簡書 編程之樂
轉(zhuǎn)載請注明原創(chuàng)出處，謝謝！
本文參考的源碼（7.1.1_r6）
Launcher也是一個應(yīng)用程序，和我們的App沒有什么區(qū)別，當(dāng)用戶點擊應(yīng)用圖標(biāo)時候，啟動其他的App，本文主要為分析Activity的啟動流程打基礎(chǔ)。
Launcher.java代碼量比較多，大約4500多行，但是里面的邏輯并不復(fù)雜，不過我這里分析它的意義主要為了更好理解后面的知識，了解Launcher具體的流程才是重要的，不要沉迷代碼中無法自拔！
先來張圖：
Android7.0應(yīng)用啟動過程-Launcher源碼淺析
在線源碼地址
AndroidManifest.xml
Launcher.java
LauncherModel.java
AllAppsContainerView.java
分析
先看下它的manifest文件，這里面的內(nèi)容不多，Launcher類是一個Activity，只是比我們普通的app多一個
<category android:name="android.intent.category.HOME" />
<?xml version="1.0" encoding="utf-8"?>
<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
package="com.android.launcher3">
<uses-sdk android:targetSdkVersion="23" android:minSdkVersion="21"/>
<permission
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"/>
<permission
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"/>
<uses-permission android:name="com.android.launcher.permission.READ_SETTINGS" />
<uses-permission android:name="com.android.launcher.permission.WRITE_SETTINGS" />
<uses-permission android:name="com.android.launcher3.permission.READ_SETTINGS" />
<uses-permission android:name="com.android.launcher3.permission.WRITE_SETTINGS" />
<application
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" >
<activity
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">
<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>
<!--
The settings activity. When extending keep the intent filter present
-->
<activity
android:name="com.android.launcher3.SettingsActivity"
android:label="@string/settings_button_text"
android:autoRemoveFromRecents="true">
<intent-filter>
<action android:name="android.intent.action.APPLICATION_PREFERENCES" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<!--
The settings provider contains Home's data, like the workspace favorites. The permissions
should be changed to what is defined above. The authorities should also be changed to
represent the package name.
-->
<provider
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" />
</application>
</manifest>
為了研究方便，刪除了大量代碼，完整的請查閱源碼。
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();
}
}
跟蹤mModel.startLoader() 方法，mModel是一個LauncherModel類，
class LauncherModel extends BroadcastReceiver
這個類是一個BroadcastReceiver，但是沒有發(fā)現(xiàn)在Manifest中注冊，注意上面的 app.setLauncher(this)方法，是的，它是在LauncherAppState 里面動態(tài)注冊的
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);
}
}
這個不是重點，繼續(xù)追蹤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;
}
該類中synchronized 塊有個mLoaderTask = new LoaderTask();查看LoaderTask源碼，發(fā)現(xiàn)LoaderTask是LauncherModel的內(nèi)部類，而且是Runnable 類型，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
日志寫的非常清楚，就是加載所有app，圖標(biāo)之類的。
private void loadAndBindAllApps() {
// ............ 略
loadAllApps();
}
下面邏輯是載入桌面所有app，并使用handler切換UI線程然后給所有應(yīng)用bind回調(diào)函數(shù)。
private void loadAllApps() {
// ............ 略
mBgAllAppsList.clear();
for (UserHandleCompat user : profiles) {
// ............ 略
final List<LauncherActivityInfoCompat> 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<AppInfo> 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
我們最開始提到Launcher的一個成員變量，AllAppsContainerView，這個類是一個自定義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，比較簡單。
我們看下它的成員變量-> AllAppsRecyclerView，這是個自定義的RecyclerView，說明它是用RecyclerView對桌面apps布局的。
查看AllAppsGridAdapter ，因為RecyclerView的事件監(jiān)聽 一般是在這里面設(shè)置的：
public AllAppsGridAdapter(Launcher launcher, AlphabeticalAppsList apps, View.OnClickListener
iconClickListener, View.OnLongClickListener iconLongClickListener) {
// 略 ..............
}
AllAppsGridAdapter的構(gòu)造函數(shù)的參數(shù)和AllAppsContainerView的構(gòu)造函數(shù)的方法體來次對比：
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);
}
驚喜發(fā)現(xiàn)-> AllAppsGridAdapter 構(gòu)造函數(shù)的第三個參數(shù)是mLauncher，而且是View.OnClickListener類型。
再次回到Launcher，Launcher實現(xiàn)了 View.OnClickListener，直接找到
public void onClick(View v)方法，到這步就非常簡單了，next->next->next...
這些步驟的代碼就無須貼了，最終會執(zhí)行到startActivity，即分析 Activity啟動流程的重要入口。
onClick->onClickAppShortcut->startAppShortcutOrInfoActivity->startActivitySafely->startActivity
