如何利用包名创建一个新的Context，本文主要目的是记录一次源码查找过程，以后查阅方便，所以只是一个贴代码的过程。
在ContextImpl.java中有一个createPackageContext方法可以根据包名来创建一个新的Context对象。下面来分析下这个方法的实现。
@Override
public Context createPackageContext(String packageName, int flags)
throws NameNotFoundException {
return createPackageContextAsUser(packageName, flags,
mUser != null ? mUser : Process.myUserHandle());
}
在createPackageContext方法中实际上，是调用了createPackageContextAsUser方法。
@Override
public Context createPackageContextAsUser(String packageName, int flags, UserHandle user)
throws NameNotFoundException {
if (packageName.equals("system") || packageName.equals("android")) {
return new ContextImpl(this, mMainThread, mPackageInfo, mActivityToken,
user, flags, mDisplay, null, Display.INVALID_DISPLAY);
}
LoadedApk pi = mMainThread.getPackageInfo(packageName, mResources.getCompatibilityInfo(),
flags | CONTEXT_REGISTER_PACKAGE, user.getIdentifier());
if (pi != null) {
ContextImpl c = new ContextImpl(this, mMainThread, pi, mActivityToken,
user, flags, mDisplay, null, Display.INVALID_DISPLAY);
if (c.mResources != null) {
return c;
}
}
// Should be a better exception.
throw new PackageManager.NameNotFoundException(
"Application package " + packageName + " not found");
}
在该方法中，先去检测包名是不是system 或者 android, 直接去创建一个ContextImpl对象。分析普通应用创建过程，从mMainThread.getPackageInfo中获取该包名的PackageInfo对象（LoadedApk）.分析getPackageInfo的实现过程。
ActivityThread.java 中getPackageInfo 方法分析
public final LoadedApk getPackageInfo(String packageName, CompatibilityInfo compatInfo,
int flags, int userId) {
final boolean differentUser = (UserHandle.myUserId() != userId);
synchronized (mResourcesManager) {
WeakReference<LoadedApk> ref;
if (differentUser) {
// Caching not supported across users
ref = null;
} else if ((flags & Context.CONTEXT_INCLUDE_CODE) != 0) {
ref = mPackages.get(packageName);
} else {
ref = mResourcePackages.get(packageName);
}
LoadedApk packageInfo = ref != null ? ref.get() : null;
//Slog.i(TAG, "getPackageInfo " + packageName + ": " + packageInfo);
//if (packageInfo != null) Slog.i(TAG, "isUptoDate " + packageInfo.mResDir
// + ": " + packageInfo.mResources.getAssets().isUpToDate());
if (packageInfo != null && (packageInfo.mResources == null
|| packageInfo.mResources.getAssets().isUpToDate())) {
if (packageInfo.isSecurityViolation()
&& (flags&Context.CONTEXT_IGNORE_SECURITY) == 0) {
throw new SecurityException(
"Requesting code from " + packageName
+ " to be run in process "
+ mBoundApplication.processName
+ "/" + mBoundApplication.appInfo.uid);
}
return packageInfo;
}
}
ApplicationInfo ai = null;
try {
ai = getPackageManager().getApplicationInfo(packageName,
PackageManager.GET_SHARED_LIBRARY_FILES
| PackageManager.MATCH_DEBUG_TRIAGED_MISSING,
userId);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
if (ai != null) {
return getPackageInfo(ai, compatInfo, flags);
}
return null;
}
在这个方法中其实相当于两个过程，一，从mPackages中取出之前已经存在的packageInfo， 二，本地mPackages中如果没有存储，则先去取出ApplicationInfo，然后再去创建一个LoadedApk, 分析getPackageInfo(ai, compatInfo, flags);
private LoadedApk getPackageInfo(ApplicationInfo aInfo, CompatibilityInfo compatInfo,
ClassLoader baseLoader, boolean securityViolation, boolean includeCode,
boolean registerPackage) {
final boolean differentUser = (UserHandle.myUserId() != UserHandle.getUserId(aInfo.uid));
synchronized (mResourcesManager) {
WeakReference<LoadedApk> ref;
if (differentUser) {
// Caching not supported across users
ref = null;
} else if (includeCode) {
ref = mPackages.get(aInfo.packageName);
} else {
ref = mResourcePackages.get(aInfo.packageName);
}
LoadedApk packageInfo = ref != null ? ref.get() : null;
if (packageInfo == null || (packageInfo.mResources != null
&& !packageInfo.mResources.getAssets().isUpToDate())) {
if (localLOGV) Slog.v(TAG, (includeCode ? "Loading code package "
: "Loading resource-only package ") + aInfo.packageName
+ " (in " + (mBoundApplication != null
? mBoundApplication.processName : null)
+ ")");
packageInfo =
new LoadedApk(this, aInfo, compatInfo, baseLoader,
securityViolation, includeCode &&
(aInfo.flags&ApplicationInfo.FLAG_HAS_CODE) != 0, registerPackage);
if (mSystemThread && "android".equals(aInfo.packageName)) {
packageInfo.installSystemApplicationInfo(aInfo,
getSystemContext().mPackageInfo.getClassLoader());
}
if (differentUser) {
// Caching not supported across users
} else if (includeCode) {
mPackages.put(aInfo.packageName,
new WeakReference<LoadedApk>(packageInfo));
} else {
mResourcePackages.put(aInfo.packageName,
new WeakReference<LoadedApk>(packageInfo));
}
}
return packageInfo;
}
}
同样分析，先去从本地Map中取是否有已经存在的packageInfo, 否则去new 一个新的LoadedApk对象。此时比较关键时的两个参数，aInfo，baseLoader。
public LoadedApk(ActivityThread activityThread, ApplicationInfo aInfo,
