diff --git a/Source/Modules/InputHandler_Core.swift b/Source/Modules/InputHandler_Core.swift
index ca8ae2f5..05650073 100644
--- a/Source/Modules/InputHandler_Core.swift
+++ b/Source/Modules/InputHandler_Core.swift
@@ -20,7 +20,9 @@ import Tekkon
 /// InputHandler 委任協定
 public protocol InputHandlerDelegate {
   var selectionKeys: String { get }
+  var state: IMEStateProtocol { get set }
   var clientBundleIdentifier: String { get }
+  func handle(state newState: IMEStateProtocol, replaceCurrent: Bool)
   func candidateController() -> CtlCandidateProtocol
   func candidateSelectionCalledByInputHandler(at index: Int)
   func performUserPhraseOperation(with state: IMEStateProtocol, addToFilter: Bool)
diff --git a/Source/Modules/InputHandler_HandleEvent.swift b/Source/Modules/InputHandler_HandleEvent.swift
new file mode 100644
index 00000000..96aabbd6
--- /dev/null
+++ b/Source/Modules/InputHandler_HandleEvent.swift
@@ -0,0 +1,143 @@
+// (c) 2021 and onwards The vChewing Project (MIT-NTL License).
+// ====================
+// This code is released under the MIT license (SPDX-License-Identifier: MIT)
+// ... with NTL restriction stating that:
+// No trademark license is granted to use the trade names, trademarks, service
+// marks, or product names of Contributor, except as required to fulfill notice
+// requirements defined in MIT License.
+
+/// 該檔案乃按鍵調度模組當中用來預處理 NSEvent 的模組。
+
+import InputMethodKit
+import Shared
+
+// MARK: - § 根據狀態調度按鍵輸入 (Handle Input with States)
+
+extension InputHandler {
+  /// 分診函式，會先確認是否是 IMK 選字窗要處理的事件、然後再決定處理步驟。
+  /// - Parameter event: 由 IMK 選字窗接收的裝置操作輸入事件。
+  /// - Returns: 回「`true`」以將該案件已攔截處理的訊息傳遞給 IMK；回「`false`」則放行、不作處理。
+  public func handleEvent(_ event: NSEvent) -> Bool {
+    imkCandidatesEventPreHandler(event: event) ?? commonEventHandler(event)
+  }
+
+  /// 將按鍵行為與當前輸入法狀態結合起來、交給按鍵調度模組來處理。
+  /// 再根據返回的 result bool 數值來告知 IMK「這個按鍵事件是被處理了還是被放行了」。
+  /// 這裡不用 handleCandidate() 是因為需要針對聯想詞輸入狀態做額外處理。
+  private func commonEventHandler(_ event: NSEvent) -> Bool {
+    guard let delegate = delegate else { return false }
+
+    let result = handleInput(event: event, state: delegate.state) { newState in
+      delegate.handle(state: newState, replaceCurrent: true)
+    } errorCallback: { errorString in
+      vCLog(errorString)
+      IMEApp.buzz()
+    }
+    return result
+  }
+
+  /// 專門處理與 IMK 選字窗有關的判斷語句。
+  /// 這樣分開處理很有必要，不然 handle() 函式會陷入無限迴圈。
+  /// - Parameter event: 由 IMK 選字窗接收的裝置操作輸入事件。
+  /// - Returns: 回「`true`」以將該案件已攔截處理的訊息傳遞給 IMK；回「`false`」則放行、不作處理。
+  private func imkCandidatesEventPreHandler(event eventToDeal: NSEvent) -> Bool? {
+    guard let delegate = delegate else { return false }
+
+    // IMK 選字窗處理，當且僅當啟用了 IMK 選字窗的時候才會生效。
+    // 這樣可以讓 interpretKeyEvents() 函式自行判斷：
+    // - 是就地交給 imkCandidates.interpretKeyEvents() 處理？
+    // - 還是藉由 delegate 扔回 SessionCtl 給 InputHandler 處理？
+    if let imkCandidates = delegate.candidateController() as? CtlCandidateIMK, imkCandidates.visible {
+      let event: NSEvent = CtlCandidateIMK.replaceNumPadKeyCodes(target: eventToDeal) ?? eventToDeal
+
+      // Shift+Enter 是個特殊情形，不提前攔截處理的話、會有垃圾參數傳給 delegate 的 inputHandler 從而崩潰。
+      // 所以這裡直接將 Shift Flags 清空。
+      if event.isShiftHold, event.isEnter {
+        guard let newEvent = event.reinitiate(modifierFlags: []) else {
+          IMEApp.buzz()
+          return true
+        }
+
+        return imkCandidatesEventSubHandler(event: newEvent)
+      }
+
+      // 聯想詞選字。
