded();if (bootingSystemUser) {final int callingUid = Binder.getCallingUid();final int callingPid = Binder.getCallingPid();long ident = Binder.clearCallingIdentity();try {Intent intent = new Intent(Intent.ACTION_USER_STARTED);intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY| Intent.FLAG_RECEIVER_FOREGROUND);intent.putExtra(Intent.EXTRA_USER_HANDLE, currentUserId);broadcastIntentLocked(null, null, intent,null, null, 0, null, null, null, OP_NONE,null, false, false, MY_PID, SYSTEM_UID, callingUid, callingPid,currentUserId);intent = new Intent(Intent.ACTION_USER_STARTING);intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);intent.putExtra(Intent.EXTRA_USER_HANDLE, currentUserId);broadcastIntentLocked(null, null, intent,null, new IIntentReceiver.Stub() {@Overridepublic void performReceive(Intent intent, int resultCode, String data,Bundle extras, boolean ordered, boolean sticky, int sendingUser)throws RemoteException {}}, 0, null, null,new String[] {INTERACT_ACROSS_USERS}, OP_NONE,null, true, false, MY_PID, SYSTEM_UID, callingUid, callingPid,UserHandle.USER_ALL);} catch (Throwable t) {Slog.wtf(TAG, "Failed sending first user broadcasts", t);} finally {Binder.restoreCallingIdentity(ident);}} else {Slog.i(TAG, "Not sending multi-user broadcasts for non-system user "+ currentUserId);}mAtmInternal.resumeTopActivities(false /* scheduleIdle */);if (bootingSystemUser) {mUserController.sendUserSwitchBroadcasts(-1, currentUserId);}BinderInternal.nSetBinderProxyCountWatermarks(BINDER_PROXY_HIGH_WATERMARK,BINDER_PROXY_LOW_WATERMARK);BinderInternal.nSetBinderProxyCountEnabled(true);BinderInternal.setBinderProxyCountCallback(new BinderInternal.BinderProxyLimitListener() {@Overridepublic void onLimitReached(int uid) {Slog.wtf(TAG, "Uid " + uid + " sent too many Binders to uid "+ Process.myUid());BinderProxy.dumpProxyDebugInfo();if (uid == Process.SYSTEM_UID) {Slog.i(TAG, "Skipping kill (uid is SYSTEM)");} else {killUid(UserHandle.getAppId(uid), UserHandle.getUserId(uid),"Too many Binders sent to SYSTEM");}}}, mHandler);traceLog.traceEnd(); // ActivityManagerStartAppstraceLog.traceEnd(); // PhaseActivityManagerReady}
}

  调用ActivityTaskManagerInternal类型的接口startHomeOnAllDisplays，这个接口ActivityTaskManagerService.java文件中实现。

// android/frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
final class LocalService extends ActivityTaskManagerInternal {@Overridepublic boolean startHomeOnAllDisplays(int userId, String reason) {synchronized (mGlobalLock) {// 这个对象是RootActivityContainer类型return mRootActivityContainer.startHomeOnAllDisplays(userId, reason);}}
}

  接下来调用RootActivityContainer的接口startHomeOnAllDisplays，第二个参数reson的值为“systemReady”。

// frameworks/base/services/core/java/com/android/server/wm/RootActivityContainer.java
boolean startHomeOnAllDisplays(int userId, String reason) {boolean homeStarted = false;for (int i = mActivityDisplays.size() - 1; i >= 0; i--) {final int displayId = mActivityDisplays.get(i).mDisplayId;homeStarted |= startHomeOnDisplay(userId, reason, displayId);}return homeStarted;
}

  遍历mActivityDisplays对于所有处于Active状态的Display调用startHomeOnDisplay，在每个Display上都启动Home（Launcher）。

