How does a Qt widget calculate its size?

Question

When I use QWidget to create a user interface, I am always a little confused about its size properties. There size policy , geometry and hintSize .

I just know the connection between size policy and hintSize : size policy based on sizehint . But I do not know other relationships between these properties.

I want to have a widget that can be automatically resized depending on the size of the parent or main window. But I do not know how to use the three properties to achieve this.

Answer 1

geometry: The current position and size of the widget inside the parent. For example, a widget with geometry (10, 20, 50, 70) will be located at position (10, 20) inside the parent with a width of 50 and a height of 70.

sizeHint: (perhaps what you are referring to is "hintSize"). The preferred size in which the widget will be. Override this method to change it.

size policy . How the widget will respond when it is placed in a container with dimensions other than its own. Size policies are a combination of:

• [ QSizePolicy::Maximum ] can a widget shrink below sizeHint
• [ QSizePolicy::Minimum ] whether the widget can expand over its sizeHint and
• [ QSizePolicy::Expanding ] whether the widget should expand to fill extra space.

Widgets have both horizontal and vertical size policies.

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However, you are probably looking for layouts that automatically resize widgets for your parents based on these rules. For example, for a widget to populate a parent element, set the parent layout to QVBoxLayout , and then add the child widget to the layout. When the parent size is resized, the file size will be resized automatically.