+      if let newChar = CtlCandidateIMK.defaultIMKSelectionKey[event.keyCode],
+        event.isShiftHold, delegate.state.type == .ofAssociates,
+        let newEvent = event.reinitiate(modifierFlags: [], characters: newChar)
+      {
+        if #available(macOS 10.14, *) {
+          imkCandidates.handleKeyboardEvent(newEvent)
+        } else {
+          imkCandidates.interpretKeyEvents([newEvent])
+        }
+        return true
+      }
+
+      return imkCandidatesEventSubHandler(event: event)
+    }
+    return nil
+  }
+
+  private func imkCandidatesEventSubHandler(event: NSEvent) -> Bool {
+    guard let delegate = delegate else { return false }
+    let eventArray = [event]
+    guard let imkC = delegate.candidateController() as? CtlCandidateIMK else { return false }
+    if event.isEsc || event.isBackSpace || event.isDelete || (event.isShiftHold && !event.isSpace) {
+      return commonEventHandler(event)
+    } else if event.isSymbolMenuPhysicalKey {
+      // 符號鍵的行為是固定的，不受偏好設定影響。
+      switch imkC.currentLayout {
+        case .horizontal: _ = event.isShiftHold ? imkC.moveUp(self) : imkC.moveDown(self)
+        case .vertical: _ = event.isShiftHold ? imkC.moveLeft(self) : imkC.moveRight(self)
+        @unknown default: break
+      }
+      return true
+    } else if event.isSpace {
+      switch prefs.specifyShiftSpaceKeyBehavior {
+        case true: _ = event.isShiftHold ? imkC.highlightNextCandidate() : imkC.showNextPage()
+        case false: _ = event.isShiftHold ? imkC.showNextPage() : imkC.highlightNextCandidate()
+      }
+      return true
+    } else if event.isTab {
+      switch prefs.specifyShiftTabKeyBehavior {
+        case true: _ = event.isShiftHold ? imkC.showPreviousPage() : imkC.showNextPage()
+        case false: _ = event.isShiftHold ? imkC.highlightPreviousCandidate() : imkC.highlightNextCandidate()
+      }
+      return true
+    } else {
+      if let newChar = CtlCandidateIMK.defaultIMKSelectionKey[event.keyCode] {
+        /// 根據 KeyCode 重新換算一下選字鍵的 NSEvent，糾正其 Character 數值。
+        /// 反正 IMK 選字窗目前也沒辦法修改選字鍵。
+        let newEvent = event.reinitiate(characters: newChar)
+        if let newEvent = newEvent {
+          if prefs.useSCPCTypingMode, delegate.state.type == .ofAssociates {
+            // 註：input.isShiftHold 已經在 Self.handle() 內處理，因為在那邊處理才有效。
+            return event.isShiftHold ? true : commonEventHandler(event)
+          } else {
+            if #available(macOS 10.14, *) {
+              imkC.handleKeyboardEvent(newEvent)
+            } else {
+              imkC.interpretKeyEvents([newEvent])
+            }
+            return true
+          }
+        }
+      }
+
+      if prefs.useSCPCTypingMode, !event.isReservedKey {
+        return commonEventHandler(event)
+      }
+
+      if delegate.state.type == .ofAssociates,
+        !event.isPageUp, !event.isPageDown, !event.isCursorForward, !event.isCursorBackward,
+        !event.isCursorClockLeft, !event.isCursorClockRight, !event.isSpace,
+        !event.isEnter || !prefs.alsoConfirmAssociatedCandidatesByEnter
+      {
+        return commonEventHandler(event)
+      }
+      imkC.interpretKeyEvents(eventArray)
+      return true
+    }
+  }
+}
diff --git a/Source/Modules/InputHandler_HandleInput.swift b/Source/Modules/InputHandler_HandleInput.swift
index d8fdca92..57871ea1 100644
--- a/Source/Modules/InputHandler_HandleInput.swift
+++ b/Source/Modules/InputHandler_HandleInput.swift
@@ -16,6 +16,7 @@ import Shared
 
 extension InputHandler {
