Android 侦听应用（Package）变化的方法侦听广播

应用的状态变化，包括安装、卸载、更新，是android系统上重要的事件。如何侦听到？有两种方法，一是通过侦听广播，一是实现PackageMonitor。

侦听广播

当Package状态发生变化时，系统会广播如下一些Action的Intent：

应用安装：
public static final String ACTION_PACKAGE_ADDED = "android.intent.action.PACKAGE_ADDED";

应用更新：
public static final String ACTION_PACKAGE_REPLACED = "android.intent.action.PACKAGE_REPLACED";
应用的新版本替代旧版本被安装
public static final String ACTION_MY_PACKAGE_REPLACED = "android.intent.action.MY_PACKAGE_REPLACED";
应用的新版本替代旧版本被安装，只发给被更新的应用自己
public static final String ACTION_PACKAGE_CHANGED = "android.intent.action.PACKAGE_CHANGED";
应用被改变，譬如某些组件被disable/enable

应用卸载：
public static final String ACTION_PACKAGE_REMOVED = "android.intent.action.PACKAGE_REMOVED";
应用被卸载时发出，正在被卸载的应用自身不会收到
public static final String ACTION_PACKAGE_FULLY_REMOVED = "android.intent.action.PACKAGE_FULLY_REMOVED";
应用被完全卸载时发出（数据被删除）

上述Intent都为保护型，只能够由系统发出。

针对上述定义，结合android源代码，研究几个问题。Android对于Package的管理主要逻辑在PackageManagerService（PMS）中，主要在这个类中研究上述问题：

（1）系统如何实现只发给某个应用？
ACTION_MY_PACKAGE_REPLACED是如何处理的？

private void sendSystemPackageUpdatedBroadcastsInternal() {
Bundle extras = new Bundle(2);
extras.putInt(Intent.EXTRA_UID, removedAppId >= 0 ? removedAppId : uid);
extras.putBoolean(Intent.EXTRA_REPLACING, true);
sendPackageBroadcast(Intent.ACTION_PACKAGE_ADDED, removedPackage,
extras, 0, null, null, null);
sendPackageBroadcast(Intent.ACTION_PACKAGE_REPLACED, removedPackage,
extras, 0, null, null, null);
sendPackageBroadcast(Intent.ACTION_MY_PACKAGE_REPLACED, null,
null, 0, removedPackage, null, null);
}

final void sendPackageBroadcast(final String action, final String pkg, final Bundle extras,
final int flags, final String targetPkg, final IIntentReceiver finishedReceiver,
final int[] userIds) {
mHandler.post(new Runnable() {
@Override
public void run() {
try {
final IActivityManager am = ActivityManagerNative.getDefault();
if (am == null) return;
final int[] resolvedUserIds;
if (userIds == null) {
resolvedUserIds = am.getRunningUserIds();
} else {
resolvedUserIds = userIds;
}
for (int id : resolvedUserIds) {
final Intent intent = new Intent(action,
pkg != null ? Uri.fromParts(PACKAGE_SCHEME, pkg, null) : null);
if (extras != null) {
intent.putExtras(extras);
}
if (targetPkg != null) {
intent.setPackage(targetPkg);
}
// Modify the UID when posting to other users
int uid = intent.getIntExtra(Intent.EXTRA_UID, -1);
if (uid > 0 && UserHandle.getUserId(uid) != id) {
uid = UserHandle.getUid(id, UserHandle.getAppId(uid));
intent.putExtra(Intent.EXTRA_UID, uid);
}
intent.putExtra(Intent.EXTRA_USER_HANDLE, id);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT | flags);
if (DEBUG_BROADCASTS) {
RuntimeException here = new RuntimeException("here");
here.fillInStackTrace();
Slog.d(TAG, "Sending to user " + id + ": "
+ intent.toShortString(false, true, false, false)
+ " " + intent.getExtras(), here);
}
am.broadcastIntent(null, intent, null, finishedReceiver,
0, null, null, null, android.app.AppOpsManager.OP_NONE,
null, finishedReceiver != null, false, id);
}
} catch (RemoteException ex) {
}
}
});
}

