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Android ContentProvider、ContentResolver/ContentObserver 修改监听流程

程序员文章站 2024-02-09 16:49:40
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以 Settings.System.putInt(mContentResolver, Settings.System.SCREEN_BRIGHTNESS, mCurrentValue); 为例。putInt 最后也是使用 ContentProvider 保存。

Settings 中 putInt 后最终执行 putStringForUser函数

        public boolean putStringForUser(ContentResolver cr, String name, String value,
                String tag, boolean makeDefault, final int userHandle) {
            try {
                Bundle arg = new Bundle();
                arg.putString(Settings.NameValueTable.VALUE, value);
                arg.putInt(CALL_METHOD_USER_KEY, userHandle);
                if (tag != null) {
                    arg.putString(CALL_METHOD_TAG_KEY, tag);
                }
                if (makeDefault) {
                    arg.putBoolean(CALL_METHOD_MAKE_DEFAULT_KEY, true);
                }
                IContentProvider cp = mProviderHolder.getProvider(cr);
                cp.call(cr.getPackageName(), mProviderHolder.mUri.getAuthority(),
                        mCallSetCommand, name, arg);
            } catch (RemoteException e) {
                Log.w(TAG, "Can't set key " + name + " in " + mUri, e);
                return false;
            }
            return true;
        }

所设置的 value 保存在 bundle 中调用 call 传递。

IContentProvider 是一个接口类,ContentProviderNative 是其抽象实现类。call 函数最后由 ContentProvider 内部类 Transport (继承 ContentProviderNative)中实现处理。如下


        @Override
        public Bundle call(String callingPkg, String authority, String method, @Nullable String arg,
                @Nullable Bundle extras) {
            validateIncomingAuthority(authority);
            Bundle.setDefusable(extras, true);
            Trace.traceBegin(TRACE_TAG_DATABASE, "call");
            final String original = setCallingPackage(callingPkg);
            try {
                return mInterface.call(authority, method, arg, extras);
            } catch (RemoteException e) {
                throw e.rethrowAsRuntimeException();
            } finally {
                setCallingPackage(original);
                Trace.traceEnd(TRACE_TAG_DATABASE);
            }
        }

mInterface 是 ContentInterface 实例,ContentProvider 是 ContentInterface 实现类

mInterface.call(authority, method, arg, extras);

这行实际走的是 ContentProvider 中的 call 函数。

    @Override
    public @Nullable Bundle call(@NonNull String authority, @NonNull String method,
            @Nullable String arg, @Nullable Bundle extras) {
        return call(method, arg, extras);
    }

    public @Nullable Bundle call(@NonNull String method, @Nullable String arg,
            @Nullable Bundle extras) {
        return null;
    }

可以看到结果走到最后是 

return null;

再找到它的子类,这里使用的是 SettingsProvider.java ,所以 call 函数接下来操作在这里实现。

    @Override
    public Bundle call(String method, String name, Bundle args) {
        final int requestingUserId = getRequestingUserId(args);
        switch (method) {
            ... ...

            case Settings.CALL_METHOD_PUT_SYSTEM: {
                String value = getSettingValue(args);
                insertSystemSetting(name, value, requestingUserId);
                break;
            }
            ... ... 

            default: {
                Slog.w(LOG_TAG, "call() with invalid method: " + method);
            } break;
        }

        return null;
    }

根据 method 类型继续处理。走到 mutateSystemSetting 中。

    private boolean mutateSystemSetting(String name, String value, int runAsUserId,
            int operation) {
        if (!hasWriteSecureSettingsPermission()) {
            // If the caller doesn't hold WRITE_SECURE_SETTINGS, we verify whether this
            // operation is allowed for the calling package through appops.
            if (!Settings.checkAndNoteWriteSettingsOperation(getContext(),
                    Binder.getCallingUid(), getCallingPackage(), true)) {
                return false;
            }
        }

        // Resolve the userId on whose behalf the call is made.
        final int callingUserId = resolveCallingUserIdEnforcingPermissionsLocked(runAsUserId);

        if (name != null && mUserManagerInternal.isSettingRestrictedForUser(
                name, callingUserId, value, Binder.getCallingUid())) {
            return false;
        }

        // Enforce what the calling package can mutate the system settings.
        enforceRestrictedSystemSettingsMutationForCallingPackage(operation, name, callingUserId);