   /// 對於輸入訊號的第一關處理均藉由此函式來進行。
+  /// - Remark: 送入該函式處理之前，先用 inputHandler.handleEvent() 分診、來判斷是否需要交給 IMKCandidates 處理。
   /// - Parameters:
   ///   - input: 輸入訊號。
   ///   - state: 給定狀態（通常為當前狀態）。
@@ -29,7 +30,7 @@ extension InputHandler {
     errorCallback: @escaping (String) -> Void
   ) -> Bool {
     // 如果按鍵訊號內的 inputTest 是空的話，則忽略該按鍵輸入，因為很可能是功能修飾鍵。
-    guard !input.text.isEmpty else { return false }
+    guard !input.text.isEmpty, input.charCode.isPrintable else { return false }
 
     let inputText: String = input.text
     var state = state  // 常數轉變數。
diff --git a/Source/Modules/SessionCtl_HandleEvent.swift b/Source/Modules/SessionCtl_HandleEvent.swift
index db0219f3..35cd8d94 100644
--- a/Source/Modules/SessionCtl_HandleEvent.swift
+++ b/Source/Modules/SessionCtl_HandleEvent.swift
@@ -130,145 +130,9 @@ extension SessionCtl {
     // 準備修飾鍵，用來判定要新增的詞彙是否需要賦以非常低的權重。
     Self.areWeNerfing = eventToDeal.modifierFlags.contains([.shift, .command])
 
-    // IMK 選字窗處理，當且僅當啟用了 IMK 選字窗的時候才會生效。
-    if let result = imkCandidatesEventPreHandler(event: eventToDeal) {
-      if shouldUseShiftToggleHandle { rencentKeyHandledByInputHandlerEtc = result }
-      return result
-    }
-
-    /// 剩下的 NSEvent 直接交給 commonEventHandler 來處理。
-    /// 這樣可以與 IMK 選字窗共用按鍵處理資源，維護起來也比較方便。
-    let result = commonEventHandler(eventToDeal)
-    if shouldUseShiftToggleHandle {
-      rencentKeyHandledByInputHandlerEtc = result
-    }
+    /// 直接交給 commonEventHandler 來處理。
+    let result = inputHandler.handleEvent(eventToDeal)
+    if shouldUseShiftToggleHandle { rencentKeyHandledByInputHandlerEtc = result }
     return result
   }
 }
-
-// MARK: - Private functions
-
-extension SessionCtl {
-  /// 完成 handle() 函式本該完成的內容，但去掉了與 IMK 選字窗有關的判斷語句。
-  /// 這樣分開處理很有必要，不然 handle() 函式會陷入無限迴圈。
-  /// - Parameter event: 由 IMK 選字窗接收的裝置操作輸入事件。
-  /// - Returns: 回「`true`」以將該案件已攔截處理的訊息傳遞給 IMK；回「`false`」則放行、不作處理。
-  private func commonEventHandler(_ event: NSEvent) -> Bool {
-    // 無法列印的訊號輸入，一概不作處理。
-    // 這個過程不能放在 InputHandler 內，否則不會起作用。
-    if !event.charCode.isPrintable { return false }
-
-    /// 將按鍵行為與當前輸入法狀態結合起來、交給按鍵調度模組來處理。
-    /// 再根據返回的 result bool 數值來告知 IMK「這個按鍵事件是被處理了還是被放行了」。
-    /// 這裡不用 inputHandler.handleCandidate() 是因為需要針對聯想詞輸入狀態做額外處理。
-    let result = inputHandler.handleInput(event: event, state: state) { newState in
-      self.handle(state: newState)
-    } errorCallback: { errorString in
-      vCLog(errorString)
-      IMEApp.buzz()
-    }
-    return result
-  }
-
-  /// 完成 handle() 函式本該完成的內容，但專門處理與 IMK 選字窗有關的判斷語句。
-  /// 這樣分開處理很有必要，不然 handle() 函式會陷入無限迴圈。
-  /// - Parameter event: 由 IMK 選字窗接收的裝置操作輸入事件。
-  /// - Returns: 回「`true`」以將該案件已攔截處理的訊息傳遞給 IMK；回「`false`」則放行、不作處理。
-  private func imkCandidatesEventPreHandler(event eventToDeal: NSEvent) -> Bool? {
-    // IMK 選字窗處理，當且僅當啟用了 IMK 選字窗的時候才會生效。
-    // 這樣可以讓 interpretKeyEvents() 函式自行判斷：
-    // - 是就地交給 imkCandidates.interpretKeyEvents() 處理？
-    // - 還是藉由 delegate 扔回 SessionCtl 給 InputHandler 處理？
-    if let imkCandidates = ctlCandidateCurrent as? CtlCandidateIMK, imkCandidates.visible {
-      let event: NSEvent = CtlCandidateIMK.replaceNumPadKeyCodes(target: eventToDeal) ?? eventToDeal
-
-      // Shift+Enter 是個特殊情形，不提前攔截處理的話、會有垃圾參數傳給 delegate 的 inputHandler 從而崩潰。
-      // 所以這裡直接將 Shift Flags 清空。
-      if event.isShiftHold, event.isEnter {
-        guard let newEvent = event.reinitiate(modifierFlags: []) else {
-          NSSound.beep()
-          return true
-        }
-
