Why Does the Button Stay Pressed and the UI Freeze?

When building desktop applications with Python's tkinter, implementing modal dialogs (like an IP entry prompt) is a common task. However, you might run into an issue where clicking a button to open a modal dialog causes the button to stay visually "pressed" (sunken) and freezes your UI. This behavior is caused by two main architectural issues in your Tkinter code:

  • 1. Binding to <Button-1> instead of using the command parameter: When you bind directly to the mouse-down event (<Button-1>), your handler executes immediately when the mouse button is pressed down. Because the handler blocks or starts a nested event loop before the mouse button is released, the widget never receives or processes the corresponding <ButtonRelease-1> event. As a result, the button stays stuck in its pressed state.
  • 2. Calling wait_window() inside the __init__ constructor: Calling self.wait_window() inside the ConnectView constructor is a major anti-pattern. Because wait_window() blocks execution until the window is destroyed, the constructor cannot return. This means the calling line self._connect_view = ConnectView(self._view) is suspended mid-initialization, preventing the controller from properly referencing the instance until after it has already been closed.

The Solution: Best Practices for Tkinter Modals

To resolve these issues, we need to apply two straightforward refactoring steps:

  1. Use the standard button command attribute instead of event binding.
  2. Move the wait_window() call out of the dialog's constructor and into the controller that manages the dialog's lifecycle.

Step 1: Update the View to Use command

In main_view.py, configure your buttons using the command option. This ensures the button click completes its natural visual lifecycle (down and up) before triggering your controller's methods.

# In main_view.py
def set_controller(self, controller):
    self._controller = controller
    # Use config(command=...) instead of binding <Button-1>
    self._send_message_button.config(command=self._controller.handle_button_send)
    self._connect_button.config(command=self._controller.handle_button_connect)

Step 2: Clean up the Dialog Constructor

Remove self.wait_window() from the end of the ConnectView.__init__ method in connect_view.py. The constructor should only be responsible for building the UI and setting up the initial state.

# In connect_view.py
class ConnectView(tk.Toplevel):
    def __init__(self, parent):
        tk.Toplevel.__init__(self, parent)
        # ... [your UI setup code] ...

        self.protocol("WM_DELETE_WINDOW", self.cancel)

        self.grab_set()
        self.focus_set()
        # REMOVED: self.wait_window() - Do not block the constructor!

Step 3: Manage the Modal Lifecycle in the Controller

Now, handle the blocking wait operation inside your controller. By instantiating the view first and then calling wait_window on it, the button event handler completes its initialization phase cleanly, and the modal behavior works exactly as expected.

# In main_controller.py
class MainController:
    # ... [your __init__ and run methods] ...

    def handle_button_send(self):
        print("Sending message")

    def handle_button_connect(self):
        # 1. Create the dialog instance (constructor returns immediately)
        connect_view = ConnectView(self._view)
        
        # 2. Block execution here until the dialog is closed/destroyed
        self._view.wait_window(connect_view)
        
        # 3. Retrieve the value safely after the window is destroyed
        user_ip = connect_view.get_ip()
        print("IP: " + user_ip)

Summary of Benefits

By separating the construction of your UI from its execution state, you gain several advantages:

  • Responsive UI: Buttons no longer get stuck in a "sunken" state because their event lifecycle is allowed to complete naturally.
  • Cleaner Architecture: Your __init__ methods remain pure constructors, returning instances immediately without unexpected side effects.
  • Better Control: The calling controller has explicit control over when to display the dialog and when to read its data, making your application easier to debug and scale.