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Question

我使用Tkinter条目小部件允许用户向GUI输入文本。输入小部件有默认文本，我想用一个按钮来清除它。我有以下代码：

from Tkinter import *

def delete_entries(fields):
  for field in fields:
    field.delete(0,END)

def UserInput(status,name):
  optionFrame = Frame(root)
  optionLabel = Label(optionFrame)
  optionLabel["text"] = name
  optionLabel.pack(side=LEFT)
  var = StringVar(root)
  var.set(status)
  w = Entry(optionFrame, textvariable= var)
  w.pack(side = LEFT)
  optionFrame.pack()

if __name__ == '__main__':
  root = Tk()
  fields = 'ExperimentNumber', 'OutputFileName', 'npts1', 'block1'    
  ExperimentNumber = UserInput("1", "Experiment number")
  OutputFileName = UserInput("output.txt", "Output file name")
  npts1 = UserInput("1000", "Number of points")
  block1 = UserInput("8", "Block size")

  Delete_button = Button(root, text = 'Clear all', command = delete_entries(fields))
  Delete_button.pack()

我试着用要删除的变量列表（如上所述）创建fields，并在函数delete_entries()中迭代，但是这会返回一个错误，因为字段中的条目是字符串。例如，我已经尝试用fields = ExperimentNumber替换字段，但是这会返回一个错误，因为还没有定义ExperimentNumber。最后，我尝试将ExperimentNumber放入delete函数中，即

def delete_entries():
      ExperimentNumber.delete(0,End)

但这不起作用，因为ExperimentNumber具有属性NoneType（我不明白为什么会这样，因为delete_entries()函数直到通过函数UserInput创建ExperimentNumber条目小部件之后才被调用）。如何删除条目小部件中的所有文本？我在我的实际代码中有大约20个这样的字段，希望用户能够通过一个按钮清除所有字段。

Answer 1

你在正确的轨道上，但你错过了两件小事。我在你的代码中添加了这两个，并试图用注释来解释。

from Tkinter import *

def delete_entries():
  for field in fields:
    field.delete(0,END)

def UserInput(status,name):
  optionFrame = Frame(root)
  optionLabel = Label(optionFrame)
  optionLabel["text"] = name
  optionLabel.pack(side=LEFT)
  var = StringVar(root)
  var.set(status)
  w = Entry(optionFrame, textvariable= var)
  w.pack(side = LEFT)
  optionFrame.pack()
  return w
  #this return is crucial because if you don't return your widget's identity,
  #you can not use them in another function

if __name__ == '__main__':
  root = Tk()    
  ExperimentNumber = UserInput("1", "Experiment number")
  OutputFileName = UserInput("output.txt", "Output file name")
  npts1 = UserInput("1000", "Number of points")
  block1 = UserInput("8", "Block size")
  #you are saying it does not work because of they are strings.
  #then don't assign strings to fields. assign variables.
  fields = ExperimentNumber, OutputFileName, npts1, block1
  #since fields is defined in global scope, you don't need to use it as parameter

  Delete_button = Button(root, text = 'Clear all', command = delete_entries)
  Delete_button.pack()

  root.mainloop()