-        return imkCandidatesEventSubHandler(event: newEvent)
-      }
-
-      // 聯想詞選字。
-      if let newChar = CtlCandidateIMK.defaultIMKSelectionKey[event.keyCode],
-        event.isShiftHold, state.type == .ofAssociates,
-        let newEvent = event.reinitiate(modifierFlags: [], characters: newChar)
-      {
-        if #available(macOS 10.14, *) {
-          imkCandidates.handleKeyboardEvent(newEvent)
-        } else {
-          imkCandidates.interpretKeyEvents([newEvent])
-        }
-        return true
-      }
-
-      return imkCandidatesEventSubHandler(event: event)
-    }
-    return nil
-  }
-
-  private func imkCandidatesEventSubHandler(event: NSEvent) -> Bool {
-    let eventArray = [event]
-    guard let imkC = ctlCandidateCurrent as? CtlCandidateIMK else { return false }
-    if event.isEsc || event.isBackSpace || event.isDelete || (event.isShiftHold && !event.isSpace) {
-      return commonEventHandler(event)
-    } else if event.isSymbolMenuPhysicalKey {
-      // 符號鍵的行為是固定的，不受偏好設定影響。
-      switch imkC.currentLayout {
-        case .horizontal: _ = event.isShiftHold ? imkC.moveUp(self) : imkC.moveDown(self)
-        case .vertical: _ = event.isShiftHold ? imkC.moveLeft(self) : imkC.moveRight(self)
-        @unknown default: break
-      }
-      return true
-    } else if event.isSpace {
-      switch PrefMgr.shared.specifyShiftSpaceKeyBehavior {
-        case true: _ = event.isShiftHold ? imkC.highlightNextCandidate() : imkC.showNextPage()
-        case false: _ = event.isShiftHold ? imkC.showNextPage() : imkC.highlightNextCandidate()
-      }
-      return true
-    } else if event.isTab {
-      switch PrefMgr.shared.specifyShiftTabKeyBehavior {
-        case true: _ = event.isShiftHold ? imkC.showPreviousPage() : imkC.showNextPage()
-        case false: _ = event.isShiftHold ? imkC.highlightPreviousCandidate() : imkC.highlightNextCandidate()
-      }
-      return true
-    } else {
-      if let newChar = CtlCandidateIMK.defaultIMKSelectionKey[event.keyCode] {
-        /// 根據 KeyCode 重新換算一下選字鍵的 NSEvent，糾正其 Character 數值。
-        /// 反正 IMK 選字窗目前也沒辦法修改選字鍵。
-        let newEvent = event.reinitiate(characters: newChar)
-        if let newEvent = newEvent {
-          if PrefMgr.shared.useSCPCTypingMode, state.type == .ofAssociates {
-            // 註：input.isShiftHold 已經在 Self.handle() 內處理，因為在那邊處理才有效。
-            return event.isShiftHold ? true : commonEventHandler(event)
-          } else {
-            if #available(macOS 10.14, *) {
-              imkC.handleKeyboardEvent(newEvent)
-            } else {
-              imkC.interpretKeyEvents([newEvent])
-            }
-            return true
-          }
-        }
-      }
-
-      if PrefMgr.shared.useSCPCTypingMode, !event.isReservedKey {
-        return commonEventHandler(event)
-      }
-
-      if state.type == .ofAssociates,
-        !event.isPageUp, !event.isPageDown, !event.isCursorForward, !event.isCursorBackward,
-        !event.isCursorClockLeft, !event.isCursorClockRight, !event.isSpace,
-        !event.isEnter || !PrefMgr.shared.alsoConfirmAssociatedCandidatesByEnter
-      {
-        return commonEventHandler(event)
-      }
-      imkC.interpretKeyEvents(eventArray)
-      return true
-    }
-  }
-}
diff --git a/vChewing.xcodeproj/project.pbxproj b/vChewing.xcodeproj/project.pbxproj
index a822e552..f5fdf445 100644
--- a/vChewing.xcodeproj/project.pbxproj
+++ b/vChewing.xcodeproj/project.pbxproj
@@ -84,6 +84,7 @@
