Q: notification center

This procedure will revert your settings in the Notifications preference pane to the defaults.

Please back up all data before continuing.

Step 1

Triple-click anywhere in the line below on this page to select it:

~/Library/Application Support/NotificationCenter

Right-click or control-click the line and select

          Services ▹ Open

from the contextual menu.* A folder should open. Inside it are one or more files with long names. Move the files to the Trash.

Step 2

Open this folder in the same way:

~/Library/Preferences/ByHost

There may be one or more files with a name beginning like this:

          com.apple.notificationcenterui

Move those files, and only those, to the Trash, if they exist.

Step 3

Do as in Step 2 with this folder:

~/Library/Preferences

Log out or restart the computer and empty the Trash. Recreate the settings.

*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination  command-C. In the Finder, select

          Go ▹ Go to Folder...

from the menu bar and paste into the box that opens by pressing command-V. You may not see what you pasted because a line break is included. Press return.

Step 4

Take this step only if you still have trouble after taking all the preceding steps.

Triple-click anywhere in the line of text below on this page to select it:

open $TMPDIR..

Copy the selected text to the Clipboard by pressing the key combination command-C.

Launch the built-in Terminal application in any one of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

Paste into the Terminal window by pressing command-V. Depending on which web browser you use, you may have to press the return key. A folder with a long, random name should open. Inside it, there should be a subfolder named "C". Drag that to the Trash.

Log out or restart the computer. Empty the Trash. Test.

Use trackpad gesture : swipe your two fingers left  to right on trackpad

Then click on edit on extreme right column weather , world clock , calculator will be there click on plus sign for each widget , they will be added in notification centre.