        // Mutate the value.
        synchronized (mLock) {
            switch (operation) {
                case MUTATION_OPERATION_INSERT: {
                    validateSystemSettingValue(name, value);
                    return mSettingsRegistry.insertSettingLocked(SETTINGS_TYPE_SYSTEM,
                            owningUserId, name, value, null, false, getCallingPackage(),
                            false, null);
                }

                case MUTATION_OPERATION_DELETE: {
                    return mSettingsRegistry.deleteSettingLocked(SETTINGS_TYPE_SYSTEM,
                            owningUserId, name, false, null);
                }

                case MUTATION_OPERATION_UPDATE: {
                    validateSystemSettingValue(name, value);
                    return mSettingsRegistry.updateSettingLocked(SETTINGS_TYPE_SYSTEM,
                            owningUserId, name, value, null, false, getCallingPackage(),
                            false, null);
                }
            }

            return false;
        }
    }

在这里处理下权限的,和根据设置值的类型处理。我们是 update 的,走 MUTATION_OPERATION_UPDATE 调用 updateSettingLocked

        public boolean updateSettingLocked(int type, int userId, String name, String value,
                String tag, boolean makeDefault, String packageName, boolean forceNotify,
                Set<String> criticalSettings) {
            final int key = makeKey(type, userId);

            boolean success = false;
            SettingsState settingsState = peekSettingsStateLocked(key);
            if (settingsState != null) {
                success = settingsState.updateSettingLocked(name, value, tag,
                        makeDefault, packageName);
            }

            if (success && criticalSettings != null && criticalSettings.contains(name)) {
                settingsState.persistSyncLocked();
            }

            if (forceNotify || success) {
                notifyForSettingsChange(key, name);
            }

            return success;
        }

在 updateSettingLocked 成功后,使用 notifyForSettingsChange 通知 key 更新成功。走到 notifySettingChangeForRunningUsers 中

        private void notifySettingChangeForRunningUsers(int key, String name) {
            // Important: No need to update generation for each user as there
            // is a singleton generation entry for the global settings which
            // is already incremented be the caller.
            final Uri uri = getNotificationUriFor(key, name);
            final List<UserInfo> users = mUserManager.getUsers(/*excludeDying*/ true);
            for (int i = 0; i < users.size(); i++) {
                final int userId = users.get(i).id;
                if (mUserManager.isUserRunning(UserHandle.of(userId))) {
                    mHandler.obtainMessage(MyHandler.MSG_NOTIFY_URI_CHANGED,
                            userId, 0, uri).sendToTarget();
                }
            }
        }

... ... 

            public void handleMessage(Message msg) {
                switch (msg.what) {
                    case MSG_NOTIFY_URI_CHANGED: {
                        final int userId = msg.arg1;
                        Uri uri = (Uri) msg.obj;
                        try {
                            getContext().getContentResolver().notifyChange(uri, null, true, userId);
                        } catch (SecurityException e) {
                            Slog.w(LOG_TAG, "Failed to notify for " + userId + ": " + uri, e);
                        }
                        if (DEBUG || true) {
                            Slog.v(LOG_TAG, "Notifying for " + userId + ": " + uri);
                        }
                    } break;

                    case MSG_NOTIFY_DATA_CHANGED: {
                        mBackupManager.dataChanged();
                    } break;
                }
            }
        }

通过发送 MSG_NOTIFY_URI_CHANGED 最后调用 

getContext().getContentResolver().notifyChange(uri, null, true, userId);

ContentResolver 就是接受类,内部再通过 ContentService 去调度通知。

    /**
     * Notify registered observers within the designated user(s) that a row was updated.
     *
     * @hide
     */
    public void notifyChange(@NonNull Uri uri, ContentObserver observer, @NotifyFlags int flags,
            @UserIdInt int userHandle) {
        try {
            getContentService().notifyChange(
                    uri, observer == null ? null : observer.getContentObserver(),
                    observer != null && observer.deliverSelfNotifications(), flags,
                    userHandle, mTargetSdkVersion, mContext.getPackageName());
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }
# ContentService.java

    @Override
    public void notifyChange(Uri uri, IContentObserver observer,
            boolean observerWantsSelfNotifications, int flags, int userHandle,
            int targetSdkVersion, String callingPackage) {
        ... ...

        try {
            ArrayList<ObserverCall> calls = new ArrayList<ObserverCall>();
            synchronized (mRootNode) {
                mRootNode.collectObserversLocked(uri, 0, observer, observerWantsSelfNotifications,
                        flags, userHandle, calls);
            }
            final int numCalls = calls.size();
            for (int i=0; i<numCalls; i++) {
                ObserverCall oc = calls.get(i);
                try {
                    oc.mObserver.onChange(oc.mSelfChange, uri, userHandle);
                    if (DEBUG) Slog.d(TAG, "Notified " + oc.mObserver + " of " + "update at "
                            + uri);
                } catch (RemoteException ex) {
                }
            }

        ... ...
    }

最后在系统 ContentService 中,一个for循环通知所有注册的 ContentObserver 。在 ContentObserver 中监听属性值变化。

mSettingsObserver = new SettingsObserver(mHandler);
// 注册Observer 
mContext.getContentResolver().registerContentObserver(Settings.System.getUriFor(Settings.System.SCREEN_BRIGHTNESS), false, mSettingsObserver, UserHandle.USER_ALL); 

private final class SettingsObserver extends ContentObserver {
    public SettingsObserver(Handler handler) {
        super(handler);
    }

    @Override
    public void onChange(boolean selfChange, Uri uri) {
        synchronized (mLock) {
        }
    }
}

 

相关标签: Android