boolean startHomeOnDisplay(int userId, String reason, int displayId) {// allowInstrumenting ：false// fromHomeKey : falsereturn startHomeOnDisplay(userId, reason, displayId, false /* allowInstrumenting */,false /* fromHomeKey */);
}boolean startHomeOnDisplay(int userId, String reason, int displayId, boolean allowInstrumenting,boolean fromHomeKey) {// 如果DisplayID是非法的，使用当前处于顶层焦点的 Display// Fallback to top focused display if the displayId is invalid.if (displayId == INVALID_DISPLAY) {displayId = getTopDisplayFocusedStack().mDisplayId;}// 构建一个IntentIntent homeIntent = null;ActivityInfo aInfo = null;if (displayId == DEFAULT_DISPLAY) {// 如果DisplayID是默认的Display（一般是主屏）// 调用ActivityTaskManagerService的getHomeIntent，拿到用来启动Home的IntenthomeIntent = mService.getHomeIntent();// 查找当前系统里包含 android.intent.category.HOME的Activity。// 择优选择使用哪个ActivityaInfo = resolveHomeActivity(userId, homeIntent);} else if (shouldPlaceSecondaryHomeOnDisplay(displayId)) {// 如果不是默认Display屏幕Pair<ActivityInfo, Intent> info = resolveSecondaryHomeActivity(userId, displayId);aInfo = info.first;homeIntent = info.second;}if (aInfo == null || homeIntent == null) {return false;}// 判断是否运行启动Homeif (!canStartHomeOnDisplay(aInfo, displayId, allowInstrumenting)) {return false;}// 更新Home Intent// Updates the home component of the intent.homeIntent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));homeIntent.setFlags(homeIntent.getFlags() | FLAG_ACTIVITY_NEW_TASK);// 如果是从HomeKey启动的，添加额外参数、// Updates the extra information of the intent.if (fromHomeKey) {homeIntent.putExtra(WindowManagerPolicy.EXTRA_FROM_HOME_KEY, true);}// Update the reason for ANR debugging to verify if the user activity is the one that// actually launched.final String myReason = reason + ":" + userId + ":" + UserHandle.getUserId(aInfo.applicationInfo.uid) + ":" + displayId;// 启动HomemService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,displayId);return true;
}

  startHomeOnDisplay函数中查询当前系统中包含 android.intent.category.HOME信息的Activity(resolveHomeActivity)，如果找到了多个Activity则选择高优先级的。根据查找的Activity信息构建Intent，使用ActivityTaskManagerService的ActivityStartController启动Home对应的Activity。
  getHomeIntent函数在ActivityTaskManagerService中实现。

// frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
Intent getHomeIntent() {// String mTopAction = Intent.ACTION_MAIN;Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);intent.setComponent(mTopComponent);intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {// 非FactoryTest模式下走这里。// android.intent.category.HOMEintent.addCategory(Intent.CATEGORY_HOME);}return intent;
}

  resolveHomeActivity函数用于查找包含android.intent.category.HOME信息的Activity。实现上是通过PMS完成的。

// frameworks/base/services/core/java/com/android/server/wm/RootActivityContainer.java
/*** This resolves the home activity info.* @return the home activity info if any.*/
@VisibleForTesting
ActivityInfo resolveHomeActivity(int userId, Intent homeIntent) {final ComponentName comp = homeIntent.getComponent();try {if (comp != null) {// Factory test.} else {final String resolvedType =homeIntent.resolveTypeIfNeeded(mService.mContext.getContentResolver());// 调用PMS查找信息final ResolveInfo info = AppGlobals.getPackageManager().resolveIntent(homeIntent, resolvedType, flags, userId);if (info != null) {aInfo = info.activityInfo;}}} catch (RemoteException e) {// ignore}aInfo = new ActivityInfo(aInfo);aInfo.applicationInfo = mService.getAppInfoForUser(aInfo.applicationInfo, userId);return aInfo;
}

  当找到所需信息后，调用ActivityStartController的startHomeActivity启动Home。该接口与AMS的startActivity和startActivityAsUser实现上基本原理一样，都是通过Intent启动Activity（fork一个进程出来）。

// frameworks/base/services/core/java/com/android/server/wm/ActivityStartController.java
void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason, int displayId) {final ActivityOptions options = ActivityOptions.makeBasic();options.setLaunchWindowingMode(WINDOWING_MODE_FULLSCREEN);if (!ActivityRecord.isResolverActivity(aInfo.name)) {// The resolver activity shouldn't be put in home stack because when the foreground is// standard type activity, the resolver activity should be put on the top of current// foreground instead of bring home stack to front.options.setLaunchActivityType(ACTIVITY_TYPE_HOME);}options.setLaunchDisplayId(displayId);// 启动ActivitymLastHomeActivityStartResult = obtainStarter(intent, "startHomeActivity: " + reason).setOutActivity(tmpOutRecord).setCallingUid(0).setActivityInfo(aInfo).setActivityOptions(options.toBundle()).execute();mLastHomeActivityStartRecord = tmpOutRecord[0];final ActivityDisplay display =mService.mRootActivityContainer.getActivityDisplay(displayId);final ActivityStack homeStack = display != null ? display.getHomeStack() : null;if (homeStack != null && homeStack.mInResumeTopActivity) {// If we are in resume section already, home activity will be initialized, but not// resumed (to avoid recursive resume) and will stay that way until something pokes it// again. We need to schedule another resume.mSupervisor.scheduleResumeTopActivities();}
}

三、短压Home键启动Launcher

3.1、短压Home键启动Launcher流程图

在这里插入图片描述

3.2、短压Home键启动Launcher源码分析

  短压与长按区分，点一下Home键就属于短压。短压Home键后，Android会启动Home。

// frameworks/base/services/core/java/com/android/server/input/InputManagerService.java// Native callback.
private long interceptKeyBeforeDispatching(IBinder focus, KeyEvent event, int policyFlags) {// native层的 inputservice，通过这个接口上报回调return mWindowManagerCallbacks.interceptKeyBeforeDispatching(focus, event, policyFlags);
}

