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如果更新或者升级后系统内置应用，遇到重启Android系统后内置应用被还原，那是因为手动安装的APK版本号和系统内置API版本号一样。
1、Android系统应用更新机制
系统为每个应用在AndroidMainfest.xml提供了versionName、versionCode两个属性。
versionName：String类型，用来给应用的使用者来查看版本.
versionCode：Integer类型，作为系统判断应用是否能升级的依据。
2、Android系统内置应用更新判断代码
代码来自frameworks/base/services/java/com/android/server/PackageManagerService.java 中 scanPackageLI函数的package更新判断条件(约第2580-2621行附近)
// First check if this is a system package that may involve an update
if (updatedPkg != null && (parseFlags&PackageParser.PARSE_IS_SYSTEM) != 0) {
if (!ps.codePath.equals(scanFile)) {
// The path has changed from what was last scanned... check the
// version of the new path against what we have stored to determine
// what to do.
if (pkg.mVersionCode < ps.versionCode) {
// The system package has been updated and the code path does not match
// Ignore entry. Skip it.
if (updatedPkg != null && (parseFlags&PackageParser.PARSE_IS_SYSTEM) != 0) {
if (!ps.codePath.equals(scanFile)) {
// The path has changed from what was last scanned... check the
// version of the new path against what we have stored to determine
// what to do.
if (pkg.mVersionCode < ps.versionCode) {
// The system package has been updated and the code path does not match
// Ignore entry. Skip it.
从上面代码注释可以知道：更新系统内置应用时，如果新的versionCode没有大于当前安装的版本，更新将被忽略。