C++使用初始化列表的方式来初始化字段的方法

可以来看看RecoveryUI类:

在ui.h中：

class RecoveryUI {
 public:
  RecoveryUI();
  virtual ~RecoveryUI() { }
  // Initialize the object; called before anything else.
  virtual void Init();
  // Show a stage indicator. Call immediately after Init().
  virtual void SetStage(int current, int max) = 0;
  // After calling Init(), you can tell the UI what locale it is operating in.
  virtual void SetLocale(const char* locale) = 0;
  // Set the overall recovery state ("background image").
  enum Icon { NONE, INSTALLING_UPDATE, ERASING, NO_COMMAND, ERROR };
  virtual void SetBackground(Icon icon) = 0;
  // --- progress indicator ---
  enum ProgressType { EMPTY, INDETERMINATE, DETERMINATE };
  virtual void SetProgressType(ProgressType determinate) = 0;
  // Show a progress bar and define the scope of the next operation:
  //  portion - fraction of the progress bar the next operation will use
  //  seconds - expected time interval (progress bar moves at this minimum rate)
  virtual void ShowProgress(float portion, float seconds) = 0;
  // Set progress bar position (0.0 - 1.0 within the scope defined
  // by the last call to ShowProgress).
  virtual void SetProgress(float fraction) = 0;
  // --- text log ---
  virtual void ShowText(bool visible) = 0;
  virtual bool IsTextVisible() = 0;
  virtual bool WasTextEverVisible() = 0;
  // Write a message to the on-screen log (shown if the user has
  // toggled on the text display).
  virtual void Print(const char* fmt, ...) __printflike(2, 3) = 0;
  virtual void ShowFile(const char* filename) = 0;
  // --- key handling ---
  // Wait for a key and return it. May return -1 after timeout.
  virtual int WaitKey();
  virtual bool IsKeyPressed(int key);
  virtual bool IsLongPress();
  // Returns true if you have the volume up/down and power trio typical
  // of phones and tablets, false otherwise.
  virtual bool HasThreeButtons();
  // Erase any queued-up keys.
  virtual void FlushKeys();
  // Called on each key press, even while operations are in progress.
  // Return value indicates whether an immediate operation should be
  // triggered (toggling the display, rebooting the device), or if
  // the key should be enqueued for use by the main thread.
  enum KeyAction { ENQUEUE, TOGGLE, REBOOT, IGNORE };
  virtual KeyAction CheckKey(int key, bool is_long_press);
  // Called when a key is held down long enough to have been a
  // long-press (but before the key is released). This means that
  // if the key is eventually registered (released without any other
  // keys being pressed in the meantime), CheckKey will be called with
  // 'is_long_press' true.
  virtual void KeyLongPress(int key);
  // Normally in recovery there's a key sequence that triggers
  // immediate reboot of the device, regardless of what recovery is
  // doing (with the default CheckKey implementation, it's pressing
  // the power button 7 times in row). Call this to enable or
  // disable that feature. It is enabled by default.
  virtual void SetEnableReboot(bool enabled);
  // --- menu display ---
  // Display some header text followed by a menu of items, which appears
  // at the top of the screen (in place of any scrolling ui_print()
  // output, if necessary).
  virtual void StartMenu(const char* const * headers, const char* const * items,
              int initial_selection) = 0;
  // Set the menu highlight to the given index, wrapping if necessary.
  // Returns the actual item selected.
  virtual int SelectMenu(int sel) = 0;
  // End menu mode, resetting the text overlay so that ui_print()
  // statements will be displayed.
  virtual void EndMenu() = 0;
protected:
  void EnqueueKey(int key_code);
private:
  // Key event input queue
  pthread_mutex_t key_queue_mutex;
  pthread_cond_t key_queue_cond;
  int key_queue[256], key_queue_len;
  char key_pressed[KEY_MAX + 1];   // under key_queue_mutex
  int key_last_down;         // under key_queue_mutex
  bool key_long_press;        // under key_queue_mutex
  int key_down_count;        // under key_queue_mutex
  bool enable_reboot;        // under key_queue_mutex
  int rel_sum;
  int consecutive_power_keys;
  int last_key;
  bool has_power_key;
  bool has_up_key;
  bool has_down_key;
  struct key_timer_t {
    RecoveryUI* ui;
    int key_code;
    int count;
  };
  pthread_t input_thread_;
  void OnKeyDetected(int key_code);
  static int InputCallback(int fd, uint32_t epevents, void* data);
  int OnInputEvent(int fd, uint32_t epevents);
  void ProcessKey(int key_code, int updown);
  bool IsUsbConnected();
  static void* time_key_helper(void* cookie);
  void time_key(int key_code, int count);
};
ui.cpp中，也是采用字段初始化的方式来实现构造函数：
RecoveryUI::RecoveryUI()
    : key_queue_len(0),
     key_last_down(-1),
     key_long_press(false),
     key_down_count(0),
     enable_reboot(true),
     consecutive_power_keys(0),
     last_key(-1),
     has_power_key(false),
     has_up_key(false),
     has_down_key(false) {
  pthread_mutex_init(&key_queue_mutex, nullptr);
  pthread_cond_init(&key_queue_cond, nullptr);
  memset(key_pressed, 0, sizeof(key_pressed));
}								 
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