// frameworks/base/services/core/java/com/android/server/wm/InputManagerCallback.java
/**
Provides an opportunity for the window manager policy to process a key before
ordinary dispatch.
*/
@Override
public long interceptKeyBeforeDispatching(IBinder focus, KeyEvent event, int policyFlags) {WindowState windowState = mService.windowForClientLocked(null, focus, false);return mService.mPolicy.interceptKeyBeforeDispatching(windowState, event, policyFlags);
}

  mService是WindowManagerService类型，WindowManagerService中的mPolicy是PhoneWindowManager。PhoneWindowManager作为WMS的Policy配置文件，专门用来处理与UI行为有关的事件。PhoneWindowManager会拦截HomeKey事件进行相应处理后选择不再派发Home（PhoneWindowManager处理完就不需要其他人处理了），或者继续派发HomeKey给当前焦点View。

// frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
private long interceptKeyBeforeDispatchingInner(WindowState win, KeyEvent event,int policyFlags) {final boolean keyguardOn = keyguardOn();final int keyCode = event.getKeyCode();final int repeatCount = event.getRepeatCount();final int metaState = event.getMetaState();final int flags = event.getFlags();final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;final boolean canceled = event.isCanceled();final int displayId = event.getDisplayId();// First we always handle the home key here, so applications// can never break it, although if keyguard is on, we do let// it handle it, because that gives us the correct 5 second// timeout.if (keyCode == KeyEvent.KEYCODE_HOME) {// 处理HomeKeyDisplayHomeButtonHandler handler = mDisplayHomeButtonHandlers.get(displayId);if (handler == null) {handler = new DisplayHomeButtonHandler(displayId);mDisplayHomeButtonHandlers.put(displayId, handler);}return handler.handleHomeButton(win, event);} else if (keyCode == KeyEvent.KEYCODE_MENU) {// 省略}
}/** A handler to handle home keys per display */
private class DisplayHomeButtonHandler {int handleHomeButton(WindowState win, KeyEvent event) {final boolean keyguardOn = keyguardOn();final int repeatCount = event.getRepeatCount();final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;final boolean canceled = event.isCanceled();// If we have released the home key, and didn't do anything else// while it was pressed, then it is time to go home!if (!down) {// 省略// Post to main thread to avoid blocking input pipeline.// 处理短压HomemHandler.post(() -> handleShortPressOnHome(mDisplayId));return -1;}// 省略return -1;}
}private void handleShortPressOnHome(int displayId) {// Turn on the connected TV and switch HDMI input if we're a HDMI playback device.final HdmiControl hdmiControl = getHdmiControl();if (hdmiControl != null) {hdmiControl.turnOnTv();}// If there's a dream running then use home to escape the dream// but don't actually go home.if (mDreamManagerInternal != null && mDreamManagerInternal.isDreaming()) {mDreamManagerInternal.stopDream(false /*immediate*/);return;}// 启动Home// Go home!launchHomeFromHotKey(displayId);
}

  PhoneWindowManager针对每个Display创建一个DisplayHomeButtonHandler ，通过它处理HomeKey。在启动Home期间如果开始了dream模式（类似于屏保），会先退出dream。最后调用launchHomeFromHotKey来启动Home，后续流程基本上与Home开机启动一致了。

四、Launcher异常崩溃后的自启动

4.1、Launcher异常崩溃后的自启动流程图

在这里插入图片描述

4.2、Launcher异常崩溃后的自启动源码分析

  Launcher意外退出（比如崩溃了）时，会触发AMS的forceStopPackage。AMS会再次将Home拉起。

//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
@Override
public void forceStopPackage(final String packageName, int userId) {try {IPackageManager pm = AppGlobals.getPackageManager();synchronized(this) {int[] users = userId == UserHandle.USER_ALL? mUserController.getUsers() : new int[] { userId };for (int user : users) {if (mUserController.isUserRunning(user, 0)) {// 对每个运行的User，停掉 packageName对应的应用forceStopPackageLocked(packageName, pkgUid, "from pid " + callingPid);finishForceStopPackageLocked(packageName, pkgUid);}}}} finally {Binder.restoreCallingIdentity(callingId);}
}

  forceStopPackageLocked函数中，会先Kill掉应用对应的进程。然后 resume focused app，在resume的过程中会拉起Home。

