关于tkinter中canvas.create_window()的功能、用途及返回值疑问

Great question—let’s unpack this clearly, since create_window is one of those Tkinter methods that feels odd until you get its core purpose.

1. What does create_window actually create? #

Think of a Canvas as a dedicated drawing surface for shapes, text, images, etc.—it’s not a standard container widget like Frame or Tk. create_window adds a special "placeholder element" to the Canvas that acts as a bridge between the Canvas’s drawing space and regular Tkinter widgets (like your Frame).

This placeholder doesn’t create a new OS-level window (that’s what Tk() does). Instead, it embeds your existing Frame (or any other widget) inside the Canvas’s coordinate system, making the Frame part of the Canvas’s list of drawable items.

2. Why use create_window instead of just putting the Frame in the Canvas? #

You can’t directly place a widget inside a Canvas like you do with a Frame or window. If you tried frame.pack(in_=canvas), the Frame would sit on top of the Canvas (as a sibling in the parent widget hierarchy), not as part of the Canvas’s content.

The key benefits of create_window are:

• The embedded widget moves with the Canvas: If your Canvas has scrollbars, the Frame will scroll along with other Canvas elements (shapes, text, etc.). A directly packed Frame would stay fixed in place.
• You can position the widget using the Canvas’s coordinate system (x/y values) instead of the standard layout managers (pack, grid, place).
• The widget becomes part of the Canvas’s item stack, so you can layer it with other Canvas elements (e.g., draw a rectangle behind the Frame).

3. What’s the meaning of the returned integer? #

That integer is the unique item ID for the embedded window. Every element you add to a Canvas—whether it’s a line, rectangle, text, or embedded widget—gets its own unique ID. You can use this ID to manipulate the embedded widget later, like:

• canvas.coords(item_id, new_x, new_y): Move the widget to a new position on the Canvas.
• canvas.itemconfig(item_id, anchor='se'): Change the widget’s anchor point.
• canvas.delete(item_id): Remove the embedded widget from the Canvas entirely.

Here’s a quick example to demonstrate:

import tkinter as tk

app = tk.Tk()
app.title("Canvas create_window Demo")

# Create a scrollable Canvas
canvas = tk.Canvas(app, width=300, height=200, bg="#f0f0f0")
scrollbar = tk.Scrollbar(app, orient="vertical", command=canvas.yview)
scrollable_frame = tk.Frame(canvas)

scrollable_frame.bind(
    "<Configure>",
    lambda e: canvas.configure(scrollregion=canvas.bbox("all"))
)

# Embed the frame in the Canvas and get the item ID
frame_id = canvas.create_window(0, 0, anchor="nw", window=scrollable_frame)

# Add content to the scrollable frame
for i in range(20):
    tk.Label(scrollable_frame, text=f"Line {i+1} in the embedded frame").pack(pady=2)

canvas.configure(yscrollcommand=scrollbar.set)
canvas.pack(side="left", fill="both", expand=True)
scrollbar.pack(side="right", fill="y")

# Later, we could use frame_id to adjust the frame's position
# canvas.coords(frame_id, 50, 50)

app.mainloop()

内容的提问来源于stack exchange，提问作者placid chat