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目录

Android之zygote源码剖析（一）
Android之zygote源码剖析（二）
Android之zygote源码剖析（三）
Android之SystemServer介绍（一）
Android之SystemServer介绍（二）
Android之Launcher介绍（一）
Android之Launcher介绍（二）

Launcher启动

在SystemServer类中会调用startOtherServices函数:

    private void startOtherServices() {
        ……
        mActivityManagerService.systemReady(() -> {
            Slog.i(TAG, "Making services ready");
            traceBeginAndSlog("StartActivityManagerReadyPhase");
            mSystemServiceManager.startBootPhase(
                    SystemService.PHASE_ACTIVITY_MANAGER_READY);
            traceEnd();
            traceBeginAndSlog("StartObservingNativeCrashes");
            try {
                mActivityManagerService.startObservingNativeCrashes();
            } catch (Throwable e) {
                reportWtf("observing native crashes", e);
            }
            ……
        }, BOOT_TIMINGS_TRACE_LOG);
    }

其中启动了很多的服务，主要关注下执行的mActivityManagerService.systemReady（），其中
mActivityManagerService是ActivityManagerService服务。

        mActivityManagerService = mSystemServiceManager.startService(
                ActivityManagerService.Lifecycle.class).getService();

这个写法是java的Lambda表达式。

进入systemReady(ActivityManagerService.java
)看一下：

    public void systemReady(final Runnable goingCallback, BootTimingsTraceLog traceLog) {
        traceLog.traceBegin("PhaseActivityManagerReady");
         ……

        synchronized (this) {
            ……
            mStackSupervisor.resumeFocusedStackTopActivityLocked();
            mUserController.sendUserSwitchBroadcastsLocked(-1, currentUserId);
            ……
        }
    }

resumeFocusedStackTopActivityLocked函数位于ActivityStackSupervisor.java
中，ActivityStackSupervisor.java
类主要用来管理ActivityStack的：

    boolean resumeFocusedStackTopActivityLocked() {
        return resumeFocusedStackTopActivityLocked(null, null, null);
    }

    boolean resumeFocusedStackTopActivityLocked(
            ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
        if (targetStack != null && isFocusedStack(targetStack)) {
            return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
        }
        final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
        if (r == null || r.state != RESUMED) {
            mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
        } else if (r.state == RESUMED) {
            // Kick off any lingering app transitions form the MoveTaskToFront operation.
            mFocusedStack.executeAppTransition(targetOptions);
        }
        return false;
    }

函数中只要执行了ActivityStack.java
中的resumeTopActivityUncheckedLocked函数：

    boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
        ……

        boolean result = false;
        try {
            mStackSupervisor.inResumeTopActivity = true;
            result = resumeTopActivityInnerLocked(prev, options);
        } finally {
            mStackSupervisor.inResumeTopActivity = false;
        }

        mStackSupervisor.checkReadyForSleepLocked();

        return result;
    }

其中又调用了ActivityStack.java的resumeTopActivityInnerLocked函数：

    private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
        ……

        return isOnHomeDisplay() &&
                        mStackSupervisor.resumeHomeStackTask(prev, "prevFinished");
        ……

    }

其中又回调到ActivityStackSupervisor.java
的resumeHomeStackTask函数：

    boolean resumeHomeStackTask(ActivityRecord prev, String reason) {
        if (!mService.mBooting && !mService.mBooted) {
            // Not ready yet!
            return false;
        }

        if (prev != null) {
            prev.getTask().setTaskToReturnTo(APPLICATION_ACTIVITY_TYPE);
        }

        mHomeStack.moveHomeStackTaskToTop();
        ActivityRecord r = getHomeActivity();
        final String myReason = reason + " resumeHomeStackTask";

        // Only resume home activity if isn't finishing.
        if (r != null && !r.finishing) {
            moveFocusableActivityStackToFrontLocked(r, myReason);
            return resumeFocusedStackTopActivityLocked(mHomeStack, prev, null);
        }
        return mService.startHomeActivityLocked(mCurrentUser, myReason);
    }

函数最后会调用mService的startHomeActivityLocked函数。

这个mService就是ActivityManagerService自身。

继续来看下startHomeActivityLocked函数：

    boolean startHomeActivityLocked(int userId, String reason) {
        // 判断是否是工厂模式和mTopAction是否存在
        if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL
                && mTopAction == null) {
            return false;
        }

        //  获取home intent（launcher）
        Intent intent = getHomeIntent();
        ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
        if (aInfo != null) {
            intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));

            aInfo = new ActivityInfo(aInfo);
            aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);
            ProcessRecord app = getProcessRecordLocked(aInfo.processName,
                    aInfo.applicationInfo.uid, true);
            // 如果当前launcher还没有启动就开始启动
            if (app == null || app.instr == null) {
                intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
                final int resolvedUserId = UserHandle.getUserId(aInfo.applicationInfo.uid);
         
                final String myReason = reason + ":" + userId + ":" + resolvedUserId;
                // 启动launcher
                mActivityStarter.startHomeActivityLocked(intent, aInfo, myReason);
            }
        } else {
            Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());
        }

        return true;
    }

getHomeIntent函数如下：

    Intent getHomeIntent() {
        // 根据传入的mTopAction数据生成intent
        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) {
            // 添加匹配为CATEGORY_HOME
            intent.addCategory(Intent.CATEGORY_HOME);
        }
        return intent;
    }

最终确定是启动Launcher是通过Intent.CATEGORY_HOME来匹配的。

AndroidManifest.xml文件中定义：

      <activity
            android:name="com.android.launcher3.Launcher"
            android:launchMode="singleTask"
            android:clearTaskOnLaunch="true"
            android:stateNotNeeded="true"
            android:windowSoftInputMode="adjustPan|stateUnchanged"
            android:screenOrientation="nosensor"
            android:configChanges="keyboard|keyboardHidden|navigation"
            android:resizeableActivity="true"
            android:resumeWhilePausing="true"
            android:taskAffinity=""
            android:enabled="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.HOME" />
                <category android:name="android.intent.category.DEFAULT" />
                <category android:name="android.intent.category.MONKEY"/>
            </intent-filter>
        </activity>

其中的android.intent.category.HOME和上面的代码相互对应。

这样就启动了Launcher了。^_

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