//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
@GuardedBy("this")
final boolean forceStopPackageLocked(String packageName, int appId,boolean callerWillRestart, boolean purgeCache, boolean doit,boolean evenPersistent, boolean uninstalling, int userId, String reason) {// kill进程boolean didSomething = mProcessList.killPackageProcessesLocked(packageName, appId, userId,ProcessList.INVALID_ADJ, callerWillRestart, true /* allowRestart /, doit,
*                        evenPersistent, true /* setRemoved */,packageName == null ? ("stop user " + userId) : ("stop " + packageName));if (doit) {if (purgeCache && packageName != null) {AttributeCache ac = AttributeCache.instance();if (ac != null) {ac.removePackage(packageName);}}if (mBooted) {// resume focused app// 通过这个函数重新拉起HomemAtmInternal.resumeTopActivities(true /* scheduleIdle */);}}return didSomething;
}

  调用ActivityTaskManagerServiced的resumeTopActivities函数。在 Home崩溃的情况下，调用这个函数，可以保证Home重新被拉起（这个函数最终会调用到RootActivityContainer 的resumeHomeActivity函数。感兴趣的可以继续顺着代码往下看）

//frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
@Override
public void resumeTopActivities(boolean scheduleIdle) {synchronized (mGlobalLock) {mRootActivityContainer.resumeFocusedStacksTopActivities();if (scheduleIdle) {mStackSupervisor.scheduleIdleLocked();}}
}

// frameworks/base/services/core/java/com/android/server/wm/RootActivityContainer.java
boolean resumeFocusedStacksTopActivities(ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {// 省略if (!resumedOnDisplay) {// In cases when there are no valid activities (e.g. device just booted or launcher// crashed) it's possible that nothing was resumed on a display. Requesting resume// of top activity in focused stack explicitly will make sure that at least home// activity is started and resumed, and no recursion occurs.final ActivityStack focusedStack = display.getFocusedStack();if (focusedStack != null) {focusedStack.resumeTopActivityUncheckedLocked(target, targetOptions);}}}return result;
}

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1、在pom中，将打包类型改为war <packaging>war</packaging> 2、pom中排除SpringBoot内置的Tomcat容器并添加Tomcat依赖，用于编译和测试,         *依赖时一定设置 scope 为 provided （相当于 tomcat 依赖只在本地运行和测试的时候有效，         打包的时候会排除这个依赖）<scope>provided
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Android实现任意版本设置默认的锁屏壁纸和桌面壁纸（两张壁纸可不一致）

Android实现任意版本设置默认的锁屏壁纸和桌面壁纸（两张壁纸可不一致）

客户有些需求需要设置默认壁纸和锁屏壁纸  在默认情况下 这两个壁纸是相同的  如果需要默认的锁屏壁纸和桌面壁纸不一样 需要额外修改 Android13实现 替换默认桌面壁纸： 将图片文件替换frameworks/base/core/res/res/drawable-nodpi/default_wallpaper.*  （注意不能是bmp格式） 替换默认锁屏壁纸： 将图片资源放入vendo
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内核启动时减少log的方式

内核启动时减少log的方式

内核引导选项 内核引导选项大体上可以分为两类：一类与设备无关、另一类与设备有关。与设备有关的引导选项多如牛毛，需要你自己阅读内核中的相应驱动程序源码以获取其能够接受的引导选项。比如，如果你想知道可以向 AHA1542 SCSI 驱动程序传递哪些引导选项，那么就查看 drivers/scsi/aha1542.c 文件，一般在前面 100 行注释里就可以找到所接受的引导选项说明。大多数选项是通过"_
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Android平台播放RTSP流的几种方案探究（VLC VS ExoPlayer VS SmartPlayer）

Android平台播放RTSP流的几种方案探究（VLC VS ExoPlayer VS SmartPlayer）

技术背景 好多开发者需要遴选Android平台RTSP直播播放器的时候，不知道如何选的好，本文针对常用的方案，做个大概的说明： 1. 使用VLC for Android VLC Media Player（VLC多媒体播放器），最初命名为VideoLAN客户端，是VideoLAN品牌产品，是VideoLAN计划的多媒体播放器。它支持众多音频与视频解码器及文件格式，并支持DVD影音光盘，VCD影
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Java ArrayList扩容机制 （源码解读）

Java ArrayList扩容机制 （源码解读）

结论：初始长度为10，若所需长度小于1.5倍原长度，则按照1.5倍扩容。若不够用则按照所需长度扩容。 一. 明确类内部重要变量含义         1：数组默认长度         2:这是一个共享的空数组实例，用于明确创建长度为0时的ArrayList ，比如通过 new ArrayList<>(0)，ArrayList 内部的数组 elementData 会指向这个 EMPTY_EL
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如何在Visual Studio中调试.NET源码

如何在Visual Studio中调试.NET源码

今天偶然在看别人代码时，发现在他的代码里使用了Any判断List<T>是否为空。 我一般的做法是先判断是否为null，再判断Count。 看了一下Count的源码如下： 1 [__DynamicallyInvokable]2 public int Count3 {4 [__DynamicallyInvokable]5 get
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