本文参考的源码(7.1.1_r6)

Launcher也是一个应用程序，和我们的App没有什么区别，当用户点击应用图标时候，启动其他的App，本文主要为分析Activity的启动流程打基础。

Launcher.java代码量比较多，大约4500多行，但是里面的逻辑并不复杂，不过我这里分析它的意义主要为了更好理解后面的知识，了解Launcher具体的流程才是重要的，不要沉迷代码中无法自拔！

先来张图：

在线源码地址

分析

先看下它的manifest文件，这里面的内容不多，Launcher类是一个Activity，只是比我们普通的app多一个

xmlns:android="http://schemas.android.com/apk/res/android"

package="com.android.launcher3">

android:name="com.android.launcher3.permission.READ_SETTINGS"

android:permissionGroup="android.permission-group.SYSTEM_TOOLS"

android:protectionLevel="normal"

android:label="@string/permlab_read_settings"

android:description="@string/permdesc_read_settings"/>

android:name="com.android.launcher3.permission.WRITE_SETTINGS"

android:permissionGroup="android.permission-group.SYSTEM_TOOLS"

android:protectionLevel="signatureOrSystem"

android:label="@string/permlab_write_settings"

android:description="@string/permdesc_write_settings"/>

android:backupAgent="com.android.launcher3.LauncherBackupAgent"

android:fullBackupOnly="true"

android:fullBackupContent="@xml/backupscheme"

android:hardwareAccelerated="true"

android:icon="@mipmap/ic_launcher_home"

android:label="@string/derived_app_name"

android:largeHeap="@bool/config_largeHeap"

android:restoreAnyVersion="true"

android:supportsRtl="true" >

android:name="com.android.launcher3.Launcher"

android:launchMode="singleTask"

android:clearTaskOnLaunch="true"

android:stateNotNeeded="true"

android:theme="@style/LauncherTheme"

android:windowSoftInputMode="adjustPan"

android:screenOrientation="nosensor"

android:configChanges="keyboard|keyboardHidden|navigation"

android:resumeWhilePausing="true"

android:taskAffinity=""

android:enabled="true">

android:name="com.android.launcher3.SettingsActivity"

android:label="@string/settings_button_text"

android:autoRemoveFromRecents="true">

android:name="com.android.launcher3.LauncherProvider"

android:authorities="com.android.launcher3.settings"

android:exported="true"

android:writePermission="com.android.launcher3.permission.WRITE_SETTINGS"

android:readPermission="com.android.launcher3.permission.READ_SETTINGS" />

为了研究方便，删除了大量代码，完整的请查阅源码。

先查看onCreate方法

class Launcher {

AllAppsContainerView mAppsView;// 桌面app的布局(重要)

@Override

protected void onCreate(Bundle savedInstanceState) {

// 省略.....

if (mLauncherCallbacks != null) {

mLauncherCallbacks.preOnCreate();

}

super.onCreate(savedInstanceState);

LauncherAppState app = LauncherAppState.getInstance();

mModel = app.setLauncher(this);

setContentView(R.layout.launcher);

setupViews();

lockAllApps();

// We only load the page synchronously if the user rotates (or triggers a

// configuration change) while launcher is in the foreground

if (!mModel.startLoader(mWorkspace.getRestorePage())) {

// If we are not binding synchronously, show a fade in animation when

// the first page bind completes.

mDragLayer.setAlpha(0);

} else {

setWorkspaceLoading(true);

}

// On large interfaces, or on devices that a user has specifically enabled screen rotation,

// we want the screen to auto-rotate based on the current orientation

setOrientation();

}

}

跟踪mModel.startLoader() 方法，mModel是一个LauncherModel类，

class LauncherModel extends BroadcastReceiver

这个类是一个BroadcastReceiver，但是没有发现在Manifest中注册，注意上面的 app.setLauncher(this)方法，是的，它是在LauncherAppState 里面动态注册的

class LauncherAppState {

private LauncherAppState() {

// .....................

// Register intent receivers

IntentFilter filter = new IntentFilter();

filter.addAction(Intent.ACTION_LOCALE_CHANGED);

// For handling managed profiles

filter.addAction(Intent.ACTION_MANAGED_PROFILE_ADDED);

filter.addAction(Intent.ACTION_MANAGED_PROFILE_REMOVED);

filter.addAction(Intent.ACTION_MANAGED_PROFILE_AVAILABLE);

filter.addAction(Intent.ACTION_MANAGED_PROFILE_UNAVAILABLE);

filter.addAction(Intent.ACTION_MANAGED_PROFILE_UNLOCKED);

// For extracting colors from the wallpaper

if (Utilities.isNycOrAbove()) {

// TODO: add a broadcast entry to the manifest for pre-N.

filter.addAction(Intent.ACTION_WALLPAPER_CHANGED);

}

sContext.registerReceiver(mModel, filter);

}

}

这个不是重点，继续追踪mModel.startLoader()方法。

public boolean startLoader(int synchronousBindPage) {

// Enable queue before starting loader. It will get disabled in Launcher#finishBindingItems

InstallShortcutReceiver.enableInstallQueue();

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.

runOnMainThread(new Runnable() {

public void run() {

oldCallbacks.clearPendingBinds();

}

});

// If there is already one running, tell it to stop.

stopLoaderLocked();

mLoaderTask = new LoaderTask(mApp.getContext(), synchronousBindPage);

