"Hello, world" with Wish TCL/TK, how to change the text of a widget?

Question

I’m having trouble understanding how the program works wish, to make a good old "Hello, World".

For those who don’t know what the wish, it is a TCL interpreter ready to make graphical interfaces in TK. You program in TCL, create your widgets and position them on the screen.

For example, to make a button that prints Hello World on the console (with shebang and all):

#!/usr/bin/env wish

button .submit -text "Click Me" -command { puts "\nHello World" }
pack .submit

In the first line, we create a button identified as .submit, with the saying Click Me which, when clicked, executes the TCL command to print on the console Hello World.

Then we sent for the widget so-called .submit in the pack of screen things.

See working:

So far, I was able to do a "Hello, World" on the console, but not on the screen. I would like to change the text of a label, or even the button itself, to "Hello, World". I tried to change the click command to

{ puts "\nHello World";  button .submit -text "Hello" }

but... I am greeted with the following message:

Error, window name "Submit" already exists in Parent

which in free translation would be:

Error, window name "Submit" already exists in parent

I mean, just call the button .submit tries to create again a button called .submit

I managed to put a label on the screen with a slight variation:

{ puts "\nHello World";  label .teste -text "Hello"; pack .teste }

But clicking the button again will cause the same error that the component already exists on the screen.

So my question is:

• how to change the test of a widget already placed on the screen?
• or I should remove and reinsert the component with the changes?

Answer 1

You can change the text (or any other property) of widget, with the command configure, indicating the property that will be changed and the new value.

Example:

button .submit -text "Click Me" -command { 
     .submit configure -text "Novo Texto"
     .submit configure -fg firebrick
  }

In this example, by clicking the button .submit, the properties -text (button text) and -fg (text color) is changed to "New Text" and firebrick, respectively.

Reference (in English): Widget - Configure

Answer 2

The button widget has a "textvariable" property just for this. Assign a variable any "v" by the textvariable, which will receive the new text, and every time you change it the text of the button will change as well.

button .b -textvariable v -text "Click-me" -command {set v "Hello Word!"}
pack .b