diff --git a/zero-framework.el b/zero-framework.el
index c58be182ff99fbeccb206bf499a4a0521fccda30..86a7c2121204f1b0d99b184abcc46c354ebba96b 100644
--- a/zero-framework.el
+++ b/zero-framework.el
@@ -479,7 +479,9 @@ return ch's Chinese punctuation if ch is converted. return nil otherwise"
   (make-local-variable 'zero-backspace-original-func)
   (unless zero-backspace-original-func
     (let ((func (key-binding (kbd "DEL"))))
-      (unless (function-equal func 'zero-backspace)
+      (when (and (functionp func)
+		 (not (function-equal func 'zero-backspace)))
+	(zero-debug "set zero-backspace-original-func to %s" func)
 	(setq zero-backspace-original-func func))))
   ;; DEL can't be put in zero-mode-map because I need to save the original
   ;; binding in this function.
@@ -557,11 +559,16 @@ registered input method is saved in `zero-ims'"
 if im-name is nil, use default empty input method"
   ;; TODO provide auto completion for im-name
   (interactive "SSet input method to: ")
-  ;; TODO create a macro to reduce code duplication and human error.
+  ;; when switch away from an IM, run last IM's :shutdown function.
+  (if zero-im
+      (let ((shutdown-func (cdr (assq :shutdown (cdr (assq zero-im zero-ims))))))
+	(if (functionp shutdown-func)
+	    (funcall shutdown-func))))
   (if im-name
       (let ((im-functions (cdr (assq im-name zero-ims))))
 	(if im-functions
 	    (progn
+	      ;; TODO create a macro to reduce code duplication and human error.
 	      (setq zero-build-candidates-func
 		    (or (cdr (assq :build-candidates im-functions))
 			'zero-build-candidates-default))
@@ -580,6 +587,7 @@ if im-name is nil, use default empty input method"
 	      (setq zero-backspace-func
 		    (or (cdr (assq :handle-backspace im-functions))
 			'zero-backspace-default))
+	      ;; when switch to a IM, run its :init function
 	      (let ((init-func (cdr (assq :init im-functions))))
 		(if (functionp init-func)
 		    (funcall init-func)))
@@ -591,8 +599,7 @@ if im-name is nil, use default empty input method"
     (setq zero-can-start-sequence-func 'zero-can-start-sequence-default)
     (setq zero-handle-preedit-char-func 'zero-handle-preedit-char-default)
     (setq zero-get-preedit-str-for-panel-func 'zero-get-preedit-str-for-panel-default)
-    (setq zero-backspace-func 'zero-backspace-default)
-    ))
+    (setq zero-backspace-func 'zero-backspace-default)))
 
 (defun zero-set-default-im (im-name)
   "set given im as default zero input method"
diff --git a/zero-pinyin-service.el b/zero-pinyin-service.el
index 3f5eb27a0116c10d2af1cda50951a22dbdff0b04..926a01f75816814e6502b517844f7913dde13690 100644
--- a/zero-pinyin-service.el
+++ b/zero-pinyin-service.el
@@ -9,9 +9,9 @@
 
 (defun zero-pinyin-service-error-handler (event error)
   "handle dbus errors"
-  (when (or (string-equal "com.emacsos.zero.ZeroPinyinService"
+  (when (or (string-equal "com.emacsos.zero.ZeroPinyinService1"
 			  (dbus-event-interface-name event))
-	    (s-contains-p "com.emacsos.zero.ZeroPinyinService" (cadr error)))
+	    (s-contains-p "com.emacsos.zero.ZeroPinyinService1" (cadr error)))
     (error "zero-pinyin-service dbus failed: %S" (cadr error))))
 
 (add-hook 'dbus-event-error-functions 'zero-pinyin-service-error-handler)
@@ -19,17 +19,17 @@
 (defun zero-pinyin-service-async-call (method handler &rest args)
   "call Method on zero-pinin-service asynchronously. This is a wrapper around `dbus-call-method-asynchronously'"
   (apply 'dbus-call-method-asynchronously
-	 :session "com.emacsos.zero.ZeroPinyinService"
-	 "/com/emacsos/zero/ZeroPinyinService"
-	 "com.emacsos.zero.ZeroPinyinService"
+	 :session "com.emacsos.zero.ZeroPinyinService1"
+	 "/com/emacsos/zero/ZeroPinyinService1"
+	 "com.emacsos.zero.ZeroPinyinService1.ZeroPinyinServiceInterface"
 	 method handler :timeout 1000 args))
 
