java.lang.SecurityException: Failed to find provider null for user 0

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;
        }
    }