// TODO: mDeepShortcutsLoaded does not need to be true for synchronous bind.

if (synchronousBindPage != PagedView.INVALID_RESTORE_PAGE && mAllAppsLoaded

&& mWorkspaceLoaded && mDeepShortcutsLoaded && !mIsLoaderTaskRunning) {

mLoaderTask.runBindSynchronousPage(synchronousBindPage);

return true;

} else {

sWorkerThread.setPriority(Thread.NORM_PRIORITY);

sWorker.post(mLoaderTask);

}

}

}

return false;

}

该类中synchronized 块有个mLoaderTask = new LoaderTask();查看LoaderTask源码，发现LoaderTask是LauncherModel的内部类，而且是Runnable 类型，直接查看其run方法。

private class LoaderTask implements Runnable {

// .............

public void run() {

synchronized (mLock) {

if (mStopped) {

return;

}

mIsLoaderTaskRunning = true;

}

// Optimize for end-user experience: if the Launcher is up and // running with the

// All Apps interface in the foreground, load All Apps first. Otherwise, load the

// workspace first (default).

keep_running: {

if (DEBUG_LOADERS) Log.d(TAG, "step 1: loading workspace");

loadAndBindWorkspace();

if (mStopped) {

break keep_running;

}

waitForIdle();

// second step

if (DEBUG_LOADERS) Log.d(TAG, "step 2: loading all apps");

loadAndBindAllApps();

waitForIdle();

// third step

if (DEBUG_LOADERS) Log.d(TAG, "step 3: loading deep shortcuts");

loadAndBindDeepShortcuts();

}

// Clear out this reference, otherwise we end up holding it until all of the

// callback runnables are done.

mContext = null;

synchronized (mLock) {

// If we are still the last one to be scheduled, remove ourselves.

if (mLoaderTask == this) {

mLoaderTask = null;

}

mIsLoaderTaskRunning = false;

mHasLoaderCompletedOnce = true;

}

}

}

step 1: loading workspace

step 2: loading all apps

step 3: loading deep shortcuts

日志写的非常清楚，就是加载所有app，图标之类的。

private void loadAndBindAllApps() {

// ............ 略

loadAllApps();

}

下面逻辑是载入桌面所有app，并使用handler切换UI线程然后给所有应用bind回调函数。

private void loadAllApps() {

// ............ 略

mBgAllAppsList.clear();

for (UserHandleCompat user : profiles) {

// ............ 略

final List apps = mLauncherApps.getActivityList(null, user);

for (int i = 0; i < apps.size(); i++) {

LauncherActivityInfoCompat app = apps.get(i);

// This builds the icon bitmaps.

mBgAllAppsList.add(new AppInfo(mContext, app, user, mIconCache, quietMode));

}

// ............ 略

}

final ArrayList added = mBgAllAppsList.added;

callbacks.bindAllApplications(added);

mHandler.post(new Runnable() {

final Callbacks callbacks = tryGetCallbacks(oldCallbacks);

if (callbacks != null) {

callbacks.bindAllApplications(added);

}

}

}

Launcher的布局控件

我们最开始提到Launcher的一个成员变量，AllAppsContainerView，这个类是一个自定义ViewGroup，如下：

/**

* The all apps view container.

*/

public class AllAppsContainerView extends BaseContainerView implements DragSource,

LauncherTransitionable, View.OnLongClickListener, AllAppsSearchBarController.Callbacks {

private static final int MIN_ROWS_IN_MERGED_SECTION_PHONE = 3;

private static final int MAX_NUM_MERGES_PHONE = 2;

private final Launcher mLauncher;

private final AlphabeticalAppsList mApps;

private final AllAppsGridAdapter mAdapter;

private final RecyclerView.LayoutManager mLayoutManager;

private final RecyclerView.ItemDecoration mItemDecoration;

// The computed bounds of the container

private final Rect mContentBounds = new Rect();

private AllAppsRecyclerView mAppsRecyclerView;

其中BaseContainerView extends FrameLayout，比较简单。

我们看下它的成员变量-> AllAppsRecyclerView，这是个自定义的RecyclerView，说明它是用RecyclerView对桌面apps布局的。

查看AllAppsGridAdapter ，因为RecyclerView的事件监听 一般是在这里面设置的：

public AllAppsGridAdapter(Launcher launcher, AlphabeticalAppsList apps, View.OnClickListener

iconClickListener, View.OnLongClickListener iconLongClickListener) {

// 略 ..............

}

AllAppsGridAdapter的构造函数的参数和AllAppsContainerView的构造函数的方法体来次对比：

public AllAppsContainerView(Context context, AttributeSet attrs, int defStyleAttr) {

super(context, attrs, defStyleAttr);

// 略 ....

mLauncher = Launcher.getLauncher(context);

mApps = new AlphabeticalAppsList(context);

mAdapter = new AllAppsGridAdapter(mLauncher, mApps, mLauncher, this);

mApps.setAdapter(mAdapter);

}

惊喜发现-> AllAppsGridAdapter 构造函数的第三个参数是mLauncher，而且是View.OnClickListener类型。

再次回到Launcher，Launcher实现了 View.OnClickListener，直接找到

public void onClick(View v)方法，到这步就非常简单了，next->next->next...

这些步骤的代码就无须贴了，最终会执行到startActivity，即分析 Activity启动流程的重要入口。

onClick->onClickAppShortcut->startAppShortcutOrInfoActivity->startActivitySafely->startActivity