launcher其实也是一个app，主要功能是对手机上安装的所有APP以及小部件，文件夹，快捷方式等等一个管理，在AndroidManifest文件配置上比其他app多了一个“<category android:name="android.intent.category.HOME" />”属性，在启动系统或者按Home键时会过滤这个属性，一般手机系统中只有一个应用具有这个属性，所以启动后会直接跳转到这个界面，也就是这个launcher。如果开发launcher应用，运行代码后手机系统会让用户做出选择。下面主要分析一下launcher启动过程中涉及到的主要操作。过程分析是基于Android 28 API的。我们知道再Android系统服务初始化过程中会调用ActivityManagerService.systemReady方法
public class ActivityManagerService extends IActivityManager.Stub
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
.....
synchronized (this) {
....
startHomeActivityLocked(currentUserId, "systemReady");
....
}
}
boolean startHomeActivityLocked(int userId, String reason) {
if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL
&& mTopAction == null) {
// We are running in factory test mode, but unable to find
// the factory test app, so just sit around displaying the
// error message and don't try to start anything.
return false;
}
Intent intent = getHomeIntent();
ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
if (aInfo != null) {
intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
// Don't do this if the home app is currently being
// instrumented.
aInfo = new ActivityInfo(aInfo);
aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);
ProcessRecord app = getProcessRecordLocked(aInfo.processName,
aInfo.applicationInfo.uid, true);
if (app == null || app.instr == null) {
intent.setFlags(intent.getFlags() | FLAG_ACTIVITY_NEW_TASK);
final int resolvedUserId = UserHandle.getUserId(aInfo.applicationInfo.uid);
// For ANR debugging to verify if the user activity is the one that actually
// launched.
final String myReason = reason + ":" + userId + ":" + resolvedUserId;
mActivityStartController.startHomeActivity(intent, aInfo, myReason);
}
} else {
Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());
}
return true;
}
Intent getHomeIntent() {
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) {
intent.addCategory(Intent.CATEGORY_HOME);
}
return intent;
}
}
systemReady方法里面会调用startHomeActivityLocked方法，startHomeActivityLocked首先创建一个CATEGORY_HOME类型的Intent，然后通过Intent.resolveActivityInfo函数向PackageManagerService查询Category类型为HOME的Activity，如果不为空,则startHomeActivity,调用这个函数的最后结果就是把com.android.launcher3.Launcher启动起来.
public class Launcher extends BaseDraggingActivity implements LauncherExterns,
Callbacks, LauncherProviderChangeListener, UserEventDelegate,
InvariantDeviceProfile.OnIDPChangeListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
.....
if (!mModel.startLoader(currentScreen)) {
if (!internalStateHandled) {
// If we are not binding synchronously, show a fade in animation when
// the first page bind completes.
mDragLayer.getAlphaProperty(ALPHA_INDEX_LAUNCHER_LOAD).setValue(0);
}
} else {
// Pages bound synchronously.
mWorkspace.setCurrentPage(currentScreen);
setWorkspaceLoading(true);
}
.....
}
}
这里的mModel是一个LauncherModel类型的成员变量，这里通过调用它的startLoader成员函数来执行加载应用数据的操作。
public class LauncherModel extends BroadcastReceiver
implements LauncherAppsCompat.OnAppsChangedCallbackCompat {
public boolean startLoader(int synchronousBindPage) {
// Enable queue before starting loader. It will get disabled in Launcher#finishBindingItems
InstallShortcutReceiver.enableInstallQueue(InstallShortcutReceiver.FLAG_LOADER_RUNNING);
synchronized (mLock) {
// Don't bother to start the thread if we know it's not going to do anything
if (mCallbacks != null && mCallbacks.get() != null) {
final Callbacks oldCallbacks = mCallbacks.get();
// Clear any pending bind-runnables from the synchronized load process.
