iced_lazy Responsive Widget doesn't emit Message

[maxslarsson]

Is there an existing issue for this?

• I have searched the existing issues.

Is this issue related to iced?

• My hardware is compatible and my graphics drivers are up-to-date.

What happened?

To render the pixels for an Image widget, I need to have a way of getting the current width and height of the Image widget. Wrapping it with the Responsive widget from iced_lazy, and using Length::Fill, fixes the issue, but for some reason this widget takes a lambda function and gives the size as an argument to the lambda. The problem is I need to save the Size of the Responsive widget since I am recalculating the pixels only when the user presses a button (and I don't want to do it every time view is called). However, since I am using pure widgets I don't have a mutable reference to self and can't save the Size. Why does the Responsive widget not just emit a Message, like Button and TextInput and most other widgets, so the update function can handle the message and rerender the pixel data? Am I misunderstanding where I should generate the pixels for an image?

What is the expected behavior?

The Responsive widget takes a message to produce with the size of the widget. Some ideas of what it could look like: Button or TextInput.

Responsive::new(Image::new(...)).on_resize(Message::Resize)

or

Responsive::new(Image::new(...), Message::Resize)

Version

0.4

Operative System

macOS

Do you have any log output?

No response

[hecrj]

Responsive does not emit a Message because, if it did, emitting a Message on resize would cause an update. This would, in turn, allow you to change the state of the Application and, therefore, view could change as well. As a result, the Responsive widget could have a different size and trigger another Message, making infinite loops in your application quite likely to happen.

If you want to cache the pixels of an Image after regenerating them, then I recommend you to use interior mutability.