 		5BDB7A4528D4824A001AC277 /* ShiftKeyUpChecker in Frameworks */ = {isa = PBXBuildFile; productRef = 5BDB7A4428D4824A001AC277 /* ShiftKeyUpChecker */; };
 		5BDB7A4728D4824A001AC277 /* Tekkon in Frameworks */ = {isa = PBXBuildFile; productRef = 5BDB7A4628D4824A001AC277 /* Tekkon */; };
 		5BDCBB2E27B4E67A00D0CC59 /* vChewingPhraseEditor.app in Resources */ = {isa = PBXBuildFile; fileRef = 5BD05BB827B2A429004C4F1D /* vChewingPhraseEditor.app */; };
+		5BE1F8A928F86AB5006C7FF5 /* InputHandler_HandleEvent.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5BE1F8A828F86AB5006C7FF5 /* InputHandler_HandleEvent.swift */; };
 		5BE377A0288FED8D0037365B /* InputHandler_HandleComposition.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5BE3779F288FED8D0037365B /* InputHandler_HandleComposition.swift */; };
 		5BE78BD927B3775B005EA1BE /* CtlAboutWindow.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5BE78BD827B37750005EA1BE /* CtlAboutWindow.swift */; };
 		5BE78BDD27B3776D005EA1BE /* frmAboutWindow.xib in Resources */ = {isa = PBXBuildFile; fileRef = 5BE78BDA27B37764005EA1BE /* frmAboutWindow.xib */; };
@@ -283,6 +284,7 @@
 		5BDCBB4A27B4F6C700D0CC59 /* zh-Hant */ = {isa = PBXFileReference; lastKnownFileType = text.plist.strings; name = "zh-Hant"; path = "zh-Hant.lproj/Localizable.strings"; sourceTree = "<group>"; };
 		5BDCBB4B27B4F6C700D0CC59 /* zh-Hant */ = {isa = PBXFileReference; lastKnownFileType = text.plist.strings; name = "zh-Hant"; path = "zh-Hant.lproj/frmAboutWindow.strings"; sourceTree = "<group>"; };
 		5BDCBB4D27B4F6C700D0CC59 /* zh-Hant */ = {isa = PBXFileReference; lastKnownFileType = text.plist.strings; name = "zh-Hant"; path = "zh-Hant.lproj/InfoPlist.strings"; sourceTree = "<group>"; };
+		5BE1F8A828F86AB5006C7FF5 /* InputHandler_HandleEvent.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InputHandler_HandleEvent.swift; sourceTree = "<group>"; };
 		5BE3779F288FED8D0037365B /* InputHandler_HandleComposition.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InputHandler_HandleComposition.swift; sourceTree = "<group>"; };
 		5BE78BD827B37750005EA1BE /* CtlAboutWindow.swift */ = {isa = PBXFileReference; explicitFileType = sourcecode.swift; fileEncoding = 4; indentWidth = 2; lineEnding = 0; path = CtlAboutWindow.swift; sourceTree = "<group>"; tabWidth = 2; usesTabs = 0; };
 		5BE78BDB27B37764005EA1BE /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.xib; name = Base; path = Base.lproj/frmAboutWindow.xib; sourceTree = "<group>"; };
@@ -675,6 +677,7 @@
 				5BD0113C2818543900609769 /* InputHandler_Core.swift */,
 				5B782EC3280C243C007276DE /* InputHandler_HandleCandidate.swift */,
 				5BE3779F288FED8D0037365B /* InputHandler_HandleComposition.swift */,
+				5BE1F8A828F86AB5006C7FF5 /* InputHandler_HandleEvent.swift */,
 				5B7F225C2808501000DDD3CB /* InputHandler_HandleInput.swift */,
 				5B3133BE280B229700A4A505 /* InputHandler_States.swift */,
 				5BAEFACF28012565001F42C9 /* LMMgr.swift */,
@@ -1081,6 +1084,7 @@
 				5BD0113D2818543900609769 /* InputHandler_Core.swift in Sources */,
 				5BF56F9A28C39D1800DD6839 /* IMEStateData.swift in Sources */,
 				5B21176C287539BB000443A9 /* SessionCtl_HandleStates.swift in Sources */,
+				5BE1F8A928F86AB5006C7FF5 /* InputHandler_HandleEvent.swift in Sources */,
 				5BAEFAD028012565001F42C9 /* LMMgr.swift in Sources */,
 				5B782EC4280C243C007276DE /* InputHandler_HandleCandidate.swift in Sources */,
 				5BA9FD0F27FEDB6B002DE248 /* VwrPrefPaneGeneral.swift in Sources */,