MAIN_EXECUTOR.execute(oldCallbacks::clearPendingBinds);
// If there is already one running, tell it to stop.
stopLoader();
LoaderResults loaderResults = new LoaderResults(mApp, sBgDataModel,
mBgAllAppsList, synchronousBindPage, mCallbacks);
if (mModelLoaded && !mIsLoaderTaskRunning) {
// Divide the set of loaded items into those that we are binding synchronously,
// and everything else that is to be bound normally (asynchronously).
loaderResults.bindWorkspace();
// For now, continue posting the binding of AllApps as there are other
// issues that arise from that.
loaderResults.bindAllApps();
loaderResults.bindDeepShortcuts();
loaderResults.bindWidgets();
return true;
} else {
startLoaderForResults(loaderResults);
}
}
}
return false;
}
public void startLoaderForResults(LoaderResults results) {
synchronized (mLock) {
stopLoader();
mLoaderTask = new LoaderTask(mApp, mBgAllAppsList, sBgDataModel, results);
// Always post the loader task, instead of running directly (even on same thread) so
// that we exit any nested synchronized blocks
MODEL_EXECUTOR.post(mLoaderTask);
}
}
}
首次启动时mModelLoaded为false，所以会走startLoaderForResults，接着新建一个LoaderTask任务，LoaderTask实现了Runnable这个接口，执行run方法，我们看一下这个run方法里面做了哪些事情，
public class LoaderTask implements Runnable {
public void run() {
synchronized (this) {
// Skip fast if we are already stopped.
if (mStopped) {
return;
}
}
TraceHelper.beginSection(TAG);
try (LauncherModel.LoaderTransaction transaction = mApp.getModel().beginLoader(this)) {
TraceHelper.partitionSection(TAG, "step 1.1: loading workspace");
loadWorkspace();
verifyNotStopped();
TraceHelper.partitionSection(TAG, "step 1.2: bind workspace workspace");
mResults.bindWorkspace();
// Notify the installer packages of packages with active installs on the first screen.
TraceHelper.partitionSection(TAG, "step 1.3: send first screen broadcast");
sendFirstScreenActiveInstallsBroadcast();
// Take a break
TraceHelper.partitionSection(TAG, "step 1 completed, wait for idle");
waitForIdle();
verifyNotStopped();
// second step
TraceHelper.partitionSection(TAG, "step 2.1: loading all apps");
List<LauncherActivityInfo> allActivityList = loadAllApps();
TraceHelper.partitionSection(TAG, "step 2.2: Binding all apps");
verifyNotStopped();
mResults.bindAllApps();
verifyNotStopped();
TraceHelper.partitionSection(TAG, "step 2.3: Update icon cache");
IconCacheUpdateHandler updateHandler = mIconCache.getUpdateHandler();
setIgnorePackages(updateHandler);
updateHandler.updateIcons(allActivityList,
LauncherActivityCachingLogic.newInstance(mApp.getContext()),
mApp.getModel()::onPackageIconsUpdated);
// Take a break
TraceHelper.partitionSection(TAG, "step 2 completed, wait for idle");
waitForIdle();
verifyNotStopped();
// third step
TraceHelper.partitionSection(TAG, "step 3.1: loading deep shortcuts");
loadDeepShortcuts();
verifyNotStopped();
TraceHelper.partitionSection(TAG, "step 3.2: bind deep shortcuts");
mResults.bindDeepShortcuts();
// Take a break
TraceHelper.partitionSection(TAG, "step 3 completed, wait for idle");
waitForIdle();
verifyNotStopped();
// fourth step
TraceHelper.partitionSection(TAG, "step 4.1: loading widgets");
List<ComponentWithLabel> allWidgetsList = mBgDataModel.widgetsModel.update(mApp, null);
verifyNotStopped();
TraceHelper.partitionSection(TAG, "step 4.2: Binding widgets");
mResults.bindWidgets();
verifyNotStopped();
TraceHelper.partitionSection(TAG, "step 4.3: save widgets in icon cache");
updateHandler.updateIcons(allWidgetsList, new ComponentCachingLogic(
mApp.getContext(), true), mApp.getModel()::onWidgetLabelsUpdated);
verifyNotStopped();
TraceHelper.partitionSection(TAG, "step 5: Finish icon cache update");
updateHandler.finish();
transaction.commit();
} catch (CancellationException e) {
// Loader stopped, ignore
TraceHelper.partitionSection(TAG, "Cancelled");
}
TraceHelper.endSection(TAG);
}
}
从代码中可以清晰的看到每一步操作所要做的工作。loadWorkspace和bindWorkspace，也就是加载workspace的应用并且进行绑定，waitForIdle方法主要是等待加载数据结束。sendFirstScreenActiveInstallsBroadcast发送首屏广播。loadAllApps和bindAllApps加载并绑定所有的APP信息，loadDeepShortcuts和bindDeepShortcuts加载并绑定所有的快捷方式，然后加载并绑定所有的小部件。至此launcher数据加载基本就完成了。