CompatibilityInfo compatInfo, ClassLoader baseLoader,
boolean securityViolation, boolean includeCode, boolean registerPackage) {
mActivityThread = activityThread;
setApplicationInfo(aInfo);
mPackageName = aInfo.packageName;
mBaseClassLoader = baseLoader;
mSecurityViolation = securityViolation;
mIncludeCode = includeCode;
mRegisterPackage = registerPackage;
mDisplayAdjustments.setCompatibilityInfo(compatInfo);
}
此时LoadedApk保存一些信息，如果ApplicationInfo, pacakageName等。
返回ContextImpl.java 的createPackageContextAsUser方法。
public Context createPackageContextAsUser(String packageName, int flags, UserHandle user) {
LoadedApk pi = mMainThread.getPackageInfo(packageName, mResources.getCompatibilityInfo(),
flags | CONTEXT_REGISTER_PACKAGE, user.getIdentifier());
if (pi != null) {
ContextImpl c = new ContextImpl(this, mMainThread, pi, mActivityToken,
user, flags, mDisplay, null, Display.INVALID_DISPLAY);
if (c.mResources != null) {
return c;
}
}
}
从getPackageInfo中拿到LoadedApk之后，开始创建ContextImpl对象。
private ContextImpl(ContextImpl container, ActivityThread mainThread,
LoadedApk packageInfo, IBinder activityToken, UserHandle user, int flags,
Display display, Configuration overrideConfiguration, int createDisplayWithId) {
mOuterContext = this;
// If creator didn't specify which storage to use, use the default
// location for application.
if ((flags & (Context.CONTEXT_CREDENTIAL_PROTECTED_STORAGE
| Context.CONTEXT_DEVICE_PROTECTED_STORAGE)) == 0) {
final File dataDir = packageInfo.getDataDirFile();
if (Objects.equals(dataDir, packageInfo.getCredentialProtectedDataDirFile())) {
flags |= Context.CONTEXT_CREDENTIAL_PROTECTED_STORAGE;
} else if (Objects.equals(dataDir, packageInfo.getDeviceProtectedDataDirFile())) {
flags |= Context.CONTEXT_DEVICE_PROTECTED_STORAGE;
}
}
mMainThread = mainThread;
mActivityToken = activityToken;
mFlags = flags;
if (user == null) {
user = Process.myUserHandle();
}
mUser = user;
mPackageInfo = packageInfo;
mResourcesManager = ResourcesManager.getInstance();
final int displayId = (createDisplayWithId != Display.INVALID_DISPLAY)
? createDisplayWithId
: (display != null) ? display.getDisplayId() : Display.DEFAULT_DISPLAY;
CompatibilityInfo compatInfo = null;
if (container != null) {
compatInfo = container.getDisplayAdjustments(displayId).getCompatibilityInfo();
}
if (compatInfo == null) {
compatInfo = (displayId == Display.DEFAULT_DISPLAY)
? packageInfo.getCompatibilityInfo()
: CompatibilityInfo.DEFAULT_COMPATIBILITY_INFO;
}
Resources resources = packageInfo.getResources(mainThread);
if (resources != null) {
if (displayId != Display.DEFAULT_DISPLAY
|| overrideConfiguration != null
|| (compatInfo != null && compatInfo.applicationScale
!= resources.getCompatibilityInfo().applicationScale)) {
if (container != null) {
// This is a nested Context, so it can't be a base Activity context.
// Just create a regular Resources object associated with the Activity.
resources = mResourcesManager.getResources(
activityToken,
packageInfo.getResDir(),
packageInfo.getSplitResDirs(),
packageInfo.getOverlayDirs(),
packageInfo.getApplicationInfo().sharedLibraryFiles,
displayId,
overrideConfiguration,
compatInfo,
packageInfo.getClassLoader());
} else {
// This is not a nested Context, so it must be the root Activity context.
// All other nested Contexts will inherit the configuration set here.
resources = mResourcesManager.createBaseActivityResources(
activityToken,
packageInfo.getResDir(),
packageInfo.getSplitResDirs(),
packageInfo.getOverlayDirs(),
packageInfo.getApplicationInfo().sharedLibraryFiles,
displayId,
overrideConfiguration,
compatInfo,
packageInfo.getClassLoader());
}
}
}
mResources = resources;
mDisplay = (createDisplayWithId == Display.INVALID_DISPLAY) ? display
: mResourcesManager.getAdjustedDisplay(displayId, mResources.getDisplayAdjustments());
if (container != null) {
mBasePackageName = container.mBasePackageName;
mOpPackageName = container.mOpPackageName;
} else {
mBasePackageName = packageInfo.mPackageName;
ApplicationInfo ainfo = packageInfo.getApplicationInfo();
if (ainfo.uid == Process.SYSTEM_UID && ainfo.uid != Process.myUid()) {
// Special case: system components allow themselves to be loaded in to other
// processes. For purposes of app ops, we must then consider the context as
// belonging to the package of this process, not the system itself, otherwise
// the package+uid verifications in app ops will fail.
mOpPackageName = ActivityThread.currentPackageName();
} else {
mOpPackageName = mBasePackageName;
}
}
mContentResolver = new ApplicationContentResolver(this, mainThread, user);
}
这个对象里主要就是保存了相关的对象信息，我们平时能从Context中拿到包名，ApplicationInfo，路径等信息，都在此处保存。
网友评论