Android侦听应用（Package）变化的方法（2）实现PackageMonitor

先看看PackageMonitor的基本定义：

package com.android.internal.content;/** * Helper class for monitoring the state of packages: adding, removing, * updating, and disappearing and reappearing on the SD card. */public abstract class PackageMonitor extends android.content.BroadcastReceiverstatic {    sPackageFilt.addAction(Intent.ACTION_PACKAGE_ADDED);    sPackageFilt.addAction(Intent.ACTION_PACKAGE_REMOVED);    sPackageFilt.addAction(Intent.ACTION_PACKAGE_CHANGED);    sPackageFilt.addAction(Intent.ACTION_QUERY_PACKAGE_RESTART);    sPackageFilt.addAction(Intent.ACTION_PACKAGE_RESTARTED);    sPackageFilt.addAction(Intent.ACTION_PACKAGE_DATA_CLEARED);    sPackageFilt.addDataScheme("package");    sNonDataFilt.addAction(Intent.ACTION_UID_REMOVED);    sNonDataFilt.addAction(Intent.ACTION_USER_STOPPED);    sNonDataFilt.addAction(Intent.ACTION_PACKAGES_SUSPENDED);    sNonDataFilt.addAction(Intent.ACTION_PACKAGES_UNSUSPENDED);    sExternalFilt.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE);    sExternalFilt.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);}

可以看到PackageMonitor是一个内部API，并且它实际上是一个BroadcastReceiver，在框架内部注册了接收上述Action的Intent广播。虽然目前没有对第三方App开放，但其设计思想可以借鉴，毕竟注册各种Package相关的Intent比较琐碎，在一个工程中封装一个类似的Monitor作为基本框架模块供复用很有必要。PackageMonitor的主要工作是将注册/解析Intent广播封装，对外暴露成需要实现的有语义的回调。看一下他的注册和有代表性的回调。

（1）注册

PackageMonitor有三个注册方法：

public void register(Context context, Looper thread, boolean externalStorage) public void register(Context context, Looper thread, UserHandle user, boolean externalStorage)public void register(Context context, UserHandle user, boolean externalStorage, Handler handler)

可以看到提供了注册回调执行的线程、注册侦听的用户（支持安卓多用户体系）、选择是否侦听外置存储空间（譬如SD卡）中的package变化等配置项。（2）有代表性的回调

/** * Called when a package is really added (and not replaced). */public void onPackageAdded(String packageName, int uid) {}/** * Called when a package is really removed (and not replaced). */public void onPackageRemoved(String packageName, int uid) {}/** * Direct reflection of {@link Intent#ACTION_PACKAGE_CHANGED * Intent.ACTION_PACKAGE_CHANGED} being received, informing you of * changes to the enabled/disabled state of components in a package * and/or of the overall package. * * @param packageName The name of the package that is changing. * @param uid The user ID the package runs under. * @param components Any components in the package that are changing.  If * the overall package is changing, this will contain an entry of the * package name itself. * @return Return true to indicate you care about this change, which will * result in {@link #onSomePackagesChanged()} being called later.  If you * return false, no further callbacks will happen about this change.  The * default implementation returns true if this is a change to the entire * package. */public boolean onPackageChanged(String packageName, int uid, String[] components) {    if (components != null) {        for (String name : components) {            if (packageName.equals(name)) {                return true;            }        }    }    return false;}public boolean onHandleForceStop(Intent intent, String[] packages, int uid, boolean doit) {    return false;}public void onHandleUserStop(Intent intent, int userHandle) {}public void onUidRemoved(int uid) {}public void onPackagesAvailable(String[] packages) {}public void onPackagesUnavailable(String[] packages) {}public void onPackagesSuspended(String[] packages) {}public void onPackagesUnsuspended(String[] packages) {}

可以根据自己的需求进行重写方法。针对其中几个研究一下：-onUidRemoved(int uid):自从android引入对多用户的支持，uid和user就成了容易混淆的概念。参见我的另2篇：Android下uid与多用户释疑（一） Android下uid与多用户释疑（二） 这里的uid是指应用程序。uid removed即指应用程序被删除（卸载）。如果某些业务逻辑中对于应用程序是通过uid标识管理的，可以使用这个回调。 对应的Intent Action是Intent.ACTION_UID_REMOVED。-onPackagesSuspended()/onPackagesUnsuspended():对应Intent.ACTION_PACKAGES_SUSPENDED/ACTION_PACKAGES_UNSUSPENDED。查看PMS、PackageManager的源代码看到是在调用这个api时触发的Intent广播：

/** * Puts the package in a suspended state, where attempts at starting activities are denied. * * <p>It doesn't remove the data or the actual package file. The application notifications * will be hidden, the application will not show up in recents, will not be able to show * toasts or dialogs or ring the device. * * <p>The package must already be installed. If the package is uninstalled while suspended * the package will no longer be suspended. * * @param packageNames The names of the packages to set the suspended status. * @param suspended If set to {@code true} than the packages will be suspended, if set to * {@code false} the packages will be unsuspended. * @param userId The user id. * * @return an array of package names for which the suspended status attemptis not set as requested in * this method. * * @hide */public abstract String[] setPackagesSuspendedAsUser(        String[] packageNames, boolean suspended, @UserIdInt int userId);

关于应用挂起，后续会有文章跟进。
以一个系统服务SearchManagerService为例看下对于PackageMonitor的使用：
/** * Refreshes the "searchables" list when packages are added/removed. */class MyPackageMonitor extends PackageMonitor {    @Override    public void onSomePackagesChanged() {        updateSearchables();    }    @Override    public void onPackageModified(String pkg) {        updateSearchables();    }    private void updateSearchables() {        final int changingUserId = getChangingUserId();        synchronized (mSearchables) {            // Update list of searchable activities            for (int i = 0; i < mSearchables.size(); i++) {                if (changingUserId == mSearchables.keyAt(i)) {                    mSearchables.valueAt(i).updateSearchableList();                    break;                }            }        }        // Inform all listeners that the list of searchables has been updated.        Intent intent = new Intent(SearchManager.INTENT_ACTION_SEARCHABLES_CHANGED);        intent.addFlags(Intent.FLAG_RECEIVER_REPLACE_PENDING                | Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);        mContext.sendBroadcastAsUser(intent, new UserHandle(changingUserId));    }}

上述参看代码版本为android7.1。