設計模式-行為型模式,命令模式(11)
阿新 • • 發佈:2018-03-08
不存在 delet rbo main sel creating delete == commands
命令模式(Command Pattern)是一種數據驅動的設計模式,它屬於行為型模式。請求以命令的形式包裹在對象中,並傳給調用對象。調用對象尋找可以處理該命令的合適的對象,並把該命令傳給相應的對象,該對象執行命令。
現在多數應用都有撤銷操作。雖然難以想象,但在很多年裏,任何軟件中確實都不存在撤銷
操作。撤銷操作是在1974年引入的(請參考網頁[t.cn/Rqr3N22]),但Fortran和Lisp分別早在1957
年和1958年就已創建了撤銷操作(請參考網頁[t.cn/Rqr3067]),這兩門語言仍在被人廣泛使用。
在那些年裏,我真心不想使用應用軟件。犯了一個錯誤,用戶也沒什麽便捷方式能修正它。
import os verbose = True class RenameFile: def __init__(self, path_src, path_dest): self.src, self.dest = path_src, path_dest def execute(self): if verbose: print("[renaming ‘{}‘ to ‘{}‘]".format(self.src, self.dest)) os.rename(self.src, self.dest)def undo(self): if verbose: print("[renaming ‘{}‘ back to ‘{}‘]".format(self.dest, self.src)) os.rename(self.dest, self.src) class CreateFile: def __init__(self, path, txt=‘hello world\n‘): self.path, self.txt = path, txt def execute(self):if verbose: print("[creating file ‘{}‘]".format(self.path)) with open(self.path, mode=‘w‘, encoding=‘utf-8‘) as out_file: out_file.write(self.txt) def undo(self): delete_file(self.path) class ReadFile: def __init__(self, path): self.path = path def execute(self): if verbose: print("[reading file ‘{}‘]".format(self.path)) with open(self.path, mode=‘r‘, encoding=‘utf-8‘) as in_file: print(in_file.read(), end=‘‘) def delete_file(path): if verbose: print("deleting file ‘{}‘".format(path)) os.remove(path) def main(): orig_name, new_name = ‘file1‘, ‘file2‘ commands = [] for cmd in CreateFile(orig_name), ReadFile(orig_name), RenameFile(orig_name, new_name): commands.append(cmd) [c.execute() for c in commands] answer = input(‘reverse the executed commands? [y/n] ‘) if answer not in ‘yY‘: print("the result is {}".format(new_name)) exit() for c in reversed(commands): try: c.undo() except AttributeError as e: pass if __name__ == ‘__main__‘: main()
設計模式-行為型模式,命令模式(11)