看到在广播ACTION_MY_PACKAGE_REPLACED的时候，是通过Intent.setPackage(String packageName)实现定向发送。
（2）ACTION_PACKAGE_CHANGED在什么场景下使用？
ACTION_PACKAGE_CHANGED在PMS中只有一处使用入口：

private void sendPackageChangedBroadcast(String packageName,
boolean killFlag, ArrayList<String> componentNames, int packageUid) {
if (DEBUG_INSTALL)
Log.v(TAG, "Sending package changed: package=" + packageName + " components="
+ componentNames);
Bundle extras = new Bundle(4);
extras.putString(Intent.EXTRA_CHANGED_COMPONENT_NAME, componentNames.get(0));
String nameList[] = new String[componentNames.size()];
componentNames.toArray(nameList);
extras.putStringArray(Intent.EXTRA_CHANGED_COMPONENT_NAME_LIST, nameList);
extras.putBoolean(Intent.EXTRA_DONT_KILL_APP, killFlag);
extras.putInt(Intent.EXTRA_UID, packageUid);
// If this is not reporting a change of the overall package, then only send it
// to registered receivers.  We don't want to launch a swath of apps for every
// little component state change.
final int flags = !componentNames.contains(packageName)
? Intent.FLAG_RECEIVER_REGISTERED_ONLY : 0;
sendPackageBroadcast(Intent.ACTION_PACKAGE_CHANGED,  packageName, extras, flags, null, null,
new int[] {UserHandle.getUserId(packageUid)});
}

追踪sendPackageChangedBroadcast()的调用，来自setComponentEnabledSetting()。
这是实现PackageManager的对外公开API，看一下PackageManager中对此的定义：

/**
* Set the enabled setting for a package component (activity, receiver, service, provider).
* This setting will override any enabled state which may have been set by the component in its
* manifest.
*
* @param componentName The component to enable
* @param newState The new enabled state for the component.  The legal values for this state
*                 are:
*                   {@link #COMPONENT_ENABLED_STATE_ENABLED},
*                   {@link #COMPONENT_ENABLED_STATE_DISABLED}
*                   and
*                   {@link #COMPONENT_ENABLED_STATE_DEFAULT}
*                 The last one removes the setting, thereby restoring the component's state to
*                 whatever was set in it's manifest (or enabled, by default).
* @param flags Optional behavior flags: {@link #DONT_KILL_APP} or 0.
*/
public abstract void setComponentEnabledSetting(ComponentName componentName,
int newState, int flags);

这是PackageManager提供的修改四大控件enable/disable的API，当然调用是需要检查权限的，此处不展开介绍。

（3）ACTION_PACKAGE_REMOVED和ACTION_PACKAGE_FULLY_REMOVED的逻辑关系
查看这两个Action在PMS中的使用，发现只有一处：

private void sendPackageRemovedBroadcastInternal(boolean killApp) {
Bundle extras = new Bundle(2);
extras.putInt(Intent.EXTRA_UID, removedAppId >= 0  ? removedAppId : uid);
extras.putBoolean(Intent.EXTRA_DATA_REMOVED, dataRemoved);
extras.putBoolean(Intent.EXTRA_DONT_KILL_APP, !killApp);
if (isUpdate || isRemovedPackageSystemUpdate) {
extras.putBoolean(Intent.EXTRA_REPLACING, true);
}
extras.putBoolean(Intent.EXTRA_REMOVED_FOR_ALL_USERS, removedForAllUsers);
if (removedPackage != null) {
sendPackageBroadcast(Intent.ACTION_PACKAGE_REMOVED, removedPackage,
extras, 0, null, null, removedUsers);
if (dataRemoved && !isRemovedPackageSystemUpdate) {
sendPackageBroadcast(Intent.ACTION_PACKAGE_FULLY_REMOVED,
removedPackage, extras, 0, null, null, removedUsers);
}
}
if (removedAppId >= 0) {
sendPackageBroadcast(Intent.ACTION_UID_REMOVED, null, extras, 0, null, null,
removedUsers);
}
}

看到Package removed发生时，会发ACTION_PACKAGE_REMOVED；并且只有在数据被删除且非删除系统更新的app时，才会发送ACTION_PACKAGE_FULLY_REMOVED。在PackageManager中有一个flag常量定义PackageManager.DELETE_KEEP_DATA，用以决定在删除app时是否保留数据。