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Android系统源码阅读（2）：根Activity组件的启动过程

2016-08-06 17:56 525 查看

Android系统源码阅读（2）：根Activity组件的启动过程

该系列只记录阅读代码时遇到的问题和心得体会，具体代码讲解可以参考老罗的《Android系统源代码情景分析》，我就不班门弄斧了。我编译的AOSP版本：6.0.1_r50。

Android系统源码阅读2根Activity组件的启动过程
代码摘抄
两个版本的Launcher

Android的Singleton模式的实现

ActivityManagerService

根Activity启动过程
Step1 Launcher启动一个APP

Step2 ActivityMangerService进行准备工作

Step3 旧Activity停止

Step4 ActivityMangerService继续准备

Step5 ActivityThread进程启动

Step6 ActivityMangerService继续启动

Step7 新Activity启动

代码摘抄

两个版本的Launcher

目前版本已经从Launcher2（packages/apps/Launcher2/src/com/android/launcher2）进化为Launcher3（packages/apps/Launcher3/src/com/android/launcher3）。两个版本的Launcher有着一定的差异，老罗书中以Launcher2为出发点。

packages/apps/Launcher2/src/com/android/launcher2/Launcher.java:

boolean startActivity(View v, Intent intent, Object tag) {
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

try {
// Only launch using the new animation if the shortcut has not opted out (this is a
// private contract between launcher and may be ignored in the future).
boolean useLaunchAnimation = (v != null) &&
!intent.hasExtra(INTENT_EXTRA_IGNORE_LAUNCH_ANIMATION);
UserHandle user = (UserHandle) intent.getParcelableExtra(ApplicationInfo.EXTRA_PROFILE);
LauncherApps launcherApps = (LauncherApps)
this.getSystemService(Context.LAUNCHER_APPS_SERVICE);
if (useLaunchAnimation) {
ActivityOptions opts = ActivityOptions.makeScaleUpAnimation(v, 0, 0,
v.getMeasuredWidth(), v.getMeasuredHeight());
if (user == null || user.equals(android.os.Process.myUserHandle())) {
// Could be launching some bookkeeping activity
startActivity(intent, opts.toBundle());
} else {
launcherApps.startMainActivity(intent.getComponent(), user,
intent.getSourceBounds(),
opts.toBundle());
}
} else {
if (user == null || user.equals(android.os.Process.myUserHandle())) {
startActivity(intent);
} else {
launcherApps.startMainActivity(intent.getComponent(), user,
intent.getSourceBounds(), null);
}
}
return true;
} catch (SecurityException e) {
Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();
Log.e(TAG, "Launcher does not have the permission to launch " + intent +
". Make sure to create a MAIN intent-filter for the corresponding activity " +
"or use the exported attribute for this activity. "
+ "tag="+ tag + " intent=" + intent, e);
}
return false;
}

boolean startActivitySafely(View v, Intent intent, Object tag) {
boolean success = false;
try {
success = startActivity(v, intent, tag);
} catch (ActivityNotFoundException e) {
Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();
Log.e(TAG, "Unable to launch. tag=" + tag + " intent=" + intent, e);
}
return success;
}

packages/apps/Launcher3/src/com/android/launcher3/Launcher.java:

private boolean startActivity(View v, Intent intent, Object tag) {
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
try {
// Only launch using the new animation if the shortcut has not opted out (this is a
// private contract between launcher and may be ignored in the future).
boolean useLaunchAnimation = (v != null) &&
!intent.hasExtra(INTENT_EXTRA_IGNORE_LAUNCH_ANIMATION);
LauncherAppsCompat launcherApps = LauncherAppsCompat.getInstance(this);
UserManagerCompat userManager = UserManagerCompat.getInstance(this);

UserHandleCompat user = null;
if (intent.hasExtra(AppInfo.EXTRA_PROFILE)) {
long serialNumber = intent.getLongExtra(AppInfo.EXTRA_PROFILE, -1);
user = userManager.getUserForSerialNumber(serialNumber);
}

