当我们在 8.0以上 系统调用 ContentResolver 的 notifyChange 方法通知数据更新,或者调用 ContentResolver 的 registerContentObserver 方法监听数据变化时,会出现异常:java.lang.SecurityException: Failed to find provider null for user 0; expected to find a valid ContentProvider for this authority而在 8.0 之前的版本上这两个方法都是可以正常运行。
通过错误描述我们了解到用于查找ContentProvider的authority为null,自行查看是否是因为没有获取到authority的值导致的异常。
原因:
以registerContentObserver方式为例,ContentResolver#registerContentObserver方法调用的是ContentService#registerContentObserver()方法,在注册ContentObserver时,会先判断当前URI中authority对应的ContentProvider是否已经注册,若没有注册,Android O以上版本会抛出SecurityException().
/**
* Register a content observer tied to a specific user's view of the provider.
* @param userHandle the user whose view of the provider is to be observed. May be
* the calling user without requiring any permission, otherwise the caller needs to
* hold the INTERACT_ACROSS_USERS_FULL permission or hold a read uri grant to the uri.
* Pseudousers USER_ALL and USER_CURRENT are properly handled; all other pseudousers
* are forbidden.
*/
@Override
public void registerContentObserver(Uri uri, boolean notifyForDescendants,
IContentObserver observer, int userHandle, int targetSdkVersion) {
if (observer == null || uri == null) {
throw new IllegalArgumentException("You must pass a valid uri and observer");
}
final int uid = Binder.getCallingUid();
final int pid = Binder.getCallingPid();
userHandle = handleIncomingUser(uri, pid, uid,
Intent.FLAG_GRANT_READ_URI_PERMISSION, true, userHandle);
final String msg = LocalServices.getService(ActivityManagerInternal.class)
.checkContentProviderAccess(uri.getAuthority(), userHandle);
if (msg != null) {
if (targetSdkVersion >= Build.VERSION_CODES.O) {
throw new SecurityException(msg);
} else {
if (msg.startsWith("Failed to find provider")) {
// Sigh, we need to quietly let apps targeting older API
// levels notify on non-existent providers.
} else {
Log.w(TAG, "Ignoring content changes for " + uri + " from " + uid + ": " + msg);
return;
}
}
}
synchronized (mRootNode) {
mRootNode.addObserverLocked(uri, observer, notifyForDescendants, mRootNode,
uid, pid, userHandle);
if (false) Log.v(TAG, "Registered observer " + observer + " at " + uri +
" with notifyForDescendants " + notifyForDescendants);
}
}
ActivityManagerService#checkContentProviderAccess()
/**
* Check if the calling UID has a possible chance at accessing the provider
* at the given authority and user.
*/
public String checkContentProviderAccess(String authority, int userId) {
if (userId == UserHandle.USER_ALL) {
mContext.enforceCallingOrSelfPermission(
Manifest.permission.INTERACT_ACROSS_USERS_FULL, TAG);
userId = UserHandle.getCallingUserId();
}
ProviderInfo cpi = null;
try {
cpi = AppGlobals.getPackageManager().resolveContentProvider(authority,
STOCK_PM_FLAGS | PackageManager.GET_URI_PERMISSION_PATTERNS
| PackageManager.MATCH_DISABLED_COMPONENTS
| PackageManager.MATCH_DIRECT_BOOT_AWARE
| PackageManager.MATCH_DIRECT_BOOT_UNAWARE,
userId);
} catch (RemoteException ignored) {
}
if (cpi == null) {
return "Failed to find provider " + authority + " for user " + userId
+ "; expected to find a valid ContentProvider for this authority";
}
ProcessRecord r = null;
synchronized (mPidsSelfLocked) {
r = mPidsSelfLocked.get(Binder.getCallingPid());
}
if (r == null) {
return "Failed to find PID " + Binder.getCallingPid();
}
synchronized (this) {
return checkContentProviderPermissionLocked(cpi, r, userId, true);
}
}
PackageManagerService#resolveContentProvider()
@Override
public ProviderInfo resolveContentProvider(String name, int flags, int userId) {
return resolveContentProviderInternal(name, flags, userId);
}
private ProviderInfo resolveContentProviderInternal(String name, int flags, int userId) {
if (!sUserManager.exists(userId)) return null;
flags = updateFlagsForComponent(flags, userId, name);
final int callingUid = Binder.getCallingUid();
synchronized (mPackages) {
final PackageParser.Provider provider = mProvidersByAuthority.get(name);
PackageSetting ps = provider != null
? mSettings.mPackages.get(provider.owner.packageName)
: null;
if (ps != null) {
// provider not enabled
if (!mSettings.isEnabledAndMatchLPr(provider.info, flags, userId)) {
return null;
}
final ComponentName component =
new ComponentName(provider.info.packageName, provider.info.name);
if (filterAppAccessLPr(ps, callingUid, component, TYPE_PROVIDER, userId)) {
return null;
}
return PackageParser.generateProviderInfo(
provider, flags, ps.readUserState(userId), userId);
}
return null;
}
}