如何將文本小部件的一部分標記爲只讀？

Question

如何將tkinter文本小部件的一部分標記爲只讀？也就是說，我希望只能在小部件的某些部分進行編輯。例如，我想只在提示後才能編輯，但不能在之前模擬控制檯。

Answer 1

最強大的解決方案是攔截低級插入和刪除命令，並將邏輯放在那裏以防止基於某種標準的插入和刪除。例如，您可以禁止在標籤爲「只讀」的任何文本範圍內進行編輯。

下面是這種技術的一個例子。它利用了所有插入和刪除操作最終都會調用底層tk widget命令的insert或delete子命令以及可以用Tcl proc替換widget命令的事實。

try: 
    # python 2.x 
    import Tkinter as tk 
except ImportError: 
    # python 3.x 
    import tkinter as tk 

class Example(tk.Frame): 
    def __init__(self, parent): 
     tk.Frame.__init__(self, parent) 

     text = ReadonlyText(self) 
     sb = tk.Scrollbar(self, orient="vertical", command=text.yview) 
     text.configure(yscrollcommand=sb.set) 
     sb.pack(side="left", fill="y") 
     text.pack(side="right", fill="both", expand=True) 

     text.insert("end", "You can edit this line\n") 
     text.insert("end", "You cannot edit or delete this line\n", "readonly") 
     text.insert("end", "You can edit this, too.") 

     text.tag_configure("readonly", foreground="darkgray") 

class ReadonlyText(tk.Text): 
    '''A text widget that doesn't permit inserts and deletes in regions tagged with "readonly"''' 
    def __init__(self, *args, **kwargs): 
     tk.Text.__init__(self, *args, **kwargs) 

     # this code creates a proxy that will intercept 
     # each actual insert and delete. 
     self.tk.eval(WIDGET_PROXY) 

     # this code replaces the low level tk widget 
     # with the proxy 
     widget = str(self) 
     self.tk.eval(''' 
      rename {widget} _{widget} 
      interp alias {{}} ::{widget} {{}} widget_proxy _{widget} 
     '''.format(widget=widget)) 

WIDGET_PROXY = ''' 
if {[llength [info commands widget_proxy]] == 0} { 
    # Tcl code to implement a text widget proxy that disallows 
    # insertions and deletions in regions marked with "readonly" 
    proc widget_proxy {actual_widget args} { 
     set command [lindex $args 0] 
     set args [lrange $args 1 end] 
     if {$command == "insert"} { 
      set index [lindex $args 0] 
      if [_is_readonly $actual_widget $index "$index+1c"] { 
       bell 
       return "" 
      } 
     } 
     if {$command == "delete"} { 
      foreach {index1 index2} $args { 
       if {[_is_readonly $actual_widget $index1 $index2]} { 
        bell 
        return "" 
       } 
      } 
     } 
     # if we passed the previous checks, allow the command to 
     # run normally 
     $actual_widget $command {*}$args 
    } 

    proc _is_readonly {widget index1 index2} { 
     # return true if any text in the range between 
     # index1 and index2 has the tag "readonly" 
     set result false 
     if {$index2 eq ""} {set index2 "$index1+1c"} 
     # see if "readonly" is applied to any character in the 
     # range. There's probably a more efficient way to do this, but 
     # this is Good Enough 
     for {set index $index1} \ 
      {[$widget compare $index < $index2]} \ 
      {set index [$widget index "$index+1c"]} { 
       if {"readonly" in [$widget tag names $index]} { 
        set result true 
        break 
       } 
      } 
     return $result 
    } 
} 
''' 

def main(): 
    root = tk.Tk() 
    Example(root).pack(fill="both", expand=True) 
    root.mainloop() 

if __name__ == "__main__": 
    main()