Bundle optsBundle = null;
if (useLaunchAnimation) {
ActivityOptions opts = null;
if (Utilities.ATLEAST_MARSHMALLOW) {
int left = 0, top = 0;
int width = v.getMeasuredWidth(), height = v.getMeasuredHeight();
if (v instanceof TextView) {
// Launch from center of icon, not entire view
Drawable icon = Workspace.getTextViewIcon((TextView) v);
if (icon != null) {
Rect bounds = icon.getBounds();
left = (width - bounds.width()) / 2;
top = v.getPaddingTop();
width = bounds.width();
height = bounds.height();
}
}
opts = ActivityOptions.makeClipRevealAnimation(v, left, top, width, height);
} else if (!Utilities.ATLEAST_LOLLIPOP) {
// Below L, we use a scale up animation
opts = ActivityOptions.makeScaleUpAnimation(v, 0, 0,
v.getMeasuredWidth(), v.getMeasuredHeight());
} else if (Utilities.ATLEAST_LOLLIPOP_MR1) {
// On L devices, we use the device default slide-up transition.
// On L MR1 devices, we a custom version of the slide-up transition which
// doesn't have the delay present in the device default.
opts = ActivityOptions.makeCustomAnimation(this,
R.anim.task_open_enter, R.anim.no_anim);
}
optsBundle = opts != null ? opts.toBundle() : null;
}

if (user == null || user.equals(UserHandleCompat.myUserHandle())) {
// Could be launching some bookkeeping activity
startActivity(intent, optsBundle);
} else {
// TODO Component can be null when shortcuts are supported for secondary user
launcherApps.startActivityForProfile(intent.getComponent(), user,
intent.getSourceBounds(), optsBundle);
}
return true;
} catch (SecurityException e) {
Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();
Log.e(TAG, "Launcher does not have the permission to launch " + intent +
". Make sure to create a MAIN intent-filter for the corresponding activity " +
"or use the exported attribute for this activity. "
+ "tag="+ tag + " intent=" + intent, e);
}
return false;
}

public boolean startActivitySafely(View v, Intent intent, Object tag) {
boolean success = false;
if (mIsSafeModeEnabled && !Utilities.isSystemApp(this, intent)) {
Toast.makeText(this, R.string.safemode_shortcut_error, Toast.LENGTH_SHORT).show();
return false;
}
try {
success = startActivity(v, intent, tag);
} catch (ActivityNotFoundException e) {
Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();
Log.e(TAG, "Unable to launch. tag=" + tag + " intent=" + intent, e);
}
return success;
}

Android的Singleton模式的实现

在frameworks/base/core/java/android/app/ActivityManagerNative.java中

IActivityManager

是一个单利模式，所以Android实现了一个很标准的Singleton。在老罗版本里，没有使用这个类。

framework/base/core/java/android/util/Singleton.java:

/**
* Singleton helper class for lazily initialization.
*
* Modeled after frameworks/base/include/utils/Singleton.h
*
* @hide
*/
public abstract class Singleton<T> {
private T mInstance;

protected abstract T create();

public final T get() {
synchronized (this) {
if (mInstance == null) {
mInstance = create();
}
return mInstance;
}
}
}

ActivityManagerService

显然，AcitivityManagerService的位置由

frameworks/base/services/java/com/android/service/am/ActivityManagerService.java

转移至

frameworks/base/services/core/java/com/android/service/am/ActivityManagerService.java

。同时

startActivity

函数也有所改变：

frameworks/base/services/core/java/com/android/service/am/ActivityManagerService.java:

@Override
public final int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle options) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
resultWho, requestCode, startFlags, profilerInfo, options,
UserHandle.getCallingUserId());
}

@Override
public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle options, int userId) {
enforceNotIsolatedCaller("startActivity");
userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,
false, ALLOW_FULL_ONLY, "startActivity", null);
// TODO: Switch to user app stacks here.
return mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,
resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
profilerInfo, null, null, options, false, userId, null, null);
}

主要的变化是添加了用户的概念，同时加入了mStackSupervisor（ActivityStackSuperVisor）来管理ActivityStack。