 (defun zero-pinyin-service-call (method &rest args)
   "call Method on zero-pinin-service synchronously. This is a wrapper around `dbus-call-method'"
   (apply 'dbus-call-method
-	 :session "com.emacsos.zero.ZeroPinyinService"
-	 "/com/emacsos/zero/ZeroPinyinService"
-	 "com.emacsos.zero.ZeroPinyinService"
+	 :session "com.emacsos.zero.ZeroPinyinService1"
+	 "/com/emacsos/zero/ZeroPinyinService1"
+	 "com.emacsos.zero.ZeroPinyinService1.ZeroPinyinServiceInterface"
 	 method :timeout 1000 args))
 
 ;;============
@@ -51,6 +51,11 @@ fetch-size try to fetch this many candidates or more"
   (zero-pinyin-service-async-call
    "GetCandidates" get-candidates-complete :string preedit-str :uint32 fetch-size))
 
+(defun zero-pinyin-service-delete-candidates-async (candidate delete-candidate-complete)
+  "delete candidate asynchronously"
+  (zero-pinyin-service-async-call
+   "DeleteCandidate" delete-candidate-complete :string candidate))
+
 (defun zero-pinyin-service-quit ()
   "quit panel application"
   (zero-pinyin-service-async-call "Quit" nil))
diff --git a/zero-pinyin.el b/zero-pinyin.el
index ba817eed8909d3290551f6b5dc9e205ac5b4ba5e..35091dba995e384f79e31fb59316a0c9b0a27dee 100644
--- a/zero-pinyin.el
+++ b/zero-pinyin.el
@@ -36,9 +36,15 @@
   (setq zero-pinyin-pending-preedit-str ""))
 
 (defun zero-pinyin-init ()
+  "called when this im is turned on"
+  (define-key zero-mode-map [remap digit-argument] 'zero-digit-argument)
   (make-local-variable 'zero-pinyin-state)
   (zero-pinyin-reset))
 
+(defun zero-pinyin-shutdown ()
+  "called when this im is turned off"
+  (define-key zero-mode-map [remap digit-argument] nil))
+
 (defvar zero-pinyin--build-candidates-use-test-data nil
   "if t, `zero-pinyin-build-candidates' will use `zero-pinyin-build-candidates-test'")
 
@@ -198,15 +204,41 @@ This is different from zero-framework because I need to support partial commit"
       (concat zero-pinyin-pending-str zero-pinyin-pending-preedit-str)
     zero-preedit-str))
 
+(defun zero-pinyin-preedit-str-changed ()
+  "start over for candidate selection process."
+  (setq zero-pinyin-state nil)
+  (zero-preedit-str-changed))
+
 (defun zero-pinyin-backspace ()
   "handle backspace key in `*zero-state-im-preediting*' state"
   (if (eq zero-pinyin-state *zero-pinyin-state-im-partial-commit*)
-      (progn
-	;; start over for candidate selection process.
-	(setq zero-pinyin-state nil)
-	(zero-preedit-str-changed))
+      (zero-pinyin-preedit-str-changed)
     (zero-backspace-default)))
 
+(defun zero-pinyin-delete-candidate (digit)
+  "tell backend to delete nth candidate.
+
+n is the digit selection number.
+1 means delete 1st candidate.
+2 means delete 2st candidate.
+0 means delete 10th candidate."
+  (let ((candidate (nth (mod (- digit 1) 10)
+			(zero-candidates-on-page zero-candidates))))
+    (when candidate
+      (zero-pinyin-service-delete-candidates-async
+       candidate 'zero-pinyin-preedit-str-changed))))
+
+(defun zero-digit-argument (arg)
+  "wrapper around `digit-argument' to allow C-<digit> to DeleteCandidate in `*zero-state-im-preediting*' state"
+  (interactive "P")
+  (if (eq zero-state *zero-state-im-preediting*)
+      (let* ((char (if (integerp last-command-event)
+		       last-command-event
+		     (get last-command-event 'ascii-character)))
+	     (digit (- (logand char ?\177) ?0)))
+	(zero-pinyin-delete-candidate digit))
+    (digit-argument arg)))
+
 ;;===============================
 ;; register IM to zero framework
 ;;===============================
@@ -220,7 +252,8 @@ This is different from zero-framework because I need to support partial commit"
    (:handle-preedit-char . zero-pinyin-handle-preedit-char)
    (:get-preedit-str-for-panel . zero-pinyin-get-preedit-str-for-panel)
    (:handle-backspace . zero-pinyin-backspace)
-   (:init . zero-pinyin-init)))
+   (:init . zero-pinyin-init)
+   (:shutdown . zero-pinyin-shutdown)))
 
 ;;============
 ;; public API