如何将文本小部件的一部分标记为只读？

Question

如何将 tkinter 文本小部件的一部分标记为只读？也就是说，我希望能够只允许在小部件的某些部分进行编辑。例如，我想只允许在提示之后而不是之前进行编辑，以模拟控制台。

Answer 1

最安全的解决方案是拦截低级插入和删除命令，并在其中放置逻辑以根据某种标准防止插入和删除。例如，您可以禁止在任何带有“只读”标签的文本范围内进行编辑。

这是这种技术的一个例子。它利用了所有插入和删除最终调用底层 tk widget 命令的insert 或 delete 子命令的事实，以及 widget 命令可以替换为 Tcl proc 的事实。

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()