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# Chapter 19 - Basic GUI Programming using `tkinter` (II)

###### tags: `GUI Programming`

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## Input text for one line

To create a text box to input a line of text, `Entry()` can be used. We can use `place()` to place the text box.

import tkinter
root = tkinter.Tk()             # Create the window
root.title("The first textbox") # Name the title
root.geometry("400x200")        # Configurate the size in pixel
entry = tkinter.Entry(width=20)
entry.place(x=10, y=10)
root.mainloop()                 # Display the window

By running the program, a text box is placed on the window. We can change the parameter `width` in `Entry()` to specify the number of characters.


### Operation of the string by `Entry`

We can use `get()` to get the string from `Entry`. Please input and run the following program.

import tkinter

def click_btn():
    txt = entry.get()
    button["text"] = txt

root = tkinter.Tk()             # Create the window
root.title("The first textbox") # Name the title
root.geometry("400x200")        # Configurate the size in pixel
entry = tkinter.Entry(width=20)
entry.place(x=10, y=10)

button = tkinter.Button(text="Get text",
                        command=click_btn)
button.place(x=20, y=100)

root.mainloop()                 # Display the window


## Input text for multiple lines

The input multiple lines, we can use `Text()` command. Please input and run the following program.

import tkinter

def click_btn():
    text.insert(tkinter.END, "Monsters appear!")

root = tkinter.Tk()             # Create the window
root.title("The first textarea")# Name the title
root.geometry("400x200")        # Configurate the size in pixel

button = tkinter.Button(text="Message",
                        command=click_btn)
button.pack()

text = tkinter.Text()
text.pack()

root.mainloop()                 # Display the window


The program uses `pack()` to palce the text are created by the `Text()` command. If `place()` is used, we can specify the position and the size. For example, we can specify `width` and `height`.

text = tkinter.Text()
text.place(x=20, y=50, width=360, height=120)

The text area can add text by `insert()` just like in line 4. This time, the text are added at the end of the text area by using `tkinter.END`.

## Radio Button

We can use `Checkbutton()` to create radio button. Please input and run the following program.

import tkinter
root = tkinter.Tk()                     # Create the window
root.title("The first Checkbox")        # Name the title
root.geometry("400x200")                # Configurate the size in pixel
cbtn = tkinter.Checkbutton(text="Check Button")
cbtn.pack()
root.mainloop()                 # Display the window


### Get checked status

We need to write a more complicated program to get the checked status. We can use `BooleanVar()` command to get the checked status. Please input and run the following program.

import tkinter
root = tkinter.Tk()                     # Create the window
root.title("The first Checkbox")        # Name the title
root.geometry("400x200")                # Configurate the size in pixel
cval = tkinter.BooleanVar()
cval.set(True)
cbtn = tkinter.Checkbutton(text="Check Button",
                           variable=cval)
cbtn.pack()
root.mainloop()                         # Display the window


An object is created by `BooleanVar()` on line 5, and then set the status as `True`. `True` means checked, and `False` means unchecked. After creating check button on line 7, use `variable` in `BooleanVar()` object to create the relationship of the `BooleanVar()` and the check button.

To get the check statues, we can use `get()` of the `BooleanVar()` to get the check status. Please input and run the following program.

import tkinter

def check():
    if cval.get() == True:
        print("Checked")
    else:
        print("Unchecked")

root = tkinter.Tk()                     # Create the window
root.title("The first Checkbox")        # Name the title
root.geometry("400x200")                # Configurate the size in pixel
cval = tkinter.BooleanVar()
cval.set(False)
cbtn = tkinter.Checkbutton(text="Check Button",
                           variable=cval,
                           command=check)
cbtn.pack()
root.mainloop()                         # Display the window


## Message Box

We can use the module `tkinter.messagebox` to load the message box. Please input and run the following program.

import tkinter
import tkinter.messagebox

def click_btn():
    tkinter.messagebox.showinfo("Info", "Button Clicked.")

root = tkinter.Tk()                     # Create the window
root.title("The first Msgbox")          # Name the title
root.geometry("400x200")                # Configurate the size in pixel
btn = tkinter.Button(text="test",
                     command=click_btn)
btn.pack()
root.mainloop()                         # Display the window

The following box will be shown after clicking the button.


This program uses `showinfo()` command to show the message. There are many types of messgae, as shown below.

|Command|Description|
|:------|:----------|
|`showinfo()`|Show information message box|
|`showwarning()`|Show warning message box|
|`showerror()`|Show error message box|
|`askyesno()`|Show the message box with "Yes" and "No" button|
|`askofcancel()`|Show the message box with "OK" and "Cancel"|

## Using `after()` command

We can use `after()` command to perform immediate process. The program can count up automatically. Please input and run the following program.

import tkinter
tmr = 0                     # Declare tmr as 0

def count_up():
    global tmr
    tmr += 1
    label["text"] = tmr
    root.after(1000, count_up)

root = tkinter.Tk()         # Create the window
label = tkinter.Label(font=("Times New Roman", 80))
label.pack()
root.after(1000, count_up)  # Call count_up after 1 second
root.mainloop()             # Display the window

After the program is run, the value inside the window will increase once a second (1000 ms).

`global` can change the variable outside of the scope of the function within the function.


For line 4-8, it defines the function `count_up`, and this function perform the action immediately by using `after()` command. The syntax of `after()` is shown below.

after(millisecond, function_name)

The `function_name` in the `after()` command do not need to add `()`.

## Reference
https://tkdocs.com/pyref/